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Excess Voltage Protection Circuit

IP.com Disclosure Number: IPCOM000096380D
Original Publication Date: 1963-Apr-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Ewald, L: AUTHOR

Abstract

This circuit prevents a detrimental rise in the output voltage of a transistor power supply unit. Such action occurs in case of a short circuit in one of the transistors connected in parallel as adjustable series resistances between the voltage source and the load. Safety fuses are inserted in the emitter circuits of those transistors.

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Excess Voltage Protection Circuit

This circuit prevents a detrimental rise in the output voltage of a transistor power supply unit. Such action occurs in case of a short circuit in one of the transistors connected in parallel as adjustable series resistances between the voltage source and the load. Safety fuses are inserted in the emitter circuits of those transistors.

The output voltage U2 is kept constant through a regulating circuit. In accordance with changes in the input voltage U1 and the load, respectively, circuitry, not shown, produces a control voltage St. Control voltage St through transistor T4 regulates the collector-emitter paths of transistors T1 ... T3 serving as series resistances. If a short-circuit occurs, e.g., in transistor T1, transistors T2 and T3 are cut off.

The entire current flows through the short-circuited transistor T1. As the emitter circuits of transistors T1 ... T3 contain safety fuses S1 ... S3 instead of the customary negative feedback resistances, fuse S1 melts. The short-circuit is removed and the remaining transistors T2 and T3 resume their normal regulating action. In normal operation, diodes D1 ... D3 are conductive and apply the base control currents to transistors T1 ... T3. In case of a short-circuit in one of the transistors T1 ... T3, the associated diode is blocked, so that the control currents flowing through the remaining diodes are not affected.

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