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DC/DC Voltage Converters

Discussion in 'Electronic Design' started by [email protected], Nov 13, 2005.

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  1. Guest

    Hello,

    I've got hold of a solar cell that puts out a voltage of 0.45V and a
    current of 100mA. Is there any way of converting that into a voltage of
    about 3v?

    Thanks

    Gareth
     
  2. Kryten

    Kryten Guest

    I've got hold of a solar cell that puts out a voltage of 0.45V and a
    Maybe, but it is probably cheaper and easier to just buy 5 or 6 more solar
    cells. Making a battery of cells makes the usual diode drop less
    significant.

    If your converter were 100% efficient, it would multiply the voltage by 6
    but divide the current by 6. Will that be enough?

    what did you wish to power from this cell?
     
  3. Ken Smith

    Ken Smith Guest

    My calculator makes (about 3)/(about 0.45) = (about 7)

    You should think in terms of 1/7th the current coming out.

    There was a thread about 0Vth mosfets. If you really do this, I think you
    find yourself buying some of those.
     
  4. Guest

    Hi,

    I'm looking into building solar engines so a low current really isn't a
    problem, it's just used to charge a capacitor. But the voltage needs to
    be higher so when the capacitor is charged it's at a high enough
    voltage to power the rest of the circuit.

    Multiplying the voltage by 6 should do it- it doesn't have to be
    exactly 3v.

    What's a 0Vth mosfet?? Can you point me to the thread or give me a
    keyword so I can find it myself?

    Thanks

    Gareth
     
  5. Fred Bloggs

    Fred Bloggs Guest

    Those low threshold MOSFETs have a 100K ohm RDS in that region and are
    likely unusable as a capacitor voltage multiplier. Since you "got hold"
    of one cell, why don't you "got hold" yourself another one, then you can
    use a standard voltage boost IC that runs down to 0.5V. See the Linear
    Technology LTC3424 for an example- this family of micropower regulators
    requires the least input voltage- the capacitor types do not come close.
    http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1003,C1042,C1031,C1060,P1250
     
  6. Fred Bloggs

    Fred Bloggs Guest

    Scratch that suggestion- the good for nothing low down lying vermin at
    Linear aren't worth spit with their game playing parameter charts.
    This is more of what I had in mind:
    http://pdfserv.maxim-ic.com/en/ds/MAX756-MAX757.pdf
     
  7. Jasen Betts

    Jasen Betts Guest

    The best way is to get another six of those cells and connect them in
    series.

    o.45 volts isn't enough to drive any voltage convert that I know of.

    Bye.
    Jasen
     
  8. It's easier and cheaper to buy a few of those chineese "solar powered garden
    lamps" and rip them apart.

    They cost about USD 8 retail and have a solar cell panel capable of 20 mA at
    4 Volts, two 600 mAh NiMh batteries, a controller circuit and a white LED.
    Note the 20 mA, double what you get by stepping your voltage up ten times.

    I haven't been able to locate the source for the solar panel - I have a neat
    application for it, especially since the price for that panel must be below
    USD 2 for that lamp to be profitable, but no luck yet.

    Maybe I should post some pictures??
     
  9. Kryten

    Kryten Guest

    Yes, they are a bargain.

    I bought one to take a look at the circuit, and got a 2 for 1 offer.
    I'd rather have one at half price...

    They recommend changing the NiMH cells every year (365 charging cycles!).

    Anyway, I drew the circuit in Orcad if anybody wants it.
    I can send a PNG file also.

    Not incredibly sophisticated or efficient, but adequate.
     
  10. I'd like a copy, thanks. speff (@) interlog.com


    Best regards,
    Spehro Pefhany
     
  11. Kryten

    Kryten Guest

    Okay, I've just sent it so check your mailbox.
    I'll put it on my website as well.
     
  12. Thanks, got it. A photocell operated voltage doubler.

    I'm not sure what D3 is about it just seems to steal base current from
    the PNP. And D1? Just to match the voltage better?

    BTW, why do the BJTs look like upside-down connectors?


    Best regards,
    Spehro Pefhany
     
  13. Kryten

    Kryten Guest

    Maybe I have that the wrong way round.
    I should put an error disclaimer on the page.

    I'll re-check it sometime.

    I don't fully understand the discrete voltage doubler circuit.

    I just get the general idea of what the whole system is up to.

    When I was first probing the circuit, I did not know the BJT pinout,
    so I used a 3-pin jumper symbol.
    I've since made an educated guess, and that's on the website image.
     
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