# DC/DC Voltage Converters

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

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

Thanks

Gareth

2. ### KrytenGuest

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 SmithGuest

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 BloggsGuest

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 BloggsGuest

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 BettsGuest

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. ### Frithiof Andreas JensenGuest

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. ### KrytenGuest

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. ### Spehro PefhanyGuest

I'd like a copy, thanks. speff (@) interlog.com

Best regards,
Spehro Pefhany

11. ### KrytenGuest

Okay, I've just sent it so check your mailbox.
I'll put it on my website as well.

13. ### Spehro PefhanyGuest

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

14. ### KrytenGuest

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.