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It is a device which make use of the principle of electromagnetic induction to change the AC voltage, the main component is the primary coil, secondary coil and core . In the electrical equipment and radio circuit, it commonly be used for lifting voltage, impedance matching, security isolation. The defects of transformer are as follows, firstly, measuring terminals must input alternating current or digital square wave, cannot use the DC to avoid failure. Secondly, when supply a variety of power for the load ,the volume larger and the weight increase. Thirdly, the heat-dissipation problem of itself. Fourthly, increase the cost of other peripheral circuits. Therefore, using transformers can be diversified, but on the competitiveness of their products, sometimes we have to consider the problems arising from the negative.