Voltage Conversion Query - Help please!

Discussion in 'General Electronics Chat' started by imfaizzi, Oct 11, 2008.

  1. imfaizzi

    Thread Starter Member

    Oct 11, 2008
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    hi

    Let me introduce myself to you. Im a guy who knows-nothing-about-anything in electronics, a newbie to electronics. 0% you can say :). Please help me with my querries.

    I live in Pakistan and here we have 220V power supply to our homes. Our electronics teacher has given us a project to carry out and he has restricted us to use a DC power supply to it (like AA batteries and stuff). He has obliged our projects to be operated on the same power supply on which our home does. Therefore, my question to you is

    How can I convert a 220V power input to 3V or less (while developing my project on a stripboard)?


    Please use more of the simplified english to explain the answer and also do guide me if I've posted this thread in a wrong discussion.:D

    Thank you.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Are you required to design the power supply or can you purchase the supply?

    hgmjr
     
  3. imfaizzi

    Thread Starter Member

    Oct 11, 2008
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    yes, we are required to design it. What is the procedure to build such a power supply?
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    Use google to find tutorials on designing power supplies.

    Here is just one example of just such an article.

    hgmjr
     
  5. imfaizzi

    Thread Starter Member

    Oct 11, 2008
    20
    0
    Your example was pretty much closer to the topics we've discussed in class. But can u describe (in plain english) as how to put together these components to work (as you see it)?

    Im googling though. Lets see what comes as result?
     
    Last edited: Oct 11, 2008
  6. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    I'm puzzled why a man teaching elementary electronics is exposing students to lethal voltages? Are there too many students in the class or something?
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    The first component you need is a transformer, it dictates the rest. How are the component sources in that region? Will he allow you to get a wall wart (an unregulated power supply that plugs directly into the wall outlet) and then build a regulator?

    For what it's worth, they didn't have wall warts when I was a kid, I pretty much had to build everything related to power supplies in the project. Maybe it has influenced my thinking, but I don't see it as a big deal (high school stuff) as long as you pay attention and follow safety guidelines (example, a fuse is a must!).

    If wall warts aren't acceptable, then you'll need an enclosure. You will want to surround the power supply so there are no exposed wires, like Steve said, these are lethal voltages.

    Check out the All About Circuits for building techniques. You can make enclosure out of wood and use terminal strips for most of it.

    Given you're lack of experience I do suggest the wall wart route, you can build a regulator (which is the important part).
     
    Last edited: Oct 11, 2008
  8. imfaizzi

    Thread Starter Member

    Oct 11, 2008
    20
    0

    Well for that, I must say, he has taken steps already. You see, the whole lab has been supplied with power coming from some kindda transformer (step up or step down that I don't remember right now but it does). He has guaranteed our safety.
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    That was particularly important information. We need details in order to help. It would have to be step down, basically we need the AC voltage you will be working with.

    http://www.allaboutcircuits.com/vol_2/chpt_9/index.html

    http://www.allaboutcircuits.com/vol_3/chpt_3/4.html

    Note to moderators: This is shaping up as homework from what I'm reading.
     
  10. imfaizzi

    Thread Starter Member

    Oct 11, 2008
    20
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    Yeah, we usually use 3V wall warts (We call it "adapters") but, unfortunately, they're forbidden.

    Its been only 3 months eversince been exposed to electronics course and guess what?? Im so screwed in it. I never had the brains for it. Although, my concepts are pretty much clear about logics , gates & adders etc but the only thing that pisses me off is implementing them. I guess you'll get the picture.
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    OK, back to basics though, what is the stepped down voltage you have to work with? I assume 50 Hz, since I don't have a clue what Pakistan standards are.

    So before anyone can help, we need the following.

    What is the AC voltage you have to work with? We've got contradictory answers on that one. If you have to start with 220VAC then it isn't safe, but it is doable.

    How much output current and voltage do you need?

    What kind of parts access do you have?
     
  12. imfaizzi

    Thread Starter Member

    Oct 11, 2008
    20
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    The circuit operates on 3V and What I've available is 220VAC. Im using a stepped down transformer of 12V and its doing well. I've designed my power supply for 5V (using 7805).

    Will a 5V power supply enable a 3V circuit of electrical bell?? :confused:
     
  13. beenthere

    Retired Moderator

    Apr 20, 2004
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    Yes, but it may cause a failure over time. You can place two diodes in series with the bell to drop an additional 1.4 volts. If the bell current is below 50 ma, you can use something like 1N914's. Higher than that will need a larger diode type, like the 1N4000. It's a kludge, but quite inexpensive.
     
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