Input filter capacitors

Ripple The fluctuation on the DC input signal to the voltage regulator, caused by the charging and discharging of the capacitor input filter. 

The major concern of both output and input filter capacitors is the ripple current entering the capacitor. In this application, the ripple current is identical to the inductor ac current. The maximum limits of the inductor current is 2.8 A for I peak and about one-half the maximum output current or 1.0 A. So the ripple current is 1.8 A p-p or an estimated RMS value of 0.6 A (about one-third of the p-p value). 

The approximate value of the bulk input filter capacitor is found from... 

As one can see, there is the familiar choke input filter (T-C) on the output, which is characteristic of the buck and all forward-mode converters. The configuration shown in Figure 4—10 is called a parallel resonant topology because the load impedance (the T-C filter acting as a damping impedance) is placed in parallel to the resonant capacitor. The input to the T-C filter stage... 

I usually prefer to remove any additional input filter components only after I have solved whatever problem I had been going after. In the case of the vertically stacked capacitors, for example, I would then start removing each additional capacitor one by one (with the help of two soldering irons applied simultaneously to both sides of the stack), confirming, at each step, that the problem had not come back, and that there was not a new one now ... 

The disadvantage of this configuration is the requirement for large-size input filter capacitors. The half-bridge configuration is used for power levels of the order of 500-1000 W. 

Seismic Instrument Response, Correction for. Fig. 2 RC low-pass filter. R is the resistor and C the capacitor. Input is x(f) and output y(f)... 

On the analog side, tbe filter is often the conventional resistor-capacitor or RC filter. However, other possibihties exist. For example, one type of A/D converter is called an integrating A/D because the converter basically integrates the input signal over a fixed intei val of time. By making the intei val I/60th second, this approach provides excellent rejection of any 60-Hz electrical noise. 

Sometimes the high-frequency attenuation is insufficient to meet the specifications and a third pole needs to be added to the EMI filter. This filter is typically a differential-mode filter and will share the Y capacitors from the common-mode filter. Its corner frequency is typically the same as the commonmode filter. This filter is made up of a separate choke on each power line, and is placed between the input rectifiers and the common-mode filter. 

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. 

The circuit of Fig. 4 can also be used as a detector of amplitude-modulated (AM) radio waves. Fig. 5(a) illustrates the components of an AM wave. If this is applied to the input of Fig. 4, the wave is rectified and the output appears as shown in Fig. 5(b). Placing a small-valued capacitor across Rl filters out the carrier frequency and the desired modulating signal is obtained, as shown in Fig. 5(c). 

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