Q point of transistor

Discussion in 'General Electronics Chat' started by jake7, Jan 27, 2010.

  1. jake7

    Thread Starter New Member

    Jan 26, 2010
    I cannot understand what the Q point of a transistor is.

    Please give me some ideas.
  2. awright

    Well-Known Member

    Jul 5, 2006
    The quiescent point ("Q-point") of a transistor is not a characteristic or property inherent in the transistor. You will not find it in a transistor data sheet. It is the quiescent (no-signal) operating point chosen by the circuit designer and set by the circuit component values and voltages/currents applied to the transistor in the absence of the signal to be amplified.

    Let's see... Maybe you could think of it as analogous the idle speed of an automobile engine. It is selected by the designer to put the device in a quiescent condition ready to respond to the incoming command for action. In the case of the automobile, pressing the accelerator pedal. In the case of the transistor, applying a signal to be amplified.

    The quiescent point will ideally be set by the desiger at a point on the characteristic curves of the transistor optimized for the particiular task at hand.

    (I know it's not a very good analogy, but the point is to clarify that it is a waiting state that is selected by the designer, not an inherent property of the device.)

  3. hgmjr


    Jan 28, 2005
    The Q point of a transistor can be evaluated graphically.