220V AC power is filtered through T0 bidirectional filtering to suppress interference, D1 is rectified into pulsating DC, and then filtered through C11 to form a stable DC power of around 300V. U1 is a TL3842 pulse width modulation integrated circuit. Pin 5 is the negative pole of the power supply, pin 7 is the positive pole of the power supply, and pin 6 is the pulse output directly driving field-effect transistor Q1 (K1358). Pin 3 is the maximum current limit, and adjusting the resistance value of R25 (2.5 ohms) can adjust the maximum current of the charger. Two pins are voltage feedback, which can adjust the output voltage of the charger. 4-pin external oscillation resistor R1 and oscillation capacitor C1. T1 is a high-frequency pulse transformer with three functions.

The first is to reduce the voltage of high-voltage pulses to low-voltage pulses.

The second is to isolate high voltage to prevent electric shock.

The third is to provide working power supply for uc3842. D4 is a high-frequency rectifier tube (16A60V), C10 is a low-voltage filtering capacitor, D5 is a 12V voltage regulator diode, U3 (TL431) is a precision reference voltage source, and works together with U2 (optocoupler 4N35) to automatically adjust the charger voltage. Adjusting w2 (fine-tuning resistor) can finely adjust the voltage of the charger. D10 is the power indicator light. D6 is the charging indicator light.

R27 is a current sampling resistor (0.1 ohms, 5w). Changing the resistance value of W1 can adjust the turning point current of the charger to float charging (200-300 mA). At the beginning of power on, there is a voltage of about 300v on C11. This voltage is loaded from T1 to Q1 along the way.

The second route passes through R5, C8, C3 and reaches the seventh leg of U1. Force U1 to start. U1 outputs a square wave pulse at pin 6, Q1 operates, and the current flows through R25 to ground. At the same time, the T1 secondary coil generates an induced voltage, which provides reliable power to U1 through D3 and R12. The voltage of the T1 output coil is rectified and filtered by D4 and C10 to obtain a stable voltage. This voltage charges the battery through D7 (which prevents the battery's current from flowing back to the charger).

The second route passes through R14, D5, C9, providing 12V working power to LM358 (dual operational amplifier, pin 1 is the power ground, pin 8 is the power positive) and its peripheral circuits. D9 provides a reference voltage for LM358, which is divided by R26 and R4 to reach the second and fifth pins of LM358. When charging normally, there is a voltage of about 0.15-0.18V at the upper end of R27. This voltage is applied to the third pin of LM358 through R17, and a high voltage is sent out from pin 1. This voltage passes through R18, forcing Q2 to conduct and D6 (red light) to light up. The second voltage is injected into pin 6 of LM358, and pin 7 outputs a low voltage, forcing Q3 to turn off and D10 (green light) to turn off. The charger enters the constant current charging stage. When the battery voltage rises to around 44.2V, the charger enters the constant voltage charging stage, and the output voltage is maintained at around 44.2V. The charger enters the constant voltage charging stage, and the current gradually decreases. When the charging current decreases to 200mA -300mA, the voltage at the upper end of R27 decreases, the voltage at pin 3 of LM358 is lower than pin 2, pin 1 outputs low voltage, Q2 turns off, and D6 goes out. At the same time, pin 7 outputs a high voltage, which leads to Q3 conducting and D10 lighting up. The other way through D8 and W1 reaches the feedback circuit, causing the voltage to decrease. The charger enters the trickle charging stage. Charging ends 1-2 hours later.