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Old 11th January 2008, 06:28 PM   #11
AndrewT is offline AndrewT  Scotland
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Hi Hollow,
yes that 10uF improves the 317/337 performance considerably. Without it the 7812/5/8 series is better.
Try increasing this cap all the way to 220uF. The bigger values must have the protection diode added.
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Old 12th January 2008, 05:45 PM   #12
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Default Three-terminal super regs

Quote:
Originally posted by AndrewT
yes that 10uF improves the 317/337 performance considerably. Without it the 7812/5/8 series is better.
Try increasing this cap all the way to 220uF. The bigger values must have the protection diode added.
Thx for the tip. I didn't know one could take the value of that cap THAT high.

What about the performance of some the so-called industrial regs? E.g. "LT" (Linear Technology), such as LT108x series? They cost more, can handle more current (I think) but I've heard lots of folks say they are not worth using -- at least for audio -- due to noise.

I'll also be experimenting w/ Martin's tracking pre-reg suggestion shortly.

For me, a key goal is compressing the physical layout of all these designs down to the footprint of a std-317-sized reg. Ala Tent- or LCAudio- or Audiocom-like "super regulators". Are there any DIY plans for these yet?
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Old 13th January 2008, 09:19 AM   #13
gootee is offline gootee  United States
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Check for LD1084 (mouser.com), a much-cheaper knockoff of LT1084, a 5-amp adjustable reg (But you can get free samples of the Linear parts...).

One thing you might have to watch out for, with a large adj pin bypass cap, is the input-to-output differential climbing too high, too fast, during startup, since the output is very-much "soft start"ed by having a large bypass cap, there. i.e. The input might get too far ahead of the output, and violate the in-out differential spec (during startup only, especially for higher output voltages). Installing a discrete soft-start for the input can circumvent that. See http://www.fullnet.com/gooteesp.htm , for examples of that.

With FIXED regulators, another thing you can do is to feed back only the AC part of the output , to an inverting opamp amplifier whose output takes the place of the ground for the reg's ground pin. This can actively cancel variations in output voltage, even if caused by an active load. Good Stuff. [Use a separate conductor for the feedback, all the way fom the load (i.e. "remote sense").]
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Old 31st January 2008, 06:37 AM   #14
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Default 10uF on ALL PINS of adj. regulators

Quote:
Originally posted by gootee
For adjustable regulators, bypassing the adjust pin with, for example, a small electrolytic to ground can dramatically lower the output ripple + noise.
gootee/anyone:

Can that small-value cap be a tantalum (e.g. 10uF) -- and would *that* be superior to a good , same-size/same-voltage electro you orig. suggested?

Also, would it help if that 10uF tant was placed on *all* pins (i.e. input, output and adjust pins)?
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Old 31st January 2008, 10:46 PM   #15
gootee is offline gootee  United States
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Default Re: 10uF on ALL PINS of adj. regulators

Quote:
Originally posted by hollowman

gootee/anyone:

Can that small-value cap be a tantalum (e.g. 10uF) -- and would *that* be superior to a good , same-size/same-voltage electro you orig. suggested?

Also, would it help if that 10uF tant was placed on *all* pins (i.e. input, output and adjust pins)?

Hi Hollowman,

Actually, this is all covered in the LT1083/84/85 datasheet, from linear.com . See page 7, in the 'Applications Information' section entitled 'Stability', near the bottom of the page, and continuing onto page 8.

As stated there, the input needs at least 10 uF (type not specified), and the output needs at least a 10 uF tantalum or a 50 uF aluminum, OR, if the adjust pin is bypassed with 20 uF (type not specified), then the output needs at least a 22 uF tantalum or 150 uF aluminum. (I'm guessing that the difference in the stated minimum uF values between tantalum and aluminum is probably because tantalums typically have higher ESR (Equivalent Series Resistance) per uF and there is a minimum ESR vs C requirement for the output cap, for stability.) Actually, they also say that the minimum 22uF tantalum or 150 uF aluminum on the output covers ALL cases of bypassing the adjust pin.

The datasheet also states that output capacitors of 100 uF or higher are typically used, and that even higher capacitance values can be used on the output, without limit, and that any higher C values, there, will further improve both the transient response and the stability. (But I have heard that for some regulator types, it's best to use only up to about 150 uF right at the output, and put any larger caps, if used, right at the load, if the load is more than a couple of inches from the regulator's output. That should work better, considering the inductance and resistance of intervening wires or PCB traces.)

The input cap is also often paralleled with a small-value film cap, such as 0.1 uF polyester or polypropylene, et al, as is the adjust-pin cap. But watch out for high-frequency resonances that might be created by using such low-ESR small-value parallel caps, that way.

If the regulator follows the large filter caps in a power supply, I would probably still use the 10uF input cap, especially if the regulator is more than a couple of inches away from the large caps.

