18th Dec 2004

Capacitors ApplicationEdward ChenCapacitors ApplicationEdward Chen

18th Dec 2004

Electrode Plates Dielectric

The value of a capacitor is measured in farads. For 1 farad of capacitance, 1 coulomb of charge is stored on the plates,

when 1 volt of force is applied.

1 farad = 1 coulomb / 1 volt

1 coulomb represents ~ 6 x 1019 electrons

All capacitors utilize the same basic mechanism in their structureAll capacitors utilize the same basic mechanism in their structure

2

18th Dec 2004

ESL - Inductive Reactance (XL)

opposes Capacitive Reactance

XZ

ESR

XC

XL

X

0

Impedance is now a factor of resultant

Z = (XC-X

L) + ESR

2 2

3

18th Dec 2004

Loss Factors in Capacitors

Based on Vector relationshipDF = cot(Theta) = ESR / XC

PF = cos(Theta) = ESR / ZQ = tan(Theta) = XC / ESR = 1 / DF

whereDF = Dissipation FactorPF = Power Factor Q = "Q" or figure of merit

Theta

XC

Z

ESR

4

18th Dec 2004

Self-Resonance

Rea

ctan

ce

Frequency

XC decreasing

The frequency at which XC = XL is the self-resonant frequency.

At this frequency, XC=-XL, or zero, and the impedance is equal to the ESR.

Prior to this frequency, component behaves as capacitor; after this frequency, component behaves as inductor.

XL increasing

self-resonant frequency.

LC2

1F

5

18th Dec 2004

Capacitor ApplicationCapacitor Application

•Decoupling•Coupling•Filtering•Timing/Wave-shaping

18th Dec 2004

DecouplingDecoupling

PowerSupply

Load(ex.IC)Vin Vout

Vin Vout

Function: Absorb the voltage change (noise).Suitable Cap: Tan Cap, KO Cap, MLCC, Al E Cap

18th Dec 2004

CouplingCoupling

Function: Remove the DC voltage of A circuit and Transmit the exchange voltage to B circuit. (Allow an AC signal

pass, but stop DC.)

Suitable Capacitors: Tan Cap, MLCCEx. Horn.

18th Dec 2004

FilteringFiltering

Function:• Rectified AC smoothing• Frequency selective filteringSuitable Cap: KO, Tan Cap, Hi C/V MLCC, Al E Cap

18th Dec 2004

Timing / Wave-shapingTiming / Wave-shaping

Function: Timer Circuit (RC Timer).Suitable Cap: MLCC, KO Cap.