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How to step down 130 VDC using a LM7812?

Discussion in 'Electronic Basics' started by [email protected], Jun 11, 2005.

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  1. Guest

    How can I step down 130 VDC to 12 VDC using an LM 7812. As the 130 VDC
    battery pak loses voltage I want to maintain the 12 VDC.
  2. You can't. The LM7812 has a maximum input voltage of 35V. To step down from
    130VDC to 12VDC you will need either a discrete build linear- or a switching
    (buck) regulator.

    petrus bitbyter
  3. Guest

    OK Thanks. Can you tell me how to connect the circuit using 24 VDC?
  4. Tom Biasi

    Tom Biasi Guest

  5. Guest

    Yes, thanks, I had read the info at that website. I was confused
    because I had been told to use the LM7812 by someone who I thought was
    knowledgeable. I am new to this field.
  6. Tom Biasi

    Tom Biasi Guest

    The 7812 has an "IN" (for up to 30 volts pin 1) and an "OUT" (12 volts
    regulated pin 3).
    The common (pin 2) or GND is shared between the two.
    With a battery you won't need the large input capacitor.
  7. You also need to consider bolting the 7812 to a large heat sink.

    You haven't what current you what to supply but for the sake of argument
    assume that it is 1A.

    You have a 24V source and you are delivering 12V. This means that the
    difference of 12V will be across the 7812. With 1A being supplied this
    means that 7812 will be disipating 12W (12V x 1A) which will mostly be
    turned into heat. This may not seem much compared with everyday domestic
    appliances but for an electronics component it is a lot. Without an
    effective way to get rid of this unwanted power (heat) the 7812 will cook
    and probably fail.


  8. Tom Biasi

    Tom Biasi Guest

    A heat sink is definitely called for.
  9. Guest

    The device will draw 50 t0 100 mA.
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