JPH05275187A - Flash control circuit - Google Patents

Abstract

PURPOSE:To construct a flash control circuit in a small size at a low cost. CONSTITUTION:A series circuitry of zenor diodes 109, 110 is connected between the gate and emitter of an IGBT 3, and a flash start signal TRIG is given directly to the gate of a thyristor 8. The LC resonance frequency determined by the inductance of a coil 108 and the input capacity of the IGBT 3 is made over a certain value necessary for boosting the voltage from the lowest voltage value assumed as a gate drive voltage VGG which can be taken minimally up to the value appropriate to drive the IGBT 3, and is set fixedly. The LC resonance frequency is to monitor the gate drive voltage VGG, and is made over a value necessary for boosting the voltage from the gate drive voltage VGG obtained through monitoring up to the level appropriate to drive the IGBT 3 and is set varyingly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flash control circuit suitable for use in cameras and the like.

[0002]

2. Description of the Related Art Conventionally, there is a flash control circuit of this type as shown in FIG. In the figure,
1 is a high voltage power supply, 2 is a main capacitor (flash energy storage capacitor), 3 is a MOS device as a voltage control type switching element [IGBT in this embodiment]
(Insulated Gate Bipolar Transistor)] 4 is a flash discharge tube, 100 is a gate drive circuit, 200 is a trigger circuit, and 107 is a voltage control circuit.

The IGBT 3 has three terminals of a gate, an emitter and a collector, and conduction between the collector and the main electrodes of the emitter is controlled by a gate voltage V _G applied between the gate and the emitter.

The cathode electrode of the flash discharge tube 4 is IG.
It is connected to the collector of BT3 and its anode electrode is connected to the positive polarity side of the high voltage power supply 1. That is, the flash discharge tube 4 is connected in series with the main electrode of the IGBT 3. The main capacitor 2 is connected in parallel to the series connection circuit of the IGBT 3 and the flash discharge tube 4.

The trigger circuit 200 includes a trigger transformer 5,
It is composed of a trigger capacitor 7, a charging resistor 6, a thyristor 8 and a gate-cathode resistor 9.

The gate drive circuit 100 includes a transistor 1
01, 102, logic circuits 103, 104, diode 1
05 and 106 and the inductance element 108.

The emitter of the IGBT 3 is connected to the negative polarity side (ground line) of the high voltage power source 1, and the gate is connected to the connection point between the cathode of the diode 105 and the anode of the diode 106 via the inductance element 108.

The anode of the diode 105 is connected to the emitter of the transistor 101, and the collector of the transistor 101 is connected to the gate drive voltage V _GG . The cathode of the diode 106 is connected to the collector of the transistor 102, and the emitter of the transistor 102 is connected to the ground line.

That is, in the present embodiment, the transistor 101 and the diode 105 constitute the first reverse blocking switch DS1, and the transistor 102 and the diode 106 constitute the second reverse blocking switch DS2. The reverse drive switch DS1 of No. 1 has its anode driven by the gate drive voltage V
_GG , the cathode of the first reverse blocking switch DS1 is connected to the anode of the second reverse blocking switch DS2, and the cathode of the second reverse blocking switch DS2 is connected to the ground line. The first reverse blocking switch DS1 and the second
An inductance element 108 is connected between the connection point of the reverse blocking switch DS2 and the gate of the IGBT3.

The bases of the transistors 101 and 102 are connected to the control input terminal S via the logic circuits 103 and 104.
It is connected to 1. The control input terminal S1 is provided as a pair with the control input terminal S2 connected to the ground line,
A control input V ₁ described later is applied between the control input terminals S1 and S2.

In the above description, in many cases, the high voltage power supply 1 actually boosts the voltage from the battery by the DC-DC converter.

Next, the operation of the flash control circuit will be described with the function of the voltage control circuit 107 being included.

