U.S. patent number 3,831,079 [Application Number 05/351,360] was granted by the patent office on 1974-08-20 for electronic photographic flash apparatus.
This patent grant is currently assigned to West Electric Co. Ltd.. Invention is credited to Hiroshi Iwata.
United States Patent |
3,831,079 |
Iwata |
August 20, 1974 |
ELECTRONIC PHOTOGRAPHIC FLASH APPARATUS
Abstract
An electronic photographic flash apparatus with a constant
voltage power supply, wherein the oscillation of a DC-DC converter
is controlled by a switching element such as a thyristor to always
maintain the voltage across a charged capacitor which is a load at
a predetermined value thereby maintaining the light output of a
discharge tube at a predetermined value, and at the same time a
radiation indicating element is employed to give an indication and
confirmation of said oscillation.
Inventors: |
Iwata; Hiroshi (Osaka,
JA) |
Assignee: |
West Electric Co. Ltd. (Osaka,
JA)
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Family
ID: |
26849883 |
Appl.
No.: |
05/351,360 |
Filed: |
April 16, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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152805 |
Jun 14, 1971 |
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Current U.S.
Class: |
363/28;
315/209SC; 315/241P |
Current CPC
Class: |
H02M
3/3385 (20130101) |
Current International
Class: |
H02M
3/24 (20060101); H02M 3/338 (20060101); H02m
003/22 () |
Field of
Search: |
;321/2,18
;331/112,113R,113S ;320/1 ;315/158,183,209,29CD,194,29SC,241P
;323/34 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
G E. SCR Manual, 4th Ed.; Pg. 7 relied upon, (1967) TK2798C4g (Sci.
Lib.)..
|
Primary Examiner: Goldberg; Gerald
Attorney, Agent or Firm: Stevens, Davis, Miller &
Mosher
Parent Case Text
This is a continuation of application Ser. No. 152,805 filed June
14, 1971, now abandoned.
Claims
What is claimed is:
1. An electronic photographic flash apparatus comprising:
a DC power source;
a transformer having primary, secondary and feedback windings, the
secondary winding being adapted to produce a high-frequency
voltage;
an oscillator transistor, wherein the primary winding of said
transformer and said DC power source are connected serially between
the collector and emitter electrodes of said transistor, and the
feedback winding coupled electromagnetically with the primary
winding of said transformer is connected through a first capacitor
between the base and emitter electrodes of said transistor;
a main discharge capacitor;
oscillator control means for stopping and starting oscillation of
said oscillator transistor to maintain a substantially constant
voltage across said discharge capacitor, said oscillator control
means including
switching means having a control terminal and connected between the
base and emitter electrodes of said transistor, and
voltage applying means for applying a voltage to said control
terminal corresponding to the voltage across the first capacitor
which is proportional to the voltage across the main discharge
capacitor to control the starting and stopping of oscillation of
said oscillator transistor in relation to the voltage of said
discharge capacitor;
a discharge tube having a trigger circuit associated therewith
connected to the output of said discharge capacitor; and
rectifier means interconnecting said main discharge capacitor and
the secondary winding of said transformer.
2. An apparatus according to claim 1, wherein said voltage applying
means comprises said first capacitor and a variable resistance
means connected in parallel with each other between the feedback
winding of said transformer and the emitter electrode of said
transistor, the control terminal of said switching means being
connected to said variable resistance means.
3. An apparatus according to claim 2, further including indicating
means comprising a luminescent diode connected in series with said
switching means.
4. An apparatus according to claim 2, further including indicating
means for indicating the starting and stopping of oscillation of
the transistor oscillator, said indicating means comprising a
luminescent diode connected in parallel with said switching means,
thereby to discharge an energy stored in said second capacitor
through said luminescent diode.
5. An apparatus according to claim 1, wherein said voltage applying
means comprises a diode and a smoothing circuit, including a
variable resistor and a further capacitor connected in parallel,
serially connected across the primary winding of said transformer,
the control terminal of said switching means being connected to
said variable resistor.
