Controlling slew times tames EMI in offline supplies. (design Ideas).

EDN, November, 2002 by Canny, David

EMI FROM offline switching power supplies typically causes all sorts of problems for power-supply designers. You may need a large EMI filter to meet FCC emission requirements. Switchers for high efficiency produce high-frequency switching noise that can propagate through the rest of the system and cause problems. Board layout is critical, requiring considerable experimentation, even for experienced designers. The low-noise circuit in Figure 1 significantly reduces the complexity of these issues by continuous, closed-loop control of the voltage and current slew rates. High-frequency noise suppression is particularly important for medical devices because they don't require the ac-line-to-earth ground capacitors ("Y" capacitors) that typically suppress this noise. The...

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