A diode consists of two words. “Di” means two and “Ode” means electrode, meaning that a device or component has two electrodes. (i.e. cathode and anode)
A diode is a two-terminal device that allows current to flow in only one direction. Diodes are also called rectifiers because they convert alternating current (AC) to pulsating direct current (DC). Diodes are rated by type, voltage, and current capacity.
Characteristics of Diode
The following are the characteristics of the diode:
- Forward Biased Diode
- Reverse Biased Diode
- Zero Biased Diode
Forward Biased Diode
Connecting a diode under Forwarding bias will apply a negative voltage to the N-type material and a positive voltage to the P-type material. If this external voltage is greater than the value of the potential barrier, approximately 0.7 volts for silicon and 0.3 volts for germanium will overcome the potential barrier and the current will begin to flow.
When the junction diode becomes forward-biased, the thickness of the depletion region decreases, and the diode acts as a short circuit allowing full current flow.
Zero Biased Diode
When the diode is connected in zero bias condition, no external potential energy is applied to the PN junction. However, when the diode terminals are shorted together, some holes (majority carriers) in the P-type material move across the junction against the potential barrier with enough energy to overcome the potential barrier increase. We call this “forward flow” and call it IF.
Similarly, holes generated in N-type (minority carrier) materials find this situation favorable and move in the opposite direction across the junction. This is known as “reverse current” and is called IR.
Reverse Biased Diode
When the diode is reverse-biased, a positive voltage is applied to the N-type material and a negative voltage is applied to the P-type material.
When a junction diode is reverse biased, the depletion region thickens and the diode acts as an open circuit, blocking current flow (leakage current is negligible).
Pinout of Diode
Construction of Diode
There are two types of semiconductor materials, intrinsic semiconductors, and extrinsic semiconductors.
- In intrinsic semiconductors, the number of electrons and the concentration of holes are the same at room temperature.
- In extrinsic semiconductors, impurities are added to the semiconductor to increase the number of electrons or holes. These impurities are pentavalent (arsenic, antimony, phosphorus) or trivalent (boron, indium, aluminum).
A semiconductor diode has two layers. One layer is a p-type semiconductor and the other is an n-type semiconductor.
- When trivalent impurities are added to a semiconductor (silicon or germanium), the number of holes increases, and the semiconductor becomes positively charged. This type of layer is therefore known as a p-type layer.
- When a semiconductor (silicon or germanium) is doped with a pentavalent impurity, the excess electrons create a negative charge. This type of layer is therefore called an n-layer.
Working of Diode
In the N-type region, electrons are the majority carriers and holes are the minority carriers. In the P region, holes are the majority of charge carriers and electrons are the negative charge carriers. The difference in concentration causes the majority of carriers to diffuse and recombine with opposite charges. Produces positive or negative ions. These ions are collected at the junction. And this area is known as the depletion area.
- A diode is said to be reverse biased when the anode or P-type terminal of the diode is connected to the negative terminal and the cathode is connected to the positive terminal of the battery.
- A diode is said to be forward-biased when the anode or P-type terminal is connected to the positive terminal and the cathode is connected to the negative terminal of the battery.
Types of Diode
- Light Emitting Diode
- Variable Capacitance Diode
- Tunnel Diode
- Zener Diode
- Schottky Diode
- Photodiode
- Crystal Diode
- Varactor Diode
- Laser Diode
Specifications of Diode
- Maximum Forward Current – The absolute maximum repetitive forward current that can flow through a diode.
- Maximum Reverse Voltage – The absolute maximum or peak reverse voltage that can be applied to a diode.
- Reverse Breakdown Voltage – The minimum steady-state reverse breakdown voltage at which breakdown occurs.
- Maximum Forward Impulse Current – The maximum current that can be allowed in a short time interval. This current value is much higher than the IFM.
- Maximum Reverse Current – The absolute maximum reverse current allowed at the operating temperature of the device.
- Forward Voltage – Maximum forward voltage drop for a given forward current at the operating temperature of the device.
- Power Consumption – The maximum power a device can safely consume continuously in free air at 25°C.
- Reverse Recovery Time – Maximum time it takes for the device to switch from ON to OFF state.
Advantages of Diode
- Less space required
- Lightweight
- Most reliable operation
- Low power consumption
- Increased life and efficiency
- Low Internal Resistance
Applications
- Diode as rectifier
- Boost Circuit
- Surge Suppressor
- Clipper and Clamper circuit
- Backflow Prevention Circuit
- Digital Logic Gates