Author Topic: 30V 3A power supply oscillating  (Read 12565 times)

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Offline smkb

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Re: 30V 3A power supply oscillating
« Reply #25 on: April 13, 2016, 04:37:38 pm »
Thanks, perfect tip. Funny is that it started from simple opamp + darlington and it is going to end up with network analyzers.

Danadak, did you add a resistor in series with Cout ? I added 0.1R for 10u and ESR of 0.1R for capacitors like 10u is far too optimistic.
if you didn't then try to use Cout of 10u in series with e.g. 1R.
Passive elements in spice are (nearly) ideal ones and thus capacitors have no ESR, ESL (any ac current does not heat them also do not break under too high voltage )- where one can buy such ?

the irony is that one tries to stop oscillations while someone other does as many as possible to make simulation unstable.
both can't
Isn't it ?
 

Offline polis93Topic starter

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Re: 30V 3A power supply oscillating
« Reply #26 on: April 13, 2016, 06:16:11 pm »
I see I started very interesting debate  ;) Today I sat to breadboard and build own circuit based on my first link. After some changes I have now stable power supply. I finished few minutes ago, so there is many measurements left. I selected NPN-NPN darligton pair with low h21e and with resistive load there is no oscillation...
 

Offline danadak

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Re: 30V 3A power supply oscillating
« Reply #27 on: April 13, 2016, 09:47:15 pm »
Here is a another sim. No matter the series R with Load C, even 100X load C,
I can't get it to osc. I can by increasing the darlington base C load, but as you can
see with .1 uF output still stable with an indication that phase margin is indeed
reduced. But load C, ESR, does not significantly impact loop.

Ignore the 1K ESR R, I used both .1 and 1 ohm in sims, no effect.

This sim switches full load on/off.

Regards, Dana.
« Last Edit: April 13, 2016, 09:52:54 pm by danadak »
Love Cypress PSOC, ATTiny, Bit Slice, OpAmps, Oscilloscopes, and Analog Gurus like Pease, Miller, Widlar, Dobkin, obsessed with being an engineer
 

Offline smkb

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Re: 30V 3A power supply oscillating
« Reply #28 on: April 14, 2016, 05:11:35 pm »
good to know that the psu works.

I saw that schematic for simulation differs from circuit schematic still so I found a model could be used instead of 2n2219 and gave a try.
Results are that simulation runs without oscillations for wide range of in-series Cout resistance I tried.
However damped oscillations happen for Iout transition load-> no load.

Maybe 2n3055 model is too simple.
 

Online Kleinstein

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Re: 30V 3A power supply oscillating
« Reply #29 on: April 15, 2016, 02:49:15 pm »
The simulation shows a very poorly working regulator. Even without a critical load, there is quite some ringing when going from load to no load and very slow  reaching of the final value when turning the load on.

For the simulation one needs to include the output capacitor. Also the load change is much better done by a spice current source element instead of simulating a switched load with a FET.
 

Offline danadak

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Re: 30V 3A power supply oscillating
« Reply #30 on: April 15, 2016, 03:09:16 pm »
I did it both ways, still no osc in my sim.

Regards, Dana.
Love Cypress PSOC, ATTiny, Bit Slice, OpAmps, Oscilloscopes, and Analog Gurus like Pease, Miller, Widlar, Dobkin, obsessed with being an engineer
 

Offline mikerj

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Re: 30V 3A power supply oscillating
« Reply #31 on: April 16, 2016, 07:57:59 am »
OP are you using the correct mains transformer to power the regulator?  If you try to power this circuit with DC to test it it won't work correctly.
 


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