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Diodes: Myriad of Choices, Endless Possibilities

Performing a multitude of functions that make our gadgets and circuits tick, diodes truly sit on the throne of versatility. In this blog post, we'll take a journey through the fascinating world of diodes, from the foundational PN junction diode to the cutting-edge developments in thermal and superconducting diodes. Let's dig deeper into the characteristics and considerations associated with various diode types, shedding light on their unique benefits and limitations.

The multitude of diode types in electronics arises from the diverse range of applications and requirements in various circuits. Each type is designed with specific characteristics to address precise needs. Here are some reasons why there are so many types of diodes:

1. Specialized Functions

Different diode types are tailored for specific functions allowing for optimal performance in particular applications. For instance, rectifier diodes are optimized for converting AC to DC, while light-emitting diodes (LEDs) are designed to, well, emit light efficiently.

2. Material and Construction Variations

Diodes can be constructed using various semiconductor materials, and their structures can vary significantly. The materials and construction influence the diode's electrical characteristics, making it suitable for pinpoint tasks. For example, Schottky diodes, with their metal-semiconductor junction, offer fast switching speeds.

3. Frequency and Speed Requirements

Diodes cater to a wide range of frequency and speed constraints. Microwave or high-frequency diodes like Step Recovery Diodes (SRDs) are designed for rapid switching operations, meeting the demands of high-frequency circuits.

4. Voltage and Power Ratings

Diodes come with diverse voltage and power ratings. Power diodes are engineered to handle high voltages and currents, making them suitable for power rectification and regulation, while low-power signal diodes are designed for smaller voltage and current levels.

5. Temperature Considerations

Some diodes are designed to operate in extreme temperature conditions. For example, Avalanche diodes are built to withstand breakdown without damage, making them a fit for applications where temperature variations are significant, for instance, aerospace and military applications. Using other types of diodes in these conditions, where they might be subjected to radiation and extremely low or high temperatures can result in a faulty diode.

6. Technological Advances

Advances in semiconductor technology led to the development of new diode types with improved characteristics. Superconducting diodes utilize cutting-edge materials and technology and promise zero voltage drop and infinite resistance.

7. Innovations in Power Electronics

The field of power electronics demands powerful diodes capable of handling high voltages and currents. Devices like Thyristors, which include Silicon Controlled Rectifiers (SCRs), are vital for controlling power in electronic circuits.

8. Environmental and Reliability Considerations

Diodes can be affected by factors like radiation, humidity and mechanical stress. The consistency and lifespan of diodes under different working conditions are crucial, especially in critical applications like aerospace, military or medical devices. This is why some diodes are designed with consideration for environmental factors like Avalanche diodes. Other types of diodes are engineered to dissipate heat efficiently, making them suitable for applications where heat management is crucial.

In summary, the need for various types of diodes essentially explains the variety of choices. However, to choose the right type of diode for the right application, you’ll first need to identify what each type does and how it functions.

Beyond Semiconductors: Historical Diodes

Before the era of semiconductor diodes, various historical diodes played pivotal roles. Vacuum Diodes, with their anode and cathode in a vacuum tube, were pioneers in amplification and radio transmission. Despite vacuum tubes, valve bases and related accessories haven't been mass-produced for about 35 years, they are, and will, be used in high-quality amplifiers, music gear (old and new), testing equipment, across the industries, as well as in research, education and, well eventually, museums. Although they were at the forefront of technological advancement, Vacuum diodes are larger and bulkier than their semiconductor counterparts, making them less suitable for miniaturized electronic devices, not to mention that they require heating of the cathode, leading to higher power consumption and reduced energy efficiency. Let’s take the Conrad UFA 42 = 12 S 7 Vacuum tube Diode pentode 100 V 2.8 mA; at a 60 mm height and 22 mm width, this vacuum diode is big and bulky and knows it. With an 8-pin rimlock base, the UFA 42’s amplification property stands at a flat 18, while its heating current I(F) stands at 0.1A.

The Foundation: PN Junction Diode

Let's start with the basics—the PN junction diode. This pillar is the cornerstone of rectification, power conversion, clipping, and voltage level shifting. Its simple structure, consisting of P-type and N-type semiconductors forming a junction, allows it to act as a switch—closed in forward bias and open in reverse bias. Consider the RFN20TF6SFH PN Junction Diode from ROHM: this high-speed and power SMD-mounted diode functions great as a switch. But let’s not get carried away, the PN junction can be overstressed during breakdown in voltage referencing and causes delay in high-scale operations.

