Isolated flyback secondary rectifier reverse voltage vs. SELV

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I am designing a isolated flyback with 12V SELV output, according to EN 60950.

The transformer has 4kV isloation between primary and secondary side.

But I am not shure how to deal with the secondary rectifier reverse voltage, that is 80V.

80V is to high for SELV (42V AC / 60V DC), but of course there are never 80V at the output.

Is this a problem to have 80V in the secondary side of the circuit?


best regards

Hans Günter

Hi Hans Gunter,

With 12V design and wide range input voltage, it is normal to have PIV voltage of around 80V across the diode at high line.  It is ok on the secondary circuit but not on the accessible part which is the output.  But if you look at the DC/AC component of the secondary ckt, it is still within SELV.  Thanks.