Silicon carbide transistor firm SemiSouth has announced an isolated driver board for half-bridge power modules built from its vertical-trench junction field-effect transistors (VJFETs).
Called SGDR2500P2, the driver is particularly aimed at Microsemi's 1.2kV, 100A APTJC120AM13VCT1AG, but can also be used as an evaluation board for other projects that include enhancement-mode VJFETs.
The Microsemi part uses eight SemiSouth SJEC120R050 (1200V 50mΩ VJFET) in two sets of four parallel devices.
Unlike silicon power mosfets, enhancement-mode VJFETs cannot simply be fed with a 0V and 10V (say) to turn them off and on.
Instead, a more complex wave form is required to make best use of the technology.
The SemiSouth gate driver uses a dual-stage drive scheme.
The first stage is a brief (~100ns) +15V pulse which pumps charge into the SiC device's input capacitance to turn it on.
Then comes a long lower-current (~500mA) signal, giving a voltage of 2.5-3V depending on temperature, which holds the device in a minimum RDSon conductive state.
For turn off, SGDR2500P2 applies -15V to quickly remove charge from the input capacitance.
Peak drive currents are +20A and -10A, for hard-switching use up to 100kHz. Necessary +/-15V isolated rails are generated on-board.
"Total measured switching losses are 1.1mJ," claimed SemiSouth. "The isolated high- and low-side outputs make it easy to drive half-bridge power modules without requiring additional isolation transformers."
0 to 100% duty cycle is possible, and application note AN-SS05 can be downloaded.