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Trouble shifting 5V clock down to 3.3V

Former Member

Hi Folks.

 

I have a pwm generated clock from my mcu which is at 5V. I want to step this down to 3.3V. I am using a 2N7000 N channel mosfet and the setup shown below.

 

image

 

This is the square wave generated by the mcu:

image

 

When I put it through the level shifter I get This output:

image

 

It is clearly offset and very distorted. When I apply 5V directly I get 3.3V out and when I connect ground to it I get 0V out as expected. However when I apply the 0 to 5V square wave it doesn't work.

 

Does anybody know why this is happening?

 

Thanks,

 

Mark.

Parents

  • Mark,

    I've made a few videos on this subject. Having an ugly deformed signal with a voltage divider solution is normal.

     

     

  • in reply to Jan Cumps

    I am not getting a great signal using the mosfet at 1MHz and above. Is there an off the shelf chip that anyone can recommend. DIP preferably.

  • in reply to Former Member

    Bit of a large package(20-pin DIP but  SN74LVC244ANSN74LVC244AN is a nice part to have around It is 5V tolerant so good for level conversion particularly if you have many signals

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