Regarding your question about the type of the bypass cap for the adjust pin: It will help a whole lot, regardless of whether it's tantalum or aluminum. But I think I would want to use the one with the lowest ESR at 120 Hz (or 100 Hz, for 50 Hz mains), or maybe whichever type is cheaper. If I were buying new ones, for that, I guess I'd go with aluminum, which is probably better on both counts (I'm guessing). But if you already have some 10 uF tantalums, maybe you could try one, or try paralleling two of them, there. Either way will be excellent, probably.
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Old 1st February 2008, 03:02 PM   #16
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Default Re: Re: 10uF on ALL PINS of adj. regulators

Quote:
Originally posted by gootee
Actually, this is all covered in the LT1083/84/85 datasheet, from linear.com . See page 7, in the 'Applications Information' section entitled 'Stability', near the bottom of the page, and continuing onto page 8.

As stated there, the input needs at least 10 uF (type not specified), and the output needs at least a 10 uF tantalum or a 50 uF aluminum, OR, if the adjust pin is bypassed with 20 uF (type not specified), then the output needs at least a 22 uF tantalum or 150 uF aluminum. (I'm guessing that the difference in the stated minimum uF values between tantalum and aluminum is probably because tantalums typically have higher ESR (Equivalent Series Resistance) per uF and there is a minimum ESR vs C requirement for the output cap, for stability.) Actually, they also say that the minimum 22uF tantalum or 150 uF aluminum on the output covers ALL cases of bypassing the adjust pin.

The datasheet also states that output capacitors of 100 uF or higher are typically used, and that even higher capacitance values can be used on the output, without limit, and that any higher C values, there, will further improve both the transient response and the stability. (But I have heard that for some regulator types, it's best to use only up to about 150 uF right at the output, and put any larger caps, if used, right at the load, if the load is more than a couple of inches from the regulator's output. That should work better, considering the inductance and resistance of intervening wires or PCB traces.)

The input cap is also often paralleled with a small-value film cap, such as 0.1 uF polyester or polypropylene, et al, as is the adjust-pin cap. But watch out for high-frequency resonances that might be created by using such low-ESR small-value parallel caps, that way.

If the regulator follows the large filter caps in a power supply, I would probably still use the 10uF input cap, especially if the regulator is more than a couple of inches away from the large caps.

Regarding your question about the type of the bypass cap for the adjust pin: It will help a whole lot, regardless of whether it's tantalum or aluminum. But I think I would want to use the one with the lowest ESR at 120 Hz (or 100 Hz, for 50 Hz mains), or maybe whichever type is cheaper. If I were buying new ones, for that, I guess I'd go with aluminum, which is probably better on both counts (I'm guessing). But if you already have some 10 uF tantalums, maybe you could try one, or try paralleling two of them, there. Either way will be excellent, probably.
I had dismissed the LT108x series because of somewhat-reputed accounts of these regs being very noisy for audio apps.

IAC, National's datasheet for their LM117-317 regs notes that...

Quote:
The adjustment terminal can be bypassed to ground on the LM117 to improve ripple rejection. This bypass capacitor prevents ripple from being amplified as the output voltage is increased. With a 10 uF bypass capacitor 80dB ripple rejection is obtainable at any output level. Increases over 10 uF do not appreciably improve the ripple rejection at frequencies above 120Hz. If the bypass capacitor is used, it is sometimes necessary to include protection diodes to prevent the capacitor from discharging through internal low current paths and damaging the device.

In general, the best type of capacitors to use is solid tantalum. Solid tantalum capacitors have low impedance even at high frequencies. Depending upon capacitor construction, it takes about 25 uF in aluminum electrolytic to equal 1uF solid tantalum at high frequencies. Ceramic capacitors are also good at high frequencies; but some types have a large decrease in capacitance at frequencies around 0.5 MHz. For this reason, 0.01 uF disc may seem to work better than a 0.1 uF disc as a bypass.
Iíve also heard -- though not universally -- that the output cap should have a value on the lower end of the manufís suggested range (and esp with tants). I believe Naim audio uses this strategy: i.e. 10uF tantís on each 317ís output. Maybe this is why their electronics have a rep for having excellent dynamics, rhythm and pace as well as solid, defined bass?
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Old 6th February 2008, 08:25 PM   #17
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Default Listening LM317 filtering

I wrote an article on relation between LM317 decoupling and sound rendering.

LM317, understanding and listening

Eric
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Old 6th February 2008, 08:28 PM   #18
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And here's my 2p's worth:

http://www.acoustica.org.uk/t/3pin_reg_notes1.html
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Old 6th February 2008, 11:55 PM   #19
gootee is offline gootee  United States
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Quote:
Originally posted by martin clark
And here's my 2p's worth:

http://www.acoustica.org.uk/t/3pin_reg_notes1.html
Very good stuff, Martin! Thanks!
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Old 7th February 2008, 03:06 PM   #20
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Quote:
Originally posted by martin clark
And here's my 2p's worth:

http://www.acoustica.org.uk/t/3pin_reg_notes1.html
On that page you note:

"For 5V output, a useful substitution is to use two green LEDs in series."

Do you mean substitute two green LEDs for *one* of the diodes (I think you suggest Zener + regular diode, in series), or *just* use the two green LED?

Thx,
-hm
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