2008-09-09

Semiconductor Diodes

Semiconductor Diodes

1. A semiconductor diode is called the p-n junction diode.
2. it consists of a p-type semiconductor in contact with n-type semiconductor.
3. Regions of P-type is called ANODE.
4. Regions of N-type is called CATHODE.
5. A p-type material meets an n-type material across a bounding region called the depletion layer (p-n junction).
6. In order for current to flow through the diode, the voltage applied across the diode must exceed the junction voltage.
7. Junction voltage is the potential difference that is caused by the movement of the holes and free electron.






FUNCTION OF DIODES


Diode as rectifiers

1. A diode is said to be in a forward-biased arrangement if it only allow the current to flow from the anode to cathode. It is acting as a VALVE
2. A diode can CONVERT alternating current into direct current. This is known as RECTIFICATION. Therefore a diode can act as a RECTIFIER.
3. A RECTIFIER is an electrical device that converts alternating current (AC) to direct current (DC), a process known as rectification. RECTIFIERS have many uses including as components of power supplies and as detectors of radio signals
4. There are TWO ways to convert an alternating current into a direct current.
a. Half-wave rectification
b. Full-wave rectification

Half-wave rectification

1. The current can only flow in the forward direction through the diode.
2. The process of rectification using a diode which ALLOWS CURRENT TO FLOW IN THE HALF-CYCLE is known as half wave rectification

Half Wave Rectification

Full-wave rectification

1. The arrangement of diode in Full-wave rectification is called a bridge rectifier.
2. The process of rectification using four diodes to allow current to flow in a complete cycle and in the same direction is called full-wave rectification. 
3. A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to DC (direct current), and is more efficient.


Full Wave Rectification


Smoothing



1. The output from a rectifier can be SMOOTHED by connecting a CAPACITOR across the load.
2. During the forward peaks (positive half-cycles), the capacitor is charged up. Energy is stored in the capacitor.
3. In between the forward peaks (negative half-cycles), the capacitor releases its charge (discharge). It discharges partly through the load. The energy stored in the capacitor acts as a reservoir and maintains the potential difference across the load.
4. A capacitor with greater capacitance produces a smoother current. This is because the capacitor can store more charge.

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