Constant Current Source Circuits Tutorial 

excellent demonstrations both theoretically and experimentally. These are the classic and fundamental building blocks of analog circuit design.

Thank you repeatedly for your concise explanations in all your videos with which you expertly make comprehension very easy. "Ambiguity has no space in your videos. "

As a hobbyist, it's hard to find information that doesn't immediately jump into the extreme of technicality. The first constant current circuit, which uses a single transistor as the regulatory device is very good. I've been looking for ways that you could make a simple, reliable current regulator that doesn't require the use of a modified voltage regulator. This video gave me an idea of what i need to do to have that. nifty

thank you for refreshing my memories of circuits I played around with about 40 years ago.

The last circuit is the best for leds that draw little current, but for more high current loads the HFE of the transistor shifts with temperature even though you keep the Ib very still and precise. As you will have more current running through the transistor, lets say 1A, the power dissipation will be higher and the Tj will rise over the ambient, leading to Ic deviation. My opinion is that if you want higher currents and have steady Vcc voltage, the seconds schematic with the op amp is the best. Nice video and keep up the good work!

thank you so much! you have no idea how hard is was to find this specific and very well explained information

Constant Current Sources well summarized. thank you !

New pages www.bristolwatch.com/ele/hysteresis.htm www.bristolwatch.com/ele2/comparator.htm www.bristolwatch.com/ele2/battery_charger.htm www.bristolwatch.com/ele/vc.htm

I like the information and the way you presented it in the video. Very well done sir! thanks! Already subscribed to see more.

Superb video, Lewis. A quick supplementary clarification for students: There is a fixed voltage drop across each LED in the circuit ... which is dependant on the LED colour. So .. for identical LEDs the maximum NUMBER of LEDs in series that can be driven will be the supply voltage LESS the voltage drop across the transistor all divided by the voltage drop across any ONE of the identical LED. Hope that helps. (You all can figure out what to do for NON-identical LEDs but watch out for maximum constant current settings).

5K POT SOUNDs NICE! DEFF WORTH HITTIN' IT!

Nice explanation, thanks a lot sir.

New video high power LM317 current source ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-n94xqPMhmTo.html

Hello, can I use the last circuit for charging a Li-Ion Battery at constant current? I have a 4.2 V battery and I can charge it up to 1 AMP.

0:08 how much will change in temperature affect this circuit. For example 5K will pot will be affected by temp causing change in current Ic.

thank you. very well explained and helpful to me.

Wow, thanks for sharing this to us.

Would be nice to mention the heat dissipated on the transistor. I am guessing there's heat , right? If the source is delivering 12v and the led voltage drop is 0.2V then 12V*0.12A=1.44W Not insignificant. Or am I missing something?

thank u very much sir,iam using 5white led and what should be the pnp transistor value

Would you not want to design a circuit, in the case of the LM334 example, that isn't dependent on the hfe of the transistor?

Wonderful tutorial!

Such an important topic.

What are your thoughts on using an Op-Amp together with some kind of precision voltage reference? My biggest thought on these simple constant current supplies are that most of them don't take into account that HFE may change quite a bit at different operating temperatures and loads. I was thinking at building a laser-LED driver for a project, and stability is crucial when working with those, no matter what conditions its run at.

I was hoping to find a simple circuit that could drive a laser diode scavaged from a old computer DVDRW (about 3-3.2VDC at less than 500mA, perhaps 150mA as a start) from a 5VDC PWM (arduino) to vaporize ink in spray painted PCB without too much heat dissipation in the drive. How the LM741 and LM334 circuits behave from a PWM power supply input? Is there any simple constant current circuit that can be external powered but controlled through a PWM signal? Do you have any recomendation or thoughs on my idea, if you don't mind I ask?

Seems that a "Constant Current Source" is more of a current limiting source because the current cannot exceed a given amount. However if the load resistance increased past a given limit, the current will be reduced.

Well done, easy to follow.

Great video. Thank you for the detailed explanation. Is there anything that can be purchased around that does the job with minimal modifications? Your specifications seem close to what I need: 0-120mA constant-current regulator. My load can go up to 2000 Ohm, but I don't need the power for long because I intend to drive the cc regulator intermittently, for 1 ms at a time up 100-120 Hz square wave (home-made electrical muscle stimulator).

Great video, thanks!

