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PWM Output - Doesn't Work with Low Current Load

ksilovich 2 years ago in Master modules / MC4x • updated 2 years ago • 2

I am trying to us a PWM HS Output on an MC4x to drive a signal needed for a PWM fan.  I will get an open load when I try to drive it directly, and even with disabling the open load check it still will not work. The output just stays at 12v.   

If I add a 1k resistor from the PWM output to ground, everything works as it should.   But now the issue I have is with no power to the MC4x,  I have some leakage voltage in the range of 50ma which will draw the battery down. 

Is this a software or hardware issue that will not allow me to use this PWM output to drive this fan directly??

My work around is using a relay to make and brake the resistor to ground when the MC4x is powered.  But this is not a great solution, and would like to see if this is just a software issue that could be fixed.  

Gustav Widén (System support) 2 years ago

The PWM out HS has an internal pull-up resistor on the board, it is used for open load detection when the output is off. 

This gives a leakage current that may be as high as 2 mA.

Image 3449



So to get a signal below the trig level for the device that reads this signal, you will need an external pull-down. 

Also see earlier post:  PWM to control small load / Hardware / IQAN



ksilovich 2 years ago

thanks for the reply.  Sounds like this is a hardware issue and the only solution is what I am currently doing with a pull down resistor and relay. 

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