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Flyback SMPS: Maximum power capability?

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Advanced Member level 3
Jun 13, 2011
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Can any reader clarify the maximum power capacbility of offline flyback converters?

This page about NCP1651 states flyback can be done to 250W:
ON Semiconductor NCP1651: Single Stage Power Factor Correction Controller

However, this article (near top of first page) states that the limit is 150W.

So do you know what is the limit?

I would have thought that the limit for a single switch offline flyback was around 80W.

...Surely above that, then EMC becomes too difficult to pass without severely damping the switching transition and thus needing big ,expensive heatsink on the FET.?

However, this article (near top of first page) states that the limit is 150W.
Strictly spoken, the article doesn't talk about limits:
The low cost, simplicity of design and intrinsic efficiency of flyback transformers have made them a popular solution for power supply designs of below 100W to 150W.
I basically agree, that the decision is ruled by practical criteria, e.g. EMC behaviour. But why should we assume a clear limit?
We have built single switch flybacks to 300W offline, and have seen successful interleaved flybacks (2) up to 1500watt. Intelligent turn on timing (quasi-resonant) enables high efficiency and low RFI - Regards, Orson Cart
i find it hard to believe that a 300W flyback...even quasi-resonant would be cost effective?

Surely you would have to severely damp the switching transition to make it pass EMC.....and then you would need a huge heatsink.

Not to mention for a 300W offline flyback, you would need large RCD clamp componants and a large transformer.

A 300W single switch flyback is surely possible.....but cost-effective?

This was for a commercial intelligent compact battery charger - 35VDC max 10A out max, one mosfet or igbt with low side drive, 3 o/p diodes, one carefully designed transformer with low leakage, hence minimal snubbers or RCD clamp, internal h/sink to 0VHVDC so no emc problems, 2nd wrap around h/sink for diodes (low Vf), minimal CM and DM filtering needed to comply with EMC, could be two wire or 3 wire mains input... many thousands made with good margin... Regards, Orson Cart.
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