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How to select resistor value for LED with simple calculation (Ohm’s Law)

October 12, 2019


[Music] Hello viewers, welcome to Tech StudyCell. In this video, we will see how to calculate the resistance value while connecting an LED in a circuit. It is very important to connect a resistance in series with the LED if the forward voltage of the LED is less than the input voltage of the circuit, otherwise the LED may burn. So in this video we’ll discuss the calculation of the resistance value for different input voltage with some practical experiment. Here I have used a 5 mm green LED and from the datasheet we can see the forward voltage of the LED is 3.0 – 3.6 volt and the current rating is 30 milli ampere. From this data we can conclude the current through the LED should not be greater than the 30 milli ampere. In this schematic you can see this is the input voltage (Vi) and I have use a resistance (R) in series with the LED to limit the current within 30 milliampere as the current rating of this LED is 30 milliampere. Now here I will use a 9-volt battery as an input so the input voltage will be 9 volt and we have already got the forward voltage of the LED which is 3 volt and if we deduct 3 volt from the 9 volt then we will get the voltage drop across the resistance. So the voltage drop across the resistance will be 6 volt. From this equation we can easily measure the value of the resistance. we have already got the voltage across the resistance and we know the current rating of the LED, the (I) should be within limit of 30 milli ampere which is 0.03 ampere. So if we calculate the value of the (R), we will find 200 ohm. So here in the circuit I will use 220 ohm to limit the current within 30 milli ampere. Now to find a wattage of this register we can use this simple formula which is (W)=(V)*(I). Here the (V) is 6 volt which is the voltage drop across the resistance and (I) is the current through the resistance which is 30 milliampere or 0.03 Ampere. So if you multiply these two value, we will get the wattage of the resistance should be. So here we are getting 0.18 watt so the wattage value of the resistor, we should use should be greater than this 0.18 watt. So here I will use 0.25 watt register to make the circuit. now we will build the circuit and measure the voltage and current value accordingly here I have connect a 220 ohm register with a positive terminal of the battery as you can see we have already calculated the resistance value which is 220 ohm to limit the current within 30 milli ampere and I have connected the cathode of the LED with the negative terminal of the battery as you can see the cathode is connected with a negative terminal of the battery. Now if you connect these two point you can see the LED is glowing. now we measure the voltage and current with the voltmeter and ammeter. Let me connect the voltmeter and ammeter with the circuit so that I can show you the value of the current. Now here you can see I have connected an ammeter in series, so we can measure the current and you can see the value is 26.5 milli ampere. now we will measure the voltage. First we’ll measure the input voltage. you can see the voltage is 8.8V which is aprox 9 volt. next we’ll measure the voltage across this led. now if we measure the voltage across the LED which is 3.1 Volt that is (VL)=3V. Now we are going to measure the voltage across the resistance. now you can see the voltage across resistance is 5.6 volt and from the calculation we have calculated the voltage across the resistance would be 6 volt. so all the data you can see practically which we have calculated earlier. Now we’ll change the input voltage to 12 volt and calculate the resistance value. Here if the input voltage is 12 volt and the forward voltage is 3 volt as we are using same LED. The voltage across the resistance will be (12 – 3)Volt which is 9 volt. so 9 volt should be drop across this resistance and the current rating should be 0.03 ampere which is 30 milliampere. so with the help of same formula, we can easily calculate the value of the resistance (R) for the 12 volt input. Voltage across the resistance is 9 volt as we have calculated and the current will be 0.03 ampere. so the value of the R will be 300 ohm. now here I don’t have 300 ohm resistor so I will use two 160-ohm resistors. So the total value of the resistance will be 320 ohm. Here I will use this variable power source as 12 volt source. first we will connect the 320 ohm resistor with the positive terminal of the DC source. here I have used two 160 ohm resistors in series to get total 320 ohm resistance. now we’ll connect the negative terminal of the DC power source with the cathode of LED. Now our circuit is ready if I connect these two terminal you can see the LED starts glowing. now we’ll measure the voltage and current with the help of these two multimeters. here in this multimeter you can see the value of the current through the circuit which is 28 milli ampere now we’ll measure the voltage first we’ll measure the input voltage you can see the input voltage is 12 volt. now we’ll measure the voltage across the LED, which would be 3 volt as we know the forward voltage of this LED 3 volt. so in a reading we are getting 3 volt or 3.1 volt in this multimeter. now we’ll measure the voltage across this resistance (R) which should be 9 volt. we have chosen the value of the resistance such that the voltage drop across the resistance should be 9 volt. let me show you you can see it’s showing 9-volt across the resistance. so we can easily calculate the resistance value for different input voltage while connecting an LED with the circuit to limit the current within the current rating of this LED. If you find this video helpful please hit the like button and share it with your friends. Don’t forget to subscribe our channel for more such videos, thank you for watching have a great day.

