JPH0712978Y2 - Electronic flash device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an electronic flash device, particularly an electronic flash device (hereinafter referred to as strobe) used in a silver halide camera or an electronic still video camera.

[Description of Prior Art]

Due to the recent demand for miniaturization of electronic devices, there is a tendency that the power source of a strobe and the electronic device using the strobe as auxiliary light, such as a silver salt camera or a power source of a control circuit of an electronic still video camera, are shared.

However, since the load is heavy at the beginning of charging the strobe, the output voltage of the power source is significantly reduced, and there is a problem in that the drive voltage that guarantees normal operation cannot be supplied to the control circuit section.

Therefore, if the output voltage of the power supply drops at the beginning of charging,
The charge previously charged in the power supply path of the control circuit unit is discharged to compensate the output voltage of the power supply, and the operation of the control circuit unit is normally guaranteed even at the start of strobe charging as described above. It has been proposed to provide a so-called back-up capacitor.

[Problems to be solved by the invention]

However, in this compensation method using a back-up capacitor, it is necessary to prepare a considerable space for the capacitor, which not only causes a drawback that the electronic device becomes large, but also places a severe demand on the power supply voltage of the control circuit section. It was difficult to be satisfied.

The present invention solves the above-mentioned drawbacks of the prior art and provides an electronic flash device with a short charging time. A feature of the present invention is that a power supply for supplying a driving voltage to a control circuit unit of an electronic device. The output voltage of the power supply is below the above voltage by stopping the operation of the strobe DC-DC converter when the output voltage becomes below the voltage necessary for the normal operation of the control circuit section. DC-
As a DC converter, the magnetic energy stored in the transformer is released to the output side when the transistor for oscillation is turned on when the transistor for oscillation is turned on. It is also called a fly-back type DC-DC converter. Is used to minimize the drop in the output voltage of the power supply and reduce the number of pauses or pause periods of the DC-DC converter based on the drop in the output voltage of the power supply, so that the capacitor can be charged in a short time. This is due to the fact that Hereinafter, the present invention will be described in detail with reference to the drawings.

[Explanation of Examples]

FIG. 1 is an electric circuit diagram of an embodiment of a camera system to which the present invention is applied. Reference numeral 1 is a control circuit section 3 of a camera and a battery provided as a power source for a strobe, which will be described later, and 3 is a shutter speed, an aperture, etc. A control circuit unit that executes various controls of the camera and is configured by an integrated circuit (hereinafter abbreviated as IC).
Since the circuit section 3 is composed of a well-known circuit, description of its structure and operation will be omitted. The control circuit unit 3 power terminal V _BATT connected to the output terminal of the battery 1, the power supply terminal V _CC to output a low-level voltage from the power supply terminal V _BATT, the charging start and stop charging the main capacitor 5 of the electronic flash It has a control terminal CHD for outputting a command signal, a detection terminal DET for detecting the charge level of the main capacitor 5, a trigger terminal TRi for starting the light emission of the discharge tube 7 of the strobe, and a ground terminal E. 9,11,13,43,45,47,49,51,5
Reference numerals 3, 55 and 57 are each element constituting the ringing chiyoke type DC-DC converter, 9 is an npn type transistor for oscillation control, 11 is a step-up transformer, 13 is a rectifying diode, and 43 is an oscillation transistor 9. npn type transistor, 45 is a zener diode for cutting spike noise applied between the base and collector of the transistor 9,
47 is a resistor, 49 is a diode, 51 is a resistor, 53 is a capacitor, and 55 and 57 are capacitors and resistors forming a waveform shaping circuit.

