If the so-called over-current refers to the over-current of the transformer input current, there may be the following reasons:
1. The transformer is saturated. As we all know, the transformer winding will show inductance under alternating current, its AC impedance is large, and its impedance is proportional to the magnetic permeability. At the same time, the magnetic materials all have saturated magnetic flux density. If the transformer is not designed properly or the phenomenon of magnetic bias occurs, the working magnetic density of the transformer will be too high. When it is greater than the saturated magnetic density, the magnetic permeability will drop to 0. At this time, the AC impedance of the transformer is basically the resistance impedance, which is equivalent to directly connecting the positive and negative poles of the power supply to a wire. The consequences can be imagined. In switching power supply, this phenomenon often occurs in push-pull topology. Generally, capacitors are connected in series at the primary side to solve the problem of magnetic bias.
2. Load short circuit!!
3. The transformer winding insulation is not well done, resulting in inter turn short circuit or short circuit of the original and secondary windings.
4. Some characteristic problems of magnetic core materials, such as the influence of DC bias and temperature on magnetic permeability is not considered in the design, which leads to the reduction of transformer winding impedance and overcurrent under high temperature and high DC bias.
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