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79 Comments

  • Reply Elektronik AtΓΆlyem May 11, 2018 at 12:06 pm

    Useful video

  • Reply David Friederick May 23, 2018 at 4:46 am

    Excellent presentation, I really like the way you presented and explained everything!

  • Reply Manafsaidu Saidu May 26, 2018 at 12:31 pm

    Good explained..

  • Reply Chandrashekhar Ratnakar Joshi June 8, 2018 at 3:13 pm

    Hon. How to calculate the capacitor?

  • Reply maximus fl July 1, 2018 at 6:33 pm

    Generally this explanation will work, but it is not totally accurate. The datasheet showed the voltage drop across the LED between 3.0 – 3.6 volts at a forward current of 20ma. The voltage drop across the LED will increase as you increase the applied voltage up to a maximum of 3.6 volts. You need to look at the charts in the datasheet to actually determine the correct voltage drop across the LED based on the applied voltage. Most people disregard the datasheets, but they are full of useful information when designing a circuit.

    Second point, the datasheet shows a max current of 30ma, but you saw on the datasheet the manufacturer did used 20ma to determine the voltage drop across the LED. You don't have to apply the max current in order to power the LED as you did in your example. You can use a lot less current to power this LED, which you did not talk about.

    Third point, you did not talk at all about the lumens value of the LED, it is plainly shown on the datasheet you showed in your video. The value displayed in your video is between 14250 – 28500 mcd at 20ma. You would need to look at the chart given by the manufacturer to actually figure out how much current and voltage you need in order to have the brightness level of the LED you want. You did not even talk about that.

    When you design circuits you have to look at all of these variables. Look at the voltage drops across your resistors. Complete waste of power. P=V*I for your resistors, huge waste. Power efficiency is very important when you design circuits. Another point you failed to talk about…

    Finally you did not talk about operating temps. Datasheet clearly states that these values of current and voltage were take at 25C. If you are not running this circuit in an environment that is 25C your values may change. You have to look at the charts provided by the manufacturer to determine the values at other degrees C. Maybe I want to run this outside of my house where my temps are 0 or minus C degrees. Or maybe in the middle of the summer and it is 40C outside. Most datasheet will address that. You don't talk about that either….

  • Reply Undeniable Paradox July 11, 2018 at 4:14 am

    Would it matter if he connected the resistor(s) later in the circuit?

  • Reply Gion Uein September 23, 2018 at 4:54 pm

    Namli mambli

  • Reply gulzar team 07 October 25, 2018 at 4:51 am

    Sir resistor color code

  • Reply TutuL November 8, 2018 at 7:17 pm

    Excellent

  • Reply Ankur Sharma December 15, 2018 at 8:23 pm

    how can I know the watt of my register, from datasheet?

  • Reply Adnan Ahmed December 18, 2018 at 12:56 pm

    Very practical. Keep it up.

  • Reply Zabih Basam December 19, 2018 at 9:37 pm

    thanks for video. helpfuly

  • Reply Siddarth Shrivastav December 20, 2018 at 6:11 am

    What do if I connect 2 leds in series ???

  • Reply Rohit Rajput December 22, 2018 at 1:56 pm

    220voltage par kitne ohm or watt ka resistor lgega

  • Reply Ajmal Maad December 26, 2018 at 12:40 pm

    I have questions ( is there a kind of risister which will allow current to pass when it exceeds 3v and below 3v it will not pass current)???

  • Reply Corntoll Gaday January 1, 2019 at 8:26 am

    4:53 did you get electrocuted here?

