JPS5838919B2 - Power supply circuit for flash device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flash device used in a camera, and particularly to a flash device that uses a DC-DC converter in the power supply circuit of the flash device to charge a flash capacitor when the capacitor is charged to a predetermined flash level. This invention relates to a power supply circuit for a flash device that detects the voltage of the capacitor when the capacitor is turned off, stops the oscillation of the oscillation transistor of the DC-DC converter, and keeps the amount of charge of the capacitor O constant.

Conventionally, a flash capacitor is charged using a DC-DC converter by pressing a button on a power supply circuit for a flash device, and when the capacitor reaches a predetermined level of 1, the operation of the DC-DC converter is stopped and the capacitor is charged. To keep the voltage constant, when the flash capacitor reaches a certain charge level, it is detected by a neon tube, etc., and the oscillation transistor's oscillation is stopped by controlling the bias current of the oscillation transistor. There are known ways to do this.

However, even with this method, the oscillation cannot be completely stopped due to the collector cut-off current of the oscillation transistor and the leakage current of ICBO, etc., and the flash capacitor continues to be charged, causing the flash output to become unstable. This not only causes failure in flash photography, but also has the disadvantage of causing damage to the flash condenser.

According to the present invention, when the flash capacitor is charged to a certain level, the resistance value of the control transistor connected to the base current circuit of the oscillation transistor becomes high impedance, and the base current circuit is turned off. To provide a power supply circuit for a flash device which eliminates the above-mentioned drawbacks by reliably stopping the operation of an oscillation transformer sister by applying a voltage charged in a flash capacitor to the base of an oscillation transistor. It is something.

Next, one embodiment of a power supply circuit for a flash device according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of a power supply circuit for a flash device and a flash device according to the present invention, where 1 is a power supply circuit for a flash device and 2 is a flash device.

For the flash device power supply circuit 1, 4 is a power supply, 3 is a power switch, 5 and 6 are oscillation transistors, and when the power switch is turned on, the oscillation transistors 5 and 6 are activated.
A voltage is applied from the power supply 4 to .

Reference numeral 7 denotes a transistor which is a switching means that makes the base circuit of the oscillation transistor non-conductive when the charging voltage of the capacitor is above a predetermined value and conductive when it is below a predetermined value. Connect between the base of transistor 6 and the transistor □, and turn on the transistors 5 and 6.

10 is a resistor connected in series to the collector side of the transistor 7.

An oscillation transformer 9 has a feedback winding N3 on the base side of the transistor 5, a feedback winding N4 on the base side of the transistor 6, a primary winding N1j N2, and a secondary winding N5.

A rectifier 11 rectifies the induced voltage generated in the secondary winding N5.

21 is the main voltage switch of a neon tube, etc. When the flash capacitor is charged to a predetermined level, resistors 16.17,
A voltage specified by the voltage adjusting variable resistor 28 of the flash capacitor 15 is applied, and the flash flash capacitor 15 is turned on.

18 and 19 are switching transistors, and when the main voltage switch is turned on, these transistors 18 and 19 are also turned on, and the control transistor 7 is turned off.

8 is a resistor connected in series to the emitter side of the transistor.

20 is a resistor which is an impedance means, and when the flash capacitor is charged to a predetermined level at 1, the resistor 20
A positive voltage is applied to the base sides of the oscillation transistors 5 and 6 via the oscillation transistors 5 and 6 to turn off the oscillation transistors.

In the flash device circuit section 2, 15 is a flash capacitor, which is connected to the rectifier 11.

A neon tube 30 is turned on when the capacitor 15 is charged to a predetermined level and emits light to indicate that flash photography is ready.

29 is a resistor, and 25 is a flash tube trigger capacitor, which is charged via resistors 23 and 24.

27 connects the plug 26 of the flash device to the camera with a trigger coil, and discharges the trigger capacitor 25 through a synchro contact (not shown) linked to the release of the camera;
A trigger voltage for the flash tube 22 is generated in the trigger coil 27 .

12, 13, and 14 are contact points between the flash device power supply circuit section 1 and the flash device section 2.

Next, the operation of one embodiment of the power supply circuit for a flash device according to the present invention will be described in detail.

When the power switch 3 is turned on, a voltage is applied from the power source 4 to the oscillation transistors 5 and 6, and the base current of the control transistor 7 flows through the resistor 8, so that the control transistor 7 is turned on.

When the transistor 7 is turned on, the base and emitter of the oscillation transistor 5 are connected, and the base current flows to the oscillation transistor 5 via the return winding N3 of the oscillation transformer 9 and the resistor 10, so that the oscillation transistor 5 is turned on. Transistor 5 is turned on, the collector current of transistor 5 flows through primary winding N1, and magnetic flux is generated in primary winding N1 due to the collector current.

Due to the magnetic flux generated in the primary winding N, an induced voltage is generated in the return winding N3 so as to make the base potential of the oscillating transistor 5 negative, which further increases the collector current and increases the voltage in the primary winding. The magnetic flux generated in N1 also increases further.

