Confirming whether this circuit will work

[MeatySteak]

Hi,
I am very new to circuits, as probably evident by the basicness of this one, and am especially new to LEDs. I bought some LEDs, specs are advertised as 3v, 20mA. So pretty standard. I'll link them down below this. They do come with their own resistors pre-wired, but I wanted to move things around. The pre-wired resistors are 1500ohm metal film, and there is one per resistor as you would expect. I'm using a 12v power supply, and as long as my calculations are correct, that would mean that the LED would receive 6mA of current each, well below the advertised 20mA. This setup does work however, 6mA seems to be enough to power it well enough. I'm assuming 20mA is just the maximum current aloud without it burning out.

So, what I wanted to do was instead of having a resistor for each LED, have only one to control multiple LEDs, specifically one for the blue ones and one for the white ones. I attached a very rough picture of what I plan on doing along with the basic calculations to figure out the resistance for the resistors. Hopefully I have everything right and it makes sense. Just want to confirm whether this will in fact work or if what I have done is just stupid.

In short, I want to connect 4 Blue LEDs to one resistor with a current output of 0.024A (so 0.006 for each LED), and 10 White LEDs to another resistor with an output of 0.1A (so 0.01A for each LED). Reason for this is so I dont have 14 resistors which I would need to try and fit into a very small space but instead only have 2 which is very manageable.

Please be gentle, I am not an artist and I dont work with circuits very often.

Links:
https://lighthouseleds.com/pre-wire...ngle-12v-pre-wired-led-blue-ultra-bright.html

12v 0606 / 0603 Nano 1.5Hz Flashing SMD Wide Angle Pre-Wired Cool / Clear White LED - Ultra Bright - 5 Pack - (10v, 11v, 12v, 13v, 14v, 15v, 16v, 17v, 18v)

The 12v 0606 / 0603 Nano 1.5Hz Flashing smd wide angle cool / clear white pre-wired LED makes it almost the easiest way to add light nearly any project.

lighthouseleds.com

Thanks!

 

[danadak]

Your calc should go like

R = V / I = (9V - Vled) / .024 = (9 - 3)/.024 = 250 ohms

The above is basically a Kirchhoff's loop. So writing the voltages around the
loop starting at battery 9V - Vresistor - Vled = 0, and then you algebraically
solve that. You start at a point in the loop and then walk around the loop
back to your starting point. Many youtube videos on this topic.

The same should be done for the white LEDs.

LED voltages (nominal) -

So check your datasheet voltages. Also as LEDs are in parallel important to match them for
V so that one does not hog all the current because it turns on at lower V than the others.

Are you planning on doing this with a 9V battery ? Battery life will be a little challenged.

https://www.duracell.com/wp-content/uploads/2016/03/MN1604_US_CT1.pdf

Regards, Dana.

 

[MeatySteak]

Your calc should go like

R = V / I = (9V - Vled) / .024 = (9 - 3)/.024 = 250 ohms

The above is basically a Kirchhoff's loop. So writing the voltages around the
loop starting at battery 9V - Vresistor - Vled = 0, and then you algebraically
solve that. You start at a point in the loop and then walk around the loop
back to your starting point. Many youtube videos on this topic.

The same should be done for the white LEDs.

LED voltages (nominal) -

View attachment 137695

So check your datasheet voltages. Also as LEDs are in parallel important to match them for
V so that one does not hog all the current because it turns on at lower V than the others.

Are you planning on doing this with a 9V battery ? Battery life will be a little challenged.

https://www.duracell.com/wp-content/uploads/2016/03/MN1604_US_CT1.pdf

View attachment 137696


Regards, Dana.

Thanks for the response! I was planning on doing a 12V, so I factored in a 3V drop in my calculations. Didnt realise different colours had different voltage drops tho.

I ended up looking into it a bit more and found out this works, but only in concept since these LEDs arent consistently the advertised voltage, i.e. small discrepancies leading to large differences in current draw.

I’m just going to try fit everything and hope for the best!

Thanks

 

[danadak]

Series string is good step at keeping all LEDs at same brightness as they all
have exactly the same current. But that normally requires boost converters.

Like - https://usa.banggood.com/search/led-constant-current.html?from=nav

Cons current diodes - https://www.diodes.com/assets/Datasheets/AL5809.pdf

Dont forget to calc the wattage rating of your R's

W = (I x I) x R


Regards, Dana.

 

[Nigel Goodwin]

Thanks for the response! I was planning on doing a 12V, so I factored in a 3V drop in my calculations. Didnt realise different colours had different voltage drops tho.

I ended up looking into it a bit more and found out this works, but only in concept since these LEDs arent consistently the advertised voltage, i.e. small discrepancies leading to large differences in current draw.

I’m just going to try fit everything and hope for the best!

Thanks

As long as the LED's are from the same batch (or even identical types from different batches), then as long as you have at least three in parallel they tend to share the current 'well enough', and the more you have, the better the sharing. However, if the opportunity is there, always put them in series if you can.

 

[danadak]

Extensive application notes on subjects such as matching, human eye response,
etc..

Light Emitting Diodes (LED) • Application Notes • OSRAM Opto Semiconductors | OSRAM Opto Semiconductors

Find all Application Notes for Light Emitting Diodes (LED) and General Lighting from OSRAM Opto Semiconductors

www.osram.us

Regards, Dana.