Lithium Ion Battery Charger

The circuit is shown in the attached figure: Q1 and peripheral components form a self-excited oscillator. After step-down by transformer B and D5 rectification, a DC voltage of 9.4v is obtained on C4. After R6 current limiting and Q10 (TL431) voltage stabilization, 4.2V voltage is output at Q3 emitter to charge lithium battery. Its polarity automatic identification circuit is composed of Q5 Q8 and R12 R15. When point a is connected to the positive pole of the battery and point B is connected to the negative pole, Q8 is turned on because R12 provides a positive bias voltage, and Q5 is turned on by R14. The charging current forms a charging circuit from Q5 point a battery e point B pole C of Q8. When point a is connected to the negative pole of the battery and point B is connected to the positive pole of the battery, the charging current forms a charging circuit from pole C of Q7 point B battery e point a Q6, so as to complete the function of automatic identification of battery polarity

When a charging current flows through R6, Q4 turns on and LED1 flashes (LED1 is a three-color LED with its own oscillator, which can randomly change into a colorful flash). After charging, Q4 is cut off because there is not enough on voltage, and LED1 is off. LED2 is the power indicator.

Fault 1: the power indicator is not on.

Maintenance: the Q1 tube is normal, but there is no bias voltage at pole B; Re measure that R2 is open circuit. Remove the fault after replacing R2.

Fault 2: the power indicator is not on

Maintenance: measure that Q1 has been broken down. Re measure that R1 and R3 have been open circuit. Other components tested are normal, and the fault is eliminated after replacing the above components.