Beyond Basics: Zener and Power Diodes

Moving beyond the PN junction, we encounter the Zener diode. Operating in reverse bias, it serves as a voltage regulator, finding applications in clipper circuits and shift registers. The main drawback of the Zener diode is its limited power rating. Unlike other types of diodes, the Zener diode cannot handle high-power applications as its power rating is relatively low. As a result, it is not suitable for use in power supplies or other applications that require a large amount of power. Let’s Look at the ZMD series from Diotec: this bi-directional Zener boasts a minimum reverse voltage of 0.71V and a maximum of 106V. This diode is a great fit for high-power dissipation and is compliant with both RoHS and REACH. However, for overvoltage protection, in both uni- and bi-directional applications, you’ll need to choose a diode for its voltage stability rather than their power handling, such as the TVS TGL34 series Commercial Grade 1 diodes from Diotec as well.

Power diodes, on the other hand, are the heavyweights of high-power electronics, boasting high breakdown voltage and current handling capabilities. Let’s take the SMAJ series from Littelfuse: a surface-mounted glass or plastic diode with a staggering maximum DC voltage of 748.65V. This diode is Halogen-Free and RoHS compliant with built-in strain relief and excellent clamping capability. These types of diodes find homes in DC power supplies, snubber circuits, rectifiers and voltage regulators. Concessionally, power diodes experience a lack of efficiency in certain applications. This is due to a delay in switching from conducting to non-conducting states or simply reverse recovery time. This delay can lead to power losses and reduced efficiency in high-frequency applications.

AC to DC: Rectifier Diodes

When it comes to converting AC to DC, rectifier diodes take center stage. Whether in half-wave, full-wave or bridge rectifiers, these diodes conduct and disconnect in consecutive half-cycles, shaping the input waveform to deliver

a smooth DC output. Consider Nell Power Semiconductor’s through-hole diode rectifier bridge series T0: this 4PT series is suitable for all applications where the available gate current is limited (hand tools, kitchen aids, overvoltage crowbar protection for low power supplies, etc.), and provides an optimized performance in a limited space area. However, these diodes can be inefficient at low frequencies due to their high forward voltage drop, limiting their suitability for certain applications.

Fast Switching for High Frequencies: Step Recovery and PIN Diodes

When it comes to fast-switching operations at microwave frequencies, Step Recovery Diodes (SRD) take center stage. Their low doping concentration near the junction allows for quick turn-on and off. Additionally, these diodes allow for sharp transitions and improved stability. Consider Macom’s silicone SRD MMD0151-A15: this glass packaged beam lead SRD has the industry’s fastest transition times for millimeter wave multiplication and picoseconds pulse forming. The main drawback of the SRD diode is that the switching speed decreases when the frequency increases and if the difference between input-output is high, their efficiency is substantially reduced.

Moving on to PIN diodes, with their intrinsic layer, shining in high-frequency applications, offering insulation in reverse bias and facilitating current flow in forward bias. Let’s take into consideration Broadcom’s HSMP-3866 Pin Diode: a quad attenuator in a low-cost, surface mount SOT-25 package. This wideband (300KHz to 3GHz), low insertion loss high linearity diode reduces design parasitic and improves circuit density. The four PIN diode dice are adjacent on the same wafer and therefore have very similar and matched RF performance. This improves the customer's production yield at the mass level with better product performance and application repeatability. However, PIN diodes are significantly less sensitive and have a slower response time than other diodes. These diodes also have a high reverse recovery time due to significant power loss.

Speed and Efficiency: Schottky and Super Barrier Diodes

For applications demanding fast switching speeds, the Schottky diode steps in. With no PN junction but a metal-semiconductor bond, it exhibits a lower threshold voltage, making it ideal for digital electronics. Let’s look at the Bourns CD series: this series is 100% compatible with lead-free manufacturing processes thus conforming to many industry and government regulations. With a minimum reserve voltage of 40V and a maximum of 1600V, these silicone diodes function just like a rectifier and come in very small packaging (leadless Chip Diodes 0603, 1005, 1206, 1408, 2010) allowing designers to make real estate savings on PCB layouts. However, due to their lower reverse voltage ratings, they can be more prone to leakage currents.

