I've made this simple charger circuit and I've added a resistor and a Schottky diode at the end of the circuit (pin 2). I was wondering if I could add a LED indication so it could give me an idea of the intensity of current that is flowing through the circuit. I've tried simply connecting a LED in parallel after C2 and it did work (the light did get less bright as the the battery voltage increased).
I'm wondering if this type of indication would work – would the LED eventually go out when the current reaches 0? If it does work, would there be a voltage drop caused by the LED that I need to consider? If the indication works, would I need to add a resistor before the LED and would its value play a roll in setting the current threshold for the LED? The charger is set at 5.8V/200mA, if that helps.
Best Answer
This is a simple design that should get the job done without using complicated components:
simulate this circuit – Schematic created using CircuitLab
3.5 Ohm resistor converts the current (200 mA) to 0.7 V which is enough to open the transistor and thus make the led work. 3.5 Ohm 0.25 W is enough for your application. When the battery is charged there is going to be no current through the 3.5 Ohm resistor, thus the transistor and the LED are off.
If you can guarantee that no more than 200 mA is going to go through the battery you don't need the 1 Ohm resistor. The 1 Ohm resistor is to protect the transistor from over 0.7 V voltages.
You may choose the components and may need to change the values of the resistors according to your application.