Working of Diodes

A diode is a specialised electronic component with two electrodes called the anode and the cathode.

 A diode allows current to flow in only ONE direction. If the cathode end (marked with a silver stripe) is connected to the negative and anode is connected to positive then current will flow.
A diode has a forward voltage drop. That means, when current is flowing, the voltage at the anode is always higher than the voltage at the cathode.

 The actual Forward Voltage Drop varies according to the type of diode.
For example: Silicon diode = 0.6 to 0.7v (depending on type) 
                     Schottky diode = 0.3v 
                     Germanium diode = 0.2v

In addition, the voltage drop increases slightly as the current increases so, for example, a silicon rectifier diode might have a forward voltage drop of 0.7v when 100mA is flowing but 1.0 volt when 1 Amp is flowing.

A ZENER diode does not allow current to flow until the voltage on its cathode reaches a value called the "Zener Voltage." At this voltage the diode "breaks down" and a LOT of current will flow and must be restricted by connecting a resistor in series. At this point the supply voltage can increase and the voltage across the zener will remain constant. Values of 2.4 volts to 100 volts or more are common. Zener diodes are used to "clamp" a voltage in order to prevent it rising higher than a certain value. This might be to protect a circuit from damage. Zener diodes are also used to provide a fixed "reference voltage" from a supply that varies. They are widely used in regulated power supply circuits. 


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