First, to explain the operating principle,
The inductance L of the inductance element 108 is L >> (1/4) · C _iss · R _s ^{2 with} _respect to the equivalent series resistance R _s between the gate drive circuit 100 and the gate / emitter of the IGBT 3 and the input capacitance C _{iss of the} IGBT ^3. For example, when R _s = 5Ω and C _iss = 10 nF, and L >> 62.5 nH, the gate current i _G to the IGBT3 becomes oscillating when the transistor 101 or 102 is turned on / off, and the diode 105, Due to the backflow blocking action of 106, a half-sine waveform is obtained. Thus, for example, when the inductance L is sufficiently large, the gate voltage V _G when the IGBT 3 is turned on can be stepped up to about twice the gate drive voltage V _GG by one LC resonance. In this circuit, the gate voltage V _G due to this LC resonance
Use the boost of.

Now, it is assumed that the light emission standby signal from the camera (not shown) causes the level of the control input V ₁ applied between the control input terminals S1 and S2 to start repeating high level and low level ( (Point t1 shown in FIG. 4A).

This change in the level of the control input V ₁ causes the transistor 101 and the logic circuit 1 to pass through the logic circuit 103.
The transistor 102 via 04 is alternately turned on / off, that is, the first reverse blocking switch DS1 and the second reverse blocking switch DS2 are alternately turned on / off,
The gate current i _G to T3 becomes oscillatory (see FIG. 4B).

As a result, the inductance element 108
Of LC and the input capacitance of the IGBT 3 cause LC resonance, and as the number of times of LC resonance increases, the IGBT
The gate voltage V _{G of} 3 rises (see FIG. 4C).

If the gate voltage V _G is lower than the gate withstand voltage rating of the IGBT 3 and is boosted to a value higher than a value sufficient to flow a flash current ic (described later) to the flash discharge tube 4 by turning on the IGBT 3, the gate voltage V _G is monitored. Voltage control circuit 1
07 detects this and maintains the control input V ₁ at a high level (point t2 shown in FIG. 4A).

The gate voltage V _G of the IGBT 3 can be kept above the gate voltage V _{GE (on)} required for energizing the IGBT 3 for a while due to its input capacitance.

When the flashing start signal TRIG is received from the camera when the gate voltage V _{G of the} IGBT 3 is V _{GE (on)} or more (point t3 shown in FIG. 4D), the thyristor is passed through the voltage control circuit 107. The gate of 8 is triggered and a gate trigger current flows to turn on thyristor 8.

Then, the charged charge stored in the trigger capacitor 7 is discharged in the path from the primary winding of the trigger transformer 5 to the thyristor 8 and a high voltage (trigger voltage) generated in the secondary winding of the trigger transformer 5 is generated. ) Is applied to the trigger electrode of the flash discharge tube 4. In response to the application of this trigger voltage, the gate voltage V _{G is set} to a high level to turn on the waiting IGBT 3, and the flash current ic flows to the flash discharge tube 4 (see FIG. 4).
(See (e)), the flash discharge tube 4 starts to emit light.

After the light emission of the flash discharge tube 4 is started, the flash light stop signal is given from the camera when the flash light amount required for taking a picture is reached. When this flash stop signal is received, the control input V1 is set to low level (see FIG. 4).
(T4 point shown in (a)), the gate voltage V _G drops and IG
The BT3 is turned off, and the flash discharge tube 4 stops emitting light.

After the light emission is stopped, the flash discharge tube 4 is operated for a few msec.
The gas inside is ionized, and it is easy to erroneously light up. Therefore, the control input V ₁ is kept at the low level for a while (until the point t5), and the gate voltage V _{G of the} IGBT 3 is
An off period (t _Off ) is provided before the level becomes high again.

According to this flash control circuit, the gate voltage V _G can be arbitrarily increased with respect to the gate drive voltage V _GG , that is, a relatively high gate voltage V _G is generated from the low gate drive voltage V _GG. Therefore, it is advantageous in that any voltage can be selected as the battery voltage for providing the gate drive voltage V _GG .

[0024]

However, according to such a conventional flash control circuit as described above, the voltage control circuit 107 requires components such as a voltage comparator and an oscillation circuit, which results in high cost. There was a problem. In addition, a space for securing the voltage control circuit 107 is required, which hinders miniaturization.

