Offline 70W Phase sift Full Bridge

[cupoftea]

Hi,
We are doing a 70W, 100kHz Phase shift Full Bridge for 180-265VAC input.
Current doubler output.
24V, 3A output
(Parallel 3 output diodes)x2 as synch rects not worth it for 3A.

So why isn't anybody else doing this?

Pri FETs will be 4 x DPAK (+ turn off snubber for Bottom FETs)
Transformer nice easy wind, only the pri and sec coils and no split sec.

So this is easy, and we wont even need any heatsinks, even though it will be in
totally enclosed plastic with no fan.

So why isn't anybody else doing this?, I mean, no heatsinks, easy transformer wind.

Design is no more difficult than a "plain Full Bridge"

We will only get ZVS turn on at above 70% of max power but that's fine.
We don't want an extra "leakage inductor" as it just means diodes to the rail also needed
and also more dissipation in the output snubbers.

 

[Easy peasy]

possibly because at 70W a valley switched flyback is less parts and similar efficiency ?

 

[cupoftea]

Thanks, though that would need heatsinking, and need at least a three coil transformer (interleave wound). With the PSFB, we can do it with no heatsinking,
and with all SMD parts, apart from maybe the common mode choke and HV Bus cap and transformer.
So anyway, the lack of heatsinking and the assembly effort of that makes the said PSFB well worthwhile we believe.

 

[Easy peasy]

It will be interesting to see if what you say does indeed turn out to be the case . . .

please let us all know the outcome.

--- Updated Today at 3:41 AM ---

This part here would dissipate < 50mW in a 70W flyback, valley switched design, for 250VDC ave in

https://octopart.com/datasheet/ipb65r065c7atma2-infineon-93259729

3.60 USD

--- Updated Today at 3:46 AM ---

Or two of these in parallel ( each with 4E7 gate R ) 125mW each and only 45c USD each

https://octopart.com/datasheet/ipd70r600ceauma1-infineon-70523113

ground ref GD, lots of chips to choose from - no bootstrap needed, diodes can still be // for the output and heat-sunk to the pcb quite effectively - 3A x 0.8V say = 2.4 watts ave, 3 diodes in // = 0.8 watts each so 3 x SMC package diodes with plenty of copper should suffice - or leaded.

EP