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Old 27th November 2003, 11:20 AM   #1
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Default Regs - Shunt vs Series

Why is shunt perceived to be a better topology in terms of noise and regulation performance? Surely hum at the input will be equally attenuated by a series regulator as it uses feedback to maintain the output voltage at a constant level?

I can't understand why a series regulator would have the output corrupted with a triangle wave caused by the feedback, yet this wouldn't happen with a shunt. Or is this corruption just when using ICs?

I am interested in simple discrete implementations mainly, but welcome comments on ICs, too.
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Old 27th November 2003, 11:54 AM   #2
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Default Re: Regs - Shunt vs Series

Quote:
Originally posted by richie00boy
Why is shunt perceived to be a better topology in terms of noise and regulation performance?
Who says so? Normally a series regulator has a "shunt regulator" to create a reference voltage. There are differences between those two types of regulators but there are pros and cons of these types and I think noone is the best.

Have you read the gigantic thread about Super Regulator which I believe is far better than any shunt regulator.
Super Regulator, collecting the facts

If you are looking for a discrete circuit you can check how a LM431 is done but I doubt that you can make it better than the 431.
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Old 27th November 2003, 02:53 PM   #3
jcarr is offline jcarr  United States
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Richie:

>Why is shunt perceived to be a better topology in terms of noise and regulation performance?<

It isn't, at least if you are looking at the voltage component of the regulator output

>I can't understand why a series regulator would have the output corrupted with a triangle wave caused by the feedback, yet this wouldn't happen with a shunt.<

The use of global feedback is a separate issue from the choice between series and shunt regulation. Feedback can be used in the design of both series and shunt regulators.

>Or is this corruption just when using ICs?<

Certainly the oft-mentioned TL431 IC shunt regulator does not have very good performance for audio applications. An impedance curve that rises steadily above 50kHz until it hits about 13~14 ohms in the 1~5MHz region, noise to spare...

Incidentally, I do feel that shunt regulation has its advantages, but I believe that you may need to look in a somewhat different direction from the questions that you have been asking so far.

A thread with (IMO) more pertinent information can be found here:

http://www.diyaudio.com/forums/showt...006#post135006

hth, jonathan carr
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Old 27th November 2003, 08:02 PM   #4
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Thanks guys, picked up a few things there. I think I will stick with my simple series regulator for now.
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Old 27th November 2003, 08:09 PM   #5
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Hi all,

I noticed that a series regulator can suffer from the capacitance over it's juctions.. this limmits the high frequency PSRR... still I would prefer series-rugulator with good HF decoupling

just my 2 cts,
Thijs
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Old 14th December 2012, 07:28 AM   #6
regal is offline regal  United States
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I think a lot of folks have been jumping on the Salas Shunts both the HV and the LV, they are awsome for the right application but the issue is stable absolute voltage. The Salas regs seems better than most Shunts when it comes to varying mains voltage but thermal drift is the issue. The issue with voltage drift is critical when dealing with hybrid tube amps (wrt to the HVSS) and then it crops up again with DAC's with the (LVSS.) Both problems are the same dc-offset. We all know adding a servo just sucks.

I found a company that makes big resistors with very stable ppm and they work great but they are cost prohibited, don't fit the pcbs and don't cater to folks outside industry HR Series-Axial Lead :: Ultra-Precision Resistors: HR, HVA, HVS, RX Series :: Resistors :: Precision Resistor Co., Inc. - Manufacturers of Wire Wound Resistors, Sensors and Shunts. But they do work to give less thermal drift with the SS shunts.

Thats one avenue to dealing with this.



But my question is what designs are out there for big inefficient class A mofset series regulators. I've seen/heard them in commercial designs and they sound great and give stability, but I guess I've never seen a schematic or any DIY discussion.

Anyone have input or threads here where a diyer could start in learning about this ?

Or should we take a step back and consider designing the SS Shunts to work with precision resistors?
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Old 14th December 2012, 09:07 AM   #7
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Isn't series regulators more sensitive to a varying load than shunts are ?
That's at least a something I've been told (I'm fairly new at this).

This shows the tps7a4700 going from 10-845mA with a+/-2mV ripple as result.
Is this really something that would occur feeding for instance a dac chip ?
The current draw wouldn't be that high and I would expect it to be more constant.
Click the image to open in full size.

But if so how about a combination of both types ? To be specific, I'm aiming to try the
tps7a4700 evaluation board feeding "Trident" shunts. I also have a pair of
"Placid" shunts but I'm not shure it's a good idea to place a shunt after another
shunt, especialy since the the tps7a seems to have really nice specs.
I also think that I might have better use for the "Placids" elsewhere so.....

Or maybe the tps7a might even be a better regulator then the "Tridents", I
really don't know and any input would be appreciated.
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Old 14th December 2012, 09:47 AM   #8
regal is offline regal  United States
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I am far from a power supply expert, but the concept with a "Class A" series regulator isn't an IC, but discrete mofsets biased brute force into class A (or near it) so that the load is insignificant, the problem of course is it means designing from scratch for each application. Its just a pondering, cause the shunt "drift" and resultant DC offset seems to be a common theme with shunt regs I have tried.

Maybe the shunt with precision resistors and oven boxes on the critical active devices are the better option. Just thoughts...
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Old 14th December 2012, 09:59 AM   #9
qusp is offline qusp  Australia
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yes thats why I dont use them more too, even when using zfoil TX220Z resistors (an order of magnitude more impervious to drift than those wirewounds) and large heatsinks for vref; the thermal drift of the active devices is a pita

the whole thing ends up prohibitively large and I agree so many people are just throwing these (very nice) regulators indiscriminately at their builds without a thought for whether they are best for the application.

using LEDs and standard vrefs on a breadboard build the drift is not small.

Last edited by qusp; 14th December 2012 at 10:07 AM.
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Old 14th December 2012, 10:04 AM   #10
qusp is offline qusp  Australia
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dahlberg: it depends whether you are talking about powering a digital section, or the analogue or clock sections of a dac, the digital sections can easily have large, rapidly changing transients.

honestly, as i've so often posted around these threads, its the decoupling caps that will handle the transients, there is something wrong with your design if you are expecting the external (and often remote) regulator to do that.

why is this in the Solid State amplifier section?
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