PhotoCoupler PCB hole

[BondBreaker]

I'm building a switching power supply and i've been studying commercial ones.

I've noticed that underneath the photo coupler, there is usually a hole in the PCB.
What is the purpose of this?

Thanks

 

[audioguru2]

Maybe the hole separates the high voltage side from the low voltage side of the circuit, so that current leakage on the pcb (when it is damp from humidity?) doesn't matter.

 

[indulis]

It's for "isolation" of primary to secondary. As isolation voltage levels change so do the creepage and clearances. The opto is often "weakest link" for creepage so you will often find a hole/slit under it.