LED Lesson

Printed From: the12volt.com
Forum Name: Lights, Neon, LEDs, HIDs
Forum Discription: Under Car Lighting, Strobe Lights, Fog Lights, Headlights, HIDs, DRL, Tail Lights, Brake Lights, Dashboard Lights, WigWag, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=28067
Printed Date: May 14, 2024 at 4:09 PM

Topic: LED Lesson

Posted By: tray262
Subject: LED Lesson
Date Posted: March 09, 2004 at 3:15 PM

Ok, I did a search but the anwsers I found wern't easy enough for me. So here's what's happening. I want to make some led automotive bulbs. I'm looking at these https://www.partsexpress.com/pe/showdetl.cfm?&User_ID=18811645&St=1066&St2=-39583967&St3=-78106785&DS_ID=3&Product_ID=15768&DID=7 Here are the spec incase you don't wanna look. "very bright RED at only 20 mA. 45° viewing angle. Typical forward voltage range 1.7 VDC-2.2 VDC." I want to use these to replace my 3rd breaklight. I also found this calc. https://wolfstone.halloweenhost.com/TechBase/litled_LEDCalc.html So what I'm trying yo figure out is. How many LED and what resiter do I need sorry for such a stupid question. Thanks again guys.

Replies:

Posted By: xetmes
Date Posted: March 09, 2004 at 3:56 PM

Well you want to do banks of series LEDs then hook them in parallel. I would assume the forward voltage 2V for calculations. If you string 5 together you will drop about 10V, use a resistor to get the 20mA. Since you will drop about 2V on the resistor it would have to be 100 ohms (2/.02). then just hook each bank of 5 in parallel to get as many as you want, you then need 1 resistor for each 5 leds... good luck

Posted By: tray262
Date Posted: March 09, 2004 at 9:22 PM

Ok major confusion "Well you want to do banks of series LEDs then hook them in parallel. I would assume the forward voltage 2V for calculations. If you string 5 together you will drop about 10V " I understand up till that spot.

"use a resistor to get the 20mA. Since you will drop about 2V on the resistor it would have to be 100 ohms (2/.02). " That's were the problem comes in.

"then just hook each bank of 5 in parallel to get as many as you want, you then need 1 resistor for each 5 leds... good luck" Also No problems there.

Sorry for not being too good at this. Also what formula's are you using ? Thanks so much.

Posted By: xetmes
Date Posted: March 10, 2004 at 6:11 AM

for the current calculation just used ohms law.

V = I * R

so the voltage across the resistor is 2V, we want 20mA (.02A)

so R = V / I = 2 / .02 = 100 ohms

Posted By: tray262
Date Posted: March 10, 2004 at 6:06 PM

Thank you so much, and sorry again for the dumb questions. Hope everything works out and thanks for the luck I'll need it.

Tray

Posted By: Mad Scientists
Date Posted: March 12, 2004 at 6:10 AM

https://www.semiconductor.agilent.com/cgi-bin/morpheus/home/home.jsp

On the right hand side select LED..

Tonnes of information on LEDs.. look for application papers.

Regards,

Jim