How to control voltage on a DC power supply

Discussion in 'The Projects Forum' started by Gdrumm, Feb 25, 2009.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    Hello,
    I am taking a class on DC Circuits, and I would like to be able to re-create a lab we did at school, at home. I have a 24 V power supply (AC Adaptor), but it's output is more like 30 volts....

    How can I wire in an old volume control type switch to turn down the voltage?

    The outside of the AC Adaptor plug is +, the inside is -.
    My old volume switch has three wires coming out of it, and it's only ID marks are M 5KD.

    See bitmap attached.

    Thanks,
    Gary
     
  2. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    Oh yes, and how can I protect my power supply from an accidental short?

    Where would I put a fuse, and how large a fuse do I need?
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You would need to use a device like an LM317 to do the actual control, but your 5K pot is potentially (little joke there) useful to change the output level of the LM317.

    Here is a link to a data sheet that tells you how to use it - www.national.com/ds/LM/LM117.pdf.
     
  4. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    I skipped trying to control the voltage, and moved on to re-do the lab, substituting my voltage for theirs.

    When I treid to measure current, it gave me a brief reading that quickly began to drop. The AC adaptor is rated at 24V 500mA.

    Do such adaptors have a safety mechanism built it to cause them to drop like that?

    I tried for several hours, using different meters, all with the same result.

    I was unable to measure current for each resistor in the parallel circuit.

    Any clue as to what went wrong?

    Thanks,
    Gary
     
  5. jamers

    Member

    Jan 24, 2008
    12
    0
Loading...