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wide voltage range input high voltage power supply

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francis29

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Hi,
I want to design a power supply with following specifications.
Input voltage = 250-750V
Output = 12V/2A
Isolation should be there.
What topology should i use?
is it feasible?
 

FvM

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A typical specification of an auxiliary dc/dc converter of VFD inverters. Two-switch forward, or with restrictions, two-switch flyback converter is often used for maximal utilization of transistor voltage range.
 

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Low wattage wide input power supply's are almost always single switch flybacks.

Search for "wide input flyback pdf" on the internet.
 

francis29

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thanks to all. what about transformer?
Can you suggest some good books/application notes on flyback transformer design.
 

mtwieg

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Low wattage wide input power supply's are almost always single switch flybacks.

Search for "wide input flyback pdf" on the internet.
"Wide input" usually means for universal AC inputs, e.g. 90-265VAC, so your peak input voltage is far from 700V. At that high of a voltage even 1200V FETs don't have much headroom in a single switch flyback. I agree with FvM's recommendation of a two switch forward or flyback.
 
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francis29

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Has anybody heard of single switch forward converter that uses rcd clamp for reseting the core instead of tertiary winding??
 

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Has anybody heard of single switch forward converter that uses rcd clamp for reseting the core instead of tertiary winding?
Guess I've seen it in designs. Implies that no stored inductor energy can be recovered. If the transformer main inductance is sufficiently high, this must not be a problem.
 
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mtwieg

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If you use a RCD clamp to reset the core, then the energy stored in that core will be dissipated instead of recovered. The higher the magnetizing inductance, the less energy will be stored in it each cycle, and therefore the lower your losses in the RCD clamp.

But it's fairly uncommon to see this technique used in forward converters. And I would recommend against it for a high voltage design.
 
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