U.S. patent application number 09/735344 was filed with the patent office on 2001-11-22 for flash device.
Invention is credited to Odaka, Yukio.
Application Number | 20010043810 09/735344 |
Document ID | / |
Family ID | 18441268 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010043810 |
Kind Code |
A1 |
Odaka, Yukio |
November 22, 2001 |
Flash Device
Abstract
A flash device having a charging circuit which is arranged to be
capable of changing between a flyback-type boosting action and a
forward-type boosting action. The flyback-type boosting action is
performed in the initial stage of a charging process and, after
that, is changed over to the forward-type boosting action. The
arrangement permits a charging action to be efficiently carried
out.
Inventors: |
Odaka, Yukio; (Kanagawa-ken,
JP) |
Correspondence
Address: |
ROBIN BLECKER & DALEY
2ND FLOOR
330 MADISON AVENUE
NEW YORK
NY
10017
US
|
Family ID: |
18441268 |
Appl. No.: |
09/735344 |
Filed: |
December 12, 2000 |
Current U.S.
Class: |
396/206 |
Current CPC
Class: |
H05B 41/325
20130101 |
Class at
Publication: |
396/206 |
International
Class: |
G03B 015/05 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 14, 1999 |
JP |
HEI 11-354994 |
Claims
1. A control circuit for a flash device having a main capacitor, a
charging circuit having a flyback-type boosting circuit and a
forward-type boosting circuit which differ in characteristic from
each other and arranged to charge the main capacitor by boosting a
voltage of a battery with one of the flyback-type boosting circuit
and the forward-type boosting circuit, and a flash discharge tube
arranged to emit flash light by discharging electric charge charged
in the main capacitor, said control circuit comprising: a detecting
circuit which detects a charged state of the main capacitor; and a
selection circuit which selectively causes one of the flyback-type
boosting circuit and the forward-type boosting circuit to act, on
the basis of a result of detection provided by said detecting
circuit.
2. A control circuit according to claim 1, wherein said selection
circuit performs changeover control of the charging circuit in such
a way as to cause the flyback-type boosting circuit to act at the
time of beginning of charging the main capacitor and to cause the
forward-type boosting circuit to act according to a change in the
charged state of the main capacitor.
3. A control circuit according to claim 2, wherein said detecting
circuit detects a charged voltage of the main capacitor, and said
selection circuit performs changeover control of the charging
circuit in such a way as to cause the forward-type boosting circuit
to act, when the charged voltage of the main capacitor has exceeded
a predetermined threshold value, on the basis of a result of
detection provided by said detecting circuit.
4. A control circuit according claim 2, wherein said detecting
circuit detects a state of the battery from the charged state of
the main capacitor, and calculates a predetermined length of time
related to a charged voltage of the main capacitor set according to
the state of the battery, and said selection circuit performs
changeover control of the charging circuit in such a way as to
cause the forward-type boosting circuit to act, when the
predetermined length of time calculated by said detecting circuit
has elapsed from the beginning of charging the main capacitor.
5. A control circuit according to claim 1, wherein the flyback-type
boosting circuit and the forward-type boosting circuit respectively
include oscillation transformers separate from each other.
6. A control circuit according to claim 1, wherein the flyback-type
boosting circuit and the forward-type boosting circuit include an
oscillation transformer in common.
7. A control circuit according to claim 1, wherein the flyback-type
boosting circuit and the forward-type boosting circuit include in
common an oscillation transformer provided with a center tap in a
primary winding thereof, and wherein the center tap of the primary
winding of the oscillation transformer is connected to one pole of
the battery and two end sides of the primary winding of the
oscillation transformer are connected to another pole of the
battery, and the oscillation transformer is controlled by said
selection circuit to cause a current of the battery to flow
intermittently through one end side of the primary winding at the
time of boosting with the flyback-type boosting circuit and through
the other end of the primary winding at the time of boosting with
the forward-type boosting circuit.
8. A control circuit according to claim 6, wherein a direction in
which a current is caused to flow to a primary winding of the
oscillation transformer varies between boosting with the
flyback-type boosting circuit and boosting with the forward-type
boosting circuit.
9. A control circuit according to claim 1, wherein the flyback-type
boosting circuit and the forward-type boosting circuit include in
common an oscillation transformer provided with a center tap in a
secondary winding thereof, and wherein the center tap of the
secondary winding of the oscillation transformer is connected to
one end side of the main capacitor and two end sides of the
secondary winding of the oscillation transformer are connected to
another end side of the main capacitor, and the oscillation
transformer causes a charging current to flow to the main capacitor
through one end side of the secondary winding at the time of
boosting with the flyback-type boosting circuit and through the
other end side of the secondary winding at the time of boosting
with the forward-type boosting circuit.
10. A control circuit according to claim 6, wherein a direction in
which a charging current flows from a secondary winding of the
oscillation transformer to the main capacitor varies between
boosting with the flyback-type boosting circuit and boosting with
the forward-type boosting circuit.
11. A control circuit for a flash device having a charging circuit
which performs a boosting action on a voltage of a battery in a
flyback-type manner and in a forward-type manner, and a capacitor
arranged to be charged by the charging circuit, said control
circuit comprising: an action circuit arranged to cause the
boosting action to be performed in the flyback-type manner at the
time of beginning of charging the capacitor.
12. A control circuit for a flash device having a charging circuit
which performs a boosting action on a voltage of a battery in a
flyback-type manner and in a forward-type manner, and a capacitor
arranged to be charged by the charging circuit, said control
circuit comprising: a setting circuit arranged to set the boosting
action to one of the flyback-type manner and the forward-type
manner according to a charged voltage state of the capacitor.
13. A control circuit according to claim 11, wherein said action
circuit changes the boosting action from the flyback-type manner to
the forward-type manner after a predetermined period of time
elapses from the beginning of charging the capacitor.
14. A control circuit according to claim 12, wherein said setting
circuit sets the boosting action to the flyback-type manner when a
charged voltage of the capacitor is lower than a predetermined
value.
15. A control circuit according to claim 14, wherein said setting
circuit sets the boosting action to the forward-type manner when
the charged voltage of the capacitor has exceeded the predetermined
value.
16. A control circuit for a flash device having a charging circuit
which performs a boosting action on a voltage of a battery in a
flyback-type manner and in a forward-type manner, and a capacitor
arranged to be charged by the charging circuit, said control
circuit comprising: a changeover circuit arranged to change the
boosting action from the flyback-type manner to the forward-type
manner when a rate of efficiency related to the ratio of energy
charged in the capacitor to energy outputted from the battery in
the flyback-type manner becomes coincident with or substantially
coincident with a rate of efficiency related to the ratio of energy
charged in the capacitor to energy outputted from the battery in
the forward-type manner.
17. A control circuit according to claim 11, wherein a flyback-type
boosting transformer and a forward-type boosting transformer are
provided independently of each other.
18. A control circuit according to claim 11, wherein one
transformer is provided for common use as a flyback-type boosting
transformer and a forward-type boosting transformer.
19. A control circuit according to claim 18, further comprising a
switch element arranged to change a direction of a current flowing
to a primary winding of the transformer, a changeover action
between the flyback-type manner and the forward-type manner being
performed by changing the direction of the current.
20. A control circuit according to claim 19, further comprising a
diode having an anode thereof connected to one terminal of a
secondary winding of the transformer and a cathode thereof
connected to one terminal of the capacitor.
21. A control circuit according to claim 18, further comprising a
changeover circuit arranged to change a connection state between a
first state in which one terminal of a secondary winging of the
transformer is connected to one terminal of the capacitor and the
other terminal of the secondary winding is connected to the other
terminal of the capacitor and a second state in which the one
terminal of the secondary winding is connected to the other
terminal of the capacitor and the other terminal of the secondary
winding is connected to the one terminal of the capacitor, a
changeover action between the flyback-type manner and the
forward-type manner being performed by changing the connection
state.
22. A control circuit according to claim 21, further comprising a
first diode connected between the one terminal of the secondary
winding of the transformer and the one terminal of the capacitor in
such a direction as to cause a current to flow from the secondary
winding toward the capacitor in said first state, and a second
diode connected between the other terminal of the secondary winding
and the one terminal of the capacitor in such a direction as to
cause a current to flow from the secondary winding toward the
capacitor in said second state.
23. A control circuit for a flash device having a charging circuit
which performs a boosting action on a voltage of a battery in a
flyback-type manner and in a forward-type manner, and a capacitor
arranged to be charged by the charging circuit, said control
circuit comprising: a changeover circuit arranged to change the
boosting action from the flyback-type manner to the forward-type
manner while the capacitor is in process of being charged.
24. A control circuit according to claim 23, wherein said
changeover circuit changes the boosting action to the forward-type
manner after a charging action on the capacitor in the flyback-type
manner has been performed for a predetermined period of time.
