Topics Covered

Objectives

Introduction

Thermal Modelling

Simulation & Results

Conclusion & Discussion

1. Objectives:

To examine the Quasi-Dynamic model of power MOSFET and its effects on device thermal response.

2.Introduction:

The design advantage of the simulation approach compared to analytic design is that it can reflect the

system characteristics more accurately, for example: electric machine dynamic, parasitic param-

eters, MOSFET avalanche energy and switching loss. So it is more likely to have a suitable design

basing on numerical analysis than analytic design using average method, which may end up with an

over-designed system.

There are all kinds of Pspice and SABER device models on manufacture’s websites. They provide

great flexibility for circuit and system simulation, which can offer a good guidance for system design.

However, most of the MOSFET models are electrical behaviour or physics model. And all parameters

are considered thermally independent. This is not true in real system, because several key param-

eters such as Rdson, Vth…would change following the temperature variation. So it wouldn’t be appro-

priate to decouple the electrical and thermal design of a system. The thermal loop has to be closed in

MOSFET level to reflect the device and system dynamics, which will improve the accuracy of the

simulation and make the performance prediction reasonably close to the real system.

AN-1040

System Simulation Using Power MOSFET Quasi-Dynamic Model

By

Jingdong Chen

Automotive Components Group

www.irf.com

1

International Rectifier

••••• 233 Kansas Street El Segundo CA 90245 USA