Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~4267
"EIEC~RIC FI~S~ D~VICB"
The present invention relates to a flash light generating
apparatus, and more particularly to an electric flash device
which generates a ~lash light by energizing a flash tube.
Flash apparatus has become widely used in various kinds
of optical apparatus of which the operation requires flash
light. Particularly, in the art of photography, arti~icial
light is used to illuminate an object to be photographed.
One ~orm o~ arti~icial light which is now widely used is the
so-called flash tube.
It is common practice in electric ~lash devices to
obtain high intensity illumination for photographic purposes
by discharging a chrged capacitor through a gas-~illed ~lash
tube. A low voltage D.C. power source is generally employed
together with suitable circuitry in order to obtain the rela-
tively high D.C. ~oltage which is needed to charge the flash
capacitor ~or each ~iring of the ~lash tube. Since an elect-
ric ~lash device o~ this type is generally portable, batteries
are usually employed as the source o~ low D.C. voltage. High
D.C. voltage is obtained ~rom the batteries through the use
of a voltage converter. A converter includes a trans~ormer
~or converting low A.C. voltage to high A.C, voltage9 and a
rectifier for rectifying the high A.C. voltage, the recti~ied
voltage being then applied to the fla~h capacitor in order to
charge it.
It can readily be understood that under ordinary cir-
cumstances when an electric flash dsvice is being used, a
substantial portion o~ the time during which the device is
turned on may be ~tandby time; that is~ time which elapses
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after power supply has charged the capacitor to a suitable
value and before the camera shutter is tripped thereby dis-
charging the capacitor through the flash tube, During this
time the power supply consumes energy from the batteries with-
out producing any useful result. The energy loss may be
significant, particularly when the device includes trans-
formers, ~s the batteries age their output voltage drops
and a longer period of time is required for firing the flash
tube, In addition, as the output voltage of the batteries
decreases with age, the device becomes incapable of flash-
ing the flash tube.
In order to overcome the above disadvantage, the
prior art contemplates the use of a timer circuit between
the power source and the voltage converter. However, the
power circuit itself will consume energy, and the power loss
of the timer circuit mitigates against the most effective
use of the battery.
It is therefore an object of the invention to
provide an electric flash device which overcomes the dis-
advantages of the prior art.
In accordance with a particular embodiment of theinvention, there is provided an electric flash device which
includes a direct current power source circuit for providing
a direct current voltage, a flash tube circuit including a
flash tube, a converter circuit for converting said direct
current voltage of said direct current power source circuit
to an alternating current voltage, a rectifier circuit for
rectifying said alternating current voltage to a direct
current voltage, a charging circuit for storing an electric
charge and for supplying electrical energy to said flash
tube, and a trigger pulse generating circuit for triggering
the flash tube of the flash tube circuit, The converter
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circuit includes an oscillating transformer connected to the
direct current power source circuit for generating a high
alternating current voltage and having a current flowing
therein. An oscillator performs an oscillating operation
and includes a switch element for switching the current
which flows in the oscillating transformer and functions
as a high resistance resistor and of which leakage current
is negligible when the oscillating operation of the oscil-
lator circuit ceases. The switch element includes a control
electrode circuit. A switching means is provided in the
control electrode circuit of the switch element of the
oscillator circuit for actuating the switch element of the
oscillator circuit, and means are provided for starting
oscillation of the oscillator circuit when the switching
means operates.
Certain embodiments of the invention will now ~e
described by way of examples and with reference to the
accompanying drawings, wherein like parts in each~of the
several figures are identified by the same reference
character, and wherein~
Figures 1 and 2 are circuit dlagrams of prior art
electric flash devices,
Figure 3 is a detailed circuit diagram of an
electric flash device according to the
present invention;
Figure 4 is a detailed circuit diagram of another
electric flash device according to the
present invention;
Figure 5 shows a modification of the circuit of
Figure 4; and
Figure 6 is a detailed circuit diagram of further
electric -Elash device according to the
present invention.
