mithrandiir42
New Member
First some background...
I'm working on a project that consists of 20 rgb leds powered by 2 900ma 3.7v lithium ion batteries.
each color per led needs ~20ma of current
so my project needs at least 20*3*20 = 1.2Amps if all colors of all leds were full on.
for the sake of simplicity lets just assume that each color (in reality each color has slightly different tolerances)has a max voltage tolerance of 3.8v (in reality each color has slightly different tolerances). I'm using npn transistors to control the on/off state of each color. now my problem is that I want to get full brightness from my leds and since there's roughly a 0.7 voltage drop across the transistor, the max voltage my leds could get it 3.1v which doesn't produce full brightness.
Now to the real question.
What is the best solution in terms of efficiency (longest run-time)?
put two 3.7v batteries in series to get 7.4V and then use a LDO voltage regulator such as an lm317 to output 4.5v (3.8+.7) so that my leds can receive the full 3.8 volts when the transistor is full on? What happens to the extra voltage here? is it wasted? or is it somehow put toward the load giving me more than 900ma since i'm only using little more than half the voltage?
...or place the batteries in parallel so i'd have double the current 1800ma
and find some kind of DC boost converter solution to bump my voltage from 3.7v up to 4.5v and be able to supply at least 1.2Amps? obviously this would pull more current to produce the voltage needed but that's ok.
so far I've been unable to find a module small enough for my application that can deliver that much current. If there is some kind of module that can do it. it needs to be less than .625 inches wide/tall, length isn't an issue
I've been using these in the past when i had more space to work with and they worked great:
Digi-Key - 507-1379-5-ND (Manufacturer - VRAH-02C50B0)
Please pardon my lack of accurate terminology.. I'm a software guy getting into hardware![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Thanks in advance for any guidance.
I'm working on a project that consists of 20 rgb leds powered by 2 900ma 3.7v lithium ion batteries.
each color per led needs ~20ma of current
so my project needs at least 20*3*20 = 1.2Amps if all colors of all leds were full on.
for the sake of simplicity lets just assume that each color (in reality each color has slightly different tolerances)has a max voltage tolerance of 3.8v (in reality each color has slightly different tolerances). I'm using npn transistors to control the on/off state of each color. now my problem is that I want to get full brightness from my leds and since there's roughly a 0.7 voltage drop across the transistor, the max voltage my leds could get it 3.1v which doesn't produce full brightness.
Now to the real question.
What is the best solution in terms of efficiency (longest run-time)?
put two 3.7v batteries in series to get 7.4V and then use a LDO voltage regulator such as an lm317 to output 4.5v (3.8+.7) so that my leds can receive the full 3.8 volts when the transistor is full on? What happens to the extra voltage here? is it wasted? or is it somehow put toward the load giving me more than 900ma since i'm only using little more than half the voltage?
...or place the batteries in parallel so i'd have double the current 1800ma
and find some kind of DC boost converter solution to bump my voltage from 3.7v up to 4.5v and be able to supply at least 1.2Amps? obviously this would pull more current to produce the voltage needed but that's ok.
so far I've been unable to find a module small enough for my application that can deliver that much current. If there is some kind of module that can do it. it needs to be less than .625 inches wide/tall, length isn't an issue
I've been using these in the past when i had more space to work with and they worked great:
Digi-Key - 507-1379-5-ND (Manufacturer - VRAH-02C50B0)
Please pardon my lack of accurate terminology.. I'm a software guy getting into hardware
Thanks in advance for any guidance.