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Low Power Regulator — Parallax Forums

Low Power Regulator

edgellmhedgellmh Posts: 85
edited 2008-09-19 20:59 in General Discussion
I would like to modify the SX28 Proto Board (Parallax 45302) to utilize a low quiescent current voltage regulator (TPS76850: 5V 1A) to provide for battery power operation for a project to construct a sensor that would report water levels using PING))) via Bluetooth (eb501) from our cisterns outside to a receiver inside the house.

I wonder if anyone has suggestions or advice about things to watch out for associated with this modification.

marshall hall edgell

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2008-09-19 14:54
    The main thing is to check the datasheet for the TPS76850 for the values of input and output capacitors required. Different regulators require different input and output capacitors for stability and proper function.

    You may need a small (0.1uF) ceramic capacitor on the input (in addition to the electrolytic) and a small (1uF) low ESR (1 Ohm) Tantalum capacitor on the output of the regulator. See the datasheet for details.

    Note that there's a power-on LED that you'll want to remove or disable because of its power consumption.

    Post Edited (Mike Green) : 9/19/2008 3:03:19 PM GMT
  • edgellmhedgellmh Posts: 85
    edited 2008-09-19 15:14
    Mike

    The TPS76850 spec sheet suggests using 0.1 uF on the input as you suggest but does say larger capacitors like that on the proto board are fine. The spec sheet suggests 10 uF for the output. However, the spec sheet says that larger capacitors like the 47 uF on the ProtoBoard can be used at the output as long as the equivalent series resistance is less than 1.5 ohm. I have no idea how to assess what the equivalent series is since I do not know what that means. Is this the equivalent resistance of the capacitor?

    marshall
  • Mike GreenMike Green Posts: 23,101
    edited 2008-09-19 15:35
    The equivalent series resistance (ESR) of a capacitor is essentially the resistance of the internal structure of the capacitor. This sort of information is given on the datasheet of the capacitor. Usually Tantalum capacitors have a lower ESR than Aluminum capacitors and you can parallel a smaller Tantalum with a larger Aluminum as I suggested to get a lower ESR.
  • edgellmhedgellmh Posts: 85
    edited 2008-09-19 20:59
    Do we know the number of the 47 uF capacitor used on the ProtoBoard so that its datasheet can be found?

    marshall
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