12 volts power supply

Discussion in 'The Projects Forum' started by Lightfire, Feb 17, 2011.

  1. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    Hello,

    I found this article somewhere in the internet. It's looks interesting. :)

    http://www.ehow.com/how_5923135_make-volt-dc-power-supply.html

    But as usual, I can't understand the instructions. Could somebody help me figure it out?

    1) What items do I need?
    2) It will give stable 12 dc v???
    3) Is it needed to be plugged at mains 240v ac ???
    4) What safety materials do I need?
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    The article provides a list. One thing I do NOT like about this article is that there are no pictures or schematic. Maybe I just missed them. Anyway, I would NOT build any project without those.
    Yes, that is the purpose of the 7812 voltage regulator this circuit uses. Notice however that the recommended transformer is supplying over 25v AC, and this will be still higher after the bridge rectifier converts it to DC. So most of the power will be wasted as heat when the regulator chops the voltage down to 12v.
    Yes, the transformer primary will plug into the mains (so it must be rated for that source voltage), and the secondary will supply a lower voltage - I'd look for ~15V. They may have chosen the higher voltage because those are more available. That may not be true where you live.
    First is your brain. Always think through everything you can, and assume bad things are about to happen unless you are smart. We have an expression here that a gun is ALWAYS loaded. It's too dangerous to have any other idea. Next, wear glasses or even safety glasses while soldering. Work in a ventilated area, since lead is toxic. Keep your workspace clear and clean to avoid accidental burns from your soldering iron.

    Before connecting to a live circuit, check and doublecheck your connections. Proceed with caution, watch for unexpected heat. And don't expose yourself to the mains voltage - be sure the cord is not broken or poorly connected.

    I'm sure there are many more precautions to consider, that are slipping my mind. But again, it's your own attitude that will have the most impact.
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,650
    2,348
    Hello,

    The link does not have any schematic,
    We can make a schematic for a power supply if you want.

    Do you want a fixed 12 Volts supply or do you want to make it adjustable?
    What is the required output current?

    Bertus
     
  4. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    Sure. :)

    Fixed 12 volts.

    Let's say 3 amp.
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,650
    2,348
    Hello,

    Here I composed a 12 Volts / 3A powersupply:

    [​IMG]

    As you can see it is based in the LM350 regulator.(datasheet attached).
    The regulator must be placed on a large heatsink.
    For the voltage caluculation you can take a look at this page:
    http://diyaudioprojects.com/Technical/Voltage-Regulator/

    The peak current will be about 4.5 Ampere.

    Bertus

    PS other may give comments.
     
    Last edited: Feb 18, 2011
Loading...