6. An apparatus according to claim 1, further including indicating
means for indicating the starting and stopping of oscillation of
the transistor oscillator, said indicating means comprising a
series circuit of a further capacitor and a luminescent element
connected on the secondary winding side of said transformer, said
further capacitor being operable to pass only an AC signal
component from the secondary winding.
7. An apparatus according to claim 1, further including indicating
means for indicating the starting and stopping of oscillation of
the transistor oscillator, said indicating means comprising a
luminescent diode connected across the primary winding of said
transformer, in such a polarity that the cathode of the diode is
connected to one end of the primary winding which is connected to
the collector of the oscillation transistor.
8. An apparatus according to claim 6, wherein said indicating means
comprises a luminescent diode and a diode connected in series with
said luminescent diode.
9. An apparatus according to claim 1, wherein said switching means
comprises a composite transistor composed of first and second
transistors, and said apparatus further comprises a diode connected
in parallel with one transistor of said composite transistor, said
diode having a forward voltage lower than the threshold voltage of
said one transistor, thereby to stabilize the oscillation control
voltage.
10. An electronic photographic flash apparatus comprising:
a DC power source;
a transformer having primary, secondary and feedback windings, the
secondary winding being adapted to produce a highfrequency
voltage;
an oscillator transistor, wherein the primary winding of said
transformer and said DC power source are connected serially between
the collector and emitter electrodes of said transistor, and the
feedback winding coupled electromagnetically with the primary
winding of said transformer is connected between the base and
emitter electrodes of said transistor;
variable resistance means connected in parallel with said DC power
source;
a main discharge capacitor;
oscillator control means for stopping and starting oscillation of
said oscillator transistor in relation to the discharging of said
discharge capacitor to maintain a substantially constant voltage
across said discharge capacitor, said oscillator control means
including
switching means having a control terminal and connected between the
base and emitter electrodes of said transistor, and
voltage applying means for applying a voltage to said control
terminal according to the voltage across said DC power source
through a tap of said variable resistance means to control the
starting and stopping of oscillation of said oscillator transistor
in relation to the discharging of said discharge capacitor;
a discharge tube having trigger circuit associated therewith and
connected to said discharge capacitor; and
rectifier means interconnecting said main discharge capacitor and
the secondary winding of said transformer.
11. An apparatus according to claim 10, further including
indicating means comprising a variable resistor connected in
parallel with said DC power source and a luminescent diode
connected between a given point of said variable resistor and one
terminal of said power source.
Description
The present invention relates to an electronic photographic flash
apparatus.
Hitherto, dry cells have been widely used as power sources for
electronic photographic flash devices. However, owing to the
characteristics of such dry cells, it has been inevitable that the
voltage of the dry cell gradually decreases each time there is a
flash discharge. Thus, with an electronic photographic flash device
employing a dry cell, the voltage on the charged main discharge
capacitor necessarily decreases in proportion to the decrease in
the battery voltage with the result that the light output of the
discharge tube also decreases, thereby affecting the exposure of
the photographic film.
Therefore, it is the main object of the present invention to
provide an electronic photographic flash apparatus with an improved
constant voltage power supply which eliminates the above-mentioned
deficiencies and in which the voltage across a charged main
discharge capacitor is always maintained at a predetermined value
to ensure the uniform exposure of the photographic film and at the
same time a radiation indicating element is employed so that the
oscillation condition of a DC-DC converter is readily
confirmed.
A constant voltage power supply of this type is shown, for example,
in U.S. Pat. No. 3,316,445. In this device, the oscillation is
controlled by providing a feedback via a Schmitt circuit from a
neon glow lamp disposed in the high voltage circuit on the load
side and thus the voltage is high making it necessary to employ
heavy insulation and the like, also the number of component parts
tends to be large since a complicated circuit such as the Schmitt
circuit is employed. On the contrary, the device of the present
invention is highly reliable in operation and simple in circuit
construction, since its control circuit operates with a low voltage
and the biasing circuit is adapted to be fully short-circuited.
