Meaning
Rapid voltage and current transitions during the operation of power semiconductors generate brief, high-frequency electrical disturbances. A switching noise transient can propagate through board traces and power cables, causing electromagnetic interference and degrading signal integrity. This transient is a common byproduct of high-efficiency switch-mode power supplies.
Physical Cause
The fast turn-on and turn-off times of transistors in modern converters are the primary sources of these high-frequency disturbances. These rapid transitions interact with the parasitic inductance and capacitance of the circuit, creating high-frequency ringing. This ringing can be several times the magnitude of the steady-state operating voltage.
It is particularly severe in designs that use fast switching speeds to achieve high efficiency. This noise must be managed directly at the source to prevent it from affecting other components.
Electromagnetic Emission
Conducted emissions on input and output lines are the main path through which this noise travels to other parts of the system. If the noise is not filtered, it can escape the enclosure through attached cables and radiate as electromagnetic waves. This radiation can interfere with the operation of nearby radio receivers and cause compliance failures.
Testing for conducted emissions measures these transients across a wide frequency range.
Hardware Suppression
Placing RC snubber circuits across the switching nodes and using high-quality ferrite beads on the power lines helps to dissipate these high-frequency transients. These components absorb and convert the high-frequency energy into heat before it can propagate through the system. This suppression is necessary to meet electromagnetic compatibility standards.
