Ringing Control in Switching Converters
“Ringing” is a common term referring to the undesired oscillation that occurs when a power semiconductor switch turns on or off in the presence of parasitic inductance and capacitance. Energy stored in the parasitic junction capacitance of the switch is released during the switching transition and rings with parasitic inductance coming from the stray fields of discrete power inductors and the wiring inductance of the PCB traces, component leads, connectors, etc.
In real circuits on real circuit boards parasitics are always present, and hence all switching converters produce at least some ringing. This electromagnetic interference (EMI) is typically in the range of 50 to 200 MHz, and at these frequencies PCB traces and the input and output leads act as unwanted antennas, resulting in both conducted and radiated noise.
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