A type of valve which conducts only in one direction for current. Semiconductor diodes typically have a voltage drop of 0.6 V (silicon) or 0.2V (germanium) when conducting in the forward direction.
In electronics , diode is basically two terminals component. The common used diode which is available in our daily life is a crystalline piece of a semiconductor material which is connected to two terminals as shown is figure.
Applications of Diode:
The basic purpose of using a diode in circuit is to make flow of current in one direction. Diode conducts only in when it is forward biased. It blocks the current when it is in reverse biased. So, it acts like a gate which allows only specific type of current. (only forward biasing conduction). This unidirectional property is called Rectification and this method is used in electric power supplies or rectifiers where DC current is required, diode combinations are used in circuits to rectify AC current in to Direct current.
However, diodes can have more complicated behavior than this simple on-off action. Semiconductor diodes do not begin conducting electricity until a certain threshold voltage is present in the forward direction (a state in which the diode is said to be forward biased). The voltage drop across a forward biased diode varies only a little with the current, and is a function of temperature; this effect can be used as a temperature sensor or voltage reference.