[0025]

The present invention has been made to solve such a problem, and the first invention (the invention according to claim 1) is, for example, a voltage control circuit rather than the flash control circuit described above. In which a constant voltage circuit is provided between the gate and the emitter of the voltage controlled switching element, and the rising gate voltage V _G is clamped so as not to exceed the gate breakdown voltage rating of the voltage controlled switching element. Is. The second invention (claim 2)
In the first invention, the gate drive voltage V
Assuming the minimum voltage that can be taken as _GG , from this minimum voltage, the gate voltage V _G is equal to or lower than the gate withstand voltage rating of the voltage control type switching element and is more than a value sufficient to flow the flash current ic when the voltage control type switching element is turned on. The number of times of LC resonance is fixedly set as the number of times required to increase the voltage to 1. The third invention (the invention according to claim 3) is the gate drive voltage V _{GG according to} the first invention.
From the gate drive voltage V _GG obtained by this monitoring, and the gate voltage V _G is not more than the gate withstand voltage rating of the voltage control type switching element, and the voltage control type switching element is turned on, and the flash current ic is sufficient. The number of times of LC resonance is variably set so as to be equal to or more than the number of times required to raise the voltage to a certain value or more. The fourth invention (the invention according to claim 4) is the first, second, or third invention, wherein the gate voltage V _{G is set} to the gate withstand voltage rating of the voltage-controlled switching element while waiting to receive the flash start signal. In the following, the voltage control type switching element is turned on and the voltage is raised to a value higher than a value sufficient to cause the flash current ic to flow in the flash discharge tube.

[0026]

Therefore, according to the first aspect of the present invention, when the gate voltage V _G rises as the number of LC resonances increases and the gate withstand voltage rating of the voltage controlled switching element is exceeded, , The gate voltage V _G is clamped so that the gate withstand voltage rating is not exceeded. Further, in the second aspect of the invention, the number of LC resonances is fixedly set on the assumption of the minimum voltage that the gate drive voltage V _GG can take. That is, when the gate drive voltage V _GG is the lowest voltage that can be taken, at the time when the LC resonance is completed,
The value is suitable for driving the voltage control type switching element. When the gate drive voltage V _GG is high and the gate voltage V _G is about to exceed the gate withstand voltage rating of the voltage controlled switching element at the time when the LC resonance ends, the gate withstand voltage is clamped as not exceeding the gate withstand voltage rating. .. In the third invention, the gate drive voltage V obtained by monitoring
_The number of LC resonances is _variably set according to _GG . That is, even if the gate drive voltage V _GG changes, the gate voltage V _G always becomes a value suitable for driving the voltage-controlled switching element at the time when the LC resonance ends. Further, in the fourth aspect of the invention, when the flash start signal is received, the trigger circuit applies the trigger voltage to the trigger electrode, sets the gate voltage V _G to a high level, and turns on the waiting voltage control type switching element to turn on the flash discharge tube. When the flash current ic is flowed to emit light and the flash stop signal is received, the control circuit sets the gate voltage V _G to the low level, turns off the voltage control type switching element, and stops the light emission of the flash discharge tube.

[0027]

The flash control circuit according to the present invention will be described in detail below.

FIG. 1 is a circuit diagram showing an embodiment of the flash control circuit. In the figure, the same reference numerals as those in FIG. 3 indicate the same or equivalent components, and the description thereof will be omitted.

The present embodiment differs from the flash control circuit shown in FIG. 3 in that the voltage control circuit 107 is removed and a series connection circuit of Zener diodes 109 and 110 is connected between the gate and emitter of the IGBT 3. That is, the flash start signal TRIG is directly applied to the gate of the thyristor 8.

The Zener diode 110 may be removed if it is not necessary to apply a large gate reverse bias.

Next, regarding this flash control circuit,
This will be described with reference to the operation waveforms of the respective parts shown in FIG.

Now, it is assumed that the control input V ₁ level applied between the control input terminals S1 and S2 starts to repeat high level and low level by the light emission standby signal from the camera (see FIG. 2 (a)). (T1 point shown).

