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Introduction

The demand for smaller, lighter, and more efficient AC/DC USB power delivery (PD) chargers is always a challenge for power-supply design engineers. Below 100 W, the quasi-resonant flyback is still the dominating topology, and gallium nitride (GaN) technology can push the power density and efficiency further.

However, providing bias power for the primary controller requires an auxiliary winding on the transformer as well as rectifying and filtering circuitry. To make things worse, the USB PD charger output voltage has a wide range. For example, the USB PD standard power range covers output voltages from 5 V to 20 V, and the latest USB PD extended power range allows the output voltage to go as high as 48 V. Since the auxiliary voltage is proportional to the output voltage, the bias voltage range on the primary controller will increase, requiring extra circuitry and degrading efficiency. In this power tip, I’ll introduce a self-biased flyback converter solution to address these design challenges.

Dealing with wide bias voltages

Figure 1, Figure 2, Figure 3, and Figure 4 show four different ways to deal with the wide bias voltage range in USB PD charger applications. Conventional methods include using a linear regulator, a tapped auxiliary winding, or even adding an extra DC/DC switching converter to regulate the bias voltage. All of these methods will increase component count, add cost, or increase power losses. Alternatively, self-biasing totally removes external components and increases efficiency.

Figure 1 Bias circuits for applications with wide output voltage ranges using a discrete linear regulator. Source: Texas Instruments

Figure 2 Bias circuits for applications with wide output voltage ranges using a tapped auxiliary winding. Source: Texas Instruments

Figure 3 Bias circuits for applications with wide output voltage ranges using boost converter. Source: Texas Instruments

Figure 4 Bias circuits for applications with wide output voltage ranges using a self-biased VCC. Source: Texas Instruments

VCC self-biasing

The flyback controller can always get bias power directly from the rectified AC input voltage, but this results in excessive power losses. The key to self-biasing is to harvest energy from the power stage, which can come from two sources. One is the switch-node capacitor stored energy; the other is energy stored in the primary-side winding of the transformer. As shown in Figure 5, an integrated self-biasing circuit can ideally do both, based on the input and output conditions.

Figure 5 The self-bias circuit harvests energy from the switch-node capacitance or magnetizing inductance. Source: Texas Instruments

Figure 6 shows the energy harvesting from the switch-node capacitor. This can save efficiency as it recycles the energy storage in switching node capacitor in every switching cycle. In cases such as AC low-line input when the reflected output voltage is identical to the input voltage, natural zero voltage switching will occur, and there is no energy in the switch-node capacitor, inductor energy harvesting will take effect, where a small portion of the primary switching current is directed to the VCC cap through an internal path.

Figure 6 VCC self-bias operation: (a) capacitor energy harvesting on the switching node and (b) inductor energy harvesting through the primary current. Source: Texas Instruments

Achieving auxless sensing

Many flyback controllers use the auxiliary winding to sense the input and output voltages and detect conditions such as output overvoltage or input undervoltage. With self-biased flyback converters, it is possible to use the switching-node voltage for input and output voltage sensing. As shown in Figure 7, the sensed voltage is the sum of the input and reflected output voltage. Since the average voltage across the primary winding is zero, the average of the switch-node voltage is equal to the input voltage.

For output voltage sensing, it can sample the reflected output voltage, and the controller needs to be informed of the exact turns ratio of the transformer with the use of a resistor-programmable pin [the TR pin in the Texas Instruments (TI) UCG28826].

Figure 7 Auxless voltage sensing where the sensed voltage is the sum of the input and reflected output voltage. Source: Texas Instruments

Once properly configured, self-biased devices such as the UCG28826 can accurately provide various protections like overpower and overvoltage protection. Figure 8 shows the UCG28826 in a USB PD application.

Figure 8 A self-biased USB PD design using the UCG28826 that can accurately provide various protections like overpower and overvoltage protection. Source: Texas Instruments

Figure 9 shows the overvoltage protection waveforms after intentionally disconnecting the feedback pin which is a single fault condition. The controller senses the output voltage and triggers overvoltage protection accordingly when the output ramps up to around 24.4 V for a nominal 20 V output.