According to the present invention which is based on the principle
that the voltage induced in each of the windings of a converter
transformer in a DC-DC transistor converter is in proportion to the
voltage across a charged main discharge capacitor which is the
load, the voltage induced in any one of the converter transformer
windings is detected and applied to the gate electrode of a
switching element provided between the base and the emitter of said
transistor so that the oscillation of said transistor is controlled
to maintain the voltage across the load at a predetermined value
and a radiation indicating element, such as an electroluminescence,
luminescent diode or neon glow lamp is connected to a proper
circuit so that the operating conditions of the converter are
detected and confirmed.
A better understanding of the present invention may be had from the
following detailed descriptions of the preferred embodiments when
read in conjunction with the accompanying drawings, in which:
FIG. 1 is an electrical wiring diagram of an electronic
photographic flash apparatus according to an embodiment of the
present invention;
FIG. 2 is a diagram useful for explaining the present
invention;
FIG. 3, FIG. 4 and FIG. 5 are electrical wiring diagrams showing
other embodiments of the present invention;
FIG. 6 is a characteristic diagram of a nickel cadmium (NiCd)
cell;
FIG. 7 is the voltage characteristic diagram of a charged capacitor
when a NiCd cell is used;
FIG. 8 is a diagram showing the waveforms of the output voltages of
a converter circuit;
FIG. 9 is a diagram showing the schematic symbol of a
thyristor;
FIG. 10 is a diagram showing the output waveforms obtained when the
thyristor of FIG. 9 is used;
FIG. 11a and FIG. 11b illustrate modified forms of the switching
element;
FIG. 12 and FIG. 13 are electrical wiring diagrams showing the
principal parts of further embodiments of the invention with
modified switching means;
FIG. 14 is a diagram explaining the rising characteristic of the
transistor;
FIG. 15, FIG. 16 and FIG. 17 are electrical wiring diagrams showing
the principal parts of modified electronic photographic flash
apparatus having means for indicating on and off of the
oscillations of the converter circuit;
FIG. 18 and FIG. 19 are characteristic diagrams of luminescent
diodes;
FIG. 20a, FIG. 20b, FIG. 21 and FIG. 22 are electrical wiring
diagrams showing the principal parts of modified electronic
photographic flash apparatus having indicating means employing a
luminescent diode;
FIG. 23 is a diagram explaining the temperature characteristic of
the electronic photographic flash apparatus;
FIG. 24 is an electrical wiring diagram showing a modified
electronic photographic flash apparatus incorporating a method of
temperature compensation;
FIG. 25 is a diagram illustrating the characteristic of the diode;
and
FIG. 26 is an electrical wiring diagram showing a modified form of
the switching means used with the electronic photographic flash
apparatus of the present invention.
Referring to FIG. 1 of the drawings, there is illustrated a basic
circuit diagram of the present invention in which a portion
enclosed with a dotted line A designates a constant voltage circuit
and a radiation indicating circuit according to the present
invention.
In operation, the voltage of a power supply battery 6 is caused to
oscillate and is stepped up in a DC-DC converter comprising a
transistor 8, a converter transformer 7 and so on and, after being
rectified by a diode 10, the voltage is used to charge a main
discharge capacitor 9. Numeral 12 designates a radiation indicating
element, such as an electroluminescent element. Enclosed with a
dotted line B is a trigger circuit of a conventional type for
firing a discharge tube 11.
A voltage V.sub.2 across the charged main discharge capacitor 9 is
in proportional relation with the voltages induced in windings
N.sub.2, N.sub.C and N.sub.b of the converter transformer 7
according to the following equation:
V.sub.2 = N.sub.2 /N.sub.C K.sub.1 E or N.sub.2 /N.sub.b K.sub.2
E
where E is the voltage of the power supply battery 6, and K.sub.1
and K.sub.2 are constants. Thus, any one of the voltages generated
across these windings can be employed as an effectively
corresponding value of the voltage V.sub.2 on the charged main
discharge capacitor 9.
