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I'm trying to use a simple PWM controller (this) as a dimmer for a Meanwell LED driver (this).

The driver accepts PWM dimming but needs a voltage range of ~2-8V, and the PWM controller outputs 7-12V when powered by the 12V input I'll be using.

Is there an easy way I can modify the controller to get the voltage down to this range?

Would lowering the input voltage lower the output range too? Or could I simply change the value of the pot/add in a resistor or two, or would that destroy the PWM signal?

I will be repositioning the potentiometer from the controller as space is very limited in my use case, so some soldering is required anyway. However the theory on this is a bit beyond my skill level.

Many thanks for any help on this

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  • \$\begingroup\$ A resistor in series will most probably suffice in practice, otherwise a Zener diode in series will cut come of that volage. \$\endgroup\$ – winny Oct 16 '20 at 10:42
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    \$\begingroup\$ I'd probably use a linear regulator in front of the PWM controller (to bring its supply voltage down to around 5V), but you should also be able to use a simply resistor divider, for example with 100 and 130 Ohms resistors. \$\endgroup\$ – towe Oct 16 '20 at 11:32
  • \$\begingroup\$ Strange - I tried instead with a 7V power supply I had spare and the output fell to around 3-7V which is fairly close to the driver's spec for PWM dimming, however it has no effect at all on the brightness of the LED, it just ran at full except for some flickering when turned completely off. \$\endgroup\$ – user1400504 Oct 16 '20 at 13:25
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The easiest way would be to use a transistor to pull the PWM-Dim pin down to PWM-.

The PWM-Dim is also the on/off signal for the power supply. Open (no connected, floating) is on. Connected to PWM- is off. That means it has a pull up connected internally. All you have to do is pull down PWM-Dim.

Your PWM controller provides up to 5A of current, and is complete overkill. You can still use it.

Here's how I'd go about it:

schematic

simulate this circuit – Schematic created using CircuitLab

It has the disadvantage that the dimmer knob on your PWM controller will work backwards. This circuit inverts the PWM signal. When the PWM controller generates a 1% duty cycle, the LDH45 will receive a 99% duty cycle. When the PWM controller generates a 90% duty cycle, the LDH45 will receive a 10% duty cycle.

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  • \$\begingroup\$ Thank you for this. I'm going to try this method for now, but also look for a more suitable PWM controller as I now see it probably wasn't a good match in the first place. Not entirely sure where to start looking though other than looking through random listings on eBay etc... \$\endgroup\$ – user1400504 Oct 16 '20 at 13:22

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