JPH09107680A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC-DC converter in which a main capacitor is not degraded due to its overcharge when a short circuit accident or the like is generated in a switching element. SOLUTION: A DC-DC converter circuit is provided with an oscillating transformer 20, with a power supply 1 and with a PNP oscillating transformer 2 used to boost a power-supply voltage. The DC-DC converter circuit is provided with an FET 5 as a first element which is connected in series with the base of the PNP oscillating transistor so as to be controlled and with an NPN transistor 17 as a second element which is connected to a feedback winding, by which a control terminal and a control terminal at the FET 5 as the first element are connected via a diode 6, which is set to continuity together with the FET 5 as the first element so as to be charged when a charging control signal S1 given to their connection part is at an H-level and which stops an oscillation at a low level. Then, even when the FET 4 cannot be controlled due to a short circuit accident, the NPN transistor 17 is turned off so as to surely stops the oscillation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC converter circuit for a camera flash, and more particularly to a DC / DC converter provided with a safety circuit for protecting elements such as a main capacitor.

[0002]

2. Description of the Related Art Conventional DC / DC converters for flash include forward converters and flyback converters.

FIG. 5 shows an example of an electronic flash device incorporating such a conventional DC / DC converter. In FIG. 5, 100 is a power supply battery, 200 is a power supply capacitor, and 30.
0 is an oscillation transistor, 400 is a capacitor, 500 is a resistor, 600 is an NPN transistor, 700 and 280.
0 and 3100 are resistors, 800 and 900 are diodes,
1700 is an oscillation transformer, 2000 is a rectifier diode,
2300 is a main capacitor voltage detection circuit, 2400 is a light emitting circuit, 2500 is a flash discharge tube, 2600 is a main capacitor, 2700 is a control circuit, 2900 is a constant voltage circuit, and 30
00 is a switch circuit, which is configured as described above.

In operation, an oscillation control signal "CGON" from the control circuit 2700 causes the oscillation transistor 300 to start oscillating, the oscillation transformer 1700 boosts the voltage, and the rectifying diode 2000 rectifies the voltage. Main capacitor 2 due to current I _S2
Charge 600. After the charge level is confirmed by the detection circuit 2300, the light emission circuit 2400 causes the discharge tube 2500 to emit light.

[0005]

However, in this case, when the collector / emitter or the collector / base of the transistor 600, which is the switching element for oscillation control in the DC / DC converter circuit, is short-circuited, oscillation is started. There is a problem that the charging voltage rises regardless of the output of the signal (“CGON” in this case), and the main capacitor 2600 may be overcharged and deteriorated.

Therefore, an object of the present invention is to prevent an overvoltage from being applied to the main capacitor when the first element, which is an n-channel FET or NPN transistor for oscillation control, is short-circuited. Another object of the present invention is to provide a DC / DC converter capable of preventing deterioration of a main capacitor.

Further, an object of the present invention is to provide an n-channel FET or an NPN transistor for controlling oscillation of two oscillation transistors constituting a push-pull type DC / DC converter circuit. An object of the present invention is to provide a DC / DC converter capable of preventing an overvoltage from being applied to the main capacitor when the first element and the third element are short-circuited and preventing deterioration of the main capacitor.

[0008]

To achieve the above object, the present invention provides an oscillating transformer composed of a primary winding, a secondary winding and a feedback winding, and an oscillating transistor for boosting a power supply voltage. The DC / DC converter has a first element for controlling ON / OFF of the oscillation transistor and a second element for controlling ON / OFF of the feedback current, and a diode is provided between the control terminals of the first and second elements. The first and second elements are connected to each other to be charged when the charge control signal is at a high level, and the oscillation is stopped at a low level.

Further, in a push-pull type DC / DC converter having two oscillating transistors for performing a switching operation for boosting the power supply voltage, a first element and a second element for controlling ON / OFF of the first oscillating transistor are provided. It has a third element for controlling the on / off of the oscillation transistor and a second element for controlling the on / off of the feedback current, and connects between the control terminals of the first and third elements and the control terminal of the second element. It is connected through a diode, and when the charge control signal is at a high level, the first, second, and third elements are turned on to perform charging, and the oscillation is stopped at a low level.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A structure for realizing an object of the invention according to the present application is such that an oscillating transformer composed of a primary winding, a secondary winding and a feedback winding and a power supply are provided as described in claim 1. A DC / DC converter circuit having an oscillation transistor for boosting a power supply voltage, the first element for control connected in series to the base of the oscillation transistor;
When the charging control signal applied to the feedback winding of the oscillation transformer is connected between the control terminal and the control terminal of the first element through a diode and is at a high level, the charge control signal is applied together with the first element. DC comprising a second element that conducts to charge and stops oscillation at a low level
/ DC converter.

