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Dual power supply using TPS54383

HPB
Expert 1350 points
Other Parts Discussed in Thread: TPS54383

Hi, I'm trying to simulate a dual output power supply (12V and 5V each at 2A) using the TPS54383 (schematic on page 42 of the datasheet. Datasheet can be found here - http://www.ti.com/lit/ds/slus774b/slus774b.pdf). A bridge rectifier supplies 24Vrms to the PVDD1 and 2 pins. This is a sine wave source simulating the secondary of a step-down transformer. However the output waveforms are very choppy and they seem to be switching with the rectifier (please see the attachment). When I remove the bridge rectifier and make VG1 a unit step source of 24V DC, everything works great. What is going wrong here?

TPS54383-3.zip
  • 0
    TI__Guru**** 191445 points

    It looks like your voltage ac ripple is falling below the UVLO for the device, or possibly falling below the drop out voltage for your outputs.  For a 12 V output, the input voltage cannot fall below about 13.5 V.  TPS54383 is a buck converter only, it cannot boost a lower voltage to a higher voltage.  You will need to provide some type of regulation on the output of your rectifier.

  • 0 in reply to JohnTucker
    Expert 1350 points

    You were right. The AC ripple was falling below one of the output voltages (12V) causing the output to switch off. I added a 4700u capacitor after the bridge and it seems to be simulating just fine now. Thanks for helping me out!