How to select resistor value for LEDs
ฝัง
- เผยแพร่เมื่อ 14 พ.ค. 2024
- Using Ohm's law to help with selecting the resistor value for LED circuits. There are online calculators and apps, but I think knowing how to calculate it yourself is beneficial.
- วิทยาศาสตร์และเทคโนโลยี
Another great tutorial, that was so simple to follow, even I grasped it. Thank you John.
The explanation of how to calculate using 2 leds was EXACTLY what I needed thank you.
You're a great teacher for a NOOB like me. You talk slowly and clearly - thanks for this great video. Cheers!
Nice tutorial -- thank you. I'll keep an eye open for more.
This was a great video. Very useful when the whole construction will be powered by battery. Thanks
It brings back fond memories from the late 70s. As a kid, I had picked up a few red LEDs from Radio Shack, without really having a use for them. Until I looked at my slot-car set. The cars had grain-of wheat incandescent headlights, but no tail lights. I measured the track voltage range, which varied with the hand-throttles, then I found the maximum current on the package somewhere. I worked out the resistance needed using Ohm's law, drilled some holes, glued them in, and voila. Tail lights on my slot-cars.
Since an incandescent bulb is a regulator of sorts, I could have wired the LEDs through the headlights to stabilize the LED light levels throughout the range of voltages somewhat. Since resistance is very low when the bulb filaments are dim, and high when the filament is hot, it would have allowed higher current to the LEDs when the car was going slow, and limited current when the headlights were bright, and the car was going faster. I'm not sure if the voltage drop would have been sufficient, so perhaps a shunt-resistor may have been required.
I remember that if you accidentally got the polarity wrong on those LEDs in those days, they burned out immediately. Thankfully not the case any more.
The bug in your resistance formula comes in at 7:58 and I smacked my monitor to kill it. Great video bug and all.
What harm did the bug do to you, man? Show some compassion to innocent animals and you shall be saved from hell.
really clearly explained. :) Im sure people starting out will find this a godsend. wish someone has explained it this simply when I first started. :)
Thank you so much for this wonderful tutorial.
Nice and simply explained.
Venkatesan S ;(
I'm convinced, this is the voice of Felix from Wreck It Ralph. Good video btw. Thank you for sharing.
Very good video, simple and easy to understand.. I'm little bit ashamed because I never did the calculation, I always used any resistor in the 270omhs range and if the led was too bright or too dim, I changed the resistor :-)
I use 350 ohm first, and then go lower if it's not bright enough, but same here.
Remembered most of the high school physics I needed thnaks to your video
Very clear explanation. Thank you.
Very well done tutorial!
I loved the video in all but I just need to know what what fraction of a watt my resistor needs to be for each led
Great video. When you were explaining the reason for the same resistance value in the parallel circuit as opposed to the series circuit, the current was doubled but the voltage drop across the LED's is one half the value of the series circuit, not double. That is the why the resistance value is the same. E is directly proportional to R, while I is inversely proportional to R.
Great tutorial, thanks!
Nice vid, it wasn't able to answer a question I have so I'm hoping you can. I bought after market tail light assembly and the brake and day running lights are the same bulb. No additional resistors or capacitors were included. I was wondering how would I go about wiring them so the load will restrict wen not hitting the brakes. Thanks for any help and I'm re using the stock tail light harness.
Parallel LEDs in a Red/Green (single LED 2 color LED) pair (street light scenario) would benefit from the last circuit shown. Is there an issue substituting the single color in your example for a 2 color LED (reversing one orientation)?
Also - Resistor on cathode or anode normally, and what about on 2 color situation?
Thank you this is very helpful to me
Nicely done man! This is very informative 😇, many thanks.
very useful thank you.
Very helpful video
Some of it i understand. I wished I was smart like this guy.
What if you don’t know the fwd voltage drop if the LED?
Got a bunch of old LEDs, no idea what they are (some IR).
So nothing to calculate without that figure, you’d be trying around until you get there...or not?
Very good presentation
Thanks for the video. I have a quick question about my third brake light on my car which are LED’s. There are 4 lights in a row on a metal strip with a plastic backing. There are 2 light blue cylinders between each set of bulbs which say 240 J I’m guessing that’s jules. And it says .07 on the same cyclinder. The cylinders are tiny maybe the size of a large grain of rice. Sorry for my lack of terminology I’m trying to learn as we speak. On the far left there is an even smaller black cylinder. All the cylinders have these metal connections on the sides and are connected to the metal strip. The metal strip sticks into the plastic backing and forms a socket in middle on the back of the plastic backing. Sorry I’m typing so much I don’t think I can post pics on TH-cam and I really want to figure out if this is fixable. The lights don’t work and I want to know why. As far as I know the whole light went out all at once. I’m trying to figure out if I can replace some of those cylinders would it fix the light? If you can’t answer I understand thanks again for the knowledge.
