JPH0529894B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a strobe power supply circuit used in a strobe device built into a camera that is controlled by a control circuit composed of a microcomputer or the like.

[Conventional technology]

Figure 3 shows the configuration of a conventional strobe power supply circuit.
Their operating states are shown in FIG. 4. In FIG. 3, charging of the main capacitor _CM for applying a predetermined high voltage to the discharge tube DT constituting the strobe device is performed as follows. First, a charging start signal is sent from the microcomputer side to terminal TM ₂ at time t ₁ .
When input to transistor Q ₂ via resistor R ₅ (Fig. 4a), resistor R ₃ , capacitors C ₁ , C ₂ ,
The oscillation circuit composed of the transistor _Q3 and the transformer T starts oscillating, and its oscillation output is applied to the main capacitor _CM via the diode _D1 . At the time t ₂ when the terminal voltage V _CM of the main capacitor _CM reaches the predetermined high voltage V ₁ , the Zener diode ZD,
This state is detected by a voltage detection circuit consisting of resistors R ₇ and R ₈ and transistor Q ₅ , and the transistor
A charging completion signal is output from _Q5 to the microcomputer via terminal _TM3 (Fig. 4 b, c).

On the other hand, the microcomputer receives the charge completion signal and outputs a charge stop signal from the terminal _TM1 to the transistor _Q1 via the resistor _R2 (FIG. 4d). As a result, transistor Q ₁ becomes conductive, and the base and emitter of transistor Q ₃ forming the oscillation circuit are short-circuited, so transistor Q ₃ becomes non-conductive, stopping the oscillation operation, and the main capacitor C _M charging operation is stopped.

In addition _, the terminal voltage of main capacitor C _M is set to
_{The resistor R 7 , _ _}
A constant of R ₈ is selected. When transistor Q ₄ becomes conductive, the base of transistor Q ₃
The emitters are shorted and charging to the main capacitor C _M is stopped.

[Problem that the invention seeks to solve]

As mentioned above, in conventional strobe power supply circuits, the microcomputer that controls the charging operation of the main capacitor uses two types of signals: a charging start signal to start the charging operation and a charging stop signal to stop the charging operation. Since the circuit was constructed on the premise of outputting , there was a problem that the circuit configuration became complicated.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a strobe power supply circuit with a simplified circuit configuration.

[Means for solving problems]

To achieve the above object, the present invention provides a strobe power supply circuit used in a strobe device built into a camera controlled by a control circuit composed of a microcomputer, etc., in which both ends of a discharge tube constituting the strobe device are provided. a main capacitor connected to the discharge tube for applying a predetermined high voltage to the discharge tube; an oscillation circuit that generates a voltage signal for charging the main capacitor in synchronization with a clock pulse output from the control circuit; A voltage detection circuit that outputs a charging completion signal to a control circuit when the terminal voltage of the capacitor reaches a predetermined level, and a coupling capacitor provided at the input stage of the oscillation circuit to which the clock pulse from the control circuit is input. It is characterized by having.

[Effect]

In the strobe power supply circuit according to the present invention, a clock pulse is inputted via a coupling capacitor from a control circuit composed of a microcomputer, etc., and an output signal from an oscillation circuit that operates in synchronization with the clock pulse is used to generate a discharge tube that constitutes a strobe device. A main capacitor is charged to apply a predetermined high voltage to the main capacitor.

When the terminal voltage of the main capacitor reaches a predetermined level, the voltage detection circuit outputs a charging completion signal to the control circuit.

Upon receiving this charge completion signal, the control circuit stops outputting clock pulses.

