LM317L/LM337L as CCS

[Samuel Groner]

Hi

Has anyone experience with the LM317L/LM337L used as a CCS? I would be interested how this compares regarding impedance to a two-transistor CCS (for reference look i.e. at [removed], Q6 and Q7) and regarding tempco to a LED-biased CCS.

What about noise? Suitable for low-noise work?

I'm aware that using a voltage regulator will result in a highish drop-out voltage.

Thanks for input!

Samuel

 

[bcarso]

They are going to be noisier for the same voltage drop I think. The tempco should be low, essentially that of the reference voltage. You will have to pull enough current for the innards to function, so they won't be appropriate for low currents.

 

[adrianh]

Samuel;

The old LM317 regulator that sounds bad as a voltage regulator.
Actually sounds quite good as CCS on the filament of a tube.
Don't question it, build it and listen.

Good sonics do not lie, bad designs do.

 

[Svart]

You can configure the Lm3x7s as preregulators that drive a diode/transistor setup that is SUPER low noise. It would seem reasonable that you could do the same configured as a CCS.


I use lm317s as CCS's for 5w LEDs and they work fairly well. Make sure your program resistors are very tight tolerance.

 

[analag]

The old LM317 regulator that sounds bad as a voltage regulator

Lately I have resorted to wirewound and very large value caps only, actually sound better the LM317/LM350 on the filament of my tubes.

 

[rafafredd]

In this test it´s regarded as excellent...

http://www4.head-fi.com/forums/showthread.php?t=103618
http://www.headphoneamp.co.kr/bbs/zboard.php?id=diy_sijosae&no=145

 

[Samuel Groner]

Thanks for the answers. Looking a bit closer at the datasheet, I find that it is usuable at currents at and above 5 mA only, which is a bit high for many purposes. So maybe a LM134 set up for zero tempco could be better? Or is there a suitable voltage regulator for low currents?

Samuel

 

[pstamler]

Anyone see any reason a 317 with its ADJ terminal grounded couldn't be used as a clean, quiet 1.25V source to drive the bases of several transistors, each of which is a current source? You'd need to load the 317 for 10mA draw, but a 124R resistor would take care of that.

Peace,
Paul

 

[bcarso]

[quote author="pstamler"]Anyone see any reason a 317 with its ADJ terminal grounded couldn't be used as a clean, quiet 1.25V source to drive the bases of several transistors, each of which is a current source? You'd need to load the 317 for 10mA draw, but a 124R resistor would take care of that.

Peace,
Paul[/quote]

Sure that would work, and would have good ripple etc. rejection, but it would still be relatively random-noisy. If we take national's word for the output noise as 30 p.p.m. of the output voltage and assume it is white (which it is not, but it's a start) we have e sub n of 375nV/root Hz to deal with, which is still a bunch.

The temperature coefficient is low, but then that's not what you want to feed bipolar current sources with, typically, unless you want a positive tempco of collector current magnitude.

EDIT: Here's a ref I've posted before that has some decent data on regulator noise: http://www.tnt-audio.com/clinica/regulators_noise2_e.html

 

[Samuel Groner]

Interesting idea, Paul. Couldn't we solve the noise issue by bypassing the 124r to ground? Would probably reduce interaction of the different CCS as well.

http://www.tnt-audio.com/clinica/regulators_noise2_e.html

Good reading - the discrete regulators look like something I want to use as local regulators on my latest mic pres.

Samuel

 

[Samuel Groner]

BTW, 3.3 V zeners seem to have a tight and Vbe matching tempco - at least the 1N5333B does. Unfortunately, the zener voltage is very current dependent. At reasonable currents, it is more like 1.5 V.

Do you have a zener to recommend which is better in this regard and still maintains the tempco property? Oh, and if it's a better-than-5% part, I don't mind either!

Samuel

 

[bcarso]

[quote author="Samuel Groner"]BTW, 3.3 V zeners seem to have a tight and Vbe matching tempco - at least the 1N5333B does. Unfortunately, the zener voltage is very current dependent. At reasonable currents, it is more like 1.5 V.

Samuel[/quote]

That's just the nature of low voltage zeners---that is, the dynamic impedance is roughly in reciprocal relation to the voltage.