  • Reply balesh dalawai January 6, 2019 at 1:48 am

    Nice but hindi next k

  • Reply Piash Ahmed January 11, 2019 at 12:40 pm

    Why u give 9-3=6 or 12-3=9.this can't understand. Plz tell again

  • Reply Piash Ahmed January 11, 2019 at 12:42 pm

    And 1pic led how voltage. All same or no same

  • Reply Randy E January 12, 2019 at 8:29 am

    Fantastic videos for a rookie like me, thank you for taking the time to make these videos! I'm in the process of watching all of your other videos πŸ‘πŸ˜‰

  • Reply Rex makepeace January 13, 2019 at 1:53 pm

    Thank you for your time and effort in making this video. It was very helpful πŸ™‚

  • Reply Nader Nad January 19, 2019 at 9:36 pm

    Great vedio brother

  • Reply captain black body January 25, 2019 at 1:35 pm

    Too good bro thank you very much yar plz
    Ese hi video bnate rhe

  • Reply Piyush Patankar February 5, 2019 at 6:40 am

    How can glow led use a transistor & how can find resistance value please make a video

  • Reply Mac STRANGE February 5, 2019 at 9:37 pm

    Thanks for lesson

  • Reply Rajesh Chandrasekharan February 10, 2019 at 1:40 am

    Excellent video , sir.Thank you

  • Reply Hemant Kapadia February 26, 2019 at 2:37 pm

    Sir..torch banane ke liye 1watt led ke sath 3.7 v ki lithium battery connection me kon sa resister use karna chahiye??pls reply

  • Reply king Lyon March 3, 2019 at 11:45 am

    I am sorry but I can not understand a single word your saying

  • Reply G VIJAY KUMAR March 4, 2019 at 5:57 pm

    nice . 12v 1led = R6V but 2 led = R?

  • Reply Pranab karmakar March 7, 2019 at 12:54 pm

    What is the current value of 4V white smd led light ?

  • Reply π™ˆπ˜Όπ™Žπ™π™€π™ π™Žπ™„π™Šπ™ˆπ˜Όπ™„ March 11, 2019 at 2:26 pm

    Yo what resistor do i need on orange led

  • Reply Ajaya kumar Maharana March 14, 2019 at 6:25 pm

    πŸ‘ŒπŸ‘ŒπŸ‘Œ

  • Reply abenwinUT Wee March 16, 2019 at 10:24 pm

    Excellent, informative video. Great detail but not overly complex. Audio very easy to follow.

  • Reply The HyBriD March 19, 2019 at 3:07 pm

    For 1w power led required current is 350ma then what will the value of resistor and power rating of resistor ??from 12 v 10ah battery , and will it require to put any current limiting diode ??

  • Reply raghavendra raghav March 22, 2019 at 12:13 pm

    Super more information send sir . Good teaching and good information tq

  • Reply jobish April 1, 2019 at 3:45 pm

    How u know that ampere

  • Reply Maiklas Pakautikas April 5, 2019 at 5:50 am

    Thank you!!!

  • Reply T Suleman W April 5, 2019 at 2:33 pm

    Nicely Explaination . what if the current source is 20 A and the Voltage is 12 V is that equation still relevance. just asking. thank

  • Reply Tus Pat April 12, 2019 at 2:51 am

    Excellent video…. πŸ™‚

  • Reply Sir Walter Raleigh April 14, 2019 at 9:35 pm

    Well explained video.

  • Reply cali818 April 16, 2019 at 3:25 am

    how about if you want to use 1AA battery on led?

  • Reply suresh n April 20, 2019 at 5:40 pm

    Very good teaching. No complexicity. thank u

  • Reply Fahad Shariff April 29, 2019 at 8:00 am

    How u Caledonian simply writing

  • Reply Anand Patel May 7, 2019 at 3:39 am

    4.5 valt ki battery par me konsa register. Lagaye Jaya he .

  • Reply Nader Nad May 11, 2019 at 11:13 pm

    Great experience and explanation my dear. ….πŸ‘

  • Reply Abraham Acibar May 12, 2019 at 1:09 am

    amazing video sir. i'm working on a DIY led Tail Light for my motorcycle. using LED. it burns out. please help.

  • Reply Sourav Bera May 13, 2019 at 1:57 pm

    When 3 led connected across the battery then how value resister require.

  • Reply Fez Mechanic May 14, 2019 at 10:19 am

    They should add a google translate feature in the sub titles…….

  • Reply Sahil Ameen May 15, 2019 at 6:06 am

    If I use 6 led how many resistors should I use please reply someone and which resistors

  • Reply Yousif Al Qallaf June 1, 2019 at 10:43 pm

    Excellent

  • Reply Nowhereman JK June 2, 2019 at 10:56 pm

    Is there any universal resistor value for use with LEDs of different colors? More or less?

  • Reply Sourav Roy June 22, 2019 at 5:24 am

    nice explanation bro….thanks a lot….

