Page 26 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Fig 3 Fig 4

Fig 5 Fig 6

The current in the forward direction increases rapidly upon reaching the forward voltage Vb which is known as the
barrier potential or the junction potential and the barrier potential for germanium is 0.3 V and for silicon it is 0.7 V.
The behaviour of the PN junction is limited by the maximum forward current, as too much of current may destroy
a diode due to the excess heat generation.
The current in the reverse direction of the junction is very small. Upon reaching —Vb in the reverse direction,
the reverse current suddenly increases. —Vb in the reverse direction where the current starts increasing is called
the knee potential or breakdown voltage. Normally the diode should not be operated in this region. The knee
voltage depends on the type of diode which varies from 3V to 20 kV or more.

Application of diodes : Semi conductor diodes are used for various applications. Some of the major areas of
application are listed below.
• Modulation and demodulation in communication receivers.

• Switching high speed digital circuits

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CITS : Power - Electrician & Wireman - Lesson 60-69