Solar Panel, Voltage Regulation

[novice88]

I want to charge my Mp3 player with solar panels, i'm thinking of getting a 2w panel, and connecting it thro a diode and then to USB. How do i control the voltage? will a simple voltage regulator like 7805 do? Or are there panels with specific voltage ratings? I want a 5v output. Please help. 

[Pratheek]

A 7805 will work as long as the solar panels can provide anything above 6V. But the charger with a 7805 will be highly inefficient at higher input voltages because of the way the 7895 works - it converts electrical energy to heat energy to regulate the voltage. So if efficiency is not a concern for you, then go for the 7805.

[nottoooily]

How about just bang a zener diode across it? Could be more efficient than a 7805/etc because there's no drop-out(?) voltage. I think this kind of cheap-ass regulator would be OK for solar because there's no worry about overloading the panel it like there is with a battery or mains transformer.

[Admin]

You need to use a LDO regulator (low drop out voltage). A 7805 will waste ~30% of your energy.

[Soeren]

Hi,

For greatest efficiency, you could use a MOSFET as the diode. It will have a lower voltage drop than even the best Schottky and with a little extra circuit, it can be the active part of the regulator => max efficiency possible.

[novice88]

I think i will try the zener and the mosfet and see which one works best, i like the zener idea coz i want the cut-off and it can also prevent the panel from leaking back... will post the results.

[Admin]

Hi,

For greatest efficiency, you could use a MOSFET as the diode. It will have a lower voltage drop than even the best Schottky and with a little extra circuit, it can be the active part of the regulator => max efficiency possible.

good point, I wasn't thinking . . .

Look into switching regulators.

[nottoooily]

Look into switching regulators.

Yea those mosfets are great for reverse polarity protection. With a switching regulator you get to choose what voltage and current to operate the panel at, so if you're really clever you can design it to always draw the maximum power possible by staying in the peak efficiency region.

Having said that, the concept of efficiency isn't entirely relevent here. If the battery is already receiving the most power it needs, it's no more wasteful to dump the rest into a heater than it is to never use it at all.

[novice88]

Thank you guys, I used LM2575, but am getting a very low output current, am i using the wrong regulator here or are my inductor values wrong, i'm using it coupled with a L-150 inductor, can anyone suggest me any other regulators or atleast what i'm doing wrong here...

[Admin]

What is the rated output of the solar panel that you are using, and what are you actually getting?

[novice88]

Works perfectly once i had a panel suiting my rating. Used a zener coupled with a normal diode. Just that the panel is taking the longest time to reach its peak voltage everytime... Otherwise it works fine. Thanks!

[ekanshmishra1210]

If you will use 7805 then inductive transient are generated. You must use voltage detector 1381C that is used by evryone who is using solar pannel based project .You may purachase it from solarbotics canda .Which is the best.



Ekansh Mishra
([email protected])

[Soeren]

Hi,

Works perfectly once i had a panel suiting my rating. Used a zener coupled with a normal diode.

What are the specs of the panel you're using now and how did you couple it?

Just that the panel is taking the longest time to reach its peak voltage everytime...

When put directly into bright sunlight or with slowly increasing light?