According to this structure, both the first element and the second element conduct when the charge control signal is at the high level to start oscillation, and when the charge control signal is at the low level, the second element is turned off. Make sure DC / DC by making it conductive
Oscillation of the converter can be stopped.

A specific configuration for realizing the object of the invention according to the present application is, as described in claim 2, in claim 1, wherein the oscillation transistor is a PNP transistor. It is in.

According to this configuration, the DC for controlling the base current is used.
A / DC converter oscillation circuit can be configured.

Another specific configuration for achieving the object of the invention according to the present application is, as described in claim 3, in claim 1, wherein the first element is an n-channel FET or NP.
A DC / DC converter characterized by being an N-transistor.

According to this structure, the n-channel FET is used as the base of the oscillation transistor using the PNP transistor.
Alternatively, the oscillation can be controlled by the configuration in which the first element using the NPN transistor is connected in series.

Another specific configuration for achieving the object of the invention according to the present application is, as described in claim 4, in claim 1, the second element is an n-channel FET or NP.
A DC / DC converter characterized by being an N-transistor.

According to this structure, the control terminals of the first element and the second element using the n-channel FET or NPN transistor are controlled by the same charge control signal, so that the second element is controlled. ON / OFF control of the feedback circuit can be performed.

Another specific configuration for achieving the object of the invention according to the present application is, as described in claim 5, in claim 1, when the first element is damaged and short-circuited, The DC / DC converter is characterized in that the second element is made non-conductive to stop the oscillation.

According to this structure, when the first element is damaged and short-circuited, the feedback circuit is cut off by the second element, and D
The oscillation operation of the C / DC converter can be stopped. Another structure for realizing the object of the invention according to the present application is, as described in claim 6, a feedback coil and two separate ones.
A push-pull DC / DC converter circuit having an oscillating transformer composed of a secondary winding and a power supply, and having two oscillating transistors for performing a switching operation for boosting a power supply voltage, wherein a first oscillating transistor and a first oscillating transistor An oscillation control circuit configured by a first element connected in series to the base of the second oscillation transistor and connected in parallel to the battery; and a third element connected in series to the bases of the second oscillation transistor and the second oscillation transistor. And an oscillation control circuit that is connected in parallel to a battery, and is connected to a feedback winding of the oscillation transformer to connect the control terminal and the control terminals of the first and third elements via a diode DC / DC characterized by comprising a second element which conducts and charges both when the charge control signal applied to the point is at a high level and stops oscillation at a low level. In the converter.

According to this structure, the first and third elements and the second element are both turned on when the charge control signal is at the high level to start oscillation, and when the charge control signal is at the low level, the second element is turned on. Make sure the element is non-conducting DC
The oscillation of the / DC converter can be stopped.

A specific configuration for achieving the object of the invention according to the present application is, as described in claim 7, in claim 6, wherein the first and second oscillation transistors are PNP transistors. There is a DC / DC converter.

According to this structure, the oscillator circuit of the push-pull type DC / DC converter of the base current control can be formed.

Another specific structure for achieving the object of the invention according to the present application is, as described in claim 8, in claim 6, wherein the first and third elements are n-channel FETs.
Or a DC characterized by being an NPN transistor
/ DC converter.

According to this structure, the n-channel FET or the N-channel FET is formed at the base of the two oscillation transistors of the push-pull type DC / DC converter using the PNP transistor.
Oscillation can be controlled by the configuration in which the first element and the third element using the PN transistor are connected in series.

Another specific configuration for achieving the object of the invention according to the present application is, as described in claim 9, in claim 6, wherein the second element is an n-channel FET or NP.
A DC / DC converter characterized by being an N-transistor.

According to this structure, a push-pull type DC / DC circuit using an n-channel FET or NPN transistor is used.
By configuring the control terminals of the first, third and second elements of the DC converter to be controlled by the same charge control signal, it is possible to perform on / off control of the feedback circuit by the second element.

Another specific configuration for achieving the object of the invention according to the present application is, as described in claim 10, in the case where in claim 6, the first and third elements are damaged and short-circuited. The DC / DC converter is characterized in that the second element is made non-conductive to stop oscillation.

According to this structure, when the first and third elements are damaged and short-circuited, the second element is made non-conductive to interrupt the feedback circuit and the oscillation of the DC / DC converter can be stopped. .

[0029]

【Example】

(First Embodiment) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of an electronic flash device according to a first embodiment of the present invention.

FIG. 1 shows the configuration of an electronic flash device (strobe device) using a DC / DC converter, which has a power source section for a battery 1 and has a PNP oscillation transistor 2 for boosting the voltage of the battery 1. Connects the emitter to one end of the battery 1 and the collector to the primary side 20a of the oscillation transformer,
A resistor 3 and a capacitor 4 are connected in parallel between the emitter and the base.

