Depleation Mode MOSFET current sink.

rlaury · 8th July 2011, 10:47 PM

Hi Group:

Can anyone point me to the proper way to calculate the resistor value to
set the current in a simple 1 depletion mode-MOSFET current sink? I know it's the voltage drop across the resistor, but do I set this to the threshold voltage or what. I've been using spice to get me in the ballpark but I would like to know the correct way.

Any help appreciated.

RonL

jcx · 8th July 2011, 11:07 PM

it depends on device gm, Vth which vary part-to-part so you really have to select the R once you have the mosfet in hand

tack solder a pot in place and adjust for the desired current, measure it and install the same value fixed R

rlaury · 8th July 2011, 11:45 PM

Thanks. That's what I've kinda been doing. I guess I'll have to bin the parts by Gm.

RonL

sawreyrw · 9th July 2011, 02:21 PM

The source current will be (Vgate-Vgs)/Rs. Of course Vgs varies from part to part and is a function of Is.

AndrewT · 9th July 2011, 02:54 PM

How do we find "depletion" mode mosFETs?

I searched my datasheet file and the only depletion mode are lateral Power devices.

lineup · 9th July 2011, 03:04 PM

Supertex has got depletion mode MOSFETs.
And spice models for them.

Supertex: Selector Guides

For example DN2530 and DN2540
There are TO-92 and TO-220

jcx · 03:24 PM

IXYS also has some higher V, higher current devices - we realy should start seeing these in hybrid SS + tube amp, maybe electrstatic amp designs soon

http://www.ixys.com/product_portfoli...2Easpx%3Fi%3D3

8th July 2011, 10:47 PM	#1
rlaury diyAudio Member Join Date: Sep 2005	Depleation Mode MOSFET current sink. Hi Group: Can anyone point me to the proper way to calculate the resistor value to set the current in a simple 1 depletion mode-MOSFET current sink? I know it's the voltage drop across the resistor, but do I set this to the threshold voltage or what. I've been using spice to get me in the ballpark but I would like to know the correct way. Any help appreciated. RonL

9th July 2011, 02:54 PM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	How do we find "depletion" mode mosFETs? I searched my datasheet file and the only depletion mode are lateral Power devices. __________________ regards Andrew T.

9th July 2011, 03:04 PM	#6
lineup diyAudio Member Join Date: Dec 2005 Location: the north	Supertex has got depletion mode MOSFETs. And spice models for them. Supertex: Selector Guides For example DN2530 and DN2540 There are TO-92 and TO-220 __________________ lineup

9th July 2011, 03:21 PM	#7
jcx diyAudio Member Join Date: Feb 2003 Location: ..	IXYS also has some higher V, higher current devices - we realy should start seeing these in hybrid SS + tube amp, maybe electrstatic amp designs soon http://www.ixys.com/product_portfoli...2Easpx%3Fi%3D3 Last edited by jcx; 9th July 2011 at 03:24 PM.

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8th July 2011, 11:07 PM	#2
jcx diyAudio Member Join Date: Feb 2003 Location: ..	it depends on device gm, Vth which vary part-to-part so you really have to select the R once you have the mosfet in hand tack solder a pot in place and adjust for the desired current, measure it and install the same value fixed R

8th July 2011, 11:45 PM	#3
rlaury diyAudio Member Join Date: Sep 2005	Thanks. That's what I've kinda been doing. I guess I'll have to bin the parts by Gm. RonL

9th July 2011, 02:21 PM	#4
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	The source current will be (Vgate-Vgs)/Rs. Of course Vgs varies from part to part and is a function of Is.

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