Soft ferrite materials are commonly used in high-frequency transformers, inductors, pulse transformers, and boost inductors in PFC. They are a very important component in PD power adapter chargers. However, we cannot fully grasp the characteristics of magnetic materials, their dependence on temperature, frequency, air gap, etc., and their difficulty in measurement. When choosing ferrite, it is not measurable like other electronic components, and its specific parameters and characteristic curves are not clear at a glance on the display measuring instrument. Why should high-frequency transformers and inductors be designed by ourselves? Because there are too many parameters involved, such as voltage, current, temperature, frequency, inductance, transformation ratio, leakage inductance, magnetic material parameters, copper loss, iron loss, AC magnetic field strength, AC magnetic induction, vacuum permeability, correction More than a dozen parameters such as tenacity. The design and production of high-frequency transformers for design and development personnel is the most important task in the design and production of PD power adapter chargers. It is very difficult for manufacturers to design and produce ready-made products for users. Ferrite is affected by many factors, including the selection of components, the layout of components on the circuit board and the way of wiring. Whether the color of the ferrite core, the shielding of the winding is appropriate, and whether the heat dissipation is properly handled… It is impossible for the design engineer to produce a good product for the user without any mistakes.
In short, even if the manufacturer has a stock supply, and also introduces the characteristics, parameters and service conditions of the magnetic components, the user cannot choose the magnetic material. Therefore, the best way is to entrust design and processing. When designing a high-frequency transformer, it is necessary to correctly select the characteristics, shape and dimensions of the magnetic core material. If it is not selected properly, it will increase loss and reduce efficiency. In severe cases, the output power cannot meet the design requirements, or even fail to work.
one. The role of magnetic components in PD power adapter chargers:
Magnetic components are necessary devices in power conversion, and are widely used in high-frequency oscillation transformers, low-pass filter inductors, power output smoothing reactors, and active power factor correction boost inductors. All these functions have great impact on the converter The quality of performance plays a crucial role. When the core is used in a transformer, it acts as:
1. Electromagnetic coupling. Transmission of electric energy, with the magnetic core, the transmission of electric energy is smooth.
2. Implement electrical isolation. The primary voltage and secondary voltage of the transformer are voltages of different potentials. With it, the safety of the PD power adapter charger in the converter is guaranteed, and it serves the purpose of high and low voltage isolation.
3. According to the needs of use, change the voltage ratio of the transformer to achieve voltage rise and fall.
4. Due to the action of magnetic components, the secondary large current rectification of the transformer undergoes phase shifting, which reduces the ripple voltage of the secondary current output. Suppress the peak voltage and protect the switch tube from being damaged by the inrush current, so it is often said that the magnetic transformer has a current-limiting effect.
5. The electronic switch of the power adapter PD charger continuously transmits electric energy to the secondary side of the transformer through charging and discharging. In this process, it is because it has energy storage that it can release energy. The size of the energy storage is related to the saturation magnetic induction of the magnetic element. Proportional to strength and initial permeability. In addition, due to the presence of inductance on the primary and secondary sides of the transformer, it is convenient to form resonance with the circuit capacitance. On the one hand, the resonance wave transmits electric energy, changes the direction of current or voltage, and outputs it to the load. On the other hand, it also changes the voltage level. All of these are the roles played by the magnetic elements in the transformation process. However, the working condition performance of magnetic components is not easy to fully grasp. It is not as easy to measure and select as other electronic components. The cumbersome technical data, scattered and highly variable parameters will make it difficult for manufacturers to choose. Therefore, only through production experiments and scientific design can the maximum function of magnetic components be brought into play.
two. Basic characteristics of magnetic materials
As mentioned above, although the structure and appearance of various magnetic core materials are similar, the performance and characteristic parameters of the magnetic core are quite different. The magnetic core of the power adapter PD charger is a soft ferrite material that operates under low magnetic field and high frequency environmental conditions. This magnetic material has the basic characteristics of low coercive force, high resistivity and high magnetic permeability. This means that the excitation current flowing through the transformer winding will generate a higher magnetic induction intensity, therefore, under a certain output power condition, the volume of the magnetic core can be greatly reduced. The coercive force is low, the hysteresis loop area of the magnetic core is small, so the iron loss is low. Similarly, the cathode rate is high, the eddy current is not, and the iron loss is low. However, the high resistivity of magnetic materials is suitable for use in aerospace fields with high frequencies.
1. Magnetic field strength H and magnetic induction B. Magnetic field strength is a physical quantity that expresses the strength and direction of the magnetic field, and its unit is ampere/meter (A/m). Magnetic induction is the magnitude of the force that a magnetic field acts on a magnetic substance, and its unit is Te (T). The higher the temperature, the lower the magnetic induction.
2. Saturation magnetic induction: Under the action of the magnetic field, when the magnetic field strength H increases, the B value when the magnetic main body is saturated is called the saturation magnetic induction Bs.
3. Initial magnetic permeability: The maximum value of the magnetic susceptibility of the magnetic material at the beginning of the magnetization curve.
4. Effective magnetic permeability: The magnetic permeability of the magnetic core in a closed magnetic circuit.
5. Curie temperature: When the magnetic state of the magnetic core changes from ferromagnetic to paramagnetic, on the u-T curve, the intersection point of the straight line with the root permeability equal to 1 between 80% of the maximum permeability and 20% of the maximum value The corresponding temperature is called the Curie temperature.
6. Coercive force: After the magnetic core removes the magnetic field from the saturation state, it continues to reverse magnetization until the magnetic induction intensity decreases to zero. The magnetic field strength at this time is called coercive force (coercive force).
7. Magnetic flux: The product of the magnetic induction intensity and the area perpendicular to the direction of the magnetic field is called magnetic flux.
8. Magnetic induction: per unit area is the size of the passing magnetic flux called magnetic induction (also known as magnetic flux density).
Saturated magnetic materials have good switching characteristics. If used in high-frequency oscillation circuits, they can generate excellent oscillation waveforms. This magnetic material has an approximately rectangular hysteresis loop. This hysteresis loop has obvious saturation point and saturation break, and its top and bottom have good symmetry. The approximately rectangular hysteresis loop can make the front edge of the current pulse waveform in the winding steep and the trailing edge short when performing pulse electrical signal transmission, and can completely transmit various waveform electrical signals. If the S rectangular curve of the magnetic core is compressed downward or stretched upward in the B direction, the magnetic core with this deformation curve is used in the high frequency transformer of the PD power adapter charger or the pulse transformer used in the electronic ballast On the other hand, it will seriously affect the oscillation waveform of the transformer, resulting in signal distortion and frequency imbalance, which will cause the temperature of the switching power tube to rise, and the iron loss and copper loss of the transformer will increase, which is extremely detrimental to the quality of the PD power adapter.
The rectangular hysteresis loop is a special curve for saturated magnetic materials. The shape of the hysteresis loop is very important. When selecting a magnetic core, it will be regarded as an important basis for selecting a magnetic core. It can only be measured with a high-frequency ferrite core characteristic curve tester.
Post time: Apr-03-2023