Battery Charger Circuit

Posted on Apr 6, 2012

The circuit is capable of supplying either a trickle (50 mA) or high-current (1-A) charge. You can select either charging method or an automatic mode that will first trickle charge a battery if it is particularly low before switching to high-current charging.If the battery`s voltage is low, Zener-diode D5 will not conduct sufficient current to produce a voltage drop across R6 to turn Q2 on. With Q2 off, R4 pulls the base of Ql high, turning it on. That activates Kl. With K1 active, the only thing between the battery and the power supply is R2 and D4 (which prevents current from flowing through the circuit from the battery).

Battery Charger Circuit
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Once the battery charges a bit, the current through D5 increases, causing a voltage drop across R6 that is of sufficient magnitude to turn on Q2. Transistor Q2, in turn, grounds the base of Ql, keeping it off. With Ql off, Kl remains in its normally closed state. That places Rl in series with the battery, thereby reducing the current to a trickle.

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