LT4320 with dual windings switching between single and series


I'm trying to build below circuit and I'm getting unexpected results.

Goal is to be able to switch between single winding and both windings in series using a P-FET "T1". If this is built with ordinary diodes, results are as expected but as soon as the LT4320 comes into play, it seems like C2 isn't being charged at all, which results in way too low voltages at the outputs.

My suspicion is, that something is out of phase maybe or something like that and I'm wondering whether there is a feasable solution with the same effects of this circuit:

- switchable using a P-FET, no relay
- ideal diode controllers to avoid dissipation in regular diodes (obvious).
- two windings in parallel are not needed but of course it wouldn't hurt, if a possible solution would inherit that.


  • 0
    •  Analog Employees 
    on Jun 15, 2021 11:52 PM


    Can you try moving the mid-point of C1/C2 to the output of the LTC4357? I suspect your design will work if the center tap doesn't have any capacitance directly at that node. Or, connect C1 from OUTP to OUTN and C2 from +12/24V to OUTN? The capacitors should be at the output of the rectifiers, either only the LT4320 for both windings, or the LT4320 + LTC4357 for the single winding output.

    Best Regards,


  • Hello,

    thanks for your reply. I had it that way, when I was try&erroring. Results were always the same. Some fellow EE told me that this design won't work because "The problem with the LT4320 is that the load current must be purely between its OutP and OutN terminals, and cannot use a center tap of a secondary feeding In1 and In2 for a split supply."

    Can you confirm that?

    Best Regards