April 2013

3-terminal filters for EMI suppression in power lines

Superior EMC performance in a space-saving component

LCD and plasma displays for TVs and computer monitors demand high power integrity and EMI suppression in the power lines to prevent interferences with RF signals. A single TDK YFF-HC 3-terminal feedthrough filter replaces multiple components in traditional LC filter circuits.

In signal lines, high-frequency EMI can generally be decoupled using a capacitive or inductive low-pass filter (LPF). In power lines, however, LC filters, which combine capacitors and inductors in parallel, are more effective circuits for suppressing noise than the relatively simple LPFs. For this reason, TDK developed the YFF-HC 3-terminal feedthrough filter, which combines a capacitor and two inductors in a single component. The result is a space-saving LC filter able to suppress and decouple the high-frequency interference in both signal and power lines.

Figure 1: Attenuation characteristics of TDK YFF-HC-3 3-terminal feedthrough filters


Thanks to the component’s internal multilayer structure design, the combined component can handle currents up to 10 A and is thus suitable for applications in the power line. Moreover, it features attenuation characteristics that are superior to those of discrete multilayer chip power beads with much lower rated current of 6 A (Figure 1). The YFF-HC 3-terminal feedthrough filter is, therefore, especially well suited as an output filter in switch-mode power supplies in order to ensure the power integrity for displays and monitors with high-frequency signals.

Excellent anti-resonance performance
A further challenge for the design of power supplies for these displays and monitors is the phenomenon of anti-resonance. Multiple capacitors with different self-resonance frequencies (SRF) are often connected in parallel to the power supply line of an IC in order to decouple HF noise over a wide frequency range. Each capacitor generates high impedance with an undesirable side effect: The impedance peaks at the points between the SRFs (Figure 2). By comparison, the YFF-HC 3-terminal feedthrough filter exhibits excellent attenuation characteristics over a wide range of frequencies from the MHz range into the GHz range (green curve). This EMC performance is superior to that of both discrete LC filters and multiple decoupling capacitor constellations.

Figure 2: Superior EMI suppression with the TDK YFF-HC series


The TDK YFF-HC series of 3-terminal feedthrough filters effectively suppresses impedance peaks that occur between the SRFs of multiple decoupling capacitors.


Fewer components and a smaller footprint

Because the YFF-HC 3-terminal filter combines both a capacitor and two inductors in a single component, fewer parts are needed for EMI suppression. This not only simplifies the layout on the PCB and assembly processes but also helps improve the overall reliability and saves space.

Key data of the TDK YFF-HC 3-terminal feedthrough filter

Type

Rated capacitance
[µF]

Rated voltage
[V DC]

Rated current
[A]
YFF31HC2A105MT000N1.00 ±20%1006
YFF31HC2A104MT000N 0.10 ±20%10010

YFF31HC2A103MT000N

0.01 ±20%10010
YFF31HC1A153MT000N0.015 ±20%5010

Main features

  • Small and high-performance EMC components
  • Excellent attenuation characteristics over a wide range of frequencies
  • High current capability (6 A to 10 A)
  • Reduces number of components and footprint and simplifies layout on the PCB

Main applications

  • Power supply lines of LCD and plasma displays in TVs and computer monitors
  • EMI suppression measures for power supplies in communication infrastructures

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