Searching the "best" CCS

[MikeB]

Originally posted by kubeek
MikeB, what simulation software did you use for the initial measurements?

I used some PSpice version... I really need to switch to LTspice. Orcad might be At least i don't make any profit.

Mike

[gerhard]

Originally posted by dshortt9
Not what I meant. Imagine stacking 2 CR300 diodes. A good thing or not?

Probably not. Best thing that could happen would be twice the
impedance. There are ways to get more for doubling the
investment.

More probable is, that the diode with the slightly smaller current value
determines the current that flows and the second does nothing but
stealing voltage headroom from the first.

The result would be worse performance than using the first diode
alone. This is especially true if you have only a low voltage to
spend; the situation where a good current source would be needed most.


Gerhard

[sajti]

Originally posted by MikeB
I made more sims, also adding the "self cascoding" jfet ccs. (see attachment)
The self cascoding shows an impressive -114db...

Than i ran a transient analysis to check stability of these circuits.
I quickly rejected the "self cascoding", it has ringing like hell, asking for problems. Also i rejected all circuits showing any ringing or beeing ugly slow, this left over 3 circuits, the zener referenced ones and the cascoded jfet.
Number 7 (the cascoded jfet) seems to be best option regarding psrr AND stability. (the most stable one)
2nd choice would be Number 3, simple but efficient and stable. Better than my favourite (until today), the No1....

Mike

If You add some filter capacitors paralell with the zener (with the zener referenced version), You can increase the PSRR. Or is it bad idea?

sajti

[MikeB]

Principally a good idea, but my supply rails to the frontend are already filtered. As i want increased psrr at very low freq i have to use ccs circuit without filtering. (or giant caps)

Mike

[sajti]

Giant caps? 220uF looks more than enough...

sajti

[MaxS]

Hello boys ! and girls

I'm looking for in my head about CCS solutions and i remember i have found some ideas of a korean DIYern named Sijosae.
He have putted some schematics on a picture. I put this picture here.

[wwood]

Mike,

You indicated that many (most) of the current sources you sim'ed had stability issues or were very sluggish. This seems rather important as most of our amplifier testing would not reveal this. Power supply "artifacts" can be rather nasty and would tend to excite any instabilities. Have you tried listening to your symasym using one of the solid ccs's ?


Bill

[MikeB]

Sajti, when putting the cap parelell to zener diode you gain not much, psrr already degrades below 100hz. Using bootstrap cap to the feeding resistor (split into 2x10k) lowers that to 0.1hz with the same cap, which is already not bad. But for this "experiment" i'd like to get psrr flat down to dc. Also caps like these ask for turn on thumps.

MaxS, thank for this huge collection, stored to disk...

Hi Bill, haven't tried yet, but right now symasym uses the 2bjt ccs, this also shows minor stability problems.

Mike

[sajti]

If You replace the 22kohm resistor with another simple ccs?

sajti

[MikeB]

Originally posted by sajti
If You replace the 22kohm resistor with another simple ccs?

sajti

That's No8 in my collection... It gives a +12db and is one of the candidates. But No7 (cascoded jfet) is even faster and has higher psrr.
I still need to research jcx's suggestion with the bootstrapped version.

Mike