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Old 8th September 2001, 10:44 PM   #11
haldor is offline haldor  United States
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Quote:
Originally posted by Samuel Jayaraj
Better than the 78xx and 79xx regulators are the LM317T/K and LM337T/K three pin variable regulators.
Samuel, I'm with you. The LM317/337 regulators aren't nearly as likely to oscillate as the 78XX/79XX parts are and they are generally lower noise.

Phil
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Old 9th September 2001, 09:07 AM   #12
ALW is offline ALW  United Kingdom
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Default Reg's

Another vote for 317 / 337, I've never had these oscillate in any circuit, it would have to be very badly designed for this to happen!

The BIG advantage of 317 / 337 over fixed 78xx and 79xx series is the significantly increased ripple rejection, providing the reference voltage is decoupled (see data sheet).

They're also generally lower noise, although there is a reasonable variation between samples. Look at Linear Tech Application note 83 (AN83-1) for a scheme for testing regulator noise.

The LT parts should offer lower noise, but all of the ultra low noise parts only work up to 20V - bit of a pain when I want 24V.

Andy.
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Old 9th September 2001, 11:29 AM   #13
lohk is offline lohk  Europe
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Default LT versus LM

Has somebody ever compared the LM317 (ST) against the LT317 (Linear Technology) soundwise?.
The LTs are afaik higher rated, but maybe also more prone to a tendency of oscillation. I personally never had any troubles. I have got mine quite a time ago as spare parts from Exposure, but I do not know, if they are available any more.

greetings
Klaus
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Old 22nd October 2001, 04:18 PM   #14
ALW is offline ALW  United Kingdom
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Default Good lead

Klaus,

I've just checked the data sheet spec for the LT317 - it has a significantly lower noise spec. than the LM parts. I could kick myself for not realising this before.

I need to get some now - I'll let you know if I find a source.

Andy.

P.S. The noise spec is also lower than LT1086 etc.
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Old 23rd October 2001, 04:56 AM   #15
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C Simpson, in addition to the ferrite beads you mentioned I had very good results replacing the decoupling resistors feeding a commercial DAC with small inductors having the same DC resistance. These are readily available and will not affect the DC conditions intended by the original designer. However the reduction in “trash” on the power supply was remarkable.

Cheers,

Pete
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Old 23rd October 2001, 06:48 AM   #16
hifiZen is offline hifiZen  Canada
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hey, no prob.

The only thing you'll want to watch for with inductors is that you don't form an L-C resonant circuit. I like to put something resistive in there which will dissipate unwanted energy...

What's so nice about ferrites is that their impedance is nil at DC, but can go up to 90 ohms or more at the high frequencies of interest. And, ferrite beads are very lossy, so that impedence will be almost purely resistive. In combination with a cap, this is enough to effectively block anything in the 10MHz+ range, depending of course on the bead size and composition.
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Old 1st November 2001, 03:19 PM   #17
ppl is offline ppl  United States
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I have used all these types of IC regulators and what i like to do with them is use the 78XXX and the 79XXX as Preregulators. then follow these with the Three termanal adjustable Type Like The LM-317 and the LM337 or the LT-1085 and LT-1083. types. I have noticed that most Circuits showing the adjustable regulator Applications are just taken right out of the data sheet. While this works it is not the way to get the Best performance out of them. First off replace the resistor fron the Adj. term to ground with a Zener diode or a voltage reference of your Choice. Next replace the Resistor from the Output to the Adj termanal with a current source to drive the Voltage reference. On the Negitive regulators Place a small resistor about 1-2 ohms in series with the Input termanal and the power supply. make sure the Bypass cap on the regulators input is still directly connected to the reg's input Pin. Ferrite beeds are on the output of the Preregulators as well as the Input of the Preregulators. The concept hear is to get all the bandwidth and speed you can out of the Adjustible reg's in Addition to improving the Rejection of the regulators with the current source. Note the Adj. termanal is at a high Impedance so using a voltage reference will Provide this Termanal with a low impedance to ground and using the Current source will provide High Impedance isolation from the Output of the regulator. The regulators output can be quite noisy because of the Transients the Load places on it and you dont want this to get feed into the Adjust termanal, The low value resistor recomended in the data sheet allows this to happen. The ferite Beeds are as stated in an above post to block Line Noise. If the Best performance obtainable is what you want then the Classic three termanal regulator is not going to provide that. Then eather a discreet component regulator or a shunt type made from a Voltage reference and a Current source is what is needed. Beware most people take the circuit for the shunt regulator right out of the data sheet and use a resistor to Drop the voltage this can be improved alot by using a current source in place of the resistor.The resistor i am refering to is not the voltage devider used to set the Output Voltage but the resistor in series with the Powersupply and the shunt regulator. Regarding the voltage devider, a Voltage reference and current source can replace this as was done in the Three termanal Adjustable regulator i talked about above.
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Old 2nd November 2001, 10:19 PM   #18
ALW is offline ALW  United Kingdom
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Default For Lohk

Re:LT317AT's

I managed to secure some smaples of these, and they measure better than the NS LM317AT's I'd been using up until now.

Unfortunately I can't log into my website at present, but have a JPG of the FFT analyses I've done if your interested. Let me have an email and I'll send it.

I'd try and get some to play with, they're good.

Andy.
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Old 4th November 2001, 11:51 AM   #19
lohk is offline lohk  Europe
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Andy,

from where did you get these ? - I recently tried to find new ones, but in vain...
Where can I find a data spec ?

Klaus


To all:

Is there a significant difference (in resultant sound quality) between the positive and the negative regulator ?
Have you already tried f.e. LM337T and reverse the poles for a single side supply (so that the "ground" is reguated and the positive is connected to the rectifier/transformer) ?
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Old 4th November 2001, 01:01 PM   #20
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Default LT317/337

Hi Klaus!
Youm might have a look here:
http://www.linear.com/prod/datasheet.html?datasheet=709
Unfortunately, those LT guys have discarded the LT337.

Holger
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