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As electronic products become more common in our daily lives, most users know only a few device types. The Internet can search for semiconductors, microprocessors, and transistors, but rarely mentions the magnetic components necessary for these devices.
Even chatting with electronic engineers, these humble inductors and transformers are considered to be very low-tech. In fact, designing and manufacturing these passive devices requires a great deal of technology and knowledge.
From the perspective of technology and application, magnetic elements can be divided into four types: low frequency, high frequency, isolation and non-isolation. Custom designs are often required to meet specific electrical and physical parameter requirements. The importance of maximizing the efficiency of materials according to standards drives the design engineer of the transformer, and material research drives innovation in the field of wound components.
In Europe, the low frequency is usually 50 Hz - 500 Hz, and it is connected to 220V-240V AC single-phase power input, and in the Americas it is 115V AC power input. Applications include linear filters, motor drives, uninterruptible power supplies (UPS), pump circuits, conveyor systems, HVAC equipment, linear power supplies, and power metering.
With the advent of high-efficiency switching power supplies, the use of high frequency magnetic components has become increasingly popular. Its initial frequency is about 16 kHz, slightly above the human hearing limit, but it can now reach megahertz. This type of power supply is now mainly used for charging mobile devices, as well as switching and protection of LEDs, TVs, computers, communications equipment, and even electric cars.
Non-isolated magnetic components include inductors, filters, and transformers that raise or lower the AC voltage to reduce electrical noise or store energy temporarily. For example, a step-down transformer can reduce input to 400V ac (British AC 415V) to 230V.
Where humans are likely to be exposed to electricity (such as laptop power supplies), using an isolation transformer can avoid electric shock. Transformers are used to isolate the main (main) circuit on the secondary side. Internally, the transformer windings will have one or more layers of insulation, which may include plastic skeletons or insulating tape. Among the most demanding products are the products of the medical industry, whose isolation needs require triple insulation and a few millimeters of clearance. Electronic products may be in direct contact with the patient, so ring-shaped isolation transformers usually provide additional protection.
The magnetic element consists of a winding (a wire or foil wound core), a bobbin or mandrel (air core inductance required), and an insulating layer with or without it. Although most transformers and inductors are labor-intensive industries, automation is feasible for mass production of very simple devices.
Low-frequency magnetic elements typically use steel or iron laminations as the core material. These magnetic cores may be E-type and I-type structures and are interleaved around the bobbin and the windings. The other is the use of a toroidal core that wraps the oriented silicon steel to form an annular shape. The wire and insulating material then wind the magnetic core. This process is relatively time-consuming, but due to the shape of the core, this type of transformer has a very low stray magnetic field and high efficiency, resulting in a smaller overall size.
High-frequency magnetic elements usually use ferrite or power iron materials as the magnetic core, and the magnetic core can be made into various shapes. More complex transformer designs and processes are determined by the transformer structure's standard, size, impedance, creepage, and creepage distance. The higher the nominal frequency, the smaller the inductance. To overcome this, multiple strands are used, or the foil must be insulated. In some cases, the primary winding will split into two separate windings, sandwiching the secondary windings to increase magnetic coupling. In the Hi-pot test, TIW (three-layer insulated wire) is often used to ensure better performance.
Although the machine can be used to wind the wire around the bobbin, the insulating tapes between the windings, the lacquer-lacquered paint film, and the bushing still need to be assembled by hand. This protects the integrity of all safety insulation and makes it suitable for the core. .
Depending on the application, transformers and inductors may be affected by safety certification. In this case, independent testing organizations such as VDE, CENELEC, UL, and CSA will check the process structure of the magnetic components and perform electrical tests. Therefore, it is very important to carry out the acceptance test and simulate the transformer under the working conditions. This can ensure that the part will not short-circuit the windings due to overheating during normal operation. Stereotype tests (such as heat or surge tests) need to be agreed with the end customer. The environment and operating temperature of the part also determine the choice of insulation class; 130 C(B), 155 C(F) and 180 C(H) are typical temperature classes.
Transformer design standards include safety margins. For example, the maximum operating temperature of a Class H transformer design must reach 125°C. This is because the H-class design project allows ± 40oC ambient temperature and + 15oC safety range adjustment.
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