Conditions for use of the transformer in the power supply

First, the conditions of use

The conditions of use of the transformer in the power supply include: useability and use of electromagnetic compatibility. 1. The use of the stipulation means that the transformer can work normally until the service life under the specific conditions of use. The most important factor affecting the transformer in the conditions of use is the ambient temperature. It is the Curie point that determines the strength of the core material to be affected by temperature. The core material has a high Curie point and is less affected by temperature; the core material has a low Curie point and is greatly affected by temperature. The Curie point of MnZn soft ferrite is generally only 215 ° C, which is relatively low, and the magnetic flux density, magnetic permeability and loss all change with temperature. In addition to the normal 25 ° C, we also give various parameter data at 60 ° C, 80 ° C, 100 ° C, iron core made of MnZn ferrite, the general working temperature is limited to below 100 ° C. ------

Silicon steel has a Curie point of 730 ° C and can work below 300 ° C.

Second, complete the function

The electromagnetic devices in the power supply are functionally distinguished mainly by transformers and inductors. There are three main functions performed by the transformer: power transfer, voltage conversion, and isolation. There are two inductor completion functions: power transfer and ripple rejection.

The power transfer of the transformer is accomplished by applying an alternating voltage across the primary winding of the transformer, causing a change in the magnetic flux in the core, causing the secondary winding to induce a voltage that is output to the load, thereby transferring electrical power from the primary to the secondary of the transformer. The amount of transmission power depends on the induced voltage, that is, the induced voltage, that is, the amount of change ΔB in the magnetic flux density per unit time. ΔB is independent of magnetic permeability and is related to saturation magnetic flux density BS and residual magnetic flux density Br. The saturation magnetic flux density of the silicon steel sheet is 1.5-2.03T, and the saturation magnetic flux density of the MnZn soft ferrite is 0.3-0.5T. As a core material for transformers, silicon steel is dominant, iron-based amorphous alloy is second, and MnZn soft ferrite is at a disadvantage.

The power transfer of the inductor is accomplished by the electrical energy input to the inductive winding, the ten-core excitation, the magnetic energy being stored, and then de-magnetized into electrical energy that is released to the load. The amount of transmission power is determined by the energy stored in the core, which is determined by the inductance of the inductor. The amount of inductance is not directly related to the saturation flux density, but to the permeability. The magnetic permeability is high, the inductance is large, the transmission energy is large, and the transmission power is large.

The amount of transmit power is also related to the number of transfers per unit time, which is related to the operating frequency of the transformer and inductor. The higher the operating frequency, the greater the transmission power under the same size of core and the same number of coils.

The voltage conversion is done by the turns ratio of the primary and secondary windings of the transformer. Regardless of the transformer power transfer size, the turns ratio of the primary and secondary windings is equal to the voltage conversion ratio of the input and output.

Insulation isolation: achieved by the insulation structure of the primary and secondary windings of the transformer. The higher the applied voltage, the more complicated the insulation structure.

The ripple rejection of the inductor is achieved by the self-inductance potential.

Third, improve efficiency

Power transformer losses include core losses and coil losses. When designing and manufacturing a transformer core, it is necessary to select a core material with a relatively low loss. The core material loss is related to the working flux density and operating frequency of the transformer core.

The core material loss includes hysteresis loss, eddy current loss and residual loss, and the eddy current loss is related to the core material resistivity. The greater the resistivity, the smaller the eddy current loss. The MnZn soft ferrite has a resistivity of 108-109μΩ CM, and the high-frequency eddy current loss in the power supply is small. The application of the high-frequency transformer in the power supply is dominant. The silicon steel resistivity is 20-40μΩ CM, and the eddy current is in the high frequency. Big.

Fill factor

Transformer coil losses in the power supply are a major part of the load loss. The coil loss is determined by the resistivity of the conductive material. At present, most of the conductive materials in the power transformer use copper instead of the rate, because the resistivity of copper is small, and the coil loss is small. In some small-sized high-frequency planar transformers and thin film transformers, the conductive materials also use resistors. The rate is smaller and gold and silver.

Fourth, reduce costs

Transformer costs in power supplies include material costs, manufacturing costs, and management costs. Material costs typically account for 40% to 60% of total cost and are the most important part. The cost of core materials and conductive materials accounts for about 80% of the material cost. Therefore, the market trend of core materials and conductive materials, price changes have a significant impact on the cost of power transformers. According to the ratio of core material and conductive material (copper to iron ratio).

Manufacturing costs are also related to design and process.

Management costs are determined by the full use of human and financial resources.

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