Heating in LLC HB mosfets ?

[Mark Tillotson]

I borrowed a better scope at work and made a few measurments.

This is a test-setup with a DC-source instead of the mains.

The two gate-signals look fine to me: ( shot taken without anything connected to the HB-midpoint, to get a "clean" reading).

The "clean" reading is not relevant, the waveforms under load are all-important due to the plateau charging step. It takes more charge on the gate to form a channel with load current flowing.

One other thing I note is the very low voltage rating of 200V for a mains component. If the supply is 120V, the rectified rail is 170V, much too close to 200V giving that the inductor will ring. Something more like 400V rating seems wise, perhaps IFRP360? Avalanche breakdown currents generate huge amounts of heat in a MOSFET.

 

[TroelsM]

The "clean" reading is not relevant, the waveforms under load are all-important due to the plateau charging step. It takes more charge on the gate to form a channel with load current flowing.

Not sure what charging-step you are talking about? - if its the gate-voltage: this a resonant design operating in ZVS so we have no step on the gate-voltage at turn-on.

One other thing I note is the very low voltage rating of 200V for a mains component. If the supply is 120V, the rectified rail is 170V, much too close to 200V giving that the inductor will ring. Something more like 400V rating seems wise, perhaps IFRP360? Avalanche breakdown currents generate huge amounts of heat in a MOSFET.

Its a 230Vac design and components are rated to fit. The schematic may be a bit misleading.

Kind regards TroelsM