The role of electronic transformers in power supply technology

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, pulse power transformers that convert voltage and power ;

2) Broadband transformers, audio transformers, and mid-frequency transformers that transmit broadband, audio frequency, and mid-frequency 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 acting as switches;

14) Controllable inductor and saturation inductor for adjusting 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 converting voltage, current or pulse detection signals . From the above list, it can be seen that whether it is DC power supply, AC power supply or special power supply, it is inseparable from electronic transformer . Some people define power supply as DC power supply and AC power supply converted 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, various transformers occupy a major position among the soft magnetic electromagnetic components used in electronic power supplies. Therefore, transformers are used as representatives of soft magnetic components in electronic power supplies and are called " electronic transformers ."

2. Power supply technology Requirements for electronic transformers

Power supply technology The requirements 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 conditions of use of electronic transformers include two aspects:

Reliability and electromagnetic compatibility. In the past, we only paid attention to reliability. Now, due to the increased 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 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℃, and it 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℃～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℃～400℃. Electromagnetic compatibility means that the electronic transformer neither generates electromagnetic interference to the outside world nor withstands 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 electronic transformers 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, so please pay attention to them in application. The magnetostriction coefficient of 3% oriented silicon steel is (1～3)×10-6, and the magnetostriction coefficient of microcrystalline and nanocrystalline alloy is (0.5～2)×10-6. These two soft magnetic materials are materials that are more likely 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 less than 0.1×10-6. These three soft magnetic materials are materials that are less likely 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.