Resonating LC output of Full-Bridge SMPS?

[grigson]

Hi,

I was recently sacked from my job as a SMPS designer at a new start-up Class D amplifier company

Was i sacked because my voltage mode, full-bridge SMPS with +/-40V rails would have resonated at the output LC resonant frequency when audio pulses at that frequency were drawn from it?

It was a dual rail output , so there were two LC's.

Each individual LC had a resonant frequency of 630Hz.

Vin was = 90-265VAC...it had a voltage doubler link for USA/Japan mains...(no PFC).
Output power was 330W.
Type 3 compensation.

For the first few months they were lauding me as there new messiah......then all of a sudden they were ranting at me as if i'd just stolen the whole year's profits...then sacked me.

I think that they showed my schematic to a SMPS colsultancy...and the consultancy told them something.....but what they said i dont know.

Do you think it was the danger of the resonating LC output stage of the Full-Bridge?

 

[MacGyverS2000]

Aren't you tired of these types of threads yet? I know I am...

Nothing is resolved, and you try to convince us... well, I'm not really sure what you try to convince us of, because you don't seem to be arguing any substantial point. My guess is you were fired because your boss(es) finally caught on to the same...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[MikeHalloran]

In 45 years in the workforce, I have seen a lot of people sacked.
The number sacked for a technical issue, cumulative, is still approximately zero.

Look inward.
Figure out what part of your personality they just couldn't stand any more, and do something about it.

Can't figure it out?
Ask your spouse.

Don't have a spouse?
You know that one friend, the one who would help you bury a body, and retain no clear memory of having done so, under oath?
Ask that friend.


Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

Well, it still speaks volumes about your ex-company, given cited behavior, and that they actually hired you in the first place.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[LionelHutz]

If you really must post then, then you should be posting in the "How to Improve Myself to Get Ahead in My Work" Forum to try and figure out why, not here.

The reason would have been more than a relatively small error or two in the design. Most likely, this design was more vapourware then real.

IR - It does not speak too badly, we had a vapourware developer that managed to stay around for a number of years.

 

[bobmcbride]

I always hated the situations where people are sacked early on... I have seen some of the best guys get sacked in a few months just cause management changes their minds and or actually realizes what top notch people cost in salary.

Could it be because of your design.. probably not.
However the question being:
If a power supply that powered a class D amplifier had a resonant frequency (LC or otherwise ) at 630Hz would the audio output resonate at 630Hz? Yes some.. or in other words the gain of the class D amp would change as the power rails rang (since the gain of class D amps is related to the voltage on the rails).
Could you get some non harmonic distortion under transients at this frequency? Yes...
Even so, there are many other factors involved. For instance if the class D amp had feedback it's self this might not be a problem at all. How much ringing there is depends on your bode plot. I assume the 630Hz would be a pole-zero dip in your gain-phase margin. With type 3 compensation this can be accommodated for to some extent.
And last to mention what would a class D's frequency plot look like if it had such ringing? We would see a peak at this frequency. Well would that be all bad? It depends on how much of a peak. Most speakers aren't very flat in their response either.

With this all said I'd like to say building SMPS for class D amplifiers can be VERY hard.
I would think you were on the right track.. and given enough time for design revisions you would have got it.

 

[zappedagain]

start up? Whole years profits? Isn't that an oxymoron?

There could have been all sorts of reasons at a start up. Like a deal falling through and they can't pay all the salaries so the new guy gets let go.

I worked for a start up once and we all voted anonymously to take a 10% pay cut instead of laying anyone off. I was impressed with that. Later it worked out that the lost pay was reinstated, stock options were offered for all, and we went public. Overall a very rewarding roller coaster ride!

Z

 

[zzzjim]

Better luck next time .

Brilliant designs usually make your employer Rich !