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Old 15th January 2013, 03:54 PM   #1
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Default Accurate voltage regulation

Hello people,

I am going to build a power supply to power some guitar effects up.
The voltages that I am going to need are:
  • 6x9V,0.5A
  • 2x9 to 30V,1.5A

So I need 6 fixed supplies, and two that I will be able to alter depending on my needs. Note that I don't need the adjustment to be controlled easily, without opening the chassis etc. No external pots or switches needed, to be accurate.

I was leaning towards using LM317 voltage regulators, with which I am familiar. Actually I have designed the power supply based on LM317's (and LM350's for the variable supplies), but here I am seeking for a better alternative.

So, I have come across some transistor regulators appearing to have better noise specs than ordinary LM317 designs (how about ripple rejection?). I am mainly referring to this site, which should be known to many people in here, I suppose: Simple Voltage Regulators Part 1: Noise - [English]
But I am not familiar with this circuitry, and it seems to me that using zener diodes with fixed reverse voltage characteristics does not leave much room for flexibility.

So, should anyone be able to explain to me how to modify these circuits to produce 9V,0.5A outputs or even better to turn them into variable regulators, I would be glad to know.

Is there really any cheap and simple circuit out there to beat the ordinary LM317 design? That could be the thread's title in the first place, actually.

Last edited by audiostrat; 15th January 2013 at 04:01 PM.
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Old 15th January 2013, 04:29 PM   #2
Jenyok is offline Jenyok  Russian Federation
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For 9V use L(M)7809 for positive polarity and L(M)7909 for negative polarity.
And preregulator for those chips are as LM317, LM337 .
.
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Old 15th January 2013, 05:46 PM   #3
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Quote:
Originally Posted by Jenyok View Post
For 9V use L(M)7809 for positive polarity and L(M)7909 for negative polarity.
And preregulator for those chips are as LM317, LM337 .
.
I am sorry but I did not understand! You mean to use L7809 exclusively for the 9V supplies or to use LM317 first and after that the L7809?

Are L(M)7809 considered to be any better than LM317?
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Old 15th January 2013, 05:50 PM   #4
Jenyok is offline Jenyok  Russian Federation
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First use LM317 as a preregulator, L(M)7809 as a main regulator.
For negative polarity is the same, if needed.
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Old 15th January 2013, 05:52 PM   #5
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I need only positive polarity, thanks!
And what about input and output caps for each regulator?
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Old 16th January 2013, 03:38 AM   #6
Minion is offline Minion  Canada
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well a transformer that puts out 12v AC at 1A and 24v AC at 3 A would be good , you can use a couple lm7809 regs for the 2x9v DC from the 12v AC tap and a LM317 or lm338 for the 9v -30v DC using the pot on the adjust leg of the reg off the 24v AC tap .... Using a TX with 2 seperste taps will give you some isolation between the 9v dc and 30v dc supplies ......

Cheers

PS if you want to go super simple and cheap you could use a single 12v DC Xformer and rectify the 12v ac to 17v dc and regulate down to 9v dc and then use a voltage doubler off the 12v ac to get your 34v DC and regulate down to 30 v and adjust with a trim pot on the adjust leg of the regulator ......
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Old 24th January 2013, 05:30 PM   #7
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Please tell me your opinion on this: I was planning to use LM350T's for the 1.5A supplies - do you think it is better to do so, or is it better to use a LM317 stage in addition with a transistor or mosfet to provide the extra current? I know LM317 is specified at 1.5A load, but I don't want to push it that far.
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Old 14th June 2013, 08:19 PM   #8
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Default Symmetrical power supply

I am wondering whether the following two options are equally good:

(1) creating a +/-16V supply using a LM317 plus one LM337 with separate rectifiers and secondaries
(2) creating a +/-16V supply using two LM317's with separate rectifiers and secondaries, by means of connecting the output of the second one to ground - thus, it could provide the negative rail

I think the second option has the following advantages:
  • easier layout for the pcb construction (ok a bit subjective)
  • LM317 has better noise characteristics (maybe not audible, but this is what I got from a site that performed measurements)
  • I can be more familiar with LM317's behaviour, since there is a lot of information about it everywhere
  • costs - well that is no issue speaking of one power supply, but being able to order only one IC drops the price, so one can invest in buying better LM317's

Other than these assets, which drawbacks do you assume option (2) could have? Or in what sense could the circuit behave differently?
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Old 14th June 2013, 08:55 PM   #9
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Quote:
Originally Posted by audiostrat View Post
Is there really any cheap and simple circuit out there to beat the ordinary LM317 design? That could be the thread's title in the first place, actually.
Buy a bag of LM317 regs, it will cost you few . Then check this link: Using 3-pin regulators off-piste: part 4 and go to the bottom, last picture is tracking preregulator with LED. Cheap, easy to build, good PSSR, better than single LM317.
Yes, there are better regulators, but they are more comlicated or more expensive or...

And yes, IMHO option (2) is better than (1).
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Old 15th June 2013, 10:43 AM   #10
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Thank you vey much!

Do you think that there are comparable differences between various manufacturers? STMicroelectronics vs Texas Instruments for example?
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