Figure 9 Auxless sensing example for overvoltage protection. Channel 1 (CH1) is Vout and channel 2 (CH2) is Vsw. Source: Texas Instruments

Prototype and test result

Figure 10 shows the TI universal AC-input 65W dual USB type-C port USB PD charger reference design with an integrated GaN power switch. Due to the simplified self-bias feature and integrated GaN switch in the UCG28826, the reference design achieves a power density of 2.3 W/cm3 and 93.2% efficiency for the AC/DC stage. The auxless design also simplifies transformer manufacturing and reduces costs. Table 1 summarizes the design parameters of 65 W design for reference. 

Figure 10 A universal AC-input 65-W reference design board. Source: Texas Instruments

Parameter	Value
AC input voltage	90-264 VAC
Output voltage and current	5-20 V, 3.25 A maximum
Transformer	ATQ23-14
Turns ratio	7-to-1
Transformer inductance	200 µH
Switching frequency (full load)	90-140 kHz
Efficiency	93.2% at 90 VAC (AC/DC stage only)
Power density	2.3 W/cm3

Table 1 Universal AC-input 65W reference design parameters.

Simplified USB PD charger

A high-level integration with a controller and GaN switch can simplify USB PD charger design, but the bias circuitry for the controller and associated auxiliary winding on the transformer are still there, degrading efficiency and affecting size and cost. An integrated self-biasing circuit can eliminate that portion of the circuit and increase the power density for power supplies with wide-range outputs. Additionally, it is still possible to achieve proper input and output voltage sensing in the absence of an auxiliary winding on the transformer.

Max Wang is a systems engineer and Member, Group Technical Staff at Texas Instruments. He has over 18 years of experience in the power semiconductor and power-supply industries in computing, industrial, and personal electronics markets; specializing in isolated AC/DC and DC/DC applications. His design and research interests include high-efficiency and high-power-density power conversion, soft-switching converters, and GaN implementation in AC/DC converters. Max obtained a master’s degree in electrical engineering from Zhejiang University in 2006. He has worked at Delta, Power Integrations, Infineon and Texas Instruments.

Related Content

• Ungluing a GaN charger
• USB Type-C PD 3.0 Specification, Charging and Design
• Power Tips #138: 3 ways to close the control loop for totem-pole bridgeless PFC
• Power Tips #127: Using advanced control methods to increase the power density of GaN-based PFC
• Power Tips #115: How GaN switch integration enables low THD and high efficiency in PFC
• Power Tips #131: Planar transformer size and efficiency optimization algorithm for a 1 kW high-density LLC power module

The post Power Tips #139: How to simplify AC/DC flyback design with a self-biased converter appeared first on EDN.

Metal soldering is a process used to join two or more metal surfaces by melting a filler metal, known as solder, without melting the base metals. The solder, which has a lower melting point than the metals being joined, flows into the joint through capillary action and solidifies upon cooling, creating a strong bond. Unlike welding, where the base metals are melted, soldering relies on a low-heat process, making it ideal for delicate components and applications where excessive heat can cause damage.

Soldering is widely used in electronics, plumbing, automotive repairs, jewellery making, and industrial metalworking. It is favoured for its precision, conductivity, and versatility, allowing for secure, reliable connections between different metal components. With recent advancements, lead-free solder alloys and improved flux formulations have made soldering safer and more environmentally friendly.

How Metal Soldering Works?

Metal soldering works by applying heat to a joint and introducing a solder alloy, which melts and adheres to the metal surfaces, forming a secure connection. The process involves several key elements, including a heat source, such as a soldering iron, torch, or induction heater, flux to clean and prepare the metal surface, and solder wire or paste to create the bond.

