variable 3 A power supply

As far as construction is concerned, this is a real mini power supply, but it can deliver up to 3 A at an output voltage of 1.25...25 V. Note, how- ever, that integrated voltage regulator IC1has on-chip overload protection that comes into operation when the dissipation in the device reaches 30 W. The ADJ(ust) pin of the regu- lator is connected to the junction of potential divider R1-P1. The output voltage, U0, is calculated from U. = [1.25 (1 + P1/R1)] V where P1and R1are in ohms (the value of P1is measured between the wiper and the junction with R1, i.e., 0...2.5 K2). Capacitor C1is a conventional filter capacitor, while C2 and C3 improve the regulation. Protection diodes D1 and D2 ensure that at switch-off the potential at the output of IC1is more positive than that at its input. The value of R1has been chosen to ensure that the minimum load current through IC1is about 3.5 A. It is essential that IC1is mounted on a heat sink rated at about 1 K/W — do not scrimp on the heat co...