Introduction to Printed Circuit Board Diode (PCB Diode)

PCBs rise with silicon semiconductors' development due to the emergence of modern technologies in the contemporary world. When considering PCBs, the diodes, resistors, inductors, and capacitors play a significant role in developing the PCBs for the different requirements. The diodes in the PCBs identifies as the main component in controlling voltage signals which allows current to flow in one direction and blocks it in the opposite direction according to the user requirements.

In this article, we will cover the following topics:

• What is the PCB Diode?
• PCB Diodes Symbol Used in Designing
• What are the Purposes of PCB Diodes?
• Different Types of PCB Diodes?
• Applications of Diodes
• Connect PCB Diodes to a PCB
• How to Replace a PCB Diode?
• How to Test PCB Diode?

What is the PCB Diode?

A PCB diode is a semiconductor device that allows current to flow in only one direction. It is made of semiconductor material, such as silicon, and has two terminals, called the anode and the cathode. The anode is the positive terminal, and the cathode is the negative terminal.

When a positive voltage is applied to the anode and a negative voltage is applied to the cathode, current will flow through the diode. However, if the polarity of the voltage is reversed, no current will flow. This is because the diode has a built-in electric field that prevents current from flowing in the opposite direction.

PCB Diodes Symbol Used in Designing

Since the above figure represents the physical view of the diode, electronic engineers and related professionals use an internationally accepted symbol to represent the PCB  diodes. So, with a standard diagram for the diode, all the enthusiastic electronic people will be able to identify the PCB diodes and the process of the PCB according to the diode assembling patterns.

The above figure illustrates the diode symbol used when the electronic circuit is designed. As a result of having a common internationally accepted symbol for the PCB diodes, the simulation software in the electronics domain uses this symbol in their software.

According to the above figure, the symbolic illustration of the diode will be used to identify the process of the diode in a PCB. Moreover, the symbol will represent the direction of the current flow through the related diode-connected components. Since this is the main symbol for the diode, the symbol gets changed according to the other available functioning diodes.

What are the Purposes of PCB Diodes?

The main function of PCB diodes in the industry is as follows. A diode works based on the PN junction's unidirectional conductivity. The PN junction is transformed into a diode.

The interplay between the P and N junctions determines how a diode functions. The electrons will flow towards P in a typical scenario where P has a high number of holes and a small number of free electrons, and N has a lower density of holes and a greater density of free electrons, allowing the current to pass through P alone. This is the usual process that takes place when the circuit board diode is functioning.

This would happen if the voltage were gradually increased from zero while connecting the positive terminal of a source to the P junction and the source's negative end to the diode's N junction.

The potential barrier will prevent any current from flowing through initially.

This would happen when the voltage source is linked to both the positive terminal of the N junction and the negative terminal of the P junction. In contrast to the forward-biased diode, this produces the opposite effect. The electrostatic attraction would cause the P junction holes to move farther away from the depletion region, exposing additional negative ions. When this happens, the circuit will get closed off, and no electricity will be able to pass through it.

Light-Emitting Diodes (LEDs)

LEDs are arguably the most well-known modern use for diodes. These use a unique doping type, producing light when an electron passes through an n-p junction and emits a photon. This is the case because LEDs illuminate when a positive voltage is present. Any light frequency (color) can be emitted by changing the doping type from infrared to ultraviolet.

Power Conversion

The conversion of AC electricity to DC using diodes is the most widespread. Diodes can be used to build various rectifier circuit types, the most fundamental of which are full wave center tapped, half wave, and full bridge rectifiers.

Over-voltage Protection

The circuit board diode is the ideal device to guard against voltage surges in sensitive electronic equipment. Diodes are nonconducting when employed as voltage protection devices, but they short any high-voltage spike by sending it to the ground where it cannot damage delicate integrated circuits. Specialized diodes called "transient voltage suppressors" are created for this purpose. These can withstand significant power spikes for brief periods, which would typically ruin sensitive components.