The key principle behind soldering is capillary action, where the molten solder flows into the tiny gaps between metal surfaces. This ensures that the joint is uniform, strong, and conductive. Proper temperature control is crucial because overheating can damage components or weaken the bond, while insufficient heat may result in a poor connection.

Different types of soldering are used based on the temperature and strength required, including soft soldering, hard soldering (silver soldering), and brazing. Each method serves different industrial needs, ranging from electronic circuit board assembly to high-strength mechanical joints in automotive and aerospace applications.

Metal Soldering Process

The metal soldering process follows a step-by-step approach to ensure a strong, reliable joint.

1. Surface Preparation

Before soldering, the metal surfaces must be thoroughly cleaned to remove any oxidation, oil, or dirt that could interfere with solder adhesion. This is done using abrasive pads, sandpaper, chemical cleaners, or specialized fluxes that dissolve impurities. Flux is particularly important because it prevents oxidation during the heating process, ensuring a smooth flow of solder.

2. Heating the Joint

The joint is then heated using a soldering iron, gas torch, or induction heater, depending on the type of soldering being performed. The temperature must be carefully controlled to prevent excessive heating, which can weaken the joint or damage heat-sensitive components. The goal is to heat the metal surfaces just enough to allow the solder to flow and bond properly.

3. Applying the Solder

Once the joint reaches the correct temperature, solder wire, paste, or pre-formed solder pieces are introduced. The solder melts upon contact with the heated surface and flows into the joint through capillary action, ensuring an even distribution. The use of flux helps the solder adhere properly by removing any remaining oxides and improving wetting.

4. Cooling and Solidification

After the solder has flowed into the joint, the heat source is removed, and the connection is allowed to cool naturally. Rapid cooling should be avoided, as it can create thermal stress and weak bonds. The solder solidifies as it cools, forming a strong electrical and mechanical connection.

5. Cleaning the Joint

Once cooled, the joint is inspected for smoothness, strength, and uniformity. Any excess flux residue is cleaned using isopropyl alcohol (IPA) or water, as leftover flux can cause corrosion over time. In electronics soldering, a multimeter may be used to check electrical continuity and ensure a reliable connection.

Types of Metal Soldering 1. Soft Soldering (Low-Temperature Soldering)

Soft soldering is the most commonly used method, particularly in electronics and plumbing. It uses a low-melting-point solder alloy, typically containing tin and lead (Sn-Pb) or a lead-free alternative (Sn-Ag-Cu). The temperatures in soft soldering typically range from 180°C to 300°C. Since soft soldering does not require extremely high temperatures, it is ideal for delicate applications such as circuit board assembly and small metal components.

2. Hard Soldering (Silver Soldering)

Hard soldering, also known as silver soldering, uses a higher-melting-point solder, often containing silver or other strong alloys. This technique requires temperatures between 450°C and 800°C and is commonly used in jewellery making, refrigeration systems, and aerospace applications. Hard soldering produces stronger and more heat-resistant joints than soft soldering, making it suitable for high-stress environments.

3. Brazing (High-Temperature Soldering)

Brazing is similar to soldering but uses a filler metal with a melting point above 800°C. The process involves heating the metal surfaces and allowing brass or bronze-based solder to flow into the joint. Brazing is widely used in automotive manufacturing, HVAC systems, and heavy-duty industrial applications where high-strength, heat-resistant joints are required.

Uses & Applications of Metal Soldering 1. Electronics & PCB Manufacturing

Soldering is an essential process in electronics assembly, used to join circuit board components, connectors, and microchips. It ensures electrical conductivity and mechanical stability, making it crucial for manufacturing computers, smartphones, and consumer electronics. With the rise of lead-free soldering due to environmental regulations (RoHS compliance), manufacturers now use tin-silver-copper (SAC) alloys for improved safety and durability.

2. Plumbing & Pipe Fittings

Soft soldering is widely used in plumbing systems to create leak-proof seals in copper pipes and water lines. It provides durable, corrosion-resistant joints that withstand water pressure and temperature fluctuations.

