Guide For High Speed MOSFET

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Design And Application Guide For High Speed MOSFET Gate Drive Circuits

By Laszlo Balogh

ABSTRACT
The main purpose of this paper is to demonstrate a systematic approach to design high performance
gate drive circuits for high speed switching applications. It is an informative collection of topics offering
a “one-stop-shopping” to solve the most common design challenges. Thus it should be of interest to
power electronics engineers at all levels of experience.
The most popular circuit solutions and their performance are analyzed, including the effect of parasitic
components, transient and extreme operating conditions. The discussion builds from simple to more
complex problems starting with an overview of MOSFET technology and switching operation. Design
procedure for ground referenced and high side gate drive circuits, AC coupled and transformer isolated
solutions are described in great details. A special chapter deals with the gate drive requirements of the
MOSFETs in synchronous rectifier applications.
Several, step-by-step numerical design examples complement the paper.

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INTRODUCTION

MOSFET – is an acronym for Metal Oxide
Semiconductor Field Effect Transistor and it is
the key component in high frequency, high
efficiency switching applications across the
electronics industry. It might be surprising, but
FET technology was invented in 1930, some 20
years before the bipolar transistor. The first
signal level FET transistors were built in the late
1950’s while power MOSFETs have been
available from the mid 70’s. Today, millions of
MOSFET transistors are integrated in modern
electronic components, from microprocessors,
through “discrete” power transistors.
The focus of this topic is the gate drive
requirements of the power MOSFET in various
switch mode power conversion applications.

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FINAL COMMENTS, SUMMARY
Like all books, this article should be read from
the beginning to the end to get the whole story.
36
Every consideration described earlier regarding
switching speeds, dv/dt immunity, bypassing
rules etc. are equally applicable for all circuits
including transformer coupled gate drives. As the
topics build upon each other, only the unique and
new properties of the particular circuit have been
highlighted.
This paper demonstrated a systematic approach
to design high performance gate drive circuits for
high speed switching applications. The procedure
can be summarized by the following step-by-step
checklist:
……………………………………………………………………
……………………………………………………………………

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In a reliable design, these steps should be
evaluated for worst case conditions as elevated
temperatures, transient voltage and current
stresses can significantly change the operation of
the driver, consequently the switching
performance of the power MOSFET.
Of course, there are many more gate drive
implementations which are not discussed in this
paper. Hopefully, the principles and methods
presented here can help the reader’s
understanding and analyzing of other solutions.
For those who are looking for quick answers in
the rather complex field of high speed gate drive
design, Appendix A through E offer typical,
numerical examples of the different calculations.
Appendix F provides a complete, step-by-step
gate drive design example for an active clamp
forward converter with a ground referenced and a
floating gate drive circuits.

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