1. Foreword
In electronic equipment, in order to prevent noise from using a squelch filter, when selecting a squelch filter to be used, it must be noted that the filter not only needs to properly remove noise, but also does not cause a decrease in signal quality, resulting in malfunction of the device. Here, we introduce the performance of filters that should be noted when using noise suppression countermeasures, and the noise suppression filters that improve these performances.
2. Squelch filter should pay attention to the performance
When using a squelch filter, the squelch element must be distinguished according to the circuit used and the noise countermeasure frequency. As shown in Figure 1, the squelch components used in the power line are divided into three large categories.
"1" DC overlap characteristics
"2" low frequency squelch performance
Can "3" be suitable for high current
This time, the DC overlap characteristics of "1" are explained.
"1" DC overlap characteristics
Usually, the electrical characteristic data is attached to the specification table of the squelch filter. Of course, once it is inserted into the circuit, the same characteristics as the specification table cannot be obtained. One of the reasons is the current dependence of the squelch filter, so there is a case where the predetermined performance cannot be achieved.
The electrical characteristics (ie, DC overlap characteristics) at power-on are one of the important criteria for selecting a squelch filter.
Since the impedance curve of the impedance type squelch filter changes greatly when DC is energized, this characteristic must be considered when selecting components. (figure 2)
The NFZ5BBW series introduced this time has a very small change in electrical characteristics when it is energized, and is a product with superior DC overlap characteristics.
Figure 2. Example of the electrical characteristics of the squelch filter during DC power-on
3. NFZ5BBW series
The electrical characteristics of the NFZ5BBW series are shown in Figure 3. With a lineup of impedance peaks in the 10MHz to 300MHz range, components that meet the squelch frequency can be selected. There are practical examples of the radiation noise suppression measures for LED illumination. From these characteristics, the series is expected to be suitable for noise countermeasures (power lines) for low frequency (10 MHz to 300 MHz).
Click here for NFZ5BBW series
Figure 3. Electrical Characteristics and Specifications of the NFZ5BBW Series
In addition, the important characteristics when the current is energized are shown in Figure 4. The NFZ5BBW series has almost no change in electrical characteristics even when the currents overlap. Therefore, even if a current close to the rated current is supplied, the same squelch effect as that recorded in the specification sheet can be obtained.
Figure 4. Current Dependency Data for the NFZ5BBW Series
4. to sum up
When using a squelch filter on the power cord, you must pay attention to the performance changes when the currents overlap. The NFZ5BBW series introduced this time is one of the squelch components with superior DC overlap characteristics. In the case where the current is not passed, a general noise filter can be used. It is important to select components with superior DC overlap characteristics like the NFZ5BBW series depending on the situation.
This talk about the DC overlap characteristics of the squelch component, will also use other opportunities to tell whether the "2" low-frequency squelch performance "3" can be suitable for large currents.
Author: Wakatake Nobuyuki Murata EMI Technology Division commodity technology goods Lesson 3
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