The simplistic Salas low voltage shunt regulator - Page 40 - diyAudio
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Old 9th June 2009, 02:21 PM   #391
iko is offline iko  Canada
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Stuey, you were spot on.

I don't know Jam, whatever the winner wants

Oh I see Mike, you were talking about the high freq compensation cap. No amount of compensation could deal with this kind of loop gain, I think.
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Old 9th June 2009, 09:47 PM   #392
iko is offline iko  Canada
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Hey guys, I have a question. Does any of you have some experience with DACs, in terms of what kind of load it presents to a power supply? Is it fairly steady, or is it varying, and if so, roughly how many mA would it jump around, and what what frequencies. Any pointers are appreciated! Thanks.

Basically I'm trying to assess if a regulator with a flat low output impedance up to around 200kHz would benefit DACs.

Edit: typo and clarification.
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Old 9th June 2009, 11:35 PM   #393
Salas is offline Salas  Greece
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It would be very different for every chip's principle of conversion and other design peculiarities I suppose.

Such a question will have stronger chances of being thoroughly covered in the digital forum.

My mind first goes to provision for a very low noise Vref in the shunt, especially when the loop gain is high. And very good decoupling at the chip.
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Old 9th June 2009, 11:45 PM   #394
iko is offline iko  Canada
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Thank you salas. Hmmm, I guess I thought about DACs because of some vague recollection about them requiring a stiffer psu in the higher frequencies. Was only trying to find a motivation for developing a wider bandwidth regulator, I mean, a practical motivation, as opposed to a theoretical one. Do you think there is any particular application that would benefit from flat low output impedance up to, say, 100 or 200kHz?

Edit: yes, I agree, but a quiet Vref is generally wanted and it affects everybody, I guess. Maybe even more a phono stage?
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Old 9th June 2009, 11:57 PM   #395
Salas is offline Salas  Greece
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I think that it is most useful for a DAC, considering the dynamic range it can reach. A phono stage can give us an excellent low noise background if everything is designed and executed towards such a goal, but vinyl on a TT will not surpass 70dB as a source.

If you consider that wide bandwidth of keeping up the psrr and low output impedance in a reg will require strong gain, Vref considerations are rendered even more central.

I too know that density dacs work very fast, so your idea seems right to me. But I know from experience that I can not be certain since dacs are not something I know much of. There will be peculiarities for any chip.

I would put the question at the digital section of DIY audio.
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Old 10th June 2009, 01:17 AM   #396
iko is offline iko  Canada
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OK, I think I may owe myself that case of beer. I know you guys are all tired of my ramblings, but hopefully it will end with this version. I will build it soon and hopefully it will be as stable in reality as it is in simulation. The design simulates as follows. V(x) is v1, V(y) is v2e. Dashed lines depict the phase.

PSRR
Click the image to open in full size.

Output impedance in db
Click the image to open in full size.

Output impedance of both v1 and v2e
Click the image to open in full size.

Output impedance of v2e, detail; top value on the X axis is 100uOhm.
Click the image to open in full size.

The promising fact about this circuit is that the calculated phase margin is quite high, about 60 degrees, so, in theory, it should be stable. I plan to build a prototype and will post whatever results.

Here's the circuit. The parts need not be the same, but one must be careful with anything that might change the phase profile. The BD140 passes constantly about 75mA (1.5W); I chose a load of 100mA and the shunt passes about 137mA. The shunt mosfet here is an irf510 because it's the smallest input capacitance mosfet I have on hand and want to try it out.

salas, do you remember when I first contacted you about your original shunt, and asked about driving the shunt mosfet with more current. It's a bit ironic to come full circle; if this works, then the simple solution was all along a higher loop gain and a strong buffer for the mosfet.
Click the image to open in full size.

Any comments and suggestions would be appreciated.
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Old 10th June 2009, 02:15 AM   #397
jam is offline jam  United States
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Iko,

With all due respect I would leave out the mosfet and make the darlington (discreet) the shunt element......now that would be something worh simulating.

Jam
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Old 10th June 2009, 02:52 AM   #398
iko is offline iko  Canada
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Quote:
Originally posted by jam
Iko,

With all due respect I would leave out the mosfet and make the darlington (discreet) the shunt element......now that would be something worh simulating.

Jam
Thanks Jam, it's a good idea which I've explored already. It does not do better though, but I might come back to it. And don't worry about making any suggestion, I welcome all input.
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Old 10th June 2009, 04:15 AM   #399
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mikelm,
Quote:
I mean't the miller type cap - but perhaps it's not necessary unless someone intends to build it
Hopefully, no-one will make that serious mistake. All you would get is a lot of headaches.
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Old 10th June 2009, 04:52 AM   #400
iko is offline iko  Canada
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Quote:
Originally posted by Lumba Ogir
mikelm,

Hopefully, no-one will make that serious mistake. All you would get is a lot of headaches.
Well, I too hope nobody's building that one; I explicitly said the circuit was a joke and it should not be built.

Now, this other one, may be another matter. I wouldn't mind a capable regulator for my chipamp.
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