The Versatile Power Supply is a DC...
S&T - PS 002
The Versatile Power Supply is a DC regulated variable power supply that is capable of delivering DC voltages ranging from 3.3 Volts to up to 15 Volts with 1Amp current output using an variable voltage regulator IC LM317.
In the Versatile Power Supply circuit, the AC mains is stepped down by transformer (X1) to deliver the secondary output of 18V AC at a maximum current of 1A dependent upon the load. The transformer output is rectified by the bridge rectifier comprising of four diodes (D1 through D4), filtered by a capacitor (C1) and fed to th voltage regulator IC LM317 (denoted as IC1). IC1 is a 3-terminal positive regulator capable of providing 1.2V to 37 volts at 1.5A current to the load.
Resistor R13 and selected combinations of several other resistors (R1 through R12) are used to produce approximately 3.3V, 5V, 6V, 9V, 12V and 15V at the output. The desired resistors are selected by switching into conduction one of the six PNP transistorsBC558 (T1 through T6) by grounding the corresponding transistor base using a rotary switch (S1). For example, to get regulated 3.3V, simply rotate the knob of rotary switch to 3.3V position. Consequently, transistor T1 is forward biased to switch resistors R1 and R2 (in series) across Adj pin of LM317 and ground to produce
Other voltages can be produced in the same way by using rotary switch S1. Capacitor C2 bypasses any ripple in the output. Diode D5 is used as the protection diode. Use a heat-sink for dissipation of heat from IC LM317. The fuse-rated lamp provides protection against short circuit.
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