What is a capacitor ?

▲ WHAT IS A CAPACITOR ?

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What it really is:

It's an electrical component made of 2 conductive armatures (called electrodes) separated by an isolating layer. Its main property is to store electrical charges on its armatures.

There is a direct link between the voltage put on the capacitor and the value of the charge at the armatures

This coefficient C, the capacitance, is the value caracterizing mathematically the capacitors.

As we can identifie a direct link between U and I in the capacitor we can caracterize it as a dipole this way:

3 main dipoles :

In the physical reality:

•   Contacts with the PCB (terminations) + Other internal contact suh as the metallic contacts, or the physical internal resistivity of the used materials. → Resistance in the circuit
•   Other losses due mainly to the leads → inductive effect in the circuit.

Example of possible caracterization:

That’s why the Esr is always written « at a certain frequency »  which should be the resonnance frequency.

This is also why the capacitors have frequency optimal ranges. The higher the resonance frequency is, the higher the frequencies are withstanded by the capacitor.

In terms of energy

Efficient energy is Ec.

In reality E= Ec+Er+Ei with:

Ec = Energy due to the ideal capacitor

Er = Energy to the ESR

Ei = Energy due to the leakage.

So Er and Ei are caracterized by heating (Joule effect).

So even if that’s not always a key paramter, the lower the esr the better it is for the circuit.

If the capacitor is polarized :

If the capacitor is not polarized :

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▲ MAIN CARACTERISTICS

1) Voltages (V)

2) Capacitance of Capacitor

3) Capacitance / volume

4) Tan Delta / ESR

5) Price of the function

Whatever the function, the price of capacitors is important !

A cheap function does not mean a cheap product:

10 caps at 10€ is less expensive than 1 cap at 50€ … 

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▲ FINAL OVERVIEW

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