Switching element FET which is the first element
A drain 5 is connected to the base of the PNP oscillation transistor 2 to control ON / OFF of the PNP oscillation transistor 2. A resistor 7 is placed between the gate of the FET 5 and the other end of the battery 1.
The cathode of the diode 9 is connected to the source, and the anode of the diode 9 is connected to the other end of the battery 1.

The diode 6 has a cathode connected to the gate of the FET 5 and an anode connected to one end of a resistor 18 described later and the S1 terminal of the control circuit 200 to perform one-terminal control.

The primary winding 20a of the oscillation transformer 20 for boosting the oscillation is connected to the collector of the PNP oscillation transistor 2 and 20c is connected to the other end of the battery 1. The feedback winding 20e is connected to the source of the FET 5 as the first element and the cathode of the diode 9, 20d is connected to one end of the feedback resistor 8, and the other end of the feedback resistor 8 is connected to the second end.
It is connected to the collector of the NPN transistor 17 which is the element of. The transistor 17, which is the second element, turns on / off the feedback current loop, and cuts off the feedback circuit to stop oscillation when an accident occurs.

The high voltage rectifier diode 22 has its anode connected to the secondary winding 20f of the oscillation transformer 20, and its cathode connected to the voltage detection circuit 300 and the anode of the diode 29.

In this embodiment, a safety circuit is formed by the second element, and the NPN transistor 17 which is the second element.
A resistor 19 is connected between the base of the battery 1 and the other end of the battery 1, one end of the resistor 18 is also connected to the base, and the other end of the resistor 18 is the anode of the diode 6 and the oscillation start signal (or charge control) of the control circuit 200. Signal) terminal S1. The collector of the second element NPN transistor 17 is connected to the other end of the resistor 8.

Here, the oscillation start signal (charge control signal) S
When the output of 1 is at H level, the NPN transistor 17 is turned on, the feedback resistor 8 is connected to the other end of the battery 1 to form a feedback loop, and the FET 5
Turn on to start oscillation. When the oscillation start signal is at the L level, the NPN transistor 17 is turned off, the feedback loop is cut off, the FET 5 is also turned off, and the oscillation is stopped.

The configuration from the oscillation transistor 2 to the high voltage rectification diode 22 described above operates as a booster circuit D.
It is a C / DC converter. It should be noted that the second element N
The PN transistor may be an n-channel FET.

The detection circuit 300 for detecting the charging voltage has a capacitor 25 having one end connected to the cathode of the high-voltage rectification diode 22 and the other end connected to the other end of the battery 1, and a main capacitor 38 connected via the diode 29 to both ends. The voltage dividing resistors 26 and 27 that are connected to each other and detect the divided voltage of the main capacitor 38.
And a capacitor 28 connected to both ends of the resistor 27, and the connection point of the resistor 26 and the resistor 27 is S of the control circuit 200.
It is connected to two terminals.

The light emitting circuit of the next stage has a diode 29 at one end.
Resistor 30 connected to the cathode of the
The other end of the thyristor 31 has a cathode connected to the other end (GND) of the battery 1, a gate of the thyristor 31 has a resistor 32 having the other end connected to the S3 terminal of the control circuit 200, and a gate-cathode of the thyristor 31. A capacitor 33 and a resistor 34, which are connected to, are connected. In addition, it is composed of a trigger capacitor 35 whose one end is connected to the anode of the thyristor 31 and the other end of the resistor 30, and a trigger transformer 36 whose primary side is connected to the other end of the trigger capacitor 35.

The flash discharge tube 37 is connected to both ends of the main capacitor 38 and is trigger-connected to the secondary side of the trigger transformer 36. The main capacitor 38 is a capacitor that charges the energy required for flash emission, and one end (+ side)
Is connected to the cathode of the diode 29, one end of the resistor 30 and the anode of the flash discharge tube 37, and the other end (− side) is connected to the other end of the battery 1 and the cathode of the flash discharge tube 37. Control circuit 20
In response to a pulse signal output from the S3 terminal of 0, a high-voltage pulse is applied from the light emitting circuit to the flash discharge tube 37 to cause it to emit light.

The constant voltage circuit 100 outputs a constant voltage V _CC even if the voltage of the battery 1 changes. The control circuit 200 is composed of a one-chip microcomputer or the like for performing a sequence operation of the camera, and includes a CPU and RO.
A one-chip IC circuit including an M, a RAM, an input / output control circuit, a multiplexer, a timer circuit, a comparator, an A / D converter, a D / A converter, etc., and controls the camera system by software. The power supply uses the output of the constant voltage circuit 100. The signal terminal related to the strobe of the control circuit 200 is S1 terminal,
There are S2 terminal and S3 terminal. First, the S1 terminal is connected to the anode of the diode 6 to start oscillation by changing from LL (abbreviation of Low Level) to HL (abbreviation of Hi LEVEL), and by dropping to LL. Represents an oscillation control signal that stops oscillation.

