Safety capacitance capacity, frequency and capacitive reactance

Today, there is a customer consultation editor: What is the relationship between capacitance capacity, frequency and capacitive reactance? After answering the customer, the editor thinks that it is still shared with everyone. Then I will edit the following to tell you about the relationship between capacitance capacity, frequency and capacitive reactance.

We all know that the safety capacitor has the principle of AC-DC blocking, and DC power cannot pass. This is because the capacitor is charged to full voltage at the moment of power-on. Since the voltage is exactly equal to the applied voltage and the direction is opposite, there is no current. The capacitor is on during this charging process. In an AC circuit, the direction of the voltage is constantly changing, and the capacitor is always charged and discharged. Therefore, the capacitor is always in the on state.

The capacitance is large, the required charging time is long, and the voltage rise of the capacitor is slow. Since the capacitor voltage is opposite to the applied voltage polarity, the resistance voltage generated by the capacitor in the circuit is small, that is, the capacitive reactance is small. If the frequency of the applied AC voltage is increased (that is, the time for charging and discharging the capacitor is reduced), since the voltage on the capacitor is opposite to the applied voltage, the voltage is lowered and the reactance is small. Formula C=Q/V, V=Q/A

Others may ask: The resistance voltage is the voltage that discharges the safety capacitor. If it is small, the discharge current is not small? In this case, the capacitance is proportional to the tolerance, right? Therefore, the editor here should explain: Because the capacitor charging takes time, under the AC signal, the voltage on the safety capacitor is always less than the applied voltage. The capacitor is repeatedly charged in the forward and reverse directions, and the impedance is the mainstream. After the frequency is high, even if the amplitude of the signal voltage is constant, the voltage on the safety capacitor is significantly reduced, so that the impedance is greatly reduced, that is, the capacitive reactance is lowered.

Let's talk about the relationship between frequency and capacitive reactance: except for other conditions of frequency, the charge and discharge time will not change, but the high frequency means that the applied voltage changes quickly. For example, the fast-capacitance capacitor voltage reaches 1/5 of the applied voltage, and the applied voltage has already passed the voltage below 1/5 of the applied voltage, and then the capacitor begins to discharge again, and this situation will continue. The capacitor voltage is never more than 1/5 applied voltage, so the capacitor reactance can only be 1/5 applied voltage. The higher the frequency, the lower the voltage ratio. However, the actual capacitance may be different. The frequency of the capacitor may appear to be high to a certain extent, rather than the high frequency and low impedance.