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Old 22nd September 2005, 04:29 PM   #11
lgreen is offline lgreen  United States
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Quote:
Originally posted by rjm

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Can we build a credible regulator from, say, 8 parts and $5?

-rjm
I agree with jackinnj, the Linear Technologies regulators have superior specifications, at least as to noise, i've been using those tiny surface mount devices for over a year in various projects like for the buffer/driver in my
Gainclone. Circuit is on that page or here, but it is very similar to the LM317 circ in terms of the parts to use.
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Old 26th September 2005, 06:15 AM   #12
rjm is offline rjm  Japan
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I've been comparing the datasheets (always a bad idea...) of the LM340 (LM78Mxx) and LM317. The output impedance and ripple rejection curves vs. frequency are, with Cadj on the LM317 omitted, essentially the same.

So is the main performance advantage of the LM317 simply due to its optional bypass cap, or is there something I'm missing?


-rjm
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Old 26th September 2005, 11:49 AM   #13
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Quote:
Originally posted by lgreen


I agree with jackinnj, the Linear Technologies regulators have superior specifications, at least as to noise, i've been using those tiny surface mount devices for over a year in various projects like for the buffer/driver in my
Gainclone. Circuit is on that page or here, but it is very similar to the LM317 circ in terms of the parts to use.
btw, i found that the LTC low noise regulators behaved better with tantalums than aluminum electrolytics -- could just have been my layout.
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Old 26th September 2005, 12:26 PM   #14
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Adding 10uF as Cadj improves the LM317 response dramatically.
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Old 26th September 2005, 01:13 PM   #15
rjm is offline rjm  Japan
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Quote:
Adding 10uF as Cadj improves the LM317 response dramatically.
Yes, yes... but is that all there is to it, Cadj?

Or could it be that its not the ripple rejection, but the intrinsic output noise that's important?

/R
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Old 26th September 2005, 01:48 PM   #16
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Pretty much just Cadj. The noise level of the 317 is lower than the 78 series, so IMO using it and adding Cadj are no brainers.
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Old 26th September 2005, 04:07 PM   #17
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Quote:
Originally posted by rjm
[snip]The super-reg is about two dozen parts. The LM317 is four.

So to with regards to Jan's suggestion that I use a small signal pass transistor: yes, I'm receptive to the idea, but can it be done without the trappings of the zener, the LED, all the extra passive components found in the super reg.?

Can we build a credible regulator from, say, 8 parts and $5?

-rjm
rjm,

This being DIY, I am little surprised that the # of parts (cheap ones at that) is so important to you. Maybe you want to limit board area, I can also understand that. But, what you could do is to use an integrated current source diode or a suitable jfet current source instead of the LED and transistor current source. That is only one part, but it might be as expensive as the LEd etc.

Jan Didden
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Old 28th September 2005, 04:41 PM   #18
rjm is offline rjm  Japan
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Jan,

I'm interested in providing separate regulation for each op-amp, which necessitates a total of eight units. Board area is, if I keep them on the main PCB, extremely limited... although a daughterboard is an option.

I could of course drop the condition of individual regulation, and its an open question whether two Superregs beats eight 3-terminal ICs. However, for the purposes of this thread, I wanted to restrict the discussion to solutions which were not too much more complicated than an LM317. i.e. an opamp and voltage reference, for example, possibly with a pass transistor... just to see if anything useful along those lines presented itself.

I am, as you might guess, now thinking I should just stick with the LM317...

/Richard
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Old 28th September 2005, 04:48 PM   #19
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Quote:
Originally posted by rjm
I could of course drop the condition of individual regulation, and its an open question whether two Superregs beats eight 3-terminal ICs.
I think noone can tell you the right answer, you'll have to test this by yourself.
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