emc chokes

Series-mode choke standard ranges

Experience gained from working with customers for over twenty years, to find the best balance between performance and cost, allows us to offer standard ranges of chokes optimised for particular applications, with well defined inductance and current capabilities.
The choke types shown below are all from our low cost ranges, using iron powder cores. Our Power Choke section shows premium types, including compact and HF chokes.

WE range
General purpose chokes, with a wide range of inductance and current ratings. Multilayer windings are mainly used, for optimum energy storage.
VSM range
Similar to the WE range, but mounted on an industry-standard vertical mounting base. Single-layer windings are used to minimise choke self-capacitance, for improved high frequency performance.
WP range
General purpose chokes, with a wide range of inductance and current ratings. Iron powder cores in a low permeability grade give a low inductance swing, allowing high current ratings up to 95 amps
WSO range
SMPSU output chokes, similar to the WE range but extended to higher current, lower inductance designs. Single layer windings are used for minimum self-capacitance and low cost.
WSR range
Switching regulator chokes for use at around 50kHz to 100kHz, with inductance values and current ratings optimised for the popular switching regulator chips. Single layer windings give very low cost.

Series-mode emc chokes

Series-mode noise is generated by interference currents flowing from line to neutral.
A particular example is the fast current rise in phase-angle control circuits, where harmonics of the repetition frequency extend well into the 0.15MHz to 30MHz conducted emc band. Series-mode noise is also usually present on the input to switched mode power supplies, but can be at a level some 10dB to 20dB below the common-mode noise level.
As series-mode noise appears on line and neutral simultaneously, the phase-cancelling technique of common-mode chokes cannot be used, and the magnetic core must be able to maintain inductance in the presence of the full phase current.
This is a very severe requirement in equipment with high peak currents, such as storage capacitor charging currents on SMPSU inputs. Soft saturation, distributed-gap cores are normally used, using iron powder, Hi-Flux powder or the latest Super-MSS sendust.
As the harmonics of the switching waveform generally fall away as the interference frequency increases, it is often possible to accept an amount of choke self-capacitance and use a multi-layer winding to achieve the required inductance from the relatively low permeability of the powder cores.

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