Capacitor Application Essentials Note 1

2.1. Multiple capacitors of the same specification are used in parallel

If the ripple voltage tolerance of a single capacitor is not enough, multiple capacitors can be used in parallel, and the number of parallel capacitors is based on the ripple voltage. The parallel use of multiple capacitors of the same specification can not only reduce the ripple voltage, but also reduce the ESR and increase the insertion loss.

图10：不同数量同规格电容并联使用阻抗曲线

2.2. Multiple capacitors of different specifications are used in parallel

When the frequency range of noise is very wide, the filter frequency band of a single capacitor cannot meet the filtering requirements, and it is necessary to use capacitors of different specifications to widen the passband. When multiple capacitors of different specifications are used, the inductive region and the capacitive region of different capacitors will produce an intersection point, which will produce parallel resonance, so that the filter impedance becomes larger and reduces the filtering effect, and the intersection point is called reverse resonance.

Figure 11: Impedance curves for parallel connection of capacitors of different specifications (with anti-resonance points)

Therefore, when connecting capacitors with different capacitance values in parallel, the difference of capacitance values should be fully considered, and it is recommended that the capacitance difference should be 100 times, and the minimum difference should not be less than 10 times, so as to reduce the anti-resonance point filter impedance.