Enter the Super Barrier Diode (SBR), a proprietary device offering low forward voltage, minimal leakage current and optimal switching performance. Dubbed the next-gen Schottky Rectifiers, the Diodes Incorporated SBRFP10U60D1 SBR utilizes a MOS (Metal-Oxide-Semiconductor) manufacturing process, creating a superior two-terminal device with a lower forward voltage. This field-plated, wide operating temperature range (-55°C to +150°C) SBR Diode is offered in a robust, industry-standard RoHS-compliant TO252 (DPAK) package. Then again, these do not come without some limitations, as SBR may have limited application due to their specific design constraints. (power supply circuits, voltage regulators and DC-DC converter)

Light to Electricity: Photodiodes

On the flip side of LEDs, Photodiodes convert light energy into electrical energy. With applications in light detection, remote controls and optical filters, these diodes operate in either photovoltaic mode or photoconductive mode. Consider the BPW20 and BPW21 series of silicon photodiodes from Vishay; ideal for high-precision linear applications, these 2-pin diodes are suitable for sensors for light measuring in cameras, photometers, color analyzers, exposure meters, and other general medical industrial measuring and control applications. This through-hole mount diode has a maximum Wavelength Detection of 1100 nm. The primary drawback of photovoltaic mode lies in its sluggish response speed. When the system is unbiased, the photodiode's capacitance reaches its maximum, resulting in a slower speed. Additionally, its non-linear response has the potential to affect the accuracy of light intensity measurements in specific applications.

Illuminating the World: LED and Laser Diodes

Light-emitting diodes (LEDs) have become universal, converting electrical energy into light through electroluminescence. The LEDs’ performance largely depends on the ambient temperature of the thermal management properties or the operating environment. In concession, let’s look at Kingbright’s high-temperature SMD LED that can withstand harsh environments and high operation temperatures from -40°C to 100°C. Although globally known for lighting and indication applications, LEDs are proving to be quite versatile with applications in Industrial equipment and machinery, transportation, electrical equipment, and networking and enterprise solutions. Additionally, LEDs must be supplied with a voltage above their threshold voltage and current below their rating.

The LEDs’ counterparts, Laser diodes, produce coherent light and are instrumental in diverse applications such as laser printing, fiber optics and industrial processes. However, the most common application for Laser diodes is in LiDAR. Consider the Hamamatsu pulsed Laser diode L15326-01; this diode is mounted on a highly reliable hollow ceramic package, facilitating short pulse operation and high peak power output. This diode has an operational temperature of -40℃ to + 105 ℃ and wavelengths of 895 nm, 905 nm and 915 nm. However, Laser diodes are expensive when compared to other light-emitting devices and are not suitable for high-power operations.

Protection and Control: TVS Diodes

Moving to Transient Voltage Suppressor (TVS) Diodes, which dissipate high transient power surges, clamp overvoltages to protect sensitive components from threats such as electrostatic discharge (ESD) and electrically fast transients (EFT). The TVS is a solid-state P-N junction diode, a silicon avalanche device with a fast response time, low leakage current and low junction capacitance. TVS diodes can respond to over-voltages faster than other common over-voltage protection components such as varistors or gas discharge tubes (GDT). Let’s look at the GreeGoo Electric TVS diode DO-9; this panel-mount power diode has a high surge current capability with a stud cathode and stud anode version. However, their high capacitance limits frequency and they are on the more costly side compared to other types of diodes.

Cutting-Edge Diode Technologies

Superconducting Diodes, also called Josephson diodes, still in the research phase, exhibit ideal characteristics with zero voltage drop and infinite resistance, promising breakthroughs in various fields. These superconducting diodes, non-dissipative circuit elements, offer novel applications in superconducting electronics, spintronics and quantum information technology. They differ from conventional semiconducting diodes, manifesting in Josephson junctions and junction-free superconductors. This quantum phenomenon arises from symmetry-driven transport and unique features of superconducting structures. The efficiency of a superconducting diode can be finely tuned using external parameters like temperature, magnetic field, and quantum functionalities such as Berry phase and spin–orbit interaction. Recent experimental progress has demonstrated nonreciprocal current flow in both Josephson junctions and junction-free superconductors, paving the way for future developments in emergent topological superconducting technologies.

From the humble PN junction to the futuristic thermal and superconducting diodes, these electronic mainstays have come a long way. As technology evolves, diodes continue to play integral roles in shaping the electronic landscape, enabling the devices and innovations that define our modern world. At McKinsey Electronics, we recognize the immense value of each type of diode in circuit design. Through experience and extensive understanding of each application’s needs, our expert engineers navigate the diode mazes with ease. We provide leading-edge authentic electronic components and ensure that your circuits are designed to meet the utmost efficiency standards. Contact us today for all your diodes inquiries.


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