Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Negative voltage regulator.

  1. Oct 8, 2013 #1
    So for a power supply project I need a voltage regulator giving me a positive output at around 40v.
    Obsessively you can not buy these, So i am useing a circuit which consists of a resistor, npn transistor, and zener diode. the positive input goes to the collector of the transistor and through the resistor to the base of the transistor, and a zener diode of 39v is on the base to ground. Then my output is the emitter. This works fine, but...

    As some of you may know I do a lot in audio and need a negative voltage regulator for the split audio power supply, is there a modification I need to do to make this the same thing just as a negative voltage regulator?

    Also what the heck does a negative voltage regulator do anyway? I understand a positive obsessively but am not sure about the negative.
  2. jcsd
  3. Oct 9, 2013 #2


    User Avatar

    Staff: Mentor

    LM723, positive voltage regulator (linear)

    If you have a negative voltage supply and it varies a bit, the regulator delivers you part of that, but fixed at a steady value. A handy circuit to have. :smile:

    Not much different from how the positive voltage regulator works, really. :wink:
    Last edited: Oct 9, 2013
  4. Oct 9, 2013 #3


    User Avatar
    Gold Member

    LM317 can be had for 57 volts

    http://www.mouser.com/ProductDetail/Texas-Instruments/LM317HVT-NOPB/?qs=sGAEpiMZZMug9GoBKXZ75%252bmFNJYHX7LMu0gFc3QRd28%3d [Broken]

    there are lots of high voltage regulators.

    negative voltage regulators regulate a negative voltage relative to ground. -40V in, -12v Out, for example. You can't just hook -40V into a positive regulator. (can't take the input below ground without destroying it --- look at the absolute max specs for the input voltage range)
    Last edited by a moderator: May 6, 2017
  5. Oct 10, 2013 #4
    do you have a variable negative regulator? also will this give me 3a of current.

    The info you guys have given me helps but my first question was never answered, do you guys know?
  6. Oct 10, 2013 #5


    User Avatar
    Gold Member

    You didn't say 3 amps. Any other secret specifications?
    Using a zener diode and emitter follower is sloppy. google "lm317 current booster" for a better controlled supply architecture. You can use any regulator. I'll let you figure out the negative supply stuff.
  7. Oct 12, 2013 #6
    that helped thanks
  8. Oct 13, 2013 #7
    Nagative Voltage Regulator

    The Negative regulated power supply provides for the negative half cycle of a the audio sine wave. It is typical for audio amps to be powered by positive and negative supplies to produce high fidelity reproduction.
    An LM723 is typically a 10 pin positive regulator with an output current of 150mA...it is used with lots of peripheral components to make fine precision power supplies.
    If you have a solid dc source that provides +40V and -40V with respect to common you can use positive and negative 3 terminal regulators with some peripheral components to provide the voltage and current that you need.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook