Solar Cells + Volatge 1

[cnick]

How can I increase the voltage output on a solar cell from .5V to 1.5+V ? I would like to do this without adding additional cells. Is there a way to do this with a transistor charging the primary coil of a transformer? If so, any idea what type of transistor would work? I would like the profile to be as small as possible. I am trying to power a diode straight from the cell, no battery.

 

[cbarn24050]

Hi, its very dificult to get transistors to work at that voltage, adding more cells is your only realistic solution.

 

[Lewish]

When you say diode, do you mean LED?
If you truly mean diode and not LED, then there are diodes that work down to 0.2Volts. Check the better shottkey diodes.

 

[melone]

Are you trying to use the output of the solar cells to power something? If so, what voltage and current requirements do you have? How much ripple?

If you are just using the solar cell as a light intesity detector, then you can use a simple voltage translator circuit. The can be accomplished with op-amps.

Good Luck and keep us posted!

 

[cnick]

Thanks for all the feedback!

Yes, this is an L.E.D (red so far, lowest voltage I found), and I was not aware of the lower .2 V on the market. I thought for the whole npn deal to work, each L.E.D is within a fixed range of voltage, therefore determining the color of light. I’ll look around for a source for the shottkey diodes– THANKS

I researched the op-amp idea some time ago. The circuits I reviewed relied on a 9V battery to power the op-amp (logic) itself, and I would like to use a solar cell only. Any further input on this would be appreciated.

Thanks again!

 

[melone]

I thought that LED's turn on around 2V? I think that schottky diode are not LED's. To get your booster supply idea working, you will obviously need a switching voltage signal. I can tell you from experience, that solar cells have a very slow reaction time. This means that the signal will not change quick or repeativly enough for you to create a satisfactory input into the booster supply.

About the only other thing you can try is to add a DC to DC converter to the solar cell output. I am not sure how low the input voltage can be, but maybe you can take a look on the web. However, if you are going to get that involved, then maybe it might be easier to simply add another solar cell?

Good luck and keep us posted!

 

[melone]

Can you use a higher power solar cell? How about increasing the light intesity?

 

[cnick]

Problem with using a higher power solar cell is my space limitations. It seems like it’s pretty much linear, higher power- larger the cell (not to mention $$).

 

[Lewish]

O.K., now that I know it is a LED you want, a shottkey isn't the right answer. Sorry.
The lowest input DC-DC converter I have seen takes a 1.5Volt input.
See app. notes at

http://www.linear-tech.com/

I think are stuck with adding more cells. If you are only trying light an LED, you might find some cheap hobbyist cells which have only 50mA or so of current output.

 

[melone]

Can you put more light on the solar cell (use mirrors for reflection, increase light source intesity, etc.)?

 

[electricuwe]

To melone:

even with more light the voltage of one solar cell will not rise significantly, have a look in a datasheet. More light will increase the short circuit current available from the cell.

 

[melone]

Very good observation, however, if you plan to step up the voltage, how do you plan to do it without current? Since you cannot create energy out of nothing, and you know that the voltage is virtually fixed once it reaches a certain output, you need to increase the current so that the total energy output increases. All I am trying to do is get more energy out of the system, so you have a chace to convert it.

 

[busbar]

Consider also that the PV-junction voltage goes down with increasing PV-junction temperature.

 

[cnick]

I am more about horsepower than voltage (one of those mechanical guys); however, I could have a sacrifice in amps to increase the voltage, for it seams like this diode thing is all about power & getting those little critters (horses) to jump the np bridge (exceed the threshold voltage). I seem to have the amps to give up on (avg. output .275 -.3 A), just not enough voltage to do it 2.1 V @ 20mA). Maybe I’m looking at the wrong type of LED (silicon vs. gallium arsenide). Apparently silicon emits near infrared at .6 V (still not quite low enough for one cell).

Thanks for the continued feedback!

 

[electricuwe]

You will not find an LED working on a voltage of a single solar cell.

If you realy want to solve the problem with voltage conversion try to find of germanium transistor and built an self-oscillating flyback converter with it. This should be possible since a germanium junction needs only 0,2..0,3 V to operate.

 

[salec]

It just struck me when I read electricuwe's post:

Maybe a tunnel-diode oscilator would be appropriate for that, as it normally works only at small voltage supplies? Search the web for "tunnel diode oscillator".

 

[peebee]

Why don't you smash up a couple old solar calculators? I don't know what voltage or current ratings their panels are rated at, but I bet it's enough to drive one LED. Seems like three cells in series would be a lot cheaper than any kind of DC/DC converter.

 

[JohnSP]

Hi. Have you checked Maxim? I recall that they have a lot of Dc convertors that could possibly go that low.

 

[jarvis]

Lowest converters I've seen is like .8v or something. I like the germanium and tunnel diode ideas, I might look into it for a project I am working on.

Good luck!

Jarvis

 

[nbucska]

If you have low voltage with high enough current, you
can use electromechanical chopper/xformer

OR

Use MOSFET's to chop low VTG into XFORMER.
Drive their gates with CMOS OSC. running from
e.g. 6V battery. Recharge this from XFORMER
secondary.

<nbucska@pcperipherals.com>