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LM337: LM337 output ripple problem

Okan Boler
Prodigy 30 points
Part Number: LM337

I am using LM337T to regulate -15v to -10v. So far I am able to see -10v. But I am also having a ripple at the output. It is a triangular shaped 40mVpp signal at around 8-10kHz. My input has 10mV ripple. LM337T was supposed to reduce it but it amplifies the ripple by a factor of 4. I've followed the schematics and layout that is in this link: . So do you have any suggestion or anything that we need to double check? I am attaching our schematics. I have everything on my board that shown in the schematic except the protection diode. (D5 in my schematics).

  • 0
    TI__Guru 55940 points
    Hi Okan,

    Could you provide a multi-channel scopeshot showing Vin and Vout?

    Are your output capacitors ceramic? LM337 is an older device that was developed and released before ceramic capacitors became common. You may need to add ESR in order to achieve stability.

    Very Respectfully,
    Ryan
  • 0
    Genius 3030 points
    Hi Okan,

    Why did you use five 10 uF in parallel at the output of regulator?

    In addition to what Ryan mention, I should say that generally lower ESR increases overall reliability. The ESR of ceramic capacitors is considerably lower than ESR of the equivalent tantalum capacitors. BUT for the frequencies below 10KHz, the ESR of ceramic capacitors increases. Therefor using tantalum capacitor is suitable for this frequency range. e.g. you can use two 10 uF capacitors, one ceramic and the other tantalum for the output.

    Regards,
    Hossein
  • 0 in reply to Hossein Forouzani
    TI__Guru 55940 points
    Hi Okan,

    Since it has been a week without a reply, I assume that this thread is resolved. If this is not correct, please feel free to post again.

    Very Respectfully,
    Ryan