7905 voltage regulator

Discussion in 'Homework Help' started by jrekha, Apr 15, 2010.

  1. jrekha

    Thread Starter New Member

    Mar 31, 2010
    Using 7905 voltage regultor can i produe +5V and -5V.
    my Vin is 7V
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    No. If you had a source of -7 volts, you could produce a regulated -5 volts.
  3. shivashankari.c14

    New Member

    Apr 6, 2010
    u can produce -5v by using 7905...if u use 7805 u can produce +5v..
  4. jrekha

    Thread Starter New Member

    Mar 31, 2010
    so i need +5v and -5V, suplly is +7vand -7V.
    how to do it using both 7805 and 7905?can i simply connect both together to respective supply, and ground together, to get the outputs??
  5. Wendy


    Mar 24, 2008
    2 volts difference is pushing it a bit, but that is the idea.

    You will need 0.1µF caps on the output of each regulator, as well as caps on the input (say 3.3µF) to keep the regulators from oscillating.

    The 7805 and 7905 are pretty close to mirror images of each other. They both have overcurrent and thermal protections. If you push much current through them at all a heatsink is strongly encouraged. With a heatsink they are basically indestructible.

    You also need a minimum load. If they will be disconnected from the circuit you might think about adding a 10ma LED circuit on them.
  6. Audioguru

    AAC Fanatic!

    Dec 20, 2007
    7805 and 7905 regulators do not need a minimum load current. Their voltage regulation is spec'd with a load starting with 5mA but without a load the regulation is fine.

    The LM317 adjustable regulator needs a minimum load current that is usually set with its veltage setting resistors.