JPH03156433A - Flash control circuit - Google Patents

Abstract

PURPOSE:To more surely control the emitting time of a flash tube and to obtain the proper quantity of emitting light by providing the flash control circuit with a switching circuit for impressing a pulse signal to the control terminal of a non-self holding type switching element and a switching element whose collector terminal is directly connected to the control terminal of the non-self holding type switching element. CONSTITUTION:A driving circuit 20 is constituted of a switching circuit 20A for impressing a pulse signal to the control terminal of a switching element S to turn on/off the element S and a switching element TR 6 whose collector terminal is directly connected to the control terminal of the element S, and almost simultaneously or prior with/to the OFF of the circuit 20A, the element TR 6 is turned on. A microcomputer 30 controls a main capacitor CM, a trigger capacitor CT and a capacitor C2 so as to be prescribed charged values and controls also the emitting time of the flash tube based upon the output signals of output ports 02, 03. Since the switching element S is turned off without delay and the emitting time of the flash tube is more surely controlled, the proper quantity of emitting light can be obtained.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a flash control circuit that controls the amount of light emitted from a flash tube in order to obtain an appropriate amount of exposure from a subject when taking a photograph with a camera.

[Conventional technology]

FIG. 5 is a block diagram showing a flash control circuit that controls the amount of light emitted by controlling the discharge time of a flash tube using a general non-self-holding type semiconductor switching element. Note that a non-self-holding semiconductor switching element refers to an element that operates only while an external control signal is input to its gate, such as a transistor, FET, or IGBT element. The flash control circuit 100 includes a power supply circuit A1, an oscillation boosting means B1 that oscillates and boosts the output voltage from the power supply circuit A, and charges a main capacitor CM; a flash tube F1 that emits light by discharging the charge stored in the capacitor CM; A main capacitor CM charged with the energy for the discharge, a resistor R1, a flash tube F, a trigger circuit C1 that applies a trigger voltage to the flash tube F, and a trigger circuit C1 that activates the trigger circuit C to start the flash tube F emitting light. a non-self-insulating semiconductor switching element 31 that stops the flash tube F from emitting light; a drive circuit 120 that drives the switching element S by applying a pulse signal to its control terminal; a microcontroller that sends a signal that drives the drive circuit 120 The computer 130 connects one terminal of the flash tube F and one terminal of the trigger transformer primary coil of the trigger circuit C to the switching element S.
Connect to the collector terminal of the microcomputer 130.
By applying a pulse signal from the drive circuit to the control terminal of the switching element S based on the drive signal from the drive circuit to turn on/off the switching element S, the energy stored in the main capacitor CIJ in the flash tube F is reduced. The amount of light emitted is controlled by controlling the discharge time.

[Problems to be solved by the invention]

Tr12 of the drive circuit 120 is turned on by the Hi-Level signal from the microcomputer 130, and S
The old signal is added to the gate and light emission begins. When the signal from the microcomputer becomes LO, Tr12 turns OFF L, Tr
13 is turned on and the gate of S is set to Lo, but at this time, during that transition period, Tr12 and Tr13 are simultaneously ONI,
There is a risk that an excessive current will flow through the device and eventually cause its destruction. To avoid this, if you try to pull the gate to Lo using only the pull-down resistor RPC without connecting Tr13, due to the time constant with the stray capacitance of S, Tr1
2 is OFF! There is a problem in that it takes time for S to turn off after this happens, making it difficult to control light emission. SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a flash control circuit that can obtain an appropriate amount of light emission by more reliably controlling the light emission time of a flash tube.

[Means to solve the problem]

The present invention achieves the above object by transmitting a pulse signal from a drive circuit to a control terminal of a non-self-holding switching element connected to one terminal of a flash tube and a trigger circuit that applies a trigger voltage to a trigger terminal of the flash tube. A switching circuit that applies a pulse signal to a control terminal of the non-self-holding switching element via a resistor element, the flash control circuit causing the flash tube to emit light using the light emission energy that is applied and stored in the main capacitor; A switching element directly connected to a control terminal of the non-self-holding switching element, and a drive circuit that turns on the switching element substantially simultaneously or before turning off the switching circuit. .

