Have you noticed the densely packed LED beads on top of the LED display, which is actually what we often call a light emitting diode. This kind of diode is used in a very wide range, and there are many kinds of diodes, in order to distinguish them, engineers by using different symbols to indicate. Let’s learn together.
What is a diode?
A diode is an electronic device made from semiconductor material. It has unidirectional conductivity and when energized, the direction of current flows from the positive pole through the tube to the negative pole.
If the current flows from the negative terminal to the positive terminal, then the current in the diode is blocked and the current cannot be allowed to pass through.
What is the diode symbol?
The diode symbol represents a diode in a circuit diagram. It consists of a long line connecting a triangle perpendicular to the long line and a pattern of short lines in series. The triangle represents the positive terminal of the diode and the short line perpendicular to the long line represents the negative terminal of the diode.
How to read diode symbols?
Judge the two terminals (positive and negative) of a diode
The positive terminal is usually a triangle indicating the direction of current flow. And the short line near the flat side of the triangle or marked (banded or striped) on the diode package represents the cathode.
Direction of Current Flow
When a diode is forward biased, the current flows from the positive terminal through the diode channel to the negative terminal, which means that the positive terminal will be more positive than the cathode, allowing the diode to conduct normally in this particular state.
When a diode is reverse biased, the current flows from the negative terminal through the diode path to the positive terminal, which means that the cathode will be more positive than the positive terminal, preventing the current from passing through and acting as an insulator.
Types of diodes and their symbols
General Purpose Diode
A general purpose diode can also be referred to as a rectifier diode. This diode converts alternating current (AC) to direct current (DC) and has a unidirectional conductivity that allows current to flow in the same direction, that is, the positive terminal of the power supply is connected to the positive terminal of the diode and the negative terminal of the power supply is connected to the negative terminal of the diode. At the same time, a general-purpose diode is able to block the flow of current in its opposite direction.
The symbol for a general-purpose diode is a hollow or solid triangle plus a straight line, with the triangle in the center next to a vertical line that looks like a pause button.
Zener Diode
A Zener diode is a specialized diode that provides a stable reference voltage. It allows forward and reverse currents to flow, provided that the reverse current can reach the breakdown value, which is also known as the Zener voltage.
The symbol for a Zener diode is a triangle with a short vertical line, the lower end of which extends a small amount in the direction of the triangle, while the upper end will extend a small amount in the opposite direction.
Schottky Diode
The Schottky diode is a diode made of a tiny structure formed by a metal and an N-type semiconductor, and it is a diode made specifically for RF applications. It is mainly used where there is a need to limit losses and high frequencies. The reason for this is that it does not have a PN junction like a normal diode, so it has a very low forward voltage drop and fast switching.
The symbol of a Schottky diode is similar to that of a Zener diode, but the symbol of a Schottky diode builds on the symbol of a Zener diode by putting the two small extended line segments a vertical distance further into the center region.
Tunneling Diode
Tunneling diodes operate on the principle of the quantum mechanical effect of tunneling, and are primarily composed of highly doped P&N semiconductors. Tuning” occurs when the highly doped PN junction allows electrons to escape. At the same time, the tunnel diode operates in the negative resistance region where the current decreases as the voltage increases.
The symbol for a tunnel diode is expressed in two ways: a short line and a semi-ellipse. One is a solid triangle with a line segment similar to “[“or “]”.
PIN Diodes
The “PIN” in PIN diode stands for the three-layer structure inside: P-layer, I-layer, and N-layer. The strongly doped P-type and N-type semiconductors are located between the “I” semiconductor layers. When reverse biased, high voltages are blocked by the I layer. Also, due to the slow reverse recovery time of PIN diodes, they are not suitable for high frequency applications.
The symbol for a PIN diode is a parallelogram or the letter “P” between a solid triangle and a short vertical line.
Light Emitting Diode(LED)
Light Emitting Diode is a PN junction formed by connecting a P-type material (with an excess of positive charge) to an N-type material (with an excess of negative charge), so it is also called a PN junction diode.
When an LED – Light Emitting Diode is forward biased, it is able to convert electrical energy into light energy for light emitting action. The material of the semiconductor determines the color of the light.
The symbol for LED – Light Emitting Diode is based on a solid triangle and a short line with two outwardly dispersing arrows tilted at 45 degrees drawn in the upper right area.
Two Color Light Emitting Diode
Two Light Emitting Diode and LED and Light Emitting Diode are generally the same, the only difference is that the Two color Light Emitting Diode is capable of connecting two different colors of LEDs in reverse parallel in a single package and glowing two different colors with more polarity.
The symbol of Two Color Light Emitting Diode is different from the symbol of ordinary diode, it is composed of a circle and four arrows, in which, inside the circle there is a rectangle, the upper and lower edges have a solid triangle and vertical line, the upper pattern and the lower pattern staggered symmetrically.
45 degrees of the four arrows were two by two in the upper left area and the lower right area presenting an outwardly dispersed layout.
Photodiode – A photodiode is a device that converts light energy into electricity.
A photodiode is a semiconductor device that converts light energy into electrical energy. It works on the principle that photons react with the semiconductor material to produce electron-hole pairs. When these charge carriers are separated by an electric field or a PN junction, a current proportional to the intensity of the incident light is generated.