25. A flash device having a charging circuit which performs a
boosting action on a voltage of a battery in a flyback-type manner
and in a forward-type manner, and a capacitor arranged to be
charged by the charging circuit, said flash device comprising: a
changeover circuit arranged to change the boosting action from the
flyback-type manner to the forward-type manner while the capacitor
is in process of being charged.
26. A flash device according to claim 25, wherein said changeover
circuit changes the boosting action from the flyback-type manner to
the forward-type manner when a charged voltage of the capacitor has
reached a predetermined value.
27. A flash device according to claim 25, wherein said changeover
circuit changes the boosting action to the forward-type manner
after a charging action on the capacitor in the flyback-type manner
has been performed for a predetermined period of time.
28. A camera having a flash device having a charging circuit which
performs a boosting action on a voltage of a battery in a
flyback-type manner and in a forward-type manner, and a capacitor
arranged to be charged by the charging circuit, said camera
comprising: a changeover circuit arranged to change the boosting
action from the flyback-type manner to the forward-type manner
while the capacitor is in process of being charged.
29. A camera according to claim 28, wherein said changeover circuit
changes the boosting action from the flyback-type manner to the
forward-type manner when a charged voltage of the capacitor has
reached a predetermined value.
30. A camera according to claim 28, wherein said changeover circuit
changes the boosting action to the forward-type manner after a
charging action on the capacitor in the flyback-type manner has
been performed for a predetermined period of time.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a flash device and a camera
having the flash device.
[0003] 2. Description of Related Art
[0004] It has recently become popular to incorporate an electronic
flash device into a camera for the purpose of a reduction in size
of a camera system. With regard to the camera body, it has become a
general trend to equip cameras with zoom lenses instead of
conventional fixed-focus lenses.
[0005] As a result, cameras of these days permit taking an enlarged
picture of an object of shooting located far away, by setting the
zoom lens at a telephoto position where it has a long focal length.
Meanwhile, the magnification rate of a lens has advanced to make
the F-number which indicates the brightness of the lens on the
telephoto side larger. The larger F-number so to say indicates a
darker lens. The darker lens requires a flash device to be arranged
to have greater light emission energy.
[0006] Such being the situation, a built-in flash device which is
incorporated in a camera is generally arranged to require a large
amount of flash-device charging energy and a large main-capacitor
discharging energy for each shot of flash photography. On the other
hand, however, a general desire for reduction in size of cameras
urges use of a smaller power supply battery. As a result, the
battery has come to have a smaller capacity.
[0007] However, it is deemed to be prerequisite to a flash device
to have a high charging speed. Therefore, a charging circuit which
charges a main capacitor by boosting the voltage of a battery is
generally arranged to derive large energy from the power supply
battery by raising the turn ratio of a transformer according to the
so-called forward converter method.
[0008] The flash device having such a charging circuit is, however,
inferior in the efficiency of use of energy of the battery.
Therefore, under the requirement for a reduction in size of the
battery and an increase in charging and discharging energy, it has
been desired to enhance the efficiency of use of the battery energy
in charging the main capacitor.
BRIEF SUMMARY OF THE INVENTION
[0009] It is an object of the invention to provide a flash device
arranged to enhance the efficiency of use of battery energy for
charging a main capacitor thereof, and also a camera having the
flash device.
[0010] To attain the above object, in accordance with an aspect of
the invention, there is provided a control circuit for a flash
device having a main capacitor, a charging circuit having a
flyback-type boosting circuit and a forward-type boosting circuit
which differ in characteristic from each other and arranged to
charge the main capacitor by boosting a voltage of a battery with
one of the flyback-type boosting circuit and the forward-type
boosting circuit, and a flash discharge tube arranged to emit flash
light by discharging electric charge charged in the main capacitor,
the control circuit comprising a detecting circuit which detects a
charged state of the main capacitor, and a selection circuit which
selectively causes one of the flyback-type boosting circuit and the
forward-type boosting circuit to act, on the basis of a result of
detection provided by the detecting circuit.
[0011] In accordance with another aspect of the invention, in a
flash device having a charging circuit which performs a boosting
action on a battery voltage in a flyback-type manner and in a
forward-type manner, and a capacitor arranged to be charged by the
charging circuit, the boosting action is performed in the
flyback-type manner at the time of beginning of charging the
capacitor.
[0012] In accordance with a further aspect of the invention, in a
flash device having a charging circuit which performs a boosting
action on a battery voltage in a flyback-type manner and in a
forward-type manner, and a capacitor arranged to be charged by the
charging circuit, the boosting action is set to one of the
flyback-type manner and the forward-type manner according to a
charged voltage state of the capacitor.
[0013] The above and further objects and features of the invention
will become apparent from the following detailed description of
preferred embodiments thereof taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0014] FIG. 1 is a circuit diagram showing the arrangement of a
flash device circuit, according to a first embodiment of the
invention, in a camera in which a flash device is incorporated.
[0015] FIG. 2 is a block diagram showing the arrangement of
circuits on the side of a camera body including a CPU which
controls the flash device circuit, according to each embodiment of
the invention.
[0016] FIG. 3 is a flow chart showing the basic actions of the CPU
and other parts.
[0017] FIG. 4 is a flow chart showing actions to be performed in a
flash mode.
[0018] FIG. 5 is a graph showing the characteristic of a
flyback-type converter and that of a forward-type converter in
comparison with each other.
[0019] FIG. 6 is a block diagram showing the arrangement of a flash
device circuit according to a second embodiment of the
invention.
[0020] FIG. 7 is a block diagram showing the arrangement of a flash
device circuit according to a third embodiment of the
invention.
[0021] FIG. 8 is a block diagram showing the arrangement of a flash
device circuit according to a fourth embodiment of the
invention.
[0022] FIG. 9 is a block diagram showing the arrangement of a flash
device circuit according to a fifth embodiment of the
invention.
[0023] FIG. 10 is a flow chart showing actions to be performed in a
flash mode according to a sixth embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] Hereinafter, preferred embodiments of the invention will be
described in detail with reference to the drawings.
[0025] In the case of each of the embodiments described below, the
invention is applied to a camera in which a flash device is
incorporated.
(First Embodiment)
[0026] FIG. 1 is a circuit diagram showing the arrangement of a
flash device circuit, according to a first embodiment of the
invention, in the flash-device-incorporated camera. FIG. 2 is a
block diagram showing the circuit arrangement on the side of a
camera body including a CPU which controls the flash device
circuit, according to each embodiment of the invention.
[0027] Referring to FIG. 1, the circuit arrangement of the flash
device circuit according to the first embodiment is first
described. In FIG. 2, a battery 1 is used for a power supply. The
flash device circuit includes a capacitor 2, a resistor 3 and a
first oscillation transistor 4. A parallel circuit composed of the
capacitor 2 and the resistor 3 is connected between the base and
emitter of the first oscillation transistor 4. The flash device
circuit further includes a resistor 5, an FET (field effect
transistor) 6 arranged as a first switch element, and a pull-down
resistor 8 for the control terminal of the first switch element
6.
[0028] The flash device circuit further includes a capacitor 9, a
resistor 10 and a second oscillation transistor 11. A parallel
circuit composed of the capacitor 9 and the resistor 10 is
connected between the base and emitter of the second oscillation
transistor 11.
[0029] The flash device circuit further includes an FET 12 arranged
as a second switch element, a resistor 13, and a diode 14. The
resistor 13 is connected to the second switch element 12 as a
pull-down resistor for the control electrode thereof. The diode 14
has its anode connected to the negative pole of the battery 1 and
its cathode connected to the second switch element 12.
[0030] An oscillation transformer 15 has a primary winding P which
is provided with an intermediate tap (center tap). An intermediate
electrode which is mounted on the intermediate tap is connected to
the negative pole of the battery 1. In the oscillation transformer
15, the two ends of the primary winding P are connected
respectively to the collector of the first oscillation transistor 4
and the collector of the second oscillation transistor 11. A
junction between the secondary winding S and the feedback winding F
of the oscillation transformer 15 is connected to the second switch
element 12 and the cathode of the diode 14, as shown in FIG. 1.
[0031] A resistor 16 is connected to the feedback winding F of the
oscillation transformer 15 for current limiting purposes. The flash
device circuit further includes a high-voltage rectifying diode 17,
a voltage detecting circuit 18, a trigger circuit 19, a discharge
tube 20, and a main capacitor 21. The output terminal of the
trigger circuit 19 is connected to the trigger electrode of the
discharge tube 20. The discharge tube 20 is connected in parallel
with the main capacitor 21. The voltage detecting circuit 18 is
also connected in parallel with the main capacitor 21 for the
purpose of detecting the voltage of the main capacitor 21.
