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source resistor
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Old 6th February 2007, 10:52 AM   #1
svemir is offline svemir  Croatia
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Default source resistor

I have built Aleph 5 before 6 months and it works fine. But i notice that one heatsink heats a litle bit more than the other so I measure voltage accros source resistors and all vlotages are around 0.6 and 0.65V but on one source res. is 0.8 V. So what could be the problem mosfet Off-toleranc of source resistor or something else?
Sorry obout my bad english.
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Old 6th February 2007, 11:09 AM   #2
wuffwaff is offline wuffwaff  Netherlands
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Hi,

if its just one than probably the fet wasnt matched good enough.

William
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Old 6th February 2007, 12:21 PM   #3
svemir is offline svemir  Croatia
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Could it be off tolerance of source resistor rather than the unmatched irfp240. Thats the first thing that came on my mind?
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Old 6th February 2007, 01:11 PM   #4
sek is offline sek  Germany
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That would indicate a resistance value about 33% off. Unlikely, but possible. You can actually measure this in-circuit.

Indeed, a FET which has it's channel "opened wider" (!?) due to unmatched gate characteristics is much more likely, as just a little deviation from the rest of it's bank would make this FET conduct more of the total current than each of the other FETs in this bank. We're talking 33% here...

Cheers.
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Old 6th February 2007, 01:22 PM   #5
svemir is offline svemir  Croatia
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On R42
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Old 6th February 2007, 01:22 PM   #6
svemir is offline svemir  Croatia
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ok thank for the advice FET is going out.
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