  • Reply Gopalapuram Srikanth June 27, 2019 at 5:00 am

    ఀెలుగులో ΰ°šΰ±‡ΰ°ͺΰ°‘ΰ°‚ ΰ°°ΰ°¦

  • Reply aaron casto June 30, 2019 at 12:17 am

    Okay, I have a question. I'm trying to power 4 LED's off two AAA batteries. what would be the best way to wire this? Would it be in parallel? The LED's are 3v and 20ma. Thanks!

  • Reply bhuveer chauhan July 1, 2019 at 4:08 pm

    Nice way of teaching

  • Reply Niyaz createvety July 3, 2019 at 2:02 pm

    Super

  • Reply Zakary DeLaura July 4, 2019 at 1:01 pm

    Does each LED need a resistor if wired parallel or just the first LED in the chain? Or do both wired parallell and wired in series need to have each LED have a resistor?

  • Reply Paramhans Baluni July 18, 2019 at 12:58 am

    Nicely explained. Keep it up πŸ‘

  • Reply The Driver July 18, 2019 at 10:52 am

    Hi nice video. May i ask if the temperature shud be any problem in this circuit. (resistors temp)

  • Reply Paul Sih July 19, 2019 at 12:49 am

    2:18 You found the solution of the equation to be 200 ohms but you said you will use 220 ohms instead. Why is that? why extra 20ohm ?

  • Reply Taufeek Khan July 26, 2019 at 9:54 am

    Good

  • Reply Engr Tarik ul Alam Ruman July 28, 2019 at 7:01 am

    Brother can you tell in 6v or 5v supply what will be the resistance

  • Reply Gaming with Casmiro August 4, 2019 at 11:17 am

    Nice man

  • Reply Vijaya Kumara August 7, 2019 at 8:43 pm

    Good explanation if you explained about watt also it could be complete and more helpful anyway thank you

  • Reply Raj Balachandran August 25, 2019 at 5:23 pm

    It is very helpful… Thank you..

  • Reply Allen Braithwaite August 31, 2019 at 9:15 am

    Can’t understand the guy.,

  • Reply Sandeep naik September 5, 2019 at 6:28 am

    1000mA=1A =>0.003 and not 0.03

  • Reply Bhanu Pratap Singh September 10, 2019 at 12:03 pm

    Please sir my question one r.g.b led how many volt and amp .

  • Reply Ahmed Sherbiny September 13, 2019 at 11:55 am

    Thank you so much this video is so helpful

  • Reply Utkarsh Srivastava September 15, 2019 at 8:09 am

    Very nice explanation, this video cleared my doubts. Thanks a lot. Keep posting such videos.

  • Reply Epic Guy September 16, 2019 at 1:50 pm

    We got the .03 by dividing the LED by 100 right?

    I am new to all of this and trying to figure it out.

  • Reply Wasim Khan September 19, 2019 at 7:56 am

    nice video

  • Reply Printingg zonne September 25, 2019 at 5:09 pm

    Agar 2 led use kre to voltage drop 9v battery me
    9v – 6v = 3v

  • Reply Pallav Pal September 27, 2019 at 4:05 pm

    My son is facing the following problem — "I have followed the video from the first. I have used a 9V battery and connected a resistor & LED in series as shown by you. But on measuring the output voltage it still comes 9v. I am not able to retect the error. Please help. "

  • Reply Debojit Acharjee September 29, 2019 at 12:11 pm

    I have a problem with the clculation: 1) If supply voltage is 9v then the resistor will be R = 9-3/0.02=300 but if we try to find the forward voltage from R then why we get negative value? If R=450 then 450=(9-V)/0.02 and V = 9-9 = 0v. So does it mean that if we use a 450 ohm resistor with 9v battety then output voltage to the LED will be zero volts?

  • Reply AMJAD ALI October 1, 2019 at 7:50 am

    how to find the maximum permissible current and applied voltage of a resistor? if I don't have the data sheet of the resistor. looking forward for your hopeful response.

  • Reply Ahle Sunnat Channel October 2, 2019 at 4:52 am

    How you got I=0.03?
    Can anyone explain me?

  • Reply Omkar Pasalkar October 3, 2019 at 7:36 am

    Such a gr8 video sir , thank you

  • Reply brwnyes56 October 6, 2019 at 2:37 pm

    Listening to this video…. I have to watch it several times since the person talking is talking in a Foreign Accent to me. And some he talks too fast thru.

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