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Figure 1 shows an example of a prior art electric
flash device. The device shown in Figure 1 comprises a
direct current power source circuit A, a voltage converter
circuit B for converting direct current voltage from the
direct current power source circuit A into alternating
current voltage, a rectifier circuit C for rectifying the
alternating current voltage, an electric charge storing
circuit D for supplying electrical energy to a flash tube,
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a trigger pulse generating circuit E for triggering the flash
tube, and a flash tube circuit F including a flash tube,
The direct current power source circuit A includes
a battery 10 and a power source switch 12 which is connected
to the battery 10 in series relationship. The power source
switch 10 is a mechanical switch which is manually operated.
The voltage converter circuit B comprises an oscillator cir-
cuit, an oscillating time constant circuit having serially
connected resistor 14 and capacitor 16, an oscillating trans-
former 18 having a primary winding 18a, a secondary winding18b and a third winding 18c, and an oscillation switching
element in the form of a PNP type Gerumanium transistor 20
whose internal resistance is extremely low.
The rectifier circuit ~ consists of a diode 22
whose anode electrode is connected to one terminal of the
second winding 18b of the oscillating transformer 18. The
electric charge storing circuit D includes a main storage
capacitor 24, a current-restricting resistor 26 and an indi-
cating lamp such as a neon lamp, and is connected as shown.
The trigger pulse generating circuit includes a triggering
time constant circuit having a charging resistor 30 and a
triggering capacitor 32, and a trigger transformer 36 having
a primary winding 36a and a secondary winding 36b. The
flash tube circuit F includes a flash tube 38 whose main
current c~nducting electrodes 38a and 38b are connected to the
main storage capacitor 24 and whose trigger electrode 38c is
connected to the secondary winding 36b of the trigger trans-
former 36.
In the electric flash device of Figure 1, when the
power source switch 12 is c~losed, the voltage converter cir-
cuit B activates an oscillating operation, and thereby the
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high voltage is induced at the secondary winding 18b of the
transformer 18. The boosted alternating current voltage is
rectified by the rectifier circuit C, and thereafter electric
charge is stored on the main storage capacitor 24, When the
electric charge stored on the capacitor 24 reaches a predeter-
mined value, tube 38 is triggered and the capacitor 24 dis-
charges through the flash tube 38.
In this known electric flash device, when the main
storage capacitor 24 discharges the electric flash, the vol-
tage converter circuit B is adversely affected since part ofthe discharging current flows into the voltage converter cir-
cuit through the transistor 20, This can put the transistor
20 in an ON condition when it should be in an OFF condition.
Further when the electric charge in the main storage capacitor
discharges the voltage converter circuit B tries to recharge
the main storage capacitor 24 in order to prepare for the next
flash operation so long as the power source switch 12 is not
turned OFF. Accordingly, if the power source switch 12 is
left in its conductive condition for a long time interval, the
voltage converter circuit B continues an activation so as to
maintain the charging of the main storage capacitor 24, and
therefore, the current from the battery 10 flows until the
- power source switch 12 is opened,
During this time the power supply consumes energy
from the battery 10 without any useful result, As the
battery ages its output voltage drops and a longer period
of time is required for the main storage capacitor 24 to be
charged to the necessary level for firing the flash tube 38.
Eventually the electric flash device becomes incapable of
operating.
One known method of resolving the above described
drawbacks, is embodied an electric flash device as shown in
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Figure 2 in which a timer circuit T is provided between a
power source circuit A and a voltage converter circuit B in
order to interrupt the current which flows from the power
source circuit A to the voltage converter circuit B, if a
flash tube 38 is not fired within a given time period. rrhe
timer circuit T, however, includes a semiconductive element
such as, for example, a power transistor Q which is serially
connected to the power source circuit and the voltage conver-
ter circuit B, and, as a result, the actual power input to
the voltage converter circuit B is reduced due to the high
and specific power loss of the power transistor Q. Accord-
ingly, the device of Figure 2 does not make effective use
of the battery 10.
