HANDY_HOBBY_POWER_SUPPLY

Published:2009/7/16 22:24:00 Author:Jessie | From:SeekIC

The input voltage to the power supply at mini phono jack J1 must be from 7 to 20 Vac or from 7 to 30 Vdc. You can use any transformer or ac-to-dc wall adapter that meets those input requirements. An ac input at J1 is rectified by bridge rectifier BR1; a dc input passes through half of the rectifier unmodified, except that its value drops by the sum of two diode voltage drops. Two MC7805 5-V regulators are in the circuit: IC1 provides a fixed 5-Vdc output at J2, while IC2 has a variable dc output at J3. The variable output ranges from +5 Vdc to 2 V less than the input voltage to the power supply. The output of the fixed regulator is made variable by varying the voltage at pin 2 with potentiometer R1. (Pin 2 is normally grounded to produce the fixed-voltage output.) Each voltage regulator can safely handle up to 1 A of current, provided that the transformer or power adapter can handle the demand and that the regulator is properly heatsinked. The voltage regulators must be heatsinked if more than a few milliamperes is to be drawn from the supply. Power indicator LED1 is connected across the fixed 5-V output; it lights whenever the supply is powered.



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