Fully variable from +/- 3V to +/- 15V, this 500mA workshop tool is short-circuit proof, and highly useful!

Some time ago the author urgently needed a split-level power supply and for quickness copied a previously published circuit. It worked well, with one exception, that it had no protection against accidental short circuits.

In the author's case, these could happen with the negative output, mainly due to the fact that on most of his printed circuit boards (PCBs) the negative and earth lines were in close proximity. The slightest contact between the two would cause instant destruction of the negative feed transistor. So, on the last occasion this occurred, it was decided to revisit the circuit, and the design described here is the result of that investigation.