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Unable to remove ripple in supply using regulators

S Fighter
Intellectual 540 points
Other Parts Discussed in Thread: TPS793, TPS7A49

Hello,

I have a power supply which gives 12V DC, 120mA with ripples of about 200mV (at a frequency of 60 Hz). I want a 3.3V clean supply using this source.

I tried using the high PSRR solution from TI: TPS79333. But, it didn't remove the ripples, and consumed more than 120mA. I have also tried other LDO regulators, Zener diode, different capacitances after a 3.3V LDO. But, the ripple remains.

Can someone please help me figure out how to remove this ripple?

Thanks,
SF 

  • 0
    TI__Prodigy 570 points

    Hello SF,

     

            TPS793 will not be able to even take 12V at Vin (its maximum rating for Vin is 6V). I highly recommend using TPS7A4901DGN for this application (Vinmax=36V).

           Also, bear in mind that, for this application, you are looking at ~1W of power dissipation  [ (12V-3.3V)*0.12A = 1.044W ]. You need to take this into consideration when selecting the right package for your LDO. Again TPS7A49 comes in a MSOP-8 package with PowerPad that is able to dissipate ~1.8W at room temperature.

     

                      Victor.

  • 0 in reply to Victor Ceron
    TI__Prodigy 570 points

    By the way, when there is a 60Hz signal in  your system, consider checking your grounding and/or shielding your application. Sometime ground loops or high impedance nodes (long cables acting as antennas) may cause this kind of problems.

     

    Hope this helps,

     

               Victor.