Flash voltage converter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters
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As an autonomous power source for the FIL-46 flashlight, I use a voltage converter PN-70 manufactured by the Kharkov enterprise "ECHO". During the operation of this device, its significant drawback was revealed: after the storage capacitor is charged and the indicator lamp lights up, signaling readiness for operation, the current consumed by the converter decreases from 1,5 A to Approximately 1 A, that is, the batteries do not turn off and continue to discharge. This leads to their rapid failure. You can stop discharging the batteries by manually disconnecting the flash from the unit, removing the plug from the socket or using a toggle switch installed in the socket circuit. However, both methods are inconvenient due to the fact that they distract from the shooting itself.
To eliminate these shortcomings, I developed and manufactured an automation unit, which in the "pause" mode reduces the current consumed by the converter from 1 A to 0,1 A, that is, 10 times. During the design of the machine, recommendations from the book by G. A. Fedotov "Electrical and electronic devices for photographs" (L., Energoatomizdat, 1984) were used.
The schematic diagram of the modified power supply is shown in the figure. The part of the circuit that has undergone alteration is highlighted in color. The automatic regulator works like this. As the flash storage capacitor charges, the voltage across the divider R5-R6 increases. As soon as the capacitor is charged to the desired voltage (280 ... 300 V), the VD2 diode opens, and the current across the resistor R4 also increases; this leads to the locking of transistors VT4 and VT3 and an increase in the resistance on the transistor VT2. The current drawn from the batteries is reduced, and in addition, the flash energy is stabilized.
Rice. 1. Schematic diagram of the upgraded power supply unit PN-70 (click to enlarge): GB1 - type 3336 batteries (2 pcs.), TV1 - converter transformer, R1 - 360 Ohm, R2 - 36 Ohm, C1 - 50 uFH12 V, C2 - 0,025 uF, VT1-KT837K, VD1 - KD105B, VT2 - KT837K, VT3 - GT403B, VT4 -MP42B, VD2 - D814V, R3 - 47 Ohm, R4 - 150 kOhm, R5 - 2,4 MΩ, R6 - 360 kΩ.
Rice. 2. Printed circuit board of the device with the arrangement of elements A - hole Ø 3 mm for fixing the board in the converter housing
Rice. 3. Appearance of the upgraded power supply
The device is mounted on a printed circuit board. Its dimensions are selected taking into account placement directly in the converter housing without any additional changes. The board with parts is fastened to the converter board using an M3 screw and three nuts. In this case, carefully bend the terminals of the capacitor C1 and resistor R1 with tweezers to reduce their height. The change in the converter circuit consists in breaking the jumper from the "plus" of the power source to the emitter of the transistor VT1 and turning on the "plus" emitter VT2 instead, and the collector VT1 to the emitter VT2.
The VT2 transistor is equipped with a heat sink made of a copper strip 0,5 mm thick, with dimensions of 22x50 mm. For ease of placement in the case, the heat sink is bent.
Setting up the block is reduced to selecting the voltage necessary to open the VD2 diode using resistors R5-R6 (while maintaining a voltage of 280 ... 300 V at the output of the converter).
Author: O. Panchik
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