[0032] The arrangement of the camera control circuit which controls
the flash device circuit as well as other parts on the side of the
camera body is next described. In FIG. 1, reference numeral 22
denotes a circuit block on the side of the camera body (hereinafter
referred to as the camera body block). FIG. 2 shows in detail the
camera body block 22, in which a microcomputer is provided. The
camera body block 22 includes a CPU 125 arranged to control the
whole camera and circuits of varied kinds arranged to be controlled
by the CPU 125. The above-stated flash device circuit is connected
to the CPU 125 through connection lines "a" to "e" and is
controlled by the CPU 125.
[0033] As shown in FIG. 1, the connection line "a" is connected to
the control electrode of the first switch element 6 of the flash
device circuit, and the connection line "b" is connected to the
control electrode of the second switch element 12. The connection
line "c" is a voltage detection driving signal line provided for
driving the voltage detecting circuit 18. The connection line "d"
is arranged to output a voltage value of the main capacitor 21
detected by the voltage detecting circuit 18. When a voltage
detection driving signal is received from the CPU 125 through the
connection line "c" the voltage detecting circuit 18 detects the
voltage of the main capacitor 21, divides the detected voltage and
supplies the divided voltage to the CPU 125 through the connection
line "d".
[0034] The connection line "e" is connected to the input terminal
of the trigger circuit 19. When a light emission start control
signal is received from the CPU 125 through the connection line
"e", the trigger circuit 19 outputs a trigger voltage from its
output terminal to cause the discharge tube 20 to emit flash
light.
[0035] The circuits of varied kinds disposed on the side of the
camera body as shown in FIG. 2 are next described. A constant
voltage circuit 120 is arranged to supply the various circuits with
electric power (VCC) under the control of the CPU 125 through a
terminal VCCEN.
[0036] A switch detecting circuit 121, which is made operative by
the battery or the VCC power supply, is arranged to transmit,
through a terminal SWD to the CPU 125, information on the state and
change of state of each of switches of varied kinds, such as a
power supply switch, a release switch (SW1 and SW2) corresponding
to a shutter release button, etc. The camera body block 22 further
includes a temperature detecting circuit 122, a film sensitivity
detecting circuit 123 which is arranged to obtain information on
the film sensitivity and the number of frames of film, a distance
measuring circuit 126 which is arranged to measure a distance to an
object of shooting, and a light measuring circuit 127 which is
arranged to measure the luminance of the object. These circuits are
arranged to send necessary information to the CPU 125 through
applicable terminals in response to control signals coming from the
CPU 125.
[0037] A shutter driving circuit 124 is arranged to drive a
shutter. A lens driving circuit 129 is arranged to drive a lens. A
film driving circuit 130 is provided for transporting a film. These
circuits are arranged to drive various motors to perform a shutter
driving action, a lens driving action and a film transport action
on the basis of control signals from the CPU 125. A display circuit
128 is composed of an LCD, etc., and is arranged to display the
states of the camera body and the flash device circuit and
necessary information to inform the user of these states and
information.
[0038] Referring to the block circuit diagram of FIG. 2 and the
flow chart of FIG. 3, the basic actions of the CPU 125 and other
parts are described as follows. In the following description, the
power supply on the side of the camera body block 22 is assumed to
have been turned on and the CPU 125 is assumed not to be operating
with the microcomputer in a low power consuming mode.
[0039] When a power supply switch (not shown) is turned on, the
switch detecting circuit 121 detects the turning-on of the power
supply switch and sends a detection signal to the CPU 125. This
causes the microcomputer of the CPU 125 to begin to operate. The
CPU 125 sends a signal through the terminal VCCEN to the constant
voltage circuit 120. Then, the constant voltage circuit 120
supplies each circuit block with electric power Vcc to cause a flow
of processes to begin from step S1.
[0040] At the step S1, the CPU 125 performs an initial setting
action on the microcomputer. At step S2, on the basis of a
detection signal from the switch detecting circuit 121, information
necessary for a photo-taking shot is obtained.
[0041] At step S3, the CPU 125 waits until a first stroke signal
indicating a state of having a release button pushed halfway for
photo-taking preparation is sent from the switch detecting circuit
121 (steps S3 and S2). When the first stroke signal is obtained,
the flow of operation proceeds from the step S3 to step S4. At the
step S4, a predetermined counter is reset to its initial
position.
[0042] At the next step S5, the CPU 125 makes a battery check. At
step S6, a check is made to find if the power supply is in a state
necessary for photo-taking by the camera. If not, the flow returns
to the step S2. If so, the flow proceeds to step S7. At the step
S7, a distance measuring action is controlled for automatic
focusing (AF). In performing control over the distance measuring
action, the CPU 125 sends a control signal from a terminal AFEN to
render the distance measuring circuit 126 operative. Then, a
distance to the object is measured on the basis of distance
measurement information sent from the distance measuring circuit
126 through a terminal AFD.
[0043] At step S8, the CPU 125 sends a control signal from a
terminal AEEN to render the light measuring circuit 127 operative.
Then, the luminance of the object is measured on the basis of
luminance information sent from the light measuring circuit 127
through a terminal AED. At step S9, a check is made to find if the
object luminance is darker than a predetermined luminance value. If
so, the flow proceeds to step S10 for a flash mode.
[0044] The operation in the flash mode at the step S10 is shown in
the flow chart of FIG. 4.
[0045] In the flash mode, at step S20 of FIG. 4, the CPU 125 first
sets a charging timer, which is arranged to cut off a charging
process when the charging time becomes longer than a period of time
of, for example, 10 to 15 sec. or thereabout. At the next step S21,
the CPU 125 gives a predetermined oscillation signal to the control
electrode of the first switch element 6 through the connection
terminal "a" shown in FIG. 1. The predetermined oscillation signal
is a signal (pulse signal) for separate excitation which is
outputted at low and high levels repeating in a predetermined
cycle.
[0046] At the flash device circuit, when the high level signal is
given to the control electrode of the first switch element 6, the
first switch element 6 turns on to cause the base current of the
first oscillation transistor 4 to flow through the current limiting
resistor 5. Then, with the first oscillation transistor 4 rendered
conductive, a collector current which is "hfe" times as large as
the base current flows in a loop of "the positive pole of the
battery 1--the emitter and collector of the first oscillation
transistor 4--the intermediate terminal of the primary winding P of
the oscillation transformer 15--the negative pole of the battery
1".
[0047] Therefore, an induced electromotive force is generated at
the secondary winding S of the oscillation transformer 15. However,
since the induced electromotive force is of such a polarity that is
blocked by the high-voltage rectifying diode 17, no excitation
current flows from the oscillation transformer 15, so that energy
is stored in the oscillation transformer 15.
[0048] When the low level signal is next given to the control
electrode of the first switch element 6, the first switch element 6
turns off to cut off the base current of the first oscillation
transistor 4. The first oscillation transistor 4 thus becomes
nonconductive to generate a back electromotive force at the
secondary winding S of the oscillation transformer 15. Then, the
energy stored in the oscillation transformer 15 is discharged by
the back electromotive force. At this time, a current flows in a
loop of "the high-voltage rectifying diode 17--the main capacitor
21--the diode 14". Then, electric charge is accumulated at the main
capacitor 21.
[0049] When the high level signal is given again to the control
electrode of the first switch element 6 with the energy discharged
further from within the oscillation transformer 15, the first
switch element 6 and the first oscillation transistor 4 are again
rendered conductive to allow the oscillation transformer 15 to
store energy. After that, a low level signal next given to the
control electrode of the first switch element 6 renders the first
switch element 6 and the first oscillation transistor 4
nonconductive. Then, the energy stored in the oscillation
transformer 15 is discharged to charge the main capacitor 21 with
electric charge. With these actions repeated in the flash device
circuit, the potential of the main capacitor 21 rises. The manner
in which the oscillation and the boosting action of the circuit
arrangement are carried out as described above represents the
so-called flyback converter method.
[0050] At step S22, while the above-stated actions are repeated to
charge the main capacitor 21, the CPU 125 gives a voltage detection
driving signal to the voltage detecting circuit 18 through the
connection line "c". Then, by obtaining a divided voltage of the
main capacitor 21 from the voltage detecting circuit 18 through the
connection line "d", the CPU 125 detects the charged voltage of the
main capacitor 21. The CPU 125 makes this voltage detection through
an A/D converter shown in FIG. 2.
[0051] At the next step S23, the CPU 125 makes a check to find if
the charged voltage of the main capacitor 21 has reached a
predetermined voltage level. If not, the flow of operation returns
to the step S22. If so, the flow proceeds to step S24.
