[Amps] Step start

[Han Higasa]

Hi all,

The primary and the only purpose of a step-start circuitry is to avoid
inrush current and to protect filaments, rectifier diodes, capacitors
and other circuit components from a disaster by a rapid power-up.

Patrick you are right.
Sensing a secondary voltage via a safety way such as photo-isolator and
control a relay to short a resistor R in series of primary supply voltage
when a secondary voltage reaches to a sufficient level, is a very good 
idea but it is just one of the way to limit an inrush current. 

Instead I am just using a power-relay, R and a 5-sec time-delay relay 
for a step-start of my HVPS. 
I am also using same method for a step-start of filaments.

I think the R plus AC relay with its coil connected on the primary line
is not adequate or reliable -- R plus time-delay relay will provide more 
robust way.

All HVPS (+ its primary line connected)  has its inherent dV/dt (or 
voltage variation versus time) characteristics.
So one can determine an adequate step-start circuitry suited for the dV/dt
by choosing R and delay time instead of a closed-loop configuration.
I think the open-loop is simple and enough.

de Han JE1BMJ