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I have a Paulmann 70975 24V LED touch dimmer that I want to use with 12V LEDs. The input voltage is provided by a MeanWell LPV-60-12 12V 5A power supply. The consumer is a 12V 2835 white LED stripe of about 4.5m. Here are pictures of the dimmer: front back

The input voltage is split for the controller circuit and reduced to 5V using a 78L05 voltage regulator. The output is regulated by the controller using a FQD50N06 MOSFET. Judging from the components' datasheets, everything should work fine with 12V.

It worked as expected at first, but after a few hours the switch becomes hot and won't react anymore. The LEDs are still on at the same brightness, but can't be dimmed or turned off. After disconnecting the power supply and waiting for a day, the switch still won't work anymore, LEDs still at the same brightness.

What am I missing? I also tried with another dimmer and another power supply of the same type. Still the dimmer becomes unresponsive after a few hours.

Update

The LEDs draw 2.6A (measured without dimmer) which should be within the specs of the MOSFET.

Here are the schematics. Photodiode = LED. Sorry in advance, I don't have a good program for that, suggestions welcome ;)

schematics

Update 2

I measured some values:

The 78L05 has an output of 3.8V, not 5V, which seems strange.

The FQD50N06 has 0.25-0.3V at the gate (depending on "on" or "off"), measured from source, which probably seems not to be enough threshold?

So any suggestions for different voltage divider resistors?

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    \$\begingroup\$ Your link claims the dimmer should handle 144W@24V, which is 6A. I wonder, how many W your LED strip draws? I assume you are not overloading your 5A 12V power supply, so that is probably not the issue. Next idea: What about the MOSFET gate voltage? 24V is probably outside spec of most, so perhaps there is a voltage divider, which lowers 24V to safe levels, let's say half. But from 12V source, the gate might become too low, resulting in poor conductivity and excessive power dissipation on the MOSFET. \$\endgroup\$
    – akwky
    Commented Jun 26 at 9:18
  • \$\begingroup\$ If you have very heavy load, you could consider to replace the MOSFET in the top left hand corner with a beefier one. \$\endgroup\$
    – winny
    Commented Jun 26 at 9:21
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    \$\begingroup\$ That MOSFET can easily handle the current but needs Vgs of 10V to do it, while absolute max Vgs is 20V. I suggest you figure out the schematic so you can see if this is going to be an issue on a 12V supply. It seems likely. \$\endgroup\$
    – Finbarr
    Commented Jun 26 at 9:53
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    \$\begingroup\$ The MCU drives the MOSFET directly with 5V level via R5, there should be no difference at suply voltages between 12 and 24 V. FQD50N06 from VBsemi should be full conducting above 4 V, FQD50N06 from ISC probably not. \$\endgroup\$
    – Jens
    Commented Jun 26 at 12:01
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    \$\begingroup\$ @PeterJennings They would probably say something like it is designed for 24V, not for 12V... \$\endgroup\$
    – redspider
    Commented Jun 26 at 12:27

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