15 to 42 are elements for controlling the oscillation of the ringing yoke yoke DC-DC converter, 15 is an npn type transistor, and 17 is a p-type transistor.
np type transistors, 19 and 21 are resistors, 23 is a zener diode for setting the minimum drive voltage that guarantees the normal operation of the control circuit section 3 of the camera, 25 is a capacitor, 2
7, 29, 31 are resistors, 33 is an npn type transistor that controls the on / off of the oscillation starting transistor 15, 35, 37 are resistors, 39
Is a Zener diode that detects the charging voltage of the main capacitor 5, 42 is a capacitor, 59 and 61 are resistors, 63 is a coil, and 65
Reference numeral 127 denotes an element for controlling the above-mentioned DC-DC converter, an oscillation control circuit of the DC-DC converter, and a light emission control circuit described later, and 65 is a pnp type switching transistor, 67,
69 is a resistor, 71 is an npn type power supply control transistor, 73 and 75 are resistors, 77 is an npn type transistor, 79 and 81 are resistors, and 83 and 84 are diodes that accelerate the inversion speed when the transistor 85 turns off, And capacitors, 87 and 89 are resistors, 91 is an npn-type transistor that controls the sub-thyristor 139, and 93 and 95
Is a resistor, 97 is an npn-type transistor connected to the collector of a transistor 85 that generates a trigger signal via a resistor 93, 99 is a resistor, 101 is a capacitor forming a timer, 1
05 and 107 are resistors, 103 is a pnp type switching transistor,
115 and 117 are resistors and capacitors forming a timer, 1
11,113 is a resistor, 109 is an npn type transistor, 121 and 123 are resistors, 119 is a pnp type transistor, and 125 and 127 are voltage dividing resistors.
The divided power of the voltage dividing resistor is connected to the gate of the sub-thyristor 139. 151 is a capacitor, 153 is a resistor, 135 is a main thyristor connected in the discharge path of the main capacitor 5, 137 is a commutation capacitor, 141, 143, 145 are capacitors and resistors for applying a trigger signal to the gate of the main thyristor 135, 147, 149. Is a resistor that forms a charging path of the commutation capacitor 137, 129 is a known trigger circuit that applies a trigger signal to the trigger electrode of the discharge tube 7, 131 is a coil that suppresses the peak value of the discharge current, and 133 is connected in parallel with the coil 131. The diode is

Next, the operation of the camera system having the above configuration will be described.

By turning on the power switch (not shown), the IC
The output of the control terminal CHD of the control circuit unit 3 configured by is from high level (hereinafter referred to as H level) to low level (hereinafter referred to as L level).
(Referred to as a level) and a base current flows to the base of the transistor 65, the transistor 77 in the standby state is turned on in response to the turning on of the power switch to turn on the transistor 77, the transistor 65, and the base resistor 31. A base current flows to the base of the transistor 15 via the gates 27 and 27, and the transistor 15 can be turned on, that is, the standby state. At this time, the output voltage of the battery 1 is the above-mentioned minimum drive voltage, that is, the minimum drive voltage V _L for ensuring the normal operation of the control circuit section 3 of the camera (the zener voltage V _z of the zener diode 23 and the emitter voltage of the transistor 17). If the sum of the base-to-base voltage V _17eb and the saturation voltage V _15sat of the transistor 15 is equal to the minimum drive voltage V _L , the _zener voltage of the _zener diode 23 is selected). At the same time as the standby state, the transistor 17 is turned on and the transistor 15 is also turned on. Transistor 17
Is turned on, a base current flows to the base of the transistor 43, the transistor 43 is turned on, a base current flows to the oscillation control transistor 9, and the primary winding of the transformer 11 is turned on.
The collector current of the transistor 9 flows through 11a, and D
The oscillation operation of the C-DC converter starts.

When an exciting current flows through the coil 11a as described above, a voltage is generated in the feedback winding 11b of the transformer 11 by a known method. Since this voltage has a polarity as shown in the drawing, it acts as a positive feedback voltage for further making the switching transistor 9 conductive, thereby rapidly turning on the switching transistor 9. In this case, the voltage generated in the secondary winding is applied to the rectifying diode 13 in the opposite direction, so that
No current flows in the secondary winding, and the magnetic energy generated in the secondary winding is stored in the transformer 11. Therefore, the current flowing in the primary winding 11a of the transformer 11 is 11 _{LP for} the inductance of the primary winding and t is the time. (However, V ₄₂ is a current represented by the terminal voltage of the capacitor 42) and increases in proportion to time. Then, when the collector current of the switching transistor 9 increases and the base current of the transistor 9 becomes a value that makes it impossible to maintain the saturated state of the transistor 9, the transistor 9 deviates from the saturated state and the collector-emitter of the transistor 9 The voltage increases and the voltage of the primary winding 11a drops. When the voltage drops, the feedback winding 11 proportional to the primary winding voltage
The voltage of b also drops, and as a result, the collector-emitter voltage of the transistor 9 further increases. Since this change is positively fed back, the switching transistor 9 is rapidly turned off.

As described above, when the transistor 9 is inverted from on to off, the rectifying diode 13 on the secondary winding side becomes conductive, and the magnetic energy accumulated in the transformer 11 when the transistor 9 is on passes through the diode 13. As a discharge current to the main capacitor 5, and the main capacitor 5 is charged.

The discharge current I is (However, L _11s is the inductance of the secondary winding of the transformer 11, V _O is the output voltage of the secondary winding 11c, and V _D is the voltage drop of the diode 13).

