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Old 16th July 2011, 05:17 AM   #121
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I still dont understand how these didn't work. input capacitance was almost half on the new fets (28n15) compared to the ones that were in there sfh154, the turn on/off and delay were higher but still the worst one is 250ns which is still good for a signal in the mhz range...

i just hope the driver isn't still broken somehow
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Old 16th July 2011, 05:28 AM   #122
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This is why I always recommend getting an amp working with the originals or those which you know will work. I've found it to be very difficult to predict what will and what will not work in a class D amp. It can even be a problem in non class D amps. Look at the example of the IRF540N as a sub for the IRF540 in class AB amps. It seems like the 540N would be a drop in replacement but it can cause all sorts of different problems.
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Old 16th July 2011, 05:30 AM   #123
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crazyness... so theres not any particular specification that is off? just gotta kinda design around a fet?
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Old 16th July 2011, 05:36 AM   #124
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There are some amps that I've tried about 8 different FETs (originals obsolete) and only one would work. The IRF3415 was one of the FETs that was more likely to work than any others. Another that seems to work when no others will work (particularly in 4080 based amps) is the IRF3710Z (must have the Z). In the case of the 3710, the new parts with the original part number (no Z), would not work. I looked at specs until my brain hurt and could find no single spec that would make one more suitable than others.
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Old 16th July 2011, 05:38 AM   #125
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crazy; 4080 is the chip that makes a class d amp class d?
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Old 16th July 2011, 05:41 AM   #126
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4080 = HIP4080.

It's a class D driver IC that's used extensively in amps under 1500 watts.
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Old 16th July 2011, 05:42 AM   #127
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ahh thats what i thought...

why under 1500 watts?
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Old 16th July 2011, 05:48 AM   #128
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Because there's a limit to the supply voltage that it can withstand (80v, not 80v, 80v) and a limit to the number of FETs it can drive.
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Old 16th July 2011, 05:49 AM   #129
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ahhh i see
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Old 7th January 2012, 08:19 PM   #130
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Quote:
Originally Posted by gwada971 View Post
replaces by sfh154 irfp250 and it will work we need to change the resistance certainly power 4watt 0.1ohm
well I finally got around to messing with this amp again. I replaced all the fets with IRFP250s and still no go. i dont know what resistance you were talking about to change. As soon as i apply power to the remote lead the amp pulses and pulls down my 3a power supply pretty good. q208 and q209 got warm after about 2sec the other outputs didnt seem to warm up any...

any more ideas?
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