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  1. #21
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    Re: Use an OR wired with diodes to control the gate in a PMOSFET

    I need an OR logic, if one input is 1 then the output of the wired is 1 and the PMOSFET is turn off.
    That's only one input condition out of four possible.
    What about both inputs zero?
    What about both inputs one?
    Zapper
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  2. #22
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    Re: Use an OR wired with diodes to control the gate in a PMOSFET

    I implemented this but it is not working

    Click image for larger version. 

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  3. #23
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    Re: Use an OR wired with diodes to control the gate in a PMOSFET

    I implemented this but it is not working
    Please use clear annotation of logic levels. Presently you have "0" and "1" placed near the same signal out12.

    Showing Ltspice voltage measurements for each node instead would help.

    I'm also not aware of a TS391 type with the shown pin assignment. Thus it's not clear what are inverting and non-inverting input. Why did you introduce a new part instead of referring to the original problem definition?

    Click image for larger version. 

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  4. #24
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    Re: Use an OR wired with diodes to control the gate in a PMOSFET

    Since you still haven't clearly stated what you need, I can't help you any further.
    Zapper
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  5. #25
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    Re: Use an OR wired with diodes to control the gate in a PMOSFET

    The inputs to the OR logic should be these onesClick image for larger version. 

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  6. #26
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    Re: Use an OR wired with diodes to control the gate in a PMOSFET

    Quote Originally Posted by d123 View Post
    Hi,

    Just to add to what FvM has already provided, the schematic below is a small variation of the same premise:

    Attachment 154586

    As this is only a simulation, although most work with occasional fine tuning of component values, skepticism never hurts. Simulators solve maths problems with idealised components.

    Notice lovely ground bounce here and there, that's why I added the two Schottky diodes. One of life's necessary evils.

    Hopefully, you should be able to use either schematic in the real world and get on with fine tuning pertinent details to your application now.

    Good luck!
    I have simulated this circuit with the first input the output of a comparator and it is not working as you show in the diagram. Could you help me?



  7. #27
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    Re: Use an OR wired with diodes to control the gate in a PMOSFET

    Hi,

    Quote Originally Posted by tiraxinas View Post
    I have simulated this circuit with the first input the output of a comparator and it is not working as you show in the diagram. Could you help me?
    Post #16 isn't the right one, I understand the schematic in post #18 fulfils the requirement. The requirement is still that either of two inputs when high make the output go low, right?

    Could you post a schematic of the comparator circuit that you mention, please?



  8. #28
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    Re: Use an OR wired with diodes to control the gate in a PMOSFET

    Hi,

    The requirements depends of the outputs 20 and 12 (Post #25). The output 12 need to be inverted. In the #25 is wrong, it is not inverted.These outputs control the gate of the PMOSFET.
    If one of these outputs is high the PMOSFET is shut down.



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  9. #29
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    Re: Use an OR wired with diodes to control the gate in a PMOSFET

    Hi,

    You can just swap the comparator inputs over to invert the output.

    If it won't work that way, I'd try using two equal devices as the PMOS gate controllers/drivers, e.g. Two NPNs.
    Not sure why you chose a PNP when suggestions were NPNs, but if it produces the desired outcome, great.



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