Selection of Filter Capacitor

Selection of PCB plate-making capacitors.

When there are contactors, relays, buttons and other components in the PCB. It is necessary to use RC absorption circuit to absorb discharge current. The normal R is 1 ~ 2 ~ 2 k Ω ~ (-1) C = 2. 2 ~ 2 ~ 4. 7 μ F, and the normal capacitance about 10PF is used to filter the interference signal of high frequency, about 0.1 UF, to filter the low frequency ripple interference, and it can also play a stabilizing role.

The specific capacity of the filter capacitance depends on the main operating frequency on your PCB and the harmonic frequency that may affect the system. You can check the capacitance information of the relevant manufacturer or reference the database software provided by the manufacturer. Choose according to specific needs. As for the number is not certain, see your specific needs, plus one or two is very good, temporary useless can not paste, according to the actual debugging situation again choose the value. If your main frequency on the PCB is low, add two capacitors, one to deripple and the other to high frequency signals. If a larger instantaneous current occurs, it is recommended that a larger tantalum capacitor be added.

In fact, filtering should also include two aspects, that is, what you call large and small, that is, decoupling and bypass. Principle I will not say, practical point, the general digital circuit decoupling 0.1uF can be used for less than 10 meters above 20m with 1 to 10 UF, remove high frequency noise better, about 1 / f. The bypass is generally smaller, generally based on the resonant frequency of 0.1 or 0.01uF.