[0052] At the step S24, the CPU 125 performs a charging circuit
changeover process. The changeover process is performed in the
following manner. The oscillation signal, i.e., a
high-level/low-level signal, which has been outputted through the
connection line "a" with the charged voltage of the main capacitor
21 being lower than a predetermined voltage is brought to a stop,
after the charged voltage comes to exceed the predetermined
voltage, and only a low level signal is outputted. Then, a high
level signal is sent through the connection line "b" to the control
electrode of the second switch element 12. By this, the first
switch element 6 is kept in its off-state (nonconductive), while
the second switch element 12 is turned on.
[0053] When the second switch element 12 is turned on in the flash
device circuit, the base current of the second oscillation
transistor 11 flows from the battery 1 through the emitter and base
of the second oscillation transistor 11, the second switch element
12, the feedback winding F of the oscillation transformer 15 and
the resistor 16. As a result, a collector current which is "hfe"
times as large as the base current comes to flow to the negative
pole of the battery 1 through the primary winding P and the
intermediate terminal of the oscillation transformer 15.
[0054] This collector current causes an induced electromotive force
to be generated at the secondary winding S of the oscillation
transformer 15. By this, the main capacitor 21 is charged through a
loop of "the high-voltage rectifying diode 17--the main capacitor
21 --the battery 1--the base and emitter of the second oscillation
transistor 11--the second switch element 12 --the secondary winding
S of the oscillation transformer 15--the high-voltage rectifying
diode 17". Since the induced electromotive force, at the same time,
becomes also the base current of the second oscillation transistor
11, the base current of the second oscillation transistor 11 comes
back in an increased state. The return of the base current thus
increased causes positive feedback to instantly bring a voltage
between the collector and emitter of the second oscillation
transistor 11 into a saturated state.
[0055] After the lapse of a period of time from the flow of the
above-stated current, a magnetic flux within the core of the
oscillation transformer 15 comes to saturate to generate a back
electromotive force in each of the secondary winding S and the
feedback winding F of the oscillation transformer 15. The back
electromotive force generated in the secondary winding S of the
oscillation transformer 15 gives a reverse bias to the base of the
second oscillation transistor 11 through a loop of "the second
switch element 12--the base and emitter of the second oscillation
transistor 11--the battery 1--the main capacitor 21--the parasitic
capacity of the high-voltage rectifying diode 17--the secondary
winding S of the oscillation transformer 15". At the same time, the
back electromotive force generated at the feedback winding F of the
oscillation transformer 15 gives a reverse bias also to the base of
the second oscillation transistor 11 through a loop of "the second
switch element 12--the base and emitter of the second oscillation
transistor 11--the battery 1--the resistor 16--the feedback winding
F". Therefore, the second oscillation transistor 11 suddenly
becomes nonconductive.
[0056] When the saturated state of a magnetic flux within the core
of the oscillation transformer 15 is canceled, the base current of
the second oscillation transistor 11 again flows to charge the main
capacitor 21 by repeatedly rendering the second oscillation
transistor 11 alternately conductive and nonconductive. The
oscillating and boosting actions described above represent the
so-called forward converter method.
[0057] At step S25 in FIG. 4, while the main capacitor 21 is in
process of being charged in the above manner, the CPU 125 sends a
voltage detection driving signal to the voltage detecting circuit
18 through the connection line "c" to obtain a divided voltage of
the main capacitor 21 outputted from the voltage detecting circuit
18 through the connection line "d". The charged voltage of the main
capacitor 21 is thus detected.
[0058] At the next step S26, the CPU 125 makes a check to find if
the charged voltage of the main capacitor 21 has reached a charging
completion voltage. If not, the flow proceeds to step S27 to find
if the charging timer has counted a predetermined period of time.
The steps S25, S26 and S27 are executed in a looped manner to make
the check for the charged voltage. If the charged voltage of the
main capacitor 21 reaches the charging completion voltage before
the count-up of the charging timer, the flow proceeds from the step
S26 to step S28. At the step S28, a charging completion flag is set
to indicate the completion of charging, and the flow proceeds to
step S30.
[0059] In a case where the count of the charging timer comes to an
end before the charged voltage of the main capacitor 21 reaches the
charging completion voltage, the flow proceeds from the step S27 to
step S29. At the step S29, a charging incompletion flag is set to
indicate that the charging action has not been finished, and the
flow proceeds to step S30.
[0060] At the step S30, to bring the charging action to a stop, the
CPU 125 turns off the second switch element 12 by shifting the
level of the connection line "b" from a high level to a low level.
At step S31, the action of the charging timer is brought to a stop,
and the flow returns to the main routine shown in FIG. 3.
[0061] At step S11, after the flash mode, the CPU 125 checks the
flag set up at the step S28 or S29 in the flash mode to find if the
process of charging has been completed. If not, i.e., if the flag
is the charging incompletion flag, the flow returns to the step S2.
If so, i.e., if the flag is the charging completion flag, the flow
proceeds to step S12.
[0062] At the step S12 and the next step S13, the CPU 125 checks
the release switches SW1 and SW2 for their states. The flow of
operation of the CPU 125 waits for a second stroke of the release
button (full pushing operation on the release button) while
monitoring the first stroke of the release button. When the release
button is freed from the first stroke of operation thereon, the
flow returns from the step S12 to the step S2. If the second stroke
is made, the flow proceeds from the step S13 to step S14. At the
step S14, the lens driving circuit 129 is caused to adjust the
focusing state of the lens on the basis of distance measurement
data obtained at the step S7. The flow then proceeds to step
S15.
[0063] At the step S15, the CPU 125 controls through the shutter
driving circuit 124 a shutter opening action according to the data
of object luminance obtained at the step S8 and the film
sensitivity. In a case where the luminance of the object is low
requiring the use of flash light, the discharge tube 20 of the
flash device circuit is caused to emit light at an aperture value
apposite to the distance measurement data and the film
sensitivity.
[0064] The discharge tube 20 is caused to emit light by giving a
high level signal to the connection line "e" shown in FIG. 1. With
the high level signal given to the connection line "e", a high
pulse voltage is generated from the output terminal of the trigger
circuit 19. The high pulse voltage is sent to the trigger electrode
of the discharge tube 20 to excite the discharge tube 20. This
excitation causes the impedance of the discharge tube 20 to drop at
once. Then, the charged energy of the main capacitor 21 is
discharged and converted into light energy to illuminate the object
of shooting with light thus emitted. In a case where the discharge
tube 20 is caused to emit light, the CPU 125 sets a flash flag FAL,
which indicates the use of the flash device, to "1".
[0065] At step S16, when the opening of the shutter is controlled
to close the shutter, the CPU 125 brings the lens, which has been
at a focal point position, back to its initial position. At step
S17, the film driving circuit 130 is caused to wind one frame
portion of the film which has been used for taking a shot.
[0066] At the next step S18, the CPU 125 makes a check to find if
the flash flag FAL is set at "1". If so, the flow proceeds to step
S19 to shift the mode of the camera to the flash mode. At the step
S19, the main capacitor 21 is charged, in the same manner as at the
step S10, and a sequence of processes comes to an end. Further, if
the flash flag FAL is found at the step S18 not to be at "1", a
shot is considered to have been taken without using the flash
device, and the flow returns from the step S18 to the step S2
without performing the process of charging the main capacitor
21.
[0067] In the case of the first embodiment, as described above, the
charging action is performed by using a boosting circuit of the
flyback converter type (hereinafter referred to as the flyback
type) when the charged voltage of the main capacitor 21 is lower
than a predetermined level and by using a boosting circuit of the
forward converter type (hereinafter referred to as the forward
type) when the charged voltage of the main capacitor 21 exceeds the
predetermined level. FIG. 5 shows the characteristics of the two
types of boosting circuits. In FIG. 5, the abscissa axis shows the
charged voltage (V.sub.MC) of the main capacitor 21. The ordinate
axis shows a rate of real-time efficiency (.eta.), which is the
ratio of the energy with which the main capacitor 21 is charged to
the energy outputted from the battery. A curve "A" represents the
efficiency of the converter of the flyback type and a curve "B"
represents the efficiency of the converter of the forward type.
[0068] As apparent from FIG. 5, the characteristic of the converter
of the flyback type is such that, with respect to the real-time
efficiency for each of charging voltages, the input current from
the battery does not change from the initially set current to show
a flat characteristic, and the efficiency gradually drops
accordingly as the charged voltage of the main capacitor 21
increases.
[0069] On the other hand, the characteristic of the converter of
the forward type is as follows. As shown in FIG. 5, the efficiency
is extremely poor when the charged voltage of the main capacitor 21
is low, but rapidly improves accordingly as the charged voltage
increases. In other words, in the case of the converter of the
forward type, the value of current increases accordingly as the
charged voltage of the main capacitor 21 is lower. The so-called
rush current flows at the time of initial charging. The battery
energy using efficiency thus becomes extremely poor at that
time.
