The simplistic Salas low voltage shunt regulator - Page 522 - diyAudio
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Old 9th August 2012, 05:33 PM   #5211
Salas is offline Salas  Greece
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Quote:
Originally Posted by samoloko View Post
Salas

Is that correct - your shunt PS got to have no local decouple caps on load
Better not if you can't scope. Type and position can create a problem or not.
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Old 10th August 2012, 07:56 AM   #5212
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thank you for reply

what to look at with scope - ripple with / without decouple cap
what do you recommend as a value of load decouple cap - always lower than shunt V out cap or not If we power supply dac chip or line amplifier
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Old 10th August 2012, 05:28 PM   #5213
Salas is offline Salas  Greece
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You engage AC input on scope. You set the horizontal (time button) at 20-50us. You set your vertical button at 5-10mV. You hook up the probe on power rail, crock clip at nearest ground. You look for a straight line outcome, no sinus or weird patterns, no thick noise fuzz.
Can't recommend for load decoupling in general, there are very specific needs many times. But solid tantalum 10uF or 22uF local capacitors did show good overall rail in some reported reg-load combinations.
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Old 10th August 2012, 10:14 PM   #5214
judby is offline judby  Denmark
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Post "KISS" v1.0 18V prototype

Hi

I build a v1.0 18V prototype, main purpose is to power a couple of B1's (not symmetric).
I changed a couple of things:

1) CCS I = 100mA (R1=6,2)
2) Used TL431 for Vref
3) Used IRF9610 for FETs

The thing is powered from a 10VAC toroidal that I salvaged from an old traffic light giving me some 25,5VDC; see attached schematic (from Eagle).

Schematic intentionally illustrates the components "placement" in the breadboarded prototype.
Click the image to open in full size.
Initially I was having issues with the CCS as the current would decrease when input voltage (from lab psu) rose above some 21-22V, getting as low as 60mA at about 29V in.
Not good as it also hurt the performance of the shunt - set at 18,04V it decreased to below 18V when Vin got over 29V...
I therefore changed the current through the current sensing BJT by changing the 4k7 resistors to 47k.
Then it works nicely to atleast 35V in
According to my PicoScope the noise is well below -92dBu, only a spike hitting -92dBu at 50Hz - I'm amazed!!

Now I wanted a KISS shunt, and the TL431 does not really makes things easier. I do not fancy remote sensing as 1) it's not KISS 2) if not done properly you can end up introducing more issues than you try to solve. I suggest using high-quality caps close to power-need instead.
So, I'll experiment with some variations over v1.0 and eventually actually listening to it on my friends B1 ;-)
Attached Images
File Type: jpg shunt 18 prototype 1.jpg (108.3 KB, 312 views)
File Type: jpg shunt 18 prototype 3.jpg (108.9 KB, 305 views)
File Type: png shunt sch.png (43.9 KB, 582 views)
File Type: png LF noise.png (37.2 KB, 260 views)
File Type: png wideband noise.png (40.1 KB, 88 views)
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Old 10th August 2012, 10:56 PM   #5215
Salas is offline Salas  Greece
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TL431 is still rather noisy for Vref IMHO, make your C7 a 1000uF cap and see if it lowers the FFT noise floor. Here is a member's measurement from Mezmerize DCB1's shunt reg rail with LEDS Vref and 100uf filtering. 0dbu=0.775VRMS. Don't know if the ref level was set otherwise than 0dbu though.
Attached Images
File Type: jpg PSUNoise+.jpg (315.2 KB, 98 views)
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Old 10th August 2012, 11:02 PM   #5216
Salas is offline Salas  Greece
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P.S. Is the second picture representing your Picoscope self noise floor limit?
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Old 10th August 2012, 11:05 PM   #5217
judby is offline judby  Denmark
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Hi, thanks, yes, I know.
And it's no longer KISS with all the "support Rs, Cs".
I was considering a string of blue LEDs until I a couple of 100's pages back read they are too noisy too ;-)
Will probably go with a string of red LEDs or just a single resistor.
I'll get back :-)
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Old 10th August 2012, 11:07 PM   #5218
judby is offline judby  Denmark
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Quote:
Originally Posted by Salas View Post
P.S. Is the second picture representing your Picoscope self noise floor limit?
Yes, I think so. Just for sanity I measured the lab PSU and it was about 12dB above, with clear spikes at 50, 100 and 300Hz...

Edit: It is actually measured at output of the prototype, but I think the noise is just below/on level with my scope... Quite amazing giving the circumstances

Last edited by judby; 10th August 2012 at 11:11 PM.
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Old 10th August 2012, 11:07 PM   #5219
Salas is offline Salas  Greece
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OK.
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Old 10th August 2012, 11:10 PM   #5220
Salas is offline Salas  Greece
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Quote:
Originally Posted by judby View Post
Yes, I think so. Just for sanity I measured the lab PSU and it was about 12dB above, with clear spikes at 50, 100 and 300Hz...
So you know you at least hit your test gear floor level apart from a bit of hum pick up (move that toroid a bit). OTOH you don't know if you really are even below. What lab PSU model?
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