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Self Clamping Driver

IP.com Disclosure Number: IPCOM000077744D
Original Publication Date: 1972-Sep-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Scotto, VA: AUTHOR

Abstract

The circuit reduces the cost of self-clamping drivers by replacing zener diode clamp with a resistor feedback circuit.

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Self Clamping Driver

The circuit reduces the cost of self-clamping drivers by replacing zener diode clamp with a resistor feedback circuit.

A down level at input terminal turns on transistor Q1 through voltage divider R1, R2. Darlington circuit Q2, Q3, R5 and R6 turns on when collector current flows from Q1 through R3 and RS. Darlington circuit provides drive current for inductive load L1.

When the input signal returns to an up level, Q1 turns off. This causes Q2 and Q3 to turn off interrupting the current through load L1. Inductive load L1 generates a voltage with a polarity opposite to the applied voltage when the current is interrupted. This voltage is coupled to the base of Q2 through voltage divider R4, R5. As the voltage goes positive, and exceeds the sum of the base- emitter voltage drops for Q2 and Q3, transistors Q2 and Q3 turn on thus clamping the voltage across inductive load L1.

When the current through inductive load L1 has decayed to zero, a reverse bias provided by -V, R4 and R5 will cause transistors Q2 and Q3 to be turned off, as shown in the waveforms.

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