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resistor measurement
- Thread starter m.d.
- Start date
Welcome to AAC!
Cheap LED flashlights operate on 3 AAA batteries. They connect all of the LEDs in parallel and don't bother with any current limiting. I have one where most of the LEDs are no longer functional.
What is the battery capacity/chemistry? What is the maximum continuous current for the LED (and its color/forward voltage)?
Cheap LED flashlights operate on 3 AAA batteries. They connect all of the LEDs in parallel and don't bother with any current limiting. I have one where most of the LEDs are no longer functional.
Welcome to AAC!
It depends on the LED and how bright you want the LED to be.
If we design for 2V LED and 1mA current,
R = (3.5V - 2V) / 1mA = 1500Ω
So start with 1500Ω and gradually decrease the resistance value until you achieve the desired brightness.
If you use a variable resistor, make sure that you have at least 100Ω fixed resistor in series so that you don't burn out the LED.
It depends on the LED and how bright you want the LED to be.
If we design for 2V LED and 1mA current,
R = (3.5V - 2V) / 1mA = 1500Ω
So start with 1500Ω and gradually decrease the resistance value until you achieve the desired brightness.
If you use a variable resistor, make sure that you have at least 100Ω fixed resistor in series so that you don't burn out the LED.
MisterBill2
- Joined Jan 23, 2018
- 27,501
For a classic 20 mA LED, (3.5V-2v)/20 mA=75 ohms . But that is not a standard value, so use a 68 ohm resistor (blue, grey, ,black, or an 82 ohm resistor, (grey, red, black.)
