Stop supply current going to zero

[treez]

Hello,


i am trying to stop the current into a 3W SMPS ever going below 40mA.
(i posted before but now have a new design)

It goes to zero when the smps fails or when there is a transient input voltage step (momentarily). -or during start-up

Here is the circuit (smps represented by resistor)

here is the LTSpice simulation file

http://rapidshare.com/files/252509861/___33946__cap_r_zener_trxient_catcher__window_2.asc.html

Please does any reader know any simpler (less component) solution?

For transient voltage detection, i use an npn + cap feeding a window comparator which switches a load on for the duration of a monostable's period. -keeping the input current above 40mA.

-the CLC resonance of the input EMC filter makes the supply current go to zero for a short while when a supply voltage transient occurs.

 

[MacGyverS2000]

A resistor in parallel with anything will draw a current... about as simple as you can get, even if not the most elegant. If you want to gussy it up, add in a current-controlled FET switch that pulls the resistor out of the line when current draw in the loop goes above 40mA.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[ijl]

What about an inductance somewhere in the supply line?