One choice, and it sets both the frequency you can run and how long the bridge lives.
What decides it
A MOSFET's conduction loss is I²·R, quadratic in current. An IGBT's is V_ce·I, linear. So at hundreds of amps in short pulses the IGBT wins, and at moderate current and high frequency the MOSFET does.
Everything below is that one sentence meeting a datasheet.
What you decide
Which type
Criterion: the current, and then the frequency.
- An SSTC takes MOSFETs. There is no resonant primary, the current is modest, the switching frequency is the same, and an IGBT's current tail becomes the dominant loss.
- A DRSSTC takes IGBTs. Hundreds of amps in a tank, in short bangs, is exactly their ground.
Which family, within the type
Field-stop IGBTs are the de facto standard for QCW. The old trench bricks without field-stop, the CM300 and CM600 family and their relatives, are good for an ordinary DRSSTC and lose on long ramped pulses both thermally and on switching.
Superjunction MOSFETs are poor in a high frequency resonant circuit. Their non-linear Coss gives voltage overshoot and low efficiency even under soft switching.
Whether to parallel
Criterion: whether the gate drives are identical, because that is what decides sharing.
Budget no more than fifty per cent extra for a pair, and only when three things are true: the devices are matched, they share a heatsink, and their gate drives are identical. Different gate delay means one of them takes all the current.
What will get you
The numbers
- The crossover:
I²RagainstV_ce·I. Hundreds of amps in pulses favours the IGBT; moderate current at high frequency favours the MOSFET. - IGBT frequency ceiling: a few hundred kilohertz.
- TO-247 dependable peak: 250 to 300 A, and 250 for a long ontime.
- Paralleling: budget 1.5 times one device, not 2.
- SiC body diode forward drop: about 3.3 V.
- Voltage margin: about a third. From 320 V, 600 V parts.
What people actually fit, for a QCW at 420 kHz and up, from one builder's bench and worth checking on yours: IXXH75N60C3D1 and STGWA75H60DFB2 gave a strange waveform and were unreliable; AOK75B60D1, AOK60B65H2AL, FGA60N65SMD and IRGP50B60D1 worked.
What goes wrong
- Devices die weeks in, for no visible reason, well below
Tjmax. Not the peak temperature: the size of the swing. It tears bond wires and die attach over thousands of cycles, and it is covered with the bridge. - A paralleled pair where one device is much hotter. Gate drive mismatch. One of them is taking the current.
- An IGBT that will not turn off. Latch-up from a high collector current.
- Voltage overshoot and poor efficiency despite soft switching. Superjunction
Cossnon-linearity. Wrong family for a resonant circuit. - A SiC upgrade that performed worse. The body diode is in the resonant path every half cycle.
- A device that survived the bench and died on the arc. The datasheet number was a hard-switched millisecond pulse, not your duty.
Where next
- The bridge and what kills it, the failure mechanism in full.
- Reading a gate waveform, because an over-damped or ringing gate puts any of these devices through its linear region several times per transition.
- What the bridge does, if the half or full question is still open.
Every department diagram draws the bridge out rather than boxing it, because whether it is a full bridge or a half is the first decision, and what is in each leg is the second.