What is a capacitor ?

Discover the basic information about capacitors, to improve your choice


▲ WHAT IS A CAPACITOR ?

 

Definition from the dictionnary: « Capacitor »: Device able to accumulate charges and to relaunch them in a very short time. 

 

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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

  Technology

                                        Benefits of capacitors

                         Constrains

 Aluminum

  • The least expensive
  • The highest energy density
  • Polarized
  • Difficulties in storage
  • High ESR and tan Delta
  • Lowest temperature range

 Ceramic

 

  • Ideal for high frequencies
  • The biggest range of values (CAPA voltage)

 

  • Highest Price of the functions
  • Low energy density
  • Low values of capacitance

 Film

  • Highest ripple curents
  • Highest voltages
  • Lowest ESR and tan Delta
  • Most expensive
  • Lowest energy density
  • High price of the function

 Tantalum

  • Lower ESR than aluminum,
  • Good energy density and price of the function
  • Polarized
  • Solid can burn
  • High ESR and tan Delta

 

 

 

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Published on 10 Jan 2022 by Stephane PERES

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