Basic Electrical and Electronics Engineering: Unit III: Analog Electronics
Forward Biased PN Junction
We connect voltage source to the PN junction, such that the positive terminal is connected to the P-region and negative terminal to the N-region, the PN junction is said to be forward biased.
FORWARD
BIASED PN JUNCTION
We
connect voltage source to the PN junction, such that the positive terminal is
connected to the P-region and negative terminal to the N-region, the PN
junction is said to be forward biased as shown in Figure 3.23.
When
PN junction is forward biased as shown in Figure 3.23 (a). The holes are
repelled by the positive terminal of the voltage source and are forced to move
towards the junction. Similarly, the electrons are repelled by the negative
terminal of the voltage source and move towards the junction. Because of their
acquired energy, some of the holes and electrons enter the depletion layer and
recombine themselves. This reduces the width as well as height of the potential
barriers (VB) as shown in figure 3.23 (b). In other wards, the width
of depletion layer and the barrier potential reduces with the forward bias.
As
a result of this, more majority carriers diffuse across the junction. Therefore
is causes a large current to flow through the PN junction.
Effect of Barrier Potential on the Forward Biased PN Junction
The
barrier potential of the depletion layer can be considered as a small battery,
which opposes the external DC voltage as shown in Figure 3.24.
The
resistance Rp and Rn represent the bulk resistance of the
P-type and N- type semiconductors.
The
PN junction does not permit the current to flow, until the external bias
voltage overcomes the barrier potential (V>VB). For example,
silicon PN junction, does not conduct as long as the external applied voltage
is below 0.7 V.
Basic Electrical and Electronics Engineering: Unit III: Analog Electronics : Tag: : - Forward Biased PN Junction
Basic Electrical and Electronics Engineering: Unit III: Analog Electronics
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