U.S. patent number 3,857,062 [Application Number 05/391,768] was granted by the patent office on 1974-12-24 for flashing lamp circuits.
This patent grant is currently assigned to C.A.V. Limited. Invention is credited to Gordon Harris Leonard, Anthony John Ramshaw.
United States Patent |
3,857,062 |
Leonard , et al. |
December 24, 1974 |
FLASHING LAMP CIRCUITS
Abstract
A flashing lamp circuit for flashing a lamp includes
intermittently operable switch means connected in series with a
resistor with the lamp to be flashed, voltage sensing means
including a transistor for detecting the voltage across the
resistor when the lamp is illuminated, said voltage sensing means
including a capacitor which is charged in the event that the
voltage across the resistor is below a predetermined value when the
switch means is closed. A transistor switch including transistors
controls the operation of a warning lamp and when the switch means
is open the warning lamp will be illuminated. In the event that the
capacitor has been charged, the transistor switch will be rendered
non-conductive and the warning lamp will remain in an extinguished
condition. This invention relates to a flashing lamp circuit and of
the kind comprising terminals for connection to the lamp or lamps
to be flashed, contact means operable to cause flashing of said
lamp or lamps and a resistor in series with said contact means and
across which when said contact means is closed, a voltage is
developed indicative of the magnitude of the current flow through
the lamp or lamps. The object of the invention is to provide such a
circuit in a simple and convenient form. According to the invention
a flashing lamp circuit of the kind specified includes a warning
lamp, a transistor switch operable to cause illumination of said
warning lamp when said contact means is open, voltage sensing means
for sensing the voltage developed across said resistor, a capacitor
associated with said voltage sensing means and which is charged by
the voltage sensing means in the event that the voltage across said
resistor falls below a predetermined value when said contact means
is closed, the voltage across said capacitor acting to prevent said
transistor switch operating to cause illumination of the warning
lamp when said contact means is opened. Two examples of flashing
lamp circuits in accordance with the invention will now be
described with reference to the accompanying circuit diagrams.
Inventors: |
Leonard; Gordon Harris
(Gerrards Cross, Bucks., EN), Ramshaw; Anthony John
(Middlesex, EN) |
Assignee: |
C.A.V. Limited (Birmingham,
EN)
|
Family
ID: |
23547855 |
Appl.
No.: |
05/391,768 |
Filed: |
August 27, 1973 |
Current U.S.
Class: |
315/136;
340/641 |
Current CPC
Class: |
H05B
39/09 (20130101) |
Current International
Class: |
H05B
39/09 (20060101); H05B 39/00 (20060101); H01j
007/42 () |
Field of
Search: |
;315/130,131,132,133,134,135,136,77 ;340/251,79 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Heyman; John S.
Attorney, Agent or Firm: Holman & Stern
Claims
We claim:
1. A flashing lamp circuit comprising a pair of supply terminals,
contact means connected in series with the lamp to be flashed, a
resistor connected in series with said lamp and across which when
said contact means is closed is developed a voltage indicative of
the current flow through said lamp, a warning lamp, a transistor
switch including a transistor having its collector emitter path
connected in series with said warning lamp across said contact
means, said transistor switch being operable to cause illumination
of said warning lamp when said contact means is open, voltage
sensing means for sensing the voltage developed across said
resistor, a capacitor associated with said voltage sensing means,
said voltage sensing means establishing a charging path for said
capacitor in the event that the voltage across said resistor falls
below a predetermined value when the contact means is closed, the
voltage across said capacitor acting to prevent conduction of said
transistor when said contact means is next opened and thereby
preventing illumination of the warning lamp.
2. A circuit as claimed in claim 1 in which said voltage sensing
means includes a further transistor having its base connected to a
potentiometer chain which ensures that the base potential is a
fixed proportion of the voltage across said supply terminals when
said switch means is closed, the emitter collector path of said
further transistor being connected in series with said resistor and
with a further resistor across said supply terminals when said
contact means is closed, said capacitor being connected in parallel
with said further resistor, so that the capacitor is charged only
when said further transistor is rendered conductive.