This change in the level of the control input V ₁ causes the transistor 101 and the logic circuit 1 to pass through the logic circuit 103.
The transistor 102 via 04 is alternately turned on / off, that is, the first reverse blocking switch DS1 and the second reverse blocking switch DS2 are alternately turned on / off,
The gate current i _G to T3 becomes oscillatory (see FIG. 2B).

As a result, the inductance element 108
Of LC and the input capacitance of the IGBT 3 cause LC resonance, and as the number of times of LC resonance increases, the IGBT
The gate voltage V _G of No. 3 rises (see FIG. 2 (c)).

Here, the number of times of LC resonance is fixedly set to n times, assuming the lowest possible voltage as the gate drive voltage V _GG . That is, when the gate drive voltage V _GG is the lowest voltage that can be taken, the gate voltage V _G is below the gate withstand voltage rating of the IGBT 3 and the IGBT 3 is turned on from this lowest voltage, and the flash current i is supplied to the flash discharge tube 4.
The LC resonance number n is fixedly set to be the number of times required to raise the voltage to a value higher than a value sufficient to flow c.

Therefore, according to the present embodiment, when the gate drive voltage V _GG is the lowest voltage that can be taken, the gate voltage V _G is inevitably generated at the end of the LC resonance of n times.
Is a value suitable for driving the IGBT 3. When the gate drive voltage V _GG is high and the gate voltage V _G is about to exceed the gate withstand voltage rating of the IGBT 3 at the time when the LC resonance is completed, the Zener diode 109 acts so that the gate withstand voltage rating is not exceeded. To be done. That is, _whether the value of the gate drive voltage V _GG is low or high,
When the LC resonance is completed n times, the gate voltage V
_G has a value suitable for driving the IGBT 3.

When the LC resonance is completed n times, the control input V
₁ is kept at a high level (t2 shown in FIG. 2 (a))
point).

After this, the flash start signal TRIG is sent from the camera.
When receiving (point t3 shown in FIG. 2D), the thyristor 8
The gate is triggered, the gate trigger current flows, and the thyristor 8 is turned on.

Then, the charged charge stored in the trigger capacitor 7 is discharged in the path from the primary winding of the trigger transformer 5 to the thyristor 8 to generate a high voltage (trigger voltage) in the secondary winding of the trigger transformer 5. ) Is applied to the trigger electrode of the flash discharge tube 4. In response to the application of the trigger voltage, the gate voltage V _{G is set} to a high level to turn on the IGBT 3 in standby, and the flash current ic flows to the flash discharge tube 4 (see FIG. 2).
(See (e)), the flash discharge tube 4 starts to emit light.

After the light emission of the flash discharge tube 4 is started, the flash light stop signal is given from the camera when the flash light amount required for photographing is reached. When the flash stop signal is received, the control input V ₁ is set to low level (see FIG. 2).
(T4 point shown in (a)), the gate voltage V _G drops and IG
The BT3 is turned off, and the flash discharge tube 4 stops emitting light.

After the light emission is stopped, the flash discharge tube 4 is operated for a few msec.
The gas inside is ionized, and it is easy to erroneously light up. Therefore, the control input V ₁ is kept at the low level for a while (until the point t5), and the gate voltage V _{G of the} IGBT 3 is
An off period (t _Off ) is provided before the level becomes high again.

In the above description, the Zener diode 109 is used as a constant voltage circuit so that the gate voltage V _G does not exceed the gate withstand voltage rating. However, the constant voltage circuit may be configured by another method such as a comparator. Good.

In the above, the number of LC resonances is n.
Although the gate driving voltage V _GG is fixed as the number of times, the gate driving voltage V _GG is monitored and the gate driving voltage V _GG obtained by this monitoring is monitored.
To IGBT3 gate breakdown voltage rating or less and IGBT3
Is turned on and the number of times required to raise the gate voltage V _G to a value higher than a value sufficient to flow the flash current ic is equal to or greater than LC
The number of resonances may be variably set.

By doing so, even if the gate drive voltage V _GG changes, the gate voltage V _G always becomes a value suitable for driving the IGBT 3 at the time when the LC resonance ends.

