Introduction to different types of diodes

Introduction to different types of diodes

A diode is a two terminal electronic device/component used as a unidirectional switch, which allows current to flow only in one direction. These diodes are made from semiconductor materials such as silicon, germanium, and gallium arsenide.

The two terminals of a diode are called the anode and cathode. According to the potential difference between these two terminals, the operation of the diode can be divided into two ways:

If the potential of the anode is higher than that of the cathode, the diode is called forward biased, which allows current to flow.

If the potential of the cathode is higher than that of the anode, the diode is called reverse biased and does not allow current to flow.

Different types of diodes have different voltage requirements. For silicon diodes, the forward voltage is 0.7V, and for germanium diodes, the forward voltage is 0.3V. Usually, in silicon diodes, the dark band at one end of the diode represents the cathode terminal, and the other end is the anode.

One of the main applications of diodes is rectification, which converts alternating current into direct current. Due to the fact that diodes only allow current to flow in one direction and prevent current from flowing in another direction, they are used in applications such as reverse polarity protectors and transient protectors.

There are many different types of diodes, some of which are listed below.

Different types of diodes

Now let's briefly introduce several common types of diodes.

1. Small signal diode

It is a small device with disproportionate characteristics, mainly used in high-frequency and extremely low current applications, such as radios and televisions. To protect the diode from contamination, it is wrapped in glass and is therefore also known as a glass passivated diode. One of the popular diodes of this type is 1N4148.

In terms of appearance, compared to power diodes, signal diodes are very small. To indicate the cathode terminal, one edge is marked in black or red. For high-frequency applications, the performance of small signal diodes is very effective.

Compared to other functions, signal diodes typically have smaller current carrying capacity and power consumption. Usually, they are in the range of 150mA and 500mW respectively.

Small signal diodes can be made of silicon or germanium type semiconductor materials, but the characteristics of the diode vary depending on the doping material.

Small signal diodes are used in general diode applications, high-speed switches, parametric amplifiers, and many other applications. Some important characteristics of small signal diodes are:

Peak Reverse Voltage (V) - This is the maximum reverse voltage that can be applied to a diode before it breaks down.

Reverse current (IR) - the current flowing in reverse bias (very small value).

Maximum forward voltage (VF) under peak forward current

Reverse recovery time - the time required for the reverse current to decrease from the forward current to I

2. Large signal diode

These diodes have a large PN junction layer. Therefore, they are commonly used for rectification, which converts alternating current into direct current. The large PN junction also increases the forward current carrying capacity and reverse blocking voltage of the diode. Large signal diodes are not suitable for high-frequency applications.

The main applications of these diodes are power supplies (rectifiers, converters, inverters, battery charging equipment, etc.). In these diodes, the forward resistance value is a few ohms, and the reverse blocking resistance value is megaohms.

Due to its high current and voltage performance, it can be used in electrical equipment to suppress high peak voltages.

3. Zener diode

It is a passive component that operates under the principle of "Zener breakdown". It was first produced by Clarence Zener in 1934 and is similar to a regular diode under forward bias conditions, allowing current to flow.

But under reverse bias conditions, the diode only conducts when the applied voltage reaches the breakdown voltage, which is called Zener breakdown. It aims to prevent other semiconductor devices from generating instantaneous voltage pulses. It acts as a voltage regulator.

4. Light Emitting Diodes (LEDs)

These diodes convert electrical energy into light energy. The first production began in 1968. It undergoes the process of electroluminescence, in which holes and electrons recombine to generate energy in the form of light under forward bias conditions.

In the early days, LEDs were very expensive and only used for special applications. But over the years, the cost of LED has significantly decreased. This and the fact that they are very energy-efficient make LEDs the primary lighting source for homes, offices, streets (used for street lighting and traffic signals), cars, and mobile phones.

5. Constant current diode

It is also known as a current regulating diode, current limiting diode, or diode connected transistor. The function of a diode is to regulate the voltage at a specific current.

It is used as a current limiter at both ends. In this case, JFET acts as a current limiter to achieve high output impedance. The symbol of the constant current diode is shown below.

6. Schottky diode

In this type of diode, the junction is formed by the contact between semiconductor material and metal. Therefore, the forward pressure drop is minimized. The semiconductor material is N-type silicon, which serves as an anode and metal, such as chromium, platinum, tungsten, etc. Serve as a cathode.

Due to their metal structure, these diodes have high conductivity, thus reducing switching time. Therefore, Schottky diodes have greater applications in switch applications. Mainly due to the metal semiconductor junction, the voltage decreases, which in turn improves the performance of the diode and reduces power loss. Therefore, these are used for high-frequency rectifier applications.

7. Transient voltage suppression diode

In semiconductor devices, transients occur due to sudden changes in state voltage. They will damage the output response of the device. To overcome this problem, a voltage suppression diode was used. The operation of a voltage suppression diode is similar to that of a Zener diode.

These diodes work normally like p-n junction diodes, but their operation changes during transient voltages. Under normal circumstances, the impedance of a diode is very high. When any transient voltage occurs in the circuit, the diode enters the avalanche breakdown region that provides low impedance.

This is very spontaneous because the duration of avalanche breakdown is measured in picoseconds. The transient voltage suppression diode clamps the voltage to a fixed level, and its clamping voltage is mostly within the minimum range.

These have applications in the fields of telecommunications, healthcare, microprocessors, and signal processing. It responds faster to overvoltage than varistors or gas discharge tubes.