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CONSTANT_CURRENT_NiCd_CHARGER

2014-11-18 02:37  
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CONSTANT_CURRENT_NiCd_CHARGER
A tapped transformer(T1)with two rectifier diodes (D1 and D2) and capacitor C1 provides the primary dc supply from the 230 Vac The power MOSFET device TR3 is initially biased into conduction by a positive gate voltage from resistor R3 Current flowing through the load flows through Current-sensing resistor R4,developing a voltage When this reaches about 0.5 V, transistor TR2 begins to conduct,reducing the gate (g) voltage of TR3 The circuit stabilizes at the load current that gives 0.5 V across R4 Zener diode D4 prevents excessive gate voltage from being applied to power MOSFET TR3,which might happen if the circuit was powered without the load connected,Diode D6 compensates for the base-emitter voltage drop of transistor TR1 so that the voltage across R4 is duplicated across resistor R1,controlling the current flow through LED D3 The apparent brightness of LED D3 therefore depends on the charging current,so any problems with connection to the cells on charge will be immediately apparent to the user Diode D5 prevents any “back feeding” of current from the batteries power supply fails while the batteries are still connected