[0070] The flash device circuit according to the first embodiment
is, therefore, arranged as follows. The converter of the flyback
type is changed over to the converter of the forward type at a
point of time where a charged voltage of the main capacitor 21
becomes a predetermined voltage V1, indicated by a broken line in
FIG. 5, at a part where the efficiency value of the converter of
the flyback type crosses the efficiency value of the converter of
the forward type between a charged voltage Vo of the main capacitor
21 obtained at the time of beginning of charging and a charging
completion voltage Vstop, as shown in FIG. 5. The changeover
arrangement enables the flash device circuit to obtain the
efficient charging performances of the two different types of
converters. The efficiency of use of the battery 1 thus can be
enhanced. Incidentally, the changeover may be effected at a point
in the neighborhood of the voltage V1.
(Second Embodiment)
[0071] FIG. 6 shows the arrangement of a flash device circuit
according to a second embodiment of the invention. The flash device
circuit according to the second embodiment is arranged to make the
changeover of use of separate-excitation converters of two
different types by using two transformers. In FIG. 6, all parts
that are the same as those of the first embodiment, such as the
connection lines, etc., are indicated by the same reference
numerals and symbols as those used for the first embodiment. The
main routine of the sequence of control actions of the second
embodiment is also the same as the flow chart shown in FIG. 3. For
the second embodiment, therefore, only the arrangement of the flash
device circuit and processes to be performed in the flash mode
(steps S10 and S19 in FIG. 3) are described here.
[0072] Referring to FIG. 6, a battery 1 is used for a power supply.
The flash device circuit includes an FET 30 which is a first
oscillation element. The first oscillation element 30 has its
control electrode connected to the connection line "a" of the CPU
125 disposed within the camera body block 22 and is arranged to be
turned on (become conductive) and off (become nonconductive) by a
predetermined oscillation signal outputted from the CPU 125 through
the connection line "a". A resistor 31, which is arranged to serve
as a pull-down resistance for the first oscillation element 30, is
disposed between the control electrode of the first oscillation
element 30 and the negative pole of the battery 1. A first
transformer 32 has one end side of its primary winding P connected
to the positive pole of the battery 1 and the other end side of the
primary winding P connected to the negative pole of the battery 1
through the first oscillation element 30.
[0073] An FET 33 is a second oscillation element. A resistor 34 is
arranged to serve as a pull-down resistance for the second
oscillation element 33. The second oscillation element 33 has its
control electrode connected to the connection line "b" of the CPU
125 and is arranged to be turned on or off by a predetermined
oscillation signal outputted from the CPU 125 through the
connection line "b". The resistor 34 is connected between the
control electrode of the second oscillation element 33 and the
negative pole of the battery 1. A second oscillation transformer 35
has one end side of its primary winding P connected to the positive
pole of the battery 1 and the other end side of the primary winding
P connected to the negative pole of the battery 1 through the
second oscillation element 33, as shown in FIG. 6.
[0074] Diodes 36 and 37 are provided for rectifying a high voltage.
Each of the high-voltage rectifying diodes 36 and 37 has its anode
connected to the one end side of the oscillation transformer 32 or
35 and its cathode connected to one end side of the main capacitor
21. The other end side of the secondary winding of each of the
oscillation transformers 32 and 35 is connected to the other end
side of the main capacitor 21.
[0075] The camera body block 22, the voltage detecting circuit 18,
the trigger circuit 19, the discharge tube 20 and the main
capacitor 21 in the second embodiment are arranged in the same
manner as the corresponding parts of the first embodiment described
in the foregoing.
[0076] In the flash device circuit according to the second
embodiment, the first oscillation transformer 32 is the converter
of the flyback type, and the second oscillation transformer 35 is
the converter of the forward type. A sequence of control actions of
the flash device circuit according to the second embodiment is next
described referring to the flow chart of FIG. 4 as follows.
[0077] At step S20 of FIG. 4, in the flash mode, the CPU 125 first
sets the charging timer. At the step S21, to start charging, the
CPU 125 gives a predetermined oscillation signal to the control
electrode of the first oscillation element 30 through the
connection line "a". The predetermined oscillation signal is a
separately-exciting signal which is outputted repeating a high
level signal and a low level signal in a predetermined cycle, as
mentioned in the foregoing.
[0078] In the flash device circuit, with the high level signal and
the low level signal applied to the control electrode of the first
oscillation element 30, the first oscillation element 30 is
rendered conductive and nonconductive. When the high level signal
is applied to the control electrode of the first oscillation
element 30, the first oscillation element 30 becomes conductive to
allow a current to flow from the battery 1 through the primary
winding P of the first oscillation transformer 32 and the first
oscillation element 30.
[0079] Therefore, an induced electromotive force is generated at
the secondary winding S of the first oscillation transformer 32.
However, since the induced electromotive force is of such a
polarity that is blocked by the high-voltage rectifying diode 36,
no excitation current flows from the first oscillation transformer
32, so that energy is stored in the first oscillation transformer
32.
[0080] When the low level signal is given to the control electrode
of the first oscillation element 30, the first oscillation element
30 turns off (nonconductive) to generate a back electromotive force
at the secondary winding S of the first oscillation transformer 32.
The energy stored in the first oscillation transformer 32 is
discharged by this back electromotive force. Then, a current flows
in a loop of "the high-voltage rectifying diode 36--the main
capacitor 21--the secondary winding S of the first oscillation
transformer 32" to accumulate electric charge in the main capacitor
21.
[0081] When the high level signal is again given to the control
electrode of the first oscillation element 30 with the energy
discharged further from within the first oscillation transformer
32, the first oscillation element 30 again becomes conductive to
allow energy to be stored in the first oscillation transformer 32
in the same manner. Then, the low level signal given to the control
electrode of the first oscillation element 30 next time renders the
first oscillation element 30 nonconductive to allow the stored
energy of the first oscillation transformer 32 to be discharged and
to allow the main capacitor 21 to be charged with electric charge.
In the flash device circuit according to the second embodiment,
these actions are repeated to cause the potential of the main
capacitor 21 to rise.
[0082] At step S22, while the above-stated actions are repeated to
charge the main capacitor 21, the CPU 125 detects the charged
voltage of the main capacitor 21 by giving a voltage detection
driving signal to the voltage detecting circuit 18 through the
connection line "c" to obtain a divided voltage of the main
capacitor 21 which is outputted from the voltage detecting circuit
18 through the connection line "d". This voltage detection is made
through the A/D converter which is disposed at the CPU 125 shown in
FIG. 2.
[0083] At step S23, the CPU 125 makes a check to find if the
charged voltage of the main capacitor 21 has reached a
predetermined voltage level V1 (shown in FIG. 5). If not, the flow
of operation returns to the step S22. If so, the flow proceeds to
step S24.
[0084] At the step S24, the CPU 125 performs a charging circuit
changeover process. The changeover process is performed in the
following manner. The oscillation signal, i.e., a
high-level/low-level signal, which has been outputted through the
connection line "a" with the charged voltage of the main capacitor
21 being lower than a predetermined voltage is brought to a stop,
after the charged voltage comes to exceed the predetermined
voltage, and only a low level signal is outputted. Then, the
oscillation signal (the high-level/low-level signal) is sent
through the connection line "b" to the control electrode of the
second oscillation element 33. By this, the first oscillation
element 30 is kept in its off-state (nonconductive), while the
second oscillation element 33 is caused to take a state of
repeatedly becoming conductive and nonconductive in a predetermined
cycle.
[0085] Under this condition, when a high level signal is given to
the control electrode of the second oscillation element 33, the
second oscillation element 33 becomes conductive to allow a current
to flow from the battery 1 through the primary winding P of the
second oscillation transformer 35 and the second oscillation
element 33.
[0086] Therefore, an induced electromotive force is generated at
the secondary winding S of the second oscillation transformer 35.
Then, since the directions of the primary winding and the secondary
winding of the second oscillation transformer 35 differ from those
of the first oscillation transformer 32, as shown in FIG. 6, the
induced electromotive force comes to have such a polarity that is
not blocked by the high-voltage rectifying diode 37. As a result,
an excitation current flows from the second oscillation transformer
35 to allow the main capacitor 21 to be charged with electric
charge through the high-voltage rectifying diode 37.
[0087] In the case of the flash device circuit, before the magnetic
flux within the core of the second oscillation transformer 35
becomes saturated, a low level signal is given to the control
electrode of the second oscillation element 33 to turn off (to
render nonconductive) the second oscillation element 33 to
annihilate the magnetic flux. Then, a high level signal is given
again at the timing of the annihilation of the magnetic flux within
the core. The electric charge is accumulated at the main capacitor
21 by thus repeatedly rendering the second oscillation element 33
conductive and nonconductive. As a result, the potential of the
main capacitor 21 rises.
