I have 16 red led's in a parallel circuit that are attached to one 9V Battery with one resistor. I need to know what resistor size that can be used to light all 16 red LED's at one time and only one of the 16 LED?

 

You can't get there from here. First, LEDs in parallel do not work well. There is always a current hog that will be the first of many to burn out. Second, a third of an amp from a 9 volt battery is a VERY temporary condition.

 

put them in series + use a booster circuit

 

If your circuit will work with all of the LEDs in series, a quick mental estimate over the coffee machine says the idea from takao can save about 75% of the wasted energy of a parallel circuit.

 

I'm guessing that his question has to do with this other post (Why he split it into two threads, I don't understand).

If so, he needs a resistor per LED.

 

3v, 2n3906, 10mH inductor, pushbutton - thats all.

LEDs do have some internal resistance, if you think of 20 Ohms for each you get 400 for 20. Gives you about 10v extra leeway.

Anyway I didnt work further on the circuit for instance trying a larger 10mH inductor which could carry more turns. Or different than 10mH.

For sure optimization is possible. And there are LEDs which can be purchased unseparated (I think most LEDs originally are that way, seperated by a machine before distribution).

Driving current is just a few mA I think havent tested efficiency.

Parallel also is possible with LEDs from one batch I've operated panels with smaller parallel strings for months, using a MC34063 (actually with a current sense/limit). This IC is only good for smaller panels.

Connecting single LEDs in parallel isnt so good- one LED could hog current and burn out and doesnt really look good. If you must use parallel strings.

9v battery? These only have small cells inside and arent really good to light up LED arrays.

But 2x AAA or AA can be done. There are commercial string lights which use 2x AA and guess its all in parallel with small equalization resistors.