What is a capacitor ?
▲ 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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