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Hybrid Zener Circuit

IP.com Disclosure Number: IPCOM000080782D
Original Publication Date: 1974-Feb-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Morgan, C: AUTHOR [+2]

Abstract

This circuit provides zero impedance at zener voltages below levels normally attainable with zener diodes.

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Hybrid Zener Circuit

This circuit provides zero impedance at zener voltages below levels normally attainable with zener diodes.

Zener diodes normally exhibit sharp-kneed low-impedance breakdown characteristics at potentials in excess of 6 volts. At lesser potentials, the impedance of the known zener diodes after breakdown is higher than desired. The present circuit provides its low-impedance Zener characteristics at potentials between 1 to 5 volts.

Referring to the drawing, the present hybrid zener is a two-terminal circuit between terminals A and B. Transistor Q1 is a grounded-base amplifier sensing changes in the potential between terminals A and B. Transistors Q2 and Q3 invert these changes and apply these inverted changes at terminal A. Resistor R3 controls the positive (local) feedback around transistor Q1 and, therefore, controls the gain of the circuit. When the gain of the circuit approaches a value equal to the sum of the resistances of R1 and R2 divided by the resistance of R1, then the impedance of the circuit between terminals A and B approaches zero. Resistors R4 and R5 have values chosen to provide proper bias for transistors Q2 and Q3.

At potential levels between terminals A and B of less then 3 volts, the switch is connected to R2 as shown. At potential levels in excess of 3 volts the alternate switch position is utilized, connecting diode D1 instead of R2. D1 may either be a device as shown, a transistor, a forward-biased diode, or an inexpensive...