using Capacitors to block variations in source voltage?

I've seen several circuit diagrams having a 0.1 microfarad capacitor connected to the supply voltage.

How do capacitors work to prevent fluctuations in DC source voltage? Why don't they completely block DC and act as a sort of break in the circuit


The power distribution network (PDN) in a PCB is not ideal. It has non zero resistance and inductance.

Let's say an IC needs a sudden increase on supply current. The resistance and inductance of the PDN could cause that such a sudden increase in current consumption generates a temporary voltage drop (a local drop, close to the IC).

A local capacitor, very close to the IC, has the capability to provide the extra needed current until the PDN can keep up to the pace of change and provide that current by itself, recharging in the process the capacitor.

The 0.1uF capacitor, is there to avoid high frequency noise. Generally is very useful on digital circuits to prevent microprocessor reset, or false High states on logic inputs. The capacitor will receive energy and will retain it for some time, like a water tank with a little hole is it bottom. If the water supply is constant, the tank will never be empty, but, if you close a little the water supply for a moment, the tank will start to discharge its contents, making the flow change less notorious.

Category: capacitor Time: 2016-07-28 Views: 0
Tags: capacitor

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