SEMICONDUCTOR DIODE
A pn junction is known as a semi-conductor or *crystal diode.
The outstanding property of a crystal diode to conduct current in one direction only permits it to be used as rectifier. A crystal diode is usually represented by the schematic symbol shown in fig 1. The arrow in the symbol indicates the direction of easier conventional current flow.
fig. 1
A crystal diode has two terminals. When it bis connected in a circuit one thing to decide is whether the diode is forward or reverse biased. There is an easy rule to ascertain it. If thew external circuit is trying to push the conventional current in the direction of arrow, the diode is forward biased. On the other hand, if the conventional current is trying to flow opposite to arrowhead, the diode is reverse biased. Putting on the simple words :
1) If arrowhead of diode symbol is positive w.r.t. bar of the symbol, the diode is forward biased.
2 ) If the arrow head of the diode symbol is negative w.r.t. bar, the diode is reverse biased.
Identification of crystal diode terminals. While using a crystal diode, it is often necessary to know which end is arrowhead and which end is bar. For the purpose, the following methods are available :
1) Some manufacturers actually paint the symbol on the body of the diode e.g. BY127 , BY114 crystal diodes manufactured by BEL.
2)Sometimes, red and blue marks are used on the body of the crystal diode. Red mark denotes arrow whereas blue mark indicates bar e.g. OA80 crystal diode.
The outstanding property of a crystal diode to conduct current in one direction only permits it to be used as rectifier. A crystal diode is usually represented by the schematic symbol shown in fig 1. The arrow in the symbol indicates the direction of easier conventional current flow.
fig. 1A crystal diode has two terminals. When it bis connected in a circuit one thing to decide is whether the diode is forward or reverse biased. There is an easy rule to ascertain it. If thew external circuit is trying to push the conventional current in the direction of arrow, the diode is forward biased. On the other hand, if the conventional current is trying to flow opposite to arrowhead, the diode is reverse biased. Putting on the simple words :
1) If arrowhead of diode symbol is positive w.r.t. bar of the symbol, the diode is forward biased.
2 ) If the arrow head of the diode symbol is negative w.r.t. bar, the diode is reverse biased.
Identification of crystal diode terminals. While using a crystal diode, it is often necessary to know which end is arrowhead and which end is bar. For the purpose, the following methods are available :
1) Some manufacturers actually paint the symbol on the body of the diode e.g. BY127 , BY114 crystal diodes manufactured by BEL.
2)Sometimes, red and blue marks are used on the body of the crystal diode. Red mark denotes arrow whereas blue mark indicates bar e.g. OA80 crystal diode.
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