16v Power Supply, from 24v one?

Discussion in 'The Projects Forum' started by Detonator, Apr 2, 2010.

  1. Detonator

    Thread Starter Member

    Mar 6, 2010
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    Hi all

    I only know very basic electronics right now so please keep replies in basic laymans terms! (doing a course though)

    I bought a PIC programmer kit (as i have a pile of PICs i was given) from local electronics shop, started building it and then noticed it needed an unusual 16v 500mA power supply. Kit is now finished so i went back to shop to see what 16v power supply they had, Crazy but they dont have any :mad: (other than a very expensive bench supply, way out my price league). Crazy they sell a kit that they dont have power supplies for!

    So i sat here thinking what do i have in my box of junk parts! I have an old photo printer supply here thats 2A 24V, only thing i got thats over 16v. So sorry for sounding completely noob here but how can i simply use my 24v supply and make it into a safe stable 16v one? I figure maybe a voltage regulator but i dont see any 16v options in the catalogue, they do have a 1-37v voltage regulator though LM317T which i have no idea if it would work, or how it would work?

    If anyone can shed some light on getting my 24v supply to 16v i would be very grateful, wanted to play with some PICS over the Easter break, but the local shops only open today and closed rest weekend, so really need get down there and get anything i may need.

    Thanks all
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    you can try my circuit
     
  3. R!f@@

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    Apr 2, 2009
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  4. Detonator

    Thread Starter Member

    Mar 6, 2010
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    Thankyou my friend, that looks like something i may build at a later date. But for today i think i need a quick simple fix.
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I don't think u understand what I am saying.
    This schema can be changed to suite ur need and can really simple.

    You have a 24V supply. So with this you can have a variable supply from 0 to 20V at the same current the adapter is handling.
    Do you want me to simplify it?
     
  6. R!f@@

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    Apr 2, 2009
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    Or do you want another fixed 16V circuit from 24V
     
  7. Detonator

    Thread Starter Member

    Mar 6, 2010
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    yes essentially i need 16v 500mA, from 24v 2A

    Sorry just starting out in electronics so bear with me, thanks for help.
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Hmm. Simple.
    Get 7815 3 terminal regulator and two 1N4001 diodes.
     
  9. R!f@@

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    do you think you can get them. If you can , I can give you a diagram
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    This should do it for you:

    [​IMG]

    C1 probably doesn't have to be nearly that large. You might do with 100uF.
     
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    yeah !! two choices . My way or the high way :p hehehe. kidding

    My way or Sgt's way, depends on the components you can get.
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    A LM317 is a super simple regulator, cheap, easy to get. Radio Shack even sells them. They need output capacitors to suppress oscillation, and use two resistors to program the voltage. Exactly what you need.

    [​IMG]

    R1 is 120Ω, R2 is 1416Ω (Use a 1500Ω in parallel with 24KΩ). Ignore C1 and C2.
     
  13. Detonator

    Thread Starter Member

    Mar 6, 2010
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    Thankyou both for your help, i think Sgt has nailed what i need. I best shoot down the shop before it shuts for three days. I let you know how i get on.

    EDIT: And thankyou Bill too
     
  14. Detonator

    Thread Starter Member

    Mar 6, 2010
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    Thanks to the three of you, i went with Bills / Sgts circuits and i substituted R2 for a 2k trimpot so i could fine tune it..

    Supply is fine and now to test out the programmer kit :)
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    What value did you use for R1, and what value did the pot resistance wind up being in order to get 16v out?

    Note that in the "quickie" circuit I put up, I used 100 Ohms for R1, and 1.2k Ohms for R2.

    This should result in a nominal 12.5mA flowing through R1 towards ground, as the regulator tries to keep the voltage between OUT and REF at a nominal 1.25v (Vref) by sourcing current from the output.

    Just to keep things simple, you wanted 16v out.
    16v - Vref = 14.75v.
    14.75v / 12.5mA = 1180 Ohms. 1.2k Ohms is the closest standard value.

    Bill Marsden's schematic uses a 120 Ohm resistor and a pot. This is a standard configuration that is right in the datasheet. The LM317 requires a minimum 10mA current for guaranteed regulated output. 1.25v / 120 Ohms = 10.417mA, which is why the 120 Ohm resistor is a standard value.

    I used a 100 Ohm and 1.2k Ohm resistor in my schematic, simply because those are both very common values, and relatively easy to get.

    If you are going to use this set-up for your programmer permanently, I suggest that you replace your pot with a fixed resistor of the same value. That way you won't have to worry about it changing value on you.
     
  16. t06afre

    AAC Fanatic!

    May 11, 2009
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    Just some things worth mentioning. Check if your power supply is DC output and not AC output. I will guess it is DC but check it anyway. Also Place the 317 on a cooling fin. It might get to hot without it.
     
  17. Detonator

    Thread Starter Member

    Mar 6, 2010
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    I used R1=120 and R2 a small pcb trimpot set approx 1450, output seems pretty stable at about 16.1v.

    Certainly is DC and i have a fairly large heatsink on the REG as i had a few laying around.
     
  18. t06afre

    AAC Fanatic!

    May 11, 2009
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    Even if you claim to be beginner you seem to have control over the things you are doing, and you are able to absorb the information given to you. Keep up the good work:)
     
  19. Detonator

    Thread Starter Member

    Mar 6, 2010
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    Beginner in Electronics, but i am a 20yrs Electrician so AC/DC and Heatsinks are second nature :) and i been soldering kits together for years but i never "cared" how things work just that it did what it was meant to when i finished.

    But now i want to come up with my own ideas and designs its just getting my head around how electronic components "do what they do".. I am doing an online course too right now, enjoying loads.
     
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