【Example】

Next, embodiments of the present invention will be described based on the accompanying drawings. FIG. 1 is a block diagram schematically showing the configuration of an embodiment of a flash control circuit according to the present invention. The flash control circuit 200 starts the power supply circuit A, the oscillation boosting means B, the main capacitor CM, the flash tube F, the resistor R, the trigger circuit C, and the trigger circuit C to start the flash tube F and start the flash tube F. It is the same as the prior art in that it consists of a non-self-holding type semiconductor switching element S that stops light emission of F, a drive circuit 20, and a microcomputer 30, and the drive circuit 20 is unique. The configuration of each part of the flash control circuit 200 of this embodiment will be explained below. The main capacitor CM stores energy for discharging the flash tube F as described above, and the flash tube F is, for example, a xenon tube filled with xenon gas. below,
Flash tube F is called cannon tube F. The main capacitor CM is
One terminal of a parallel circuit is connected to the output terminal of the xenon tube F and the resistance element R4, and the emitter terminal of the non-self-holding switching element S and the trigger circuit C are connected to the other terminal of the parallel circuit. be. Trigger circuit C connects a trigger capacitor CT and a trigger transformer T2 in series, and connects the secondary coil end of the trigger transformer T2 to a xenon tube F.
By discharging the trigger capacitor 13, a high voltage of 2 kV, for example, is excited in the secondary coil of the pulse transformer T2, and this is applied to the trigger electrode of the xenon tube F, causing an arc inside F. It causes electric discharge and flash light emission. A non-self-holding switching element (hereinafter referred to as a switching element) S has a high gate impedance and a large current can flow.
BT is preferable, and by connecting the input terminal of the trigger circuit C and the terminal of the xenon tube F to the collector terminal as described above, when the switching element S is turned on, the trigger circuit C
When the xenon tube F is activated and the switching element S is turned off, the current conduction in the xenon tube F is stopped and discharge is stopped. The drive circuit 20 includes a switching circuit 20A that applies a pulse signal to the control terminal of the switching element S to turn it on/off, and a switching element Tr6 whose collector terminal is directly connected to the control terminal of the switching element S.
It is characterized in that the switching element Tr6 is turned on substantially simultaneously or prior to turning off the switching circuit 20A. The configuration of the drive circuit 20 will be explained below. The switching element Tr6 is a transistor whose emitter is grounded, the collector terminal of the transistor Tr6 is connected to the control terminal of the switching element S, and the control terminal of the transistor Tr6 is connected to the output port of the microcomputer 30. As a result, transistor Tr6
is turned on to release electric charge due to stray capacitance existing in the switching element S to the ground point, and the switching element S is turned off. The switching circuit 20A includes transistors Tr4. Tr
5, a capacitor C2, and resistance elements R5 and R6. Transistor Tr4 has capacitor C2 on its emitter terminal.
is connected to the ground, the collector terminal is grounded via a resistive element R5, and the non-grounded terminal of the resistive element R5 is connected to the control terminal of the switching element S via a resistive element R6. The collector terminal of the transistor Tr5 whose emitter is grounded is connected to the control terminal of the transistor Tr4, and the control terminal of the transistor Tr5 is connected to the output port o2 of the microcomputer 30. The switching circuit 2OA turns on/on the switching element S with the pulse signal from the output port o2 of the microcomputer 30 due to the above configuration. The microcomputer 30 controls the charging of the main capacitor CM, trigger capacitor CT, and capacitor c2 to predetermined values by controlling the operation of the oscillating boosting means B using the input/output signals from the output port 01 and the input port [N], and also controls the charging of the main capacitor CM, trigger capacitor CT, and capacitor c2 to predetermined values. The amount of light emitted is controlled by controlling the light emission time of the flash tube F based on the output signals from -1-02 and -1-03. The power supply circuit A is a DC power supply such as a mercury battery, and charges the capacitor ci. Oscillation boosting means B includes resistance elements R1 to R3 and a diode D.
I, D2, Zener diode ZD, field effect transistor F, transistor Trl-Tr3, and transformer TI
The output voltage from the transformer Tl charges the main capacitor CM, trigger capacitor CT, and capacitor C2 to a predetermined value. The configuration of the oscillation boosting means of this embodiment will be explained below. The emitter-grounded transistor Tri has its collector terminal connected to one end of one primary coil L2 via a diode D2 and a resistance element R2, and is also connected to a control terminal of a field effect transistor F.
It is connected in series to the capacitor CI via the capacitor CI. The control terminal of the transistor Tri is connected to the output port O1 of the microcomputer 30.
The transistor Tri is turned on/off by a pulse signal from the output port 01 of the transistor Tri. The field effect transistor F and the transistor TR2 are connected in a Darlington manner, and one end thereof is connected to the primary coil Ll as described above. Further, a diode Di is provided between the source and drain of the field effect transistor F. The transformer TI (for protection of F) consists of primary coils Ll, L2 and secondary coil L3, and the output terminal of the secondary coil is connected to the main capacitor CM via a diode D3. The tap terminal is connected to a capacitor C2 via a diode D4. In addition, the collector terminal of the transistor TR3 whose emitter is grounded is connected to the input port of the microcomputer 30, and a Zener diode ZD is connected in series to the control terminal via a resistive element R3 to form a voltage detection circuit. This detects that the main capacitor CM has been sufficiently charged. FIG. 3 is a time chart showing the charging operation in the flash control circuit 200 of this embodiment. In the figure, the output port O of the microcomputer 30
1, the input signal of the input port IN of the microcomputer 30, and the terminal voltage VC of the main capacitor CM.
It shows the terminal voltage VCG of M and capacitor C2. The charging operation in the flash control circuit 200 will be explained below based on the time chart. The flash control circuit 200 in this embodiment will be described as a high active circuit that is turned on when the voltage at the control terminal is at a high level. First, when the pulse signal from the output port 01 of the microcomputer 30 rises from a low level to a high level, the transistor Trl turns on, and the transformer TI
A current is conducted through the primary coils Ll and L2 of the transformer TI.
The boosted output voltage is excited in the secondary coil L3. The main capacitor CM sequentially boosts the terminal voltage VCM, and the capacitor C2 sequentially boosts the voltage with a slight delay. When it reaches a predetermined value, the Zener diode ZD conducts and turns on the transistor Tr3, thereby lowering the collector voltage of the transistor Tr3. I will do it. Furthermore, the trigger capacitor CT is simultaneously charged via the resistive element R4 during the above-described charging operation. The microcomputer 30 has an input port IN
The pulse signal from output port 01 is lowered to a low level by the voltage value input at . This ends the charging operation. FIG. 2 is a time chart showing the light emitting operation of the flash tube in the flash control circuit of this embodiment. In the figure, C3 is a pulse signal from the output port 02 of the microcomputer 30, C2 is a pulse signal from the output port 03 of the microcomputer 30, VG is the potential of the control terminal of the switching element S,
VM is the terminal potential of the xenon tube F. Here, the description will be made assuming that the capacitor is charged as described above. When the pulse signal CI from the output port 02 of the microcomputer 30 rises to a high level, the pulse signal CI from the output port of the microcomputer 30 rises to a high level.
is at low level. CI rises to a high level'
Then, the transistor Tr5 is turned on, the transistor Tr4 is turned on, and the switching element S is turned on. As a result, the trigger capacitor CT starts discharging and excites a primary current in the primary coil of the trigger transformer T2, and the primary current excites a high voltage in the secondary coil. By applying this high voltage to the trigger terminal of the xenon tube F, the xenon gas inside the xenon tube F is excited and the inside of the xenon tube F is brought into a low resistance state, so that the electric energy stored in the main capacitor CM is used to discharge the electric energy stored in the main capacitor CM. It emits light while doing so. C2 then raises cl to high level shortly before falling to low level. Transistor Tr
6 is turned on, and current is conducted from the control terminal of the switching element S to the ground point. As a result, the control terminal voltage VG of the switching element S falls to a low level, and the voltage 01 falls to a low level. In this way, the switching circuit 2OA and the switching element Tr6
With the cooperation of the above, the switching element S can be turned off without delay, and light emission within the xenon tube F can be stopped. Further, FIG. 4 is a time chart showing the light emission characteristics of the flash tube when multiple light emission is performed by the flash control circuit of this embodiment. In the figure, (a) is the control terminal voltage VG of the switching element S, and (b) is the terminal voltage V of the main capacitor CM.
CM, and (C) shows the amount of light emitted from the xenon tube F. The flash control circuit 200 of this embodiment is also suitable for multiple flashes. It should be noted that the flash control circuit 200 of this embodiment includes a row actuator,
That is, when the pulse signal applied to the control terminal of the switching element S and the transistor is in the low state, the same effect can be obtained even if the pulse signal is in the on state.

