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[SOLVED] Spikes at SMPS output

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papaisou11

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Hi...

I designed a smps of 9V 3A from PI Expert tool and constructed the transformer by hand as per the spec. The SMPS is working but I am getting Spikes at output. (Image attached Output Waveform.jpg )
the Red line represent final voltage output and the yellow line represent the output from Transformer secondary side. The spike and ripple is increasing when I increasing the load.

Schematic pdf file :- View attachment 9V_3A.pdf
Schematic and board layout eagle files are :- View attachment schematic and layout.zip.
Also I am attaching the transformer specification View attachment transformer_construction.pdf.

Please help me to identify the issue.

Thanks and regards.
 

Hi,


Transformer power output (Pad6, 7):
This is called "ringing". It should be suppressed by R7, C7.
R7 needs to be a high frequency, low impedance resistor. No wire wound!

Spikes:
All your elecrolytic capacitors are not good to suppress HF switching noise. I recommend to add parallel ceramics capacitors (foil for primary side).
I`m no friend of single sided PCBs, expecially for switching power circuits. GND wiring becomes critical.
TOP_PIN4 is power GND, therefore use thick and short wire to C2.
TOP_PIN5 is signal GND, therefore route it separately to C2, width is not that critical.

Safety:
* I doubt that optocoupler wiring is according (european) safety regulations. Check creepage distance, clearance.
* C6 needs to be safety approved "Y" capacitor.

Klaus
 

I concur with all Klaus's great answers aswell.
You will indeed suppress it with what Klaus says and you should do it.

Though the scope shot that you show shows what is usually made worse by "pickup" in the scope probe. This can indeed be made less with what Klaus says.

And what you should also try is to just use a piece of plain, good quality, coaxial cable (50 or 75 ohm is fine) to view the output...not a scope probe with a swinging ground clip.
As you know, there is loads of capacitance at the output, so dont worry about the extra capacitiance of the x1 coax scope probe.

here are some other threads on this, it is one of my favourite topics....i was at a hige telecoms co once, and a department was on stop for a whole day because they couldnt get rid of the noise which you show...then the gaffer went in and told them it was pickup.

- - - Updated - - -

https://www.edaboard.com/threads/358562/

https://www.edaboard.com/threads/254629/
 
Last edited by a moderator:

Hi...
Thanks to Both you. I followed the guidelines provided by KlausST and treez.
The issue is solved now :)

Sorry for a very late reply, I was outside of my state.

Regards and Thanks :)
 

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