03320336| Datasheet

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Chokes for Power Lines Current-Compensated Chokes
General
Magnetic flux induced in core by operating current

Operating current

Core

Line

Windings through which current flows

Source of interference

Magnetic flux induced in core by interference current

Common-mode interference current, asymmetrical interference

Fig. 1

Current-compensated ring core choke Double choke shown as an example

Compact electrical and electronic equipment primarily generates common-mode interference. In order to be able to meet the safety requirements (keeping within the leakage current limits and thus limiting the capacitance of Y capacitors) specified in the safety standards, chokes with a high asymmetrically effective inductance must be used. Current-compensated chokes with a closed core topology are especially suitable for this purpose. The problem of core material saturation due to the operating current is solved in these designs by winding two windings with equal numbers of turns on the core. These windings are connected in such a way that the magnetic flux induced by the operating current flowing in the upper winding is opposite to that induced by the current flowing through the lower winding, so that the two fluxes cancel, i.e. compensate one another (cf. fig. 1). This enables the use of highly permeable ring cores, so that high inductance ratings per winding are obtained. When current-compensated double cho
kes with ferrite cores are used, the full inductance attenuates common-mode interference. The operating current is only affected by the stray inductance (order of magnitude: 1 % of the rated value) and the ohmic resistance, which is generally low. As a result, the suppression of differentialmode interference by current-compensated chokes is accordingly low. In many cases, a combination with symmetrically connected capacitors or powder core chokes is therefore required. In comparison to I core chokes, current-compensated chokes have higher inductances, very low stray fields and smaller dimensions at comparable current ratings.

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