Resistor Value Calculation for LED
In this blog I am going teach you calculation for the value of resistor that is used in the protection of led. Currently LED’s ( Light Emitting Diodes ) are used for wide range of purpose mainly as indicators.
Light emitting diodes are very sensitive. They easily get blown off with a slight higher voltage or current, to protect them we should add a resistance in series.
So before I show you the calculations, you must know that every colour of LED has a specific voltage drop across its terminal.
Now lets come to the calculation part
The value of resistance can be easily calculated by Ohm’s law
V ( Voltage ) = I ( Current ) x R ( Resistor )
Here,
Voltage = Source Voltage – Voltage drop by LED
Example
Suppose we need to calculate the value of resistance for green LED
Then,
Source voltage = 9v ( Applied voltage )
Voltage drop by Green LED = 4 Volt
Current = 25mA = 0.025 Ampere ( This is the current consumed by LED )
R = ?
By Ohm’s law
Resistance = voltage / Current
Resistance = ( source voltage – Voltage drop by LED ) / Current consumed by LED
Resistance = (9 – 4) Volt / 0.025 Ampere
Resistance = 5 V / 0.025 A = 200 Ohm
Power of resistor
Power of resistor can be easily calculated by
P ( Power ) = V ( Voltage ) x I ( Current )
P = ( Source voltage – Voltage drop by LED ) x I ( Current consumed by LED )
P = 5Volt x 0.025 Ampere
P = 0.125 W ( power of resistor must be greater than this value )
Every value of resistor is not available in market so we go for the nearest value available.
Resistor from market = 200 Ohm, 0.25 Watt
Frequently asked questions
- How to calculate resistance if two or more LED’s are connected in parallel ?
- When two or more LED’s are connected in parallel. Voltage across parallel combination of LED remains constant and current gets added.
- For example, if there are two led of 4v and 25 mA each. The parallel combination of two led will consume 4v and 50mA.
- How to calculate resistance if two or more LED’s are connected in series ?
- When two or more LED’s are connected in series. Current across the parallel combination remains the same and voltage gets added.
- For example, if there are three led of 4v and 25mA each. Then the series combination of three led will consume 12v and 25mA.
Author
Akash Sharma
Learn more about electronics on my website –
Great article. Thank you for sharing. I’m retired Aircraft mechanic but now learning the electronics side of things. I take most available courses and buy equipment as required. Will look at the articles on this page. Thanks for sharing Artie 😊
Thank you for your valuable comment. It means a lot to me.