With the circuit construction designated by the dotted line A in
FIG. 1, the oscillating voltage produced in the base winding
N.sub.b of the converter transformer 7 is employed so that this
induced voltage is rectified by the diode characteristic between
the emitter and the base of the transistor 8 and it is then applied
to a capacitor 3 in the polarity shown producing a DC voltage
V.sub.C across the capacitor 3 which effectively corresponds to the
voltage V.sub.2 of the charged main discharge capacitor 9. The
graph of FIG. 2 represents the relationship between the two
voltages. In the graph, the ordinate represents the voltage across
the charged main discharge capacitor 9 and the abscissa represents
the voltage across the charged capacitor 3 connected between the
base winding N.sub.b of the converter transformer 7 and the emitter
of the transistor 8.
Therefore, if the voltage across the main discharge capacitor 9 for
providing a predetermined quantity of light is chosen to be 330
volts, for example, then the voltage across the capacitor 3 is
V.sub.C1. Then, if a control element 1 such as a thyristor provided
between the base and the emitter of the transistor 8 is caused to
conduct to stop the oscillation of the converter circuit at the
value of the voltage V.sub.C1, the oscillating current in the base
winding N.sub.b is shortcircuited by the control element 1 such as
a thyristor so that the oscillation of the converter circuit is
stopped and hence the charging of the main discharge capacitor 9 is
stopped, thereby maintaining the voltage V.sub.2 of the charged
main discharge capacitor 9 at a predetermined value. However, since
the main discharge capacitor 9 shows a leakage current and a
circuit such as the trigger circuit B is connected in parallel with
the main discharge capacitor 9, the voltage V.sub.2 across the
capacitor 9 gradually decreases until the control element 1 such as
a thyristor is rendered nonconductive again so that the converter
circuit starts oscillating again to compensate for the aforesaid
energy loss.
Repetitions of this process maintain the voltage V.sub.2 across the
main discharge capacitor 9 at a predetermined value. The time
interval at which the oscillation of the converter circuit is to be
interrupted is chosen such that the stored energy in the capacitor
3 is discharged by virtue of the control element 1 which may be a
thyristor and the voltage V.sub.C or the terminal voltage of the
capacitor 3 becomes zero (the control element 1 is simultaneously
turned off), whereupon the capacitor 3 is recharged through a
biasing resistor 4 so that when the voltage across the capacitor 3
exceeds a base voltage V.sub.BE of the transistor 8, the converter
circuit is caused to start oscillating again. In other words, the
aforesaid time interval is practically determined by the time
constant of the resistor 4 and the capacitor 3.
On the other hand, there is a feature in that the connection of the
radiation indicating element 12 to the high-voltage winding N.sub.2
side of the converter transformer 7 enables the radiation
indicating element 12 to flash in response to on and off of the
oscillations of the converter circuit thereby giving an indication
of the constant voltage across the main discharge capacitor 9,
whereas provision of an electroluminescence (EL) element or the
like connected to the radiation indicating element 12 and adapted
to produce light when excited by an AC current causes the EL
element to start producing light upon the oscillation of the
converter circuit thereby enabling observation of the oscillation
of the converter circuit.
FIG. 3 illustrates another embodiment of the present invention
wherein the oscillating waveform across a collector winding N.sub.C
is rectified by a diode 13 and it is then converted in a smoothing
circuit comprising a resistor 14 and a capacitor 15 into a DC
signal which is in turn used as a control signal for a control
element 1.
With the embodiment illustrated in FIG. 4, the voltage generated
across a secondary winding N.sub.2 of a converter transformer is
rectified by a rectifier 16, divided by a variable resistor 17
connected in series with the rectifier 16, and then used as a
control signal for a control element 1.
