How to Drive LEDs - Easy Constant Current Circuit

[@RealationGames]

What a conicidence. I was just troubleshooting a soldering station with this TLV431 and had the part removed to test it on breadboard. I can definitely use this information right now.

[@Dad-ij2qy]

Cool constant current driver, Kevin Darrah. Thank you for bringing this device to my attention.

[@_P0tat07_]

Nice seeing again Kevin! Hoping for more videos from you!

[@dushanp]

At last a video :D We need more cool tutorials and projects :D

[@jeronimomurruni]

Really nice totorial, mainly because you explained pretty well how the TLV431 ic works

[@NicuIrimia]

so, that's what those playing cards were for! I saw the three packs under the some monitor a few videos ago and wondered wiuwt. Very nice content by the way! So much information! Thank you! Great job!

[@RuiSantosdotme]

Thanks for taking the time to post these great tutorials! Good with your new "project". (USA Firmaware!)

[@SaturdayScience]

For 3.3 volt logic I use a NPN Darlington with 100ohm resistor between emitter and ground. Because logic voltage is stable and Vbe=1 then Ie is reasonably stable. You can then series up a few leds from 12volt to the collector. Simple, cheap and effective. Thanks for your excellent videos.

[@karllaun2427]

RE: Cube Kit - Interested in learning more. Enjoy your vids, keep 'em coming.

[@jeffreyevans2947]

Thank You Kevin for a great Video, Actually Thank You for ALL Your Videos!!! I have built this circuit as I am building a Traffic Arrow Stick for the rear of my pickup. I am a FireFighter 25 years and am currently Chief of our Fire Police Unit. The problem I was having was the LED's were dimming at 13vdc and higher. I want to run this using the voltage in my truck, 12.5 to 14.4vdc and drive the trigger points with an arduino. I have 4 - 3v 20ma 5mm Piranha / Superflux LED's connected in series to the circuit as you have it drawn. From 12v to 13v they seem to be constant but over that to 15.5v they would noticeably dim. I was connecting my digital oscilloscope to different points and noticed when I connected it across the 62 ohm resistor it would not dim??? I installed a .1uf ceramic cap across the 62 ohm resistor and the circuit works perfectly! maybe you can shed some light on this but it does work... Thank You Jeff Evans

[@johnacsyen]

When you keep repeating 1.24V, I am reminded of Back to the Future line by Prof. Brown: 1.21GigaWatts!

[@thevideoboy87]

Nice video, will use it for constant current low-power led drivers. Please note : your idea of using this circuit as dummy load @ 9:15. It's not good practice to use a trimpot for currents of 1 amp, because at 1.24v, the poor trimpot will let the internal smoke out! And of course use a larger transistor/mosfet.

[@jordangladden]

If you don't have a TLV431, you can replace it with an NPN transistor with the base connected to the emitter of the first transistor. You then change the resistor to a value that will raise the voltage to Vbe(on) (typically ~.6 volts). For 20 mA, a resistor value around 30 ohms would work (.6/.020). I have used this cheap design many places.

[@bhavinrathod406]

Hey Jordan , I want to use this concept to drive 3w rgb led where 350 ma current running and make it dimmable as we input pwm at base of 2n3904 ,, will it work without any worries?

[@not-my-name187]

Great video, nice and informative. I do have one thing to add, however. The tlv431 could also be replaced by a regular transistor (the 2n3904 works great). Current is set by the same resistor, so I = 0.5 / R

[@RinksRides]

current will drift with temperature. TLx431 compensate for Vin and transistor Hfe changes.

[@ElectronFunCom]

Nice and very useful video, thanks!

[@PilotPlater]

my psu doesn't have a current limit on it, so this circuit could be handy for me for testing new board designs without fire and chaos. :)

[@williammakinen2238]

Definitely carry through with the cube kit!

[@johnmeisenheimer9843]

As usual, another great upload... And beer :)

[@Kevindarrah]

Thanks John!

[@pplo]

can you say if the TL431 would do the same job that the TLV431 do?

[@Kevindarrah]

pplobr yep, just different reference voltage

[@pplo]

thanks pal

[@haz939]

TLV431 that's one IC to remember!! Been wanting a constant current source for a 50w high power LED this circuit looks ideal!! I think an TIP31 will be a good alternative to an 2N3904 in this application. I also would like a dummy load to test DC to DC converters as well!! Thank you.

[@CodeMasterRapture]

Very elegant solution. I am working on something simliar where I use a BD139 in place of the 2N3904 and a BD547 in place of the TLV431. I like yours because you don't need to add another BD547 and 2.2Kohm resistor for a trigger pin. Can you elaborate on your 1K pull up in series with the LEDs? how does this cut off the LEDs when you need to?

[@MrPterasaur]

You can do the same thing with the LM317 regulator in CC mode and it is a more common and easy to obtain part that will handle up to 1amp.

[@jonasgilje1645]

MrPterasaur Will the resistor between out and adj handle it though?

[@GeekLabsMusic]

Is it possible to substitute a mosfet for the load transistor?

[@bhavinrathod406]

At the base pin, can we apply pwm and dim the LEDs ?

[@amratsingh5206]

How far can you push the TLV431, If I use PWM signal on the control pin. How high can the frequency go? Are transient rise and fall times fast enough?

[@bcwhite153]

Hi Kevin. I tried using the TLC5490 in my project and found the timing to get this right was a bear. I found the 18 channel ws2803 to be much much easier to program without all the timing issues. Also, 18 channels dived by 3 per led worked out nicer as I didn't have to add a second chip just to use get two channels. Just wondering why you used the TLC5940 instead of the WS2803 chips. Great videos and great projects. I love it when I get notified that you have a new video. Thanks.

