A diode has two electrodes, the anode and the cathode. The resistance offered by a diode to the flow of electric current is very low in one direction and very high in the other direction. The diode is thus a unidirectional device. To obtain maximum current in the low resistance or forward direction, the anode must be at a positive potential with respect to the cathode. A graph of voltage against current has the shape shown in figure 3.1 for a semiconductor diode. Notice that in the reverse direction the semiconductor diode allows a very small current flow up to the point of breakdown. Breakdown in these diodes is discussed in more detail later.
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