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Second Breakdown Free Switch Transistor

IP.com Disclosure Number: IPCOM000086481D
Original Publication Date: 1976-Sep-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Perner, FA: AUTHOR

Abstract

Turn-off second breakdown (S/B) in epitaxial collector switch transistors is governed by two key parameters: (a) a critical electrical field strength at the collector high-low junction necessary for secondary ionization, and (b) the width of the collector and base regions of the transistor. The above two factors combined yield a sustaining voltage for the transistor which is limited by "current mode" S/B. This voltage limit is defined as VCEX (S/B).

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Second Breakdown Free Switch Transistor

Turn-off second breakdown (S/B) in epitaxial collector switch transistors is governed by two key parameters: (a) a critical electrical field strength at the collector high-low junction necessary for secondary ionization, and (b) the width of the collector and base regions of the transistor. The above two factors combined yield a sustaining voltage for the transistor which is limited by "current mode" S/B. This voltage limit is defined as VCEX (S/B).

Fig. 1 shows that VCEX (S/B) is essentially independent of collector current and base off-drive. Thus, turn-off S/B can be prevented by clamping the maximum collector-emitter voltage of the switch transistor to levels less than VCEX (S/B).

Considering VCEX (S/B) as a primary transistor design parameter, the switch transistor structure (Fig. 2) can be realized to yield a transistor that will be free of S/B during and after turn-off switching transitions. The equivalent circuit is shown in Fig. 3.

The essential feature of the S/B free switch transistor is the implementation of an avalanche breakdown diode (D1) in the extrinsic base-collector region with sufficient breakdown voltage and current capacity to meet the following conditions: 1) the current capacity of D1 must be approximately equal to IC (max) divided by HFE (common emitter forward current gain) of the transistor, and 2) the breakdown voltage of D1 must be (a) less than the S/B voltage limit of the intrinsic transistor,...