High-frequency transformer is a power transformer with a working frequency exceeding 10 KHz. It is principally used as a high-frequency switching transformer in a high-frequency switching power supply as well as a high-frequency inverter in a high-frequency inverter welding machine. It can be classified into several grades based on its working frequency:10kHz-50KHz, 50KHz-100kHz,100kHz~500kHz,500kHz~1MHz and more than10MHz.
Taking into account the following 5 principles will help you when selecting the type of core for your high-frequency transformer:
- Take into account the transfer of energy;
- Consider using the existing transformer skeleton, keeping in mind the geometric limitations;
- Comply with the specified cross-sectional area, saturation magnetic flux density, etc., during circuit design;
- Comply with the structural installation requirements and the total power and frequency requirements;
- Magnetic core insulation materials selected are safe and reliable;
In a high-frequency transformer, there is a magnetic core and a coil. The coil has two or more windings, the primary winding connected to the power supply, and the secondary windings that are not connected to the power supply. In the market, there are several core types of high-frequency transformers. These include POT cores, EE, EF cores, EI cores, EC, ETD and EER cores, RM cores, PM cores, PQ cores, Er cores, and EP cores etc.
When designing high-frequency transformers, we can select a core compatible with our needs in order to get the best performance from the transformer. Various types of cores will have a different impact on the performance of the transformer.
1.POT core
Choosing the POT core bobbin and winding ensures that they are almost completely enclosed by the core, which provides excellent EMI shielding. It can provide a simple skeleton without pins and a skeleton with a PINPCB board installed. It conforms to the IEC standard, and it is interchangeable. However, due to the shape of the pot, it will be slightly more expensive than other types of cores.
Application：Carrier filters, high-sensitivity sensors, high-efficiency sensors, power converter transformers, etc.
2.EE,EF core
The cost of EE and EF cores is much lower than that of POT cores, in addition to winding and assembly being relatively simple. These cores are now most widely used in the design of high-frequency transformers. Its disadvantage is that it cannot provide self-shielding, and the E-type magnetic core can be oriented in different directions and superimposed to increase power output. A planar transformer or a flat shape transformer can be designed using these core. EE and EF cores have excellent heat dissipation properties, and they can be used in superposition, making them ideal for high-power inductors and transformers.
Application：It is widely used in programmable switch power supplies, LCD display power supplies, UPS inverters, computer power supplies, and energy-saving lamps.
3.EI core
It features a compact structure, small size, high operating frequency, wide operating voltage range, tight air gap coupling at the top of the coil, and low loss. The losses are negatively correlated with the temperature, which prevents the temperature from continuously rising.
Application：Electronic equipment such as power conversion transformers and choke coils, DVD power supplies, camera flashes, communication equipment, etc.
4.EC,ETD and EER core
Core constructions of this type fall between those classified as E-types and those classified as pot-types. It is similar to E-type magnetic cores, in that they can provide enough space for large-section lead wires to be drawn, which makes them ideal for the design of high-frequency transformers for switching power supplies. The EC, ETD, and EER cores have an excellent heat dissipation, and the central column is cylindrical. Compared with the cuboid with the same cross-section, the single-turn winding is shortened by 11%, thus reducing copper loss by 11% and enhancing output power. Furthermore, compared to a rectangular parallelepiped central column, which has edges and corners that might damage the insulation of the winding wire during winding, the cylindrical central column is cylindrical.
Application：These tpye cores wide variety of fields, including home appliances, communications, lighting, medical equipment, office automation, military products, optical equipment, electronic instruments, aerospace, and a variety of other areas.
5.RM core
RM cores are designed to remove the two symmetrical sides of POT cores, resulting in a core that is more conducive to heat dissipation and lead diameters of larger sizes. It saves approximately 40% of the installation space when compared to the POT core. It is also possible to design RM cores as flat shape transformers.
Application：Mainly used in carrier communication, networks, digital, television, electronic instruments, etc.
6.PM core
Flux leakage is small, loss is low, power is high, and distributed capacitance is small.
Application：It is mainly used in ultrasonic cleaning, laser equipment, and other fields.
7.PQ core
PQ cores are designed specifically for switching power supply inductors and transformers. PQ shapes optimize the relationship between core volume, surface area, and winding area. With this core, the largest inductance and winding area can be achieved with the smallest core. Designed with this core, the high-frequency transformer is small, light, and achieves the maximum output power with minimal board space requirements.
Application：Mostly used in network, communication, electrical equipment, and medical treatment.
8.EP core
EP cores incorporate a three-dimensional structure that encloses the winding except for the point of contact with the PCB board, resulting in a very effective shielding. It is this shape of the core that minimizes the effect of the air gap formed at the contact surface of the two cores that results in a higher volume-to-overall space ratio.
Application：Transformers, inductors, isolation transformers, and matching transformers, widely used in program-controlled switch terminals, precision electronic equipment, and other applications.
9.ER core
It has a good coupling position and the center column is circular, which allows for easy winding. The winding area is also increased, allowing a high power transformer to be designed with a small leakage inductance.
Application：Transformers for switching power, pulse transformers, electronic ballasts, etc.
10.U core
With its small impedance deviation, large output current, and high inductance, it can suppress harmonics of high order.
Application：It is widely used in electronic equipment, including color televisions, computers, monitors, etc., as a common mode transformer.
11.ET,FT core
Stray capacitance is low, the ripple coefficient is low, flux leakage is less, and inductance is high.
Application：An LCD TV, monitor, computer, videophone, intercom, and so on.
12.T core
It has a large output current, a small loss, a high withstand voltage, a high inductance, and a low price. While winding is relatively inexpensive, it is difficult to produce in large quantities due to the high cost.
Application：Choke coils, EMI/RFI filters, and audio transformers are widely used in energy-saving lamps, audio, and control circuits as well as other electronic devices.
