Working principle: It consists of three parts: power supply circuit, trigger circuit and main control circuit. 220V mains via the power switch S-S' After the power transformer T1 is depressurized, the full wave rectifier circuit composed of diode VD1-VD4 is rectified and becomes a pulsating DC power supply.
Through resistor R1 current limiting and diode DW voltage regulating, the trapezoidal wave synchronous voltage regulating power supply of about 18V is transported as the power supply of the unstable oscillator RC delay link composed of time-base integrated circuit NE555 and its peripheral components. The other way through the three-terminal voltage regulator IC IC1 AN7812 to send 12V stable ladder wave synchronous voltage regulator power supply IC2 working power supply.
The trigger circuit is composed of IC2 NE555 and R2, R3, RP, C1, C2 and other components, the oscillation period is less than 10ms fixed, only can change the output rectangular wave duty cycle of the astable oscillator and R4, pulse transformer T2 trigger pulse.
The reason why the oscillator uses 18V and 12V synchronous voltage regulator power supply 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 the trigger circuit is greater than 120°, and the trigger pulse of different trigger angles can be output by adjusting the potentiometer RP, so as to achieve the purpose of controlling the thyristor VS on-angle.
At the beginning of charging, the voltage at both ends of the battery pack is low, which is not enough to make the transistor VT conduction. The phase shifting circuit composed of RC provides trigger current to the thyristor. The phase shift Angle is determined by RP2. Thyristor cutoff at negative half cycle. Therefore, the thyristor is charged by the battery pack in a controlled half-wave rectification mode. Charging current can be adjusted by adjusting RP2, and the maximum charging current is set by R1. Indicators are strung in the circuit to indicate the charging status and the size of the charging current. R3 is used to adjust the brightness of the indicator. When the battery voltage rises slowly and reaches a predetermined value, the transistor begins to switch on, the switching Angle of the thyristor decreases, and the charging current drops until it is completely cut off, so that the charging stops automatically and the battery pack remains at a predetermined voltage
Generally, the thyristor in the electric vehicle charger is used to achieve anti-reverse connection protection, installed in the output end of the charger, to prevent the output end of the battery when the reverse connection caused by equipment damage; When the battery anode and cathode are reversely connected to the charger, the thyristor is not on, and the charger will not charge. When the battery is connected to the charger normally, the thyristor is reliably switched on under the action of the battery voltage, the charger output is normal, and the work is normal.