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optocoupler output problem noise

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yassin.kraouch

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Hi, please i am blocked in this project and i need help, attached is the circuit of the project, the problem is with the optocoupler output, please i need help*

 

My first thoughts are what are you taking the output from. Each of the opto-outputs is sittling 3.3v above the previous one, relative to the negative side of the bottom battery. There is no zero volt reference point for the output side and so no current can flow through the FET or LED side.

It would also be a good idea to add a resistor between the gate and source of the FET to ensure it turns off in the absence of drive voltage.

Brian.
 

i am taking the output from PIN 5 of each optocoupler
 

there isn't any ground connected to any battery so how can current flow through the leds?
 

there is current flow as shown in the picture, this is a practical result, the ground of the MOSFET is connected to the global ground ( see attached)
 

That is a different schematic than the one you showed first!

Are you connecting the oscilloscope ground to the source of the FET ?

What are you actually trying to achieve? All you should get outputs at 0, 3.3V and 6.6V when the FET is turned ON and at 3.3V, 6.6V and 9.9V when it is turned off. These figures assume you are not significantly loading the outputs.

Brian.
 

You should clarify about the voltage probe connections first. It's not understandable, how you get a negative output voltage in the second waveform. One could guess, that the first waveform is mainly showing unsuitable trigger conditions.
 

I would say the "noise" is possibly something to do with your triggering and measurement. Regards Orson Cart.
 
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I think you need to rethink your circuit. As mentioned by others here, there's no good reference for the opto outputs, as each one is sitting on some battery. And are those really batteries in your circuit? Where do you have you scope probe ground lead connected? Ground? And what's really the point of this circuit? It might help if you could explain that.
 

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