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The working principle of film capacitor in ac circuit
Jan 17, 2019

In high school, there is a saying that ac, dc resistance, said that is the nature of capacitance. In a dc circuit, a film capacitor is equivalent to an open circuit.


We can start with the structure of the film capacitor, the simplest capacitance is due to the structure of the dielectric insulation. After electrification, the electrode plate is charged, forming a voltage (potential difference), but the middle is not conductive because of the insulating material. However, this is provided that the critical voltage of the capacitor (breakdown voltage) is not exceeded.


We all know that any material is relatively insulated, when the material at both ends of the voltage increase to a certain extent, the material can conduct electricity, we call this voltage breakdown voltage. Capacitors are no exception. When they are broken, they are no longer insulators. However, in middle school, such a voltage is not seen in the circuit, so it works under the breakdown voltage and can be regarded as an insulator.


In an ac circuit, however, the direction of the current varies as a function of time. The charging and discharging process of the film capacitor is time-dependent. At this time, the changing electric field formed between the plates is also a function of time. In fact, the current is passed between the film capacitors by the formation of a field.

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