Non-Linear Capacitance of Si SJ MOSFETs in Resonant Zero Voltage Switching Applications

Manuel Escudero,Nico Fontana,Diego Pedro Morales,Matteo-Alessandro Kutschak,Noel Rodriguez

doi:10.1109/access.2020.3004440

Manuel Escudero, Nico Fontana + Show 3 more

Open Access

https://doi.org/10.1109/access.2020.3004440

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Abstract

The parasitic capacitances of modern Si SJ MOSFETs are characterized by their non-linearity. At high voltages the total stored energy Eoss(VDC) in the output capacitance Coss(v) differs substantially from the energy in an equivalent linear capacitor Coss(tr) storing the same amount of charge. That difference requires the definition of an additional equivalent linear capacitor Coss(er) storing the same amount of energy at a specific voltage. However, the parasitic capacitances of current SiC and GaN devices have a more linear distribution of charge along the voltage. Moreover, the equivalent Coss(tr) and Coss(er) of SiC and GaN devices are smaller than the ones of a Si device with a similar Rds,on. In this work, the impact of the non-linear distribution of charge in the performance and the design of resonant ZVS converters is analyzed. A Si SJ device is compared to a SiC device of equivalent Coss(tr), and to a GaN device of equivalent Coss(er), in single device topologies and half-bridge based topologies, in full ZVS and in partial or full hard-switching. A prototype of 3300 W resonant LLC DCDC converter, with nominal 400 V input to 52 V output, was designed and built to demonstrate the validity of the analysis.

Highlights

The development of Switched Mode Power Supplies (SMPS) continuously moves towards improvements in efficiency, volume and cost, which can be observed in the trend of high efficiency standards, like the Climate-Savers-Computing Initiative (CSCI) [1] or the 80 PLUS qualification program [2], with increasing requirements extending to light load operation
The parasitic capacitances of modern Si Super Junction (SJ) MOSFETs are characterized by its non-linearity
At high voltages the total stored energy Eoss(VDC) in the output capacitance Coss(v), differs substantially from the energy in an equivalent linear capacitor Coss(tr) that stores the same amount of charge

Summary

INTRODUCTION

The development of Switched Mode Power Supplies (SMPS) continuously moves towards improvements in efficiency, volume and cost, which can be observed in the trend of high efficiency standards, like the Climate-Savers-Computing Initiative (CSCI) [1] or the 80 PLUS qualification program [2], with increasing requirements extending to light load operation. The rest of the energy would have been stored in the resonant inductor (15-16) After both Coss and Vsupply have reached the same voltage, VDC, the scenario becomes equal to the one analyzed in the previous section for single device topologies, where the initial energy required in the inductor is equal to Eind,1(8). Like in the other two previous scenarios for single device topologies, the non-linear distribution of charge in the output capacitance of Si SJ devices requires comparatively more initial energy stored in the inductor than SiC or GaN for achieving full ZVS.

SINGLE DEVICE AT A LOWER VOLTAGE

MILLER FEEDBACK EFFECT

CONCLUSION