The S2 terminal detects the input signal from the charge voltage detection circuit 300, monitors the charge voltage of the main capacitor 38, performs a level detection by comparing, and oscillates by S1 when the charge completion voltage is reached. Represents a charging detection signal for stopping.

The S3 terminal is an output terminal connected to the resistor 32 connected to the gate of the thyristor 31 of the light emitting circuit, and sends a one-shot pulse to the gate of the thyristor 31 via the resistor 32 to turn on the thyristor 31 to turn on the trigger capacitor. 35 discharges the electric charge charged to the trigger transformer 3
6 outputs a high-voltage pulse signal, and the flash discharge tube 37
It represents a light emission signal for triggering and emitting light.

Next, the operation will be described. Regarding the operation, only the strobe operation in the camera sequence will be described.

The control circuit 200 monitors the charging voltage of the main capacitor 38 by the detection circuit 300, detects the charging level of the main capacitor 38 by the S2 signal, and sets it to the charging completion level (hereinafter, abbreviated as the charging completion level). Determine if you have arrived.

When the charge level is the full level, the S3 signal is permitted and the trigger is enabled. If the charge is not completed, set the signal of the S1 terminal to LL
It is set to L and the FET 5 is turned on via the diode 6. At the same time, the transistor 17 is turned on via the resistor 18, and the feedback loop (source of the FET 5, feedback winding 20
e, 20d, resistor 8 and transistor 17) are connected.
When the FET 5 is turned on, the base current of the PNP oscillation transistor 2 is drawn and turned on. In this way, a current flows from the battery 1 to the primary windings 20a and 20c of the oscillation transformer 20 via the emitter / collector.

When the FET 5 is turned on, the current from the battery 1 is P
Via the emitter / base of the NP oscillation transistor 2,
Part of the feedback winding 20 through the drain and source of ET5
A feedback current flows through the collector and the emitter of the transistor 17 through the resistors 8 and 20e. In addition, an induced current flows through the secondary windings 20f and 20g due to the current flowing through the primary windings 20a and 20c, and FE
The current flowing through the source of T5 flows through the secondary windings 20g and 20f, and charges the main capacitor 38 via the rectifying diode 22 and the diode 29.

The primary current flowing through the primary windings 20a, 20c flows rapidly, but when a certain constant current flows and the oscillation transformer 20 is magnetically saturated, the primary current is blocked and does not flow rapidly, so that the oscillation current of the oscillation transformer 20 decreases. The polarity is reversed. At this time, the secondary windings 20f and 20g and the feedback windings 20e and 20d
Since the polarities of both are reversed, the secondary current stops flowing and F
ET5 turns off, the PNP oscillation transistor 2 turns off, and oscillation stops. However, since the S1 signal of the control circuit 200 remains HL, even if the oscillation is stopped due to the magnetic saturation, the oscillation is performed again when the magnetic saturation is resolved, and the main capacitor 38 is charged by repeating this.

The DC / DC converter is the main capacitor 38.
During the charging of the battery 29, a current flows in the diode 29 in the forward direction, so that the detection circuit 300 can detect the charging voltage of the main capacitor 38, and the voltage of the main capacitor 38 changes to the resistance 2
The divided voltages of 6 and 27 are input to the S2 terminal of the control circuit 200 and detected. The capacitors 25 and 28 are capacitors for stabilizing the S2 signal.

Converter in control circuit 200 or A
As a result of detecting the charging voltage by the / D converter, when the charging of the main capacitor 38 is completed, the control circuit 200 switches the S1 signal from HL to LL to stop the oscillation.

It is determined whether or not a release switch (not shown) of the camera is turned on, and when it is turned on, known photographing preparation operation and exposure operation are started. At this time, the one-shot pulse of the light emission signal is output from the S3 terminal of the control circuit 200 at the determined light emission timing. This pulse is a thyristor 3
The gate of No. 1 is turned on to discharge the electric charge of the trigger capacitor 35, the discharge tube 37 is triggered by the high voltage pulse generated on the secondary side of the trigger transformer 36, and the main capacitor 38
It discharges the electric charge and emits light. Then, the known shutter operation is completed and the strobe operation is completed.

The DC / DC converter of the strobe device operates as described above. However, for example, a defective component or a defective mounting of the control system substrate of the low voltage drive and the light emitting circuit substrate of the high voltage drive portion is the cause. FET5 which is the first element
If an accident occurs in which a short circuit occurs, a short circuit current flows between the drain and the base of the FET 5 or between the drain and the source. The current flowing through the drain and gate of the FET 5 flows into the negative terminal side of the battery 1 through the resistor 7, but the influence of the short circuit of the FET 5 does not reach the base of the second element transistor 17 due to the separating diode 6. Therefore, the transistor 17 is in a state controllable by the oscillation control signal S1.

