12 or 5V down to 3.3V

Discussion in 'The Projects Forum' started by Edmunds, Jun 16, 2011.

  1. Edmunds

    Thread Starter Active Member

    Sep 27, 2010
    85
    0
    Hi all,

    I need to get down to 3.3V from 5V or 12V. 5 is better. My consumer is supposed to eat 1.8A @ 3.3V, but I would like to have some reserve and excessive heat is an issue.

    I have built a simple thing based on LF33C with adjustable resistor, capacitors and everything. The spec sheet says, it is rated for 1.5A and I was hopping my consumer was asking for more it actually needed. The circuit works very well with no load.

    As soon as you connect the load, however, the thing gets cooking grill hot and does not put out anything more than 0.9V. So I need another solution. More powerful, I guess.

    Can you suggest a more powerful regulator? How to build a circuit that would maintain the voltage irrespective of the load? Difficult? ;)

    Regards,

    /Edmunds
     
  2. imperatormk

    Member

    Mar 1, 2011
    96
    2
    Last edited: Jun 17, 2011
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    How tight does the regulation need to be?
     
  4. Edmunds

    Thread Starter Active Member

    Sep 27, 2010
    85
    0
    You mean, what tolerances are acceptable? Difficult to say. I suppose 0.1V here or there should be ok.

    /Edmunds
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    imperatormk's suggestion is a good one. It's a very simple switching regulator circuit Make sure to use an inductor that is rated for about double the current that you need, as it will have a lower resistance and thus lower power dissipation as heat.

    Linear regulators just won't work well for you. Going from 12.5v to 3.3v means that for every 1 amp of output current at 3.3v, you will have ~9.2 Watts power dissipation in the regulator. With a 1.8A output, that's 16.56 Watts. A linear regulator would be pretty cooked. Switching regulators are far more efficient.
     
    Edmunds likes this.
  6. Edmunds

    Thread Starter Active Member

    Sep 27, 2010
    85
    0
    Great, thank you! I'll read up on "switching PSU".
    /Edmunds
     
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