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Short Circuit Protection of Power Supply Series Pass Element

IP.com Disclosure Number: IPCOM000082083D
Original Publication Date: 1974-Oct-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Walewski, LG: AUTHOR

Abstract

In a series regulator circuit, the series-pass transistor current under short-circuit load conditions is reduced without reduction of the power supply output current, by paralleling the series-pass element with current-sharing components. Prior series regulator circuits required the series-pass transistor to dissipate power equal to the unregulated input voltage Vin times the limit current I1, when the output is shorted to ground.

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Short Circuit Protection of Power Supply Series Pass Element

In a series regulator circuit, the series-pass transistor current under short- circuit load conditions is reduced without reduction of the power supply output current, by paralleling the series-pass element with current-sharing components. Prior series regulator circuits required the series-pass transistor to dissipate power equal to the unregulated input voltage Vin times the limit current I1, when the output is shorted to ground.

The circuit of Fig. 1 significantly reduces the series-pass transistor power dissipation and thus the cost, size and heat sink requirements under shorted load conditions. Unregulated input power Vin is introduced to terminals 14 and 15 and series regulated power produced at output terminals 16 and 17. The current source voltage Vcs at input 10 and the current source 11 are chosen to supply Ics approximately equal to the load current when the output terminals 16 and 17 are shorted, thereby reducing or eliminating transistor 20 emitter current. The circuit may consist of a resistor connected in parallel with the emitter collector of transistor 20. Alternatively, a transistor and another voltage source may be used as shown in Fig. 2.

The Fig. 2 circuit accepts unregulated plus Vin and produces a regulated output at 21. A short at output 21 for an indefinite period will not damage the circuit elements. The output power can be turned off by applying a logical enabling signal to th...