【Effect of the invention】

As explained above, the present invention includes a switching circuit that applies a pulse signal to the control terminal of the non-self-holding switching element via a resistance element, and a collector terminal that is directly connected to the control terminal of the non-self-holding switching element. By providing a drive circuit that turns on the switching element almost simultaneously when the switching circuit is turned off, the switching element S is immediately turned on without delay.
By turning off the flash tube and controlling the light emission time of the flash tube more reliably, it was possible to provide a flash control circuit that can obtain an appropriate amount of light emission. FIG. 2 is a block diagram schematically showing the configuration; FIG. 2 is a time chart showing the light emitting operation of the flash tube in the flash control circuit of this embodiment;
Fig. 3 is a time chart showing the charging operation in the flash control circuit of this embodiment, Fig. 4 is a time chart showing the light emitting characteristics of the flash tube when multiple flashes are emitted by the flash control circuit of this embodiment, and Fig. 5 is a time chart showing the charging operation in the flash control circuit of this embodiment. FIG. 2 is a block diagram showing a schematic configuration of a flash control circuit that employs a non-self-holding switching element. 20...Drive circuit 2OA...Switching circuit 200...Flash control circuit C...Trigger circuit F...Flash tube S...Self-holding switching element

Claims (1)

[Claims] A pulse signal from the drive circuit is applied to the control terminal of a non-self-holding switching element connected to one terminal of the flash tube and a trigger circuit that applies a trigger voltage to the trigger terminal of the flash tube, and the pulse signal is stored in the main capacitor. A flash control circuit that causes the flash tube to emit light using luminous energy includes a switching circuit that applies a pulse signal to a control terminal of the non-self-holding switching element via a resistance element, and a switching circuit that applies a pulse signal to the control terminal of the non-self-holding switching element through a resistance element. 1. A flash control circuit comprising: a directly connected switching element; and a drive circuit that turns on the switching element substantially simultaneously with or prior to turning off the switching circuit.