THEORY
The PN junction diode is a device formed from a junction of n-type and p-type
semiconductor material. The lead connected to the p-type material is called the anode
(A) and the lead connected to the n-type material is the cathode (K). In general, the
cathode of a diode is marked by a solid line on the diode, as shown in Figure 1.
A K
Figure 1. Diodes circuit symbol
The equation for the voltage and current relation is known as Shockley equation.
( 1)
D
t
V
nV
D s I I e
(1)
where the emission coefficient n varies between 1 - 2 depending on the level of
recombination effect and IS is the diode reverse saturation current. And Vt = kT/q is the
thermal voltage (approximately 25.8 mV at 300K).
The primary function of the diode is the rectification. When it is forward biased
(higher potential at the anode lead), it will pass current. When it is reverse biased
(higher potential at the cathode lead), the current is blocked. The typical characteristic
curves of an ideal diode and a real diode are illustrated in Figure 2.