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Old 9th January 2013, 02:14 PM   #981
chiily is offline chiily  United Kingdom
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Quote:
Originally Posted by analog_sa View Post
Wow. The simulated waveform is very similar to what i see on the scope. Seems like the simulation predicts something like 4MHz, right?
Looks close to what I see too...
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Old 9th January 2013, 02:19 PM   #982
PMA is offline PMA  Europe
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Thanks for the feedback, guys. Though there was a lot of emotions, please believe me that I would like to give a helping hand and such a help should be an engineering analysis as a basis for the issue solution.
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Old 9th January 2013, 05:19 PM   #983
FdW is offline FdW  Netherlands
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Thanks, I will try it/this (and some variations) (this evening) and report back.
Here are some, preliminary, results.

After some experimentation:
V(tst1) Uncompensated CVS+CCS (left schema)
V(tst2) Compensated CVS+CCS (2nd schema)
V(tst3) Uncompensated CVS+CCS+Shunt (3rd schema)
V(tst4) Compensated CVS+CCS+Shunt (2nd schema)
V(n001) Input voltage.

The V(tst1) track shows some ringing, this may lead to oscillation (especially on a very noisy mains). 1st-ring about 8Mhz 2nd-ring about 4Mhz.

The V(tst2) seems well dampened.

The complete standard Paradise PSU, V(tst3) performs excellent, but one should consider that this is a simulation. Placing real world components on a PCB and connecting an actual power source will have its, negative, influence. The complete compensated Paradise PSU, V(tst4) performs excellent also, the compensation as added in the attached schema, e.g. Cc1=470pF and Cc2=2.7n has no real impact in the functioning of the PSU.

As I’m sure that this is not the final word on compensating (when the PSU oscillates (and if)) we have to wait what kind of results compensation gives on the currently misbehaving PSU’s.
Attached Images
File Type: png Paradise PSU Vstep sim a.PNG (80.7 KB, 347 views)
File Type: png Paradise PSU Vstep sim b.PNG (16.9 KB, 338 views)

Last edited by FdW; 9th January 2013 at 05:22 PM.
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Old 9th January 2013, 05:40 PM   #984
PMA is offline PMA  Europe
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OK, now there is a MicroCap and LTSpice simulation result, different simulation software, little bit different excitation voltage and scale of observed voltage plots. To me, based on simulation, the original circuit is only conditionally stable. Now the frequency compensations have to be verified on misbehaving boards.
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Old 9th January 2013, 09:11 PM   #985
PMA is offline PMA  Europe
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This amplitude and phase response might reveal possible oscillations. Please see circuit without compensation and with 2 compensation capacitors. Caps make the circuit stable, but reduce HF suppression.
Attached Images
File Type: png shunt_uncomp.PNG (60.1 KB, 313 views)
File Type: png shunt_reg_comp_2C.PNG (59.8 KB, 305 views)
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Old 10th January 2013, 08:19 AM   #986
Take5 is offline Take5  Germany
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After some experiments, in my setup 2k works very fine.
After a few hours of listening and more LPs I changed the load resistance to 1k.

Chris
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Old 10th January 2013, 08:44 AM   #987
RCruz is offline RCruz  Switzerland
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Originally Posted by PMA View Post
This amplitude and phase response might reveal possible oscillations. Please see circuit without compensation and with 2 compensation capacitors. Caps make the circuit stable, but reduce HF suppression.
Incredibly good response up to 2M in the first (uncompensated) case.
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Old 10th January 2013, 08:46 AM   #988
FdW is offline FdW  Netherlands
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Incredibly good response up to 2M in the first (uncompensated) case.
I know/knew
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Old 10th January 2013, 08:47 AM   #989
FdW is offline FdW  Netherlands
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Quote:
Originally Posted by PMA View Post
This amplitude and phase response might reveal possible oscillations. Please see circuit without compensation and with 2 compensation capacitors. Caps make the circuit stable, but reduce HF suppression.
Yes that is what I said.

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... I did/do prefere option 1 as it preserves the speed of the circuit.
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Old 10th January 2013, 08:49 AM   #990
FdW is offline FdW  Netherlands
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Incredibly good response up to 2M in the first (uncompensated) case.
That is where the pre-regulator works, it will stop anything in that range (1M and above) before it enters the CVS/CCS/Servo
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