Stepping down -12V supply to -4V

Discussion in 'The Projects Forum' started by xenlab, Jul 5, 2015.

  1. xenlab

    Thread Starter New Member

    Jul 5, 2015
    2
    0
    Hello,
    i have +12V/-12V DC power supply and want to establish a ground potential at -4V. I have seen this done with +-15V using a 7905 to create -5V, but unfortunately there is no 7904 (max current 1A, better even 1.5A) which would deliver stable -4V DC.
    Could anyone recommend a component with which this could be realized correctly?

    Thank you
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,010
    3,785
    Try LM337 - a three pin regulator with adjustable voltage.
    It allows any voltage (you just need two resistors to program the voltage you want). Works just like lm317 except for negative voltages as you want.
     
  3. xenlab

    Thread Starter New Member

    Jul 5, 2015
    2
    0
    Thanks a lot GopherT. This is exactly what i was looking for.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,010
    3,785
    Also, if you need more than an amp of current, you could use a 7905 regulator and a darlington PNP transistor (see the datasheet). The darlington will drop 1.2 volts and allow much higher current. That works if 3.8 volts works for you. I would go for the LM 337 option if you have to place an order for either part. The lm7905 is an option if you have sone in your parts bin.
     
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