MCU and negative voltage signal

Discussion in 'General Electronics Chat' started by andrea.rafg91, Jul 22, 2017.

  1. andrea.rafg91

    Thread Starter New Member

    Jul 22, 2017
    2
    0
    Hi,

    I have a MCU with +3.3V output pins, I will need to power down a device which expects -3.3V signal (it takes no more than 0.5mA current from this signal, it only expectes the negative voltage level).



    How could I accomplish this? should I use a P-channel MOSFET, N-Channel? JFET? do you have a recommendation for a +3.3V logic level transistor?

    Thank you very much in advance!
    Andrea
     
  2. ericgibbs

    Moderator

    Jan 29, 2010
    5,458
    1,022
    hi 91,
    A P MOSFET usually requires a negative Gate to Source control voltage.
    E
     
  3. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
    6,189
    1,443
    The circuit below assumes that a 10k resistor to -3.3V will activate the power down signal. Note that the power down signal will be activated when the MCU output is low which is the reverse of your circuit.
    upload_2017-7-22_12-33-22.png
     
  4. andrea.rafg91

    Thread Starter New Member

    Jul 22, 2017
    2
    0
    Thank you for such fast answers. So I understand I should use n-Mosfet or BJT. Thank you AlbertHall for your schematic, the simulation looks good.

    Another issue I have is that I should reduce to the minimum the power consumption. How ist it BJT vs N-Mosfet? which one would be better for power efficiency?
    Thank you very much again for your help.
    Andrea
     
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