Super Regulator, collecting the facts

[Fred Dieckmann]

"Where is the pull-down?"

Preloading has been mentioned a couple of times in this thread and is most definitely recommended for the decreased output impedance and improved transient response for loads with some kick back.

http://www.diyaudio.com/forums/showt...46#post252646\

http://www.diyaudio.com/forums/showt...719#post252719

[andy_c]

Originally posted by john curl
(...)4.What is its transient response, both to load changes, and source changes?
There may be many other factors that I cannot think of just now.
When you change op amps, you change many of these factors.
Please keep this in mind.

Understood. When I mentioned the op-amp idea, it was mostly offered to Fred for consideration, and I know he's well aware of these issues too. I've done quite a bit of SPICE simulation of a 90 Volt version of the Jung super regulator and would be glad to post the results if anybody's interested. This includes transients of load current and unregulated input voltage as well as stability analysis. However, I suspect that the interest in the 90 Volt version would be much less than for the classic version of the regulator. For the 90 Volt version, I had to use a slower pass element, which was also combined with an additional bipolar in a Darlington configuration for increased output current. Because of the extra phase lag from this, I wasn't able to achieve stability with the feedback resistor bypassed.

I simulated the performance with a number of op-amps, and indeed the AD825 had the best transient response for pulses of load current. The AD797 was a complete disaster in this application both for stability and transient response. However, I found that the OP37 gave transient response almost as good as the AD825, but with about a 40 dB improvement in line rejection at 120 Hz. Since this is for a power amp application, the low-frequency ripple rejection is important to me. Those results were what prompted me to mention the idea of op-amp substitution.

[andy_c]

Here's the schematic from the simulator. Bypass capacitors on the unregulated input are not shown. The Zobel network of R17 and C5, together with R7 killed a 50 MHz parasitic in the pass transistor that showed up in transient. All the 100 uF electrolytics have 30 nH and 0.25 Ohms in series internal to the model. I've got multiple zeners in series because the tolerance on the lower voltage ones is tighter than the high voltage devices. The dissipation in the TL431A is such that the DIP version is necessary. It's too much for the TO-92 unfortunately. Based on Walt's post earlier, I'll probably replace the green LED with a voltage reference. I may use a MOSFET for Q2 based on Fred's input. The dissipation in some of the resistors is much higher than I'd like.

[Fred Dieckmann]

Put another 100 uF across the TL494 in addition to the 0.01 uF. The Shunt Regulator from the 90v out for the op amp supply looks like a great idea. I think 0.25 ohms is too big for your cap models and I bet you could go down to an ohm for your 0.01 uF caps without any problems.

[andy_c]

Thanks Fred. I was looking at the Rubycon YXF series, 160 Volt. It shows 0.24 Ohms at 100 kHz. This seems close to series resonance, so I used this for the Rs. Now, for the .01 uF, I'm not sure what you mean by the 1 Ohm thing. Do you mean this is the parasitic series resistance? Or are you saying the Zobel network should have 1 Ohm instead of 10 Ohms?

[Fred Dieckmann]

The Zobel network should have 1 Ohm
or could. What ever you find works well.

For the Panasonic FC 35V 100uF the ESR is about 0.12 ohms and the FC series 100 V 100uF is about 0.18 ohms. These are very low ESR caps and your figures sound about right for some other electrolytic capacitor series. The Rubicon ZA series 35 V 100 uf would have an ESR of about 0.05 ohms. You might even want to look for some low ESR 50V 220 uF caps and change the value for the low voltage part of the circuit and stack two in series with resistor voltage dividers to put 45 Volts across each one for the output . i will double the ESR numbers shown here but still give lower total ESR


Some 50 V 220uF caps:

NIC NRSJ 0.023

Rubicon ZL 0.042

UCC LXY 0.073

Elna RSL 0.08

Panasonic FC 0.09

A sort of fun toy:
http://www.kemet.com/kemet/web/homep.../KSpice205_32/$file/KSpice205_32.EXE

[Christer]

Originally posted by peranders

Ok, I have created a monster (in number of posts), I'll guess 90 V would suite a high power amp. Not very common to have ultra low noise PS for power amps.

I just thought I should tell you before Fred woke up. I thought
you might prefer me telling you.

[Fred Dieckmann]

"When Fred talks here about JFET current sources he forgets that 1 MOhms isn't true at high frequencies, much less or at least less. "

The Jfet current sources has a capacitance between 2 and 3 pF. Impress us and do the math to find out where to the rejection starts to roll off with frequency for one megohm. It is above the audio range BTW.

[peranders]

3 pF => 53 kohms at 1 MOhms but don't forget stray capacitance also. I think it's equally important how the regulator performs in the > 1 MHz range also unless your living room is a measurement chamber.

[Christer]

Originally posted by peranders
3 pF => 53 kohms at 1 MOhms but don't forget stray capacitance also. I think it's equally important how the regulator performs in the > 1 MHz range also unless your living room is a measurement chamber.

Excuse me, Per-Anders, maybe I am mixing you up with
somebody else, but I thought it was only about two or three
days ago when you recommended someone to remove the
input RFI filter of a phono amp, which none of us others seemed
to agree with. Have you attend a weekend course on RFI?

Edit: Yes, we are nice today.