App note: Minimizing switching regulator residue in linear regulator outputs

Posted on Saturday, November 10th, 2012 in app notes by DP

Jim Williams from Linear Technology explains how to battle switching regulator residue in linear regulator outputs. If you want to clean up the switching regulator output by using a linear regulator, you’ll run into difficulties.

Linear regulators are not very good at suppressing high frequency noise, and switching regulators output loads of it. The “secret sauce” to suppress the high frequency noise is to add ferrite beads on both the input, and the output of your linear regulators. More about this is covered in the app note.

This entry was posted on Saturday, November 10th, 2012 at 11:00 am and is filed under app notes. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

4 Responses to “App note: Minimizing switching regulator residue in linear regulator outputs”

  1. Casey O'Donnell says:

    sounds expensive. big hunk of metal strapped to a lm317 gets the job done

    • Drone says:

      @Casey O’Donnell,

      The end concept here is to introduce a switching regulator/converter (buck, boost. buck+boost) to efficiently handle a wide range of input voltages, and then take the switching output which is closer to the linear regulator’s designed input voltage to avoid the losses which will happen with a linear regulator alone (thereby requiring a “hunk of metal” as you said to dissipate the linear regulator’s input vs. output voltage difference). The added advantage is that linear regulators will then reject the noise generated by the switching “pre-regulator” and present a cleaner DC output to the following subsystems. Switching pre-regulation, especially in the case of battery powered devices which are sensitive to power supply noise makes post-regulation linear regulators highly desirable as they reduce the switching noise. The combination allows (especially with buck-boost switching pre-regulators) to get every last drop of energy out of a battery while still providing cleaner DC power to the system.

  2. JBeale says:

    A good reminder of basic circuit techniques! Sometimes switchers are required, for example right now I’m working on reducing noise on the output of an isolated DC-DC converter. That can’t be done without using some kind of AC signals, as far as I know.

  3. r4k says:

    Wasn’t the posted a few months ago?

Leave a Reply

Notify me of followup comments via e-mail. You can also subscribe without commenting.

Recent Comments

  • Daniel: Do I comment here or on FB?
  • Craig B: Shouldn't the default be 00xxx010? Note that bit 0 appears out of order in the documentation. In that case I think the initial value is...
  • JJM: From the datasheet extract you are showing, the power up status should be 00xxx010, not 000xxx01. Bit numbering is misleading since 'measurement resolution' is apparently...
  • Jan Ciger (@janoc200): Hmm, that could actually explain why the three sensor IMU breakout I have bought a few years ago had all sorts of issues - I...
  • Travis: Is it preset to the windows 3 fingered salute?