[0088] At step S25 of FIG. 4, while the main capacitor 21 is in
process of being charged in the above manner, the CPU 125 sends a
voltage detection driving signal to the voltage detecting circuit
18 through the connection line "c". The CPU 125 thus detects the
charged voltage of the main capacitor 21 by obtaining a divided
voltage of the main capacitor 21 from the voltage detecting circuit
18 through the connection line "d". After that, steps S26 to S29
are executed in the manner described in the foregoing.
[0089] At step S30, which is provided for bringing the process of
charging the main capacitor 21 to a stop, the CPU 125 changes the
level of the connection line "b" from a high level to a low level
to turn off the second oscillation element 33 (render
nonconductive). At the next step S31, the operation of the charging
timer is brought to a stop, in the same manner as in the first
embodiment, and the flow returns to the main routine shown in FIG.
3.
(Third Embodiment)
[0090] FIG. 7 shows the arrangement of a flash device circuit
according to a third embodiment of the invention. In the case of
the third embodiment, the flash device circuit uses one transformer
and the changeover between charging with the converter of the
flyback type and charging with the converter of the forward type is
effected by switching the primary current of the transformer. In
FIG. 7, all components, connection lines, etc., that are the same
as those of the first embodiment described in the foregoing are
indicated by the same reference numerals and symbols, and the
details of them are omitted from the following description. The
sequence of processes of the main routine shown in FIG. 3 and the
sequence of control processes in the flash mode shown in FIG. 4 are
executed by the third embodiment in the same manner as described in
the foregoing. Therefore the following description covers only the
arrangement and the charging action of the flash device
circuit.
[0091] Referring to FIG. 7, the flash device circuit includes a
capacitor 41, a resistor 42 and an oscillation transistor 43. A
parallel circuit composed of the capacitor 41 and the resistor 42
is connected between the base and the emitter of the oscillation
transistor 43.
[0092] The flash device circuit further includes a current limiting
resistor 44, a switch element 45, a pull-down resistance 46 for the
switch element 45, switch elements 47 and 49, and pull-down
resistances 48 and 50 connected respectively for the switch
elements 47 and 49.
[0093] In the third embodiment, as the connection lines for
connection between the flash device circuit and the CPU 125 of the
camera body block 22, there are additionally provided a connection
line "f" connected to the control electrode of the switch element
47 and a connection line "g" connected to the control electrode of
the switch element 49.
[0094] The charging action of the flash device circuit in the flash
mode is performed as follows. When the charged voltage of the main
capacitor 21 is lower than the predetermined changeover voltage V1
shown in FIG. 5, the main capacitor 21 is charged first by using
the boosting circuit (or converter) of the flyback type, which does
not bring about any initial flow of rush current.
[0095] For the flyback-type boosting circuit action, the CPU 125
controls, through the connection lines "a" and "f", the switch
element 6 and the switch element 47 by turning them on or off. In
other words, to start charging the main capacitor 21 with the
flyback-type boosting circuit, the CPU 125 outputs a high level
signal to the connection line "f" to turn on (to render conductive)
the switch element 47. After that, a predetermined oscillation
signal is given to the control electrode of the switch element 6
through the connection line "a". The predetermined oscillation
signal is arranged to be such that a high level signal and a low
level signal are repeatedly outputted in a predetermined cycle as
described in the foregoing.
[0096] With the switch element 6 rendered conductive by the high
level signal through the connection line "a", a current from the
battery 1 flows, as a base current of the oscillation transistor 4,
through the base and emitter of the oscillation transistor 4, the
current limiting resistor 5 and the switch element 6. Then, a
collector current which is "hfe" times as large as the base current
flows from the battery 1 through the primary winding P of an
oscillation transformer 51 and the switch element 47.
[0097] The collector current brings about an induced electromotive
force in the secondary winding S of the oscillation transformer 51.
However, since the induced electromotive force is of such a
polarity that is blocked by the high-voltage rectifying diode 17,
no charging current flows to the main capacitor 21, so that energy
is stored in the oscillation transformer 51.
[0098] Next, when the connection line "a" is caused to be at a low
level to give a low level signal to the control electrode of the
switch element 6, the switch element 6 turns off to become
nonconductive and to cut off the base current of the oscillation
transistor 4. The oscillation transistor 4 is rendered
nonconductive by this. The potential of the secondary winding S of
the oscillation transformer 51 is inverted to generate a back
electromotive force. Then, the energy stored in the oscillation
transformer 51 is discharged by the back electromotive force to
cause a charging current to flow to the main capacitor 21 through
the high-voltage rectifying diode 17.
[0099] With the energy discharged further from within the
oscillation transformer 51, when a high level signal is again given
to the control electrode of the switch element 6 through the
connection line "a", the switch element 6 and the oscillation
transistor 4 again become conductive to store energy in the
oscillation transformer 51. After that, when a low level signal is
given to the control electrode of the switch element 6, the switch
element 6 and the oscillation transistor 4 become nonconductive, so
that the energy stored in the oscillation transformer 51 is
discharged to charge the main capacitor 21 with electric charge. In
the flash device circuit, the potential of the main capacitor 21 is
caused to rise by repeating these actions.
[0100] While the main capacitor 21 is in process of being charged
by repeating these actions as mentioned above, the charged voltage
of the main capacitor 21 is detected by the voltage detecting
circuit 18 in response to a voltage detection driving signal sent
from the CPU 125 through the connection line "c". The voltage
detecting circuit 18 then sends a divided voltage of the charged
voltage thus detected to the CPU 125 through the connection line
"d" (at step S22 of FIG. 4) When the charged voltage of the main
capacitor 21 is found by the CPU 125 through the A/D converter
(FIG. 2) to have reached the predetermined changeover voltage V1 on
the basis of the result of the voltage detection, the use of the
boosting circuit is changed from the flyback type over to the
forward type (at steps S23 and S24).
[0101] In effecting the changeover of the boosting circuit, the CPU
125 sends low level signals respectively from the connection lines
"a" and "f" to keep the switch elements 6 and 47 nonconductive,
sends a high level signal from the connection line "g" to keep the
switch element 49 in an on-state (conductive), and then sends the
predetermined oscillation signal from the connection line "b" to
bring the switch element 45 into an on-off oscillating state.
[0102] With the high level signal given to the switch element 45
through the connection line "b", the switch element 45 becomes
conductive. Then, a current from the battery 1 flows as a base
current of the oscillation transistor 43 through the base and
emitter of the oscillation transistor 43, the current limiting
resistor 44 and the switch element 45. Then, a collector current
which is "hfe" times as large as the base current flows from the
battery 1 through the primary winding P of the oscillation
transformer 51 and the switch element 49.
[0103] This collector current brings about an induced electromotive
force at the secondary winding S of the oscillation transistor 51.
Since the direction of the collector current generated this time is
reverse to that of the force last generated, the induced
electromotive force of the secondary winding S of the oscillation
transformer 51 is not blocked by the high-voltage rectifying diode
17 and is allowed to flow through the high-voltage rectifying diode
17 to the main capacitor 21 as a charging current.
[0104] In the case of the flash device circuit according to the
third embodiment, a low level signal is arranged to be given to the
control electrode of the switch element 45 through the connection
line "b" before the saturation of the magnetic flux within the core
of the oscillation transformer 51. The low level signal turns off
the switch element 45 and the oscillation transistor 43 to render
them nonconductive and to annihilate the magnetic flux. A high
level signal is given again to the switch element 45 at the timing
when the magnetic flux is annihilated within the core of the
oscillation transformer 51. The potential of the main capacitor 21
is raised by causing the switch element 45 and the oscillation
transistor 43 to be repeatedly turned on and off in the manner
described above.
[0105] The actions to be performed after the actions described
above are the same as the steps S25 to S31 described in the
foregoing with reference to FIG. 4.
(Fourth Embodiment)
[0106] FIG. 8 shows the arrangement of a flash device circuit
according to a fourth embodiment of the invention. While a
separately-excited converter (boosting circuit) of the fourth
embodiment is arranged to be changed between the flyback type and
the forward type in the same manner as in the other embodiments
described above, the flash device circuit according to the fourth
embodiment differs in the following point. In the case of the
fourth embodiment, a transformer has its secondary winding S
provided with an intermediate electrode, and a secondary current is
arranged to be switched from one current over to another by using
this intermediate electrode.
[0107] In FIG. 8, all components, connection lines, etc., that are
the same as those of the embodiments described in the foregoing are
indicated by the same reference numerals and symbols, and the
details of them are omitted from the following description. The
sequence of processes of the main routine shown in FIG. 3 and the
sequence of control actions in the flash mode shown in FIG. 4 are
executed by the fourth embodiment in the same manner as described
in the foregoing. The following description, therefore, covers only
the arrangement and the charging action of the flash device
circuit.
