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Bipolar Transistor with Controllable Peak Emitter Current

IP.com Disclosure Number: IPCOM000088443D
Original Publication Date: 1977-Jun-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Malaviya, SD: AUTHOR

Abstract

Fig. 1 shows s two-emitter NPN vertical bipolar transistor of conventional design except that the main emitter EM#1 can be larger than the auxiliary emitter EM#2. Also, unlike the conventional design, the spacing d between the two emitters is made small in order to enhance lateral NPN action.

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Bipolar Transistor with Controllable Peak Emitter Current

Fig. 1 shows s two-emitter NPN vertical bipolar transistor of conventional design except that the main emitter EM#1 can be larger than the auxiliary emitter EM#2. Also, unlike the conventional design, the spacing d between the two emitters is made small in order to enhance lateral NPN action.

A Schottky barrier diode SBD1 is connected across the base and emitter EM#2. SBD1 has its anode connected to the P-base region and its cathode connected to emitter EM#2.

Emitter EM1 is used as the emitter of the vertical transistor in the conventional manner.

Emitter EM#2 acts as the collector of the lateral NPN transistor whose beta is negligible in the normal range of DC current in emitter EM#1. However, when the current in emitter EM#1 becomes large, lateral beta of the NPN device becomes significant, and part of the current of emitter EM#1 is collected by emitter EM#2 and flows through the Schottky barrier diode SBD1.

As the current in emitter EM#2 increases further, lateral beta improves rapidly and the Schottky barrier diode is able to divert excess base drive away from the base and into emitter EM#1 via emitter EM#2. Total current in emitter EM#2 is thus limited to a safe value.

Since lateral beta is negligible at lower currents in emitter EM#1, normal device operation is not interfered with by the auxiliary current limiting means.

Use of an external resistor (R2) in emitter EM#2, returned to a suitable positiv...