Yageo Electrolytic capacitor snap-in 10 mm 220 µF 400 V 20 % (Ø x H) 30 mm x 30 mm LG400M0220BPF-3030 1 pc(s) LG400M0220BPF-3030 Data Sheet
Product codes
LG400M0220BPF-3030
4. Impedance (Z)
Re is the most temperature dependant component of electrolytic capacitor
The impedance of an electrolytic capacitor results from here below circuit
equivalent circuit . The electrolyte resistivity will decrease if the temperature rises .
formed by the following individual equivalent series components :
In order to obtain a low impedance value all over the temperature range , Re
must be as little as possible , but too low Re values means a very aggressive
electrolyte and then a shorter life of the electrolytic capacitor at the high
temperatures . A compromise must be reached .
Fig 1-11
5. Leakage current (L.C.)
5. Leakage current (L.C.)
Duetothealuminum oxidelayer that serves as adielectric , a small current will
continueto flow even after a DC voltage has been applied for long periods .
Co = Aluminum oxide capacitance (surface and thickness of the dielectric).
This current is called leakage current . A high leakage
current flows after
Re = Resistance of electrolyte and paper mixture (other resistances not
applying a voltage to the capacitor and then decreases in few minutes (e.g. after
depending on the frequency are not considered : tabs , plates , and so on).
a prolonged storage without any applied voltage) . In the course of the
Ce = Electrolyte soaked paper capacitance.
continuous operation , the leakage current will decrease and reach an almost
L = Inductive reactance of the capacitor winding and terminals.
constant value .
After avoltage free storage the oxide layer may deteriorate , especially at high
The impedance of an electrolytic capacitor is not a constant quantity that retains
temperature . Since there are no leakage current to transport oxygen ions to the
its value under all the conditions : it changes depending on the frequency and
anode , the oxide layer is not regenerated . The result is that ahigher thannormal
the temperature .
leakagecurrent will flow whenavoltageis appliedafter prolongedstorage . As the
oxide layer is regenerated in use , the leakage current will gradually decrease to
The impedance as a function of frequency (sinusoidal waveform) for a certain
its normal level .
temperature can be represented as follows :
The relationship between the leakage current and the voltage applied at constant
temperature can be shown schematically as follows :
Fig 1-14
Where :
V
F
= Forming voltage
Fig 1-12
If this level is exceeded a large quantity of heat and gas will be generated and
- Capacitive reactance predominates at low frequencies
the capacitor could be damaged .
- With increasing frequency , the Capacitive reactance Xc=1/
Z
Co
decreases
V
R
= Rated Voltage
until it reaches the order of magnitude of the electrolyte resistance Re (A)
This level represents the top of the linear part of the curve .
- At even higher frequencies , the resistance of the electrolyte predominates :
V
S
= Surge voltage
Z= Re (A - B)
It lies between VR and VF: the capacitor can be subjected to VS for short periods
- When the capacitor's resonance frequency is reached (
Z
0) , capacitive
only .
and cancel each other 1/
Z
Cinductive reactance mutually cancel each other
1/
Z
Ce =
Z
L ,
Z
0=SQR(1/LCe)(C) .
- Above this frequency , the inductive reactance of the winding and its terminals
(XL=Z=
Z
L) becomes effective and leads to an increase in impedance .
Generally speaking it can be estimated that Ce
0.01 Co .
The impedance as a function of frequency (sinusoidal waveform) for different
temperature values can be represented as follows (typical values) :
Fig 1-13
I