microcomputer power supply - provides 1 x 5 V and 3 x 12 V

provides 1 x 5 V and 3 x 12 V The attraction of this power supply is based on two of its characteristics. First of all it is extremely compact and secondly it supplies three, or strictly speaking four, voltages: +5 V/3 A, +12 V/2 A, and a sym- metrical + 12 V/250 mA. The credit for the compactness is due to the fact that only one transformer is used for the three voltages. It is a toroidal transformer made by ILP (they call it a 4T344) and has three secondary windings of 9 V/7.2 A, 15 V/3.2 A, and 15 V/0.5 A. It could, 2 of course, be replaced by three separate transformers but then the circuit would lose a lot of its charm. We felt no need to re-invent the wheel as regards the voltage regulating circuitry. A pair of 723s followed by TIP 142s to do the heavy work are used for the 5 V and 12 V. The symmetrical ± 12 V is provided via a 7812 and a 7912 (IC3 and IC4). Thanks to the printed circuit board of figure 2, building this power supply is very straightforward. It is important ...