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Electromagnetic Interference EMI Filter

The last filter that will be looked at in this chapter is the EMI filter. This filter is commonly used on the input of a power circuit to reduce conducted and reflected emissions. For instance, a flyback converter can draw current from the bus that looks like a sawtooth waveform with [Pg.52]

They are several concerns when designing an EMI filter. The parameters of the EMI filter examined in this book reflect these concerns. If the EMI filter is to be used on a converter, the input impedance of the converter must be greater than the output impedance of the filter at all frequencies. It is good practice to allow 6 dB of margin for this parameter. If the output impedance of the filter gets too close to the input impedance of the converter, there can be problems with the stability of the converter. It may be important to note here that this output impedance is sensitive to the effective series resistance (ESR) of the output capacitors. For the hardware data taken for this unit, tantalum capacitors, which have unspecified ESR, were used. The ESR of a similar capacitor was measured for the simulations. [Pg.55]

Other important characteristics of the converter are the reflected ripple attenuation and the turn-on characteristics. It is expected that the turn-on characteristics will be difficult to simulate because of the nonlinear characteristics of a saturating core. A nonsaturating core is simply described by Faraday s law, and it can be easily modeled by any of the SPICE simulators. The model used for the EMI filter is shown in Fig. 3.66, and the results of each of the simulators output and the measured impedance plots are shown in Figs. 3.67 to 3.70. [Pg.55]

The inrush current of an EMI filter is usually examined to ensure that no parts are overstressed during power-up. If the inductor does not saturate, the inrush current is described by Faraday s law and can easily be modeled by mathematics or a simple SPICE model. It is also not too difficult to determine if a core is saturated during turn-on. A slightly more difficult calculation is to determine what the maximum current will be under a given turn-on condition. The hardware used for measurements used a transformer made of two stacked 55025 cores [Pg.56]

Note that a current probe was used to measure the inrush current (Figs. 3.72 and 3.73). It was set on 10 mA/mV, which means that the plot above the -axis settings are in 5 A/div. It was only measured for Fig. 3.73, and it is 5A/div for the scale. [Pg.58]


Fig. 10.4. Mounting of electromagnetic interference (EMI) filters inside a shielding box. Fig. 10.4. Mounting of electromagnetic interference (EMI) filters inside a shielding box.
FIGURE 7.12 Typical electromagnetic interference (EMI) filter schematic and outline the filter yields 60 dB common-mode attenuation and 50 dB transverse mode attenuation between 100 kHz and 1 Mhz. [Pg.168]

Some manufacturers recommend using a filter at the output of the inverter to smooth the waveform applied to the motor and to reduce the sharp rise and fall in the notches that may be present, as in the case of current-fed motors. Steep sided notches cause a high dV/dt across the insulation of the motor, which can reduce the life expectation of the insulation. The filter may also be required to reduce electromagnetic interference (EMI). [Pg.399]

Ferrites represent the most widespread technological solution to reduce electromagnetic interference (EMI), because they allow the directly induced noise to be filtered. These ferrimagnetic ceramics produce magnetic flow density in response to small magnetization forces applied. Currently, ferrites used for EMI suppression above 30 MHz are composed of mixtures of oxides of iron,... [Pg.479]

Electromagnetic fields are all around us and are not necessarily evil. For instance, without these fields radios and televisions would not work, and cell phones would be useless. The garage door opener could not be used from the comfort of a car and the door would not automatically open. Electromagnetic energy is needed for day-to-day lives. It just so happens that some electronic devices may be sensitive to the fields. Fortunately, exposure of such devices to the fields can be reduced. As discussed earlier, shields, filters, and isolation techniques are useful tools that allow us to live in the EMI environment. It is a matter of determining the source of the interference, the tolerance level of the victim, and the medium that is providing a means of interaction between the two. All EMI problems require knowledge of all three factors for an effective solution. [Pg.171]


See other pages where Electromagnetic Interference EMI Filter is mentioned: [Pg.240]    [Pg.244]    [Pg.52]    [Pg.225]    [Pg.229]    [Pg.240]    [Pg.244]    [Pg.52]    [Pg.225]    [Pg.229]    [Pg.339]    [Pg.339]    [Pg.339]    [Pg.441]    [Pg.1082]    [Pg.1817]    [Pg.81]    [Pg.9]    [Pg.186]    [Pg.375]   


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