Please tell me why in my preamp circuit where I include a blue LED powered by the 48 volts from the phantom circuit in my mixer- I can use between 2.2 megs to 5 megs and the blue Led shows up nicely.
If i have 20 watt led nd i want to on those all on 220 watt so wt resistence should i use nd if i use with my byck then wt resistance nd wht circuit should i make to start pls help tell me.
hi just want to ask. how can i compute if how many ohms should I use to light up a 40 smd led (blue) which has a 3.2 volts each and 20 ma each using a 12v battery (motorcycle battery) (when charging goes to 13 - 14v) thank you and i will wait for your answer thanks
should i use resistor if i have the same volt from battery to my led.
battery 3volt led 3volt..use resistor?
Great info💯
If you have to add resistance to a circuit in order to run the LED, does that counteract the energy savings? Do the resisters plus the LEDs burn up the same power as the standard bulb, but instead of having the energy loss through heat in the incandescent bulb, the heat is now generated in the resistor?
Great video. How did you do it without injecting annoying background music into the video? I thought it must be a TH-cam rule that electronic content videos must have annoying and unnecessary background music injected. Thank you very much for you doing it the right way.
I thought there was a bug on my screen @7:50. Good primer info, thank you.
I've got an LED running off of 5v with a stock resistor of around 350 ohms. can't get this replacement to light up. are these so far off from one another to where that restistor value is way too much?
In the case of the parallel LEDs, why not put the same 5 volts as in the first example (the one on the left with a single LED?)
does this apply not just for the led but for also things like buzzers?
Great and simple.
Am using a 12v automotive lead acid battery and it can output around 10A consistently (it can light 130W 12v halogen without any issue). So to light a single 3V led from it, do I need a 0.9ohm resistor.?
tnx for sharing sir john..
Good video, thanks!!!
It wasn't mentioned in the video but generic LEDs come with a set of generic numbers for typical forward Voltage (R:2v, G & Y;3v W:3.8v, blue:4.5v) and Current (usually always 20-30mA). These are only approximate, when you buy the listing should give actual - but it's usually good enough. then always round resistor values up not down, the higher the resistance the longer the LED will last (but it will be dimmer).
Google "current rating of led by color" to see typical ratings.
If you work with "ordinary" LEDs and common voltages (3, 5, 9 &12v) the resistances are pretty standard and quite forgiving 56, 150, 390 and 470ohm are pretty common values.
google "LED resistor calculator" or visit led.linear1.org/1led.wiz this site does the job for you
Thank you
Where did you get those forward voltages from? Because only the Red one is close, the rest is wrong.
I never saw a 0.020 mA LED.
Youve quoted what's wrong - Shame you didn't take the time to give the figures you think are correct.
I'll take the currents, had a brain fart! I was thinking in mA and then entered it longhand - I've amended that to mA.
I did say that the voltages were ballpark numbers - often white is quoted at 3.4@20mA I'd usually work with the numbers I quoted because I find they work. As I said intended to be approximate with a safety margin I'll stand by them. Unless I'm particularly pushing as I also said I'd always round up and put a generous resistor into my stuff, things last longer that way.
Feel free to give your take - none of the numbers are set in stone - and I'm sure we all have had different experiences.
Andy White Well it's good LED are voltage limited Because they last longer heathier on battery.
Thank you sir Andy I learned also from you
Is there any universal resistor value for use with LEDs of different colors? More or less?
what are the specs of the resistor you used on this string?
Love this thumbnail!
Hi sorry i try to understand but its not for me. But can you tell me what kind of resisters i want to dimmer a 12v led thanks.. ?
I am trying to build a 20 LED voltage checker for the leisure battery in my camper van. I watched a video where the guy made one with only LEDs and resistors, but his was only ten LEDs. Could you make a video explaining how to figure out the correct resistors needed for each 5% increase? Even after watching your video I can’t figure out how to do it. As the voltage rises, more LEDs slowly come on and vice versa. I have read conflicting numbers for what a fully drained battery is ranging anywhere from 10.5V to 11.4 V and 12.8 to 13.6V fully charged. Does that affect resistor size?
Thanks for making this video, I learned something...
im confused. for the first example if instead of 20ma, what if i had 1800mah? how would 2/18 or 1/9 get me my ohms....