[@SirArghPirate]

Whats the advantage over the lm317 set up as current regulator?

[@Isuis66]

According to the datasheet the TLV431 switches on much faster than the venerable LM317.

[@farazsayed5730]

I think I figured it out just after I posted. The extra voltage must drop across the transistor. When there's a higher voltage the current regulator pulls the base lower, producing a larger potential difference or voltage drop across the collector to emitter. This does mean you need a transistor with a Vmax above Vcc. And that the transistor could get hot if Vcc is big?

[@farazsayed5730]

Great video, it's a useful component to known about. I'm confused a bit on where the extra voltage drops. Does the led have Vcc - 1.24 across it but it doesn't blow because of the restricted current? Or is that extra voltage dissipated elsewhere in the circuit?

[@MrDexter9i3]

Soooo, I guess this doesn't apply to multiple diodes, I mean, I'm making some LED rings with SMD diodes, and need to fit them as close as possible... Can I make some sort of a voltage regulator that will drop it from my battery source of 12V to 1.8V needed for red LED's and then connect several LED's to the regulator in parallel...this is kinda off topic, but I would appreciate the answer... :)

[@jp040759]

This should work with driving a power transistor too I would think. Something like a TIP41. It should work with a TIP120 darlington. This would allow for higher constant current load apps. The TL431 can driver 100 ma loads so there should plenty of base drive current available for driving those power trannys. Thoughts?

[@SmallBoysProductions]

Likes the video before watching it :D awesome and very educating videoes!

[@Inquire98]

Hello, "Thank You", thank you very much. PLEASE any additional information about your kit. I look forward to hearing from you...

[@QDuckselbstreich]

your videos are very interesting and usefull thx a lot!

[@KHLin]

Thanks for the great sharing!

[@VolthausLabElectronics]

Def thumbs up on the wall art. I have an LM7805 poster on my wall (yeah made it myself) Just another indicator that, YES i have no wife ha ha. good video too.

[@scottmarshall6766]

Good info. I have a few places it may be useful. Thanks!

[@imranmohiddin5303]

Can I use this for Laser diode 445nm of 2watt power which need constant current of 1.7amp?

[@GregKarz]

Could you do a video on multiplexing vs using shift registers, please?

[@Bllinker]

6:45 Well, plus 0.2V for the collector-emitter drop, but that's negligible :)

[@mbnesley]

great video, the data sheet says you can have the output up to 6 volts how is this possible with the reference pin being at 1.24 volts i thought only that much can be applied?

[@ImaginationToForm]

Good information.

[@saarike]

Very interesting. Nice, thanks a lot.

[@MyCatHatesYouDotCom]

Dropped the pen. Too much beer. Love the video.

[@pakcheesy2]

Is the kit done?

[@FutureAIDev2015]

Why is it that for a current source, current flows out of the load into the transistor? Shouldn't it be the other way around?

[@jkrupke]

I would like to be on the list for a RGB cube

[@Edmorbus]

Bravo Thanks for sharing

[@wb5rue]

What happens if you want 1A of current, large wattage resistor? If I'm driving a 10 watt LED at 12volts and it needs 900ma that's a BIG resistor.

[@AlexLaw_Qld]

900ma at 1.24V you need 1.38ohms. Thats going to dissipate under 1.2W. You can get that with a good safety margin with 2 2W resisters, in parallel, and selecting standard values, use a 1.5ohm and an 18ohm.

[@macro820]

This is going to be hot

[@johnallan6350]

How about light for the camera so we can see the video! Then it would be good.

[@KillJD]

I'm really confused about the 1.24 part of this. Hence I'm not getting the rest.

[@jeffreyevans2947]

+KillJD The TLV431 is a device that will try to maintain that 1.24v across its reference and anode pins by shorting itself out between the anode and cathode pins thereby turning off the transistor. this happens very fast so as to keep the voltage stable across the resistor. To size the resistor and to set the current, I=E/R, for 20ma, divide the voltage 1.24 by the current .02 to get 62 ohms.

[@drphu]

Lm334 works better as long as it (the lm334) sees 40VDC or less.

[@MOJICA7257]

Why the shunt regulator is in reverse? thnks im Noob :)

[@XenophonKtistakis]

It act's like a zener diode. TLV431 it is actually a programable zener.

[@MegaInformazione]

shot during the total eclipse?

[@TeddyB1957]

Good information but you need to get some light on the schematic. Too dark, hard to see for people like me who are visually challenged in low light situations.

[@liney118]

You can aready buy kits for $40

[@e.h.lipton73]

Very nice! But hey, I have spent a small fortune on package mail and small quantities of electronic components. I have so many even I can't remember what they do or where there shelved. How about showing your intellect by directing us novices on how to use discreet parts,, like transistors and such too BUILD thee ic you mentioned. Or how to BUILD an op amp with those part's,, modify it with inverted and such tutorials. I know for one, I have given enough money towards the corporate capitalist's with out much return!

[@gajimafeet]

Design a system where u can drive 6 strings of leds from a card battery for 6 hours Ull make monkey we have continuous power failures from our only supplier

[@defamatt]

this is useless. just connect led to batteries and good to go

[@johnolsen1452]

+MrDefamatt™ - 1K You are so full of your self -- hang around, you might learn something (if you keep the comments down). BTW: Do you sell LEDs? That would be a good way to 'quick fry them'.

[@GeekLabsMusic]

Is it possible to substitute a mosfet for the load transistor?