Hello everyone, I am Rose. Today I will introduce diode to you. A diode is an electronic device made of semiconductor materials (silicon, selenium, germanium, etc.). It has unidirectional conductivity, that is, when a forward voltage is applied to the anode and cathode of the diode, the diode conducts. When a reverse voltage is applied to the anode and cathode, the diode is turned off.

Ⅰ. What is Diode?

A die, a casing, and two electrodes make up a diode. As indicated in the image below, the die is a PN junction, and a lead is drawn at both ends of the PN junction, and a plastic, glass, or metal material is used as packaging to make a crystal diode. The positive electrode, also known as anode, is pulled from the P region, while the negative electrode, also known as cathode, is drawn from the N region.

What is Diode

Ⅱ. Diode Packaging

1) Plug-in package (as shown below)

DO-41 (eg: plastic 1N4007/SR240/SR260, glass 1N47 series and BZX85C series, etc.)

DO-35 (34) (eg: 1N4148, BZX55C series, etc.)

DO-15 (eg: plastic SR240, SR260, etc.)

DO-201AD (eg: plastic package SR340, SR360, SR540, etc.)

TO-220 (eg: Schottky MBR10100CT, MBR20100CT, etc.)

TO-92 (eg: S8050, SS8050, S8550, SS8550, etc.)

TO-251 (eg: 2SB1412, etc.)

TO-126 (eg: B772, D882, etc.)

Bridge heaps such as KBP, KBL, KBU, KBJ, GBP, GBL, GBU, GBJ, etc. are all packaged by plug-ins.

Plug-in Package

2) SMD package (as shown below)

SOT-23 (eg: MMBT3904, MMBT3906, etc.)

SOT-89 (eg: 2SB772U, etc.)

SOD-123 (eg: 1N4148W, etc.)

SOD-323 (eg: 1N4148WS, etc.)

SOD-523 (eg: 1N4148WT, etc.)

DO-214AC (SMA, SMX) (eg: M7, etc.)

DO-214AA (SMB) (eg: SK24, etc.)

DO-214AB (SMC) (eg: SK34, etc.)

LL-34 (eg: LL4148, etc.)

SOD-123FL (eg: RS07M, etc.)

MD-S (eg: bridge heap MB6S, etc.)

ABS (such as: ABS10, etc.), etc.

SMD Package

Ⅲ. How does a Diode Work?

Atomic Bond Architecture Diagram of Pure Silicon

In pure silicon, replacing Si with phosphorus P with a valence electron of 5 yields free electrons.

Generation of Free Electrons

Holes are generated when silicon is doped with boron with a valence electron of three.

Creation of Holes

N-type semiconductors have 5-valent elements doped in them, while P-type semiconductors have 3-valent elements doped in them. A diode is generated when N-type and P-type semiconductors are combined.

Interesting things happen at the junction of the two semiconductors. The holes and electrons at the connection successfully "hold hands" due to mutual attraction.

Holes and Electrons Join Hands to Succeed

At the same time, the edge of the N portion will be somewhat positively charged due to the departure of electrons. The edge of the P portion, on the other hand, is negatively charged. The potential barrier, or internal electric field, that results prohibits either electron from traveling any farther. As a result, there is no current in the diode when it is turned off.

Diode Connected to Power

After that, we connect the diode to the power supply. The power supply draws electrons and holes to the two extremes at this point, and no current can be generated, resulting in the circuit being severed.

What happens if the power is reversed?

If the power supply has enough voltage to overcome the internal electric field's blocking, the electrons will cross the potential barrier, jump into the P-type holes, and eventually migrate to the external circuit, turning it on. The forward bias of the diode is also known as the external voltage at this moment.

Reverse Power

Ⅳ. Types of Diode

1. Diodes are divided into 2 categories according to semiconductor materials:

1) Silicon diode (Si tube)

2) Germanium diode (Ge tube)

2. Diodes are divided into 2 categories according to the package installation form:

1) Plug-in package

2) SMD package

3. Diodes are divided into 3 categories according to the chip welding structure

1) Point contact diode

A pulse current is conducted via a very thin metal wire pushed on the surface of a smooth semiconductor wafer, causing one end of the contact wire and the wafer to be firmly sintered together to form a "PN junction."

Point Contact Diode

2) Surface Contact Diode

The surface-contact diode's "PN junction" area is enormous, allowing a large current (several amps to tens of amps) to pass through. It is mostly employed in the "rectifier" circuit, which converts alternating current to direct current.

Surface Contact Diode

3) Planar Diode

A planar diode is a type of silicon diode that can not only carry a huge current but also performs consistently and reliably, and is commonly used in switching, pulse, and high-frequency circuits.

Planar Diode

4. Diodes are classified by usages

Rectifier diodes, Schottky diodes, TVS tubes, Zener diodes, switching diodes, PIN diodes, varactor diodes, tuning diodes, light-emitting diodes, etc.

