Constant Current Source
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- เผยแพร่เมื่อ 26 ส.ค. 2017
- How to use an LM317 as both a voltage regulator and constant current source.
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Please watch: "Diodes: The basic building block of all digital circuits"
• Diodes: The basic buil...
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Great information, just what I needed. I recently salvaged the guts from an old Gilbert Dot Matrix exit sign. Gonna make it into a decorative piece and hang the bare circuit board with the LEDs on my wall. Original supply is a 120 to 12 VAC transformer feeding a driver board for the LEDs. Need a constant 5.4v at 720mA. 108 LEDs total, 36 sets of 3 in series with all the sets parallel. This'll do nicely
About the drift and sensitivity issues with that small trim pot. I found in usage the constant current output will vary based on temperature rise of the LM317 and more importantly the current setting resistors that are placed in the circuit. These components should be able to handle the power dissipated through them, and then some, to make sure the temperature doesn't cause changes to the resistance. Depending how accurate we need the circuit to be, it's worthy to consider heat sinking or cooling these components. Additionally, if there is a certain target current range you will be working with, consider having high wattage resistors handling the lowest current in the range, and adding a trimming resistor in parallel to decrease the resistance for that higher current in the range.
For instance, I just built a 100 mA constant current source, and I wanted some adjustability and stable resistance by minimal temperature increase. I chose the following: (27R, 2W) || (27R, 2W) || (120R,1/2W + 100Pot) for a target 12.5 ohms near center of the pot. This potentiometer is 20 turns type capable of fine adjustment, instead of a 3/4 turn which lacks precision. The current rating is less important in this case because most of the current travels through the two 2W resistors, much less goes through the 168 ohms trimming branch. I found this accurate enough to not require cooling, although I need to make my current adjustment at a nominal operating temperature.
The reason I chose a 120 ohm fixed resistor in series with a 100 ohm pot - and not just 200 pot? Avoids the risk of having the potentiometer set to 0 ohms and shunting out the other resistors, causing an unlimited current situation.
I suppose I could have also considered special zero temperature coefficient resistors, but I wanted something easy and inexpensive to source. Like you , I find breadboarding the solution making a perf board or etched PCB.
Very few people realize this but.....just about ANY 3 pin regulator can be setup the same way as a constant current source. It does NOT have to be a variable regulator.
Excellent video, easy to understand. Appreciate your self deprecating sense of humor. Not taking yourself too seriously in this complicated world. (Was meant to be a compliment, hope it is taken that way)
Years ago I fixed a couple of modems they were 6V. but had been used with 9V and 12V plug packs, the 317's were totalled, I replaced them and the modems came to life, no apparent damage at all.. Cheers.
David Price very cool. Yeah the 317's will burn out and USUALLY protect other components.
That's a good one Paul, simple robust and elegant. Could be handy for me, my psu limits current, but only at max. 4-5 Amps. IE. it's not adjustable for lower values. Those LM317 critters are excellent, they will sacrifice themselves rather than damage the circuit they feed.. gonna make me one for sure.. Thanks..
Thanks very much. You are a great teacher.
Thanks man
Crazy heatsink tip: use tuna/sardine cans and toothpaste(white color one) as thermal paste. Just temp until you get one.
you drill or make a whole in the can and may also fill it with water, about half or a quarter. Do this only if it's needed!
I learned this from an old guy that used a soop can as a heatsink for some guitar amp.
igrewold tuna-can heat sink you say....I will try it. I've done the toothpaste trick in the past. It works Just fine. Thanks!
Thanks to you too man, this guy got some interesting info on using PCB as a heatsink.
store.curiousinventor.com/blog/pcb-as-a-heat-sink-calculating-trace-width-for-given-current
Dude this is interesting, since I can't afford anything ever really I make my own resistors and was thinking instead of just having bare nichrome since I don't make casts for them since I can't afford that either, doing basically this, only submerged in mineral oil in a non conductive container. ;p
Man, your content is soooo goooddd... it is helping me a LOT! Thanks for creating content for us!
You probably dont give a shit but if you are stoned like me atm then you can stream all of the new movies on InstaFlixxer. Been streaming with my girlfriend lately :)
@Hayden Dominic Yea, I've been using instaflixxer for since november myself :)
Very nice, now I can make my own led driver.
dwpetty3723 just make sure you put heat sinks on those ICs. The LM317 is good to about 200ma in free air, above that you will need some cooling. Let me know how your project goes and if you need any help.
Great video and I learned something! I see they sell a few variants at Banggood.
This is a great learning area. Thanks for sharing your time and knowledge. I have a favor to ask of you, can you make a constant current source consisting only of transistors? variable voltage constant current....
THANK YOU SIR FOR THIS VALUABLE INFORMATION.
Hello and thanks for the good video. The current is limited but if the load res is high, the current might be lower than the limit current? Another thing is there will be another coltage drop on the second stage lm317. So the output voltage is not the set valur on the first stage lm317?
I'm not sure but if you could make to changes add a link to the other two videos that you have done with the Lm317 and secondly add a play list for the Lm317. I Enjoyed this Video the most out of the 3...
Your the Best thank you.
Hey Man,
I didn't know how else to get in touch but thanks for checking out the stream yesterday!
