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LM5155-Q1: Understanding the waveform of a SEPIC architecture for making a variable dual output (+/-60 V)

Part Number: LM5155-Q1

Tool/software:

Dear Engineers,

I'm analyzing the following reference design from Texas instrument for making a variable dual output (+/-60V form 11V):

What I'm curious to know is to understand the signal waveform for the following simulation:

The waveforms:

What I do not understand is PULESED-WAVE-P and PULESED-WAVE-N, What I expect is the D1 just pass the positive pules (cycles) and D2 just pass negative pules (cycles), but what we see is that they both are passing positive and negative pulse at the same time:

If we zoom in, we can that both have crossed the zero level (Time scale 14.42 ms to 14.46 ms):

Regards 

 

  • Hi Behnam,

    Thanks for reaching out.

    In this design you have a SEPIC powerstage for the positive rail, combined with a CUK powerstage for the negative rail.

    SEPIC and CUK works similar, but the power stage looks different:

    CUK: The diode points from the coupling cap to the GND

           

    SEPIC: Diode points from coupling cap to the output.

        

    As you can see, the shape of the voltage and current waveforms looks the same.

    I recommend to download the powerstage designer: https://www.ti.com/tool/download/POWERSTAGE-DESIGNER

    Here you can have a look at the waveforms of different topologies and play around with the parameters.

    Best regards

    Moritz