Bench top power supply

Posted on Oct 24, 2012

A tapped transformer drives a diode bridge (D1-D4) and two 2500 µ¥ filter capacitors (Cl and C2), that provide a no-load voltage of 37 or 47 volts, depending upon the position of switch S2a. The unregulated dc is then fed to a pre-regulator stage composed of Ql and D5. Those components protect IC1 (the 723) from an over-voltage condition; the 723 can't handle more than 40 volts. The LED (LED1) and its 2.2 k current-limiting resistor (Rl) provide on/off indication. The current through the LED varies slightly according to the transformer tap selected, but that's of no real consequence.

Bench top power supply
Click here to download the full size of the above Circuit.

The series-pass transistor in IC1 drives voltage-follower Q2, providing current amplification. The transistor can handle lots of power. It has a maximum collector current of 15 amps and a maximum VCE of 70 V, both of which are more than adequate for our supply.

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