simple 0v to 15V / 5 or 6 Amp power supply

Discussion in 'The Projects Forum' started by french_guy, Oct 21, 2009.

  1. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    Hello

    I’m looking for an adjustable power supply from 0V to 15V @ 6 Amp (and I will most likely use it within the 10V to 15V range)
    I want to keep it simple, and I want to use basic components I can buy at Radioshack (LM317T, 2N3055, etc..)
    I’m planning to buy a laptop power supply (19V @ 7.5 Amp) to feed it
    Any idea for the design?
    I’m thinking about a LM317T and 2 x 2N3055 as pass transistors?
    But I don’t know how to do it…!!!

    Thanks
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Going all the way to zero makes it complicated. Starting from 19V, and dropping most of that across the regulator at 6A means you are dissipating over 100W when the supply is delivering low voltage. 100W is about where you need a fan to cool the heatsink.

    You might be ahead of the game to start from a multi-winding transformer supply, where you can do some series-parallel switching of windings to reduce the unregulated voltage at the input of the regulator when the supply is delivering high current at low voltage.
     
  3. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    And what if I only need 10V to 15V (no real need to go under 10V)
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Have you considered simply converting an ATX form factor computer power supply into a bench supply? The voltages are fixed, but you generally have a good variety of them; +3.3v, +/-5v, +/-12v - and it's inexpensive to convert one.

    Google "ATX bench supply" for lots of ideas
     
  5. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    I already have one for my battery charger (I do RC cars)
    I'm more looking for an adjustable power supply for my Scalextric 1:32 slot car track
    I think I need something from 10V min to 15V max, and the power should be something like 3 Amp per lane...this is why I want 6 amp since it's a 2 lanes track

    Thanks
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Sounds very similar to a project I'm thinking of. No progress yet, but my thread is here...

    http://forum.allaboutcircuits.com/showthread.php?t=28820

    I'm thinking of going switching mode because of the potential heat dissipation. Where is your source power coming from?

    I was thinking of setting the minumum voltage spec around 1½ to 3V, max around 18V (or whatever I can get by with).
     
  7. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    My source power will be a laptop power supply 19V - 7.5A
    The advantage of those power supplies is that they are not too bulky, relatively cheap and works wtih 220V AC as well (I'm french and that can be usefull)
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Seems to me that PWM would be a better choice than a linear regulator. To get an average 15v from 19v, you could run the maximum PWM at around 79% ON; to avg 10v around 53% ON.

    You'll probably find that throttle control is a good bit more smooth at lower speeds over a linear supply, too.

    Is 3A the maximum current draw of the cars' motors at 15v?
     
  9. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    Yeah,,,doing RC cars, I know PWM will be better. However it’s not widely used in the slot car world (some hand controllers are “digital” and use PWM, but they are way too expensive)
    Anyway, like I said, I want something easy to build. Unless you have an easy to build PWM solution!!!
    Regular hand controllers use a resistor (Parma economy series with a 45Ω or 35Ω resistor seems to be a good pick)
    I want an adjustable power supply to adjust the power depending on the cars: some of them might require 14V, others may be 12V or 13V only. And being able to adjust to 10V can be interesting if my daughter wants to play with my cars (and I’d like to keep them on the track…!!!)
    It seems that having 3 Amps per lane is a safe minimum….
     
  10. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    Hi SgtWookie

    Were you talking about adjusting the power supply output by PWM, or were you talking about the hand controller by PWM?
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    I confess that I am not privy to the guts of current hand controllers.

    If they are basically the equivalent of rheostats or potentiometers, they might be made to drive PWM circuitry.
     
  12. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    Yes, they are equivalent to rheostats...
    So what was your solution?
     
  13. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    So how do you see an adjustable power supply to deliver 10V to 15V @ 6Amp from a 19V/7.5A laptop power supply ?
    With a MOSFET I guess, but what else? And again, I'd like to keep it simple?

    Thanks

    My other option would be to use 1 or 2 LM338K in parallel....
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    LM317 datasheets have current boosters included. The reason I decided against linear for my project is the heat. Figure 6A X 10A is 60W, which is worst case. Plan on good heat sinks and probably some fans.
     
    Last edited: Oct 23, 2009
  15. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    My power source will be a laptop power supply (19V DC @ 7.7 Amp)
    What do you suggest to make an adjustable power supply (10V to 15V, able to deliver between around 6 Amps)?
    And like I said, something simple

    Thanks
     
  16. SgtWookie

    Expert

    Jul 17, 2007
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    OK, so what is the minimum and maximum resistance of the hand controller?
     
  17. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    The Parma Economy serie can have different resistors
    2 common values are 45 Ohms or 35 Ohms
    Let’s consider a 35 Ohms
    I guess the cursor can go from 1 extremity to the other, so Rmin = 0 and Rmax = 35
     
  18. SgtWookie

    Expert

    Jul 17, 2007
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    OK, so the highest speed is when the resistance is zero, right?
     
  19. french_guy

    Thread Starter Active Member

    Apr 16, 2009
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    Yes
    And the resistor is fed by this power supply I'm looking for: from 10V to 15V
    the choice of the voltage depends on the car and your skills...
    Like I said between 12 and 14V may be, and 10V for younger drivers
     
  20. SgtWookie

    Expert

    Jul 17, 2007
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    OK, this schematic is rather poorly drawn I'm afraid, but have a look anyway.

    [​IMG]

    C1, C2, U2, R8, R9 supply a 1.6v reference for opamp U1's noninverting input. R9 may need to be adjusted slightly in order to get exactly 1.6v at the output of U2. You could replace it with a 50 Ohm or 100 Ohm pot. Decreasing U2's output voltage will scale down the maximum and minimum voltages output.

    R1 is your 35 Ohm controller.
    R1, R2, and R5 make up a voltage divider whos' output (at the junction of R1/R2) ranges from about 0.66v to 1v.
    R6 and R7 set the gain of opamp U1 to 15.
    Q1 is used as a voltage follower, amplifying the output current capability of U1.
    Q2 is an NPN power transistor. It will need a large heat sink.
     
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