Introduction to flash power automatic control circuit

Flash off lights are commonly used tools for indoor and backlit photography. If the charging power is not cut off in time, it will be wasteful, and the flash index will be different due to the voltage difference of the energy storage appliances. The controller can automatically cut off the power immediately after it is fully charged, and can guarantee the consistency of the flash index.
The circuit is as shown. 7555 constitutes a pulse oscillator, B1 is a step-up transformer, B2 is a secondary boost pulse transformer, and AN is a trigger Switch that is linked with the camera shutter.
During charging, the voltage on C2 goes from low to high, the neon lamp NE does not light (no current), and BG1 is turned off. 7555 oscillates, the oscillating signal is amplified by BG2, B1 is boosted, and diode D is rectified and charged to C2. When the voltage on C2 is charged to the rated value of 250V, the NE is turned on, the current is injected into the base of BG1, and BG1 is turned on to make the 7555 in the state of reset and stop, and the charging of C2 is automatically stopped. If you do not immediately press the flash button AN to take a picture, the voltage of C2 will gradually drop, and will drop to the point that the NE will be charged quickly and will automatically stop.
When taking a picture, the AN acts with the shutter, and a high-voltage trigger pulse is generated by B2 boosting to ignite the flash, and the charge of C2 is immediately released by the flash. The electric energy of C2 is equal to C2UC/2 Joule (UC is the voltage of two sections of C2), and the constant UC can make the brightness of the flash uniform.
B1 can be wound with E5 ferrite core first with 0.08mm high-strength enameled wire around 2100匝 as the secondary, after insulation paper isolation, and then use 0.3mm enameled wire around 15匝 as the primary. B2 uses a ferrite core, the primary is wrapped with a 3mm enamelled wire 15 turns, and the secondary is wound with a 0.08mm high-strength enamelled wire around 1500 turns. Pay attention to the polarity of the flash lamp. There is a spiral-shaped cathode in the lamp tube and the anode is connected at the other end. +250V.BG2 requires hFE to be larger than C2. It is necessary to use a flash-specific small electrolytic capacitor, and the withstand voltage of 300V.NE is 80-90V. If you use a high-voltage fluorescent lamp starter, you should increase R3, C3 with a metal film capacitor, withstand voltage of 250V. The rest of the components have no special requirements. D can be used 2CP20 or after installation, if the voltage on C2 is less than 250V, R2 should be reduced to change the waveform of the pulse oscillator and increase the voltage.