Voltage sharing scheme for series-connected power semiconductors

Dynamic voltage-sharing schemes have been investigated which allow high-voltage power-semiconductor devices, such as thyristors, IGCTs, IGBTs or power MOSFETs, to be series connected in strings and switched, as simply in high-voltage applications, as when used as single devices. The circuits have many of the advantages of simply using RC or RCD snubbers, including being easily applicable to both low- and high-side switches. However, because the snubber capacitors are not fully discharged their associated reset current and power-losses are minimized. To illustrate the principle of operation experimentally, a string of three series-connected power MOSFETs switching 100 A from 330 V has been used to obtain practical waveforms. The schemes are discussed and illustrated, using SPICE simulation results. The new, relatively simple voltage-sharing schemes are much easier to design and optimize than recently reported active gate-control and regenerative-snubber methods, allow very rapid turn-on and turn-off switching, and give composite-device switches a usable voltage rating similar to the aggregated voltage ratings of the string.