Question

Draw and describe the VI characteristics of zener diode

Answer 1

A zener diode is operated only in the reverse-bias region. (generally written as VR) is increased, the reverse current (usually called zener current, IZ) remains negligibly small up to the ‘knee’of the curve point. At this point, the effect of breakdown process begins.

From the bottom of the knee, the breakdown voltage (also called zener breakdown voltage or simply zener voltage VZ) remains essentially constant. This ability of a diode is called regulating ability and is an important feature of a zener diode. It maintains, an essentially a constant voltage across its terminals over a specified range of zener current values.

Following two points are important from the characteristics of a zener diode : 1. There is a minimum value of zener current called breakover current designate a IZX or IZ(min) which must be maintained in order to keep the diode in breakdown (or regulation) region. When the current is reduced below the knee of the curve, the voltage changes drastically and the regulation is lost. 2. There is a maximum value of zener current designated as IZM or IZ(max) above which the diode may be damaged. The value of this current is given by the maximum power dissipation of the zener diode. As long as the maximum power dissipation is not exceeded, the diode will not be damaged. It will come out of the breakdown region, when the applied reverse voltage is reduced below the breakdown voltage.