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Power Transistor Switch

IP.com Disclosure Number: IPCOM000091986D
Original Publication Date: 1968-Jul-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Leung, WC: AUTHOR

Abstract

This self-forced-off transformer driving circuit for a power transistor switch automatically provides fast turn-off of a power transistor switch and automatic maintenance of a reversed bias condition until the next on period. Power transistor switch 5 is turned on in response to an input signal to its base 5B via transistor 12 and windings 10A and 10D of transformer 10. The input signal also causes a voltage to appear in winding 10C which charges capacitor 15 through resistor 18, while causing transistor 14 to remain cut off. When the input signal is removed, the voltages produced by windings 10A and 10B reverse, causing transistor 12 to be cut off while transistor 14 becomes conducting.

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Power Transistor Switch

This self-forced-off transformer driving circuit for a power transistor switch automatically provides fast turn-off of a power transistor switch and automatic maintenance of a reversed bias condition until the next on period. Power transistor switch 5 is turned on in response to an input signal to its base 5B via transistor 12 and windings 10A and 10D of transformer 10. The input signal also causes a voltage to appear in winding 10C which charges capacitor 15 through resistor 18, while causing transistor 14 to remain cut off. When the input signal is removed, the voltages produced by windings 10A and 10B reverse, causing transistor 12 to be cut off while transistor 14 becomes conducting. Thus the current 12 flowing in winding 10B causes a much higher reverse bias voltage to be induced in winding 10D to provide rapid turnoff of switch 5. Such occurs in a much shorter time than would otherwise be provided if reliance were just on the reverse voltage appearing in winding 10A. The period for which transistor 14 remains conducting is determined by the time required for capacitor 15 to discharge to a level which causes the voltage applied to base 14B to fall below that required for conduction. In order to provide for the maintenance of a reverse bias voltage on base 5B of switch 5 until the occurrence of the next on period, the transformer windings are such that the voltage-time product, produced with respect to the voltage applied to the power...