Therefore, as a safety measure, the control circuit 200
If the S2 signal is checked and the oscillation is stopped when a predetermined time has elapsed after switching the oscillation control signal to HL on the side, the transistor 17 is set to LL even if the FET 5 is short-circuited and becomes uncontrollable. It is possible to prevent a situation where the main capacitor 38 is turned off by a signal, the feedback circuit is cut off, the oscillation of the DC / DC converter is stopped, and the main capacitor 38 is deteriorated due to overcharge.

As described above, according to this embodiment,
The FET 5 and the transistor 17 perform one-terminal control in which the oscillation control signal S1 simultaneously turns on when oscillation starts,
If the FET 5 is once short-circuited and becomes uncontrollable, it is separated by the separating diode 6 to separate it from the transistor 1.
Since it is configured so as not to affect 7), when an accident occurs, the transistor 17 is controlled to be turned off to surely stop the oscillation of the DC / DC converter, thereby ensuring circuit safety.

(Second Embodiment) Next, a second embodiment of the present invention will be described. FIG. 2 is a circuit block diagram of an electronic flash device according to a second embodiment of the present invention. In the second embodiment shown in FIG. 2, the first element FET5 of the previous embodiment shown in FIG.
The NPN transistor 50 is replaced with the resistor 7, and a resistor 70 is connected between the base and emitter of the NPN transistor 50 instead. The rest of the configuration and the boosting charging operation are exactly the same as in the previous embodiment of FIG.

In the circuit of FIG. 2 as well, if the first element NPN transistor 50 is short-circuited, a short-circuit current flows between the collector and base of the NPN transistor 50 and between the collector and emitter, but is separated by the diode 6. Since the transistor 17, which is the second element, can be controlled even if the transistor 50 cannot be controlled, when the accident occurs, the transistor 17 is turned off to stop the oscillation of the DC / DC converter and prevent the deterioration of the main capacitor and the like. .

In the first embodiment, the first element and the second element are composed of the FET 5 and the transistor 17, and in the second embodiment, both are composed of the transistor.
It may be configured with T or other combinations.

As described above, according to the second embodiment, a safety circuit against a short circuit accident of the switching element can be constructed as in the first embodiment.

(Third Embodiment) Next, a third embodiment of the present invention will be described. The third embodiment is a push-pull type DC / DC in which a two-stage oscillator circuit is connected in parallel to a battery.
This is in consideration of the safety circuit of the converter. FIG. 3 is a circuit block diagram of an electronic flash device according to a third embodiment of the present invention. In FIG. 3, a first PNP oscillating transistor 2 having a power supply section for a battery 1 and for boosting the voltage of the battery 1 as a first oscillation control circuit has an emitter connected to the battery 1
The collector is connected to the oscillating transformer 20a at one end, and the resistor 3 and the capacitor 4 are connected in parallel between the emitter and the base.

The FET 5 which is the first element has a drain P
It is connected to the base of the NP oscillation transistor 2 to control ON / OFF of the PNP oscillation transistor 2. FET
A resistor 7 is connected between the gate of 5 and the other end of the battery 1, the cathode of a diode 9 is connected to the source, and the anode of the diode 9 is connected to the other end of the battery 1. The above constitutes the first oscillation control circuit.

The diode 6 has its cathode connected to the gate of the FET 5, and its anode is connected to one end of the resistor 18 and the control circuit 20.
One-terminal control is performed by connecting to the S1 terminal of 0.

Next, as the second oscillation control circuit, the battery 1
The second PNP oscillating transistor 10 for increasing the voltage is connected with the emitter at one end of the battery 1, the collector connected to the split winding 20b of the oscillating transformer 20, and the resistor 11 and the capacitor 12 in parallel between the emitter and the base. Connected to.

In the FET 13 which is the third element, the drain is connected to the base of the PNP oscillation transistor 10, and P
The NP oscillation transistor 10 is on / off controlled.
The gate of the FET 13 is connected to the cathode of the diode 6 and the resistor 14 having one end connected to the other end of the battery 1, the source is connected to the cathode of the diode 16, and the anode of the diode 16 is connected to the other end of the battery 1. There is.

Both of these two oscillation control circuits are connected in parallel to the battery 1.

The primary winding of the oscillation transformer 20 is divided into 20a and 20b by 20c, and the primary winding 20a is a PNP.
Connected to the collector of the oscillation transistor 2 and connected to the primary winding 20
b is connected to the collector of the PNP oscillation transistor 10,
The primary winding 20c is connected to the other end of the battery 1. In addition,
The connection between the primary winding 20a and the collector of the PNP oscillation transistor 2 is connected to the black dot mark side of the winding start, and the connection between the primary winding 20b and the collector of the PNP oscillation transistor 10 is connected to the winding end. As you can see, the polarities are different.

