The selection principle of filter capacitance(II)

Selection of filter capacitor size, PCB plate making capacitor selection.

There are contactors, relays, buttons and other components in PCB. When they operate, they will produce larger spark discharge. The RC absorption circuit must be used to absorb the discharge current. In general, R takes 1~2k Omega, and C takes 2.2~4.7 mu F.

The general 10PF capacitance is used to filter the high frequency interference signal, 0.1UF is used to filter the low frequency ripple interference, can also play a stabilizing effect of the filter capacitor specific selection of what capacity depends on the frequency of the main working frequency on your PCB and the possible impact of the frequency of the system, can look up the related manufacturers The capacitance data or the reference software provided by the manufacturer are selected according to the specific needs. As for the number is not necessarily, see your specific needs, add more than one or two are also good, temporarily not to use the first do not stick, according to the actual debugging situation, then choose the capacity. If the main frequency of your PCB is relatively low, add two capacitors. If there is a relatively large instantaneous current, it is recommended to add a larger tantalum capacitor.

In fact, filtering should also contain two aspects, that is, what you call large capacity and small capacitance values, that is, decoupling and bypass. The principle I do not say, practical point, the general digital circuit decoupling 0.1uF can be used for 10M below; 20M above the use of 1 to 10 uF, high frequency noise is better, about C=1/f. Bypass is generally smaller, generally based on the resonance frequency is generally 0.1 or 0.01uF.