Simplistic Mosfet HV Shunt Regs - Page 223

king4joy · 26th December 2011, 05:42 AM

I try to use small sinks just try to get the board into the amp box...seems not quite possible especially if I may use 1 board per channel in the future...just hope that this board with remote sensing, I can get by with putting the board in the PSU box (with about 0.5 meter wires connecting) without too much negative...

vgeorge · 26th December 2011, 06:25 AM

Seems you have to adjust your SSHV2 for two channels at 70mA then.
Maybe you could use the chassis as a sink for the 840, in order to save space inside?

AndrewT · 26th December 2011, 09:39 AM

What voltage is on the drain of these high voltage FETs?
The backplate of these FETs are able to be touched and prodded and wires dropped on etc.

vgeorge · 26th December 2011, 10:38 AM

The first fet drain is at Vin.
I didn' t took temperature readings, but with 50mA and 200V there was no problem touching the sink for extended period.

AndrewT · 26th December 2011, 11:50 AM

With 200V on the drain and the drain being within the thickness of the electrical isolator of the heatsink, be very careful about where you put tools and fingers.

king4joy · 27th December 2011, 02:27 AM

should we use two pieces of the isolator for high voltage??

AndrewT · 27th December 2011, 10:11 AM

The high voltage of itself is not a problem.
It's the accidental shorting of the copper backplate to anything at a different voltage that is the problem. Extra insulators cannot cure that.
The screwdriver tip will still span the gap from backplate to heatsink. The Finger can still touch the 200V.

luvdunhill · 27th December 2011, 02:23 PM

Plastic devices are the best choice here.

Tea-Bag · 27th December 2011, 02:59 PM

Quote:

Originally Posted by luvdunhill

Plastic devices are the best choice here.

Luvdunhill, what are you refering to - caps or insulators?

luvdunhill · 27th December 2011, 04:11 PM

Transistors.

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26th December 2011, 05:42 AM	#2221
king4joy diyAudio Member Join Date: Apr 2011	I try to use small sinks just try to get the board into the amp box...seems not quite possible especially if I may use 1 board per channel in the future...just hope that this board with remote sensing, I can get by with putting the board in the PSU box (with about 0.5 meter wires connecting) without too much negative...

26th December 2011, 06:25 AM	#2222
vgeorge diyAudio Member Join Date: Mar 2004 Location: poros island	Seems you have to adjust your SSHV2 for two channels at 70mA then. Maybe you could use the chassis as a sink for the 840, in order to save space inside?

26th December 2011, 09:39 AM	#2223
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	What voltage is on the drain of these high voltage FETs? The backplate of these FETs are able to be touched and prodded and wires dropped on etc.

26th December 2011, 10:38 AM	#2224
vgeorge diyAudio Member Join Date: Mar 2004 Location: poros island	The first fet drain is at Vin. I didn' t took temperature readings, but with 50mA and 200V there was no problem touching the sink for extended period.

26th December 2011, 11:50 AM	#2225
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	With 200V on the drain and the drain being within the thickness of the electrical isolator of the heatsink, be very careful about where you put tools and fingers.

27th December 2011, 02:27 AM	#2226
king4joy diyAudio Member Join Date: Apr 2011	should we use two pieces of the isolator for high voltage??

27th December 2011, 10:11 AM	#2227
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	The high voltage of itself is not a problem. It's the accidental shorting of the copper backplate to anything at a different voltage that is the problem. Extra insulators cannot cure that. The screwdriver tip will still span the gap from backplate to heatsink. The Finger can still touch the 200V.

27th December 2011, 02:23 PM	#2228
luvdunhill diyAudio Member Join Date: Jul 2006	Plastic devices are the best choice here.

27th December 2011, 04:11 PM	#2230
luvdunhill diyAudio Member Join Date: Jul 2006	Transistors.