ZENER_DIODE_SIMULATOR_CIRCUIT

Published:2009/7/16 23:09:00 Author:Jessie | From:SeekIC

Conventional zener diodes, unless specially compensated, all exhibit a similar problem: As the zener bias current increases, the temperature coefficient also increases in a positive direction. Also, the temperature compensation can be negative or positive, depending on the zener voltage and the particular bias current used-even for a single diode over its characteristic curve! Also, zener diodes available for less than approximately 5.0-V values exhibit very weak knees, where the zener impedance causes a large voltage change over the full bias-current range. This circuit is an attempt to reduce those problems. The bias current range is 1 to 20 mA, and this can be extended by using a higher-power transistor for Q2. This circuit has an adjustable zener voltage of from 1.5 to 6.5 V. That voltage (VZ)can be determined using VZ=1.5=(5R2/104) For any setting of R2, the voltage varies less than 1 percent over the 2- to 20-mA bias current. The base-emitter voltage of Q1 provides the reference voltage that is temperature D1, a 1N34A germanium diode. A stable voltage of about 375 mV is then present across R1, and a constant current of 0.5 mA flows through the resistor divider. The net temperature coefficient is complex, but it remains below -2mV/℃ because of the interaction of the diode and transistors. Darlington pair Q2 handles all the bias current, except for the 600 μA needed to bias the reference.



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