SMPS / LED Driver Harmonics
Switched-mode power supplies and LED drivers switch at between tens of kHz and a few hundred kHz; the harmonics they produce extend up to the order of tens of MHz. Cheap supply units with a weak input filter can noticeably raise the receiver's noise floor in the enclosure where they are installed.
The near-square shape of the switching current produces harmonics at multiples of the fundamental frequency. The faster the rising edges, the higher the harmonics extend. Without sufficient input and output filtering, this energy gets onto the supply cables and from there into the air.
- Symptom: range dropping after the receiver's supply is taken from a new adapter.
- Diagnosis: temporarily running the receiver from a battery or a linear supply and observing the difference.
- Precaution: using a supply with an EMC filter and a declaration of conformity, adding a ferrite to the supply cable, and placing the receiver in a separate compartment from drives and LED supply units.
This source is insidious and so goes unnoticed: it sits small and quiet inside the enclosure, but it is right next to the receiver and the coupling distance is very short. When planning the layout, putting distance between the receiver and the switched-mode supply is more effective than many measures taken afterwards.
Context in which this term is used: Wireless remote control installation: pairing, relay, safety