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Transformer-Isolated Power MOSFET Switch Driver

IP.com Disclosure Number: IPCOM000034704D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Feduke, RJ: AUTHOR [+2]

Abstract

In the design of switched-mode power converters, it is often desirable to use a metal-oxide semiconductor field-effect transistor (MOSFET) as a power switch. It is almost always a requirement, either for reasons of safety or because of limitations of electrical components, that there be no direct electrical connection between the power MOSFET and the circuits which control it. Control of the power MOSFET under these circumstances is usually accomplished by means of a driver circuit which uses a pulse transformer to provide galvanic isolation between the control circuitry and the MOSFET (Fig. 1). The control circuit can then switch the MOSFET on and off without having any common conductors between the driver circuit and the power circuit.

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Transformer-Isolated Power MOSFET Switch Driver

In the design of switched-mode power converters, it is often desirable to use a metal-oxide semiconductor field-effect transistor (MOSFET) as a power switch. It is almost always a requirement, either for reasons of safety or because of limitations of electrical components, that there be no direct electrical connection between the power MOSFET and the circuits which control it. Control of the power MOSFET under these circumstances is usually accomplished by means of a driver circuit which uses a pulse transformer to provide galvanic isolation between the control circuitry and the MOSFET (Fig. 1). The control circuit can then switch the MOSFET on and off without having any common conductors between the driver circuit and the power circuit. The chief disadvantage of most driver circuits of this type is that a separate bias voltage is required to supply the secondary circuits on the MOSFET side of the pulse transformer. In most cases, this bias voltage must be floating (electrically isolated from any other bias voltage in the power circuit), and a small power transformer is required to provide this isolation. In addition to the isolation transformer, several components are usually required to generate and regulate the floating bias voltage(s). The circuit described in the following offers a two-fold advantage: The driver makes use of the magnetization current of the pulse transformer to turn off the power MOSFET, thereb...