[SOLVED] [help] can mosfet work in linear (triode) region in pics (with op amps)?

[pover]

[help] can mosfet work in linear(triode) region in vccs(with op amp)?

HI,
I used the attached circuit to drive led about 10A. if mosfet operate in saturation region, the dissipation power of mosfet is large.
so is it possible that mosfet operate in triode region in vccs. and what is differences between them, for example In triode region will cause the current stability problem or mosfet broken.

 

[dick_freebird]

Re: [help] can mosfet work in linear(triode) region in vccs(with op amp)?

Somebody somewhere has the job of handling the voltage
drop. Too bad for them.

Yes, you can make a current source. But a current source
that only works right over a limited voltage range, isn't
a very good one unless your environment conforms to the
happy assumption.

Stability could be an issue especially when you get to the
margins, small signal gives way to large signal misbehaviors.
Gain is very variable. That kind of thing. Destructive, I doubt.

 

[FvM]

Re: [help] can mosfet work in linear(triode) region in vccs(with op amp)?

I'm not sure what kind of stability is addressed here. If you look at feedback loop stability, the MOSFET input capacitance can cause problems with high speed OPs and require additional compensation. Apart from this point, it's a well known and usually good working current source topology.

MOSFET power dissipation occurs according to requested current and applied voltage and doesn't depend on transistor operation region, provided the circuit is able to drive the current.

 

[pover]

Re: [help] can mosfet work in linear(triode) region in vccs(with op amp)?

Thanks, dick_freebird & FvM

but I want to know what is limited voltage range("But a current source
that only works right over a limited voltage range")

and MOSFET Power dissipation P_dis = Vds*Ids, the need Vds is smaller working in linear range than saturation. so the power will be reduced, isn't it?

BTW, In my testing board, there will be a periodic Pk-pk 50mA 50Mhz ripple reducing vds into linear range, is it the only negative factor working in the linear range?