A Self-Adaptive Measurement System for IGBT Collector Current using Package Parasitics

Insulated gate bipolar transistor (IGBT) collector current measurement based on the package parasitics between the power emitter ( E ) and the Kelvin emitter ( E′ ) is a lossless and real-time monitoring method. A step to improve accuracy is to precisely match the time constant ( Rf × Cf ) of the measurement circuit against the package parasitics ( LEE′ / REE′ ). This article proposes an automated time constant matching method to realize the tuning of Rf × Cf to LEE′ / REE′ , and a detection circuit to continuously measure the IGBT collector current using the package parasitics. In the proposed method, the Miller plateau voltage is first sampled, and a polynomial curve fit is carried out to determine the fitting parameters associated with the IGBT collector current ( IC ). A programmable resistor Rf is then adjusted automatically based on the step response of the readout voltage until the time constant is matched. A ratio between the readout voltage and a known IC is then calculated based on the Miller plateau voltage. The proposed system is verified using a field-programmable gate array controller and discrete components. Experimental results confirmed the functionality of the proposed method, showing that the readout voltage versus IC relationship has good agreement in the range of 0–165 A, with less than 3% error. The proposed method can also be used for overcurrent protection with a detection time of less than 0.7 μ s.