Browse Prior Art Database

Second Breakdown Protection of a Power Supply's Pass Transistor

IP.com Disclosure Number: IPCOM000052861D
Original Publication Date: 1981-Jul-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Ernst, LM: AUTHOR [+2]

Abstract

Breakdown of a power transistor is prevented by circuitry which monitor the transistor operation and forces corrective responses by the transistor whenever operation of the transistor exceeds its design parameters.

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Second Breakdown Protection of a Power Supply's Pass Transistor

Breakdown of a power transistor is prevented by circuitry which monitor the transistor operation and forces corrective responses by the transistor whenever operation of the transistor exceeds its design parameters.

Second breakdown is a potentially destructive phenomenon that can occur in all bipolar (N-P-N and P-N-P) transistors. To avoid circuit failure due to second breakdown of a transistor, it is important to assure that the transistor's operation be restricted to the manufacturer's recommended safe operating area. The present circuit reduces overall cost, guarantees safe area operation, and thus greatly prolongs transistor life and component reliability.

Transistor Tl is subjected to significantly high voltages and currents, and thus needs protection. Transistor T2 together with transistor Tl form a darlington pair which effects high current amplinafication. Transistor T3 along with its three resistors Rl, R2, and R3, and zener diode Zl, sense the voltage from collector to emitter on transistor Tl. When the voltage exceeds a desired limit, T3 turns on, robs base drive from T2 and T1, and causes both devices to turn off and reduce collector current to zero. Zener diode Z1 assures a sharp, well-defined turn-on level of T3. Resistor R3 conducts leakage current of Z1 away from the base of T3 when Z1 is in the off state. Diode D1 enables T3 to pull charge out of both bases T1 and T2 simultaneously....