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Capacitors Application
Edward Chen
18th Dec 2004
All capacitors utilize the same basic mechanism in their
structure
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
18th Dec 2004
2
ESL - Inductive Reactance (X )
L
opposes Capacitive Reactance
ESR
X
L
0
Z
X
XC
X
Impedance is now a
factor of resultant
Z=
2
(X -X ) + ESR
C
2
L
18th Dec 2004
3
L
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X
D
F
=
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o
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(
T
h
e
t
a
) =
E
S
R
/
X
C
Z
P
F
=
c
o
s
(
T
h
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t
a
)=
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S
R
/
Z
Q
=
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n
(
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t
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) =
X
/
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S
R
=
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/
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F
C
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F
=
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=
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Q
=
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t
18th Dec 2004
4
Reactance
Self-Resonance
Frequency
The frequency at which XC = XL is the self-resonant
self-resonantfrequency.
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.
1
F
2 LC
18th Dec 2004
5
Capacitor Application
• Decoupling
• Coupling
• Filtering
• Timing/Wave-shaping
18th Dec 2004
Decoupling
Power
Supply
Vin
Vin
Vout
Load
(ex.IC)
Vout
Function: Absorb the voltage change (noise).
Suitable Cap: Tan Cap, KO Cap, MLCC, Al E Cap
18th Dec 2004
Coupling
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, MLCC
Ex. Horn.
18th Dec 2004
Filtering
Function:
• Rectified AC smoothing
• Frequency selective filtering
Suitable Cap: KO, Tan Cap, Hi C/V MLCC, Al E Cap
18th Dec 2004
Timing / Wave-shaping
Function: Timer Circuit (RC Timer).
Suitable Cap: MLCC, KO Cap.
18th Dec 2004