Towards a sensorless current and temperature monitoring in MOSFET-based H-bridge

Chip temperature in power MOSFETs is commonly obtained (e.g. for thermal characterisation purposes) by feeding a known, controlled low DC-current in the body diode and measuring the forward-voltage drop. Drain current might be estimated by a voltage measurement across drain and source terminals, on-state resistance acting as a shunt, assuming that the temperature is known and constant. Such voltage-based measurements are attractive, but dependencies limit their application to laboratory environment. In industrial converters, neither temperature nor current are known a priori. Here we show that by combining the two techniques, previous limitations are overcome. Temperature and current come as two separate polynomial expressions. The application to a low-cost monitoring system is presented and results are discussed. The validity of the system over the full temperature and current ranges is verified and a confidence map is given.

I. Introduction

Current and Temperature are critical parameters in power converters. The monitoring of their values is at a premium to ensure reliable operation. Extensive work and literature relate techniques based upon an estimator to avoid the cost and pitfalls of dedicated sensors [1]–[3]. The method proposed in this paper is based on the measurement of the drain source voltage at the terminals of one MOSFET in an inverter.