Searching the "best" CCS

MikeB · 16th September 2006, 04:45 PM

I am looking for an "ideal" ccs, i attached a small collection of 9 different ccs circuits, all rated with a psrr. This db value is the voltage ripple visible at the 1k resistor with the power supply contaminated with 1v AC, all ccs giving ~3ma. The LED style is missing because i have no model...

Did i forget other / better circuits ? Right now the cascoded jfet-ccs seems to be the candidate. Number 9 is also very interesting as it is floating style like a single jfet-ccs.
What i want is a ccs with high psrr, but not too complicated.

Mike

leadbelly · 16th September 2006, 05:04 PM

Quote:

Originally posted by MikeB
I am looking for an "ideal" ccs...

What i want is a ccs with high psrr, but not too complicated.

Those are somewhat at odds. I have read references on this forum and AA that Gary Pimm's hybrid CCS is the cat's meow, but it takes some effort to implement. His MOSFET CCS is again very well respected, but it is more complex than those circuits you listed.

If you search for CCS or constant current, you will find MANY threads.

sam9 · 16th September 2006, 05:31 PM

As far as PSRR goes, Self presented some measurements indicating that adding a decoupling cap impoved the PSRR of several different CCS's to where they had about the same low figure. He claimed, but didn't present data tables, that a sufficiently large cap would drive the PSRR too low for him to measure. And below what any CCS achieved on it's own.

If this is valid, the choice would be to choose the CCS that gets you the best current stability then add the decoupling chain.

MikeB · 16th September 2006, 05:48 PM

I forgot to mention, i want to have the psrr high down to very low frequency (practically DC). That's why none of the circuits has any cap.

I suspect PSRR at low frequencies to be responsible for proper reproduced dynamics.

Mike

sawreyrw · 16th September 2006, 05:56 PM

You might consider an LM334. By itself it doesn't have a real good PSRR, but the data sheet shows a circuit with a FET and this should have excellent PSRR.

BTW, how can a cap improve the PSRR of a CCS?

jcx · 16th September 2006, 06:01 PM

MikeB · 16th September 2006, 06:10 PM

Quote:

Originally posted by sawreyrw
BTW, how can a cap improve the PSRR of a CCS?

By filtering the voltage supplied to the ccs...

Jcx, can you repeat sims using AC-sweep ? (maybe 0.01hz to 100khz)
I would love the left circuit if jfets wouldn't have that limited max voltage rating.

Mike

leadbelly · 16th September 2006, 06:11 PM

Quote:

Originally posted by jcx

Nice!

tvi · 16th September 2006, 06:19 PM

I posted this sometime ago, you might find it of interest
Constant Current Source article (Old)

Regards
James

jcx · 16th September 2006, 06:27 PM

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16th September 2006, 05:31 PM	#3
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	As far as PSRR goes, Self presented some measurements indicating that adding a decoupling cap impoved the PSRR of several different CCS's to where they had about the same low figure. He claimed, but didn't present data tables, that a sufficiently large cap would drive the PSRR too low for him to measure. And below what any CCS achieved on it's own. If this is valid, the choice would be to choose the CCS that gets you the best current stability then add the decoupling chain.

16th September 2006, 05:48 PM	#4
MikeB diyAudio Member Join Date: Apr 2004 Location: Gütersloh	I forgot to mention, i want to have the psrr high down to very low frequency (practically DC). That's why none of the circuits has any cap. I suspect PSRR at low frequencies to be responsible for proper reproduced dynamics. Mike

16th September 2006, 05:56 PM	#5
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	You might consider an LM334. By itself it doesn't have a real good PSRR, but the data sheet shows a circuit with a FET and this should have excellent PSRR. BTW, how can a cap improve the PSRR of a CCS?

16th September 2006, 06:01 PM	#6
jcx diyAudio Member Join Date: Feb 2003 Location: ..

16th September 2006, 06:27 PM	#10
jcx diyAudio Member Join Date: Feb 2003 Location: ..

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