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Help with parts for Voltage regulator

Discussion in 'General Electronics Discussion' started by gormly, Aug 3, 2011.

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  1. gormly


    Jun 23, 2011
    I would like to make a voltage regulator for a variable power modification to an ecigarette. The voltage is coming from 2 3.7v batteries and I'd like to vary the voltage between 3 and 6 volts.

    I am not that great with projects but I get the jist of them and I am pretty handy with a soldering iron and I know how to wire the batteries.

    The below instructions and parts are on another website, can someone tell me what to change to make what I need?

    :::::::::::::::::: Start of Parts and instructions::::::::::::::::::
    All of the parts except for the LM 338T and the 1µF capacitor are available from Radio Shack. Radio Shack part numbers are shown in parenthesis. The 5K ohm potentiometer is not the perfect value, but it is easy to find at a reasonable price. The two (2) resistors were chosen to work well with input voltages ranging from 10 - 12 VDC.

    •LM 338T adjustable voltage regulator
    •1µF 35 volt polarized electrolytic capacitor
    •5K ohm linear taper potentiometer (RS# 271-1714)
    •470 ohm 1/2 watt resistor (RS# 271-1133)
    •150 ohm 1/2 watt resistor (RS# 271-1109)
    •0.1µF 50 volt ceramic disc capacitor (RS# 272-135)
    •Perfboard (RS# 276-1395)
    •heat sink (RS# 276-1363)
    •knob (RS# 274-407)

    Top row: 5 K ohm potentiometer, heat sink

    Bottom row: resistors, 0.1µF capacitor, 1µF polarized capacitor, LM 338T

    Design and Fabrication Notes

    A circuit diagram for the adjustable voltage regulator is shown below. As you review the circuit diagram, please note the following:
    •A 150 ohm and a 470 ohm resistor are wired in series to get 620 ohms.
    •The wires from the plus input to pin 3, pin 2 to the plus outlet and from the minus input to the minus output should be at least 16 AWG stranded copper. The other wires do not carry any significant amount of current so smaller gauge wire can be used.
    •The 1uF capacitor is marked and the negative side should be connected to the negative side of the circuit.
    •The center tap of the potentiometer is connected to the wiper, the other two taps are the opposite ends of the resistor. Only use one of the end taps
    :::::::::::::::::: End of Parts and instructions::::::::::::::::::

    Thank you! :D
  2. TBennettcc


    Dec 4, 2010
    ...I don't see a circuit diagram? Any way to either link to the original site or maybe post a copy on a site like Flickr or PhotoBucket?
  3. gormly


    Jun 23, 2011
  4. duke37


    Jan 9, 2011
    I had alook at the LM338T data sheet. You need about 3V more input than output to give a few amps. So, to get 6V out you will have to provide 9V in which could be provided by three batteries.
  5. gormly


    Jun 23, 2011
    is there something else I could use? I am stuck with the two battery option.
  6. duke37


    Jan 9, 2011
    The necessary difference between input and output is called the dropout voltage. I have an old RS calalogue and this shows a MIC2941ABT regulator with a dropout voltage of only 0.6V, It will supply 1.25A. I have not checked the data sheet.
    You could trawl the web for information on other devices which are available to you.
  7. gormly


    Jun 23, 2011
    LOL Thank you...

    I think this is all starting to go over my head a bit :)
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