How do I create a constant 5V Source?

Discussion in 'The Projects Forum' started by corner_boy, Dec 2, 2008.

  1. corner_boy

    Thread Starter Active Member

    Jun 24, 2008
    36
    0
    The chips I have need a 5 volt power source. I originally wanted to use batteries, but i need to know if theres other ways to make a power supply for this. I only ask because the person I'm making this for may like the fact that a change of batteries wont be needed. Set it and forget, in a way.

    I got a 4-AAA battery source with a switch i got from radioshack for now.

    P.S.
    I have a battery charger for a motorlla cell phone i GOT. It says:
    --Input: 100-240V~50/60Hz 0.2 A
    --Output: 5.0V----- 550 mA
    (What do you guys think??)

    edit---- where can i buy a charger plug like the one mentioned on the PS, if that might be the best solution?
     
    Last edited: Dec 2, 2008
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The charger for the phone won't be regulated - the charging circuit was inside the phone itself. 5v unregulated won't give you enough "headroom" to regulate the voltage.

    You could get something like this wall-wart:
    http://www.mpja.com/prodinfo.asp?number=17419+PD

    and a 7805 regulator IC, a heatsink for it, a couple of capacitors, one for the input, one for the output, and a small box to put it in.
     
  3. corner_boy

    Thread Starter Active Member

    Jun 24, 2008
    36
    0
    wow, thanx. i almost made a mistake assuming that the charger would have been fine.

    ---questions---
    What are the capacitors needed for?

    Since a heatsink seems needed to prevent overheating, which ones would be the best for a circuit that uses about 5 chips (ISD, mt8870, 2 potentiometers, and 2 LM386 amplifiers)?
    http://search.digikey.com/scripts/D...gle&cshift_ck=1119267935cs501936302&WT.srch=1
     
  4. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Well that depends on whether your charger is "heavy" or light. A heavy(relatively speaking) one contains an iron transformer and would not be suitable. However, most chargers supplied by phone companies are now of another type.

    A light one, however, means it contains a switching regulator and that might be usable as a power source for your experiment.

    To check if it is suitable, connect a voltmeter to the charger output and reads the voltage. Then place a resistor of 47 ohm across the charger output and reads the voltage again. If there is only a drop of perhaps 0.2~ 0.5V, then the charger is usable.
     
  5. corner_boy

    Thread Starter Active Member

    Jun 24, 2008
    36
    0
    using the charger as a source to a board i got the 2 values from a multimeter.

    1) connected to the wall - 5.083 volts
    2) with a 47ohm resistor - 5.1 volts
     
  6. kahafeez

    Active Member

    Dec 2, 2008
    150
    0
    dude just use a simple 7805. dont make it complicated. just use an adapter and a 7805. in my country we've adapter which have a switch on it with which u can select its output. i keep the adapter to 9v. it gives me 9v dc and then i put a 7805 which turns the 9v dc to a 5v dc. simple. no capacitors. no nothing. easy. but if u need more current u'll have to put some extra stuff. if u want to run an ic or something of that sort its ok. i've been running an 8051 using the technique i mentioned. it works.
     
  7. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    The voltage seems perfect. You can use it then.

    Do you know a 0.1uF capacitor is needed on the output of the 7805? I bet you don't.
     
    Last edited: Dec 2, 2008
  8. corner_boy

    Thread Starter Active Member

    Jun 24, 2008
    36
    0
    Thanx for the assistance, really appreciated it. ill keep you posted how it goes.
     
  9. eagle eye

    New Member

    Jul 8, 2009
    1
    0
    can u plz explain it to me why it is needed?
     
  10. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    The capacitors at the inout and output of the regulator are there for better stability.
    Without the capacitors there is a possibility of oscillation, wich can cause the regulator to become instable.
    Sometimes the osciilation heats up the regulator so it will go in thermal shutdown.

    Greetings,
    Bertus
     
  11. millwood

    Guest

    most (all?) of phone chargers are regulated smps.

    yeah, you can get one of those from walmart for next to nothing, or to get it from friends who have unused phones.
     
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