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Stand-by Battery Charger

2014-11-25 21:44  
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This simple circuit will find many applications as a battery eliminator for low power requirements. It consists of a transformer, a bridge rectifier and an electrolytic capacitor followed by a zener controlled series pass transistor. The output is stabilized at +7.5V. The stand-by battery, 7.5V, in series with D7, floats across the output terminals, ready to take over in case of main failure. The voltage drop across D7 will then reduce the power supply to about 7V. The R3 has an additional function, when working off the mains it will trickle charge the dry cells or storage battery. It?s correct resistance can be found by dividing the voltage potential difference between the zener D6 and the battery by the safe trickle current, which may amount to some 0.7 milliamps. visit page.Stand-by Battery Charger - schematic
Part ListR1-2-3=1KohmD5=Led Red 3mmF1=50mA FuseC1=1000uF 16VD6=8V2 0.4W zenerB1=5X1.5V BatteryC2=100uF 16VQ1=BD139D1...4-7=1N4002T1=230Vac// 10Vac - 0.5A transform. visit page.