1. Introduction to the pn-junction Diode
The schematic symbol for the pn-junction diode is shown in the fig.

2. Introduction to the pn-junction Diode
A diode will conduct when it meets the condition that the voltage difference between the anode and the cathode exceeds the barrier voltage of approximately 0.3 volts for a germanium diode and 0.7 for a silicon diode.

3. Introduction to the pn-junction Diode
In the figures to follow it may be noted that the arrow points to the more negative potential in each case.

5. Introduction to the pn-junction Diode
A pn-junction diode is reverse biased when the n type material (cathode) is more positive than the p type material (anode). This causes the depletion region to widen and prevent current. A diode will not conduct when the arrow points to the more positive of the diode potentials.

8. The Ideal Diode
The ideal diode may be considered the most fundamental non linear circuit element.
It is a two terminal device and the i-v characteristic is shown

10. The Ideal Diode as a Rectifier

11. Impression of VD

12. The Ideal Diode as a Rectifier
Note that while V1 alternates in polarity and has a zero average value, Vo is unidirectional and has a finite average value or a dc component. Thus the circuit rectifies the signal hence is called a rectifier.,

13. Example: For the circuit draw transfer characteristic v0 VS vI