The symbol for a photodiode is similar to that of an light emitting diode, except that the arrow direction of a light emitting diode points in the direction of a triangle, not outward.
Bidirectional Photodiode
General photodiodes are designed to operate only in reverse bias, but the bi-directional photodiode breaks through this limitation and can operate in both forward and reverse bias, having a bi-directional nature of operation.
The symbol for a bidirectional photodiode is a combination of a diamond shape and two inward facing arrows.
TVS Diodes
A TVS diode is a type of diode used to suppress high voltage spikes and is also known as a transient voltage suppression diode. It is capable of protecting a circuit in one direction with reverse bias.
The symbol for a TVS diode resembles a “bow tie”. Specifically, a mirrored “L” pattern appears in the lower center of two opposing solid triangles.
Reverse Diode
A reverse diode has a negative resistance characteristic over a range of voltages, so that as the voltage across the diode increases, the current through the diode decreases. Therefore, it can be used as a tunnel diode when forward biased and as a Zener diode when reverse biased.
The symbol for a reverse diode consists of a triangle and a vertical line segment in the shape of a “dumbbell”.
Thermal diode
A thermal diode can also be called a Peltier diode. It efficiently dissipates heat from electronic components and improves the overall performance of electronic devices. At the same time, it can capture waste heat on the energy harvesting field and convert it into useful energy.
The symbol for a thermal diode is based on a solid triangle and a short line, with the word “t°” added to the lower area.
Laser Diode
A laser diode is a semiconductor device that converts electrical energy into light energy, which is emitted as a laser beam. When an electric current is passed through the diode, it causes the photons to condense and thus be emitted as a narrow, intense beam, producing coherent light amplification.
The symbol of a laser diode is a combination of a triangle pattern with a large arrow running from bottom to top parallel to a vertical line and a vertical line segment.
Magnetic Diode
A magnetic diode controls the flow of magnetic flux, thereby realizing a unidirectional flow of magnetic field. It is an innovative technology that may drive future developments in various fields such as electronics, energy and information technology.
The symbol for a magnetosensitive diode is based on the symbol for a general-purpose diode, with two vertical downward arrows added to the upper area and the letter “B” added to the lower area.
Varactor Diode
A varactor diode, also known as a tuning diode, is a voltage-controlled capacitor with a variable PN junction capacitance. The capacitance of the varactor diode can be adjusted over a wide range by controlling the reverse voltage. When a varactor diode is reverse biased, this results in a reduction in capacitance.
Varactor diodes can have a variety of symbols, with four common ones. When all of them are added to the typical general-purpose diode symbols, various patterns are added. The first is the addition of an extra short vertical line.
The second is the addition of “卝” in the lower area. The third is to add a small 45-degree arrow pointing outward in the upper right area of the short line. The fourth adds a line segment like “)” in the center of the triangle.
Step Recovery Diodes
A step recovery diode, sometimes referred to as a transient diode, is able to quickly switch from a conducting to a non-conducting state.
When current flows in the opposite direction, the doped areas of the PN junction are quickly removed, resulting in an increase in reverse current that drops off sharply as the charge is depleted.
This rapid transition produces sharp voltage pulses and high-frequency harmonic content, making step recovery diodes more suitable for a variety of high-frequency applications.
The characters of a step recovery diode are not much different from typical diode characters, except that the line segments in the lower area are varied to resemble lightning bolts for better differentiation.
Shockley Diodes
A Shockley diode, also known as a “pnpn” diode or quadruple layer diode, is a semiconductor diode with a unique four-layer structure. It consists mainly of two P-type semiconductors and two N-type semiconductors.
When a forward voltage is applied to the diode, the two PN junctions become forward biased and current begins to flow. However, as the current increases, the voltage across the diode decreases.
The symbol of the Shockley diode is a small flag similar to a triangle with a pattern of short vertical lines, rotating the pattern 90 degrees counterclockwise. You can see a pattern similar to the “1/4” appears.
Diode symbols in the circuit design of practical applications
Power supply
The diode symbol in the circuit diagram represents the power supply, providing energy for the entire circuit, capable of changing the AC voltage into DC voltage. This feature is particularly important for most electronic devices that can only use DC voltage.
Signal Protection
It can also be used for signal protection, for example, clamping and voltage suppression, the diode is effective in preventing damage to sensitive components due to voltage spikes.
Current control
In digital logic circuits, diodes are used to control the flow of current along specific paths, ensuring that the overall circuitry operates correctly and accurately.
Reverse Polarity Protection
Diodes are placed in circuits to prevent unintentional reverse connections, and without the diode’s reverse polarity protection, components would be damaged.
Voltage Regulator
It can also be used as a voltage regulator, the most representative diode is the Zener diode. When connected with reverse bias, the diode maintains a constant voltage across its terminals even when the input voltage fluctuates.
This characteristic is vital both in electronics and circuits to protect sensitive components from voltage spike damage.
Conclusion
Reading through the contents of the article, we can learn about diode symbols along with their categories and applications. Knowing this is essential to accurately read circuit diagrams and ensure proper placement of components. Moreover, it broadens our knowledge and enriches our insights.
