Simplistic Mosfet HV Shunt Regs - Page 286

merlin el mago · 9th April 2012, 02:50 PM

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?

Salas · 9th April 2012, 03:02 PM

Its not OK to have continuity between 840's metal tab and sink.

vgeorge · 9th April 2012, 03:04 PM

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.

merlin el mago · 04:13 PM

Quote:

Originally Posted by Salas

Its not OK to have continuity between 840's metal tab and sink.

Isolated

Quote:

Originally Posted by vgeorge

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?

Salas · 9th April 2012, 04:20 PM

Use 10k to be light and try turning the trimmers. Led should be on.

vgeorge · 9th April 2012, 04:27 PM

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.

merlin el mago · 9th April 2012, 04:38 PM

With 10K dummy load (two 4k75 in series) fixed 17 Vout can go up or low using R11 1K trimmer

merlin el mago · 9th April 2012, 04:47 PM

Quote:

Originally Posted by vgeorge

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

vgeorge · 9th April 2012, 04:57 PM

Then the 840 is OK.
Check the BE voltage of the SA1381. Should be around 0,6V.
Led is lit?

merlin el mago · 9th April 2012, 05:05 PM

0,15V
Yes

9th April 2012, 03:04 PM	#2853
vgeorge diyAudio Member Join Date: Mar 2004 Location: poros island	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. __________________ "Without deviations from the norm, progress is not possible" - Frank Zappa

9th April 2012, 04:27 PM	#2856
vgeorge diyAudio Member Join Date: Mar 2004 Location: poros island	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. __________________ "Without deviations from the norm, progress is not possible" - Frank Zappa

9th April 2012, 04:57 PM	#2859
vgeorge diyAudio Member Join Date: Mar 2004 Location: poros island	Then the 840 is OK. Check the BE voltage of the SA1381. Should be around 0,6V. Led is lit? __________________ "Without deviations from the norm, progress is not possible" - Frank Zappa

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9th April 2012, 02:50 PM	#2851
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Catalonia new Europe state	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?

9th April 2012, 03:02 PM	#2852
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Its not OK to have continuity between 840's metal tab and sink.

9th April 2012, 04:20 PM	#2855
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Use 10k to be light and try turning the trimmers. Led should be on.

9th April 2012, 04:38 PM	#2857
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Catalonia new Europe state	With 10K dummy load (two 4k75 in series) fixed 17 Vout can go up or low using R11 1K trimmer

9th April 2012, 05:05 PM	#2860
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Catalonia new Europe state	0,15V Yes

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