# 90 led's circuits

Discussion in 'Homework Help' started by myosff, Aug 18, 2013.

1. ### myosff Thread Starter New Member

Aug 18, 2013
6
0
dear all
i need full diagram circuits for 90 led's sheet led's 5 mm blue and white and power supply 12 v

many thanks

Last edited: Aug 18, 2013
2. ### LDC3 Active Member

Apr 27, 2013
920
161
JoeJester and Metalmann like this.
3. ### myosff Thread Starter New Member

Aug 18, 2013
6
0

Last edited by a moderator: Aug 19, 2013
4. ### LDC3 Active Member

Apr 27, 2013
920
161
How can we help if we do not know anything about what you want. It's like saying, build me a car!

5. ### myosff Thread Starter New Member

Aug 18, 2013
6
0
need help to define all part for circuits

6. ### DerStrom8 Well-Known Member

Feb 20, 2011
2,428
1,333
You're not making any sense. I am guessing you are not a native English speaker. In that case, I suggest you try translate.google.com. It might help you to better explain what you want, and help us to better understand you.

Matt

7. ### absf Senior Member

Dec 29, 2010
1,664
445
You have to tell us more about the LED. How many are blue and how many are white. How much current and voltage is required for each color of your LED......etc

Allen

8. ### WBahn Moderator

Mar 31, 2012
20,229
5,755
And let's not forget that this is the HOMEWORK Help forum. You need to show what efforts YOU have made to at least attempt a solution for YOUR homework problem.

DerStrom8 likes this.
9. ### myosff Thread Starter New Member

Aug 18, 2013
6
0
all led's are 3.6 volt 75 mA and power supply 12 volt

Feb 20, 2011
2,428
1,333

11. ### WBahn Moderator

Mar 31, 2012
20,229
5,755
Still waiting to see this "attempt" thing.

12. ### myosff Thread Starter New Member

Aug 18, 2013
6
0
now i don't need any help

Jul 18, 2013
13,161
3,630
14. ### myosff Thread Starter New Member

Aug 18, 2013
6
0
many thanks max

15. ### WBahn Moderator

Mar 31, 2012
20,229
5,755
So, either you figured it out on your own once you decided to make the attemp -- which is a great thing; or you concluded that we weren't going to just do your work for you and gave up -- which is a great thing.

16. ### ScottWang Moderator

Aug 23, 2012
5,478
864
If you want to light up the 90 LEDs, then you should doing as this:
12V/3.6V=3.333, 90V/3=30 strings, the power only has 12V, so you only can using 3 LEDs in a string, and then you have to calculate the limited resistor for LED current limitation.

17. ### RRITESH KAKKAR Senior Member

Jun 29, 2010
2,831
91
Don't now what r u doing are u making light system??
anyway just make 4 or 3 led series with series resistance of 100/220ohm 1/4watt as per requirement of intensity.
and then connect all these series in parallel to 12v source...

18. ### WBahn Moderator

Mar 31, 2012
20,229
5,755
How do you figure that the OP will be able to power 3 LEDs in series if they are using 12 V and each LED has a forward drop of 3.6 V?

At the requested intensity of 75 mA, a 100 Ω resistor will drop 7.5 V and dissipate well over 500 mW while a 220 Ω resistor will drop 16.5V and dissipate nearly 1.25W. So just where did you come up with the recommendation of using "100/220ohm 1/4watt" resistors?

With three LEDs in a string, the voltage that needs to be dropped across the current limiting resistor would be

Vdrop = 12 V - 3 x 3.6 V = 1.2 V

To do this at a current of 75 mA would require a 16 Ω resistor and would dissipate about 90 mW. This may work just fine, but small variations in the forward LED voltage or the supply voltage could move the actual current around by perhaps 50%. If that's acceptable, then this is probably the way to go.

But if the OP needs a more consistent and uniform current, it would probably be better to go to two LEDs in a string, meaning that the resistor would have to drop

Vdrop = 12 V - 2 x 4.6 V = 4.8 V

which would require a 64 Ω resistor (use a 62 Ω if you need it close or a 56 Ω or a 68 Ω if you can be a little loose) capable of dissipating 360 mW. So two 1/4 W 33 Ω resistors in series might be a way to go. With this, it is probably unlikely that the current will vary more than about 10% from the nominal value.

Last edited: Aug 20, 2013
19. ### RRITESH KAKKAR Senior Member

Jun 29, 2010
2,831
91
OK, if there are 8 Led white in series with 220ohm at 1/2 or 1/4 watt resistor(in paraallel there are more than 1000's led) driving from 26V source is not giving good brightness, increasing voltage to 46V will damage the led?

20. ### WBahn Moderator

Mar 31, 2012
20,229
5,755
What, on Earth, are you rambling about? Who said anything about 8 LEDs in series? Or thousands of LEDs? Or about 26 V sources? Or about 46 V sources?

Are you sure you are in the right thread on the right plane of existence?

DerStrom8 likes this.