Check out a video by Marco Reps on the Ts100, the thermal mass on it's actually very impressive (Sorry i completely forgot about it yesterday)
He got it from Bangood too so maybe you get get one for review. I'm very happy with mine
Brian Lough no problem. I enjoyed it. I keep kicking around the idea to do a live stream but yet I never do.
Lol I just made a circuit like this through trial and error. Wish I saw this first XD
Mine still acts wonky tho.. I think it's from the laptop supply I power it from tho..messin' with me.
Question comrade, I see no capacitors in line there? In mine I got 2 going from adj. an out. on my voltage regulator, which gives me nice stable voltage.. But I ACTUALLY just noticed(I put non on the current limiting end) I am still getting amp spikes an dips..(thought the caps there would have been enough an if voltage was smooth an stable to .20v, then amps would be to, but I'm still getting amp spikes to -.3 -- 1.0 full amp whenever on/off or especially loadon/off. lol.. Whatcha think comrade? Probs need get some caps smoothing my current? is that even possible? Again I thought the two would be one in the same as far as smoothing goes?) Note: They are both Electrolytic caps smoothing the voltage in the 20-50-uf rating rage.
Awesome vid as always, thanks. =)
Thanks a lot.
Thanks
nice video
very nice ...i wonder how the current pas throw lm317 without being attached to the ground!!! i think the second lm317 has no rule in this circuit. the current is determined in the circuit by the value of the resistor only
now on the market many dc-dc step-up-down converter modules use the term constant current (CC) & constant voltage (CV). and in the discussion distinguish constant current from the term current limiter (current regulator). What is the difference between constant current & current limiter?
Thank you.
Could I place two lm317's in parallel to handle more current? I'm trying to use these to charge a 12.6v liion battery. I have a boost converter boosting 5v input to the 12.6v necessary to charge the battery. The battery has a bms with multiple safety features but does not limit current enough for the boost converter and it is getting hot passing upwards of 3amp (rated for 3a but to much for comfort). I'm trying to limit current draw of the battery to the 500mA - 1amp range. To minimize footprint with large heat sink could I place two lm317s in parallel? And what resistor values would u recommend? The boost converter output voltage can be increased to whatever voltage needed in order to compensate for voltage drop...
Peace to you too! :-)
Hi there, may you explain why you didn't use a Battery-Charger Circuit from spec? How i understood such circuit also must regulate voltage and current like in your.
Can you help me in explaining why when i put my 317 set up in the same basic adjust config and connected to my load circuits . The volatge dropped to about 0.87. These same circuits were powered by 7812 vregs beforehand with no probs . What i tried to do was step down from +15v to a more precise +12v for tuning a Vco tuning refrence voltage.
+Adamski A. Draw a schematic and email it to me arduino0169@gmail.com
learnelectronics Thankyou so much for offering the help. I will try and do that now .
learnelectronics Schematic sent. Thanks again :-)
+Adamski A. Ok I'll have a look
Just had something very similar, even tho I checked my circuit 20 times and rearranged it at least the same, I had one wrong leg in a spot an it was messing the whole thing up. I notice LMs default to around .04 .06 ma(same voltage if I recall to) when not gettin' what they need to do the deed. Check it check it check iittt,. Then checccck itttt sommee moreeeee. Hope you got help already tho =p
I have an off the wall question to ask you.. on the NTE 2902 transistor, which leg can be used as an antenna? Is it the source leg? Gate, drain, source.
J. Clowers I'm sorry I don't have an answer for you. RF is black magic to me.
learnelectronics i think i can use the source for an antenna. Thanks though.
Are you able to create a higher voltage on the constant current side than the output?
hey, i want to limit and vary the current of a 24V/1A power adapter between 2mA and 12mA, using a LM317, 1k ohm pot and a 1k ohm resistor. would that work or is it better I get a 2k ohm pot?
so like im watching along thinkinking wow i like this circuit wonder if if could be implemented as a variable constant current source (for a low tech cc charger design idea) and im like shouting at the screen saying "but can it be used with pots instead of fixed resistors" then video gets to 04:05 and Paul must have heard me lol and brings in breadboard and "pretends" he didnt have any fixed value resistors of the values he needed, yeah right, only joking , thanks so much for this video, very clearly and simply explained, off to ebay to spend £0.99p and buy me some LM317's
thanks .
I have used a Lm317L. It has a different structure. When i change the load between 10 ohms and 1k, it changes the output current like 30 miliamps. Should it do it? My resistor between adj and out of the regulator is 12ohms.
Maybe I will buy the normal Lm317
I've not used that variation.
I was wondering if it is safe to add a 0.1mF and a 1.0mF capacitor to this circuit and if so, does IT really add to the circuit?
As bypass caps? Sure.
It is possible to feed -1.25v in the adjust pin to achieve 0 volts at the output?????
only in the southern hemisphere
Is the output pwm rather than a true drop in volts?
Yeah not less you doing the modulating manually ;p
You wrote greater than 1.5 amps when you should have said less than, and that is assuming you have enough heat sink to deal with the watts getting burned off as heat. (Input voltage - output voltage) * amps = heat watts. An LM317 cannot provide more than 1.5 amps, and will throttle or burn if you exceed that(cheap generic ones tend to let out magic smoke). I have managed to cause a cheap generic Chinese one to light up like a light bulb accidentally shorting the output xD
you showed us the math yet the resistance does not add up when doing the math.... like at all
Writing to small, can’t make it out.