V regulation for digital circuits

DECKY999

Member
2007-07-18 7:06 am
I know there were endless posts on these pages regarding usfulness of super (descrete) regulators in digital circuits and their possible advantages over standrad LM78xx chips.

I know that good old 78xx are not made for audio but how about using some more modern regulators.

What are people opinions on lets say LM2940 or LM1086. Or is there any other better alternative for regulating digital 5V supply that does not cost 30euro a piece?
 
DECKY999 said:
I know that good old 78xx are not made for audio but how about using some more modern regulators.
IMO, a better (but slightly more $$) option in upgrading from 7805 is the LM340-T5 (thx to CarlosFM of diyhifi for that suggestion).

Also, Martin Clark suggested the pre-tracker, found in LM317's datasheet:
- Ref 1
- Ref 2

I've used this pre-tracking regulator with success, but only for "higher" voltages (+/- 15VDC). Not sure how well it'll perform at 5VDC.

Also be aware that you can do quite a lot of tweakling to these regulator ckts afterwards, like snubbering. In DIY, you'll never get bored!
 
Re: Re: Re: V regulation for digital circuits

Peter Daniel said:
LM340 is the same series as 78xx: http://www.national.com/ds/LM/LM340.pdf
In fact, if you try to order LM7815 from DigiKey, only LM340 comes out.
Yup -- know about the "duplicity" WRT the datasheet (dunno what's up with that ??). I do know that Fairchild 7805's are different from National 7805/LM340T-5.0's: Digi-Key Part Numbers LM7805CT-ND vs. LM340T-5.0-ND, respectively.

IAC, my LM340-T5 looks like CalosFM's image capture of this reg. in this post. It is different from any 7805 I'm using or have ever used -- both in external labeling and performance.

I got mine from Digi-Key.
 

DECKY999

Member
2007-07-18 7:06 am
Just to summarize (if I can) as far as the price/performance ratio is concerned good old 78xx are as good as it gets.

The only step-up from there would be some of the super-regulator varieties. However, if I can remeber old posts there were some suggestions that super regs have more or less the same noise levels at high frequencies as the 78xx and that for digital regulation they are waste of money. Does that stand or someone has different experiences?

Reragding the 78xx vs LM340T - they are on the same family spec sheet but the performance is smidgen different ; 40uV vs 50uV voltage noise and a bit better regulation on the LM340 side.

http://www.farnell.com/datasheets/64424.pdf