XY-MOS Power Mosfet Module

Thread Starter

shanham67

Joined Oct 12, 2021
3
Hello all and thanks in advance...

I am trying to use a Raspberry PI to control a 12V signal using a XY-MOS Power Mosfet module (xy-mos, qty5 for $10 @ Amazon). I am using the pigpio library and I that I am sending a good PWM signal to the xy-mos. I cannot seem to affect the output voltage of the module. I get 12V no matter what I do. I have screenshots of a scope of the outputs from the Rpi and the XY-MOS. The 'recommended' connection is shown on the left in the first image below. My connection is on the right. I have attached two screen shots of my scope. In the first scope image the pwm is set at 180 out 255 (71% duty cycle). In the second scope image the pwm is set to 16/255 (6% duty cycle). Notice in both cases the the channel 1 signal is a 'noisy' 12v. (BTW, I just got this oscilloscope, my first, and don't really know what I am doing). There is an led on the xy-mos module that varies with intensity when I change the duty cycle so I believe that it is 'seeing' my pwm signal. When I set the duty cycle to 0% the led goes off. I received 5 of these modules and I have tried two of them with the same result. Do I have to attach a 'load' to the output for it to work? What am I doing wrong?


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Image 021.png
Image 022.png
 

ElectricSpidey

Joined Dec 2, 2017
1,971
You are not doing anything wrong.

PWM does not change the voltage, only the duty cycle which affects the "average" voltage seen by the load.

Your signals look pretty good.
 
Last edited:

bertus

Joined Apr 5, 2008
21,681
Hello,

Do you have a load when measuring with the scope?
I can be that no change will happen when no load is used.

What is the output voltage of the Rpi ?
The mosfets will start conducting at about 2.9 Volts.
See the attached datasheet for more info.

Bertus
 

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Thread Starter

shanham67

Joined Oct 12, 2021
3
Hello,

Do you have a load when measuring with the scope?
I can be that no change will happen when no load is used.

What is the output voltage of the Rpi ?
The mosfets will start conducting at about 2.9 Volts.
See the attached datasheet for more info.

Bertus
There was no load present when I took the pictures of the scope. I did try it with a 3K resistor between OUT+ and OUT- on the xy-mos and it didn't change anything. The resistor that I am trying may not be 'enough' load. In an effort not to burn up the resistor I sized the resistor based on the assumed power rating (1/8W). I will try to find a 'power resistor' so I can put a bit more load on it.

The magenta line on the scope is the 3.3V output of the Rpi. The scope is showing pretty close to 3.3V I think.

I am trying build a device to control the resistance on my step-mill (exercise machine). Ultimately I would like for the xy-mos to modulate the field current to the alternator that provides resistance in order to control the step-rate of the machine. I am using the raspberry pi to calculate the rpm of the alternator by measuring the frequency of the ac signal that is provided by the 'W' (tachometer) output of the alternator. I have the rpm reading part of this project working. I just realized that I can go ahead and hook up the output of the xy-mos to the alternator field. That is the 'actual' load I will be working with. I will try that next.
 
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