I've noticed that when repairing amps recently with my last few orders of FDA24N40F's I from Mouser, that the sections I am replacing with the new parts, are heating up faster than sections with stock parts still installed. I am replacing entire sections driven by each driver IC, and I have consistently noticed temps 10-15* hotter than non-repaired sections among multiple amplifiers.
After noticing the difference on my last amplifier, I confirmed my suspicions by going back in and replacing the remaining banks with the new replacements. I changed nothing else. I then noticed the amplifier heated up evenly after all banks were changed, however, it heated up faster than normal.
The amplifiers function normally, no excessive idle current draw, no DC offset issues, and have gone through load tests with no issues. Heated them up to around 130-140*F multiple times with no issues other than the un-even and slightly faster warm up where the new parts were installed.
Any thoughts?
After noticing the difference on my last amplifier, I confirmed my suspicions by going back in and replacing the remaining banks with the new replacements. I changed nothing else. I then noticed the amplifier heated up evenly after all banks were changed, however, it heated up faster than normal.
The amplifiers function normally, no excessive idle current draw, no DC offset issues, and have gone through load tests with no issues. Heated them up to around 130-140*F multiple times with no issues other than the un-even and slightly faster warm up where the new parts were installed.
Any thoughts?
Some circuit manufacturers test them individually and match the pairs by their unique characteristics to reduce heat and consumption. I understand that it is the replacement FET that heats up and not the original ones but I don't know the original circuit design you are dealing with. If I was you, I'd build a simple wire circuit with all of your FDA24N40F FETs to test them separately and see first of all whether they do the specs. If there are significant issues, I would contact Fairchild first. Good luck.
That I understand mate, but how did you test them? You can still have a blown gate while it conducts DC perfectly. A practical example: here is an IRFP460 on my bench, that I blown, with a slightly different Vt than its 3 other brothers that it arrived with. It conducts when the gate is on, but when I put it on a PWM there is a crazy high frequency ringing in the pulses and heats up really fast for minimal current unless the others. Not to mention that its PWM performance is around 10% of the normal.
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