[0045]

As is apparent from the above description, according to the present invention, the gate voltage V increases as the number of LC resonances increases.
_{When G} rises and tries to exceed the gate withstand voltage rating of the voltage control type switching element, the gate voltage V _G is clamped so as not to exceed the gate withstand voltage rating, so that it has been conventionally required. It becomes possible to remove the voltage control circuit, and it becomes possible to promote cost reduction and miniaturization.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a flash control circuit according to the present invention.

FIG. 2 is an operation waveform diagram of each part for explaining the operation of the flash control circuit shown in FIG.

FIG. 3 is a circuit configuration diagram showing a conventional flash control circuit.

FIG. 4 is an operation waveform chart of each part for explaining the operation of the flash control circuit shown in FIG.

[Explanation of symbols]

1 High Voltage Power Supply 2 Main Capacitor 3 IGBT (Insulated Gate Bipolar Transistor) 4 Flash Discharge Tube 100 Gate Drive Circuit 200 Trigger Circuit 103 Logic Circuit 104 Logic Circuit 108 Inductor Element DS1 First Reverse Blocking Switch DS2 Second Reverse Blocking Type switch 109,110 Zener diode

Claims (4)

[Claims] 1. A voltage-controlled switching element having three terminals of a gate, an emitter and a collector, wherein conduction between the main electrodes of the collector and the emitter is controlled by a gate voltage V _G applied between the gate and the emitter. A flash discharge tube connected in series with the main electrode of this voltage control switching element, a flash energy storage capacitor connected in parallel with the series connection circuit of this flash discharge tube and voltage control switching element, and a flash start signal. In response to the trigger circuit, the trigger circuit applies a trigger voltage to the trigger electrode of the flash discharge tube, the first reverse blocking switch whose anode is connected to the gate drive voltage V _GG , and the first reverse blocking switch. A second reverse blocking switch having a cathode connected to the anode and a cathode connected to the ground line; the first reverse blocking switch and the second reverse blocking switch. And connected to the inductance element between the gate and the connection point of the form switch the voltage-controlled switching device, the second inverse and the first reverse blocking type switch according to the level change of the control input V ₁ A control circuit that alternately turns on and off a blocking switch, causes LC resonance between the inductance of the inductance element and the input capacitance of the voltage control switching element, and boosts the gate voltage V _G ; And a constant voltage circuit provided between the gate and the emitter of the switching element, for clamping the rising gate voltage V _G so as not to exceed the gate breakdown voltage rating of the voltage controlled switching element. Flash control circuit. 2. The gate drive voltage V _{GG according to} claim 1.
Assuming the minimum voltage that can be taken, the gate voltage V _G is lower than the gate withstand voltage rating of the voltage-controlled switching element from this minimum voltage, and the voltage-controlled switching element is turned on to allow the flash current ic to flow through the flash discharge tube. The flash control circuit is characterized in that the number of times of LC resonance is fixedly set to be equal to or more than the number of times required to boost the voltage to a certain value or more. 3. The gate drive voltage V _{GG according to} claim 1.
From the gate drive voltage V _GG obtained by this monitoring, the gate voltage V _G is below the gate withstand voltage rating of the voltage control type switching element, and the voltage control type switching element is turned on to turn on the flash current ic in the flash discharge tube. As the number of times required to raise the voltage to a value higher than the value sufficient to flow
A flash control circuit, wherein the number of LC resonances is variably set. 4. The flash discharge according to claim 1, wherein the gate voltage V _G is equal to or lower than the gate withstand voltage rating of the voltage control type switching element and the voltage control type switching element is turned on while waiting to receive the flash start signal. It is assumed that the voltage is raised to a value higher than a value sufficient to cause the flash current ic to flow through the tube, and when the flash start signal is received, the trigger circuit applies the trigger voltage to the trigger electrode, sets the gate voltage V _G to a high level, and stands by. When the voltage control type switching element is turned on and a flash current ic is caused to flow through the flash discharge tube to emit light, and a flash stop signal is received, the control circuit sets the gate voltage V _G to a low level, and the voltage control type switching element is turned off to cause a flash. A flash control circuit characterized by stopping the light emission of a discharge tube.