Analysis of Electric Bike Charging Principles
the 220V AC power is filtered by LF1 to suppress interference and then rectified by D1-D4 into a pulsating DC. This pulsating DC is further smoothed by C2 into a stable 300V DC. IC1 is a TL3842 pulse width modulation integrated circuit. Pin 5 is the negative power supply, pin 7 is the positive power supply, and pin 6 is the pulse output that directly drives the field-effect transistor V1 (8N60). Pin 3 is for maximum current limiting. Adjusting the resistance of R5 (0.51 ohms) or R24-R27 (2 ohms) can adjust the maximum current of the charger.
Pin 2 is for voltage feedback, allowing adjustment of the charger's output duty cycle. Pin 4 is connected to an external oscillation resistor R13 and an oscillation capacitor C12. T1 is a high-frequency pulse transformer. Its first function is to step down the high-voltage pulse to a low-voltage pulse. The second function is to isolate the high voltage. The third function is to provide a working power supply for KA3842. D17 is a high-frequency rectifier tube (5A400V). C11 is the output filter capacitor. IC2 (TL431) is a precision reference voltage source, which, along with PC1 (photocoupler 817C), automatically adjusts the charger voltage. Adjusting R6 can fine-tune the charger's output voltage. LED2 is the power indicator, and LED1 is the charging indicator. R9 is the current sampling resistor (0.1 ohms, 3 watts). Changing the resistance of R11 can adjust the charger's charging current (1.8A) and the knee point current (400mA).
When power is turned on, C2 has a voltage of around 300v. This voltage is routed in two ways: one path loads V1 through T1, and the other path goes through R18, R21, and C4 to reach pin 7 of IC1, forcing IC1 to start. IC1's pin 6 outputs a square wave pulse, activating V1. The current flows through R5 to ground. Simultaneously, the secondary winding of T1 generates an induced voltage, which, through D6, R15, and R16, provides auxiliary power to IC1. The voltage output by the T1 coil is rectified and filtered by D17 and C11 to obtain a stable voltage. This voltage is routed in two ways: one path goes through D17 and D14 (an isolation diode that prevents battery current from flowing back into the charger) to charge the battery. The other path goes through D13 and C8, providing a 15V working power supply for LM324 (a four-operational amplifier) and its peripheral circuitry. D9 provides a reference voltage for LM324.
During normal charging, there is a voltage of about 0.18V at the upper end of R9. This voltage is applied to pin 13 of LM324 through R38, resulting in a high-level output from pin 14. This voltage activates the LED1/R (red light) through R58. At the same time, it injects the LM324's pin 9, causing pin 10 to output a low level, extinguishing the LED1/G (green light) (note that LED1 is a dual-color light). The charger enters the constant current charging stage. As the battery voltage rises to about 58.8V, the charger enters the constant voltage charging stage, maintaining an output voltage of about 58.8V. During this stage, the current gradually decreases. When the charging current decreases to 400mA, the voltage at the upper end of R9 drops, and pin 8 outputs a high level, turning on the LED1/G (green light). Another path sends a signal through D16 and R59 to the voltage control loop, reducing the output voltage. The charger enters the voltage-reduction floating charge stage.
