Specifications
5-2
Table 5-1. Capacitor types
5.1.1 Parasitics of a capacitor
A typical equivalent circuit for a capacitor is shown in Figure 5-2. In this circuit model, C denotes
the main element of the capacitor. Rs and L are the residual resistance and inductance existing in
the lead wires and electrodes. Rp is a parasitic resistance which represents the dielectric loss of the
dielectric material.
Figure 5-2. Capacitor equivalent circuit
R
s
L
R
p
C
Z = R
s
+
1 + w
2
R
p
2
C
2
R
p
+ j
1 + w
2
R
p
2
C
2
wL - w R
p
2
C+ w
3
R
p
2
L C
2
Real part
(R)
Imaginary part (X)
Type Application Advantage Disadvantage
Film • Blocking, buffering, • Wide range of capacitance • Medium cost
bypass, coupling, and and voltage values
filtering to medium • High IR, low D, good Q
frequency • Stable
• Tuning and timing • Low TC
• High voltage
Mica • Filtering, coupling, and • Low dielectric losses and good • Low capacitance-to-volume ratio
bypassing at high temperature, frequency, and
frequencies aging characteristics
• Resonant circuit, tuning • Low AC loss, high frequency
• High-voltage circuits • High IR
• Padding of larger • Low cost
capacitors • Extensive test data, reliable
Ceramic • Bypassing, coupling, and • High capacitance-to-volume ratio • Poor temperature coefficients
filtering to high • Chip style available and time stability
frequency • Low D (low k type) • Large voltage dependency and
• Low cost susceptible to pressure
(high k type)
Tantalum • Blocking, bypassing. • High capacitance-to-volume ratio • Voltage limitation
electrolytic coupling, and filtering • Good temperature coefficients • Leakage current
in low–frequency • Extensive test data • Poor RF characteristics
circuits, timing, color • Medium cost
convergence circuits, • Failure mode: short
squib firing,
photoflash firing
Aluminum • Blocking, bypassing. • Highest capacitance-to-volume • Affected by chlorinated
electrolytic coupling, and low ratio of electrolytics hydrocarbons
frequency filtering • Highest voltage of electrolytics • High leakage current
• Photoflash • Highest capacitance • Requires reforming after period
• Lowest cost per CV unit for of storage
commercial types • Poor RF characteristics
• High ripple capability • Poor reliability
• Short life