[sdiy] soft PSU turn on circuit needed

[Martin Czech]

Yes, I also thinking about rc delays in series connection.
rc1*10=rc2 . So the voltage difference tells if it is switched on
or off. I guess I need some voltage differfence sensing and a flip flop.
All discrete, of course, it must work from 2-18V or so.

I've already scetched something up...

m.c.

:::Date: Mon, 26 Mar 2001 00:38:59 -0500
:::From: harry <harrybissell at prodigy.net>
:::To: Neil Johnson <nej22 at hermes.cam.ac.uk>
:::CC: Martin Czech <czech at Micronas.Com>, synth-diy 
<synth-diy at node12b53.a2000.nl>
:::Subject: Re: [sdiy] soft PSU turn on circuit needed
:::Content-Transfer-Encoding: 7bit
:::
:::In rapid power cycling mode... this will kill you !!!
:::
:::H^) harry
:::
:::PS> I'm thinking of this Martin, I've done it before with two circuits, one
:::long
:::time constant, and one short time constant. I'll try to draw it tomorrow if
:::noone
:::gets there first.
:::
:::Neil Johnson wrote:
:::
:::> Martin,
:::>
:::> One trick used in SwitchMode PSUs is to put a highpower NTC resistor in
:::> series with the primary.  At turn-on the high cold resistance limits
:::> current flow and heats up the resistor.  As it warms up its resistance
:::> drops, so the current flow ramps up to "normal", keeping the resistor at a
:::> high enough temperature to keep its resistance low.
:::>
:::> I think all this happens in about 1sec.  Also not sure what would happen
:::> in rapid power cycling mode (apart from "Don't Do It!")
:::>
:::> Neil
:::>
:::> --
:::> Neil Johnson :: Computer Laboratory :: University of Cambridge ::
:::>   http://www.cl.cam.ac.uk/~nej22           +44 (0) 1223 334 477