Xbee -> solar panel voltage question

Hi, I have a Xbee that I want to connect to 3x C cell batteries(in series, 3,6v) and a 4,8v solar panel in parallel to charge the batteries(with a diode to prevent battery drain when it's dark). The Xbee will talk to another Xbee connected to an Arduino that is powered.

How can I get the 2,8 to 3,3v required by the Xbee from a source that fluctuates between 3 and 5v? I can't use a LM7833, because that requires a minimum of almost 2v difference between Vin and Vout. I have searched for voltage regulators but both the IC and the Circuits all seem to require that same 2v difference. And if I just use a resistor the output will be to low when the sun doesn't shine.

Thank you for helping me!

Try this:-

However, you need 8 volts to drive it so you could use two solar cells.

However, if you use a resistor to limit the charging current to say 20mA maximum then the battery will prevent it from going over voltage. But I would also include a zenner to clamp the voltage if the battery was removed.

I'm afraid that wouldn't really work. If I really have to I can up the voltage a little by buying a bigger solar panel and adding more batteries (costly though and heavy, the goal is to keep it wearable). At 8v it would mean 7 batteries and a either a really big solar panel or a panel that delivers only 50ma.

And if I am able to boost the output over 5v I can use a LM7833 anyway. I am trying to avoid that and see if there is a different solution.

Thanks!

OK try:-

Down load the data sheet and look at the variants. The 3v3 output parts have max 5V input and will go down below 3v3 input.

Maybe a little on the pricey side for you app, but check this out: AnyVolt Micro - Universal DC-DC converter steps voltage down and up

It's a switching regulator that takes any input voltage and outputs whatever output voltage you adjust it for. It sounds like it would work perfectly for your application.

Ah both suggestions look like they will work. The Murata has a output current of 163MA, which is a little low. And the AnyVoltMicro has an output current of 500MA, still too low for my project, but I will have to limit current draw anyway if I want to operate succesfully on solar power and batteries (I plan to operate ultrabright LEDs, so I will look into multiplexing to lower the power consumption).

I will probably go for the AnyVolt Micro, because the Murata is out of stock (and on the other side of the big pond) and because this was in the product description of the Anyvolt:

"AnyVolt Micro is the smaller, lighter and cheaper successor to AnyVolt Mini. It also adds thermal, overcurrent and short circuit protection, making it very hard to kill (like zombies)."

:slight_smile:

Thanks for looking this up for me!