3. A circuit as claimed in claim 2 including a diode
interconnecting the capacitor and said transistor switch.
Description
Referring to FIG. 1 there are provided terminals 10 and 11 for
connection respectively to the negative and positive terminals of a
source of d.c. supply. The lamps to be flashed are indicated at 12
and comprise one or more lamps connected in parallel with each
other and with one terminal thereof connected directly to terminal
10 and the other terminal connected to one terminal of a switch 13.
The other terminal of the switch 13 is connected to one end of a
resistor 14 the other end of which is connected by way of contact
means 15, to terminal 11. A point intermediate the resistor 14 and
switch 13 is connected to the emitter terminal of a p-n-p
transistor 16 the collector of which is connected by way of a
resistor 17, a diode 18 and a resistor 19 to terminal 10. The base
of transistor 16 is connected to terminal 10 by way of resistor 20
and to a point intermediate resistor 14 and contact means 15 by way
of a resistor 21 and diode 22.
Connected between terminals 10 and 11 is the series combination of
a resistor 23 and a zener diode 24 and a point intermediate the
resistor 23 and diode 24 is connected to the cathode of a diode 25
the anode of which is connected by way of a resistor 26, to the
base of transistor 16.
Also provided is a p-n-p transistor 27 the base of which is
connected to terminal 10 by way of resistor 28 and to terminal 11
by way of resistor 29. In addition, the base is connected to the
cathode of a diode 30 the anode of which is connected to a point
intermediate the diode 18 and resistor 19. Resistor 19 is bridged
by a capacitor 31. The emitter of transistor 27 is connected to
terminal 10 by way of resistor 32 and to terminal 11 by way of
resistor 33. The collector of transistor 27 is connected by way of
resistor 34 to the base of an n-p-n transistor 35. The emitter of
this transistor is connected to a point intermediate the resistor
14 and contact means 15 and the collector of transistor 35 is
connected by way of a warning lamp 36, to terminal 11.
Transistors 27 and 35 constitute a transistor switch for the
warning lamp 36 and transistor 27 is biased by the resistors 28, 29
and 32, 33 associated with its base and emitter respectively so
that it conducts. With transistor 27 conducting transistor 35 can
also conduct. With transistor 35 in a conducting state the warning
lamp 36 will be illuminated. When the switch 13 is closed and the
switch 15 open, the two transistors 27 and 35 will be rendered
conductive by the base drive to transistor 27 by way of resistor
28. When the switch 15 closes, the warning lamp will be
extinguished.
Contact means 15 is a switch which may be operated at regular
intervals by means of a mechanism or electric circuit which is
rendered operative when the switch 13 is closed. With switch 13
closed and the contact means 15 in operation the lamps 12 will be
flashed and by virtue of the current flow to the lamps a voltage
will be developed across resistor 14 which is proportional to the
current flowing through it. If the lamp or lamps are functioning
correctly the current flow through the resistor is such that
transistor 16 is not turned on. However, in the event that one or
more lamps fails, the voltage developed across the resistor will
fall to such an extent that transistor 16 is turned on and when
this occurs capacitor 31 will be charged a sufficient extent to
turn transistor 27 off by way of the diode 30. With transistor 27
in a non-conducting state there will be no base drive for
transistor 35 so that when the contact means 15 is opened the
warning lamp will not be illuminated thereby an indication will be
given that one or more of the lamps 12 has failed. Thus when the
lamps 12 are operating correctly the warning lamp will be on when
the lamps 12 are off, but if one or more of the lamps 12 has
failed, the warning lamp will remain extinguished.
The purpose of the Zener diode 24 is to apply to the base of the
transistor 16 by way of the diode 25 and resistor 26 a potential
which ensures that the potential at the base of the transistor 16
does not vary linearly with the supply voltage. The arrangement
permits matching of the variation of lamp current with supply
voltage, so that the circuit operates correctly whatever the
voltage of the supply. The diodes 22 and 18 are provided to protect
the transistor 16.
