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Suppressing unwanted spikes in DC_DC converters

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reshmi

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We are designing some DC-DC converter circuits.We have used the boost, Flyback and Sepic configurations.
We have used LC filters and capacitor filters to suppress the switching noise and to meet the EMI/EMC requirements. The noise is getting suppressed by the filter, but there are unwanted spikes at the rising and falling edges which are of considerable amplitude and may cause a problem.( I have attached the waveform that we are getting)
Can anyone suggest a method by which this spike can be either removed or suppressed to a lower value.
\]
 

Without knowing the dimensioning of existing filters and the circuit layout, one may only guess how the spikes spread out. It could be, that they simply bypass your filter.
 

try to add snubber circuit.
 

What type of capacitors do you use in the design?

I have managed to reduce switching spikes from 5 Vp-p to 100 mVp-p
by replacing the output capacitor for a type with low ESR and adding
a 100 nF X7R capacitor in parallel to that.

After the change e.g. the 13th harmonic of the switching frequency was
reduced by 30 dB.

No LC or snubber filter were necessary.

/Ram
 

It may be caused by the circuit layout itself. what frequency is the converter running at? Is your filtering close to the switcher?

oddbudman
 

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