Diac and Triac at SMPS output area?

[RHeTTRoNiCS]

Hello EP forum...most of the smps power supply that has been encountered have diac and/or triac after power transformer area...Anyone can please help me understand why and how it operates? thanks in advance.

 

[(*steve*)]

I don't think I've ever seen either in a SMPS.

I've seen plenty of mosfets and zener diodes though.

There are many different types of SMPS regulators. The most common ones (at least the mains operated ones) are fairly complex to understand.

I would start by looking at a simple SMPS buck regulator. Understand that, then the various simple derivatives (boost, generating a negative rail) and then go on to other topologies.

Look here and here and here.

Depending on how deep you want to understand, some may be more applicable than others.