With the embodiment illustrated in FIG. 5, the terminal voltage of
a power supply battery 6 is employed as a control signal for a
control element 1 through a variable resistor 18. In this case, if
a battery such as a NiCd battery whose characteristic is indicated
by a curve A in FIG. 6 is employed, the battery voltage remains
practically unchanged until the capacity of the battery is
terminated, thus showing a characteristic indicated by a straight
line E in FIG. 7 so that this battery terminal voltage can be
employed as a control signal for maintaining the voltage across a
charged main discharge capacitor at a predetermined value. While
provision of the constant voltage circuit appears to be unnecessary
since the characteristic of the NiCd battery shows practically no
change in the terminal voltage as indicated by the curve A in FIG.
6, the constant voltage circuit is advantageous in that the circuit
functions to maintain the voltage across the charged main discharge
capacitor 9 at a predetermined value and at the same time only the
required energy is intermittently supplied from the power supply
battery in response to on and off states of the converter circuit,
thereby eliminating any energy loss due to the oscillations of the
converter circuit. Thus, the detection of the required signal from
the voltage across the power supply battery can be effective. It
should be noted, however, that since the detected signal has a
negative polarity because of the circuit construction, a negative
gating element must be employed as a control element and, as will
be explained later, this can be easily met by employing a composite
transistor (the term "composite transistor" as used herein includes
four-layer four-electrode construction elements as well as
four-layer four-electrode four-terminal switching elements).
Next, means for controlling the oscillation of the converter
circuit will be explained. As shown in FIG. 8 illustrating a
typical output waveform of the converter circuit, a voltage
containing very high frequency components at portions C is applied
between the anode and the cathode of a control element 1. Thus,
with an ordinary thyristor available on the market such as is shown
in FIG. 9, the high frequency component indicated as C in FIG. 8 is
allowed to pass from the anode side to the gate side through the
junction capacitance at J.sub.2 in the schematic symbol of FIG. 9
and therefore there is a possibility that the control element 1 is
turned on with no gating signal being applied thereto or
alternately a leakage current flowing from the anode side by virtue
of the oscillation component increases as the gating signal for the
control element gets closer to the turn-on voltage with the result
that the control signal for the control element tends to be
unstable and hence the voltage V.sub.2 across the charged main
discharge capacitor also tends to be unstable.
FIG. 10 illustrates this leakage current in superimposed relation
with the oscillating waveform of FIG. 8 showing the state of the
leakage current flowing from the anode side to the gate side of the
control element 1 or the thyristor. It is evident from the figure
that the gate current flows only when the oscillating waveform
across the base winding changes critically.
FIG. 12 illustrates a modified embodiment of the invention wherein,
in order to prevent such leakage current, a composite transistor
(FIG. 11a) comprising a combination of transistors 19 and 20 or a
four-terminal switching element (FIG. 11b) is employed and a DC
bias is applied externally to the third electrode CG so that almost
no displacement current flows through the junction capacitance at
J.sub.2. In this case, the DC bias is applied through a resistor
21. When a combination of transistors as shown in FIG. 11a is
employed, these transistors themselves involve a very large degree
of variation in their characteristics. More specifically, if there
is a large degree of variations in V.sub.BE of the transistor 20,
when considered as a control element, the control input
characteristic between terminals G and K changes considerably and
this constitutes a factor which indirectly causes variation in the
voltage across the charged main discharge capacitor, while on the
other hand it generally involves considerable problems to limit the
characteristics of such transistors within the prescribed
standards, in view of selection procedures and the like in the mass
production of transistors.
Therefore, in order to limit variations in the V.sub.BE of the
transistor 20, a diode 22 is connected in parallel with the
transistor 20 as shown in FIG. 13. The diode 22 has a rising
characteristic V.sub.b lower than V.sub.BE1 of the transistor 20
and it is connected so that the control circuit is stabilized by
means of the combined transistors (FIG. 11a).
