On 28 Jun 2013 01:57:13 GMT, Jim Mueller wrote:

On Wed, 26 Jun 2013 22:09:25 -0500, Arid ace wrote:

So, does that 3mH inductor have an air core as is shown on the
schematic? If so, what purpose does bridge X2 serve? Why not just
connect L7 in series with the primary of the transformer without the
bridge?

Funny question: the simulation only regards an inductor with value of 3mH.
Without the bridge, what remains is an inductive voltage divider (when ignoring
eventual nonlinear effects).


If L7 were iron core, I can see it having a large reactance until the
core saturates from the DC flowing in it. That would give the kind of
results shown, but only the first time it is used. After that, the core
would have some residual magnetism that would seriously reduce the surge
limiting effect.

Please explain.

Steady state (constant load), the current through L7 is DC - hence no inductive
loss. But when switching on (or a nearby (s)hit from lightning), the current
change causes a large peak voltage across L7 and a transient voltage divider
forms. My goal was to limit the voltage to the mosfet in a switching 1.5 KW
power supply to a safe value and this type of surge limiter appears to be
working very well.