Analytical modeling and experimental evaluation of MOSFET switching characteristics

Abstract

In this thesis, analytical modeling of a MOSFET as well as investigation of its gate drive was studied. Firstly the performance of the gate drive during switching transients under different test conditions were studied. In order to do so, the elements in the drive were checked separately and their effect on the gate voltage and current were observed. Then two simple case set-ups consisting RC circuit were switched by the gate drive. For the first case a large capacitor and resistor was selected (C = 68nF;R = 209Ω). The results match well with the simulations. The rise time of the voltage was 39 s. For the second case very small values were selected to check the gate drive performance in higher currents(C = 13nF;R = 22Ω). The results in this case also were in agreement with the results from the simulation test set-up, the voltage rise time was 898ns in this case. The next step was modeling a MOSFET analytically, using its turn-on and turn-off equations in MATLAB. Two cases were considered for this part. First large capacitors were attached between the gate-source and gate-drain of the device in order to overrule its inherent capacitors and slow down the switching transient(Cgs = 68nF;Cgd = 5nF). The results from the simulation were in agreement with the experimental results. Afterwards the capacitors were detached and only the inherent capacitors of the MOSFET were charged and discharged during switching transients. For both cases gate voltage/current and drain-source voltage/current from the simulation were compared with the experimental results. Finally switching losses were calculated and compared for both experimental and simulation, which at switching frequency of 2kHz losses for simulation and measurement were 21mW and 28mW during turn-on and 28mW and 30mW during turn-off respectively.