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Old 19th June 2007, 03:28 PM   #1
Eva is offline Eva  Spain
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Talking Self oscillating fun

This is my new self oscillating control scheme, it's similar to UCD but I suppose it's not covered by the patent because there is no damn RC network or any other thing in parallel with the feedback resistor... It's actually better than UCD because oscillating frequency drops less when the output approaches the rails.
Click the image to open in full size.

Now with fast acting current limiting too... Something missing in UCD.
Click the image to open in full size.

Blue trace: Input voltage multiplied by gain (expected output voltagE).
Red trace: Real output voltage.
Green trace: PWM going to the filter.

Output filter is 120uH and 2.2uF. Switching frequency is intended to swing between 30 and 80Khz. Load is 5 ohms in series with 100uH (to prevent it from damping the output filter and producing too optimistic results).

This is only simulation but a prototype is coming soon...
Enjoy!!
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Old 19th June 2007, 09:45 PM   #2
alfsch is offline alfsch  Germany
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..current limiting..nice :-)
i assume mixed feedback, pre+post filter, right?
but if scale is v, 400vss, hey, you make 5kw output ??

and what output switches? mos or igbt?
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Old 19th June 2007, 09:52 PM   #3
BWRX is offline BWRX  United States
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Quote:
Originally posted by alfsch
and what output switches? mos or igbt?
to add: mos, igbt, or mos+igbt?
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Old 20th June 2007, 12:50 AM   #4
Gyula is offline Gyula  Hungary
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Default Re: Self oscillating fun

Hi Eva! We would like to build an FPGA-based digital amplifier for a Student Conference this year October. Join us and come to the school for the discourse. Are you with it?
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Old 21st June 2007, 09:04 AM   #5
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I know you don't like me..... but....

Is that using an internal average current mode control loop?

I've had a fiddle with one like that me-self. I'd guess the frequency doesn't change so much because the phase slope (?) is not so severe being first order in the current loop rather than second order with a voltage loop.

Cute

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Old 24th June 2007, 03:09 PM   #6
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Hi Eva ! Do you promote such low switching frequencies?
Or is this just in or order to keep the first proto less troublesome?
During my experiments I came to the conclusion that especially for higher power the low switching frequencies and remaining unpleasant high output ripple can cause some headache heat in the tweeters.
Also I was thinking about a 4th order filter. ... or playing around with higher order coupled inductor beasts... But somehow already in simulation all this was not really promising.
Finally I ended up in the opinion that for a full range design I would like to have like something 300kHz switching frequency at least. Preferred 400kHz. And using a simple 2nd order LC output filter with RC damping.

If I look to your 120uH output choke then this filter cannot be intended for a full range design. Right?
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Old 24th June 2007, 03:35 PM   #7
BWRX is offline BWRX  United States
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Quote:
Originally posted by ChocoHolic
If I look to your 120uH output choke then this filter cannot be intended for a full range design. Right?
I think it's safe to assume this is intended for subwoofer use just by looking at the switching frequency.
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Old 24th June 2007, 03:40 PM   #8
luka is offline luka  Slovenia
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Hi

Try current limited inverter...
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Old 2nd July 2007, 08:51 AM   #9
fumac is offline fumac  China
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no damn RC network or any other thing in parallel with the feedback resistor
-------------------------------
Dear EVA

this is right choice,
i have test pre-post filter , for about 1 years ago

a saying: oscillator like a oscillator, amp like an amp


best RG
fumac
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Old 7th July 2007, 08:30 AM   #10
RX5 is offline RX5  Philippines
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Hello Eva,

you say "just removed the RC network in parallel with the feedback resistor" and much better? ill give it a try with the sim....
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