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Adjustable LM317 High Powered Current Source

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Use a LM317 to control up to 15 amps through a PNP transistor. The actual schematic is on the webpage. http://www.bristolwatch.com/ccs/LM317b.htm
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Text Comments (39)
Popeye (3 months ago)
The LM317 is rubbish as a variable regulated power supply. it's Inefficiency low with high heat dissipation especially at higher voltages
Lewis Loflin (3 months ago)
This is a video on circuit theory not a finished product.
Is lam (5 months ago)
suppose we have connected this circuit with 12 volts dc supply at its input and after this we set lm317 to 5 dc volts now at this point the transistor is in off condition and after this we connected a 5v dc load at circuit's output the load is high power and take more then 1 amps current due to this the transistor becomes on and as we know that the transistor works as close switch after on let suppose transistor don't drop voltage which mean 12 volts will be appear across the output capacitor as well as 5v load these 12 voltage can damage 5 volts load can you explain how we can safe our load at this point?
Lewis Loflin (5 months ago)
This is about current not voltage. Voltage is set by the load resistance times current.
Elektronik Atölyem (7 months ago)
Excellent project
SkyCharter (7 months ago)
What happens to the current through your load if, all other things being equal, the load resistance changes 20%?
Valter Souza (7 months ago)
Good Nice
Charles Bonnici (7 months ago)
Please keep on doing what you are doing. Our students can learn a lot from you including myself. Very refreshing. Thanks for the information. People like you make a difference. Some people do lot of talking and criticizing but you put everything into practice. God bless you, though you are already blessed with knowledge.
Dave (9 months ago)
with great sadness the LM317 has been deemed obsolete. although it is still available to support older designs it is highly recommended that you do not use this component in future designs. stock up while you can:( it is no longer available through digikey... so far as i can tell. i am indeed bumbed out. this little guy has adorned literally every hobby guys work bench since the beginning of time. most of the through hole components are about to get the axe as well so if your into playing with circuits you better get to know SMDs and their absolutely confusing packaging. the high voltage/high current guys should be OK...
gizmoguyar (10 months ago)
This is an extremely bad circuit, and I suggest that anybody who is looking for a current regulator circuit look elsewhere. There is no feedback in this circuit, which means it relies entirely on the gain of the power transistor. This is all but useless in high current transistors as the gain is so low (typically <15 at currents over 1 amp.). The LM317 draws a constant current through the transistor base, but because the input is already a constant 15 volts (even if unregulated) the base current being regulated is useless as well.  This is why you had such a discrepancy between your calculated and actual current. It will continue to change with current, voltage, temperature, etc.  If your requirements are okay, with such a shoddy circuit, you might as well save some time and money and just use a zener diode shunt on the base of an NPN transistor. It'll cost about half the cost of this circuit, and perform just as poorly.  If you want a proper current regulator, you need a shunt resistor to provide a feedback voltage to the control pin of the LM317 (As shown in the data sheet, if you bothered to look at it).
Lewis Loflin (10 months ago)
Read below - this is a test circuit to teach transistor theory.
idiyer Bill (11 months ago)
Are u musering curent in parallèle ! ??? Wtf !
Lewis Loflin (11 months ago)
What are you talking about? Current is measured in series.
Axel Werner (11 months ago)
Have you successfully tested this circuit under high current like 15A continuously ?? does it survive short circuit ?
gizmoguyar (10 months ago)
It really depends on the heat removal rate from that power transistor. The heat sink he's using in this video is rather small, and not adequate for much more than a few watts dissipation. But with the proper heat sink design, a power transistor can handle 15 amps easily.  I do recommend, though, that you never use this circuit for current regulation, and use a properly designed circuit instead.
Lewis Loflin (11 months ago)
Yes I did and it blew the transistor. It ran fine at 10 AMPs, as for short circuit, It depends on the level of the short circuit.
bilal mahmood (1 year ago)
Dear sir how i increase amps same power supply i have 25 volt power supply its operate motor controlling board but control board damage now i was make a simple circuit for motor drive but motor not proply work because low amps
Jarif Rahman (1 year ago)
juliusvalentinas (1 year ago)
Any way to control the LM338 Constant Current Regulator Circuit digitally using arduino?
juliusvalentinas (1 year ago)
And the digital alternative with LM338 like linear current adjustment no PWM is?
Lewis Loflin (1 year ago)
No there isn't.
electronics nerd (1 year ago)
https://www.youtube.com/watch?v=QV_p4syM6UI tutorial on variable voltage and variable current ciruit using LM317.
sanjeev kumar (1 year ago)
can i use an ultracapacitor(2.7V, 120F) for charging it as a load in this circuit?????
Lewis Loflin (1 year ago)
See this webpage: http://www.bristolwatch.com/ccs/LM317.htm
sanjeev kumar (1 year ago)
sir, i want to charge an ultracapacitor 2.7V, 120F using a constant current source of 1.2A for 2min , so i need a constant current source. how to design a 2A constant current source????
Lewis Loflin (1 year ago)
Not sure what you are trying to do. The voltage for this purpose is too low.
Lewis Loflin (1 year ago)
This is a test circuit to teach transistor theory. The schematic in the video is not the main schematic but is on the webpage at http://www.bristolwatch.com/ccs/LM317b.htm
Daves Tech (1 year ago)
It would be better with a npn transistor with the 317 in current mode driving the base instead.
Lewis Loflin (1 year ago)
Are you talking current or voltage? This is about CURRENT.
Daves Tech (1 year ago)
So the variable battery charger I used when I raced rc cars didn't work? Could have fooled me.... The battery must have charged itself.... No the circuit would work and it did.
Lewis Loflin (1 year ago)
An NPN won't work in this circuit.
Joey Mac (1 year ago)
Is there a more efficient way to deliver constant current to a load. The transistor is dissipating quite a bit of energy.
Loundre3 (1 year ago)
AFAIK buck converter regulating current is the closest to most efficient.
Lewis Loflin (1 year ago)
Yes I said that I believe. Step down the input voltage closer to what is required.
Mahdi Barati (1 year ago)
Thanks for video excuseme if my question is a little ridiculous I am a beginner Is it possible to use MJ11033 (DARLINGTON POWER TRANSISTORS) with have very diferent hfe instead of MJ2955 (POWER TRANSISTORS) for getting higher power dissipation, lower thermal resistance and higher current
John Conrad (1 year ago)
the circuit is crap. yes u can use the darlington and the current will be all over the place.
Lewis Loflin (1 year ago)
No. The gain is so high it would be impossible to control. In addition many of these Darlingtons have internal diodes and resistors.
Neonblue Industries (1 year ago)
Thanks for doing a video on my question to you about driving higher loads. Do all LM317 have this ability to run in Constant Current mode? and do the low dropout versions also? Thanks Lewis.
Lewis Loflin (1 year ago)

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