what are the needs of capacitors in many electronic circuits ?


what are the needs of capacitors in many electronic circuits ?

In: Engineering

among many others, mainly two things:

1. filters: for example, filter out interference by filtering out high frequencies in the signal

2. voltage spikes prevention: if there is voltage spike in the circuit, it could potentially damage some parts. Capacitor is there to be charged by this spike, thus effectively removing it

Basically, signals are noisy, there’s lot of things that can cause noise, so we use capacitors to keep the noise down.

In an ideal world, there would be no need for many of the capacitors in electronic circuits.

There is a relationship between current flowing through a wire and magnetic fields. This is essentially how electromagnets are made, by taking advantage of this effect and magnifying it. This is called inductance.

In a perfect world, wires are perfect conductors meaning they don’t have any resistance and they don’t have any inductance. But in reality they do have a bit of both these things. So when signals are changing (especially at high speeds) the inductance causes more and more issues, because the magnetic field keeps developing (stores some energy) and going away (releases energy).

This is where most applications for capacitors come in. Capacitors store energy as well, but to put it simply they behave opposite to inductors. So if we put the capacitors at the end points of a signal, it will make a shorter path for the electrons to flow and lower the resistance and inductance.

Without capacitors, this “parasitic” inductance and resistances can cause noise (variations in the signal that we don’t want). In digital circuits, If it’s big enough, it can even make it so that one transition between 0s and 1s be read as multiple.

We also use different size and value capacitors on one signal line because different capacitors can reduce different frequencies of noise, which is why we can’t just stick one big on on there and call it a day. Also if the capacitance is too high, the signal might not be able to transition at all because the capacitor stored too much energy.

The noise doesn’t always just come from the inductance of a wire. For example, wires that run next to each other can create noise in the other one because of the magnetic field that it creates when current runs through it. Radio waves (electromagnetic waves), and even tapping (piezoelectric effect) can introduce noise into a signal.