Mosfet Newbie Question.

Discussion in 'The Projects Forum' started by huwilerp, Jan 10, 2013.

  1. huwilerp

    Thread Starter New Member

    Jan 10, 2013
    10
    0
    I am curious, if I wanted to use a mosfet to control a different circuit that is using a different power source, I.E 6V going the Gate and 9V on the drain side for an N type, why do the grounds have to be common...
     
  2. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    Because the gate control is referenced to the source which is one end of the controlled channel (the silicon between the source and drain).

    Actually, the gate control is referenced to the substrate (the body of the chip) not the channel. But in most MOSFETs the substrate is connected to the source. This is usually shown on the symbol.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,014
    3,234
    A more general answer is that any voltage, by definition, is the EMF between two points. There is no such thing as a single point voltage. Thus the voltage to drive the MOSFET gate must be referenced to something and that typically is ground or common. If the two grounds aren't common than the voltage on one ground isn't seen by the voltage on the other ground.
     
  4. huwilerp

    Thread Starter New Member

    Jan 10, 2013
    10
    0
    Is there an issue if I have both negative leads going into the same channel bank on a break board to ensure all components have the same common ground?
     
Loading...