Further, the feedback winding 20d of the oscillation transformer 20
Is connected to the source of the third element FET 13 and one end of the resistor 15, the feedback winding 20e is connected to the source of the first element FET 5 and one end of the resistor 8, and the resistors 8 and 15 are connected to the other end. Is connected to the collector of the NPN transistor 17, which is the second element.

The NPN transistor 17 which is the second element constituting the safety circuit of this embodiment turns on / off the feedback current loop as in the previous embodiment, and the feedback windings 20d and 20e have two oscillations. It will be commonly used in the control circuit and the feedback current loop will be turned on / off.
Off is also done at the same time.

A resistor 19 is connected between the base of the transistor 17 of the second element and the other end of the battery 1, and one end of the resistor 18 is connected to the base. The other end of the resistor 18 is connected to the anode of the diode 6, and is further connected to the oscillation start signal (or charge control signal) terminal S1 of the control circuit 200, and the collector of the transistor 17 is connected to the other ends of the resistors 8 and 15. doing.

As a result, when the oscillation starting signal (charging control signal) S1 is HL, the transistor 17 is turned on, the feedback resistors 8 and 15 are connected to the other end of the battery 1 to form a feedback loop, and the FET 5 and FET
13 is also turned on to start oscillation. When the oscillation starting signal S1 is switched to LL, the transistor 17 is turned off to interrupt the feedback current loop, and the FETs 5 and 13 are also turned off to stop the oscillation.

Next, the cathode of the high-voltage rectifying diode 21 is connected to the secondary winding 20g of the oscillation transformer 20, and the anode is connected to the feedback winding 20e and the source of the FET 5. The cathode of the high-voltage rectifier diode 23 is the transformer 2
It is connected to the next winding 20f, and the anode is the feedback winding 20d and F.
It is connected to the source of ET13. The anode of the high-voltage rectifier diode 22 is connected to the cathodes of the secondary winding 20f and the diode 23, and the anode of the high-voltage rectifier diode 24 is connected to the secondary winding 20g and the cathode of the diode 21. Connected to the anode of the diode 300 and the diode 29, these four high-voltage rectifier diodes 21 to 24 form a bridge rectifier circuit.

The PNP oscillation transistor 2 shown above
~ Push-pull DC up to high-voltage rectifier diode 24
This is the configuration of the / DC converter. Moreover, FET may be used for the transistor 17 of the second element. With respect to the configuration after this, the diode 29 to the main capacitor 38, the constant voltage circuit 100, the control circuit 200, the detection circuit 300, etc. are the same as the configuration of the previous embodiment, and the description thereof will be omitted.

Next, the operation will be described. First, the control circuit 200 monitors the charging voltage of the main capacitor 38 with the detection circuit 300, detects the charging level of the main capacitor 38 from the S2 signal, and determines whether the charging completion level sufficient for light emission has been reached. If it has reached, the S3 signal is permitted and the trigger is enabled.

If the charging is not completed, S of the control circuit 200
1 signal is changed from LL to HL and FE is passed through diode 6.
Turn on T5 and FET13. At the same time, the transistor 17 of the second element is turned on via the resistor 18, and the feedback loop (source of the FET 5, feedback windings 20e, 20
d, the resistor 15, the transistor 17, the source of the FET 13, the feedback windings 20d and 20e, the resistor 8, and the transistor 17) are connected. The FETs 5 and 13 are turned on, and the base currents of the PNP oscillation transistor 2 and the PNP oscillation transistor 10 are respectively drawn and turned on. However, as a one-terminal control operation, there is a timing variation in the elements of the PNP oscillation transistor 2 and the PNP oscillation transistor 10. Due to (variation in current amplification factor h _FE ), a transistor with a large h _FE starts oscillation first.

For example, h _{FE of the} PNP oscillation transistor 2
Is larger than the PNP oscillating transistor 10, first, the oscillating transistor 2 is turned on, and a current flows from the battery 1 to the primary windings 20a and 20c via the emitter / collector.

Next, when the FET 5 is turned on, from the battery 1 through the emitter / base of the PNP oscillation transistor 2, the drain / source of the FET 5, the feedback windings 20e, 2
0d, resistor 15, collector of NPN transistor 17
Feedback current flows through the emitter.

In addition, an induced current flows in the secondary windings 20f and 20g due to the current flowing in the primary windings 20a and 20c.
The current flowing to the source of ET5 flows through the diode 21 to the secondary windings 20g and 20f, and charges the main capacitor 38 via the diode 22 and the diode 29.

The primary current flowing through the primary windings 20a and 20c flows rapidly, but a certain constant current flows and the transformer 2
When 0 is magnetically saturated, the primary current is blocked, the current does not flow rapidly, and the polarity of the transformer 20 is reversed. At this time, the polarities of both the secondary windings 20f and 20g and the feedback windings 20e and 20d are inverted, and the secondary current does not flow, the FET 5 is turned off, the PNP oscillation transistor 2 is turned off, and the oscillation is stopped.

