NE555 portable thyristor charger circuit design

　　The charger introduced in this article directly uses 220V AC mains power and adjusts its output voltage from 0V through the control of the trigger circuit. It is suitable for charging 12V-220V batteries (groups).

　　Working principle of the circuit: It consists of three parts: power supply circuit, trigger circuit and main control circuit. After the 220V mains is stepped down by the power switch SS and the power transformer T1, it is rectified by the full-wave rectifier circuit composed of diodes VD1-VD4 and becomes a pulsating DC power supply. One path is limited by resistor R1 and stabilized by voltage-stabilizing diode DW, and delivers about 18V of trapezoidal wave synchronous regulated power supply as the power supply for the RC delay link of the astable oscillator composed of the time base integrated circuit NE555 and its peripheral components; the other path is sent out through the three-terminal voltage-stabilizing integrated circuit IC1 AN7812 to deliver a 12V stable trapezoidal wave synchronous regulated power supply IC2. The trigger circuit is composed of IC2 NE555 and components such as R2, R3, RP, C1, C2, etc. The oscillation period is less than 10ms and fixed. The astable oscillator and R4 and pulse transformer T2 that can only change the duty cycle of the output rectangular wave form a trigger pulse. The reason why the oscillator uses two synchronous regulated power supplies of 18V and 12V is to increase the duty cycle of the output rectangular wave, that is, to increase the phase shift range of the trigger pulse. The phase shift range of this trigger circuit is greater than 120°. By adjusting the potentiometer RP, trigger pulses with different trigger angles can be output, thereby achieving the purpose of controlling the conduction angle of the thyristor VS.

　　The pulse output by this trigger circuit is several times wider than the pulse output by any trigger circuit composed of a single junction transistor, and can reliably trigger the thyristor in the back-EMF load and large inductive load circuit to conduct reliably. The main control circuit consists of a fuse FU, an ammeter and a thyristor VS. After connecting the battery or battery (group) to be charged, the thyristor VS obtains a trigger pulse and controls the conduction angle of VS with pulses of different pulse widths. By adjusting RP, the charging of batteries (groups) with different charging currents or voltages can be satisfied.