[sdiy] soft PSU turn on circuit needed

Martin Czech czech at Micronas.Com
Tue Mar 27 09:28:44 CEST 2001


:::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!")

I know this one. Fast on/off is the problem. Not foolproof (musician proof).
Also I don't like the idea of something getting very hot under normal
operation.

m.c.




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