Working Principle Of An Electric Vehicle Charger

220V AC power is filtered by T0 to suppress interference, rectified into pulsating DC by D1, and then filtered by C11 to form a stable DC power of approximately 300V. U1 is a TL3842 pulse width modulation integrated circuit. Pin 5 is the negative power supply, pin 7 is the positive power supply, pin 6 is the pulse output to directly drive the MOSFET Q1 (K1358), pin 3 is the maximum current limit, and adjusting the resistance of R25 (2.5 ohms) can adjust the charger's maximum current. Pin 2 is the voltage feedback, which can adjust the charger's output voltage. Pin 4 is connected to an external oscillation resistor R1 and an oscillation capacitor C1. T1 is a high-frequency pulse transformer with three functions:

1. Stepping down the high-voltage pulse to a low-voltage pulse.

2. Isolating high voltage to prevent electric shock.

3. Providing power to the TL3842. D4 is a high-frequency rectifier diode (16A 60V), C10 is a low-voltage filter capacitor, D5 is a 12V Zener diode, U3 (TL431) is a precision reference voltage source, which, together with U2 (optocoupler 4N35), automatically regulates the charger voltage. Adjusting W2 (fine-tuning resistor) allows for fine-tuning of the charger voltage. D10 is the power indicator. D6 is the charging indicator.

R27 is a current sampling resistor (0.1 ohm, 5W). Changing the resistance of W1 adjusts the inflection point current (200-300 mA) of the charger when it switches to float charging. At the start of power-on, there is approximately 300V on C11. This voltage is applied to Q1 via T1.

The second path, via R5, C8, and C3, reaches pin 7 of U1, forcing U1 to start. Pin 6 of U1 outputs a square wave pulse, Q1 operates, and current flows to ground via R25. Simultaneously, the secondary coil of T1 generates an induced voltage, which provides reliable power to U1 via 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 is used to charge the battery via D7 (D7 prevents reverse current from the battery flowing to the charger).

The second path, via R14, D5, and C9, provides 12V operating power to the LM358 (dual operational amplifier, pin 1 is ground, pin 8 is positive) and its peripheral circuitry. D9 provides a reference voltage to the LM358, which is divided by R26 and R4 to reach pins 2 and 5 of the LM358. During normal charging, there is approximately 0.15-0.18V at the top of R27; this voltage is applied to pin 3 of the LM358 via R17, and a high voltage is output from pin 1. This voltage, through resistor R18, forces Q2 to conduct, illuminating D6 (red light). The second path injects voltage into pin 6 of the LM358, causing pin 7 to output a low voltage, forcing Q3 to turn off and D10 (green light) to turn off, thus initiating the constant current charging phase. When the battery voltage rises to approximately 44.2V, the charger enters the constant voltage charging phase, maintaining the output voltage at around 44.2V, and the current gradually decreases. When the charging current decreases to 200mA-300mA, the voltage at the top of resistor R27 drops, and the voltage at pin 3 of the LM358 becomes lower than that at pin 2, resulting in a low voltage output at pin 1, turning off Q2 and extinguishing D6. Simultaneously, pin 7 outputs a high voltage, which in turn turns on Q3 and illuminates D10. Another path, through D8 and W1, reaches the feedback circuit, causing the voltage to decrease. The charger then enters the trickle charging phase. Charging ends after 1-2 hours.