(7) Low EMI, and (8) High reliability. There are a number of conventional approaches to the design of AC/DC converters. The most common approaches are briefly discussed below: 1. Link AC/DC Converters In this type of converter, the AC input voltage is first converted into unregulated DC voltage. The unregulated voltage is then converted to regulated DC voltage by using a known DC/DC converter topology. A block diagram showing the basic conversion stages is given in Fig. 24(a). To meet the input requirements (distortion less input current and close to unity power factor) and output requirements (ripple free constant DC voltage), link AC/DC converters employ several conversion stages and have a high count of power components. Therefore, this type of converter is less efficient, less reliable and has relatively high weight and volume. 2. Switch Mode Rectifier (SMR) The SMR circuit has been used in low frequency applications for AC to DC conversion with a good quality input current waveform. In this approach an active filter is used at the output diode rectifier to reduce the size of input filter which is very bulky at lower frequencies. Figure 25(b) shows a block diagram of a switch mode rectifier. The active filter used in a SMR is essentially a boost or buck converter whose switching frequency is approximately 500 times greater than the input supply frequency to eliminate the lower order harmonics from the input current. Therefore, this circuit in the high frequency power distribution system, where the distribution frequency is in the order of 20 kHz, will be very inefficient due to very high switching losses of the buck or boost
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