power supply circuit help

Discussion in 'General Electronics Chat' started by hemuz, Mar 30, 2010.

  1. hemuz

    Thread Starter New Member

    Mar 7, 2010
    14
    0
    hi all
    i need to design power supply that`s used in powering micro-controller chip, the required circuit can operate from 4.5V AC source to 40 AC source to provide 3.4 to 1.9 V to power up the micro-controller chip , i tried to design it but the problem in case of 40 V is the massive heat , and in case of 4.5v source the circuit output is lower than 1.9 v that`s needed to power the controller

    note that i need only 15 mA to be supplied from this power supply load

    thanks
     
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    Look at the LM2574HV series, either the adjustable or 3.3V versions.

    This is a 'Simple Switcher' device, it takes anything from 4.5V to 60V DC in for 3.3V out.

    You may need to add a simple resistor and zener diode to limit the DC to under 60V after rectification, but the current will be so low that heat should not be a problem.

    That's probably the nearest you will get to the range you are after in a simple design.

    Datasheet:
    http://www.national.com/ds/LM/LM2574.pdf
     
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  3. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    Show us what you've done schematic wise. It might be possible to drop this voltage with a switching setup, maybe even one chip.
     
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  4. zhgart

    New Member

    Dec 28, 2009
    19
    1
    lm317 can do.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The LM317 would not be suitable for this application.

    The original poster needs a switching buck-boost regulator solution.
     
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  6. hemuz

    Thread Starter New Member

    Mar 7, 2010
    14
    0
    thanks all, to the post i think the LM2574HV a solution but i need to implement the circuit by simple discrete components , the attached picture contain the circuit i make, the voltage drop across the 7812 regulator makes the voltage on the load lower than 1.5v i need to modify this value to more than 1.9v , noted that all diodes after 7812 regulator i need, and all diodes is .4v forward .

    thanks
     
  7. hemuz

    Thread Starter New Member

    Mar 7, 2010
    14
    0
    any suggests??
     
  8. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    You are using two integrated circuits, so hardly descrete components ;)

    If you want to do it that way, either find a low drop out equivalent of the 7812 or use a lower voltage reg (7809?) to feed the shunt stage so you can do away with the series diodes.
     
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  9. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    You could try this simple LDO voltage regulator.
     
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