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Zen Mod
Official Court Jester
diyAudio Member

Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Quote:
 Originally Posted by nashbap ...... Now could you help me to figure out from this how to calculate the turn on Vgs needed for the IRFP240 fet which I believe is about 4.5V? Thanks. Nash
Vgs needed for common FW range of Iq is around-ish 4V
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nashbap
diyAudio Member

Join Date: Jul 2012
Location: New Jersey USA
Quote:
 Originally Posted by Zen Mod Vgs needed for common FW range of Iq is around-ish 4V
ZM what I meant is how does this circuit produce the approx 4Vish ?

I understand that the voltage across the 5k pot is the same as the zener voltage and that the current thru the pot is 1.36ma as per your example but how does this translate into getting the desired Vgs?

thanks again.

Nash

palstanturhin
diyAudio Member

Join Date: Jun 2011
Quote:
 Originally Posted by nashbap ZM what I meant is how does this circuit produce the approx 4Vish ? I understand that the voltage across the 5k pot is the same as the zener voltage and that the current thru the pot is 1.36ma as per your example but how does this translate into getting the desired Vgs? thanks again. Nash
The trimmer is the voltage divider for the Zener voltage.
You take the gate voltage for the mosfets from the trimmer viper.

nashbap
diyAudio Member

Join Date: Jul 2012
Location: New Jersey USA
Quote:
 Originally Posted by palstanturhin The trimmer is the voltage divider for the Zener voltage. You take the gate voltage for the mosfets from the trimmer viper.
OK but it goes thru R9/10 and R11/12 before reaching the gate. So how does one calculate the Vgs ?

thanks. nash

 14th September 2015, 12:47 PM #45 Zen Mod   Official Court Jester diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain just do it it's pretty obvious .... from pot viper to gate there is no significant current , so voltage at wiper is practicaly same at gate __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
nashbap
diyAudio Member

Join Date: Jul 2012
Location: New Jersey USA
Quote:
 Originally Posted by Zen Mod just do it it's pretty obvious .... from pot viper to gate there is no significant current , so voltage at wiper is practicaly same at gate

OK got it. Thanks. Nash

audiok
diyAudio Member

Join Date: Oct 2008
My I use LU1014D at the output stage ?
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 16th September 2015, 06:08 AM #48 2 picoDumbs   diyAudio Member     Join Date: Sep 2013 Lu1014d is depletion mode mosfet. You would also need to cascode to dissipate power. You would need to completely change the circuit to make it work __________________ "If you leave this point unattached to some circuitry, an ideal constant current source will emit a small lightning bolt which will travel until it connects to something." Nelson Pass
 16th September 2015, 06:21 AM #49 audiok   diyAudio Member     Join Date: Oct 2008 Thanks you comment. Would you please show me the cascade circuit. Thank you.
 16th September 2015, 07:19 AM #50 2 picoDumbs   diyAudio Member     Join Date: Sep 2013 Look at Zen 8. Probably best to look at that first, as it directly relates to lu1014d. __________________ "If you leave this point unattached to some circuitry, an ideal constant current source will emit a small lightning bolt which will travel until it connects to something." Nelson Pass

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