Positive feedback.
John
How to bias a CS mosfet
Aug 03, 2011
280 Replies
Oops! Got my OA inputs swapped! Redo:
o-----------------------------------o | | .-. .-. | | GND | | | | R | | | '-' --- '-' | --- | . . . | | ___ | | .-----'------|___|--------------o | | | | | ' | | |\| ||-+ |----|----|-\ ___ ||------|___|---------||-+ | -----|+/ | | |/| | | ' .-. .-. | | | | | | | | R '-' '-' | | | | === === GND GND (created by AACircuit v1.28.6 beta 04/19/05
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Thanks, John.
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Thanks! :-)
Version 4
SHEET 1 880 680
WIRE -112 -96 -208 -96
WIRE 80 -96 -112 -96
WIRE 400 -96 80 -96
WIRE 400 -80 400 -96
WIRE -112 -32 -112 -96
WIRE 400 32 400 0
WIRE 400 32 0 32
WIRE 400 64 400 32
WIRE 80 112 80 -96
WIRE -112 128 -112 48
WIRE 48 128 -112 128
WIRE 352 144 112 144
WIRE 0 160 0 32
WIRE 48 160 0 160
WIRE -208 192 -208 -96
WIRE -112 192 -112 128
WIRE 0 208 0 160
WIRE 400 208 400 160
WIRE -208 336 -208 272
WIRE -112 336 -112 272
WIRE -112 336 -208 336
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WIRE 0 336 -112 336
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WIRE 80 336 0 336
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WIRE 400 336 80 336
WIRE -208 400 -208 336
FLAG -208 400 0
SYMBOL voltage -208 176 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 30 0 1 0 1.5)
SYMBOL Opamps\\LT1037 80 80 R0
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SYMBOL res -128 -48 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res -128 176 R0
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL nmos 352 64 R0
SYMATTR InstName M1
SYMATTR Value IRF7468
SYMBOL res 384 -96 R0
SYMATTR InstName R5
SYMATTR Value 1000
SYMBOL cap -16 208 R0
SYMATTR InstName C1
SYMATTR Value 10µ
SYMBOL res 384 192 R0
SYMATTR InstName R3
SYMATTR Value 500
TEXT -194 368 Left 0 !.tran 1
Thanks.
Okay, so it needs a little (.1uF) from OA output to inverting input.
BTW, it also needs some resistance between OA output and the FET gate so he can have a point to insert his signal.
OK, I missed that part.
Thanks! :-)
JF and JT meet a lot of those criteria, but aren't likely to actually be dangerous. JT has threatened me with violence (and with car racing! Whatta man!) but I don't expect the old geeze will actually show up at my door and threaten me with his cane.
John
I keep wondering which of the two would be most likely to shoot me in the back while I was unarmed had I been their side of the pond.
That will complicate the loop dynamics some. And the DC servo clearly fights the signal, over some bandwidth range.
John
What do you recommend to fix it?
John S
IMO an op-amp as a bias generator for a MOSFET is way OTT when a single BJT,
4 resistors and an electrolytic will do the job just fine.
Can you post a schematic?
I wonder if you really mean: Is there any way to bias a mosfet CS
*using* source degeneration so that ....If you mean using only source degeneration to achieve your goal, I'm not aware of any.
Its simple enough to describe - and I already did.
Do you mean the common-base PNP thing?
John
Schematic, please?
A picture is worth a thousand words, so why don't you just shut the
fuck up and post the picture?
"Old fart" has come to mean useless old fogey. It's like "crap" has come to mean "junk."
Get used to both terms.
John
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