Author Topic: Baxandall converter strange output  (Read 2140 times)

Offline dreamth

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Re: Baxandall converter strange output
« Reply #40 on: March 04, 2021, 09:08:55 AM »
With these types of symmetrical circuits the transient sim can sometimes get stuck in perfect balance - since all the parts are mathematically identical. It helps to deliberately unbalance the circuit (like the real world) to get things started. I find adding a few pF to one of the power fet gates is usually enough.
Oh, and V1 should be a single step from 0 to 12V, not a fixed 12V.

And always include the series resistance of any inductors, even just a token milliohm - that helps with convergence.
here's what i "love" about LtSpice: restarting it next day all its results are screwed:

Offline dreamth

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Re: Baxandall converter strange output
« Reply #41 on: March 04, 2021, 09:34:59 AM »
restarted the computer again and it seems that my ltspice math models are  unbalanced by default...well...not quite right, thre's the csunt .option there, but i have very unstable results from time to time...so i need to restart the computer sometimes to be sure about ltspice results.
« Last Edit: March 04, 2021, 01:39:27 PM by dreamth »

Offline Twospoons

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Re: Baxandall converter strange output
« Reply #42 on: March 04, 2021, 09:27:58 PM »
Must confess I've never liked like LTSpice. Always found it to be slow, and the UI not very friendly.  And when I look at those graphs you've posted I can't tell where in the schematic its getting its data from.

I much prefer Simetrix.  The free version is enough for most of my sims.

Offline dreamth

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Re: Baxandall converter strange output
« Reply #43 on: March 04, 2021, 09:35:40 PM »
Never tried simmetrix, but thanks for suggestion!

Offline davekni

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Re: Baxandall converter strange output
« Reply #44 on: March 05, 2021, 12:43:03 AM »
I've never had repeatability issues with LTSpice.  It is a bit cryptic - many hidden commands that aren't officially documented.  However, there are great online resources - wiki and user groups.  It is the most powerful free simulator to my knowledge.

For optimum convergence, the 2016 release is better than later ones.  I've reverted to that version recently.  Don't know of any useful added functionality since 2016.
David Knierim

Offline dreamth

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Re: Baxandall converter strange output
« Reply #45 on: March 05, 2021, 08:40:02 AM »
I've never had repeatability issues with LTSpice.  It is a bit cryptic - many hidden commands that aren't officially documented.  However, there are great online resources - wiki and user groups.  It is the most powerful free simulator to my knowledge.

For optimum convergence, the 2016 release is better than later ones.  I've reverted to that version recently.  Don't know of any useful added functionality since 2016.
I am on the last spice version...
As for your converter design i can only say thank you! I finished the circuit and tried it today with 2sk941 as driver and 2 paralleled irfz46 on each side.Much better power transfer, much higher achievable frequency range, less heat dissipation.I tried it from 49khz to 190khz.At some frequencies it interfered with the power supply switching frequency which got squeacky at some frequencies.The power supply operates at 220khz and it produces less noise when the converter is operating at a quarter or half its frequency .At around  50khz , the converter got te best power transfer with transistor switching losses being the lowest so the transistors were  cold there. I may consider to modify the power supply frequency and hopefully it will work.At higer frequencies the irfz46(with no heatsink) would get warmer but not by much...
I got +-11.5v with one winding and  a doubler. 420v on 20 kohm and 6v on 3 ohms which is all i need for my phono preamp.I will use this converter to check also an an electrostatic headpones amplifier that needs 600 vdc for anode and 12v for fillaments which was halted in development a year ago due to the lack of a suitable supply.
« Last Edit: March 05, 2021, 09:21:38 AM by dreamth »

Offline dreamth

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Re: Baxandall converter strange output
« Reply #46 on: March 05, 2021, 09:16:51 AM »
and my final schematic, except the resonant capacitor value which depends on the chosen frequency of operation which seems to  be better a  subharmonic of the power supply frequncy.Not sure if i can sinc my power suply with the converter but i'll try.
« Last Edit: March 05, 2021, 10:14:01 AM by dreamth »

Offline davekni

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Re: Baxandall converter strange output
« Reply #47 on: March 05, 2021, 07:12:26 PM »
Glad to hear that it is working well now!

Do you have a capacitor across the 12V input to your inverter?  If so, perhaps it has too high internal resistance or too low capacitance.  With enough capacitance on your 12V input, it shouldn't matter what frequency your inverter runs relative to the 12V supply switching frequency.
David Knierim

Offline dreamth

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Re: Baxandall converter strange output
« Reply #48 on: March 05, 2021, 07:18:02 PM »
apart from 6 X 470uf paralleled capacitors of the power supply , i have another 3 x 6800uf paralellled capacitors...

Offline dreamth

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Re: Baxandall converter strange output
« Reply #49 on: March 05, 2021, 07:22:17 PM »
The output of sony playstation smps is quite interesting as there's a resonance that's 1/2...2/3 of the whole duty cycle...which puts it in the quasiresonant smps cathegory.Acually that resonance is 220khz, the main switching frequency is lower .I suspect that resonance get lower...but i need to make some measurements on the power supply itself.
« Last Edit: March 06, 2021, 03:47:39 PM by dreamth »

Offline dreamth

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Re: Baxandall converter strange output
« Reply #50 on: March 06, 2021, 05:16:24 PM »
I think it must be someting linked to the q factor of converter transformer cause i found that even at higher output power of the converter, but different winding the sony power supply can have a cleaner output and no squeaking.Usually power supply  phase goes wrong when abused and the scope can't sinc properly for a clear signal picture.

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Re: Baxandall converter strange output
« Reply #50 on: March 06, 2021, 05:16:24 PM »

 


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