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MOSFET gate current... where does it go?

Discussion in 'Electronic Components' started by Tomás Ó hÉilidhe, May 31, 2008.

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  1. Consider an NMOS transistor which is turned off when there's 0 V on
    the gate, and turned on when there's 5 V on the gate.

    I've been told that a tiny bit of current flows into the gate of a
    MOSFET transistor... well where does this current go? Does it come out
    the drain, or the source, or does it split between the two?
     
  2. ian field

    ian field Guest

    The gate has a significant capacitance, any current that flows is either
    charging or discharging that capacitance.
     
  3. Eeyore

    Eeyore Guest

    It comes back out exactly where it went in. Up the gate pin. You have to
    both charge and discharge the gate.

    Graham
     
  4. Jim Adney

    Jim Adney Guest

    To add a bit of clarification:

    The gate capacitance is between gate and source, so, while you're
    charging that capacitance, the charging current is going in the gate
    and coming out the source. Discharge is the reverse.

    The actual electrons are going in the gate while charging, and back
    out the gate on discharge.

    -
     
  5. legg

    legg Guest

    The current is needed to form/discharge voltages on the circuit
    capacitances.

    Current i = dQ/dt Amps, delta-coulombs delta-seconds
    Charge q = CV Coulombs Farads Volts

    There is also a leakage current, very small, that bleeds through
    imperfect insulation in the capacitive structures.

    Other losses, in series resistance, will affect energy transfer.

    RL
     
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