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Featured products! Case Study of Onboard Motor Noise Countermeasure with PLT10HH

2012年02月14日　Category: Noise suppression filter Room

Previously, we introduced the common mode choke coil for strong electric currents. This time we follow up with a case study of an onboard motor noise countermeasure with the PLT10HH.
*An earlier article introducing the PLT10HH can be found at the following URL:
 http://www.murata.com/products/emicon_fun/2011/12/emc_en14.html


Introduction
To make automobiles more energy-efficient and lightweight, an increasing number of their components have become electrically driven.. For this reason, electric motors are used not only for traditional devices like windshield wipers, but also for power steering, fuel pumps and so on. Some DC motors use brushes to rectify the current, but because such brushes are repeatedly contacting and separating from commutators, sharp fluctuations in electric current cause noise and spark noise (Fig. 2). If such noise flows through the power line to other parts, it could have an adverse effect. While it also depends on motor speed, this noise can range widely in frequency from hundreds of kHz to hundreds of MHz, making it necessary to take adequate noise countermeasures.



Figure 2 shows a model of how noise is generated in a brush motor and illustrates key points of a basic method to counter the noise. Basically, there are two kinds of noise: differential mode noise, which is conducted similarly to a power current, and common mode noise that is conducted parallel to two power lines. Effective noise countermeasures must therefore be taken for each type. The use of a capacitor is a relatively easy and inexpensive countermeasure. A countermeasure for differential mode noise uses an across-the-line capacitor (X capacitor) that connects across two power lines. A countermeasure for common mode noise uses a line-bypass capacitor (Y capacitor) that creates a connection between both lines and a chassis ground. If the capacitor alone is not sufficient to suppress noise, the addition of a common mode choke coil can effectively suppress common mode noise that is otherwise difficult to overcome, and it is possible to take measures against even often problematic high-frequency noise.

<Cause of noise in brush motor and countermeasures>
Spark noise occurring between the brush and commutator is the cause. Noise includes both normal mode and common mode noise and occurs over a wide frequency range.

<Key points to noise countermeasures>
(1) Taking measures inside the motor (close to the noise source) is effective.
(2) Using an X capacitor and Y capacitor together is effective against both normal mode
and common mode noise



Example of motor noise countermeasure experiment
Figure 3 shows the  results from an actual experiment with a measure against power-window motor noise.
The results show that a noise countermeasure using only capacitors (across-the-line and line-bypass capacitors) is adequately effective against frequencies lower than 10 MHz, but the effect is not sufficient against frequencies greater than 30 MHz and this measure would not pass CISPR Part 25 Class 4. When a PLT10HH common mode choke coil is added to capacitors, noises of 30 MHz and above are suppressed and CISPR Part 25 Class 4 is successfully cleared. With power line noise, the differential mode is dominant at low frequencies and the common mode at high frequencies, so a common mode choke coil that suppresses common mode noise is effective and high-frequency noises can be suppressed. Additionally, because there are strong electric currents in power lines, when a strong current is passing through a regular inductor, inductance declines because of magnetic saturation and noise is less effectively suppressed. However, with its internal structure, the common mode choke coil makes magnetic saturation unlikely to occur so the noise suppression measure tends to maintain its effectiveness. In this sense also, it is efficient to use a common mode choke coil for power lines.



The PLT10HH common mode choke coil used here supports rated currents of 6 A to a maximum of 10 A and is designed to support various motor applications in which there is a large electric current during startup. It also has a highly reliable design so it can be used in severe environments such as in automobiles. Of course it can also be used for regular electronic devices, making it suitable for countering noise in a wide range of motor power lines.



Person in charge: Murata Manufacturing Co., Ltd.  Yasuhiro Mitsuya

Pick Up Products! Common Mode Choke Coils for Automotive

2011年12月14日　Category: Noise suppression filter Room

Pick-up products!　
Large-current PLT10H series SMD common mode choke coil for automotive

Up until now, we have been giving basic information about parts in the EMICON-Fun! articles. In this new series of 'Pick-up products!' articles, we will be introducing highlighted products not offered by other companies. The first part in this series is about large-current PLT10H series SMD common mode choke coil for automobiles. This article gives an overview of the product, and succeeding articles will discuss the effects of actually using the product.

The PLT10H is a revised version of the lead-type PLT09H common mode choke coil that has been a firm favorite in the past, and that was made into an SMD-type and exhibits drastic expansion of rated current and enhanced reliability. Rated current was greatly improved from the previous 3A to a maximum of 10A,* enabling its potential use in a wider range of applications. The previous type was only available with one inductance variation, but the number of variations for this type has been increased to four, ranging from 6μH to 20μH. Moreover, the coil's coupling coefficient can be controlled to give it the most appropriate differential mode inductance, making it effective against not only common mode noise, but also differential mode noise. Operating temperature ranges from -55ºC to +125ºC, making these coils perfect for vehicle accessory motor power supplies.

*Derating of rated current may be required depending on operating temperature.
For details on use of the product, please see the product specification for approval.

◆Dimensions (When you click it, the image is enlarged.)