However, since the S1 signal is still HL, the FET
13 is in the ON state, and a feedback current flows through the feedback windings 20d and 20e and the collector / emitter of the NPN transistor 17 via the resistor 8.

An induced current flows through the secondary windings 20g and 20f due to the current flowing through the primary windings 20b and 20c, and the FET1
The current flowing to the source of 3 flows to the secondary windings 20f and 20g through the diode 23 and charges the main capacitor 38 through the diodes 24 and 29, but magnetic saturation similarly occurs and the primary current is blocked, The operation of inverting the polarity of the transformer 20 and stopping the oscillation is repeated, and the main capacitor 38 is repeatedly charged by the two oscillation control circuits as the operation of the push-pull type DC / DC converter. DC / D
When the C converter charges the main capacitor 38,
Since a current flows through the diode 29 in the forward direction, the detection circuit 300 can detect the charging voltage of the main capacitor 38.

The voltage of the main capacitor 38 is the resistances 26 and 27.
The voltage is input to the S2 terminal by the voltage division of, and if the charge completion voltage is reached, the S1 signal is set to LL and oscillation is stopped.

Finally, the release switch (not shown) of the camera is judged to be on, and if it is on, a predetermined camera operation is performed, and a one-shot pulse is output from the S3 terminal of the control circuit 200 at a predetermined light emission timing. Then, the light is emitted according to the procedure described above.

In the push-pull type DC / DC converter as described above, the FETs 5 and F, which are the first and third elements now, are used.
If a short circuit accident occurs in the ET 13, for example, if a short circuit occurs between the drain and the gate, a short circuit current flows from the resistor 7 or the resistor 14 to the other end side of the battery 1.
Since the gates of the transistors 5 and 13 and the base of the transistor 17 are separated by the diode 6, the short circuit accident of the FET does not affect the base of the transistor 17, and the FET
Since the transistor 17 which is the second element can be controlled by the S1 signal even when the FET 5 or the FET 13 is in the uncontrollable state, when an accident occurs, the S17 is the same as in the first embodiment.
By setting 1 signal to LL to turn off the transistor 17 and stop oscillation of the push-pull type DC / DC converter, it is possible to avoid a situation where the main capacitor is overcharged and deteriorated.

Although the second switch element is composed of the NPN transistor 17, it may of course be composed of an FET.

As described above, according to the third embodiment, even in the case of the push-pull type DC / DC converter, the NPN transistor 17 which is the second element is turned off when an accident occurs to surely oscillate. Since it can be stopped, a safety circuit for preventing deterioration of elements such as the main capacitor of the high voltage circuit can be constructed as in the previous embodiment.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. FIG. 4 is a circuit block diagram of an electronic flash device according to a fourth embodiment of the present invention. In the fourth embodiment shown in FIG. 4, the first element FET 5 and the third element FET 13 of the third embodiment of FIG. 3 are connected to the NPN transistor 50 and the NP.
It is replaced with the N-transistor 130, and the resistors 7 and 14 in the case of the FETs are deleted, and the resistors 70 and 140 are connected between the base and emitter of the NPN transistors 50 and 130, respectively. Other configurations and boost charging operation are exactly the same as those in the previous embodiment shown in FIG.

Here again, if a short-circuit accident occurs in the NPN transistors 50 and 130 of the first and third elements,
Although the short-circuit current flows to the emitter side, the bases of the NPN transistors 50 and 130 and the base of the second element NPN transistor 17 are separated by the diode 6 so that they have no influence.
Even if 0 and 130 are short-circuited and cannot be controlled, the transistor 17 of the second element can be controlled. Therefore, when an accident occurs, the control circuit 200 sets the S1 signal to LL as in the first embodiment.
To turn off the transistor 17 and push-pull DC
By setting so that the oscillation of the / DC converter is stopped, the situation in which the main capacitor 38 is deteriorated can be avoided. A FET may be used as the NPN transistor 17.

As described above, according to the fourth embodiment, even when the push-pull type DC / DC converter has the NPN transistors as the first and third elements, a short-circuit accident occurs as in the previous embodiment. When the above occurs, the second element is turned off, the oscillation of the push-pull type DC / DC converter is surely stopped, and the safety circuit capable of preventing the deterioration of the main capacitor 38 and the like can be configured.