• As a heat sensor on the amplifier.
• Can add DC particles to the AC signal.
• As a fuse or switch and safety electrode circuit.
• As a voltage multiplier.
• As a rectifier.

Different Types of PCB Diodes?

The above image illustrates the different types of available diodes with their symbols.

Light Emitting Diode (LED)

This PCB diode generates light when an electric current flows between the electrodes. In other words,  this produces light when enough forwarding current is flowing through these diodes.

Laser Diode

Due to the coherent light it produces, it is a unique kind of diode. Developers use this kind of diode when designing CD drives, DVD players, and laser devices. These are more expensive than LEDs but less expensive than other laser producers. The only disadvantage of these diodes is their short lifespan.

Avalanche Diode

The avalanche phenomenon is functioning behind this to operate this reverse bias type of diode. The breakdown of the avalanche occurs when the voltage drop is steady and independent of the current. This type of diode is essential for picture detection purposes because of there high sensitivity to light.

Zener Diode

Due to its ability to deliver a consistent reference voltage, it is the most practical sort of diode. This malfunctions when a particular voltage is applied and is performed in reverse bias. A steady voltage is produced if the resistor's current flow is restricted. Zener diodes are frequently utilized in power supply to give a reference voltage.

Schottky Diode

It has a lower forward voltage than all other silicon PN junction diodes. Low current areas will show a drop, and voltage levels are between 0.15 and 0.4 volts at that time. To achieve that performance, these are built differently. in order to achieve functioning these diodes are built with specific differences. The usage of Schottky diodes in rectifier applications is widespread.

Photodiode

A photodiode can detect even very modest current flows brought on by light. These are highly beneficial in light detection. These reverse-biased diodes are essential components when designing Photometers and solar cells. They even serve as a source of electricity.

P-N Junction Diode

PCB diodes for rectifiers are another name for P-N junction diodes. Semiconductor material makes up these diodes employed in the rectification process. Two semiconductor layers are included in the P-N junction diode. P-type doping is present in one semiconductor material layer, while N-type doping is present in the other layer. P-N junctions are created when layers of both P and N types are combined.

Applications of Diodes

Generally, all electrical circuits use diodes. Semiconductor diodes are applied to the circuit to strengthen and increase its lifespan. Integrated circuits have improved due to the continuous development of semiconductor diodes, which has also contributed to other fields.

In Switching Circuit (Current Steering)

The unidirectional conductivity of a diode is utilized to turn on or off a circuit in digital and integrated circuits, and this technology has been widely adopted. Switching diodes, for instance, can maintain the functionality of conventional switches while providing good circuit protection, preventing short-circuit burnout, etc. The switch's quick switching speed is another advantage of the switch diode.

Limiter circuits are frequently employed in electrical circuits to process various signals. Within a predetermined level range, it is used to intentionally transmit a portion of the signal. Even while most diodes can be employed as limiters, there are instances when specialized limit diodes, like protective instruments, are required.

In Regulator Circuit (Over-voltage Protections)

Typically, voltage stabilizing circuits use Zener diodes. It was made with the utilization of a unique manufacturing process. This is a process called a cross-junction silicon semiconductor diode. This unique diode is simple to form an electric field, has a high impurity concentration, and has a high charge density in the charge space. When the voltage across the Zener diode increases to a specific value, there will be a sudden increase in the reverse current. So that leads to the reverse breakdown of the diode.

In Varactor Circuit (Signals Demodulation)

Varactor diodes are frequently employed in varactor circuits to achieve intelligent control, optimization, frequency modulation, and scanning oscillation of circuits. They are commonly used in microwave circuits, including frequency multipliers, parametric amplifiers, and electronic tuners.

The application of the diode types in the different applications varies according to the project's requirements. When considering the same product developed by other industrial companies, the diodes' types and quality change according to the customer requirements and technologies.

