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Old 30th October 2012, 01:32 PM   #11
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Old 30th October 2012, 02:54 PM   #12
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increase R3 to 510R

be back then
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Old 31st October 2012, 06:20 AM   #13
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not sure it it's relevant, but i just checked and found i'm using IRFP240 from IR,
could this explain the difference,
when i get back from work i'll try increasing R3, but with these changes will i upset NP's delicate balance in the design?
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Old 31st October 2012, 09:08 AM   #14
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Quote:
Originally Posted by gbullimore View Post
not sure it it's relevant, but i just checked and found i'm using IRFP240 from IR,
could this explain the difference,
....
no ,irrelevant

Quote:
Originally Posted by gbullimore View Post
....
when i get back from work i'll try increasing R3, but with these changes will i upset NP's delicate balance in the design?

no
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Old 31st October 2012, 11:50 AM   #15
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thanks again for the feedback,
tried R3=510R and still no luck,
with V+ at 40v, i can get the Bias to 0.89v.
but i checked again the wall voltage, and when running from the wall the V+ is 38.5
in this condition i can only get 0.68v Bias.
should i change R3 to 730R (the original 390 + 220R) or more like 780R (390+390R),
or altogether more brave at 1k,
or should i be looking at reducing R6 below 110R ?
starting to worry a little at drifting so far from stock values.

would a change in brand / type of IRF610 be better?
although it's be nice to get it up and running quickly without having to order more FET's.

by the way i have not yet changed R7, will this affect the bias much?
i'm seeing ~25v at the output cap,
but i see almost equal bias on all 4 devices
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Old 31st October 2012, 12:28 PM   #16
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Update,
I realized i'd been stupid by leaving R7,
I changed it out to 10k, now i can adjust to 23v at the output cap, but now the bias maxes out at 0.97v,
I guess if i change R7 to 47k i might be there, i might even need to undo the R3 or even R6 change.
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Old 31st October 2012, 01:24 PM   #17
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feel free to experiment
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