Home Brew a Top Quality Power Supply?

Discussion in 'General Electronics Chat' started by ajm113, Nov 28, 2011.

  1. ajm113

    Thread Starter Member

    Feb 19, 2011
    176
    5
    Well I would like to develop my own power supply from scratch and make it look run and work like it's top notch. I have some questions to ask before I tackle this. I plan on using it for a current project of mine such as the 4 bit computer, but since I want to save room on my breadboard I want to keep the power supply separate.

    1. I have a step down transformer that takes 120 volts AC and drops it down to 25v 2A. Is there a way I can increase the amps to say 7 or 5 using inductors?

    2. How would I go about making a sort of built in digital voltmeter using a few numeric LED displays and say a PIC micro controller?

    3. I've seen some power supplies use large Inductors, I know they can be used at times to smooth current just like a capacitor with volts, but is that what they are mainly used for?

    4. How would I go about making a short circuit protection to it?

    5. Lets say I want a dual power supply that can be adjustable for negative volts, would everything still apply the same way if it was positive if I was reading the volts using a built in voltmeter?

    6. When creating negative voltages, whats the best way on doing this then using a 555 timer? I dont want to overkill it by shooting 24 volts in it. :(

    7. I know a potentiometer would be maybe ideal to set the voltage, but is there a better way? Maybe using PWM and a large cap?

    8. I know things can get a little warm when dealing with a lot of parts that are working hard, is it ideal to install a fan for cooling? Especially since I'm developing a dual power supply?

    I have a normal manufacture build one, but it only does 13 volts and it doesn't have many features when it comes to setting the volts or amps, and I'm not that lazy just to go out and buy one that has it all. I'm a very hands on type of person and likes to learn from trials and errors.

    Thanks, Andrew.
     
    Last edited: Nov 28, 2011
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    Nowhere in that entire post does it say what volts/Amps the output(s) have to deliver.... always a good idea to get the specs decided before the design phase.
     
  3. ajm113

    Thread Starter Member

    Feb 19, 2011
    176
    5
    Woops I should have mentioned...

    Andrew's Goal Power Supply Output:
    Number of Outputs: 2
    Adjustable Voltage or if possible amps.
    25+ v AC/DC
    25- v DC
    5 - 7 amps
     
    Last edited: Nov 28, 2011
  4. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    This is just a suggestion, but you can get SMPS modules really cheap. They are lightweight, take up much less space, and eliminate the bulkier components such as transformers and capacitors. From there you build a variable regulator and put everything in a box. Much easier than totally from scratch, which most industries don't anymore anyhow (for the same reasons I mention, smaller, lighter, cheaper).
     
  5. ajm113

    Thread Starter Member

    Feb 19, 2011
    176
    5
    Could you recommend me a SMPS? I'm not quite sure where to find one I would be looking for that would support my output specs.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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  7. Markd77

    Senior Member

    Sep 7, 2009
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  8. Wendy

    Moderator

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  9. Pich

    Active Member

    Mar 11, 2008
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    4
    1. I have a step down transformer that takes 120 volts AC and drops it down to 25v 2A. Is there a way I can increase the amps to say 7 or 5 using inductors?

    2 amps is max for this transformer at 25 volts


    3. I've seen some power supplies use large Inductors, I know they can be used at times to smooth current just like a capacitor with volts, but is that what they are mainly used for?
    Inductors are used mostly for SMPS

    4. How would I go about making a short circuit protection to it?

    Short circuit protection could be as simple as a fuse, but if you are looking for current limit than it would need to be part of the power supply

    5. Lets say I want a dual power supply that can be adjustable for negative volts, would everything still apply the same way if it was positive if I was reading the volts using a built in voltmeter?

    The volt meter needs to respond to positive and negative voltage inputs

    6. When creating negative voltages, whats the best way on doing this then using a 555 timer? I dont want to overkill it by shooting 24 volts in it. :(

    Probably not practical for your amp specs

    7. I know a potentiometer would be maybe ideal to set the voltage, but is there a better way? Maybe using PWM and a large cap?

    This is the basics for a SMPS, if this is what you are looking for it's easier to buy one.

    8. I know things can get a little warm when dealing with a lot of parts that are working hard, is it ideal to install a fan for cooling? Especially since I'm developing a dual power supply?

    In most cases it depends on the heat sink used.

    You have not mentioned what voltage range you wish to adjust, A simple + - duel power supply can be built using the LM338 or LM317 and LM337, lots of exaples on the net.
     
  10. studiot

    AAC Fanatic!

    Nov 9, 2007
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    513
    You are not the first person to ask - and be helped here - for these sorts of all singing all dancing specifications.

    Have you searched the AAC forums there were several such projects in recent years?

    A bench or laboratory psu like the above will be very bulky, heavy and expensive.

    This is because if it is capable of producing 25 volts at 7 amps but you only set it to 5 volts 7x20 = 140 watts of power is dissipated in providing this.

    The standard way round this is to restrict the output to a single voltage or a very small range. That way the psu can be made highly efficient.

    If you must have fully variable voltage then the cheapest way is a multitap transformer and switched ranges. (Note I do not mean a switched mode psu).

    Very often higher current circuitry is much more tolerant of ripple etc on the psu so stabilisation is less of an issue. For digital or computer work this is not the case and dedicated psus are generally used.

    So look around the AAC forums and then come back to us with some more thoughts.

    go well
     
  11. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If your step down transformer can provide 2A output@24V, it can provide 2A output@24V.

    There is nothing "magical" that can be with inductors to double the current.

    The voltage can be stepped down, and the current increased, but you will lose 10% ore more of the total power in the process.
     
  12. studiot

    AAC Fanatic!

    Nov 9, 2007
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