Constant voltage regulator help please (newbie)

Thread Starter


Joined Mar 22, 2012
Hi All, I am very new to electronics so please excuse stupid questions.
I am trying to design a solar powered light to assist people in rural areas who dont have electricity. I have the following components, a solar panel which can put out 170mA and 5.5V at max performance. I have a lithium ion cell which is 4.2v 2600mA and an LED which offers max performance at 3.7v and 350mA.

What I need is a voltage regulator which will allow the lithium cell to be charged at a constant 4.2v. Also, it mustn't be over charged.

I also need a protection circuit which must prevent over discharge of the li-ion cell by the LED. (this I think I may be able to arrange with the purchase of the Li-ion cell)

any help will be appreciated


Joined Feb 17, 2010
You wouldn't charge a lithium batery with only volatge regulator, as the cells are very vulnerable to damage if charged for to long with wrong curves or if discharged to far. You can use digikey parametric search to find a charger IC that is appropriate for you. Take a look at this video

Thread Starter


Joined Mar 22, 2012
do you suggest I use a different type of cell like Nimh. what type of cells do other solar powered items usually use? thanks


Joined Nov 30, 2010
We suggest that you charge your battery correctly, no matter which one you choose.

Some chargable batteries are: lead acid, Ni-Cad, NiMh, and several types of Lithium.


Joined Dec 20, 2007
Use a battery charger IC that is made for charging a Lithium single-cell rechargeable battery. In its datasheet it will explain how to set the correct amount of charging current.
The battery charger IC will disconnect the battery to protect it when its voltage drops too low as it discharges.
You need a resistor properly calculated to set the LED current.
The LED will dim as the battery voltage runs down.
The LED will need a heatsink to prevent it from being too hot.