NEEDING HELP WITH CIRCUIT
- Thread starter metalca
- Start date
use the forward voltage rating of the LED (Vf=2.3) for example.
guess.
4 leds?
4 x 2.3=9.2.
too much!
guess again.
3 leds?
3 x 2.3=6.9
now subtract from your battery voltage.
9 - 6.9=2.1 You have 2.1 volts left. set your current limit using that value. choosing a current limit of 15 ma.
2.1 / .015 = 140 ohms for a current limit resistor.
so your series string would have 3 leds, a 140 ohm resistor and would draw 15 ma of current. Just add more series strings of leds and resistors to increase the number of leds( in multiples of 3 in this case). current used by each parallel string is additive. for 21 leds you would draw 15 x 7 ma = 105 ma and your 9 volt battery would not last very long
guess.
4 leds?
4 x 2.3=9.2.
too much!
guess again.
3 leds?
3 x 2.3=6.9
now subtract from your battery voltage.
9 - 6.9=2.1 You have 2.1 volts left. set your current limit using that value. choosing a current limit of 15 ma.
2.1 / .015 = 140 ohms for a current limit resistor.
so your series string would have 3 leds, a 140 ohm resistor and would draw 15 ma of current. Just add more series strings of leds and resistors to increase the number of leds( in multiples of 3 in this case). current used by each parallel string is additive. for 21 leds you would draw 15 x 7 ma = 105 ma and your 9 volt battery would not last very long
possibly 16leds then im new to it all this is day one of learning lol. its a 9v battery the square type ones, leds im not sure what to get only red 10mm ones.ima paranormal investigator and im tryin to make a red illuminator not infrared just a red one but unsure of what parts to get
The output of a 9V battery falls off quite fast at the load currents you will be using (~50mA). Can you scrounge an old wall-wart cell phone charger that you can devote to this project?
