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InnoSwitch-CE - High Frequency Ripple on DC Output - 5V 15W SMPS

Posted by: HimanshuRai84 on Fri, 09/03/2021


I am designing a 15W 5V SMPS Board for a universal line voltage input (85V-265V). Most of the design works well but I am seeing a lot of High-Frequency Ripple on the Output of the SMPS PCB. See the attached Schematic and Waveforms for the measurements and design.

Please can someone review and advise what I could do to reduce / eliminate this HF Ripple component from the DC output? It increases in amplitude with increase in Line Voltage input at the maximum power output level (3A / 15W).



Attachment Size
Schematic for Design 217.37 KB
SDS00061.jpg 86.48 KB
SDS00063.jpg 89.27 KB
SDS00067.jpg 86.83 KB
SDS00071.jpg 84.69 KB
SDS00073.jpg 83.99 KB


Submitted by PI-Spark on Mon, 09/13/2021

Hi HimanshuRai84,

Thank you for using Power Integrations products.

It is possible that the HF spikes you see on the ripple waveform are noise pick-up by the oscilloscope probe. The spikes you showed are in-sync with SRFET switching events and as VIN increases, SRFET VDS also increases.

Are you using a probe with short connection, preferably with a BNC adapter?

Long wires for the probe are prone to noise pick-up.

Also, can you check if a ceramic capacitor directly at the output terminal helps to reduce the noise?

It appears you have a provision in schematic (C19) but it displays not populated.



Attachment Size
DER-717_Ripple.PNG 588.22 KB