All diodes allow current to pass in one direction only. N and P type Silicon ...

In the diagram above, the 330R resistor limits the current to a low level. The volt meter reads about 0.7 volts. This is because a normal silicon diode has approximately 0.7 volts across it when current is flowing in the forward direction. With a 5 volt power supply, the ammeter reads about 13 mA.

The graph below shows the current/voltage characteristics of a typical silicon diode. The reverse leakage current has been exagerated to make it show on the graph. The forward voltage is about 0.7 volts. The reverse breakdown voltage varies between different diode types. The range of values goes from a few Volts up to about 1000 Volts.

• Germanium diodes have about 200mV or 0.2 Volts across then when conducting.
• Silicon diodes have about 700mV or 0.7 Volts across then when conducting.