0
\$\begingroup\$

I wanted to connect an LED light chain to a lamp outlet in my house in order to turn it on and off using the wall light switch. I have dismantled the 230V to 3V power supply that was built into the plug on the light chain, and put it in a junction box with a wire to the lamp outlet.

enter image description here

All is good when the switch is on, but when I turn it off, the light chain goes dark, but it flashes very briefly but quite bright every 10-20 seconds. So what is going on here?

My best guess is that there is capacitive coupling in the wire going to the lamp outlet, and this low voltage charges the capacitors in the power supply and is released in the light chain when it reaches a certain threshold. Is this a plausible explanation?

And the next question is of course what to do about it? I could built a very simple power supply like the one described here: https://diycircuits530.blogspot.com/2020/05/how-to-make-220v-ac-to-3v-dc-converter_17.html But I do not know if I would run into the same issue with this? Or have a constant faint glow from the LEDs?

I also read about Schottky diodes that, if I understand correctly, opens for the current only when the voltage reaches a certain potential. Would it be a feasible solution to install one of these on the wire from the lamp outlet to the power supply?

\$\endgroup\$

2 Answers 2

Reset to default
1
\$\begingroup\$

You don't want a diode. You can buy an off-the-shelf snubber for solving this problem. Connect one across the live and neutral supply pins of the power supply.

Typically, it would contain a capacitor of about 0.1μF, which must be rated for 250VAC. It may also contain a small resistor.

\$\endgroup\$
3
1
\$\begingroup\$

Yes this is capacitive coupling and no Schottky diodes are of no use here.

Typically a decent LED power supply in a LED bulb or luminaire with LEDs would have a resistor to slightly load down the capacitive coupling.

\$\endgroup\$
1
  • \$\begingroup\$ Hi Justme, Thank you for replying. Can you suggest a solution to the current setup? Could a simple resistor on the phase wire before the power supply solve it? Or would that also impact the actual operation when switched on? Or what about the simple power supply in the link - would this be a feasible solution? I have looked at LED drivers intended for use on a lamp outlet, but these seems to be used with higher voltages and the lowest I can find is 5V. \$\endgroup\$
    – UsernameError
    Commented Aug 16, 2021 at 12:15

Not the answer you're looking for? Browse other questions tagged or ask your own question.