Next, the indicating methods according to the on and off
oscillations of the converter circuit will be explained. If a
radiation element 12 such as an EL element is connected to the
secondary winding side of the converter circuit as shown in FIG. 1,
the EL element produces light as the converter circuit starts to
oscillate, thereby enabling a visual confirmation of the converter
circuit in operation. Then, as the voltage across the secondary
winding reaches a predetermined value, the control element 1 is
turned on to stop the oscillation of the converter circuit as
previously explained. The instant the circuit stops oscillating,
the EL element goes off. However, this voltage decreases due to the
current leakage loss in the main discharge capacitor 9 and so on,
the converter circuit begins oscillating again and the EL element
again produces light and this process of operation is repeated.
In this way, whether the voltage across the secondary winding is
maintained at a predetermined constant value can be easily observed
according to the on and off states of the EL element. Similarly,
the same effect can be obtained by connecting an indicator lamp 24
comprising a discharge lamp, for example, to the secondary winding
side through a bypass capacitor 23 as shown in FIG. 15.
FIG. 16 illustrates an arrangement wherein, for example, a
luminescent diode 25 of gallium arsenide type which radiates with a
relatively low voltage is connected across the collector winding
N.sub.C of the converter circuit. The same effect as in the
previously explained arrangements can be ensured. In this
arrangement, however, a diode 26 is connected in series with the
luminescent diode 25 as shown by a dotted line, since the backward
voltage is generally low with luminescent diodes, and this series
combination of the diodes 25 and 26 is connected across the
collector winding to substantially increase the withstand voltage
of the diode 25 with respect to the backward voltage, thereby
stabilizing the luminescent diode 25.
Of course, the voltage generated across the base winding can be
employed in similar fashion. Furthermore, instead of employing the
voltage developed across the aforesaid converter transformer
windings to give the required indication, the luminescent diode 25
may be provided in the series circuit including the control element
1 as shown in FIG. 17, so that the required indication is provided
by virtue of the energy supplied by the capacitor 3 on
discharge.
On the other hand, according to the static characteristics of
radiation elements such as the gallium arsenide luminescent diodes,
one type of such element exhibits a constant voltage characteristic
as shown in FIG. 18 and another type exhibits switching and
radiating characteristic as shown in FIG. 19. Either type of
element may be employed to effectively indicate the voltage across
the charged main discharge capacitor 9, if, as shown in the
arrangement of FIG. 20a, a variable resistor 18 is connected in
parallel with the power supply battery 6 and if a battery voltage
V.sub.E1 corresponding to the voltage V.sub.2 across the charged
main discharge capacitor 9 is obtained from the graph of FIG. 7 and
then the variable resistor 18 is adjusted so that the battery
voltage V.sub.E1 assumes a value corresponding to the voltage
V.sub.S of the luminescent diode 25. According to this method, the
radiation of the luminescent diode 25 can be provided with the
energy from the power supply battery without turning the
oscillation of the converter circuit on and off. Thus, this method
can be effectively substituted for a so-called DC lighting method,
such as the conventional type of indication method employing the
neon tube or the like of an electronic photographic flash apparatus
which is shown in FIG. 20b and in which the light is produced by
virtue of the firing voltage of the neon tube when the voltage
across the charged main discharge capacitor 9 reaches a
predetermined value.
The reason is that since there is a certain proportional
relationship between the power supply battery voltage and the
voltage across the charged main discharge capacitor as shown in
FIG. 7, it is sufficient simply to adjust the variable resistor 18
so that a forward radiation initiating voltage V.sub.S for the
luminescent diode 25 is obtained which corresponds to a suitable
voltage developed across the main discharge capacitor.
This function can be similarly performed by employing the voltages
across the respective windings of the converter transformer which
effectively correspond to the voltage across the charged main
discharge capacitor 9 as previously explained. FIG. 20a illustrates
a typical such arrangement.
