BOOK_CONTENT
From Electronics I Laboratory Manual

A semiconductor diode is a non-linear device whose most outstanding feature is the fact that current is allowed to flow – basically – in one direction only.  The diode is built by joining together two semiconductor materials: an N-Type material and a P-Type material.  The area of contact is called thejunction.  This is the reason why sometimes we refer to the diode as a PN Junction.

When an applied voltage forces the diode to conduct we say that the diode is operating in the forward bias condition; when the supply voltage is connected such that the current in the diode is minimal (practically zero) the diode is in the reverse bias condition.  When in the forward bias mode1 the diode behaves much like a closed switch; on the other hand, in reverse bias2 the diode behaves like an open switch.  To understand the operation of a diode we must understand the diode I-V characteristics.

Diode Characteristics

Figure 5.1 shows the typical I-V characteristics of a silicon diode3.  The two operating regions are clearly labeled.  Notice the different scales used to indicate the current in each case.


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Gate turn-off thyristors (GTOs) are four-layer PNPN devices that act as switches, rectifiers, and voltage regulators. Like other thyristors, GTOs can be turned on by the application of a positive gate signal (g > 0); however, unlike other more conventional devices that can be turned off only at a zero crossing of current, GTOs can be turned off at any time by the application of a gate signal equal to zero.
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