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Proportional Base Drive Structure

IP.com Disclosure Number: IPCOM000051352D
Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Radcliffe, JK: AUTHOR

Abstract

Proportional base drive in power transistors is an established method i power conversion. Such structures feed a current Ib proportional to the output current Ic into the base of a switching transistor 1, as in Fig. 1. Here the transformer 2 is used as a current transformer, and the ratio of collector current Ic (passing through winding N2) to base current Ib is given by the turns ratio, as follows: Ic over Ib = N1 over N2. Such a structure requires only some small base current to start the regenerative action. This is usually provided by control winding N3. The structure is turned off by providing a signal on control winding N3 to reverse Ib and remove any stored charge in transistor 1.

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Proportional Base Drive Structure

Proportional base drive in power transistors is an established method i power conversion. Such structures feed a current Ib proportional to the output current Ic into the base of a switching transistor 1, as in Fig. 1. Here the transformer 2 is used as a current transformer, and the ratio of collector current Ic (passing through winding N2) to base current Ib is given by the turns ratio, as follows: Ic over Ib = N1 over N2.

Such a structure requires only some small base current to start the regenerative action. This is usually provided by control winding N3. The structure is turned off by providing a signal on control winding N3 to reverse Ib and remove any stored charge in transistor 1.

The circuit of Fig. 2 is configured so that flyback action of transformer 20 initiates the proportional drive of transistor 10.

Before the start of the input pulse, transformer 20 has a small current in the control winding N3 which is limited by series resistor R. At the start of the pulse, transistor 30 turns off. This forces the current which was flowing in the primary magnetizing inductance to produce a voltage kickback, turning transistor 10 on and initiating the regenerative action.

At turn-off time, transistor 30 turns back on and pulls node V1 to ground. Because the base-emitter voltage of transistor 10 is reflected into the control winding, node V2 attempts to go below ground but is clamped by diode D1. This attempts to place a short circuit across the base of transistor 10 which initiates the turn-off. After the turn-off is complete, node...