ideal capacitor

An ideal capacitor consists only of capacitance components, and its impedance can be calculated by equation (1).

From this formula, the ideal capacitor decreases in inverse proportion to the frequency, as shown in Fig. 1, and has the characteristic of approaching 0 as much as possible.

Figure 1 Impedance characteristics of an ideal capacitor

real capacitor

An actual capacitor has resistance and inductance components in addition to the capacitance component.

Resistance is called ESR (Equivalent Series Resistance​), and inductance is called ESL (Equivalent Series Inductance​).

The equivalent circuit of an actual capacitor is shown in Figure 2.

Figure 2 Equivalent circuit of a real capacitor

The impedance of the actual capacitor can be calculated by formula (2).

From formula (2), it can be seen that the impedance becomes Z=R at the point of formula (3), which is the lower limit.

Fig. 3 shows this impedance characteristic.

Figure 3 Impedance characteristics of an actual capacitor

Like an ideal capacitor, it decreases in inverse proportion to the frequency, but rises at a certain point. This is the point of equation (3), and this frequency is called the resonance frequency.

The impedance at this resonance frequency is the ESR.

There are many types of capacitors, and even if the capacitance is the same, the ESR and ESL values will differ. Since ESR is a resistance component, it becomes a loss factor when current flows.

A capacitor is a component that charges and discharges electric charges, so current flows in and out during charging and discharging.

This is called ripple current, and capacitors with higher ESR have lower ripple current tolerance.

If the ESL is large, the resonance frequency will be low and the frequency characteristics will be poor.

Information on simulation tools

Please click the image above. Link to the simulation tool "RED EXPERT" page.

Inquiry

If you have any questions regarding this article, please contact us below.

Click here to buy now