PWM Control

[rbatta]

Hi,

I plan on using my T100MD PWM output to control a Meanwell Dimmable LED power supply.

The MW PS is looking for a Full PWM Voltage of 10V.  What is common practice here?  Should a supply 10V to the MWPS using a seperate PS or voltage divider?  Or use the 24V and limit the duty cycle to 41%?

Thanks,

Rob

[support]

Are you sure it is PWM that they are expecting? 0-10V control sounds like they are expecting an analog output. If the MW dimmable P/S is expecting analog then you cannot give it a PWM equivalent. You can use either the FMD88-10, FMD1616-10 or F1616-BA which support 0-10V analog outputs. (the two analog outputs on the two FMD PLCs are software selectable to be 0-5V or 0-10V)

If it is indeed 0-10V PWM signal, then it is safest to use two resistors to form a voltage divider. The 10V signal can be tapped from the center of the two resistors. E.g. if your power supply is 24V, you can get 10V using two resistors: 1.4K and 1K with 1.4K connected to 24V and 1K end connected to 0V. You get 10V out from the common point between the two resistors. This 10V is then connected to the PWM output via a diode (to block reverse current from the PLC's output LED) and to your dimmable power supply control input.

Note however that the duty cycle will be inverse in this case. i.e. 0% duty cycle means 10V output, and 100% duty cycle =   0.7V output (forward voltage drop of the diode mentioned above).

[rbatta]

It's definitely looking for PWM.  Thanks for the advice; I'll use a voltage divider and diode.

Thanks again.

Rob

[support]

What is the input impedance of the PWM control input of the dimmable power supply? I assume that this is just a control signal and that the dimmable power supply is not drawing much current from this input then the voltage divider method will work.

If the dimmable power supply is drawing large current from this control input then you will have to use a separate 10V power supply to supply it instead of using voltage divider constructed out of resistors as mentioned in the first reply.