When all of the magnetic energy stored in the transformer 11 is connected to the output side and transferred to the main capacitor 5 and the like, the current I becomes zero and the diode 13 becomes non-conductive again. In such a state, the base current supplied to the base of the transistor 9 through the transistors 17 and 43 causes the transistor 9 to return to the ON state again, and the transistor 9 goes through a deeper ON state through the same positive feedback process as described above. Becomes Then, after that, the transistor 9 is inverted from on to off, and the magnetic energy accumulated in the transformer 11 is released to the load connected to the secondary side of the transformer.

The oscillation is continued by repeating the above operation, but the charging voltage of the main capacitor 5 is a voltage sufficient for the light emitting operation, for example, 28
When it reaches 0 (V) and the Zener diode 39 becomes conductive,
Since the oscillation control transistor 33 is turned on to short-circuit the base and the emitter of the transistor 15, the transistor 15 is forcibly turned off, and the oscillation transistor 9 is also turned off by this, so that the DC-DC converter Oscillation is stopped. Since the charge detection outputs of the voltage dividing resistors 59 and 61 are also applied to the detection terminal DET of the control circuit unit 3, the control circuit responds to the output of the detection terminal DET when the main capacitor 5 reaches the above-mentioned predetermined voltage. Circuit in section 3 (not shown)
As a result, the control terminal CHD is inverted from the L level to the H level to turn off the transistor 65 and cut off the oscillation start signal to the transistor 15. After that, when the charge stored in the main capacitor 5 disappears due to leakage and the charging voltage of the main capacitor 5 falls below the above-mentioned predetermined value, the zener diode 39
Becomes non-conductive again, and transistor 33 becomes transistor 15
Release the short circuit of. Further, in such a situation, the control circuit unit 3
Since the control terminal CHD of is inverted from the H level to the L level again, the transistor 65 is turned on again and the oscillation start signal is supplied to the transistor 15 so that the transistor 15 can be turned on. At this time, when the output voltage of the battery 1 is higher than the above-mentioned minimum drive voltage V _L , the transistor 9 is turned on to start the oscillation operation in the same manner as described above, and the oscillation operation is continued.

The above description is for the case where the output of the battery 1 does not drop below the above-mentioned minimum drive voltage under any circumstances, but for some reason, for example, the battery has deteriorated in the process of oscillation of the DC-DC converter. When the output voltage of the battery 1 drops below the minimum drive voltage due to the load 5 at the start of oscillation, the following operation is performed.

That is, when the output voltage V _{BATT of the} battery 1 falls below the minimum drive voltage for the above-mentioned reason, the Zener diode 23 for detecting the output state of the battery immediately reverses to the non-conducting state, so that the transistors 15 and 17 are immediately turned on. It is turned off, so that the transistors 43 and 9 are also turned from on to off and the oscillation operation is stopped. Therefore, the output reduction of the battery 1 is immediately recovered, the output of the battery 1 returns to the minimum drive voltage or more necessary for the circuit of the camera control circuit unit 3 to operate normally, and the base current flows through the base of the transistor 9. Then the oscillation is started again. Therefore, the camera control circuit unit 3
Does not cause a malfunction due to the decrease in the minimum drive voltage during the oscillation operation of the DC-DC converter.

As will be understood from the above description, when the DC-DC converter is a DC-DC converter of the type that charges the unloaded main capacitor 5 when the oscillation transistor 9 is on, the output voltage of the battery 1 drops. Is big. Therefore, when the battery output is lowered like this, it is formed by the transistors 15 and 17, the Zener diode 23 and the like. The battery output detection circuit is activated
When the oscillating operation of the DC-DC converter is stopped, the battery 1 is restored again, and the oscillating idle period until the oscillating operation is started becomes a long time proportional to the degree of decrease in the output voltage. Therefore, in the case where the strobe is of a type in which oscillation is stopped according to the battery output state, a converter of the type that charges the main capacitor 5 when the oscillation transistor 9 is turned on is used as the DC-DC converter. It takes a long time to charge up to a predetermined value when it is turned on, but when the transistor 9 is on like the present invention, DC-DC
When a DC-DC converter of the type in which substantially only the exciting current is supplied to the converter and the main capacitor 5 is charged for the first time when the transistor 9 is turned off is used, the decrease in the battery 1 during the oscillating operation is also attributed to the exciting current. Since the level is low, the recovery of the battery after the oscillation is stopped is shortened, and the period during which the oscillation is stopped is shortened. As a result, the main capacitor can be charged to a predetermined value in a short period of time.

The description of FIG. 1 will be further continued. When a release button (not shown) is pressed for shooting, the camera (in this embodiment, an electronic still video camera) responds to the press.
The control terminal CHD of the control circuit section 3 is forcibly inverted from the L level to the H level. Therefore, the transistor 65 is inverted from on to off, and the oscillation of the DC-DC converter is forcibly stopped.

