Super Regulator

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#2,101
One of Walton's tried opamps was the LT1115, which share some things with the LT1028.

Haven't yet tried other sims for the AD797, like noise or impedance, which are dealt with by Walton at the end of his article.

As everybody knows, the AD797 is a can of worms which I do not wish to get into. I will anyway try it, hopefully with some guidance from this thread, to see if or what changes in the audio quality.

But I am curious about the LT1115, which I also have some, and behave quite well on the sim. The psrr curve is very much as good as that of the the AD797.

But Walton didn't try it on the four opamps he selected for the final comparisons: AD797, AD825, LME49710 and OPA134.

From that list only the AD825 seems still active, as well as the OPA134. The LME is obsolete. The OPA134 seems to be most affordable of all four chips, @ $2.95 each

Following the procedure I was taught, hopefully done well, I added the OPA134 to the library, hopefully being able to simulate and compare with the others.

But something is not going right, because it keeps calculating and doesn't seem to get to a final result.

So it seems I might need more help to get going.

My idea is to look for more candidates that we can use on the Super Reg. Let's hope I'm being helpful. Right now I'm the pawn on the field.
 
#2,105
carlmart said:
Can someone tell me if there's something wrong in the OPA134 that I can't make it work?

https://www.ti.com/product/OPA134?u...y2H0A-9TAQ9UcvnW3SBoCq8wQAvD_BwE&gclsrc=aw.ds
Click to expand...

I can't tell you what's wrong, but yeah, the OPA134 model is bad and very tricky to get working. However, I was able to get the OPA1611 to work and I'll attach the LTSpice simulation to this post. Here's a comparison between the AD825 and the OPA1611:

AD825 LTSpice AC Sim:
Vxp103B.png


OPA1611 LTSpice AC Sim:
drrdlEK.png


The schematics, LTSpice files, images, and the saved op-point are attached in a zip. What finally got the OPA1611 working (thanks again Jan) was using "savebias" to save the oppoint after it was stable and then running the AC sim on that. Additionally, I had to add some cap (~10nF) between the output and the inverting input to get the transient sim to not oscillate horribly, but this was reduced to 10femto for the AC sim.

You can use the OPA1611 schematic to start playing with the 134... if you can get it stable in transient simulation out to 1s, you can sim it in AC using "loadbias". TI's pSpice model for the 134 has terrible transient behaviour on the inputs, so it causes massive issues on startup.

Edit Note: Even with unity VCVS on the inputs, there's still startup issues. Someone with more experience with bad models might be able to work it out though.
 

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#2,112
raptorlightning said:
I can't tell you what's wrong, but yeah, the OPA134 model is bad and very tricky to get working. However, I was able to get the OPA1611 to work and I'll attach the LTSpice simulation to this post. Here's a comparison between the AD825 and the OPA1611:

AD825 LTSpice AC Sim:


OPA1611 LTSpice AC Sim:


The schematics, LTSpice files, images, and the saved op-point are attached in a zip. What finally got the OPA1611 working (thanks again Jan) was using "savebias" to save the oppoint after it was stable and then running the AC sim on that. Additionally, I had to add some cap (~10nF) between the output and the inverting input to get the transient sim to not oscillate horribly, but this was reduced to 10femto for the AC sim.

You can use the OPA1611 schematic to start playing with the 134... if you can get it stable in transient simulation out to 1s, you can sim it in AC using "loadbias". TI's pSpice model for the 134 has terrible transient behaviour on the inputs, so it causes massive issues on startup.

Edit Note: Even with unity VCVS on the inputs, there's still startup issues. Someone with more experience with bad models might be able to work it out though.
Click to expand...

You have a 1nF capacitor from the inverting IN- to OUT - not in the Jung/Didden design

You haven't specified the ESR of the various electrolytics, this is important (very)

You have a 100pF capacitor across the load -- this isn't in the Jung/Didden design.

Best test for stability is to use an DC=25m AC=1 load current on the output and look at group delay, at the impedance peak, Q=tg*f*pi
 
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#2,114
jan.didden said:
Rap, when you say that the OPA134 is hard to get working, what exactly do you mean? You mean stability and/or convergence in this particular schematic? I assume that the subckt itself works in the sense that it correctly acts as an opamp in a test circuit?

Jan
Click to expand...

Jan,

Yes it works for some circuits, but for this specific circuit there's internal oscillations that cause it to never reach stability in any reasonable amount of time/storage. Playing with abstol and reltol changes things, but nothing enough to get it to stabilize.
 
#2,118
Remember that AD825's datasheet promises only 66dB (2000X) of open loop gain. Its sister products AD744, AD797, and LT1128 all have considerably higher datasheet guaranteed open loop gains: 106dB, 126dB, and 137dB respectively. If you want gigantic ripple reduction numbers (a/k/a PSRR a/k/a line rejection), pick an opamp with gigantic open loop gain.
 
#2,120
Any normal single-dominant-pole opamp with a gain bandwidth product > 200 kHz, will have OL gain > 2000X (i.e. 66dB) at 100 Hz. {math note: 100 Hz x 2000 gain = 200kHz GBWP}

Since AD744, AD797, and LT1128 have GBWP far far FAR greater than 200kHz, they also have OL gain far greater than AD825 at 100 Hz.
 
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