Blue ones so often appear really bright.
I often use 3.3k or more with them.
1mA usually much more than enough!
What if i use 2 LED in series with a 4.5V power supply? Does that mean i don't need a resistor?
easy pleasie. good show
where did you get the .02?
Thank you sir
A useful video might be to just set your PS at 20mA and check the voltage drops on a variety of LEDs.
There is even simpler method which is U=(R1 +R2) * I . R1 is the resistor R2 is the led résistance.. If you want to know which resistance to use just do R1= R2- U/I
Thanks for the video, it was most helpful. Newbie question: Does the resistor need to be in font of the LED? The reason is I have designed a circuit with three LEDs but only one is powered at any given time so I joined the ground ends of the LED's and connected a single resistor between them and the ground. However I am now doubting the correctness of this approach.
This sounds fine to me and is a smart way of saving components since only one LED is on at any given time.
hi, nice video will need to watch it a couple of times, but at 4.20 you went on to the calc for Watt, why do we need to know? is it just for the sake of elec consumption or is it for the purpose of using the right parts so no damage is caused? thanks in advance
Yes, resistors have a max watt rating and you want to be sure you don't exceed it.
@@JohnAudioTech ahh OK, never knew that, I have watched several videos I think u might of been the first to mention that
So, by this logic, I should be able to hook up 3 leds in series with a 9v battery and not need a resistor?
what size cables do i use in my bread board is it 22 gauge? i should mention that the leads on the metal film are thinner then the composition resistors. radio shack sells traditional composite resistors that are twice the price of the film are they worth it.
22 gauge should be the thickest. Cheap Chinese resistors use the thin leads. Quality metal film resistors I get from DigiKey have the same thickness.
Hi , I am going to make a LED light cct for 2000 LED's what would be the best way to the layout? series or parallel? according to your video, I would imagine it was a series.
Parallel, and power injection about every 100 leds.
Data sheet? Where did you get that?
so using a linear circuit with for example 9V battery, how many leds could i power up to make a diy lantern for my kids project?
Depends upon how you are connecting them. If you are connecting them in parallel. The Voltage will remain the same but the current will increase. E.g. if the LED's darw 3 volts you will have to add a resistor to drop down voltage from 9v to three volts then depending upon the number of led's you have the amps required will increase e.g. if 1 led draws 20mA and you have 3 LED's then the current flowing through the circuit will be 60mA but voltage will be 3. Now of you were to connect in series (one LED after the other in a chain) you would not need to add the Voltages instead of current. So assuming each LED draws 3Volts with a 9Volt battery you can run a maximum of 3 LEDs in series because 3 + 3 + 3 Volts = 9 volts in this case the current required for the circuit will be 20mAmps. I would think using 3 LED's in series would be better as you do not need a resistor. But if you need more than 3 LEDs then you can either 1) connect the LEDs in parallel after a resistor here you can use 9volts but the more LEDs you add the more amps (current) is drawn and the shorter is the life span of the 9v battery OR 2) Add another 9volts battery so you have 18 volts. Now you can connect 9 LEDs in series without a resistor but here you need more batteries. The life span of the batteries will be longer because current drawn is constant. This is more bulkier.
Love the thumbnail
A quick average I use is 1000 ohms per volt for about 10ma and 500 ohms for about 20ma. It doesn't calculate the resistor power dissipation, doesn't work well for voltages below 5 volts, becomes inaccurate with a series string of LED's, becomes more accurate the higher the voltage is, and doesn't really work for the blue or white LED's. It's only good for getting you in the ballpark.
I am using 66 yellow led light for making series with 3 resistors of 100 ohm and it got burn .... I even tried using 6 resistor but same problem occurred...can you please help me??? Where am I getting wrong
There is a app called wova in the Google play store that will do the math easily. To find the wattage of the resistor just multiply the voltage drop across it times the current to get it. Twenty milliamps would be .02 when entering.
I have an LED bulb I removed from a "Finger Light" that was powered by three 1.5 volt hearing aid size batteries. There was no resistor in its set up, just a basic on/off switch. I want to install it in the nose of a toy drone that uses a 3.7 volt lipo battery. Do I even need a resistor added to this circuit? Just wire it pos and neg from the drones battery's circuit board terminals?
The "finger light" was relying on the internal resistance of the tiny batteries. The toy drone battery can overdrive the LED, so it is better to use a resistor.
