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Old 9th April 2012, 03:50 PM   #2851
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It's OK if I have continuity between IRF840 & heatsink? I use two mica pads & a nylon nut & screw what is no way to isolate?
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Old 9th April 2012, 04:02 PM   #2852
Salas is offline Salas  Greece
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Its not OK to have continuity between 840's metal tab and sink.
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Old 9th April 2012, 04:04 PM   #2853
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Use a dummy load around 5k, to be sure there is no other mistake and test.
Do not fire the reg until you isolate it from the sink. You have the full output voltage on the sink now, which is kind of dangerous - even lethal.
I use a sil pad and screw with washer and no problems so far.
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Old 9th April 2012, 04:54 PM   #2854
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Quote:
Originally Posted by Salas View Post
Its not OK to have continuity between 840's metal tab and sink.
Isolated


Quote:
Originally Posted by vgeorge View Post
Use a dummy load around 5k, to be sure there is no other mistake and test.
Do not fire the reg until you isolate it from the sink. You have the full output voltage on the sink now, which is kind of dangerous - even lethal.
I use a sil pad and screw with washer and no problems so far.
I use 4K75 as dummy load, Vout max 17VDC, TP 600mV = 60mA

I'm afraid IRF840 isn't working wich voltage have to measure VGS?

Last edited by merlin el mago; 9th April 2012 at 05:13 PM.
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Old 9th April 2012, 05:20 PM   #2855
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Use 10k to be light and try turning the trimmers. Led should be on.
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Old 9th April 2012, 05:27 PM   #2856
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Voltage between gate and source should be 3,5V to 5V.
Check also that you do not have long leads between last cap and reg.
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Old 9th April 2012, 05:38 PM   #2857
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With 10K dummy load (two 4k75 in series) fixed 17 Vout can go up or low using R11 1K trimmer
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Old 9th April 2012, 05:47 PM   #2858
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Quote:
Originally Posted by vgeorge View Post
Voltage between gate and source should be 3,5V to 5V.
Check also that you do not have long leads between last cap and reg.
VGS 3.9V
4-5cm
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Old 9th April 2012, 05:57 PM   #2859
vgeorge is offline vgeorge  Greece
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Then the 840 is OK.
Check the BE voltage of the SA1381. Should be around 0,6V.
Led is lit?
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Old 9th April 2012, 06:05 PM   #2860
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0,15V
Yes
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