3. Automotive & Aerospace Industries

Soldering is used in wiring, sensors, and heat-sensitive components in automotive and aerospace engineering. Hard soldering and brazing are preferred for fuel lines, air-conditioning systems, and exhaust components, ensuring high-strength, heat-resistant bonds.

4. Jewellery & Metalwork

In the jewellery industry, silver soldering is used to join gold, silver, and platinum pieces with minimal heat damage. It ensures seamless, durable joints without affecting intricate designs.

Advantages of Metal Soldering

One of the key benefits of metal soldering is its low-temperature operation, which prevents the base metals from melting or warping. It also allows for precise, clean joints, making it ideal for electronics and fine metalwork. The process provides strong, conductive bonds, ensuring reliable electrical connections in circuit boards. Additionally, soldering is cost-effective, energy-efficient, and versatile, working with a wide range of metals.

Disadvantages of Metal Soldering

Despite its benefits, soldering has some limitations. It produces joints that are not as strong as welded connections, making it unsuitable for high-load applications. Heat-sensitive materials can be damaged if temperature control is poor, and flux residues can lead to corrosion if not cleaned properly. Additionally, soft soldering has temperature limitations, as joints may fail under extreme heat or stress.

Conclusion

Metal soldering remains a critical process in modern manufacturing and repair work, offering a precise, low-temperature, and cost-effective method for joining metals. With the rise of lead-free alloys, automation, and advanced flux formulations, soldering continues to evolve, making it safer and more efficient. Whether in electronics, plumbing, automotive, or jewellery making, soldering provides reliable, durable connections that drive innovation in multiple industries.

The post Understanding Metal Soldering: Definition, Process, Working, Uses & Advantages appeared first on ELE Times.

Stealth technology, also known as low observable technology, is a collection of advanced techniques designed to reduce the visibility of military vehicles, aircraft, ships, and missiles to enemy detection systems. These systems include radar, infrared sensors, sonar, and electromagnetic surveillance tools. The primary objective of stealth technology is to increase the survivability of military assets by making them harder to detect, track, and target.

The concept of stealth technology is not new, but it has evolved significantly with advancements in material science, aerodynamics, and electronic warfare. Early efforts in stealth technology focused on reducing the radar cross-section (RCS) of aircraft through unique shaping techniques. Over time, innovations in radar-absorbing materials (RAM), infrared suppression systems, and acoustic noise reduction have led to highly sophisticated stealth platforms. Today, stealth technology is a crucial element in modern warfare, providing a significant strategic advantage in aerial, naval, and ground operations.

Types of Stealth Technology

Stealth technology can be classified into several types based on the method used to reduce detectability. Each type focuses on minimizing a specific form of detection, ensuring that military assets remain hidden from enemy sensors.

Radar Stealth (Low Radar Cross Section – RCS)

Radar stealth technology primarily aims to minimize the amount of radar waves reflected back to enemy detection systems. The radar cross-section (RCS) of an object is a measure of how much radar energy it reflects, and stealth technology works by reducing this reflection. One of the key techniques used in radar stealth is designing aircraft and naval vessels with faceted surfaces or smooth curves that scatter incoming radar waves rather than reflecting them directly back to the source.

Additionally, specialized radar-absorbing materials (RAM) are used to coat stealth vehicles. These materials absorb a significant portion of the radar energy, converting it into heat rather than allowing it to be reflected. Aircraft like the F-22 Raptor and B-2 Spirit bomber use a combination of these techniques to achieve low radar detectability.

Infrared (IR) Stealth

Infrared stealth focuses on reducing an object’s heat signature to avoid detection by thermal imaging systems. Military aircraft, ships, and land vehicles generate significant heat due to engine operations, friction with the air, and exhaust emissions. Advanced stealth technology incorporates several techniques to minimize this infrared signature.

One method involves using heat-dissipating exhaust systems that spread the hot gases over a larger area, thereby lowering their temperature before they escape into the atmosphere. Additionally, stealth aircraft often use low-emissivity materials on their surfaces to prevent excessive heat buildup. These techniques make it harder for enemy infrared sensors to detect and lock onto stealth platforms, increasing their survivability in combat zones.

