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Old 18th June 2011, 08:34 PM   #121
io is offline io  Hungary
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TL431 noise does not matter, I have a trick or two circuits, which is selected.
It is possible to achieve high parameters, just thinking alive.
CCS, Gyrator, negative resistance, and so on ...
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Old 18th June 2011, 09:00 PM   #122
io is offline io  Hungary
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real circuit:
http://www.diyaudio.com/forums/attac...cuit-snap1.jpg
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Old 21st December 2011, 08:20 PM   #123
maxpou is offline maxpou  Canada
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Default Dac PS

Hi Guys,
I would like to know if somebody tried this circuit for analog and digital DAC PS. And if yes what's your comments on the PS? Thank you! Maxpou

Improving the LM3x7 regulator circuit
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Old 28th December 2011, 03:59 AM   #124
ZLyzen is offline ZLyzen  United States
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Wow, just read this entire thread (yeah took a good hour) and I am intrigued by this. Mostly Fred's circuit with 1 bjt (post #34)

What is the typical output current that can be expected from this? is it the same as what one could get from a 317 by itself?

I'm looking to drive 5 double op amps at ±15V for an active filter setup and I want to make sure it won't be too noisy.
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Old 28th December 2011, 05:29 AM   #125
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Hi ZLyzen, The output current is unaffected by the transistor. It is used to improve the noise rejection of the reg.

I have built a dual rail supply based on this idea from Fred, though I used two LM317's not the usual LM317 and LM337. latest test results here ---> LM317 experiments and measurements

Earlier in the thread I posted differences between a standard setup and with the BJT. ---> LM317 experiments and measurements Note that at that point I had quite a few noise issues with my sound card preamp causing 50Hz interference, however the difference between the standard, and BJT circuit should be apparent The standard circuit is improved by increasing the size of the bypass cap, but as can be seen it has little effect with the BJT circuit. This was the escence of Fred's design I think. that it was possible to use a small quality film cap for the bypass, rather than a much larger electrolytic.

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Old 30th December 2011, 01:25 AM   #126
ZLyzen is offline ZLyzen  United States
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Great! would something like a 2N3904 be a good transistor (I have basically zero experience with them in circuits)

Looking at his sample diagram how do you set the voltage for the regulator?

How do Tantalum Capacitors work for the bypass? performance wise
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Old 30th December 2011, 02:34 AM   #127
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2n3904 appears to be an npn transistor, you need pnp for the LM317 circuit. I used BC560C's in my circuit. The higher the Hfe the better but aim for something with a hfe > 400 at least. The 2n3904 falls down on that as well. I think Fred may have made some suggestions for different transistors earlier in the thread.

I used a multiturn trimpot for the bottom resistor, I could not get a calculation to work to predict correct resistor values for setting the voltage.

The schematic for my overkill realisation of this idea attached below. You can ignore the CRC front end if all you want is a working version of the reg part of the circuit and if you only want a single rail just use the top half of the circuit The more traditional approach (for dual rail) would be to use an LM337 for the bottom reg, and I think you would then need to use an npn transistor for the negative part of the circuit.

Tony.

edit: note that the copyright notice on the schematic was me being anal, I always put them on my photos. It should not be in any way taken as a restriction on what you can do with the circuit
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Last edited by wintermute; 2nd January 2012 at 10:27 AM. Reason: note about the copyright on the schematic
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Old 30th December 2011, 02:42 AM   #128
ZLyzen is offline ZLyzen  United States
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awesome, thanks a lot Tony, checking out the circuit gunna throw it together in multisim and see if I can get 15V
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Old 30th December 2011, 02:59 AM   #129
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If multisim is compatible with LTSpice then a ready made spice model (somewhat older revision) is available on my blog page http://www.diyaudio.com/forums/blogs...011-02-10.html

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Last edited by wintermute; 30th December 2011 at 02:59 AM. Reason: fix typo
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Old 31st December 2011, 12:21 AM   #130
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your post #127, output voltage formula (simplified):
Vout = ((Vadj + Vbe) * (R9 + VR1)) / VR1

If R9 = 10K, VR1 = 2K, Vbe = 0.65V, Vadj = 1.25V, then:

Vout = ((1.25V + 0.65V) * (10000 + 2000)) / 2000
Vout = (1.90V * 12000) / 2000
Vout = 11.4V

This is very simplified formula, enough for rough calculation (base current left out, base resistor left out, Vbe slope left out, temperature left out,....).

Last edited by stormsonic; 31st December 2011 at 12:24 AM.
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