Referring to FIG. 2 of the drawings there are provided terminals 37
and 38 for connection respectively to a source of d.c. supply. The
lamps to be flashed are indicated at 39, two such lamps being shown
connected in parallel with one terminal connected to terminal 37
and the other terminal connected to a switch 40. The other terminal
of the switch is connected by way of a resistor 41 to terminal 38
by way of a contact means 42.
A circuit supply line 43 is provided and this is connected to
terminal 37 by way of resistor 44, a Zener diode 45 being connected
between the line 43 and the terminal 38. Also provided is a p-n-p
transistor 46 the emitter of which is connected to a point
intermediate the switch 40 and the resistor 41 and the base of
which is connected to line 43 by way of resistor 47 and to a point
intermediate the resistor 41 and the contact means 42 by way of a
resistor 48. The collector of transistor 46 is connected to the
anode of a diode 50 by way of resistor 49 and the anode of the
diode 50 is connected to line 43 by way of a resistor 49a. In
parallel with the resistor 49a is a capacitor 51. Moreover, the
base of transistor 46 is connected to terminal 37 by way of
resistor 52.
There is also provided an n-p-n transistor 53 having its emitter
connected to terminal 38 by way of resistor 54 and its base
connected to line 43 by way of resistor 55. The base is also
connected by way of diode 56 to a point intermediate diode 50 and
resistor 49a. Moreover, the base of transistor 53 is connected by
way of a capacitor 57 and a resistor 58 in series to a point
intermediate resistor 41 and the contact means 42 and a diode 59 is
connected to a point intermediate capacitor 57 and resistor 58 and
line 43.
The collector of transistor 53 is connected by way of resistor 60
to the base of an n-p-n transistor 61 the emitter of which is
connected to a point intermediate the resistor 41 and the contact
means 42. The collector of transistor 61 is connected by way of a
warning lamp 62 to terminal 38 and by means of a resistor 63 to the
base of transistor 53.
Transistor 53 is biased to the `off` condition so that there is no
base drive for transistor 61 and in the absence of resistor 58,
when contact means 42 opens the warning lamp 62 will not be
illuminated. However, because of the presence of resistor 58 when
contact means 42 opens a negative pulse is applied to the base of
transistor 53 and this is turned on thereby providing base drive
for transistor 61 and causing illumination of the warning lamp.
Transistor 53 is maintained in the on condition by reason of the
feedback path provided by resistor 63 and the warning lamp will
remain illuminated until the contact means 42 closes. Thus the
warning lamp 62 will be illuminated when the lamps 39 are
extinguished.
If the lamp or lamps 39 are functioning correctly transistor 46
will not be rendered conductive. However, in the event that one or
more lamps fails, the voltage developed across resistor 41 will
decrease sufficiently to cause conduction of transistor 46 thereby
charging the capacitor 51. When the contact means 42 again opens
the voltage developed across the capacitor 51 will prevent
transistor 53 being turned on so that the warning lamp will remain
extinguished to provide an indication of failure of one or more of
the lamps 39. When the contact means 42 opens and because of
failure of a lamp 39, transistor 53 is not conducting, it is
possible for transistor 53 to be rendered conductive by
interference appearing at the terminals 37 and 38. This may be
minimised by providing a small capacitor indicated at 64, and
connected between the base and emitter of transistor 53.
It will be appreciated that in FIG. 1 when the oscillator is turned
off by the switch 13 thecontacts 15 are normally closed, and hence
the transistor 16 becomes conductive. In other words, the warning
lamp is not illuminated on the first flash of normal flasher
operation, but is extinguished immediately in the event of a lamp
failure. In FIG. 2, because of the initial surge by way of
capacitor 57, the warning lamp is illuminated immediately on the
first flash of normal flasher operation, but does not extinguish
immediately upon lamp failure.
* * * * *