Acoustic Stealth

Acoustic stealth technology is essential for submarines and naval vessels, where sound waves are used to detect objects underwater. Noise generated by propellers, engines, and onboard systems can be detected by sonar, making it crucial to minimize acoustic emissions.

To achieve acoustic stealth, submarines and stealth ships use quiet propulsion systems that reduce cavitation—the formation of air bubbles around propeller blades that create noise. Additionally, sound-absorbing materials are used to coat the hulls of submarines, dampening vibrations and reducing noise transmission. These techniques allow stealth submarines, such as the Virginia-class and Scorpène-class, to operate undetected in enemy waters.

Visual Stealth

Visual stealth technology aims to reduce the visibility of military assets using advanced camouflage techniques. Traditional methods involve painting vehicles with camouflage patterns that help them blend into their surroundings. However, modern stealth technology has taken this a step further with the development of electrochromic materials and adaptive coatings that can change colour based on environmental conditions.

Some experimental visual stealth systems use metamaterials and active cloaking technologies that manipulate light waves, making an object appear nearly invisible to the naked eye. While full optical invisibility remains a challenge, ongoing research continues to push the boundaries of visual stealth.

Electromagnetic Stealth

In addition to reducing radar and infrared signatures, stealth technology also minimizes electromagnetic emissions from military platforms. Electronic devices, including communication and navigation systems, emit detectable signals that can be intercepted by enemy intelligence operations. To prevent detection, stealth aircraft, and naval vessels use electromagnetic shielding to contain these emissions.

Moreover, emission control (EMCON) procedures are employed to limit unnecessary electronic transmissions, reducing the risk of detection by enemy surveillance systems. By managing their electromagnetic footprint, stealth platforms can operate more securely in hostile environments.

How Does Stealth Technology Work?

Stealth technology works by integrating multiple techniques to reduce the chances of detection across various sensory domains. One of the most important aspects is the reduction of radar cross-section (RCS), which is achieved through specialized aircraft shaping and radar-absorbing coatings. By ensuring that radar waves are either absorbed or deflected away from enemy sensors, stealth aircraft like the F-35 Lightning II can remain undetected for longer durations.

Infrared suppression techniques help control heat emissions, making it difficult for heat-seeking missiles to lock onto stealth assets. Noise reduction strategies ensure that submarines and naval vessels can move through water without alerting enemy sonar systems. Additionally, electromagnetic stealth reduces radio frequency emissions, preventing enemy forces from pinpointing the location of stealth aircraft, ships, or drones.

Applications of Stealth Technology

Stealth technology has a wide range of applications in modern military operations.

Stealth Aircraft

Stealth aircraft play a crucial role in modern aerial warfare by conducting deep penetration strikes, surveillance missions, and air superiority operations. Notable examples include the F-22 Raptor, a highly maneuverable stealth fighter designed for air dominance, and the B-2 Spirit, a stealth bomber capable of delivering nuclear and conventional payloads with minimal risk of detection.

Stealth Naval Vessels

Naval stealth technology enhances the survivability of warships by reducing their radar and acoustic signatures. The USS Zumwalt (DDG-1000) is an advanced destroyer with a stealthy design that minimizes its radar cross-section. Similarly, the Type 055 destroyer, developed by China, incorporates stealth shaping to improve operational effectiveness in naval engagements.

Stealth Submarines

Submarines rely heavily on stealth to avoid detection while patrolling enemy waters. The Virginia-class submarines used by the U.S. Navy feature anechoic coatings and quiet propulsion systems that make them nearly undetectable by sonar. The Scorpène-class submarines, developed by France, are also known for their stealth capabilities and operational flexibility.

