Test-Voltage Supply

05 TEST-VOLTAGE SUPPLY For testing zener diodes, base-emitter breakdown, diacs, and so on, a fairly high voltage is needed. The usual type of laboratory power supply is not suitable, because its output is normally of the order of only about 30 V. If the re- quired current does not exceed 10 to 15 mA, it is possible to make a short- circuit-proof power supply with vari- 46 SUPPLEMENT able output voltage from 0 to 50 V from a handful of components as shown in the accompanying diagram. Circuit ICI amplifies a direct voltage set by P2 by a factor of about 6. Its output voltage should be about 25 V with respect to junction CI-C2. This voltage is inverted by IC2, whose output is thus -25 V. There is then available either a symmetrical ±25 V potential with respect to junction C i-C2, or 50 V asym- metrical across the outputs of the ICs. The actual value of the voltage is set with Pi. The maximum current is limited by the ICs to about 20 mA, so that the likelihood of damage to a compon...