On 28 Jun 2013 19:05:26 GMT, Jim Mueller wrote:

On Thu, 27 Jun 2013 23:15:25 -0500, Arid ace wrote:

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.

Is the load constant? If not, this effect will also happen when the load
changes, causing a more-than-normal change in the output voltage.
Perhaps your regulator can accommodate that.

When the resistive load in the simulation is 120 ohm and 6 ohm is switched in
parallel, the voltage over L2 decreases about 5V whereas when switching the
transformer on, the first half cycle (surge) is limited from ~170V to ~130V
peak. For my application this a good compromise. However such extreme switching
doesn't happen as the regulator keeps a battery charged when the grid is
available and the battery feeds an inverter.