Therefore, charging control for the main capacitor is performed only by clock pulses, which simplifies the circuit configuration. Furthermore, even if the clock pulse is fixed at a high level due to a malfunction of a microcomputer or the like, there is no problem with the power supply circuit because the DC component is cut off by the coupling capacitor.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an embodiment of a strobe power supply circuit according to the present invention. In this figure, the same members as those in the conventional example shown in FIG. 3 are given the same reference numerals. The strobe power supply circuit shown in Fig. 1 differs from the conventional example shown in Fig. 3 in terms of configuration in that a coupling capacitor C _C is added to the input circuit consisting of resistors R ₄ , R ₅ , R ₆ and transistor Q ₂ . The oscillation circuit consisting of a resistor R ₃ , a transistor Q ₃ and a transformer T which performs oscillation operation in synchronization with the clock pulse inputted through the coupling capacitor C _C is different from the conventional free-running oscillation circuit. Resistors R ₁ , R _{2 and} transistor Q ₁ were provided in the control circuit in order to stop the oscillation operation by a signal input from the control circuit side.
, and the other configurations are exactly the same.

In the above configuration, input of a clock pulse, which is a charging signal, is started from terminal TM ₂ by a control circuit composed of a microcomputer, etc. (second
In Figure a), the main capacitor _CM is charged by the oscillation output of an oscillation circuit consisting of a resistor R ₃ , a transistor Q ₃ and a transformer T which oscillates in synchronization with this clock pulse. At time t ₂ when the terminal voltage V _CM of the main capacitor _CM reaches a predetermined high voltage V ₁ , this state is detected by the voltage detection circuit consisting of the Zener diode ZD, resistors R ₇ , R ₈ and transistor Q ₅ , and the transistor A charging completion signal is output from Q ₅ to the control circuit side via terminal TM ₃ (Fig. 2 b, c).

On the other hand, when the control circuit receives the charge completion signal, it stops outputting the clock pulse, and the charging operation to the main capacitor _CM is stopped.

Furthermore, if the control circuit becomes unable to control charging due to a runaway of the microcomputer on the control circuit side, and clock pulses continue to be output, charging to the main capacitor _CM is stopped by the same operation as in the conventional example. That is, the terminal voltage of the main capacitor C _M
When V _CM is charged until it becomes higher than the voltage V ₁ and the voltage V _P at point P reaches the reference voltage V ₂ (>V ₁ ), the transistor Q ₄ becomes conductive and the oscillation operation of the oscillation circuit is stopped. The Rukoto.

Furthermore, even if the clock pulse remains at a high level due to a latch-up phenomenon in the control circuit, a coupling capacitor is provided at the input stage of the clock pulse to provide capacitive coupling, so that the power supply circuit is protected.

〔Effect of the invention〕

As explained above, in the present invention, one control signal output from the control circuit side controls the charging operation of the main capacitor that maintains the supply voltage of the discharge tube of the strobe device, and the control signal is inputted. Since a coupling capacitor is provided in the input stage, the circuit configuration is simplified, and therefore the number of parts can be reduced and reliability can be improved.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the configuration of an embodiment of the strobe power supply circuit according to the present invention, Fig. 2 is a timing chart showing the operation of the strobe power supply circuit shown in Fig. 1, and Fig. 3 is a conventional strobe power supply circuit. FIG. 4 is a timing chart showing the operation of the strobe power supply circuit shown in FIG. 3. C _C ...Coupling capacitor, C _M ...Main capacitor,
DT...discharge tube, _Q1 to _Q5 ...transistor,
TM ₁ to _{TM 4} ...terminal, T...transformer.

Claims (1)

[Claims] 1. In a strobe power supply circuit used in a strobe device built into a camera controlled by a control circuit composed of a microcomputer or the like, , a main capacitor for applying a predetermined high voltage to the discharge tube, a booster circuit that generates a voltage signal that oscillates in synchronization with an input clock pulse to charge the main capacitor, and a charge completion signal from the start of charging. a control circuit that outputs clock pulses to the booster circuit until input; a voltage detection circuit that outputs a charging completion signal to the control circuit when the terminal voltage of the main capacitor reaches a predetermined level; and a clock pulse from the control circuit. A power supply circuit for a strobe, comprising: a coupling capacitor provided at an input stage of a booster circuit into which is inputted;