My take on a discrete shunt voltage regulator

[MRupp]

BTW, since I don't think I posted yet the simulated total noise at the output of the regulator, here it is, up to 50kHz.

Very excellent noise figures. This confirms what is stated in the Noro patent, i.e. that shunt regs should by much quieter than conventional regulators. It would be intersting to confirm this thru simulations of a good series regulator design, and if possible thru actual noise measurements, though I acknowledge that the latter is not trivial.

[ikoflexer]

Thanks Martin. 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.

Regarding actual noise measurements, I agree, sub microvolt measurements are tough to do with any degree of confidence.

[HiFiNutNut]

Based on the successful experiment of 4uF film output cap by Ikoflexer, I did a number of experiments on the output capacitor today with my new remote sense configuration.

Since layout is important, I have to describe mine (which would be different from Ikoflexer's) so that we can discuss under the right context. There is a distance about 5cm from the shunt MOSFET to the output point, due to the space occupied by the heatsink and by the components. Form the output point to the load is 12cm. Sensing point is directly on the load.

When the output cap was placed at the output point.

Rubycon ZL 22uF/50V (ESR=0.034R) - no resonance.

4 x 2.2uF || Polyester - no resonance.

1.1uF MKP Vishay blue box - resonance with a magnitude of about 2.5mV.

6.8uF MKT Suzuki - resonance with a magnitude of about 8mV.

7.5uF/400V Solen - resonance with a magnitude of 40mV (No wonder I always found Solen to be unlistenable!)


The best so far is the 4 x 2.2uF || Polyester on the output.

I then put the 4 x 2.2uF || Polyester at the load and found there was a resonance of 8mV - 10mV.

[HiFiNutNut]

The above seems to suggest that the output capacitor should be nearer to the MOSFET than the load, because for the same 4 x 2.2uF, when placed at the output it did not resonate, but it did when placed at the load.

If that is true, then in my final build of the regulator (I consider the current one to be prototype) I will place the output cap right next to the shunt MOSFET.

Can somebody give a technical reason why the output capacitor should be placed near to the shunt MOSFET (or otherwise)?

[HiFiNutNut]

Among those caps used, the Vishay blue box 1.1uF MKP should have the lowest inductance because the capacitor was designed for high frequency application. I guess the reason it resonated may be due to insufficient capacitance. But to make up 4uF I would need to parallel 4 of them per rail, which could occupy much space. So I guess I may choose the 4 x 2.2uF polyester because of the small space they occupy. they are also cheap and available.

So I have a feeling that the regulator may not like an output capacitor less than 4uF.

But it may depend on the layout and the load. I remember that before I used remote sensing, with a dummy resistor load (i.e. not the real load), I had the 1.1uF + 0.5R at the output and it resonated. When the 0.5R was increased to 1R it did not resonate.

[Tham]

Iko, got all parts except j201. Can I simply replace it with 2SK170? Using 2n2222 in place of 2n5088 which is not available here. Caps will be generic electrolytic for now.

[massimo]

Originally Posted by HiFiNutNut

....
When the output cap was placed at the output point.

Rubycon ZL 22uF/50V (ESR=0.034R) - no resonance.

4 x 2.2uF || Polyester - no resonance.

1.1uF MKP Vishay blue box - resonance with a magnitude of about 2.5mV.

6.8uF MKT Suzuki - resonance with a magnitude of about 8mV.

7.5uF/400V Solen - resonance with a magnitude of 40mV (No wonder I always found Solen to be unlistenable!)
....

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!

[AndrewT]

Originally Posted by HiFiNutNut

Rubycon ZL 22uF/50V (ESR=0.034R) - no resonance.

4 x 2.2uF || Polyester - no resonance.

1.1uF MKP Vishay blue box - resonance with a magnitude of about 2.5mV.

6.8uF MKT Suzuki - resonance with a magnitude of about 8mV.

7.5uF/400V Solen - resonance with a magnitude of 40mV (No wonder I always found Solen to be unlistenable!)

pes/MKS/MKT are reputed to have a higher esr than PP/MKP. This difference would account for stability of the first two capacitor types and the instability of the latter three capacitor types, if the Suzuki has some special construction to lower it's esr.

Any thoughts?

[ikoflexer]

Originally Posted by Tham

Iko, got all parts except j201. Can I simply replace it with 2SK170? Using 2n2222 in place of 2n5088 which is not available here. Caps will be generic electrolytic for now.

Yes, it would work. If you use the 2sk170 you're building a different Vref, so the resistors would be different. I'd set the current through Vref at about 15% of Idss.

[ikoflexer]

Originally Posted by HiFiNutNut

The above seems to suggest that the output capacitor should be nearer to the MOSFET than the load, because for the same 4 x 2.2uF, when placed at the output it did not resonate, but it did when placed at the load.

If that is true, then in my final build of the regulator (I consider the current one to be prototype) I will place the output cap right next to the shunt MOSFET.

Can somebody give a technical reason why the output capacitor should be placed near to the shunt MOSFET (or otherwise)?

The big question is if this rule applies in all cases. I can't think of a reason why this works better than at the other end.