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Old 3rd June 2010, 05:59 PM   #11
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Just two cents:
Quasi-resonant shift-bridge type converters have high frequency rectifier recovery oscillation type noise and rather big snubbers to deal with it.
Alex
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Old 3rd June 2010, 06:09 PM   #12
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Orfeus Thanks! I have built the real life version on my bench in p2p wiring. The entire control and MOSFET drive fit on the 2" x 3" computer microprocessor style heatsink, along with the two pairs of MOSFETs.
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Old 3rd June 2010, 06:31 PM   #13
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Quote:
Originally Posted by alexberg View Post
Just two cents:
Quasi-resonant shift-bridge type converters have high frequency rectifier recovery oscillation type noise and rather big snubbers to deal with it.
Alex
Hmm, I wonder why. One ameliorating factor for mine should be that the switching frequency i use is pretty low, and I often add some extra bypass capacitance on each MOSFET totem pole.

Last edited by Electrone; 3rd June 2010 at 06:36 PM.
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Old 4th June 2010, 04:02 AM   #14
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Quote:
Originally Posted by Electrone View Post
Hmm, I wonder why. One ameliorating factor for mine should be that the switching frequency i use is pretty low, and I often add some extra bypass capacitance on each MOSFET totem pole.
As I said it's in the secondary. When diode turns off, current goes negative through it for some time (how far depends on type and recovery charge) and then diode recovers. The latter happens really fast.
The resonant circuit containing Ls and Cs is excited and rings quite badly. The reason is purposely increased Ls - to store enough energy for ZVS condition. You may start filter with capacitor instead of inductor but then it's another story.
Schottky helps somewhat but it has substantial capacitance.
BAA
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Old 4th June 2010, 08:47 AM   #15
orfeus is offline orfeus  Greece
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Quote:
Originally Posted by alexberg View Post
As I said it's in the secondary. When diode turns off, current goes negative through it for some time (how far depends on type and recovery charge) and then diode recovers. The latter happens really fast.
The resonant circuit containing Ls and Cs is excited and rings quite badly. The reason is purposely increased Ls - to store enough energy for ZVS condition. You may start filter with capacitor instead of inductor but then it's another story.
Schottky helps somewhat but it has substantial capacitance.
BAA
Guys, since you both seem so experienced with switching power supplies, i would like to ask you some more questions. Consider a Full bridge circuit with driver the LTC3722, it is a synchronus dual mode full bridge phase modulated IC. To eliminate the EMI and need of driving transformer i would like to use the FAN7393 High voltage hi-low side mosfet driver IC. The bridge IC's will be FQPF10N60C and the output IC's for synchronization will be FQB55N10 or FDD86102 (for mosfets there are lot of Spice models in fairchild site). I wonder how can i lead the input pusles to the primary windong of transformer, in a pseudo sinusoidal waveform instead of pulse waveform. If you have any idea or any negative comment, please inform me. Also i would like to know if anyone has any idea on this...
Lets say that our system runs in 100W with a small pulse duration. Suddenly the system swallows a 500Wpeak with a reasonable duration. From my knowlege this will result in a significant voltage variation and a serius change in the system transfer function. Is it possible to have an output capacitor steady charged and with a winding on the ouput supply line to measure the current peak and turn on the charged capacitor to give time to the circuit to change its pulse duration smoothly? Is it a stupid technique?
Any comment is acceptable.
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Old 4th June 2010, 09:38 AM   #16
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Quote:
Originally Posted by alexberg View Post
As I said it's in the secondary. When diode turns off, current goes negative through it for some time (how far depends on type and recovery charge) and then diode recovers. The latter happens really fast.
The resonant circuit containing Ls and Cs is excited and rings quite badly. The reason is purposely increased Ls - to store enough energy for ZVS condition. You may start filter with capacitor instead of inductor but then it's another story.
Schottky helps somewhat but it has substantial capacitance.
BAA
That oversight of mine occurred to me later. Thanks.

Last edited by Electrone; 4th June 2010 at 09:53 AM.
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Old 4th June 2010, 09:55 AM   #17
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Quote:
Originally Posted by orfeus View Post
Guys, since you both seem so experienced with switching power supplies, i would like to ask you some more questions. Consider a Full bridge circuit with driver the LTC3722, it is a synchronus dual mode full bridge phase modulated IC. To eliminate the EMI and need of driving transformer i would like to use the FAN7393 High voltage hi-low side mosfet driver IC. The bridge IC's will be FQPF10N60C and the output IC's for synchronization will be FQB55N10 or FDD86102 (for mosfets there are lot of Spice models in fairchild site). I wonder how can i lead the input pusles to the primary windong of transformer, in a pseudo sinusoidal waveform instead of pulse waveform. If you have any idea or any negative comment, please inform me. Also i would like to know if anyone has any idea on this...
Lets say that our system runs in 100W with a small pulse duration. Suddenly the system swallows a 500Wpeak with a reasonable duration. From my knowlege this will result in a significant voltage variation and a serius change in the system transfer function. Is it possible to have an output capacitor steady charged and with a winding on the ouput supply line to measure the current peak and turn on the charged capacitor to give time to the circuit to change its pulse duration smoothly? Is it a stupid technique?
Any comment is acceptable.

I experimented with synchronous rectification in the past, but didn't go very far with it.

That idea of storing separate reserve power in a capacitor seems good. I think it could be done by just making the output filter capacitor that size. I like your openness to ideas.
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Old 4th June 2010, 04:29 PM   #18
orfeus is offline orfeus  Greece
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Quote:
Originally Posted by Electrone View Post
I experimented with synchronous rectification in the past, but didn't go very far with it.

That idea of storing separate reserve power in a capacitor seems good. I think it could be done by just making the output filter capacitor that size. I like your openness to ideas.
You are probably wright. By just replace the output filter capacitor in other energy size you can have the demanding energy, but i don't know if the pulse modulator will be in place to expand it's pulse width in proper time without noise generation. (In any case i start to consider myself as a just talker). So, i'll start a design and send you for comments. Then you may help from your experience.
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Old 4th June 2010, 05:02 PM   #19
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Orfeus thanks for your kind view.
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Old 4th June 2010, 09:57 PM   #20
orfeus is offline orfeus  Greece
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Electrone, any idea how to implement a TRIAC, a DIAC and a VARISTOR in LTspice? (I am about to end the input filter suppressor,inrush current limiter,starting up circuit and soft start).
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