Hello, it has been a while, but i got some new fets, but some still heat up. Ordered a transistor tester (mk328), should arrive in 1-2 weeks. If after measuring they still heat up, what should what i do? Ive been told it could be cross-conduction. I think that could be possible, in the datasheet the rise and fall times are a little slower on the 38n20d compared to the 31n20d
Reputable parts distributor?
Do they heat randomly or is the heating associated with a specific bank of outputs?
Remember that you might have to adjust the CCS but that depends on the pattern of heating.
Do they heat randomly or is the heating associated with a specific bank of outputs?
Remember that you might have to adjust the CCS but that depends on the pattern of heating.
Yeah, ordered from tme.eu.
The heat seems to follow the fets, found that only changing one fet can make all others heat up more. only on the high side, low side stays stone cold.
The heat seems to follow the fets, found that only changing one fet can make all others heat up more. only on the high side, low side stays stone cold.
Are all of the FETs from the same production batch.
I don't know what TME-EU is (reputable or not).
I don't know what TME-EU is (reputable or not).
Yeah, all are the same batch. tme.eu is a retailer in europe, from what ive heard its reputable.
If you clamp the FETs to a heatsink (temporary heatsink is likely good enough), will the amp produce rail-rail oscillation and if so, does it produce audio?
That's OK.
DC coupling
5us/div
5v/div
negative probe on leg 3
probe tip on pin 1
post the waveforms you see on one of the cool low-side FETs and the waveform you have on one of the heating high-side FETs.
DC coupling
5us/div
5v/div
negative probe on leg 3
probe tip on pin 1
post the waveforms you see on one of the cool low-side FETs and the waveform you have on one of the heating high-side FETs.
huh, very odd looking. Probe on gate, negative on source
High side on fet which heats up:
low side which is cool:
High side on fet which heats up:
low side which is cool:
Both seem to be rising too slowly. Are the output FETs and gate resistors the original values and from reliable distributors?
The high-side has a step in the falling edge. This is OK in some instances but this one has too much amplitude at the top of that step because it's above the threshold voltage of the FETs.
What does the gate drive look like on the other side of the high-side gate resistors.
The high-side has a step in the falling edge. This is OK in some instances but this one has too much amplitude at the top of that step because it's above the threshold voltage of the FETs.
What does the gate drive look like on the other side of the high-side gate resistors.
The previous FETs were the 31n20d, current FETs are 38n20d from a reputable store, gate resistors are 47ohm and factory.
on the other side of the gate resistor it looks like this
on the other side of the gate resistor it looks like this
bands looks like red black black brown (either 10 or 20ohm depending how you look at it), but multimeter says 820ohm, exactly 5v across it
Confirm that R189 is within tolerance.
Desolder (at least) one terminal of R175 and recheck it. Yours looks like 1k but 820 is a possibility.
Desolder (at least) one terminal of R175 and recheck it. Yours looks like 1k but 820 is a possibility.
R175 indeed is a 820ohm, the grey band is on the bottom, barely visible, so it is within tolerance.
R189 also is within tolerance at 1.2k ohm
R189 also is within tolerance at 1.2k ohm