Power supply technology and electronic transformers

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Power supply technology and electronic transformers [Copy link]

introduction

　　Power supply devices, whether DC or AC, must use electronic transformers (soft magnetic electromagnetic components) made of soft magnetic cores. Although there are already air-core electronic transformers and piezoelectric ceramic transformers that do not use soft magnetic cores, up to now, the electronic transformers in most power supply devices still use soft magnetic cores. Therefore, discussing the relationship between power supply technology and electronic transformers: the role of electronic transformers in power supply technology, the requirements of power supply technology for electronic transformers, and the impact of the use of new soft magnetic materials and new core structures in electronic transformers on the development of power supply technology will surely arouse the interest of friends in the power supply industry and the soft magnetic material industry. This article puts forward some views in order to facilitate dialogue between the power supply industry and the electronic transformer industry and the soft magnetic material industry on issues related to electronic transformers and soft magnetic materials, so that they can exchange ideas and develop together.

　　1 The role of electronic transformers in power supply technology

　　Electronic transformers, semiconductor switching devices, semiconductor rectifier devices, and capacitors are called the four major components in power supply devices. According to their role in the power supply device, electronic transformers can be divided into:

　　1) Power transformers, power transformers, rectifier transformers, inverter transformers, switching transformers, and pulse power transformers for voltage and power conversion;

　　2) Broadband transformers, audio transformers, and mid-range transformers that transmit broadband, audio frequency, and mid-range power and signals;

　　3) Pulse transformer, drive transformer and trigger transformer for transmitting pulse, drive and trigger signals;

　　4) Isolation transformer for isolating the primary and secondary sides, and shielding transformer for shielding;

　　5) Phase conversion transformer that converts single phase to three phase or three phase to single phase, and phase conversion transformer (phase shifter) that changes the output phase;

　　6) Frequency multiplication or division transformers that change the output frequency;

　　7) A matching transformer that changes the output impedance to match the load impedance;

　　8) Voltage-stabilizing transformers (including constant-voltage transformers) or current-stabilizing transformers that stabilize output voltage or current, and voltage-regulating transformers that regulate output voltage;

　　9) Filter inductors for AC and DC filtering;

　　10) Electromagnetic interference filter inductors for suppressing electromagnetic interference, and noise filter inductors for suppressing noise;

　　11) Absorption inductor for absorbing surge current and buffer inductor for slowing down the rate of change of current;

　　12) Energy storage inductors that store energy and commutation inductors that help semiconductor switches commutate;

　　13) Magnetic switch inductors and transformers that act as switches;

　　14) Controllable inductor and saturated inductor for regulating inductance;

　　15) Voltage transformer, current transformer, pulse transformer, DC transformer, zero flux transformer, weak current transformer, zero sequence current transformer, Hall current and voltage detector for transforming voltage, current or pulse detection signals.

　　From the above list, it can be seen that no matter it is a DC power supply, an AC power supply, or a special power supply, it is inseparable from an electronic transformer. Some people define power supply as a DC power supply and an AC power supply that have been transformed by high-frequency switching. When introducing the role of soft magnetic electromagnetic components in power supply technology, various electromagnetic components in high-frequency switching power supplies are often cited as examples. At the same time, among the soft magnetic electromagnetic components used in electronic power supplies, various transformers occupy a major position. Therefore, transformers are used as representatives of soft magnetic components in electronic power supplies, and they are called "electronic transformers."

　　2 Power supply technology requirements for electronic transformers

　　The requirements of power technology for electronic transformers, like all products as commodities, are to pursue the best performance-price ratio in completing specific functions under specific conditions of use. Sometimes it may focus on price and cost, and sometimes it may focus on efficiency and performance. Now, light, thin, short and small have become the development direction of electronic transformers, emphasizing cost reduction. Starting from the general requirements, four specific requirements can be drawn for electronic transformers: conditions of use, completion of functions, improved efficiency and reduced costs.

　　2.1 Conditions of Use

　　The use conditions of electronic transformers include two aspects: reliability and electromagnetic compatibility. In the past, we only paid attention to reliability, but now, due to the increasing awareness of environmental protection, we must pay attention to electromagnetic compatibility.

　　Reliability means that under specific conditions of use, the electronic transformer can work normally until the end of its service life. The ambient temperature is the biggest influence on the electronic transformer in general use conditions. The parameter that determines the intensity of the temperature influence on the electronic transformer is the Curie point of the soft magnetic material. The soft magnetic material has a high Curie point and is less affected by temperature; the soft magnetic material has a low Curie point and is more sensitive to temperature changes and is greatly affected by temperature. For example, the Curie point of manganese-zinc ferrite is only 215℃, which is relatively low. The magnetic flux density, magnetic permeability and loss all change with temperature. In addition to the normal temperature of 25℃, various parameter data at 60℃, 80℃ and 100℃ must be given. Therefore, the operating temperature of the manganese-zinc ferrite core is generally limited to below 100℃, that is, when the ambient temperature is 40℃, the temperature rise must be lower than 60℃. The Curie point of cobalt-based amorphous alloy is 205℃, which is also low, and the use temperature is also limited to below 100℃. The Curie point of iron-based amorphous alloy is 370℃, which can be used below 150℃～180℃. The Curie point of high magnetic permeability Permalloy is 460℃ to 480℃, and it can be used below 200℃ to 250℃. The Curie point of microcrystalline and nanocrystalline alloy is 600℃, and the Curie point of oriented silicon steel is 730℃, and it can be used at 300℃ to 400℃.

　　Electromagnetic compatibility means that the electronic transformer neither generates electromagnetic interference to the outside world nor can withstand electromagnetic interference from the outside world. Electromagnetic interference includes audible audio noise and inaudible high-frequency noise. The main reason for the electromagnetic interference generated by the electronic transformer is the magnetostriction of the magnetic core. Soft magnetic materials with large magnetostriction coefficients generate large electromagnetic interference. The magnetostriction coefficient of iron-based amorphous alloys is usually the maximum (27~30)×10-6, and measures must be taken to reduce noise and suppress interference. The magnetostriction coefficient of high magnetic permeability Ni50 Permalloy is 25×10-6, and the magnetostriction coefficient of manganese-zinc ferrite is 21×10-6. The above three soft magnetic materials are materials that are prone to electromagnetic interference and should be paid attention to in application. The magnetostriction coefficient of 3% oriented silicon steel is (1~3)×10-6, and the magnetostriction coefficient of microcrystalline and nanocrystalline alloys is (0.5~2)×10-6. These two soft magnetic materials are materials that are relatively easy to generate electromagnetic interference. The magnetostriction coefficient of 6.5% silicon steel is 0.1×10－6, the magnetostriction coefficient of high magnetic permeability Ni80 Permalloy is (0.1～0.5)×10－6, and the magnetostriction coefficient of cobalt-based amorphous alloy is below 0.1×10－6. These three soft magnetic materials are materials that are not easy to generate electromagnetic interference. The frequency of electromagnetic interference generated by magnetostriction is generally the same as the operating frequency of the electronic transformer. If there is electromagnetic interference below or above the operating frequency, it is caused by other reasons.