rrhe electric flash device shown in Figure 3 com-
prises a direct-current power source circuit A, a voltage
converter circuit B for converting and boosting the voltage
from the direct-current power source circuit A into alter-
nating current voltage, a rectifier circuit C for rectifying
the voltage from the boosted alternating current voltage,
from the voltage converter circuit B, a charging circuit D
for storing electrical energy supplied in the form of dirèct
current from the rectifier circuit C and for supplying the
electric energy to a flash tube, a trigger signal generating
circuit E for triggering the flash tube by applying a trigger-
ing signal to a trigger electrode of the flash tube, and a
flash tube circuit F which includes a flash tube.
rrhe direct current power source circuit A includes
only a battery 10, and does not include a power source switch.
rrhe voltage converter circuit B comprises, substantially, an
oscillator circuit OC, an oscillation time constant circuit
TC and an oscillation starting circuit OS~ In more detail,
1~74267
the voltage converter circuit B includes a resistor 14 of
which one terminal is directly connected to the positive
terminal of the battery 10, a capacitor 16 of which one
terminal is connected to other terminal of the resistor 14
to form the oscillation time constant circuit TC, an oscil-
lator transformer 18, an oscillation switching element in
the form of a high performance silicon transistor 40 and an
oscillation starting switch in the form of a mechanical slide
switch 42. The oscillator transformer 18 consists of a
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primary winding 18a, a secondary winding 18b and a third
winding 18e. One terminal of the primary winding 18a is
directly connected to the positive terminal of the battery
10, and other terminal of the primary winding 18a is con-
neeted to a collector electrode in order to form the
oscillator circuit 0C. One terminal of the secondary wind-
ing 18b is connected to one terminal of the third winding 18e,
and other terminal of the third winding 18e is conneeted to a
juneture Jl of the resistor 14 and the eapaeitor 16. The
switch 42 is provided and eonnected between a base electrode
of the transistor 40 and a juncture J2 of the seeondary
winding 18b and the third winding 18e of the oseillating
transformer 18 in order to eonstitute the oscillation start-
ing circuit OS.
The oscillating transistor 40 is of a high perform-
ance NPN type, as is explained hereinabove, and has high
internal resistance. Accordingly, the leakage current of the
transistor 40 is extremely small and is almost zero in compari-
son with that of the Gerumanium transistor. It is, therefore,
unnecessary to provide the power source switeh in the power
source eireuit A.
The rectifier cireuit C ineludes an eleetric valve
in the form of a diode 22 of which the cathode is connected
to the other terminal of the secondary winding 18b of the
transformer 18, and the diode 22 is provided so as to be
reverse direction with respect to the polarity of the battery
10. The eharging circuit D comprises a main storage capacitor
24, a current restricting resistor 26 and an indicating lamp
in the form of a neon glow lamp 28 which is connected to the
main storage capacitor 24 in parallel by way of the current
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restricting resistor 26. One terminal of the capacitor 24
is connected to the anode of the diode 22, and other terminal
of the capacitor 24 is connected to an emitter electrode of
the transistor 40 and to the negative terminal of the
battery 10.
The trigger pulse generating circuit E has a charg-
ing resistor 30 of which one terminal is connected to the one
terminal of the main storage capacitor 24, a triggering
capacitor 32 of which one terminal is connected to the other
terminal of the charging resistor 30 a trigger transformer
36 having a primary winding 36a and a secondary winding 36b
and parallel connected synchronizing switch 34 which is
arranged to be switched ON and OFF in synchronizing with a
camera shutter and an open flash test button switch 44. The
primary winding 36a of the transformer 36 is connected between
the triggering capacitor 32 and the switch 34~ The flash
tube circuit E comprises a gas-filled flash tube 38. The
flash tube 38 is provided with a pair of main current conduct-
ing electrodes 38aj 38b and-a trigger electrode 38c which is
positioned adjacent but external to the flash tube 38. The
trigger electrode 38c is connected to one terminal of the
secondary winding 36b of the triggering transformer 36, and
one main current conducting electrode 38a is connected to
other terminal of the secondary winding 36b.
