Adj Voltage Regulator. 12v 8A

Discussion in 'The Projects Forum' started by NM2008, Sep 20, 2008.

  1. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Hi,
    I am looking to build an adjustable voltage regulator circuit which would have a supply of 12v and a continuous output current of 8A.
    Ideally I would like it to be controlled by a pot(similiar to the lm317 control), which would vary voltage from 12v down to 5v.

    Is there a circuit similiar to that of the LM317 regulator cct which would allow me to pass 8A, and vary the voltage.

    Thanks for you help.
    Regards NM
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Take a look at the circuit at the top of page 16 in this LM317 datasheet.

    8 Amps is a bit ambitious for even this circuit. Can you do with 4 or 5 Amps? That would be a bit more realistic.

    hgmjr
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Look for LT1038, its a 10Amp variable voltage regulator.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    If you have not already acquired your components, I would recommend you go with mik3's recommended component choice.

    hgmjr
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The LT1038 is obsolete, and may be hard to get (expensive). If you should happen to burn one up and need another down the line, it will be much more expensive.

    The LT1581 is another 10A linear regulator in a TO220 case that would do the trick.
     
  6. chrissyp

    Active Member

    Aug 25, 2008
    82
    10
    10 amp max is a bit too close for my liking to 8 amp.Why not use a bipolar and restrict the base voltage. 2N6488 is rated at 15 amps.
     
  7. bertus

    Administrator

    Apr 5, 2008
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  8. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Thanks for the help.
    hgmjr 8A is absolute max, 6A is as low as I can allow.

    chrissyp by adjusting the base current to a bipolar, will this basically act as an advanced pot, ie when I adjust down to say, 7v and apply a 6A load will the voltage drop, or will they act similiar to a regulator and keep 7v continious?

    Thanks,
    NM
     
  9. chrissyp

    Active Member

    Aug 25, 2008
    82
    10
    Hi NM
    No the current/voltage drop will be linear.But you did ask for voltage regulation not current.
     
  10. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    I would go with Bertus' solution, making a voltage regulator this way will teach you a bit and can be extended to so many different applications.

    Steve
     
  11. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Ideally what I am looking is a regulation circuit which functions similiar to the LM317 below, except it will pass 6A (8A Max)
    7Vdc1.5ARegulatedSupply.PNG
    Thanks NM
     
  12. hgmjr

    Moderator

    Jan 28, 2005
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    You can take a look at this device.

    hgmjr
     
  13. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    hgmjrThanks for the link.

    But I have been thinking, so far most of the ic's/regulators talked about in this tread are difficult to find, most of the companies I deal with for components do not stock them, or they have them at an exorbitant price.

    What I plan to do is basically vary the speed of a 12v electric fuel pump so as the fuel output can be adjusted from low to high flow.
    I thought of adjustable regulation, thinking of constant current at different voltage levels.
    So, now I am wondering would pulse width modulation do the job. I did not mention this at first because I thought DC was best.
    Also I was not sure how an electric fuel pump would handle being pulsed.

    So, kind of on a tangent here, but would anybody know will these types fuel pump in general handle PWM.
    Thanks for your help.
    Regards NM
    http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=014&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=330265946981&rd=1
     
  14. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    I'm sorry, but DC motors don't work that way. At any given motor speed, current will be proportional to voltage. Torque will be sacrificed if using a linear regulator to control the speed of the motor.
    PWM is a much better way to control DC motor speed. If you use our search function in the blue bar above, you will find much discussion about using PWM to control the speed of DC motors. You will also discover a surprising variety of affordable components which will work well for such an application.
     
  15. Tahmid

    Active Member

    Jul 2, 2008
    344
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