how to calculate resistance for LED

Thread Starter

abhimanyu143

Joined Aug 25, 2014
211
I want to do some practical. I have started with LED and resistor
I want to protect LED from high voltage and current

I have following things

bread board
multimeter
power supply
red LED

I need resistor ?

I have attached datasheet for LED
according to datasheet
forward voltage of LED = 2 v
forward current of LED = 20 mA
I know supply voltage = 5.2 v

formula R=V/I

resistance= (supply voltage - voltage drop of LED)/ current throw LED

R=(5.2-2)/ 20 mA
R=3.2/0.020 A
R= 160Ω

can I use 160 Ω resistor?
 

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mcgyvr

Joined Oct 15, 2009
5,394
Correct..

Also its common safety practice to multiply the required wattage by 2 or 3 to ensure that the resistor isn't running too hot.
If I was to calculate a resistor using the power formula and the result was 1W then I would specify/buy a 2W or even 3W resistor.
 

Thread Starter

abhimanyu143

Joined Aug 25, 2014
211
now next project
we have
bread board
4081B AND gate IC
LED as indicator
two switch

LED is connected to output Of IC
two switch are connected at Input of Ic

I have upload datasheet of IC

If we connect two switch directly to Ic without resistor, I think IC will be damaged
so I think I need resistor to protect IC

If we connect LED directly at the output of IC without resistor . I think LED will be damaged

does we need 3 register to protect IC and LED

how to calculate resistor value for LED and Ic ?
 

Attachments

Jony130

Joined Feb 17, 2009
5,487
You need two 10K pull-down resistor (from gate input to GND) for the gate input .
And one resistor for the LED. But you already know the equation for it.

PS. and don't forget to connect all unused CMOS inputs to ground.
 

k7elp60

Joined Nov 4, 2008
562
Just because a LED has a current rating of 20Ma does not mean you have to run it at that current. Many LED's are clearly visible and 1/4 to 1/2 the maximum current.
 
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