Powering LED with 12 & 9 volts

Eugalaz

Hello,
Can anybody tell me what resistor value I would need to power a LED from;
12 volt power source?
9 volt power source?
Thank you
E

W9GFO

Rich H

Franklin

It depends on the LED. Each type is different and the datasheet will give you voltage and current requirements/limits.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
- Stephen

Carl Hayes

Eugalaz said...
Hello,
Can anybody tell me what resistor value I would need to power a LED from;
12 volt power source?
9 volt power source?
Thank you
E

No.· Nobody can tell you that, which is a complete answer to the question you asked.·

No one can tell you that, unless you first tell them what current you desire through the LED, and what the voltage drop is across the LED at that current.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
· -- Carl, nn5i@arrl.net

Mike Green

You should be able to figure this out yourself using Ohm's Law. First, you have to find out the forward voltage of the diode. It can range anywhere from 1.7V for a red LED to as much as over 3V for some blue or white LEDs. Say it's a red LED with a forward voltage of 1.7V. With a 12V supply, the resistor has to drop 12V - 1.7V = 10.3V.

Next you have to figure out the current you want based on the diode itself and how much light you want. For discussion, let's say 10mA. Ohm's Law gives R = E / I = 10.3V / 0.01A = 1030 Ohms. The closest standard value is 1K. The power dissipation is P = E * I = 10.3V * 0.01A = 1/10W. I'd suggest a 1/4W resistor.

Eugalaz

Thank you everyone,
my question has been answered precisely. I understand the equation now well enough (Mike) to derive the answers I need.