"Wiebe Cazemier" wrote in message
...
On Wednesday 12 April 2006 18:10, I.F. wrote:
First the good news - after hours of searching I found the document, its
a
Shindengen MJ2400. Now for the bad news! - The chip is based on a
modified
bridge rectifier with integral thyristor to shunt the inrush limit
resistor
after start up. Sorry I made a mistake, this chip is only suitable for
SMPSU
circuits that have a mains bridge rectifier and smoothing cap input - it
won't work with a transformer.

Hours of searching? You sure are willing to invest time in helping people.
You
have my thanks, even though I can't use the chip.

Anyway, Instead, I'm gonna make a time delayed relay driver, which
bypasses a
block of resistors (which are in series with the primary coil) a short
time
after power up. I'll put a thermal fuse on the resistors to make sure it
disconnects should the transformer develop a short. A normal fuse, slow
blow,
in series with the resistors, rated at lower value than what the resistors
would use without the transformer in series with them might also be a good
idea. If I time it right, I should be able to use a fast blow fuse as main
fuse then (as noted by the PDF Ross Herbert pointed to). Experimention is
in
order.

An easy way to make a time delay is with a long tailed pair of transistors
like a differential amplifier stage and add a high value cross coupling
resistor so it acts as a Schmidt trigger and avoids relay chatter. Connect
one base to a zener about half the voltage of the secondary rail used and
the other base to a potential divider shunted by a time delay capacitor -
don't forget a discharge diode from the capacitor to Vcc, this ensures that
as Vcc falls below 1/2 value at switch off it discharges the cap. A relay
driver transistor tapped off the collector resistor of the Schmidt output
transistor completes the line up of only 3 transistors, be sure to remember
also the back emf diode on the relay coil, the relay of course must provide
adequate isolation between primary & secondary supplies!