LM317 adjustable current source/regulator

[jimw]

Very few people know this, but, it does NOT have to be an adjustable regulator.... you could use almost any 3 pin reg such as a 5v reg still works!

[jonasaskenobis]

Short and on point, thanks :) for those who are confused by schematic, the rheostat is connected like a potentiometer with R2 going into the viper

[MathewPendleton]

your the first person to actually make this clear to me. Thanks!

[howardsimpson]

Not only a good regulator tutorial but great bird sounds as well.

[hugobracamontesbaltazar]

Excelent!, I was looking for a adjustable current circuit based on LM317, thank you very much.

Regards from México.

[alexandervelasco]

H Looking for an output of 10~150mA. I chose R1 = 100, R2 = 1k, R3 = 10k. This should put me at a maximum of 137.5mA and a minimum of 12.5mA. With an input of 13V (to reach get the needed 3V headspace), my minmimum current is 20mA. Any ideas why its 20 and not 12.5mA?

[shubhamshukla]

sir i want to make a cc/cv using 2 lm 317 and i understood the circuit but i want a dynamic range of current i want current upto 1.25/1.5/1A so please suggest me best resistor values along with the power rating and which are commonly available

[libanhussein]

Excellent tutorial! Quick ?--> I'm still a bit confused about the potentiometer network. Could I use a 3 pin potentiometer, with one pin connected to R1, the middle pin connected to R2, and *the third pin connected to ground*? I noticed the 3rd pin was connected to the adjust pin but have seen these connected to GND typically

[imignap]

Very nice video, I didn't even think to look at with a voltage divider to find V_R1 knowing V_R2, it didn't occur to me until later of course. Just note the total current out includes both I_R1 & I_R2 = 1.25/R2 which would bump up your min & max current amount (i.e. +1.25V/R2). You also want to be mindful of the maximum wattage going through the pot i^2*R3.

[Danyel]

I was using this circuit as a driver for low-power diodes. One blue, one red, one IR. They are all rated for Ith ~ 25 mA so I did the calculations for making I_in ~ 5mA and Imax ~ 40 mA. However, when I connected them, they all behaved very differently. Is it possible that the load (diode) affects the output of the circuit?

[jp-umfr]

Hello Lindsay, I'd like to thank you for giving me a leg up or maybe a leg re up into an old hobby. Almost 50 years ago I was into valve amps. Google Mullard 20W - The National Valve Museum, yes I'm that old.
I was looking around YouTube and came across your video above. I was particularly interested in your current control. I had not touched electronics since my valve days and the 'gubbins' you were using intrigued me. I decided to have a go. Mind you picking a 60W soldering iron up by the wrong end made for an interesting start. I had had 410V across my nose but that's another story.
Thanks to people on Forums and YouTube videos like yours I am now into 2N3055's LM723 and all the bits for a bench power supply. Strangely enough though I think yours is one of the few videos that goes into a simple current control. I needed it as I wanted to play about with LED's. Things have moved on a bit since then but I just wanted to say - Thanks Lindsay.

[raulperezgomez]

Hi Lindsay. I am getting very confused. I am newbie trying to understand the calculations from this circuit. Could you please explain how it should be calculated taking into consideration all the resistors and then explain where are you taking from the equation you use on the video? Thanks in advance.

[briansegura]

Hello. I was trying to have an adjustable 4-20ma constant current source using your circuit and did not get the results I had hope for and was hoping you could help.

4-20 ma, using 250 ohm potentiometer

I calculated R1 = 312.5 ohms
R2 = 62.5 ohms
R3 = 250 ohms

I did not get much current adjustment

Any ideas??

[Mohitkumar-evhe]

Wow thats so easy ... but only when i saw your video...thank u

[vernonbosshard]

I had this before but I can't recall it now.

[DennisMurphey]

weird application i am considering if you are still about. My Model Train has a smoke generator. it vaporizes an oil to create white smoke that we puff into the air thru a Mini DC fan. The housing that do this are usually aluminum and a fixed size. My trains are S Scale and unique from 1950. I have made a Smoke housing that works via my 3D Printer. But if it over heats yes it will melt. I can use a 10 Ohm Heater to make good smoke at 9 volts. But the track power available ranges 5 to 20 AC Volts. My little DC Can motor needs DC so i run the track power thru a Rectifier and get a reduces DC volt, then for the Heater I run thru a 7809 With some caps to maintain the 9 volts. But it is not very stable and i have had low smoke and over heating issues. I wanted to see if i can use the 317 with a termistor Sensor to use Heater Temp to regulate the 317 output. So if it gets too hot the 317 regulates V out down. Is this practical in any way or am i dreaming up stuff that can not be done. My issue is space. My trains are not big so i need small and simple circuit. Can this be done?
Dennis

[DaroWannaKnow]

The calculation on Ir1 is correct, but you forgot to consider that final Iout current is equal to Ir1 + Ir2... I get that you omitted Ir2 since is much smaller than Ir1. But this may really confuse people trying to learn

[MACYNET]

Wich lm317 alternative with less drop out?thanks

[jamest.]

I am completely new to electronics, and trying to learn on my own, would a heatsink be needed? When used as cc supply? I have a 18 combined watt rgbwyuv LED, I'm wanting to make a driver to power all the LED's it is a "all in one" LED the size of a 3-5w bead, the kwd is red, green, blue, white, yellow, and UV/Violet, basically all but a IR LED, I am building a small portable light, powered by a couple 18650's in series if I must, I think using a buck would be better than boost, although USB charging option would be a plus, I'm thinking of using the linear regulator for 2-3 supply's, to get close to the LED's peramerters, then use a resistor, for further limiting, or is there a easier way to do this?? I thought about using a rgb controller, or two, only use it with the rgb and the wy/uv! And just use resistors for limiting, crazy dumb questions I know, and very complex to light a LED!! Thanks!

[vishal_on_yt]

In many of the circuits, ppl are using a capacitor in the beginning. Can you please tell what purpose it is serving