I have a question, what if i want to power an LED using a Lead acid 12v battery but of course the constant voltage is not going to be 12v because when it is fully charged it goes up to 13.8v. Do i take an average of that or just stick with 12v. thanks
I would design for the highest voltage so the LEDs aren't stressed from over current if the voltage is that high for long periods or you could use a constant current source driver.
what if i don't have a data sheet? like the ones from E-Bay
Connect an appropriate resistor and power supply and measure the Vd across the LED.
Datasheets can be expensive... I had to pay 10 times the LED price to download one... 😉
But where did you get the 20 milliamps figure in the first place?
The datasheet or manufacturer of the LED should be able to provide you with the recommended operating current for the LEDs.
I'm sure that it is mentioned in the data sheets but in school, back in the 70s we were told that a typical LED is around 20 Milliamps in the 80s and the 90s the white or blue LEDs it was suggested that a 40 milliamp current would be needed. Not always but myself I rarely ran across one that used a lower current. But since the 00s I haven't been in electronics hardly at all. Can not focus on the small parts.
Buy glasses.
Are you sure about the current of the LED? I did a quick test with a 3.7V (cellphone battery) and a white LED, the amp meter showed 1.4mA (0.0014A) and using this value in the formula spits out very high resistor values like 2kohms for 4 LEDs at 15V
Current rating may be various depending upon supply voltage. P = IxV , so 3v LED conception 14mlA at 3.7V
JAT is correct in what he's showing - You should always design to the figures in the specsheet, that's designed to achieve the optimum (not necessarily the "best"(for you) ) results and protect the LED. In real life other factors such as wire distance/resistance line capacitance/inductance ... la la la may need to be factored in depending on the environment. So when you go to the production stage, adjustments might be needed. If brightness is an issue you can overdrive drive the LED to the point where it only lasts for a few hours rather than the spec rating of 50,000. Actual readings can significantly vary depending on real life requirements. But you still always start from spec....
And in some circuits small differences result in (relatively) big changes in values. 2 v (3->5v) results in a jump from 50 ->150 ohm. That's just the way the fractions work
Don't worry about all the calculations. Gone on line and you will find charts that give you the resistance value for various voltages plus different colours require different resistance. Different colour LED's require different value resistors. The project I am working on operates at 3 volt. The yellow LED requires a 47 ohm resistor while the blue LED requires a 10 ohm resistor. If I get the resistors around the wrong way I will blow the yellow and the blue will not come on, Down load a resistor value chart and pin it on the wall.
Or just use your multimeter to check.
@@imho2278 Hi, the different colour LED's have different voltage ratings, you will have to check a data sheet for the voltage rating. When I know the voltage rating I then look up the resistor required for the supply voltage, his could be 3v, 6v, 24v. When I know the resistor vvalue, say it is 220 ohm I add a little bit extra resistance. The LED will last forever.
What is table of 3w, 5w, 7w, 9w, 12w and 20w LED lights capacitor condensor and Resistor value in circuits?
Anil Haldarwala ur content no.?
Wonderful voice
How to get voltage drop?
hey mate :)
I want to place 9 uv leds on a 5v source. how do i do this? uv leds need 3.2v so in series is not possible i guess. i have tried with a voltage regulator to drop the 5v to 3.18v do i need to place a resistor for this? 1? or on every led a resistor or what do i do? the led's seem to burnout realy fast. thx
the specs for these leds say: 3.2v - 3.8v and forward current is 20ma
3mm led
I would put two in series (6.4v) and select a resistor to drop the remaining 2.6v. You'll have 5 groups of two LEDs with resistor - 10 LEDs total. If you have to have 9 LEDs, you'll have to treat that one odd LED with its own resistor.
I cant put 2 leds in series because i only have 5v :)
@@kvmods Oh sorry, not sure why I was thinking of a 9 volt supply. Anyhow, 9 LEDs x 20ma = 180 ma, 5v-3.2vf=1.8v. 1.8v/180ma= 10 ohm 1/2 watt resistor limiting current to the 9 LEDs in parallel. This is fine if the LEDs are of good quality (matched). If not, use a 100 ohm resistor in series with each LED.
@@JohnAudioTech thx :) thats a clear answer
How about,9v?
So if I have a 6w power supply and my LEDs need 6w what should I use as a resistor?
I'm using 4 1.5v LEDs linked together they are IR LEDs btw
I got confused by this. It seems back-to-front to me. Now that I "get it" watching it back I see where it goes wrong. He doesn't state the value on the datasheet for max continuous current, so when its value comes up much later (0.02A) I didn't know what or where that value came from without use of a meter/measurement.