In operation, the switch 42 is manually actuated
between its ON and OFF state. When the switch 42 is in
its OFF state, electric charge is stored on the capacitor
16 from the battery 10 through the resistor 14 at the
polarity as shown in Figure 3. By turning the switch 42
ON the base electrode of the transistor 40 is biased to
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74267
cause the transistor 40 to become conductive, because the
electric charge of the capacitor 16 discharges through the
third winding 18c of the transformer 18, the switch 42,
the base electrode and the emitter electrode of the tran- -
sistor 40. When the transistor 40 turns on, current flows
through the primary winding 18a of the oscillating trans-
former 18, the collector-emitter path of the transistor 40
from the battery 10, and, at the same time, the currént
flows through the third winding 18c, the switch 42, the
base-emitter electrodes of the transistor 40, the battery
10 and the resistor 14, and the electric charge is accumula-
ted on the capacitor 16 and thereby the voltage converter-
circuit B commences the oscillation and produces high
alternating current voltage from the secondary winding 18b.
The high alternating current voltage is rectified by the
diode 22 of the rectifier circuit C, to produce a high
direct current voltage.
The main storage capacitor 24 is charged by the
high D.C. voltage from the rectifier circuit C. When the
main storage capacitor 24 is fully charged up to the pre-
determined and suitable voltage, the neon glow lamp 28
lights indicating that the device is in readiness for the
flash tube 38 to be fired. The flash tube 38 may then be
fired by closing of the camera shutter switch 34 or the
test button switch 44. It will be readily appreciated that
this closing need only be momentary during the actuation
of th~ camera shutter.
By closing the switch 34 or 44, the electric charge
on the triggering capacitor 32 discharges through the switch
34 or 44 and the primary winding 36a. Then high voltage
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pulse is induced at the secondary winding 36b of the trigger-
ing transformer 36. The high voltage thus induced in the
secondary winding 36b of the transformer 36 appears at the
trigger electrode 38c of the flash tube 38 and ionizes a
portion of the gas in the flash tube. The main storage
capacitor 24 then discharges across the gas between the main
current conducting electrodes, producing a brilliant flash of
illumination, After the main storage capacitor 24 has been
discharged, the power source circuit A builds up the charge
again in preparation for the next flash,
According to the device shown in Figure 3, since the
high performance transistor 40 is employed in the oscillation
starting circuit OS'of the voltage converter circuit B, the
loss of the battery energy is prevented even when the switch
42 is left ON state for a long time period. Further, since
the current which flows in the base circuit of the transistor
40 is small, voltage drop is eliminated even when a long lea~
wire is to be connected to the switch 42, It is, therefore,
appreciated that good characteristics of the voltage converter
circuit B are obtained, Furthermore, an advantage obtained is
that contacts of the switch 42 need only be of small current
carrying capacity because the current which flows in the base
electrode of the transistor 40 is about 1/20 of that of the
primary current of the oscillator transformer 1~.
Figure 4 is illustrative of other embodiments of the
present invention, and the device shown comprises, similar to
the device of Figure 3, a power source circuit A, a voltage con-
verter circuit ~, a rectifier circuit C, a charging circuit D,
a trigger pulse generating circuit E and a flash tube circuit
F, The only difference from the device of Figure 3 is that
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the voltage converter circuit B is actuated and controlled
by the application of a voltage from the trigger pulse
generating circuit E to an oscillation starting circuit OS,
when a flash tube 38 is triggered.
More specifically, in the device of Figure 4, the
oscillation starting circuit OS consists of a transistor 40,
a first control transistor 46, a second control transistor
48, a biasing capacitor 50, a push-button switch 54 and a
control switching element in the form of a silicon controlled
semi-conductor element such as, for example, a thyristor 56.
Further, the trigger pulse generating circuit E includes a
trigger transformer 36 having a primary winding 36a, a
secondary winding 36b and a third winding 36c.
In the oscillation starting circuit OS, an emitter
electrode of the first control transistor 46 is connected to
a base electrode of the transistor 40, and a collector
electrode of the transistor 46 is connected commonly to a
third winding 18c of an oscillating transformer 18. An
emitter electrode of the second control transistor 48 is
connected to a base electrode of the first control transistor
46. Moreover, coupled to the biasing capacitor 50 is a bias-
ing resistor 52, and the switch 54 is connected to the biasing
capacitor 50 in parallel relationship. The thyristor 56 is
also connected to the switch 54 in parallel relationship. In
addition, a gate electrode of the thyristor 56 is connected to
one terminal of the third winding 36c, and a cathode electrode
of the thyristor 56 is connected to other terminal of the
third winding of the trigger transformer 36.
