heatsink voilates primary to secondary isolation in offline SMPS?

[grizedale]

Hello, the following offline SMPS has a metal heatsink right across the primary-secondary isolation barrier.....................


SMPS1200 SMPS
**broken link removed**


surely this is not allowed?.....how would it pass a 3750Vrms flash test?

 

[andre_luis]

Actually, that´s not a good practice in layout design, and I would not recommend to use that SMPS, if above protection class is required.
However, if heatsink is connected to Earth pin, could reduce damaging impact, dur voltage spike could be drained.

+++

 

[FvM]

Test voltages and spacings will be different according to the overvoltage category. For Cat II, 2300 V test voltage will be sufficient, at least according to IEC 1010. But it's not impossible to achieve Cat III 3700 V with addtional insulation. The photo suggests something of this kind. A hypex application note clarifies, that they are considering 6 mm distance in air as necessary, which would in fact refer to Cat III requirements.

Of course component choice will be rather restricted under this conditions, but apparently, they found a way.