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Discussion in 'Electronic Design' started by Jennie, Oct 6, 2004.

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  1. Jennie

    Jennie Guest

    Where is the cheapest and decent quality place to get a DC Power Supply?
  2. Jennie

    Jennie Guest

    Student quality should be fine...
  3. mike

    mike Guest

    I'd go to Fry's and get a AA battery. Quite "decent". They're really
    cheap when they're on sale...
    unless you want a dfferent voltage, or variable, or more current or
    current limited or metered or...or...or...all the things that you didn't
    specify. Depending on where you're located, you may be across the
    street or 5000 miles from a dealer.

    It must be hard to ask a question that can be answered, cause so few do
    it. :-(

    Return address is VALID.
    Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
    Wanted GPIB Card for PC.
    Bunch of stuff For Sale and Wanted at the link below.
  4. Clarence

    Clarence Guest

    Since you have not specified a particular voltage or current I will assume you
    mean a metered, adjustable, bench supply.

    There are many places but here is one with an array of possible.

    I am not affiliated with the company, but have made several purchases from them
    with good results.
  5. John Fields

    John Fields Guest

    Input voltage and frequency?

    Single output?



    Output voltage range?

    Maximum output current?

    Constant Voltage/Constant Current capability?

    Current limiting capability?

    Budget constraints?
  6. nihoa

    nihoa Guest

    Try It seems like Ebay has tons of DC power supplies on auction.
    I'm certain you can get a quality P.S. there for cheap.
  7. Jennie

    Jennie Guest

    Just a single variable dc source up to 13 to 14 volts. Under 50..
  8. Clarence

    Clarence Guest

    NEW-Close @ $59.95

    OR For $3.95 and shipping you can get a 24 volt 2 amp supply and put an
    external regulator on it for 2.5 to 20 volts.
    Add this kit for the adjustable output

    This is the description
    1.5 to 30V Adjustable Power Supply (picture)
    This is a basic adjustable voltage power supply using the popular three pin
    regulator, LM317T. You can select any voltage between 1.5V and 30V using a
    potentiometer. The LM317T is rated at 1.5A so you must use a larger heat sink
    when drawing high currents. Unregulated AC or DC input via terminal block or
    power jack. Requires a suitable transformer.
    Documentation in acrobat format
    Order Code: CPS68 (Basic Soldering-Kit) Price $9.95

    Variable Supply 1.3 to 30V and 300mA to 1.5A (input 16VAC) (picture)
    This is a basic adjustable voltage power supply using the three pin regulator,
    LM317T. Any voltage between 1.3V and 30V can be selected using a potentiometer.
    A current limiting circuit is also included that can limit the output current
    between 300mA and 1.5A. This feature is useful when current adjustment is
    required in circuit development. The LM317T is rated at 1.5A so you must use a
    larger heat sink when drawing high currents. Unregulated AC or DC input via a
    terminal block. Requires a suitable transformer.
    Input supply: 12 - 16 VAC (or 20V DC)
    Output: 1.3 to 30V / 0.3 to 1.5A
    PCB size: 50x37mm
    Order Code: AA557 (Basic Soldering-Kit) Price $8.95

    OR this kit MODEL XP-620K............KIT....$49.95*

  9. Jennie

    Jennie Guest


    Just curious, if I hook up a led with 20mA to 3 AA battery how long will the
    light stay lit?

  10. Jennie

    Jennie Guest

    What is the equation to figure out the time...
  11. Clarence

    Clarence Guest

    Depends on the battery, and the LED.
    for ACCUPOWER "1000mAh" AAA Nimh cells it would be
    1000 / .02 = 50 hours. However that does not allow for the voltage.
    For a single led with a series resistor from .12 * 3 = 3.6 volts down to 2.7

    If you have a RED LED which has an offset of 1.8 volts the resistor to limit
    the current at full charge to 20ma is

    ( 3.6 volts - 1.8 V,LED) / .02 = 90 ohms. (2 each 180 ohm resistors in
    parallel would be closest, but a 100 ohm 1/4 Resistor would be satisfactory, I
    = .018 Amperes)

    Power max = I^2 * R

    ..02^2 * 180. .072 W (1/4 watts resistors are fine.)

    Note that as the battery becomes discharged the voltage drops.
    I'll use .9 as a limit value. (Depends on the battery.)

    2.7 - 1.8 = 10ma So the LED should be at half current when the Battery should
    be recharged. You should not allow the LED to go out before recharging, you
    may damage the battery.

    Also. The Batteries self discharge over time, between charging. So the actual
    time will vary some. Approximately 42 to 52 hours.
  12. Clarence

    Clarence Guest

    Pesky little DP fell off.
  13. Jennie

    Jennie Guest

    What book have all this good info in it?
  14. Clarence

    Clarence Guest

    There are many, I'm sure. But I didn't use a book. Been doing this sort of
    thing for decades.

    Might try the Radio Amateurs Handbook. It is good on basic electronics. Then
    there is Horowitz and Hill "The Art of Electronics." but it is rather large.
    There are many texts on basic electronics available. I usually just open one
    of my Engineering handbooks when I have a question. They are all getting
    pretty old.
  15. Robert Baer

    Robert Baer Guest

    Youse gots tah sey what youse kneeds more better.
    What voltage, adjustable or fixed, what current capability, current
    limiting?, adjustable current limiting? meters?
    Be eXplicit!
  16. Clarence

    Clarence Guest

    She was quite definite on the price, and the basic voltage adjustment range.

    You, on the other-hand are impossible to decipher. (Spelling corrected.)
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