Isolated DC-DC converters in series

Question

Hello everyone,

I am using two wireless charging modules for powering my circuit. The receiver part has 5v DC DC buck converter and I would like to connect the output of two modules in series to form a +/- 5v dual supply.

Is there any chance of damaging any of the converters if I directly connect these in series? I have found that VicroPower and SynQor suggest to use protection diode at the output. These diodes are for preventing back-feeding by load capacitance during turn-off, and assuring proper operation during start-up and dynamic loading. Also prevent the output from going negative if only one converter is operational [like in case of thermal shutdown of one converter].

Now, as my DC DC converters are totally isolated at the input side [two separate coils], do I need to use those protection diodes?

peterjcs23 · Accepted Answer

The vicor scheme looks different as it is a 0 to 10V output, where as you are proposing a +5..0..-5V scheme. The vicor scheme could end up with one output feeding through the other but your scheme will not do that. No need for diodes.

michaelkellett · Answer

I would use the diodes, if you use schottky diodes there won't be too much voltage drop. The reason is that if you have a reasonable capacitance in the load and one supply drops out for any reason then the other can get double the single supply voltage applied to its output, which may, or may not, cause problems. You could do lots of tests but the diodes are cheap.

MK