EXV226M6R3A9BAA Datasheet, PDF (10/18 Pages) Kemet Corporation – Surface Mount Aluminum Electrolytic Capacitors

C _o ^R _e ^{Surface Mount Aluminum Electrolytic Capacitors – EXV Series, +105°C}
L
Impedance (Z)
Impedance of an electrolytic capacitor results from a circuit formed by the following individual equivalent series
components:
C_o R_e
L
C_e
C_e
C_o = Aluminum oxide capacitance (surface and thickness of the dielectric)
R_e = Resistance of electrolyte and paper mixture (other resistances not depending on the frequency are not considered: tabs,
plates, etc.)
C_e = Electrolyte soaked paper capacitance
L = Inductive reactance of the capacitor winding and terminals
Impedance of an electrolytic capacitor is not a constant quantity that retains its value under all conditions; it changes
depending on frequency and temperature.
Impedance as a function of frequency (sinusoidal waveform) for a certain temperature can be represented as follows:
Z [ohm]
1,000
100
1/ω C e
10
Re
1
0.1
0.1
A
1/ω C o
1
10
100
B
1,000
ωL
C
10,000
F [K Hz]
• Capacitive reactance predominates at low frequencies
• With increasing frequency, capacitive reactance Xc = 1/ωC_o decreases until it reaches the order of magnitude of
electrolyte resistance R_e(A)
• At even higher frequencies, resistance of the electrolyte predominates: Z = R_e (A - B)
• When the capacitor’s resonance frequency is reached (ω₀), capacitive and inductive reactance mutually cancel each other
1/ωC_e = ωL, ω₀ = C√1/LCe
• Above this frequency, inductive reactance of the winding and its terminals (XL = Z = ωL) becomes effective and leads to
an increase in impedance
Generally speaking, it can be estimated that C_e ≈ 0.01 C_o.
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A4003_EXV • 12/2/2016 10