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DC/DC converter

  1. Jun 18, 2004 #1

    mrjeffy321

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    Hello,
    I want to make a DC to DC voltage converter so that I can "step up" the output voltage from what it is to something a little more useable.

    Right now it outputs about .5 volts, I was thinking that is I could step that up to around 1 or 2 (or higher, higher is no problem) volts, I could use it for something practical.

    I know that when you increase the voltage, the current will drop, but this really isnt that big of a concern for me.

    I have seen these DC/DC converters sold, but range in price and functionality, I would build one, but I have no clue on how to do it, and I have searched all over the web, but have found little that will help me.
     
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  3. Jun 20, 2004 #2

    enigma

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    Is there a reason why you can't use an amplifier?
     
  4. Jun 20, 2004 #3

    mrjeffy321

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    I suppose I could, but I know very little about them, could you explain in a little more detail, or tell me some place that could
     
  5. Jun 20, 2004 #4

    Integral

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    What kind of device are you starting with? Simply giving output voltage does not say much, what is your current capabilities? What are your current needs? More information cannot hurt.

    DC step up is not as easy as AC step up, it requires some form of circuitry which involves cost and some knowledge to create.
     
  6. Jun 20, 2004 #5

    Cliff_J

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    And are you sure its only .5V?? Most semiconductors have more voltage drop. Why not use a AAA or AA battery instead?

    Cliff
     
  7. Jun 20, 2004 #6

    mrjeffy321

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    my voltage source is a PEM Hydrogen fuel cell that I built, it is not very impressive with its current output, I would like to increase it, through some form of circuitry so that it will be a little more impressive during a demonstration, or during practical use.
    I have no definite device decided on to use the fuel cell to power, but anything practical will need a little more juice than .5 v.

    In my mind, stepping up/down AC voltage couldnt be easier, just built a transformer with the desired coil ratio, tada, you changed the voltage (while changing the current also). but DC isnt that easy, thats why I need help finding out how to do it. I can follow insrtuctions pretty well, so I could built it myself, providing it doesnt get too complicated.

    but this idea of increasing a voltage souce's voltage does not nesesarily need to apply to a fuel cell, it could be used to step up any DC voltage source to a greater voltage.
     
  8. Jun 20, 2004 #7

    Cliff_J

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    Well a switching power supply can take DC and pulse it through a transformer as pseudo-AC and voila! Or for small currents there are even ICs all ready to go to double or even triple a voltage with minimal parts. Here's some info on switching power supplies:
    http://www.smpstech.com/tutorial/t03top.htm#BUCK

    But you'd almost need a mechanical switch like a relay vibrating back and forth to pulse the DC because any regular transistor's voltage drop would be greater than or a large percentage of the .5V you have to work with.

    Is there any way to build multiple cells that can be wired in series to increase the voltage? (probably too late but never the less an idea)

    Maybe find a small DC fan or some other device that can run on your .5V and whatever current is available. Maybe a small DC motor from a slot car or something. Much simpler, wouldn't need to bother with circuitry at all then.

    Cliff
     
  9. Jun 20, 2004 #8

    chroot

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    You can buy many, many, many switch-mode IC boost converters. The problem is that few of them will function on an input as low as 0.5V..

    And you can't use an amplifier, enigma, because an amplifier does not derive power from its input.

    You can certainly build a chopper-transformer-rectifier boost converter yourself, but it'll be ugly and very lossy.

    - Warren
     
  10. Jun 20, 2004 #9

    mrjeffy321

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    I could build more than one cell and hook them up together, building a new cell (while not impossible) does require a little bit of redesigning of the cell I allready have, not to mention that it may cost anywhere from $40 to $60 to make a new cell.

    what do they use in cars, they use transformers, but they only have a DC battery.

    This is where I origianlly got the idea to make one of these things:
    http://www.fuelcellstore.com/cgi-bin/fuelweb/view=NavPage/cat=13
    but their prices are a bit high
     
  11. Jun 20, 2004 #10

    enigma

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    Yes, of course. I didn't realise that the .5V output was the actual power being provided.

    I thought it was some sort of signal which needed to be boosted.
     
  12. Jun 20, 2004 #11

    chroot

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    Most devices in cars are designed to operate off 12V. Linear or switch-mode boost or buck converters are used for devices that need larger or smaller voltages.

    A simple IC boost converter would be ideal for your application, but you'll need more than 0.5V to get them to work. There are many available that will work from 1V, however.

    - Warren
     
  13. Jun 21, 2004 #12

    mrjeffy321

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    so these IC boost converter, do I buy them, built them, how do I get a hold of one or more?

    I would like to build as much of it as possible, as long as it stays simple, I have seen some circuit diagrams of them,they look pretty complicated.
     
  14. Jun 21, 2004 #13

    Cliff_J

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    If you look here:
    http://www.micrel.com/_PDF/mic2571.pdf
    They have a diagram with 4 external parts. No DIP package to make for an easy solder/breadboard, but one of a few ICs that will go down to .9V Mouser.com part number is 803-MIC2571-1BMM and its in stock for $2.28.

    Cliff
     
  15. Jun 21, 2004 #14

    mrjeffy321

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    I think that is what I am going to end up doing, getting one of these MIC2571-1BMM IC to increase the voltage. We'll see how it works when I get it and try to assemble it.
     
  16. Jun 21, 2004 #15

    chroot

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    That Micrel IC will not function with a Vin of 0.5V.

    - Warren
     
  17. Jun 22, 2004 #16

    Integral

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    Any such circuitry will require an external power supply to operate, doesn't this sort of defeat the purpose of a fuel cell? Seems to me that you need to make several cells and tie them together for more current and higher voltage. If you get something over a volt you can drive a LED.
     
  18. Jun 22, 2004 #17

    chroot

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    Integral,

    Actually all you need is a diode drop (only about 0.6V for the standard GaAs LED) to make a LED work. It'll be dim, but it'll work off 0.5V.

    In general, a switch-mode boost converter does not need an additional power supply -- it is powered off the of the input voltage supplied to it.

    - Warren
     
  19. Jun 22, 2004 #18

    mrjeffy321

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    I will try to increase the output of my fuel cell, and/or add a small 1.5 volt battery to push it up to the minimun voltage
     
  20. Jun 22, 2004 #19

    chroot

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    Adding a battery will of course work, but you'll be drawing power from the battery as well as from the cell.

    - Warren
     
  21. Jun 22, 2004 #20

    mrjeffy321

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    yes, I know, but that is what I will have to do, untill I find a substitute
     
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