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Why have HiperTFS?...Why not Half Bridge?

Posted by: treez on

Hi,

Why does Power Integrations not do a Half Bridge controller instead of HiperTFS?....Half bridge can give you a higher duty cycle, higher even than the extended duty of the HyperTFS..

Half bridge only has to switch half the Bus. Half Bridge is better at refreshing the bootstrap capacitor. Half bridge transformer can be smaller than Two Transistor Forward transformer.

Why did Power integrations pick Two transistor forward over Half Bridge?

Was it the case of going into peak current mode when overloaded, and then unbalancing the rail splitter capacitors?

回應

Submitted by PI-Wrench on 04/12/2023

Half-bridge was the prevailing standard for PC power supplies back in the 80's. With PFC front ends now being the norm, the 2-switch forward will run at 1/2 the switch current of a half-bridge supply and allows use of single-ended output windings, simplifying the output structure  Extending the operating duty cycle beyond 50% offers even mode advantages in terms of efficiency and lower voltage rating, lower. voltage drop output rectifiers.

The TFS-2 was designed around the prevailing standard for PC power supplies at the time and added some improvements to the basic 2-switch forward design. Requirements for even higher efficiency have basically retired the 2-switch forward topology, replaced by the LLC with synchronous output rectification. That requirement is addressed by the Hiper-LCS2 chip set. 

If you want to deal with 2X the switch current, a more complex output structure, and the requirement of sourcing  a high-current coupling capacitor, that can be your choice.