Replacement mosfets for car amp - Page 2 - diyAudio
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Old 27th November 2004, 08:02 PM   #11
djQUAN is offline djQUAN  Philippines
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I have built a few SMPS's and a car amp (200W, 500W) and that circuit is similar to the one I used.

I don't think 22R is too small. I used 100R and others use 47R. with the drivers I used in my schematic (www.djquan.angelcities.com/smps.html)the 220R resistors are 1k and gate resistors are 100R. the PNP transistors are 2N3906. I was able to drive three pairs of power mosfets for the 500W SMPS. the MOSFETS I used are 90A each(2 pairs for 200W amps, and 110A each(three pairs for 500W amp).

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djQuan - i could also get IRFZ 44 or 46, they have 49 / 53 Amperes. Should i take one of these?
they are ok. just make sure the gate-source capacitance is not too large in comparison to the originals.
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Old 27th November 2004, 09:20 PM   #12
andey is offline andey  Germany
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What do you mean, "a buffer". How to buffer what where?
Why do i need that?

here's more from the psu:
M = mosfet, T= the blown transistors i replaced with BC639.

edit: picture removed at member's request
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Old 27th November 2004, 09:25 PM   #13
djQUAN is offline djQUAN  Philippines
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a buffer is the PNP transistor. it enables the output of the TL494 to drive the gates.
you don't need those since the circuit already has them.

are you sure te replacement has the same pinouts to the originals?

from what I know, 2SA transistors are ECB and BC series are CBE.
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Old 27th November 2004, 10:40 PM   #14
andey is offline andey  Germany
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The BC 640 is a special one that has ECB. I had to do with it days ago and i remembered it had the Base on the side, so that was the first fitting trans. i had in mind.

I'll build the amp up with 10x 22R and IRFZ46N (53A) next week and give you feedback.

Thank you so much for that fast help and competence.
I hope i can pay back someday.


Does anyone have a hint on how the whole thing could burn?
And how i could prevent that in future? The Amp's power cable as the amp itself were properly fused, no fuse tripped. I shut off by hand :/
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Old 28th November 2004, 02:37 PM   #15
andey is offline andey  Germany
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The input capacitance of the original Mosfets is 1200pf typ, 1600pf max.

the input capacitance of the irzf46n replacement is 1700 typ.
max is not given.

is this too much?
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Old 29th November 2004, 10:59 AM   #16
andey is offline andey  Germany
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the schematic is back on. i asked jbl if i may post it here not to run in trouble.
Attached Images
File Type: jpg image7.jpg (53.6 KB, 95 views)
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Old 29th November 2004, 11:04 AM   #17
djQUAN is offline djQUAN  Philippines
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I think it would be fine. if unsure, you could buy a few and use for the first part of the powersupply and the high power without mosfets.
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Old 29th November 2004, 12:28 PM   #18
quasi is offline quasi  Australia
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Default Go ahead

I have looked at the specs on both FETS and cannot see any problem in using them.

When looking at how the FETS are driven (in the schematic) the slightly higher capacitance will not be a problem.

Cheers
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Old 29th November 2004, 10:05 PM   #19
andey is offline andey  Germany
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THANK YOU ALL
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