This tutorial, and others like it, led me to build up an wonky mental model that the current in the circuit is somehow a property of the circuit and its components and the supply, perhaps the type of LED happens to draw 0.02A, and that I need to therefore determine the *correct* resistor for that current with the voltage drop of the LED according to its datasheet.
The right way to look at it is that you're choosing a resistor in order to limit the current in the circuit to prevent the LED from pulling too much and burning itself out while remaining as bright as you'd like it. So the value I (current and thus brightness) is determined by your choice of resistor, not the other way around; we're trying to find a value of R that gives I. It's not that we have I and we need to "figure the value" for R.
You talk about either using or not using a driver vs a resistor. What is the difference and why use one or the other? Thanks
If there is a large voltage to drop across the current limiting resistor, it may be better to use a driver circuit. This is true with higher power LEDs because a driver circuit adds complexity and cost to the circuit.
Thamks
good video
just adding a 10k in series works well most of the time.
10K!?!! It has to be damn dim at that point. Even 2.2K is a bit much. You just want a noticeable change, not day and night simulation.
yea sir can you make some more videos
Paralleling LED's is a bad idea. LED current increases exponentially with LED voltage. Any small mismatch between "identical" LEDs will cause one to draw significantly more current and be brighter than the other. You can add a small value resistor (10 ohms) in series with each of the parallel LEDs to correct for device mismatch, but you would be better off just giving each LED it's own voltage dropping resistor.
Called an LED current thief when I was in school back in the 70s.
Jess Stuart
You beat me to it with your comment. :)
From experience, even matched LED's will start drifting apart over time when run in parrallel on a single resistor. I assume it is from uneven heat distribution causing accelerated aging of one of the LED's, which gets worse and worse the further they drift apart.
Would i need a resistor if I have 3 3v leds in series and a power source of 9v?
Den Lim that sounds problematic; you should always have a resistor to limit the current to a safe level, but since the resistor itself will have a voltage drop, 9 volts supply seem too little, I would recommend using 12 volts or higher, and do the calculations based on that voltage.
On the other hand, if your supply voltage is limited to 9V, e.g. from a battery, you should probably connect the LEDs in parallel, with a resistor for each LED.
No
No but you need higher voltage source that must be greater than 9 volt e.g 12v, 15 v
No yu dont.
The answer is above me.
Hmm.....we'll try this one again ..when it's not midnight . Lol good info. Tho. Just to tired to comprehend at the moment
Thanks..
Lets say that my power supply for example is 50vdc, Can I still use this to power my led? 50vdc-3vdc=47vdc 47vdc/.02amps = 2,350ohms / Would this OK for the LED?
This would work fine although it is very inefficient as you would be wasting almost 1 watt in the resistor and the LED consumes only 60 milliwatts.
JohnAudioTech So the voltage really doesn’t matter AS LONG as you have the correct size resistor. Right?
@@tomatexelon Yes.
I am using a 30W RGB LED, what kind of resistor would work for using it with Arduino UNO R3.
Sounds like you would want a driver circuit for such a powerful LED.
@@JohnAudioTech can you explain it with more hardware examples. That'll be helpful since I don't have any electrical background
thank youu
how many ohms resistor can i use to reduce 12v to 3v
just resistors won't cut it ;), need to make a step down board
You need to know the current through the circuit. Other wise it is just a WAG.
Assuming you are talking about standard LEDs - that approximates to 3 v @ 20mA (depending on the colour).
So somewhere round 470ohm should be good.
That's calculated as 12-3=9v to drop .... R=v/i = 9/0.02 = 450ohm .... the nearest stock resistor is 470ohm (always round up).
In real life you could use any value between 400-1500ohm - depending on what you feel is acceptable ... bright = short life, dim = long life
use in4004 diode
9/I ohms.
Thanks for putting warning in thumbnail
thanks
I find it strange that this info is so simple and easy to find and yet I STILL frequently find retail packs of LEDs that don’t give me the specs I need.
Emmett Turner
If you own a multimeter, you can measure the voltage across both leads of the LED while powered up, then recalculate and pick a more optimal resistor value to pair with the LED. The maximum current is usually rated at 30 mA, but if you target around 10 mA, you'll still get very good illumination and longevity.
What a coincidence, I did this little exercise less than an hour ago
My question is: in the parallel combination, if you used a 3V blue led and a 1.8V red led, what would happen?
The LED with the lowest forward voltage drop would only light, meaning the red LED.
Plz what is the difference between electric for audio and electronics
Please help! Also need assistance with my rodin coil set up.