Then, in response to the opening of the shutter, the trigger terminal TRi of the control circuit unit 3 is inverted from the H level to the L level, the light emission start signal is applied to the base of the transistor 85, and the transistor 85 is turned on. Of course, in this case the base voltage
Transistor 77 receiving _Vcc is turned on.

When the transistor 85 is turned on,
Since the light emission trigger signal is supplied from the collector of 85 to the known trigger circuit 129, the discharge tube 7 is triggered, and the main thyristor is also triggered by the known method to be in the conductive state, and the charging charge accumulated in the main capacitor 5 is charged. Is discharged through the discharge tube 7 and the main thyristor 135 to start light emission. When the transistor 85 is turned on, the transistor 91 is turned on and the gate of the sub-thyristor 139 is prevented so that the sub-thyristor 139 does not turn on carelessly due to noise.
The cathodes are short-circuited.

When the transistor 85 is turned on, the transistors 97 and 1
03 is also turned on to start charging the capacitor 117 forming the timer. Since the setting time of this timer is short, the transistor 109 is turned on and the transistor 119 is turned on within a short time after the transistor 103 is turned on, and the output terminals of the voltage dividing resistors 125 and 127 are at the H level. However, since the transistor 91 is on at this time, the signal for turning on the sub thyristor 139 is not given to the gate of the thyristor 139.

After that, the subject is illuminated by the flash light from the discharge tube 7,
When an appropriate amount of exposure is obtained after a predetermined time when the reflected light from the subject is incident on the camera, the output of the trigger terminal TRi of the control circuit unit 3 is inverted from the L level to the H level and a light emission stop signal is generated. Therefore, the transistor 85 is turned off and the transistor 91 is also turned off. This time,
Since the transistor 119 maintains the ON state, the gate of the sub thyristor 139 becomes H level and the sub thyristor 139 is turned on. When the transistor 85 is turned off by the above-mentioned light emission stop signal, the transistors 97 and 103 are turned off, but the transistor 109 is turned off after a predetermined time determined by the amount of charge previously discharged to the capacitor 117 and the time constant of the capacitor 117 and the resistor 113. The transistor 119 is turned off, and in response thereto, the transistor 119 is also turned off. Therefore sub-thyristor 1
At the gate of 39, H for the time determined by timers 113 and 117
A pulse exhibiting a level will be applied.

When the sub-thyristor 139 is turned on as described above, the electric charge charged to the polarity as shown in the figure is discharged through the sub-thyristor 139 and the reverse bias voltage is applied between the anode and the cathode of the main thyristor 135. 135 is turned off and the discharge tube 7 stops emitting light.

[Effect of device]

As described above, the present invention is provided with the battery voltage detecting means which can be miniaturized to prevent the battery from dropping below the desired voltage, so that not only the electronic device can be miniaturized, but also
Even if the demand for the desired voltage is strict, the demand can be surely satisfied.

Further, even if the control method described above, that is, the method of preventing the battery voltage from dropping below the desired voltage by the battery voltage detecting means is adopted, the secondary winding can be used only when the oscillation transistor is off as a DC-DC converter. Ringing choke type that supplies conversion energy to the load connected to the wire
Since the DC-DC converter is used, it is possible to supply a predetermined electric energy to the load (main capacitor) in a short time.

[Brief description of drawings]

FIG. 1 is an electric circuit connection diagram of an embodiment of a camera system to which the present invention is applied. In the figure, 3 ... Camera control circuit section, 5 ... Main capacitor, 9 ...
… Oscillation transistor, 11 …… Boosting transformer, 13 …… Diode, 15,17,33,43,65 …… Transistor, 23,39 ……
It is a Zener diode.

Continuation of the front page (56) Reference JP-A-55-76333 (JP, A) Kazuo Shimizu, "Design of a continuous power supply circuit" CQ Publishing Co., Ltd. (SHO-53-2-1) P. 201 ~ 202

Claims (1)

[Scope of utility model registration request] 1. A power supply means for supplying a voltage for driving an electronic device control circuit, a ringing choke type DC-DC converter for inputting a voltage supplied from the means to perform an oscillating operation, and an output of the converter. The ringing choke type DC-DC converter, which detects the output voltage of the power source means and a main capacitor that stores flash energy, and when the voltage drops below a reference voltage corresponding to a voltage that guarantees driving of the electronic device control circuit. The electronic flash device is provided with oscillation control means for interrupting the oscillating operation of 1. and restarting the oscillating operation of the DC-DC converter after the output voltage of the power supply means is recovered.