My take on a discrete shunt voltage regulator

[AndrewT]

I wonder if the regulator output cap should be at the Sense Points rather than at the FET or the Load.

If all these coincided there would be no question to answer.

[ikoflexer]

Originally Posted by AndrewT

I wonder if the regulator output cap should be at the Sense Points rather than at the FET or the Load.
If all these coincided there would be no question to answer.

I don't know. I need to think some more about this. In the meanwhile, at the load seems to work best for hifinutnut, so let's keep this as the suggested solution. Though I wonder how much this depends on the actual individual setup.

Any experts lurking? janneman, maximus?

[keantoken]

If the cap is across the MOSFET, it has some ESR and ESL relative to the sense point. If placed at the sense point, it has only its own ESR and the ESR of the sense wires.

- keantoken

[ikoflexer]

kt, good point.

One thing to consider here is the following. Let's call the two input points of the load Vin_pos and Vin_neg. When the oscilloscope probe is connected to the Vin_pos point of the load, it shows the wave there with respect to where the ground probe is connected. The ground probe should be connected to 0 volts (ground). However, the load does not see that voltage. The load sees the difference in potential between Vin_pos and Vin_neg, which is not the same as (Vin_pos - GND).

The proper way to observe the wave seen by the load is to have an oscilloscope with differential input, so that we use the trace seen by channel A minus the trace seen by channel B.

[keantoken]

The probe itself has what, 22pF-47pF of parallel capacitance, and some reactance depending on the cable length? I kinda doubt this would have an effect.

What kind of load does Hifi use? Is it a MOSFET driven by square wave, wirewound inductive resistor?

Perhaps pictures would be helpful too.

- keantoken

[HiFiNutNut]

Originally Posted by massimo

You asked Iko about the strange 4uF MKT cap.... but as far ad odd numbers are concerned, you also have some uncommon values!
Joking aside, can you please specify the complete designation for the 1.1 uF MKP "blue box"?
Generally Ero/Roederstein now Vishay caps have 4 digits following MKP, such as 1822, 1830, etc. A Farnell/Digykey/other part no. will suffice.
Thank you!

I gave the manufacturer part number at the Salas v1 thread. The first item in the list and you can get the datasheet from the link: Film | Digi-Key

They have now been sold out at Digi-key.

[HiFiNutNut]

I think a picture illustrates better:

[HiFiNutNut]

If the regulator output is more inductive than the wire inductance, a capacitor placed near the regulator output may cancel the inductance, making it more stable. Or doesn't it?

With regards to different types of capacitors, it is possible that some ESR is required for damping, as Andrew T suggested. But I can't think that is conclusive, because 4 x 2.2uF polyester in parallel (ESR/4) still has a very low ESR, and they don't cause resonance. Is it possible that the ESL of the capacitor is playing up? possible. These 2.2uF cap is very small so inductance would be lower. The worse resonance seen was with the big 400V Solen which would technically have the highest inductance of all capacitors tested.

[keantoken]

There is a so-called "tunnel of death" when it comes to regulators. If the output cap has too low ESR, or even capacitance is too large, the regulator can become unstable.

"tunnel of death":

Aspen Headphone Amp

And possibly informative:

Aspen Headphone Amp

- keantoken

[MRupp]

I happen to have the Jung SR file handy from the time I built it. Here's the noise simulation. I'm reluctant to take seriously any noise simulation, hence, I'd consider the noise simulation only for its entertainment value.

Hmmm, not as bad as I thought. I simmed a very simple differential-amp series regulator (almost identical to the one in the Pass Pearl phono pre), then converted that into a shunt version (with CCS in front off course) and compared the noise figures in LTSpice. They were pretty much identical and I am beginning to wonder, too, how good these simulations are.

Off course, the shunt regulator's line rejection was much better - due to the current source, but when I cascaded 2 series regulators rejection was again in the same ballpark. If anything the shunt reg had a small advantage at higher frequencies.