Anatomy of Switching Power Supplies

[mhanor]

At page 4, you say "On power supplies with a MOV, surge suppressors are useless, since they have already a surge suppressor inside them.". Are you sure?

http://en.wikipedia.org/wiki/Varisto...oxide_varistor

Ballpark number for varistor life expectancy is its energy rating. As MOV joules increase, the number of transient pulses increases and the "clamping voltage" during each transient decreases. The purpose of this shunt mode device is to divert a transient so that pulse energy will be dissipated elsewhere. Some energy is also absorbed by the varistor because a varistor is not a perfect conductor. Less energy is absorbed by a varistor, the varistor is more conductive, and its life expectancy increases exponentially as varistor energy rating is increased. Catastrophic failure can be avoided by significantly increasing varistor energy ratings either by using a varistor of higher joules or by connecting more of these shunt mode devices in parallel.

Having more MOVs in parallel with the circuit doesn't mean better protection? As I understand, the energy absorbed by each MOV is smaller if there are more of them, while it increases the energy rating of the hole MOVs block. Please, correct me if I'm wrong.

[Gabriel Torres]

Can be.

BTW. This tutorial is outdated and I am writting an update for it as we speak.

Thanks,
Gabriel.

[ran]

Any update on the excellent "Anatomy of a Switching Power Supply" changes you mentioned in January?

Ran

[Gabriel Torres]

I got swamped here, I am still half way thru it. Should be done in early June. Thanks for asking.

Gabriel.