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Voltage regulation

Discussion in 'General Electronics Discussion' started by Lektrik, Dec 20, 2010.

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  1. Lektrik


    Dec 12, 2010
    Hi Everyone,
    I am new here let me introduce myself.

    I come from an ICT background and recently had the desire to learn electronics, it was not an option for me back at school and as such I only know the very basics.

    However I have built a few circuits and learnt the basics of how to use a multimeter and I am really enjoying it. :)

    Now for the question, I have a 5V DC input @ 500ma (from USB) and wish to drop this to run at roughly 3.5 V. I think that I would have to use a voltage Regulator, maybe a LM317? but im not sure

    Can anyone help me and tell me what direction to turn in as im getting a bit lost...

    Thanks a lot :)

    EDIT: Actually I have just found out about Voltage divider circuits, If I build one of these with a 1ohm + a 2.2ohm resistor according to an online calculator i found it will reduce the voltage to 3.5V so Im going to give this a go.
    Last edited: Dec 20, 2010
  2. Resqueline


    Jul 31, 2009
    Welcome to the forums here.
    Now, resistor dividers can hardly be defined as voltage regulators. They also waste a lot of power and can only deregulate an initially stable voltage.
    With those resistor values mentioned you'll overload the USB output over three times: 5V / 3.2ohms = 1.56A, wasting 5V * 1.56A = 7.8W in the process.
    An LM317 would be a viable option, but there are other ways too, like a simple zener + transistor. Do you have any goals, preferences or limitations on this project?
  3. Lektrik


    Dec 12, 2010
    Hi Resqueline,

    This is going to be powering a front Panel from an xbox 360 connected to a cut off USB Cable, this will allow a wireless controller to be used on a PC.
    From what I have read the panel isnt too fussy about voltage and needs anywhere from 3.3 to 3.8V input.
    The only goal I have here is to learn the proper way of doing this and most importantly to me, why it is the best way of doing it

    Im not sure what you mean about the USB being overloaded, is 1.56a the current flowing back into the USB port once it has run through the circuit?

    Thank you
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Earlier you mentioned:

    Placing a 3.3 ohm resistance across a 5V supply will cause a current of 1.52 amps to flow through it. Your USB can't supply that, and even if it could, the resistors would get hot and waste over 7W in heat. And that's BEFORE you start trying to take more power to supply your front panel.

    Are you just powering LEDs illuminating the front panel? Or is there something more to this? If it's just LEDs then all you may need is a series resistance to limit the current. If you actually need a particular voltage, then an LM317 would work (just).

    Do you know how much current is required?

    And why isn't this being powered from the X Box? (just a silly question)
  5. Lektrik


    Dec 12, 2010
    I dont know how much current is required unfortunately but I am going to give it a go with an LM317, I picked up a few today so will construct a basic circuit and let you know how it goes.
    Also the reason I am doing it is that I bought this panel from ebay so I could try to make a wireless PC controller. Im sure there are loads out there I could just buy but this way at least im learning something from it :)
    Thank you
  6. Lektrik


    Dec 12, 2010
    Hi everyone,

    Just to let you know that I built a circuit using an LM317, a 220ohm & a 360ohm resistor and the voltage came out at 3.3V which I have since found out is the required voltage. I tested it and it works fine, I now have a wireless reciever for an xbox 360 controller for use with a PC

    Thanks a lot for the help :)
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