[0108] Referring to FIG. 8, the flash device circuit includes a
resistor 61 and an oscillation element 62. The resistor 61 is a
pull-down resistance for the oscillation element 62. The flash
device circuit further includes an oscillation transformer 63, a
resistor 64, a light emitting diode 65, a high-voltage rectifying
diode 66, and the so-called light-activated thyristor 67, which
becomes conductive upon receiving light illumination.
[0109] The oscillation transformer 63 has one end (side) of its
primary winding P connected to the positive pole of the battery 1
and the other end (side) of the primary winding P connected to the
negative pole of the battery 1 through the oscillation element 62.
The secondary winding S of the oscillation transformer 63 has its
one end connected to one end of the main capacitor 21 through the
high-voltage rectifying diode 66 and the other end connected to the
anode of the light-activated thyristor 67. Further, the secondary
winding S of the oscillation transformer 63 is provided with an
intermediate electrode, which divides the secondary winding S into
a secondary winding S.sub.1 and a secondary winding S2, as shown in
FIG. 8. The intermediate electrode of the secondary winding S is
connected to the other end of the main capacitor 21.
[0110] In the fourth embodiment, among the connection lines
arranged to connect the flash device circuit to the CPU 125 of the
camera body block 22, the connection line "b" is replaced with a
connection line "h", which is provided for outputting electric
power to the light emitting diode 65.
[0111] The charging action of the flash device circuit in the flash
mode in the fourth embodiment is performed as follows. When the
charged voltage of the main capacitor 21 is lower than the
predetermined changeover voltage V1 shown in FIG. 5, the main
capacitor 21 is charged first by using the boosting circuit of the
flyback type, which does not bring about any initial flow of rush
current.
[0112] The flyback-type boosting circuit acts as follows. The CPU
125 controls the oscillation element 62 to make the oscillation
element 62 conductive and nonconductive. In this case, a
separately-excited oscillation signal which becomes a high level
and a low level at a predetermined frequency is given through the
connection line "a" to the control electrode of the oscillation
element 62.
[0113] When the oscillation element 62 is rendered conductive by
the high level signal of the connection line "a", a current flows
from the battery 1 through the primary winding P of the oscillation
transformer 63 and the oscillation element 62. This current brings
about an induced electromotive force at the secondary winding
S.sub.1of the oscillation transformer 63. However, since the
induced electromotive force is of such a polarity that is blocked
by the high-voltage rectifying diode 66, no charging current flows
to the main capacitor 21, so that energy is stored in the
oscillation transformer 63. An induced electromotive force is
generated also at the secondary winding S2. However, since the
light-activated thyristor 67 is in an off-state, there is also no
flow of charging current to the main capacitor 21.
[0114] When a low level signal is next given to the control
electrode of the oscillation element 62 with the level of the
connection line "a" becoming low, the oscillation element 62 turns
off (becomes nonconductive) to cut off the current flow to the
oscillation transformer 63. Therefore, the potential of the
secondary winding S of the oscillation transformer 63 is inverted
to generate a back electromotive force. By this back electromotive
force, the energy stored in the oscillation transformer 63 is
discharged. Then, a charging current flows to the main capacitor 21
through a loop of "the secondary winding S.sub.1--the high-voltage
rectifying diode 66--the main capacitor 21".
[0115] With the energy discharged further from within the
oscillation transformer 63, when a high level signal is again given
to the control electrode of the oscillation element 62 through the
connection line "a", the oscillation element 62 becomes conductive
to allow the oscillation transformer 63 to store energy in the same
manner again. After that, the next low level signal given to the
control electrode of the oscillation element 62 renders the
oscillation element 62 nonconductive to cause the oscillation
transformer 63 to discharge the stored energy, so that the main
capacitor 21 is charged with electric charge. The potential of the
main capacitor 21 in the flash device circuit is thus caused to
rise with these actions repeated.
[0116] While the main capacitor 21 is being charged by repeating
the actions mentioned above, the charged voltage of the main
capacitor 21 is detected by the voltage detecting circuit 18 in
response to a voltage detection driving signal coming from the CPU
125 through the connection line "c". The voltage detecting circuit
18 then sends a divided voltage of the charged voltage of the main
capacitor 21 thus detected to the CPU 125 through the connection
line "d" (step S22 of FIG. 4)
[0117] When the charged voltage of the main capacitor 21 is found
by the CPU 125 through the A/D converter (FIG. 2) to have reached
the predetermined changeover voltage V1 on the basis of the result
of the voltage detection, the use of the boosting circuit is
changed from the flyback type over to the forward type (steps S23
and S24).
[0118] In effecting the changeover of the boosting circuit, the CPU
125 sends a low level signal from the connection line "a" to
temporarily render the oscillation element 62 nonconductive, and
then outputs an electric current from the connection line "h".
[0119] The current outputted from the connection line "h" is
limited by the resistor 64 and flows through the light emitting
diode 65 to cause the light emitting diode 65 to light up. Then,
the light from the light emitting diode 65 illuminates the
light-activated thyristor 67 to render the light-activated
thyristor 67 conductive.
[0120] In the case of the fourth embodiment, the state of having
the light emitting diode 65 alight and rendering the
light-activated thyristor 67 conductive is arranged to continue
until the voltage of the main capacitor 21 reaches the charging
completion voltage V1. Under this condition, the oscillation signal
of the forward type the level of which repeatedly becomes high and
low in a predetermined cycle is given from the CPU 125 to the
control electrode of the oscillation element 62 through the
connection line "a".
[0121] With the high level signal given to the oscillation element
62 through the connection line "a", the oscillation element 62
becomes conductive to allow a primary current to flow from the
battery 1 to the primary winding P of the oscillation transformer
63. The primary current brings about an induced electromotive force
at the secondary winding S2 of the oscillation transformer 63.
Then, since the light-activated thyristor 67 is in a conductive
state this time, a charging current flows from the anode to the
cathode of the light-activated thyristor 67 and through the main
capacitor 21 and the intermediate electrode of the oscillation
transformer 63.
[0122] Next, before the saturation of the magnetic flux within the
core of the oscillation transformer 63, a low level signal is given
to the control electrode of the oscillation element 62 through the
connection line "a". The low level signal causes the oscillation
element 62 to turn off (to become nonconductive) to bring the flow
of the primary current of the oscillation transformer 63 to a stop.
As a result, the magnetic flux within the core decreases. Then, at
the timing of annihilation of the magnetic flux within the core, a
high level signal is given again to the control electrode of the
oscillation element 62 through the connection line a
[0123] After that, the potential of the main capacitor 21 is caused
to rise by repeatedly causing the oscillation element 62 to turn on
and off in the above-stated manner. The actions to be performed
thereafter are the same as the steps S25 to S31 of FIG. 4 described
in the foregoing.
[0124] Further, the flash device circuit according to the fourth
embodiment is arranged to avoid the interference of the secondary
winding S.sub.2 of the oscillation transformer 63 by means of the
high-voltage rectifying diode 66. However, this arrangement may be
changed to use a light-activated thyristor and a light emitting
diode in place of the high-voltage rectifying diode 66.
(Fifth Embodiment)
[0125] FIG. 9 shows the arrangement of a flash device circuit
according to a fifth embodiment of the invention. While a
separately-excited converter (boosting circuit) in the fifth
embodiment is arranged to be changed between the flyback type and
the forward type in the same manner as in the other embodiments
described above, the flash device circuit according to the fifth
embodiment differs in the following point. In the case of the fifth
embodiment, the secondary current of one and the same transformer
is changed over by a switch means.
[0126] In FIG. 9, all components, connection lines, etc., that are
the same as those of the embodiments described in the foregoing are
indicated by the same reference numerals and symbols, and the
details of them are omitted from the following description. The
sequence of processes of the main routine shown in FIG. 3 and the
sequence of control actions in the flash mode shown in FIG. 4 are
executed by the fifth embodiment in the same manner as described in
the foregoing. The following description, therefore, covers only
the arrangement and the charging action of the flash device circuit
in the fifth embodiment.
[0127] Referring to FIG. 9, the flash device circuit includes an
oscillation transformer 70, switches 71 and 72 which are
interlocked with each other, and high-voltage rectifying diodes 73
and 74. In the same manner as the oscillation transformer 63 shown
in FIG. 8, the primary winding P of the oscillation transformer 70
has one end connected to the positive pole of the battery 1 and the
other end connected to the negative pole of the battery 1 through
the oscillation element 62.
[0128] On the other hand, the secondary winding S of the
oscillation transformer 70 has, in the state shown in FIG. 9, one
end thereof connected to one end of the main capacitor 21 through
the switch 71 and the high-voltage rectifying diode 73 and the
other end thereof connected to the other end of the main capacitor
21 through the switch 72. When the connecting positions of the
switches 71 and 72 are switched from this state in association with
each other, the one end of the secondary winding S of the
oscillation transformer 70 is connected to the other end of the
main capacitor 21 through the switch 71 and the other end of the
secondary winding S of the oscillation transformer 70 is connected
to the one end of the main capacitor 21 through the switch 72 and
the high-voltage rectifying diode 74.