Another form of radiation power sources utilizing the static
characteristics of luminescent diodes is shown in FIG. 21, wherein
a variable resistor 27 is connected across a capacitor 3 and the
voltage dividing ratio of the variable resistor 27 is adjusted so
that a voltage V.sub.S across a luminescent diode 25 effectively
corresponds to a voltage V.sub.2 across a charged main discharge
capacitor 9.
Next, the adjustment of the flashing intervals of the radiation
indicating element 12 will be explained. While the flash interval
can be increased simply by increasing the resistance value of the
resistor 4 or the capacitance value of the capacitor 3, that is, by
increasing their time constant, this has disadvantages in that
increasing the resistance value of the resistor 4 results in a
decreased initial efficiency of the oscillation of the converter
circuit, while an increased capacitance value of the capacitor 3
increases the bulk of the capacitor itself.
One method of easily effecting the required adjustment of the
flashing intervals is shown in FIG. 22, wherein a relatively large
resistor 28 is connected in series with a control element 1 so that
the capacitor 3 requires a longer time to discharge its stored
energy upon the interruption of the oscillation of the converter
circuit.
Next, methods of temperature compensation for the voltage V.sub.2
across the charged main discharge capacitor 9 will be
explained.
Designated as D in FIG. 23 is the temperature characteristic of the
constant voltage electronic photographic flash apparatus shown in
FIG. 1 and the apparatus has a so-called negative temperature
coefficient with the secondary voltage of the main discharge
capacitor 9 decreasing as the temperature increases.
One method of correcting this tendency is shown in FIG. 24, wherein
a diode 29 having a negative temperature coefficient is inserted in
the gating circuit of a control element 1 so that a very flat
characteristic as indicated by a straight line E in FIG. 23 is
obtained as the temperature characteristic after correction.
The reason is that the diode 29 has a negative temperature
characteristic as shown in FIG. 25 and thus the voltage dividing
ratio of V.sub.C by resistors 31 and 32 is given as
(R.sub.32 + R.sub.29)/R.sub.31 (R.sub.32 + R.sub.29) .sup.. V.sub.C
= V.sub.G
where V.sub.G is the gating voltage of the control element 1. Thus,
since the resistance R.sub.29 of the diode 29 at 0.degree. C is
larger than the resistance at 45.degree. C, the value of V.sub.G is
higher at 45.degree. C than at 0.degree. C and therefore, assuming
that the gating voltage of the control element is fixed, at
0.degree. C the operation is initiated at a lower value of V.sub.C
and thus it is equivalent as though the value of the voltage across
the charged main discharge capacitor were effectively reduced in
FIG. 2, thereby moving the characteristic to the temperature
compensating direction as shown in FIG. 23.
Where a control element comprising a composite transistor circuit
as shown in FIG. 12 is employed, an element having a positive
temperature coefficient may be connected to the resistor 21.
Lastly, means for controlling the voltage across the charged main
discharge capacitor 9 will be explained. In the circuit illustrated
in FIG. 1, the resistor 2 may comprise a variable resistor to
effect the adjustment of the gating voltage for the control element
1. On the other hand, if a composite element such as is shown in
FIG. 11 is employed in the said circuit, an arrangement shown in
FIG. 26 results. Thus, by providing a variable resistor 30 between
the anode and the gate of the composite element, the breakover
voltage of the composite element itself may be adjusted and in this
way the same effect as the arrangement of FIG. 1 can be
achieved.
It is now apparent from the foregoing explanation that the present
invention provides a novel circuitry for electronic photographic
flash apparatus which is capable of ensuring the G.N value for the
last radiation and has no possibility of offering underexposure and
wherein the supply of energy to a DC-DC converter is effected
intermittently as occasion demands so that not only the consumption
of the power supply battery is low, but also the constant voltage
circuit itself can be simply constructed with the addition of only
a few very small-sized component parts, thereby ensuring a high
degree of performance almost independent of the size of electronic
photographic flash apparatus per se.
* * * * *