In accordance with the electric flash device of
Figure 4, when the switch 54 is opened, the capacitors 16 and
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50 are charged by the current from the battery 10, at the
polarity as is shown in the drawing. Accordingly, the second
control transistor 48 is OFF state because it is biased to
be non-conductive, and thereby the first control transistor
46 and the oscillating transistor 40 are also non-conductive
state. In this case, current does not flow in the voltage
converter circuit B because the leakage current is extremely
small in the transistor 40. Under these conditions, when
the switch 54 is closed, electric charge of the biasing capa-
citor 50 is fed back to the battery 10 by way of the switch54 and the resistor 52, then the second control transistor 48
is biased toward conductive and turns on. By turning on the
transistor 48, the first control transistor 46 becomes con-
ductive and thence the transistor 40 also becomes 0~ state for
the purpose of the commencement of the oscillation. When the
oscillation is performed in the voltage converter circuit B,
the biasing capacitor 50 is automatically charged from the
battery 10 by way of the resistor 14 and the secondary wind-
ing 18b. Since the charging time period of the biasing
capacitor 50 is determined by the resistance value of the
resistor 52, the duration of the oscillation can be adjusted.
When a voltage across the biasing capacitor 50
reaches a predetermined value, the transistors 46 and 48 are
cut off and the transistor 40 is also turned off, and thereby
the oscillation is automatically stopped. Under this con-
dition, the leakage current is less than several micro-
amperes, and a power source switch is unnecessary in the
power source circuit A.
In the trigger pulse generating circuit E, when
the triggering capacitor 32 discharges through the primary
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winding 36a of the triggering transformer 36, a high voltage
pulse appears at the secondary winding 36b. The voltage
pulse is about 3,000 volts, and this voltage pulse is applied
to the trigger electrode 38c of the flash tube 38 in order to
fire the flash tube 38. In this case, a voltage of several
volts is induced across the third winding 36c. The induced
voltage in the third winding 36c is applied to the thyristor
56 in the oscillation starting circuit OS as a gating signal
of the thyristor 56, and the thyristor 56 is made conductive.
When the thyristor 56 turns on, the electric charge of the
biasing capacitor 50 discharges through the thyristor 56,
and the voltage across the capacitor 50 reduces to turn on
the transistors 48, 46 and 40. Thence the oscillation of
the converter B begins and repeats the operation as described
hereinabove.
According to the electric` flash device of Figure 4,
the thyristor 56 actuates upon receipt of a firing pulse
from the third winding 36c of the transformer 36. In this
case, the oscillation starting circuit OS is separated from
the trigger pulse generating circuit E in D.C. voltage and
current relationship. Mamely, it will be readlly apparent
that the performance of the voltage converter circuit B is
maintained stabilized because leakage current cannot flow
from the trigger pulse generating circuit E to the biasing
capacitor 50.
When the main storage capacitor 24 is fully charqed,
if the electric flash device is left unused for a long period
such as, for example, for half a day or a full day the
electric charge on the capacitor 24 and the triggering
capacitor 32 gradually decrease, and the thyristor 56 becomes
non-conductive because the induced voltage at the third wind-
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ing 36c is lowered. Under these conditions, the voltage
converter circuit can be operated by closing the switch
54.
Figure 5 shows a more effective electric flash
device according to the present invention. In the embodi-
ment of Figure 5, the device comprises also a power source
circuit including a battery, a voltage converter circuit B,
a rectifier circuit C, a charging circuit D, a trigger pulse
generating circuit E and a flash tube circuit D. Particular-
ly, the voltage converter circuit B is greatly improved byproviding a switch for stopping the oscillation and an
indicating circuit for indicating an oscillation condition.
