weirdly behaving mosfet

I agree but, the whole saga started becuase the fet behaved like that when mounted in a Peavey class-d amplifer, that has +/-1A gate drive and a 6.8R gate resistor

@gmail.com:

in:

arkin:

nsen

down, a dual lab supply for the 12V and the gate

e gate voltage

e, load is

o zero verified with a meter doesn't turn off the FET the current just drop s to 200mA and the fet start cooking

of MHz

tly

d amplifier

is demo is unrepresentative of the MOSFET properly mounted.

n mounted in a Peavey class-d amplifer, that has +/-1A gate drive and a 6.8 R

Okay, that part is a defective design and needs to be blacklisted. Whatever the self-oscillation is, it must be high, like on the order of 100MHz, and that has always presented a problem with channel currents becoming concent rated in a smaller area, so the effect on heating and damage is much more t han a power supply readout would indicate.

Den onsdag den 27. september 2017 kl. 19.56.20 UTC+2 skrev bloggs.fred...@g mail.com:

..@gmail.com:

rkin:

sen

Larkin:

tensen

l-down, a dual lab supply for the 12V and the gate

the gate voltage

rom

age, load is

to zero verified with a meter doesn't turn off the FET the current just dr ops to 200mA and the fet start cooking

e of MHz

ently

s-d amplifier

This demo is unrepresentative of the MOSFET properly mounted.

hen mounted in a Peavey class-d amplifer, that has +/-1A gate drive and a 6 .8R

er the self-oscillation is, it must be high, like on the order of 100MHz, a nd that has always presented a problem with channel currents becoming conce ntrated in a smaller area, so the effect on heating and damage is much more than a power supply readout would indicate.

he showed it on a scope, a little over 2MHz in the bench test

te:

e:

sse

a dual lab supply for the 12V and the gate

e voltage

in linear

ons.

the gate.

left a space on the printed circuit board where you could fit a resistor b ig enough to stop the oscillation. We had enough trouble with oscillating M OSFETs (sometimes when purchasing changed the supplier without telling engi neering) that this became something hard to distinguish from a company stan dard.

caused by the gate capacitance and lead inductance R>2 x sqrt(L/C). There w as never a problem with a FET oscillating on its own with its gate driven b y a broadband low impedance source.

That wasn't our experience. Maybe our load resistors were wire-wound and in ductive, or something equally trivial, but there were a dozen or so enginee rs who ended up being neurotic about the problem ...