DESIGN CONSIDERATIONS AND NOISE REDUCTION IN SWITCHING CONVERTERS.

Some general design considerations and associated tradeoffs in switched-mode power converters are discussed. An inherent conflict is exposed, in the design of the low-pass filters, between the requirement for high efficiency and the need to damp resonances in the loop gain response. To avoid limitation of dynamic range, direct lossless damping is recommended rather than small-signal loop gain shaping in the error amplifier or by input voltage feedforward. It is shown that increased power loss in parasitic resistance always occurs if the current waveshape is not the same as the voltage waveshape, such as exists at the input of a buck converter of a simple bridge rectifier. This general result emphasizes the equal importance of the input and output current waveshapes in switched-mode power processors that are usually thought of as voltage-to-voltage converters, and leads to the definition of any deviation of the current from the voltage waveshape as a form of noise.