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Overvoltage Protection Circuit

IP.com Disclosure Number: IPCOM000091983D
Original Publication Date: 1968-Jul-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Lorenz, WM: AUTHOR

Abstract

Zener diode 35 provides a noncritical reference for one input of a differential amplifier comprised of transistors 20 and 30. The other differential amplifier input is coupled via a voltage divider formed by adjustable resistor 22 and resistor 24 so as to be responsive to an overvoltage in power supply 10. The differential amplifier output appearing at the collector of transistor 20 is fed to driver transistor 40 whose output is in turn coupled to the gate of SCR 15 connected across supply 10. The output of transistor 40 is also applied to a feedback and latching transistor 50, which controls the voltage applied to diode 35. When an overvoltage occurs, the differential amplifier begins to switch so as to begin to turn on transistor 40 whose output in turn begins to drive SCR 15 to its on state.

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Overvoltage Protection Circuit

Zener diode 35 provides a noncritical reference for one input of a differential amplifier comprised of transistors 20 and 30.

The other differential amplifier input is coupled via a voltage divider formed by adjustable resistor 22 and resistor 24 so as to be responsive to an overvoltage in power supply 10. The differential amplifier output appearing at the collector of transistor 20 is fed to driver transistor 40 whose output is in turn coupled to the gate of SCR 15 connected across supply 10. The output of transistor 40 is also applied to a feedback and latching transistor 50, which controls the voltage applied to diode 35. When an overvoltage occurs, the differential amplifier begins to switch so as to begin to turn on transistor 40 whose output in turn begins to drive SCR 15 to its on state. Transistor 50 serves to latch the circuit in its protected state. The regenerative feedback greatly accelerates the switching of the differential amplifier and transistor 40 so that SCR 15 is driven to its on state in a very much shorter time than would otherwise occur. Transistor 40 can be of relatively low-power handling capability, since it is in its high-power dissipation region for only a very short period of time.

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