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Jensen NOS Aluminium foil
Руководство по эксплуатации Страница: 18

JENSEN Jensen NOS Aluminium foil Руководство по эксплуатации онлайн [18/23] 778569

Extremely low inductance makes

excellent high frequency capabilities

The high inductance value of a capacitor is

particularly harmful when they are used for

filtering at higher frequencies, as the

impedance of a high capacitance capacitor

over the resonance frequency - which is

typically a few tens of kHz - is strongly

dominated of the inductance of the

capacitor winding.

In consequence of the construction, the

conventionally designed, even multitabbed

or extended foil electrolytic capacitors

provide a significant undesired and

increasing impedance vs. frequency

response in the critical frequency field. The

most acceptable compromise and so far the

most utilized solution for this problem was

the usage of several high capacitive

electrolytics in parallel connection, in order

to reach the desired low inductance value.

The best and the ultimate solution no doubt

a four pole electrolytic capacitor having the

same Capacitance x Voltage/Volume ratio

as the best high capacitive electrolytics with

an inductance which is only the fraction of

theirs. Let us take a typical reservoir

capacitor size of 15.000 µF 40 V and

compare the Z impedance versus frequency

characteristic of a traditional and a four

pole device. The curve B shows the

traditional two pole, and curve A the four

pole capacitors frequency versus impedance

characteristic. (Figure 1.)

Figure 1.

(The impedance of a four-pole device rather called as transfer impedance, defined as the quotient of the

output AC voltage and the input AC current and measured according to DIN 41 328 sheet 1.)

The two curves run together in a while, but

already before the resonance frequency the

curve A is falling steeper than B and

reaching a minimum value of 0.5-0.8 mΩ in

the frequency interval of 10-50 kHz. This

value is almost two orders of magnitude

lower than the impedance of a traditional

two pole electrolytic capacitors. At the

resonance point the inductive and the

capacitive part of the impedance is zero

and only the pure ohmic component (ESR)

define the impedance. From this point the

capacitor behaves as an inductor and the

impedance consisting mainly of the

inductive component increases again. It is

very easy to realize that not only the

equivalent serial resistance (ESR) but also

the inductance of a four-pole reservoir

capacitor is only the fraction of a

conventional capacitor in a wide high

frequency range. The very low transfer

impedance value at higher frequencies

make the four pole capacitor applicable also

in other high frequency and digital signal

handling equipments and circuits as

preamplifiers, A/D and D/A converters,

switched mode power supplies etc.

JENSEN Jensen NOS Aluminium foil Руководство по эксплуатации онлайн [18/23] 778569

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