[0088]

According to the first to fifth aspects of the present invention,
DC having an oscillation transformer composed of a primary winding, a secondary winding, and a feedback winding, and an oscillation transistor for boosting the power supply voltage
/ DC converter circuit, nch-FET or NPN connected in series to the base of PNP oscillation transistor
The first element, which is a transistor, is connected to the feedback winding of the oscillation transformer, and the control terminal and the control terminal of the first element are connected via a diode. When the charge control signal applied to the connection point is at high level, the first element is connected. Nch-FET or N which conducts with the element of No. 3 and charges to stop oscillation at a low level
Since it has a second element composed of a PN transistor,
It is possible to prevent the main capacitor from being deteriorated due to overvoltage when the first element is damaged and short-circuited.

According to the invention described in claims 6 to 10,
In a push-pull type DC / DC converter circuit having two oscillating transistors for boosting a power supply voltage, a first element composed of a first PNP oscillating transistor and an nch-FET or an NPN transistor connected in series to its base is provided. Oscillation control circuit connected in parallel to the battery, and oscillation control circuit in which a second PNP oscillation transistor and a third element composed of an nch-FET or NPN transistor connected in series to its base are connected in parallel to the battery. And connected to the feedback winding to connect the control terminal to the control terminals of the first and third elements via the diode, and conducts charging together when the charge control signal applied to the connection point is at high level. Nch-FE that stops oscillation at low level
Since the second element constituted by the T or NPN transistor is provided, in the push-pull DC / DC converter, when the first and third elements are damaged and short-circuited, the main capacitor is overvoltageed and the main capacitor is It is possible to prevent deterioration.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of an electronic flash device according to a first embodiment of the present invention.

FIG. 2 is a circuit block diagram of an electronic flash device according to a second embodiment of the present invention.

FIG. 3 is a circuit block diagram of an electronic flash device according to a third embodiment of the present invention.

FIG. 4 is a circuit block diagram of an electronic flash device according to a fourth embodiment of the present invention.

FIG. 5 is a circuit block diagram of a conventional electronic flash device.

[Explanation of symbols]

1 Battery 2 and 10 PNP Oscillation Transistors 3, 7, 8, 11, 14, 15, 18, 19, 30, 3
2, 34, 70, 140 Resistance 4, 12, 25, 28, 33 Capacitor 5, 13 n-channel FET 6, 9, 16 Diode 17, 50, 130 NPN transistor 20 Oscillation transformer 21, 22, 23, 24 High voltage rectification diode 26, 27 Voltage dividing resistor 29 High voltage rectifier diode 31 Thyristor 35 Trigger capacitor 36 Trigger transformer 37 Flash discharge tube 38 Main capacitor 100 Constant voltage circuit 200 Control circuit 300 Detection circuit

Claims (10)

[Claims] 1. A DC / DC converter circuit having an oscillating transformer composed of a primary winding, a secondary winding and a feedback winding and a power supply, and having an oscillating transistor for boosting a power supply voltage, wherein the oscillating transistor A first control element connected in series to the base of the device and a feedback winding of the oscillation transformer, and connecting the control terminal and the control terminal of the first element via a diode; A DC / DC converter comprising: a second element that conducts with the first element to charge when the charge control signal applied to the element is at a high level and stops oscillation at a low level. 2. The DC / DC converter according to claim 1, wherein the oscillation transistor is a PNP transistor. 3. The DC / DC converter according to claim 1, wherein the first element is an n-channel FET or N-channel FET.
A DC / DC converter characterized by being a PN transistor. 4. The DC / DC converter according to claim 1, wherein the second element is an n-channel FET or N-channel FET.
A DC / DC converter characterized by being a PN transistor. 5. The DC / DC converter according to claim 1, wherein when the first element is damaged and short-circuited, the second element is made non-conductive to stop oscillation. converter. 6. A push-pull type DC / DC converter having an oscillation transformer composed of a feedback winding and two primary windings divided from each other and a power supply, and having two oscillation transistors that perform a switch operation for boosting the power supply voltage. In the circuit, an oscillation control circuit configured by a first oscillating transistor and a first element connected in series to the base of the first oscillating transistor and connected in parallel to a battery, a second oscillating transistor and a second oscillating transistor. Third connected in series to the base of the transistor
Connected to the feedback winding of the oscillation transformer, and connected between the control terminal and the control terminals of the first and third elements via a diode. A second element which is connected and conducts and charges together when the charge control signal applied to the connection point is at high level to stop the oscillation at low level.
C / DC converter. 7. The DC / DC converter according to claim 6, wherein the first and second oscillation transistors are PN.
A type DC / DC converter characterized by being a P-transistor. 8. The DC / DC converter according to claim 6, wherein the first and third elements are n-channel FEs.
D, which is a T or NPN transistor
C / DC converter. 9. The DC / DC converter according to claim 6, wherein the second element is an n-channel FET or N-channel FET.
A DC / DC converter characterized by being a PN transistor. 10. The DC / DC converter according to claim 6, wherein when the first and third elements are damaged and short-circuited, the second element is made non-conductive to stop oscillation. DC / DC converter.