Due to the restriction of the ESR and heat dissipation capacity, each type of film capacitor has its specific “rated” ripple current value. Under the same terminal voltage, as the frequency increases, the impedance of the film capacitor decreases, the ripple current flowing increases.
When the current flowing through the film capacitor reaches the rated current allowed, the limitation of the heat dissipation capacity and the conductivity of the electrode, the current flowing will not be allowed to continue to increase.
🌞Is the derating of the applicable AC voltage of the film capacitor with frequency proportional to the product of the voltage amplitude and the frequency?
Since the current of the capacitor is proportional to the product of the capacitance of the capacitor and the rate of voltage rise, the rate of voltage rise is proportional to the product of the voltage amplitude and frequency. Therefore, when neglecting the influence of the dielectric loss of the capacitor, the current of the capacitor will be proportional to the product of the voltage amplitude and the frequency. However, for film capacitors, as the frequency increases, the dielectric loss cannot be ignored. Therefore, the derating of the applicable AC voltage of the film capacitor with frequency is not proportional to the product of the voltage amplitude and the frequency.
🌞The following figure shows the relationship between the AC voltage and frequency that can be applied to the film capacitor at different frequencies.👇
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As can be seen from the figure, in the characteristic curve with a capacitance of 220nF, the allowable effective value voltage at a frequency of 10KHz is about 190Vrms, and the allowable effective value voltage at a frequency of 100KHz is 130Vrms. The product of the effective value of the voltage and the frequency of the two is greater than the former.
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