What is the principle of automatic charging of electric vehicles?

Commonly used electric car charger can be roughly divided into two types according to the circuit structure. The first is a single-tube switching power supply, which uses uc3842 to drive FET and LM358 double operational amplifier to realize three-stage charging mode. 220v alternating current is filtered by T0 bidirectional filter to suppress interference, and D 1 is rectified into pulsating direct current, and then filtered by C 1 1 to form a stable direct current of about 300V. U 1 is TL3842 pulse width modulation integrated circuit. Pin 5 is the negative pole of power supply, pin 7 is the positive pole of power supply, pin 6 is the pulse output of directly driving FET Q 1 (K 1358), and pin 3 is the maximum current limit. Adjusting the resistance of R25 (2.5 ohms) can adjust the maximum current of the charger. Pin 2 is voltage feedback, which can adjust the output voltage of the charger. The four pins are externally connected with an oscillating resistor R 1 and an oscillating capacitor C 1. T 1 is a high-frequency pulse transformer with three functions. The first is to convert high voltage pulse into low voltage pulse. The second is to isolate high voltage to prevent electric shock. The third is to provide working power for uc3842. D4 is a high-frequency rectifier (16A60V), C 10 is a low-voltage filter capacitor, D5 is a 12V zener diode, and U3(TL43 1) is a precise reference voltage source, which can automatically adjust the charger voltage together with U2 (optocoupler 4N35). Adjust w2 (trimming resistor) to trim the voltage of the charger. D 10 is the power indicator. D6 is the charge indicator. R27 is the current sampling resistance (0. 1 ohm, 5w). Changing the resistance value of W 1 can adjust the inflection point current (200-300 mA) of the charger to floating charge.

At the beginning of power-on, there is about 300v voltage on C 1 1. The voltage is loaded to Q 1 through T 1. The second path passes through R5, C8 and C3, and reaches the 7th pin of U 1. Force U 1 to start. The 6 pin of U 1 outputs a square wave pulse, Q 1 works, and the current passes through R25 to the ground. At the same time, the secondary coil of T 1 generates an induced voltage, and through D3 and D3, R 12 provides a reliable power supply for U 1. The voltage of T 1 output coil is rectified and filtered by D4 and D4 c 10 to obtain a stable voltage. This voltage charges the battery through D7 (the function of D7 is to prevent the battery current from flowing back to the charger). The second path passes through R 14, D5 and C9, and provides 1 2v working power for LM358 (double operational amplifier, with1pin as power ground and 8 pins as power positive) and its peripheral circuits. D9 provides a reference voltage for LM358, which is divided by R26 and R4 to reach the second pin and the fifth pin of LM358. During normal charging, the terminal voltage on R27 is about 0. 15-0. 18V, which is added to the third pin of LM358 through R 17, and a high voltage is sent from 1 pin. This voltage passes through R 18, forcing Q2 to turn on, D6 (red light) to turn on, and the second voltage is injected into pin 6 and pin 7 of LM358, forcing Q3 to turn off, and D 10 (green light) to turn off, and the charger enters the constant current charging stage. When the battery voltage rises to about 44.2V, the charger enters the constant voltage charging stage, and the output voltage is maintained at about 44.2 V. The charger enters the constant voltage charging stage, and the current gradually decreases. When the charging current drops to 200 Ma-300 Ma, the terminal voltage on R27 drops, the voltage on the 3-pin of LM358 is lower than that on the 2-pin, and the output voltage of 1 pin is low, Q2 turns off and D6 turns off. At the same time, pin 7 outputs high voltage, Q3 is always on, and D 10 light is on. The other path reaches the feedback circuit through D8 and W 1, thus reducing the voltage. The charger enters the trickle charging stage. 1-2 hours after charging.