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PMP10344: Ripple in output voltage

Part Number: PMP10344

Hi,

I'm having a large ripple in output voltage when mosfet turns off. It's about 2V. I would like to know if it's normal. 

The image below shows it. In blue is the gate voltage, and in yellow is the output voltage. The output is suposed to be around 27V@3A

Here is the schematic file: ACDC.pdf

Besides that I would like to know, if possible, how can i measure the noise related to the MOSFET switching.

Thanks!

Arion

  • Hi Arion,

    How are you measuring the output voltage, are you using a tip and barrel method to keep the ground loop short? This can add noise onto the measurement that is not really there. Also I would suggest to measure across the ceramic output capacitor.

    In terms of the MOSFET switching, I am not really sure what you are asking. Do you have a differential probe?

    Thanks,

    Robert 

  • Hi Robert,

    I was not using this method, actually I used the clip to attach to ground and the tip conected to Vcc. The measurement was made in the Eletrolytic Capacitor.

    About the MOSFET, what I'm trying to ask is how can I measure a possible noise generated by the switching MOSFET, like some noise in ground or something like that. I'm starting to think that a noise problem in another part of my project is related to the switching in power supply, that's why I'm taking a look into this.

    Thanks.

    Arion

  • Hi Arion,

    If you don't use the tip and barrel method you will pick up a lot of noise that is not real, like you are seeing. Please also measure across the ceramic capacitor.

    Thanks,

    Robert