Stealth Missiles and Drones

Stealth technology is increasingly being integrated into unmanned systems and precision-guided missiles. The BGM-109 Tomahawk cruise missile is designed to have a low radar cross-section, allowing it to evade enemy air defenses. Similarly, the RQ-170 Sentinel is a stealth reconnaissance drone used for intelligence-gathering missions.

Advantages of Stealth Technology

Stealth technology provides several advantages in military operations. By reducing an asset’s detectability, it enhances survivability, allowing forces to carry out missions with lower risk. Stealth platforms also improve operational effectiveness by enabling surprise attacks and reconnaissance missions without alerting enemy defenses. Additionally, stealth technology provides a strategic advantage by forcing adversaries to invest in more advanced detection and countermeasure systems.

Conclusion

Stealth technology has revolutionized modern warfare by enabling military forces to operate with greater security and effectiveness. From radar-absorbing materials to infrared suppression and electromagnetic shielding, stealth innovations continue to evolve, shaping the future of aerial, naval, and ground combat. As research advances, stealth technology may find applications beyond the military, influencing commercial aviation and security technologies in the coming decades.

The post Stealth Technology: Definition, Types, Working & Applications appeared first on ELE Times.

BluGlass Ltd of Silverwater, Australia has established an Industry Advisory Board led by professor Steven DenBaars and Dr Richard Craig to accelerate its technical roadmap and commercial advancement of its gallium nitride (GaN) laser portfolio for the global quantum, defence and biotech markets...

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The UK’s University of Cambridge and University of Southampton have been named as participants in the PIXEurope consortium, a collaboration between research organizations from across Europe that is developing and manufacturing prototypes of their products based on photonic chips...

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At the IEEE Applied Power Electronics Conference & Exposition (APEC 2025) in the Georgia World Congress Center, Atlanta, GA, USA (16–20 March), fabless company Wise-integration of Hyeres, France — which was spun off from CEA-Leti in 2020 and designs and develops digital-control of gallium nitride (GaN) and GaN integrated circuits for power conversion — is unveiling its latest WiseGan and WiseWare advances, featuring two technical presentations and demonstration boards, including a new 1.5kW totem-pole power factor correction (PFC) module designed specifically for server and industrial applications...

Keysight Technologies Inc of Santa Rosa, CA, USA has enhanced its double-pulse test portfolio, enabling customers to benefit from accurate and easy measurement of the dynamic characteristics of wide-bandgap (WBG) power semiconductor bare chips. The technologies implemented in the measurement fixture minimize parasitics and do not require soldering to the bare chip. The fixtures are compatible with both versions of Keysight’s double-pulse testers...

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Market research firm TrendForce reports that global smartphone production grew 9.2% quarter-to-quarter to 334.5 million units in fourth-quarter 2024, driven by Apple’s peak production season and consumer subsidies from local Chinese governments. While Apple expanded production with the launch of new models, Samsung faced production declines due to intensified competition in emerging markets...

Gallium nitride (GaN) power IC and silicon carbide (SiC) technology firm Navitas Semiconductor Corp of Torrance, CA, USA has announced the first production-released 650V bi-directional GaNFast ICs and high-speed isolated gate-drivers, creating a paradigm shift in power with single-stage BDS converters, which enables the transition from two-stage to single-stage topologies. Targeted applications range widely and opens up multi-billion dollar market opportunities across electric vehicle (EV) charging (on-board chargers (OBC) and roadside), solar inverters, energy storage and motor drives...

Many industrial applications are transitioning to higher power levels with minimized power losses, which can be achieved by increasing the DC link voltage. Infineon Technologies AG of Munich, Germany is hence addressing this market trend with the CoolSiC Schottky diode 2000V G5 product family, which are claimed to be the first discrete silicon carbide diodes with a breakdown voltage of 2000V, introduced in September 2024...

As network demands grow more complex, Optical Internetworking Forum (OIF) is to showcase interoperability breakthroughs with live demonstrations and expert discussions at the Optical Fiber Communication Conference & Exposition (OFC 2025) in San Francisco, CA, USA (1–3 April)...

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