High-Power Zener Diode

047 HIGH-POWER ZENER DIODE Although its regulation characteristics are not as good as those of an integrated voltage regulator, a high-power zener diode has, nevertheless, useful applications, for instance, in shunt regulators. The circuit shown in the diagram simulates a fairly expensive and hard-to-come-by high-power zener diode. Basically a two- stage current amplifier with a low-power (400 mW) zener refer- ence, it is capable of sinking up to 500 mA at a maximum 25 V. The effective zener voltage of the circuit is about 0.7 V higher than that of the reference device, D1. Using a preset, P1, instead of a fixed resistor, R1, enables the output voltage defined by D1 to be increased slightly. This substi- tution is useful when, say, a 6V2 or 9V1 zener is to be simulated and a low-power type of this rating is not available. The next lower value in the E6 range (here, 5V6 or 8V2) may then be used for Dl. When the voltage across the circuit increases beyond the zener voltage, T1 condu...