drive mosfet through PIC16F1827

Discussion in 'General Electronics Chat' started by aniket07, Jan 10, 2011.

  1. aniket07

    Thread Starter New Member

    Jan 8, 2011
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    can we drive mosfet directly from PIC16F1827, if the Vcc applied is 2V
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Not any MOSFETs that I know of.

    You'll need some kind of driver circuit. Even most logic-level MOSFETs require 4.5v or more for Vgs in order to be considered turned on.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Maybe.

    What is the MOSFET to be driven? If it is something along the lines of a 2N7000, then it can BARELY be driven directly (Vth is 1-2V), if it is a power MOS, you'll need to use a transistor as a MOSFET Driver.

    More details will help, such as what the MOSFET will be switching, etc.

    Do you have a source other than 2V in the same circuit?
     
  4. aniket07

    Thread Starter New Member

    Jan 8, 2011
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    i have not yet decided which mosfet to use. the mosfet will actually connect an inductor across the voltage supply and the mosfet is to be driven by the output pin of the micro-controller. the basic requirement is that the power consumption of mosfet circuitry should be as small as possible.
    i think 2N7000 series mosfets can be a good choice. but what about its power consumption? can it be used for above application?
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    With only a 2V gate drive, losses will increase in any MOSFET not specifically designed for low voltage (2N7000 is not).

    If you are creating a switching power supply, there are better options, though I can't really suggest one without knowing the voltage and current needs, switching speed, etc.
     
  6. aniket07

    Thread Starter New Member

    Jan 8, 2011
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    [​IMG][​IMG]The ckt daigram is attached here. I want to use mosfet as a switch s5. S5 will be driven by micro-controller. the switch is closed when peak amplitude of the ac voltage supply is detected. My basic requirement is that the switch should consume power as minimum as possible. The voltage at output pin of microcontroller is around 2 to 2.5 volt. Plz suggest me the suitable mosfet.
     
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  7. nickelflipper

    Active Member

    Jun 2, 2010
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    Yes there are many, but since no Drain-Source voltage, or current requirements, are given, maybe not? Here is an extremely low gate threshold device http://www.diodes.com/zetex/_pdfs/3.0/pdf/ZXMN2B14FH.pdf , notice that the Drain-Source is limited to 20V, some others are even lower than that.
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    There is still no voltage or current value mentioned, or the size of the inductor.

    When you get closer, you can use Digi-Key's or Mouser's Parametric search to find devices that meet your needs, but you will most likely only find an SMD device with the properties you want.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    If you tried to implement your schematic, when the "switch" opened, the current through the inductor will have no place to go. This will result in the polarity of the voltage across the inductor to reverse, and reach a very high peak value.
     
  10. aniket07

    Thread Starter New Member

    Jan 8, 2011
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    thanks guys...
    One more doubt.. can I use a relay instead of mosfet? Are there relays available whose power consumption is very low (may be as low as of the order of uW)?

    @ SgtWookie Yes,you are absolutely right. polarity of the voltage across the inductor will reverse. Exactly thats what I want.
     
  11. SgtWookie

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    Not an electromechanical relay.
    There are solid state relays (SSR's) but they are very slow compared to MOSFETs.
    Once a MOSFET gate is charged or discharged, no gate current is required to maintain the MOSFETs' conduction state.
     
  12. tom66

    Senior Member

    May 9, 2009
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    If you want, you can use an NPN transistor common emitter switch to drive a relay from a higher voltage; 2V should easily switch it into saturation. For the higher voltage, as low as 3.3V is enough for some smaller relays.
     
  13. aniket07

    Thread Starter New Member

    Jan 8, 2011
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    hi again...its been a long time...
    so nw i have decided to use a mosfet 2n7000 for the switching purpose. But the problem i m facing is that: as per the attached circuit diagram the switch is to be connected across an ac voltage source which is nothing but the output of a transducer. N a pulse from the output pin microcontroller will be given to the gate terminal of the mosfet. Can i use the mosfet as switch in this case? I have used mosfet for swiching purposes only with DC sources so far. I guess the source terminal will remain floating and because of this there may be problem in the switching..
    Plz help me out...
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    A 2N7000 won't get turned on at that low of a Vgs.

    You'll probably have to use transistors (BJT's) instead.

    But, you mention an AC source - so I don't really know what you're doing.

    Without some sort of schematic to go by, we'll be doing this question-and-answer thing forever.
     
  15. aniket07

    Thread Starter New Member

    Jan 8, 2011
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    hi...
    i have attached the circuit diagram over here..
    The switch should be mosfet preferably. But i dont know if the mosfet or BJT
    will work with the ac source.


    [​IMG]
     
  16. SgtWookie

    Expert

    Jul 17, 2007
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    What voltage AC source?
    How much current are you trying to control/switch/whatever?

    What is it that you are really trying to do?

    MOSFETs have internal body diodes. If the polarity between drain and source is reversed, the diode will conduct.
     
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