Connect PCB Diodes to a PCB

There are two methods that can follow when connecting the diodes to the PCBs. Those use Through Hole Technology (THT) and Surface Mount Technology (SMT). The above figure illustrates a diode connected to the PCB using THT technology.

The above image is an example diode for an SMT-type diode. When connecting a diode to a PCB using the above-mentioned soldering temperature, the required amount of solder to be in the diode leads to the standards that have to follow in soldering given according to the purpose that the PCB is going to use.

The PCB designer will identify the biasing (forward and reverse) according to the requirement and the functionality of the PCB. Furthermore, you have to consider the following factors when connecting the diode to the PCB.

• Voltage drops through the diode, and the effect of that drop on the functionality of the other components.
• In the silicon-to-silicon diodes the maximum current that can pass it in the range of 100 μA to 2 mA,
• Since this is an electrical component, there is internal inbuilt resistance. Internal resistance is the resistance that generates in the diode due to the silicon parts and the functions that undergo inside the diode.
• The temperature at which the PCB will be functioning.
• The total impedance of the PN junctions.

You have to consider all the above factors when selecting the diode for the PCB. Because there are many diodes that function as the same damaged diode. Still, few of them will be suitable for the operation of the PCB.

How to Replace a PCB Diode?

For the replacement of a damaged diode in a designed PCB, you can use the following procedure,

• Power off the PCB from the main power supply.
• Identify the faulty diode in the PCB.
• Identify the best way to remove the diode.
• Heat the soldering iron and keep it around the leads of the diode.
• Allow the solder to get melt again.
• Suck the molten solder using the solder sucker.
• To be clean, use a solder wick to remove the remaining solder.
• Have to identify the best diode that is suitable for the replacement of the damaged diode.
• Check the selected diode is according to the necessary condition using the diode testing procedure.
• Keep the diode in the right direction on the PCB and solder the diode to the PCB without harming the other components.

Visual inspection is a step that you can use for verifying the soldering of the diode. Moreover, the microscopic view can check the correct soldering leads. The soldering will mostly follow the industry's IPC-A-610 standards.

How to Test PCB Diode?

Diode testing before assembling is a critical step that has to carry out in developing the PCBs. There are two standard methods for the testing of diodes. Those are,

• Diode test mode
• Resistance test mode

The diode test mode is the best way to test the PCB diodes. By following the below procedure you can check the diodes,

• Identify the anode and the cathode of the diode. above demonstrate how to identify the anode and the cathode of the diode with the physical view and the symbolic view.
• Set the digital multimeter to the diode testing mode by rotating the mode controlling knob to the diode symbol (the multimeter should be capable of handling 2 mA between the probes)
• Connect the black probe of the multimeter to the cathode of the diode and connect the red probe to the anode of the diode. It represents the forward-biased condition of the diode.
• After connecting the probes, check the reading of the multimeter. If the reading gives out values between 0.6 to 0.7 for a silicon diode, a good-condition diode will lie in between this range of values. For the germanium diodes, the values will be 0.25 to 0.3 for a good diode.
• Reverse the connection (red probe to the cathode and the black probe to the anode. This will create the reverse biased condition of the diode). In this condition, the current should not flow through the diode. Therefore, the multimeter will show the reading as OL or 1. This condition will only happen if the diode is healthy.
• A broken diode will show the values that deviate from the above range of values. Either an open or a short fault may exist in the diode.

By following the procedure above, you can identify the diode condition. From there, you can decide whether to replace it or not.

Conclusion

The diodes are the main component of developing the PCBs. The functionality of the diodes varies as reverse-biased and forward-biased. Considering factors like the impedance and the current flow, you can apply the diodes to the necessary parts of the PCB design. Since there are several types of diodes, they carry out different functionalities. You can identify the essential diode type with the consideration of the functionality, the type of PCBs that will develop, and the environment in which the PCB is used. Since there are many applications of diodes, like the other main electronic components, diodes are one of the main components in designing PCBs. With the development of electronic technology, diodes play a significant role in controlling the elements.