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I have a couple of questions regarding the use of Gallium Nitride MOSFET devices in a DC/DC converter design of mine. My topology is an LCC full bridge converter.

My knowledge is not at expert level so if anything I say is incorrect, please correct me. Typically in these converters, with Silicon devices, the body diode of the device acts as a freewheeling diode to resonant current when the switches are off. However, in Gallium MOSFETs, there is NO body diode.

Furthermore, typically to remove turn-off losses, capacitor/resistor lossy snubbers are connected in parallel to slow down the dv/dt of the switch and to avoid hard-switching at turn-off. However, since Gallium Nitride devices have no reverse recovery current - will the lossy snubbers be needed?

My questions are twofold:

  • How do Gallium Nitride devices commutate current when they are switched off? Will an external diode need to be included to provide a current path in this situation?

  • Is there any point using snubber networks across full bridge resonant circuits that include Galium devices if there is no reverse recovery charge? Or are they lossless under switch off anyway? Is there any point soft-switching GaN devices at all?

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  • \$\begingroup\$ GaN devices are highly susceptible to parasitic inductance which can cause ringing. Designing with them requires attention to detail which differs from Silicon devices. See mouser.co.uk/applications/gan-power-devices for a decent read. \$\endgroup\$ – Peter Smith Jul 11 at 11:12
  • \$\begingroup\$ GaN HEMT doesn't have an intrinsic diode, but it conducts in reverse. GaN need very comprehensive projecting phase, but then you get a tiny and powerfull device. \$\endgroup\$ – Marko Buršič Jul 11 at 11:26
  • \$\begingroup\$ I'm not sure I understand what you mean by projecting phase? To confirm then, an external diode won't be needed because the GaN can conduct in reverse? What about snubbers? \$\endgroup\$ – jvnlendm Jul 11 at 13:11
  • \$\begingroup\$ actually, if it can conduct in reverse that does not mean it will not damage the circuit usually you set up a diode for the reverse current to have a path to follow without damaging your switch. Snubbers have a purpose, depending on what you are doing you may or not need one. if your current is not rising as fast as you like, if you have uneven voltage distribution in series it can help and some ringing effects can be compensated, but the circuit needs a clear goal to be designed. \$\endgroup\$ – Juan Jul 16 at 0:57

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