As the the title, this circuit can function as a power supply or a battery charger. This Battery Charger / Power Supply circuit has a voltage output of 14 volts and can supply current up to 4 amperes.
Operational amplifier A1 CA3140 directly drives the N-Channel MOSPOWER VN64GA with the error signal to control the output voltage . Peak rectifier D1, C1 supplies error amplifier A1 and the reference zener. This extra drive voltage must exceed its source voltage by several volts for the VN64GA to pass full load current. The output voltage is pulsating DC, which is quite good enough for battery charging. To transform the system to a regulated do supply, capacitor C2 is increased and another electrolytic capacitor is added across the load. The response time is very fast, determined by the op amp. The 2N4400 current-limiter circuit prevents the output current from exceeding 4.5 A. However, maintaining a shorted condition for more than one second will cause the VN64GA to exceed its temperature ratings. A generous heatsink, on the order of 1 °C/w, must be used.
Parts list : R1 : 51 ohm R2 : 150K/2W R3 : 0.15ohm/2W R4 : 680 ohm R5 : 10K R6 : 10K VR1 : 5K C1 : 50uF/50V C2 : 1000uF C3 : 750pF C4 : 0.01uF D1,D2 : 1N4002 D3 : 1N249 D4 : 1N4100 T1 : VN64GA T2 : 2N4400 A1 : CA3140 or LM324