How can I tell if MRFE6VS25N is broken or not

otpisani · ‎05-31-2023

I read on net that LDMOS transistors need to have high resistance to be valid, they mention MegaOhms, my readings on g-s is 1.9 KOhms and on d-s 137KOhms, mosfet is on the board. Presume that you have information what is resistance for MRFE6VS25N.

ErikaC · ‎06-01-2023

Hello,

When the devices fail due to electrical overstress, either in over-voltage, over-current, excessive VSWR, oscillation or any typical failure manner, the external indicator is 99% of the time, open circuit on the drain to source and a low value impedance on the gate to source connection. You may see if you can test the device if they have opens, or shorts.

Good parts have Mega ohms of gate source resistance and blown parts have sub Kilo ohms of impedance, typically in the 10's to 100's. The silicon actually shorts out but since most applications have a Vdd current source that feeds multiple devices, there is enough instantaneous Vdd drain current available to fuse open all drain wires on the blown device. Gate bias supplies do not typically have as much current capability so the gate wire remain intact and one sees the true leaky, damaged gates. The drain fingers and gate fingers somewhat overlap so when the drains go, they take out the gates also.

otpisani · ‎06-01-2023

Thanks for that, like to further explanation more. I burned voltage regulator with excessive voltage, but with input voltage, presume that voltage regulator didn't react on time, and maybe damage was made out of voltage regulator circuit also, and that includes mosfet transistor, because now with new regulator, and with same values IN voltage 12V, I can't see any gain on drain, or output SMA connector, and resistance between gate and source is around 1.93KOhms, but with transistor on board.

Question would be, if I replace mosfet, what would be ideal current on gate side in idle operation, they have some very bad trimmer before gate, and current is around 0.4A now, that is alright, or what is best default current for gate side in idle operation