The role of the bypass capacitor

Here and there of the power supply circuit, when the schematic diagram of an electronic equipment that uses transistor and IC is seen, the capacitor might be connected with the power supply between earths. Will you have thought whether a lot of similar capacitors are such necessary?

These capacitors are formally called a bypass capacitor, and called alias "Pass Con".

Role of bypass capacitor (working)

The power supply of the electric circuit is used in tacit consent that impedance is zero. However, the foil in the power supply line of the printed wiring board might be long, be thin, it be curved, and the impedance (Reactance at alternating current) be large.

Then, the electric circuit might not do the expected operation, and it oscillates, the noise gets on the signal, and operation become unstable. Like this, the bypass capacitor does the role removed by bypassing an unnecessary signal and the noise in the power supply.

It is thought that the bypass capacitor supplies a necessary power supply.

Even if the power supply line is not so long, the impedance of wiring might become high in the high frequency circuit in the low frequency circuit when wiring from the power supply circuit is long. There must be direct current resistance in wiring, and it is thought that wiring operates like the coil in the alternating current, and it has the alternating current resistance (impedance).

When there is a bypass capacitor in each circuit, thinking the current necessary for the circuit to be a supply by this capacitor is appropriate, and it is actually supplied by this capacitor.

The bypass capacitor uses each circuit or more. I think that I only have to think that I supply it by the ceramic capacitor with good high-frequency property about the high frequency element by a mass capacitor's of the electrolytic capacitor etc. supplying the large current used with the circuit.

It is general to use the bypass capacitor of a ceramic capacitor of pieces per circuit how many and the penetration type in the high frequency circuit. And, it is a miso in the power supply line and the ground line to enlarge width and the area of the print foil as much as possible.

It is thought that it shorts between the power supply and the earth with the bypass capacitor.

Another idea is to remove it with the capacitor that puts an unnecessary noise of an unnecessary signal element and other circuits to get on the power supply between earths. After all, when the bypass capacitor is used by the same standard as the above-mentioned, it is usual to be able to do this noise removal naturally.

The slowly varying component is a mass capacitor, and the high frequency element can remove the noise element by lowering the impedance between the power supply and the earth with the ceramic capacitor and the feed-through capacitor. I think it is good when thinking that it shorts between the power supply and the earth with the capacitor exchanging it.