(1) TVS Diode

1）Introduction

Transient Voltage Suppressor (TVS) diodes, also known as transient suppression diodes, are a novel type of high-efficiency circuit protection device that is widely employed. It boasts a sub-nanosecond response time and a high spike absorption capacity.

2) Typical application

Surge absorption devices MOV and TVS are installed on the power supply line for two-level protection, and common mode and differential mode protection is done on the L and N lines.

The specific method is to install a high-power TVS at the end of the line (the front end of the equipment) as the second-level SPD protection to further weaken the overvoltage amplitude, and to install MOV at the front end of the line as the first-level SPD protection to release part of the lightning current. As demonstrated in the diagram, the grid voltage falls within the E/I safe tolerate voltage range.

Typical Applications of TVS Diodes

(2) Ultrafast Recovery Diode

1）Introduction

Fred (short for ultra-fast recovery diode) is a semiconductor diode with excellent switching characteristics and an extremely rapid reverse recovery time. It's frequently utilized for freewheeling, absorption, clamping, isolation, output, and other applications. The input rectifier allows the switching device's function to be fully used.

2) Typical application

Used as a freewheeling diode for single-phase or three-phase inverters in drag and UPS systems with PWM control and switching frequency higher than 1kHz.

Typical Applications of Ultrafast Recovery Diodes

Typical Applications of Ultrafast Recovery Diodes2

(3) Switching Diode

1）Introduction

A switching diode is a type of semiconductor diode that is specifically designed and manufactured to turn on and off circuits. It takes less time to transition from turn-on to turn-off or from turn-off to turn-on than conventional diodes. The 2AK, 2DK, and other series are the most prevalent, and they're mostly employed in electronic computers, pulse, and switching circuits.

2) Typical application

In the circuit, VD1 is a switching diode, and its function is equivalent to a switch, which is used to turn on and off the capacitor C2.

Switch Diode Circuit

 (4) Fast Recovery Diode

1）Introduction

FRD (short for fast recovery diode) is a semiconductor diode with good switching properties and a fast reverse recovery time. Switching power supply, PWM pulse width modulators, frequency converters, and other electrical circuits primarily employ it. The diodes utilized are either freewheeling or damping diodes.

2) Typical application

Fast recovery diodes can be used for reverse connection protection in the DC power input anti-reverse connection protection circuit under typical conditions, as shown in the following diagram.

This type of communication is straightforward and dependable. The circuit current can smoothly travel through the diode when the circuit connection method is correct. When the circuit is reversed, the current cannot flow because the PN junction blocks the current-carrying electrons, resulting in circuit reverse connection protection.

Typical Applications of Fast Recovery Diodes

 (5) Zener Diode

1）Introduction

Zener diode, also known as Zener diode, is a semiconductor device that has a very high resistance until the critical reverse breakdown voltage.

2) Typical application

There are two types of overvoltage protection circuits: overvoltage protection circuits and overvoltage protection circuits. Some circuits and devices are not permitted to operate at low voltage for an extended period of time. As a result, the Zener diode can be utilized as a low voltage protection circuit, as shown in the diagram below.

Typical Applications of Zener Diodes

 (6) Schottky Diode

1）Introduction

Dr. Schottky (Schottky) was the inventor of the Schottky diode, and SBD stands for Schottky Barrier Diode (Schottky Barrier Diode, abbreviated as SBD).

SBD is created utilizing the metal-semiconductor junction principle, which is formed by metal and semiconductor contact. SBD is a form of hot carrier diode that is also known as a metal-semiconductor (contact) diode or a surface barrier diode.

2) Typical application

Because of the diode's unidirectional conductivity, the power supply is reversed, and the Schottky diode is turned on directly to protect the following circuit. In actuality, the Schottky diode here primarily serves as an overvoltage absorber, and aberrant voltage or high harmonics exceed the Schottky diode's breakdown voltage. The Schottky diode conducts when the voltage is applied, protecting the circuit against breakdown.

The Schottky diode and the 5V output terminal form a parallel circuit when the voltage is reversed, and because the Schottky diode's impedance is low, there are additional shunts to protect the output terminal.

Typical Applications of Schottky Diodes

 (7) Rectifier Diode

1）Introduction

A rectifier diode is a diode that converts an AC current into a DC current. The operating frequency is low due to the considerable junction capacitance. Diodes with an IF of more than 1 A are usually packaged in a metal shell to aid heat dissipation, whereas those with an IF less than 1 A are usually packaged entirely in plastic.

2) Typical application

The main purpose of the rectifier diode circuit is to protect the three-terminal voltage regulator from being broken down by preventing the voltage of the input terminal from being suddenly reduced or accidentally short-circuited, and by releasing the charge of the large capacitor at the output terminal in time. The voltage is released through the rectifier diode when the output voltage exceeds the input voltage. When a three-terminal voltage regulator's output voltage exceeds the input voltage, the three-terminal voltage is easily destroyed.