[0129] Further, the high-voltage rectifying diodes 73 and 74 have
their cathodes respectively connected to one end of the main
capacitor 21 and their anodes connected respectively to one end and
the other end of the secondary winding S of the oscillation
transformer 70 through the terminals of the switches 71 and 72.
[0130] The charging action of the flash device circuit in the flash
mode in the fifth embodiment is performed as follows. When the
charged voltage of the main capacitor 21 is lower than the
predetermined changeover voltage V1 shown in FIG. 5, the main
capacitor 21 is charged first by using the boosting circuit of the
flyback type, which does not bring about any initial flow of rush
current.
[0131] The flyback-type boosting circuit action is as follows. The
connecting positions of the switches 71 and 72 are first set into
the state shown in FIG. 9. The CPU 125 then causes a
separately-excited oscillation signal which becomes high and low
levels at a predetermined frequency to be given through the
connection line "a" to the control electrode of the oscillation
element 62.
[0132] When the oscillation element 62 is rendered conductive by
the high level signal of the connection line "a", a current flows
from the battery 1 through the primary winding P of the oscillation
transformer 70. The current brings about an induced electromotive
force at the secondary winding S of the oscillation transformer 70.
However, since the induced electromotive force is of such a
polarity that is blocked by the high-voltage rectifying diode 73,
no charging current flows to the main capacitor 21, so that energy
is stored in the oscillation transformer 70.
[0133] When a low level signal is next given to the control
electrode of the oscillation element 62 with the level of the
connection line "a" becoming low, the oscillation element 62 turns
off (becomes nonconductive) to cut off the current flow to the
oscillation transformer 70. Therefore, the potential of the
secondary winding S of the oscillation transformer 70 is inverted
to bring about a back electromotive force. By this back
electromotive force, the energy stored in the oscillation
transformer 70 is discharged. Then, a charging current flows to the
main capacitor 21 through a loop of "the secondary winding S--the
switch 71--the high-voltage rectifying diode 73--the main capacitor
21 --the switch 72".
[0134] With the energy discharged further from within the
oscillation transformer 70, when a high level signal is again given
to the control electrode of the oscillation element 62 through the
connection line "a", the oscillation element 62 again becomes
conductive to allow the oscillation transformer 70 to store energy
in the same manner. After that, the next low level signal given to
the control electrode of the oscillation element 62 renders the
oscillation element 62 nonconductive to cause the oscillation
transformer 70 to discharge the stored energy, so that the main
capacitor 21 is charged with electric charge. The potential of the
main capacitor 21 in the flash device circuit is thus caused to
rise with these actions repeated.
[0135] While the main capacitor 21 is being charged by repeating
these actions as mentioned above, the charged voltage of the main
capacitor 21 is detected by the voltage detecting circuit 18 in
response to a voltage detection driving signal coming from the CPU
125 through the connection line "c". The voltage detecting circuit
18 then sends a divided voltage of the charged voltage thus
detected to the CPU 125 through the connection line "d" (step S22
of FIG. 4).
[0136] When the charged voltage of the main capacitor 21 is found
by the CPU 125 through the A/D converter (FIG. 2) to have reached
the predetermined changeover voltage V1 on the basis of the result
of the voltage detection, the use of the boosting circuit is
changed from the flyback type over to the forward type (steps S23
and S24).
[0137] In effecting the changeover of the boosting circuit, the CPU
125 sends a low level signal from the connection line "a" to
temporarily render the oscillation element 62 nonconductive and
then switches the connecting positions of the switches 71 and 72
over to their other connecting positions in association with each
other. After that, the oscillation element 62 is brought into an
on-off oscillating state by outputting a high-level/low-level
signal in a predetermined cycle of the forward type to the
connection line "a".
[0138] When the high level signal is given through the connection
line "a" to the oscillation element 62, the oscillation element 62
becomes conductive to allow a primary current to flow from the
battery 1 to the primary winding P of the oscillation transformer
70. The primary current brings about an induced electromotive force
at the secondary winding S of the oscillation transformer 70. Since
the induced electromotive force is of such a polarity that is not
blocked by the high-voltage rectifying diode 74, a charging current
flows to the main capacitor 21 through the high-voltage rectifying
diode 74.
[0139] Next, before the saturation of the magnetic flux within the
core of the oscillation transformer 70, a low level signal is given
to the control electrode of the oscillation element 62 through the
connection line "a". The low level signal causes the oscillation
element 62 to turn off (to become nonconductive) to bring the flow
of the primary current of the oscillation transformer 70 to a stop.
As a result, the magnetic flux within the core decreases. Then, at
the timing of annihilation of the magnetic flux within the core, a
high level signal is given again to the control electrode of the
oscillation element 62 through the connection line "a".
[0140] After that, the potential of the main capacitor 21 is caused
to rise by repeatedly causing the oscillation element 62 to turn on
and off in the above-stated manner. The actions to be performed
thereafter are the same as the steps S25 to S31 of FIG. 4 described
in the foregoing.
[0141] For switching the connecting positions of the switches 71
and 72, a plunger or a motor may be used if these switches are
mechanical switches. Further, the switches 71 and 72 may be
electrical switches.
(Sixth Embodiment)
[0142] A sixth embodiment of the invention is next described with
reference to FIG. 10 which is a flow chart. A sequence of control
actions in the flash mode (steps S10 or S19 in FIG. 3) in the sixth
embodiment differs from those of the other embodiments described
with reference to FIG. 4. With the exception of this point, the
flash device circuit according to the sixth embodiment may be
arranged in the same manner as in the case of any of the
embodiments described above.
[0143] In the sequence of control actions in the flash mode shown
in FIG. 4, the use of the boosting circuit is arranged to be
changed between the flyback type and the forward type according to
whether or not the charged voltage of the main capacitor 21 has
reached a changeover voltage level. In the case of the sixth
embodiment, however, a timer which is provided solely for
changeover of the boosting circuit is used in changing the boosting
circuit between the flyback type and the forward type.
[0144] A control operation on the flash device circuit in the flash
mode according to the sixth embodiment is described below referring
to the flow chart of FIG. 10. In FIG. 10, all steps of processes
which are the same as the steps shown in the FIG. 4 are indicated
by the same step numbers as in FIG. 4, and the details thereof are
omitted from the description.
[0145] At step S20 of FIG. 10, in the flash mode, the CPU 125 sets
the above-mentioned charging timer. At the next step S100, a
boosting-circuit changeover timer is set at a time count value for
changing from the flyback-type boosting circuit over to the
forward-type boosting circuit.
[0146] In setting the time count value of the boosting-circuit
changeover timer, the CPU 125 obtains an internal resistance value
of the battery 1 from the open voltage of the battery 1 and a
voltage obtained with a predetermined current allowed to flow on
the basis of a detection value obtained from the voltage detecting
circuit 18, and sets the predetermined time count value determined
according to the state of the battery 1. In other words, while, in
the above-described other embodiments, the voltage detecting
circuit 18 detects the voltage of the main capacitor 21 itself by
voltage division, the CPU 125 in the sixth embodiment predicts a
charged state of the main capacitor 21 by finding the state of the
battery 1 on the basis of a detection value obtained from the
voltage detecting circuit 18, and sets, as the time count value of
the boosting-circuit changeover timer, a changeover point
(changeover time) required for efficiently boosting a voltage.
[0147] At the next step S21, to perform the flyback-type boosting
circuit action, the CPU 125 sends a predetermined oscillation
signal to the flash device circuit through an applicable connection
line. This activates the flyback-type boosting circuit in the flash
device circuit to cause a charging current to flow to the main
capacitor 21. As a result, the potential of the main capacitor 21
rises.
[0148] At the next step S101, the CPU 125 checks the
boosting-circuit changeover timer to find the time interval for
changeover of the boosting circuit from the flyback type to the
forward type. At step S102, a check is made for the arrival of the
changeover time. The steps S101 and S102 are repeated to continue
the process for the flyback-type charging until the arrival of the
changeover time.
[0149] When the arrival of the changeover time is found at the step
S102, the flow of operation proceeds from the step S102 to step
S24. At the step S24, the CPU 125 changes the use of the
flyback-type boosting circuit for charging the main capacitor 21
over to the forward-type boosting circuit by sending to the
applicable connection line the oscillation signal for the action of
the forward-type boosting circuit.
[0150] Steps S25 to S31 which follow the step S24 are executed in
the same manner as already described in the foregoing with
reference to FIG. 4 and are, therefore, omitted from the
description.
[0151] While the invention is applied to a camera of the kind
having a built-in flash device in the case of each of the
above-described embodiments, the invention is applicable also to a
unitized electronic flash device.
* * * * *