This project describes a little power supply, based on a 78L15 and 79L15 in alliance with an NPN / PNP pass transistor. It is intended to show a method for boosting the output current.

The circuit consists of a transformer, two bridge rectifiers followed by large capacitors and two voltage regulators in a TO-92 case. In the input path is a 12 Ω resistor, bridging the emitter-base of the pass transistor. By that, the pass transistors start conducting somewhere near 0.6 V / 12 Ω = 50 mA.

In case the disssipated power is large, a heatsink should be added to the BC141 / BC161. For a stable and noiseless output voltage, a capacitor of 3.3 µF is added at the output.

Even so the datasheet of the transformer (BV UI 303 0163) says, that the secondary voltage under no load is 2 x 21.8 V we measured a much higher voltage of approx. 28 V. That's why the capacitors are rated 35 V.

The webmaster does not read these comments regularely. Urgent questions should be send via email. Ads or links to completely uncorrelated things will be removed.