Typical Applications of Rectifier Diodes

Ⅴ. Comparison of Diodes

Schottky Diodes VS Ordinary Diodes

The silicon tube's initial turn-on voltage drop is around 0.5V, the usual turn-on voltage drop is about 0.7V, and the turn-on voltage drop when approaching the limit current is about 1V for ordinary diodes. The germanium tube has an early turn-on voltage drop of around 0.2V, a normal turn-on voltage drop of about 0.3V, and a turn-on voltage drop of about 0.4V when nearing the limit current. The initial turn-on voltage drop for Schottky diodes is around 0.4V, the usual turn-on voltage drop is about 0.5V, and the turn-on voltage drop towards the limit current is about 0.8V.

Transient Voltage Suppressors VS ESD Protection Diodes

ESD is mostly used for electrostatic discharge prevention, while TVS is primarily utilized for transient voltage suppression. Anti-static requires a low capacitance, often between 1 and 3.5PF, which electrostatic discharge may easily meet. TVs, on the other hand, are unable to do so due to their comparatively large capacitance.

Light Emitting Diodes VS Laser Diodes

LEDs use spontaneous emission of carriers injected into the active region to produce light, whereas LDs use laser radiation to produce light. The LED light is emitted in a random direction, while the LD light is emitted in the same direction and phase. The photons produced in LDs oscillate and amplify in the resonator, whereas the photons produced in LEDs do not. The spectral density of LED is several orders of magnitude larger than that of LD, the light output power is low, and the divergence angle is large. Indicator lights for electrical equipment, such as traffic lights, typically employ LEDs. It has a long service life as well as a high photoelectric conversion efficiency.

Ⅵ. Diode Applications

1. Rectification

Based on unidirectional conductivity, diodes can convert alternating current into unidirectional pulsed direct current.

2. Switch

The resistance of the diode is extremely tiny when the forward voltage is applied, and it is in a on state, which is comparable to electrification; when the reverse voltage is applied, the resistance is huge, and it is in an off state, exactly like the switch is off. Diode switching properties can be used to create a variety of logic circuits.

3. Clipping

The forward voltage drop is almost unchanged when the diode is turned on (0.7V for silicon tubes and 0.3V for germanium tubes). Diodes are frequently used as limiting elements in circuits because of this property, restricting the signal amplitude to a specific range.

4. Freewheeling

It plays the role of free rotation in inductive loads such as inductances and relays of switching power supplies.

5. Display

Diodes are commonly used in VCDs, DVDs, traffic lights and other displays.

Ⅶ. Frequently Asked Questions

There are many various types of diodes available based on the circuit needs, including rectifier diodes, switching diodes, light emitting diodes, Schottky diodes, Zener diodes, and diodes for high frequency applications, among others.

1. What is diode?

An electronic device made of semiconductor materials is known as a diode (silicon, selenium, germanium, etc.). It exhibits unidirectional conductivity, which means that it conducts when a forward voltage is given to the anode and cathode of the diode. The diode is turned off when a reverse voltage is given to the anode and cathode. As a result, the diode's on and off states are the same as the switch's on and off states.

Diodes and resistors, capacitors, inductors, and other components are used in various electronic circuits for reasonable connection to form circuits with various functions, such as rectification of alternating current, detection of modulated signals, amplitude limiting and clamping, and power supply voltage control. Other functions include voltage regulation. Common radio circuits, as well as other household goods and industrial control circuits, use diode traces.

2. What are the different types of diodes?

There are Small Signal Diode， Large Signal Diode， Zener diode， Light Emitting Diodes (LEDs)， constant current diode， Schottky diodes， Shockley Diode， Step recovery diode.

3. What are the diodes and their types?

A diode is a two-ended electrical device that permits current to flow solely in one direction. The majority of diodes are built of semiconductors like silicon, although germanium (germanium) is also employed in a few circumstances. It can be helpful to summarize the various types of diodes available.

4. How to identify Schottky Diodes?

In both forward and reverse directions, Schottky diodes are measured. The observations in Figure 8-25 show that the tube is a silicon diode if re a. The forward voltage reading on a germanium diode should be less than 0.3V.

5. What is the purpose of a diode?

Communication systems, such as limiters, limiters, and gates; computer systems, such as logic gates, fixtures; power supply systems, such as rectifiers and inverters; television systems, such as phase detectors, limiters, and fixtures; radar circuits, such as gain control circuits, parametric amplifiers, and so on, are all examples of diode applications.

6. How do diodes limit current?

Current limiting is achieved by connecting a current limiting resistor in series.

7. What does a diode do?

The functions of diodes include rectifier circuits, detection circuits, voltage regulator circuits, and various modulation circuits.

8. What material is a diode made of?

Diodes are made of semiconductor materials (silicon, selenium, germanium, etc.).