As is shown in Figure 5, an oscillation starting
circuit OS is provided with an electric valve in the form of
a diode 58 of which an anode is connected to a resistor 52
and a cathode electrode is connected to a negative terminal
of a battery 10, an oscillation stopping switch 60 which is
manually and momentary operated for stopping the activation
of the voltage converter circuit B and a push-button switch
62 which is parallel connected to a thyristor 56. Further,
an oscillation indicating circuit OI is provided in the
output side of a transformer 18. The oscillation indicating
circuit consists of an indicating lamp in the form of a neon
glow lamp 66 which is connected between both terminals of the
secondary winding 18 by way of a current-restricting resistor
64. The neon glow lamp 66 is employed in order to confirm
whether the oscillation in the voltage converter circuit B
is normally performed or not.
The operation of the electric flash device, in
accordance with Figure 5, will now be explained: When the
switch 62 is closed for starting the oscillation, the electric
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charge discharges through the switch 62, the resistor 52
and the diode 58 from the biasing capacitor 50, and all of
the transistors 48, 46 and 40 are biased conductive. When
the transistor 40 turns O~, the voltage converter circuit
B performs the oscillating operation and at the same time
a high A.C. voltage is induced at the secondary winding 18b
of the oscillating transormer 18. The induced voltage at
the secondary winding 18b causes the electric charge to be
stored on the main storage capacitor 24 in the manner as
described earlier and causes the neon lamp to glow, and
thereby the normal operation may be confirmed.
When the main storage capacitor 24 is charged to
the predetermined and desired voltage, the capacitor 24
discharges through the flash tube 38 by activating the
trigger pulse generating circuit E. By the activation of
the trigger pulse generating circuit E, the thyristor 56
maintains the ON state.
The voltage converter circuit B performs the con-
tinuous oscillation as long as the thyristor 56 is maintained
conductive. It is, accordingly possible to flash the flash
tube 38 continuously. Under the continuous oscillating con-
dition, if the switch 60 is closed, the second control
transistor 48 becomes non-conductive, since the base
electrode is biased negative from the negative electrode
of the battery 10. When the transistor 48 is cut off, both
of the transistors 46 and 40 are also turned OFF. Accordingly,
the oscillation of the voltage converter circuit B is also
stopped by closing the switch 60. The diode 58 acts to
ensure proper charge storage in the biasing capacitor 50 and
to prevent the leakage of current from the biasing capacitor
50, thereby enhancing the performance of the voltage converter
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circuit B. In the electric flash device of Figure 5, the
operation of the voltage converter circuit B can also be
stopped automatically after a given time period which is
determined by the resistance value of the resistor 52,
because the biasing capacitor 50 is gradually charged to
the present voltage value.
Figure 6 illustrates another electric flash device
according to the present invention. In accordance with the
electric flash device of Figure 6, a transistor 68 is
employed instead of a thyristor. Namely, an emitter
electrode and a collector electrode of the transistor 68
are respectively connected to a switch 62 so that the transis-
tor 68 is connected in parallel to the switch 62 between the
emitter electrode and the collector electrode thereof.
Further, a capacitor 70 is connected between a base elec-
trode and a juncture of a diode 22 and a main storage
capacitor 24 by way of a resistor 72.
According to the device of Figure 6, the transistor
68 is, initially, non-conductive, because the negative voltage
has applied to the base electrode of transistor 68, notwith-
standing ON and OFF operations of the push-button switch 62.
Oscillation has therefore continued until the biasing capaci-
tor becomes charged up to the predetermined voltage. The
oscillation of the voltage converter circuit B ceases when
the biasing capacitor 50 is charged to the predetermined
voltage value. If the flash tube 38 is fired after or
immediately before the oscillation is ceased, the electric
charge accumulated on the capacitor 70 is discharged through
the flash tube 38, thence the induced voltage appears across
the capacitor 70 at the polarity as is shown in Figure 6, and
thereby the transistor 68 is made conductive. By the con-
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duction of the transistor 68, the electric charge on the
biasing capacitor 50 is discharged by way of the transistor
68 and thereafter and the oscillation is automatically
started.
According to the device of Figure 6, the cost of
the device is reduced because an inexpensive transistor is
used instead of an expensive thyristor, and further, the
size of the device is reduced because a triggering trans-
former having only two windings may be used.
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