Lithium battery charger design with cell polarity identification circuit, replacing the previous manual switching polarity operation, more convenient to use.
One, the circuit principle
Circuit as shown in figures Q1 and peripheral components: self-excited oscillator. Through transformer B buck, D5 rectifier in C4 9.4v DC voltage. Through the R6 current limiting . Q10 ( TL431 ) and voltage regulation. In the Q3 emitter output 4.2V voltage for rechargeable lithium batteries. The polarity identification circuit consists of Q5 ~ Q8, R12 ~ R15. When point A is connected with the battery anode, B point is connected with the negative pole, Q8 because of R12 provide a positive bias voltage and conduction, Q5 provided by R14 bias conduction. The charging current from Q5 to A point battery E, B Q8 C pole formed of charging circuit. When point A connected battery cathode, whereas B is connected with the battery anode charging current is from Q7 to B point battery E, A Q6 C pole form a charging circuit. In order to complete the automatic recognition of cell polarity function.
When the charging current to flow through the R6, Q4 conduction, LED1 flashing LED ( LED1 onboard oscillator three-color light emitting diode capable of random changing, colorful flash ). The charge after the completion of Q4 because there is not enough turn-on voltage and a cutoff, LED1 extinguished. LED2 is a power indicator light.
Circuit principle diagram
Two, common troubleshooting
Faults: the power indicator light does not shine.
Maintenance: Test Q1 normal, but B is no bias voltage; test-retest R2 is open, after replacement of the R2 troubleshooting.
Fault two: the power indicator light does not shine. Maintenance: measurements of Q1 breakdown, test-retest R1 and R3 already open. Measurement of other components in normal, replacing the element after troubleshooting.