When the magnetic flux reaches the saturation magnetic flux Φ8, which is constant due to the magnetic characteristics of the oscillation transformer 9, the collector current of the oscillation transistor 5 tends to decrease, and at the same time, the energy stored in the residual inductance of the primary winding N1 is transferred to the oscillation transistor. At the same time as the oscillation transistor 5 is cut off, an induced voltage is generated in the return winding N4 so as to make the base potential of the oscillation transistor 6 negative. In a similar operation, the collector current of the nine oscillation transistor 6 increases via the primary winding N2.

In this way, the oscillation transistors 5 and 6 are turned on alternately.
, OFF, the induced power generated in the secondary winding N5 is rectified by the rectifier 11, and the capacitor 15 is charged via the contacts 12 and 13.

When the voltage of capacitor 15 reaches an arbitrary voltage, resistor 1
A charging pressure switch 21 such as a neon tube is turned on via terminals 6 and 1γ, the base potential of the transistor 18 rises, and the transistor 18 is turned on.

When the transistor 18 is turned on, the transistor 19 is also turned on at the same time, and the base potential of the control transistor 7 is lowered, turning it off, and the collector-emitter of the control transistor 7 becomes high impedance, and the base of the oscillation transistors 5 and 6 becomes high impedance. Current no longer flows through the resistor 10 and the control transistor 7.

As mentioned above, the oscillation transistor should stop oscillating due to the high impedance between the base and the collector, or the collector cut-off current 1°Bo flowing between the collector and the base may be extremely high. A small amount of current causes the oscillation transistor to continue oscillating, or the stray capacitance between the collector and emitter of the transistor 7 or between the windings of the transformer 9 causes resonance with the inductance of the transformer 9, causing the oscillation to continue. Although the voltage of the flash capacitor 15 does not reach the predetermined voltage, the voltage charged in the capacitor 15 via the resistor 20 makes the base potential of the oscillation transistors 5 and 6 positive with respect to the emitter. Since this voltage is applied, oscillation can be completely stopped.

By stopping oscillation in this way, capacitor 1
The voltage of the capacitor 15 does not rise above a predetermined voltage and remains constant, but the voltage of the capacitor 15 drops below the predetermined voltage due to slight self-discharge.

Since this voltage drop is not large, when this voltage drop occurs, the voltage of the flash capacitor 15 is always kept at a constant value by setting the characteristics of the resistor 17 and the main voltage switch 21 to restart the oscillation with a small voltage drop. I warn you.

At the same time that the flash capacitor 15 is charged to a predetermined level, the trigger capacitor 25 also finishes charging and presses the button, and the neon tube 30 emits light when the capacitor 15 is fully charged, indicating that flash photography is ready. .

A synchro contact (not shown) operates in conjunction with the release operation of the camera to discharge the electric charge stored in the trigger capacitor 25 to the trigger coil 27.
A voltage is generated at 7, which triggers the flash tube 22 to generate a flash tube.

Incidentally, the purpose of connecting the negative pole of the power supply to the flash device power supply circuit section 1 via the contacts 14 and 13 and the flash circuit 2 is to connect the flash device power supply circuit section 1 to the flash device power supply circuit section 1 when the flash circuit 2 serving as a load is not connected. 1. By turning on the power switch 3, damage to the power supply circuit section for the flash device is prevented.

As described above, in the power source for a flash device according to the present invention, when the flash capacitor is charged to a certain level, the control transistor connected to the base current circuit of the oscillation transistor is made to have a high impedance, and the base current circuit is At the same time, by applying the voltage charged in the flash capacitor to the base of the oscillation transistor, the operation of the oscillation transistor is stopped, and the charge level of the flash capacitor is set to a predetermined voltage. This makes it possible to prevent oscillation due to extremely small collector cut-off currents of the oscillation transistor, and it is possible to always charge the flash capacitor to a predetermined level, making it possible to prevent the oscillation from occurring due to the extremely small amount of collector cut-off current of the oscillation transistor. It is effective.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a flash device power supply circuit and a flash device circuit according to the present invention. DESCRIPTION OF SYMBOLS 1... Flash device power supply circuit section, 2... Flash device circuit section, 4... Power supply, 5, 6... Oscillation transistor 7... Control transistor, 9... Oscillation transformer, 11... Rectifier, 15... Flash capacitor,
18°19°...Switching transistor, 20.
...Resistor, 21...Main power switch.

Claims (1)

[Claims] 1. A DC device comprising an oscillation circuit configured by connecting a base circuit and a collector-emitter series circuit of an oscillation transistor to the feedback winding and negative winding of an oscillation transformer, respectively, and a flashing capacitor connected to the output side. - In a flash device having a DC converter, a detection means for detecting the charging voltage of the flash capacitor, and a base circuit of the oscillation transistor is made non-conductive when the charging voltage of the capacitor is equal to or higher than a predetermined value according to the output of the detection means. and an impedance means for applying a reverse bias to the base of the oscillation transistor when the base circuit becomes non-conductive due to the switching means. Power supply circuit for flash device.