7905 voltage regulator

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

  1. jrekha

    jrekha Thread Starter New Member

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

    beenthere Retired Moderator

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

    shivashankari.c14 New Member

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

    jrekha Thread Starter New Member

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    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. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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    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

    Audioguru New Member

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    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.
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