Here is a simple power supply circuit that can be used for citizenband and VHF walkie-talkies of power rating up to 10 watts. The circuit uses a step-down transformer, followed by bridge rectifier, filter, regulator, and current booster stages. A pnp power transistor is added to the circuit to increase its current sourcing capabilities. Regulator 7812 can support around 100 mA current. When the current flowing through R1 nears 100mA value, the voltage (>0.65V) across the emitter-base junction makes transistor T1 to conduct and provide a path for additional current.
Circuit diagram :
Power Supply for Walkie Talkies Circuit Diagram
The circuit can source around one ampere of current at 12+1.4 volts=13.4 volts. Both the regulator IC and the power transistor must be mounted on heat sinks.
Author :Pradeep G. - Copyright : Electronics For You November 2001
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