Hi Lewis, Thanks for the great tutorial video and clear schematic. I need to make a higher amperage C.C Power source (from Battery pack 4.2-7.4V) that allows up to 12A. As the LM334 is limited to working at 10mA, this wouldn't be enough to run the TIP36C PNP power trans I have. So could I connect say a medium PNP power trans so it's controlled by the LM334, and then the TIP36C on the end stage to control the higher current? I need a c.c source as the battery supply voltage will vary from 4.2 - 7.4v. What would you recommend? Do you think there is a single PNP power trans that can run at 10mA through it's base and allow 12A through the Collector Emitter? Thanks so much for your time and effort.

nice tutorial thank you!

Mr. Loflin, now on the market many dc-dc step-up-down modules use the term constant current. and in the discussion distinguish constant current from the term current limiter. What is the difference between constant current & current limiter? Thank you.

Hello, I don't understand why hfe is 180. The datasheet tells that hfe=Vce/Ic=12V/0,12A=100. Another question is if I could use the 2SB1202s-TL-E PNP instead of the 2N2907. I need higher currents for my power led, which is greater than 0,6A.

Hi Lewis, I would like to power 7x 3w LEDs rated at 3.2 to 3.6v forward voltage and 700mA. With your first basic circuit I see no typical resistor that will drop whatever voltage is left 'unused' by the LEDs. How is the voltage controlled here? IE: at worse case I will need 7x3.6v = 25.2V at minimum plus some overhead say 28v. At best I will need 7c3.2v = 22.4V. So in my case I may have up to (28 - 22.4) = 5.6V of extra voltage. Would you not need a resistor with power rating of 5.6v x 700mA = 4W and in this case what value would it have? Thanks a lot

Hi, great video thak you very much! Can this circuit manage a 12VDC 800mA (10W LED) courrent led? Thanks again!

In your second design, using the op-amp, what's the reason behind using the PNP transistor at the output of the 741 op-amp? At 3:52, you mentioned that the current flow is dependent on the reference voltage, the 741 op-amp, and Re. I built a conversion circuit that converts 1-5volts analog voltage signal into 4-20ma analog current signal, the output current level will control a valve opening percentage. without the PNP transistor, it worked just fine. So I'm wondering whether I'd really need to add a PNP transistor at the 741 output, or just leave the circuit as it is without any transistors? Your videos are appreciated!

Hi, I tried to use the LM741 based circuit to charge a tiny 2.4V nimh battery pack (80mAh). It did kind of work but it was not really a constant current. I used a different RE from yours because there is quite some power/heat to stand for this resistor, if I got this correctly. I used a 270 Ohms and 2Watts (or 4?), which I had at hand. I adjusted the pot so the current was around 30mAh which I wanted to use to load the pack. And instantly the current started to drop, slowly but steady. After 30 mins of charging time, the current was only about the half of the current (not sure about that, but it was significantly lower) Is this normal? What would I need to modify in your circuit to use it for charging a battery? Sorry for asking a probably dumb question! Jojo

Great video, thanks for this! In my country we use 240V, is it possible to change the 12v source to 240V and put more LEDs in series? Im a noob so yeah

Hi: Great Video Thanks I'm new in electronics. I Have a old Condor Power supply from 1990 I think. It came out out of a Stress Test ECG machine.. The PS works fine. It puts out +5v at 10 amps ; +12v at 3 amps ; -12v at 3 amp ; +15v at 3 amp; +28v at 1.25 amps ; -28v 1.25 amps, I would like to regulate the voltage between 1.2 to 30 volts and be able to control the current output from 10 uA to 1.10 amps on the plus and minus side of the 28 volts output of the PS. On the 12 volt and 5 volt output I would like to control the current output from 10 uA to 1.5 amps in order to avoid toasting or damaging any components when testing on a test board... I’m very prone to shorts and mistakes. The video shows lower amperage on the current limiter. How I can increase the capacity of amps of my output and make the output in amps changeable .. I appreciate the help. Thank you

Can this be used to drive precision 405nm laser diodes?

LM334!!!! WOOO WOOO WOOOO WOOOO

The first circuit you talked about is not a Constant Current source. As soon as the load change or any other parameter, the current will change. There is no FeedBack to prevent that.

I need to make a constant current source using LM334 and 10-turn potentiostat. But I have tested many ways but when i change the resistance of the load, the current is changed which should not happen. Would you please guide me ? It is very urgent.

It's a grate video. thanks!!!. I have a question. What would i do if i want to switch the position of led to that of current sensing resistor? can you, please, put the link to the original circuit that elaborate on it in detail if possible.

Will the second circuit work if I will put the NPN transistor and connect the feedback to the emitter?

HOW do you get the Vref?

4:44 Ic for LED 150 mA?

Hi, for constant current using pnp transistor, do I need to worry about power dissipated in the transistor, as it is partially "on", is it not a bit like a resistor ?

Fix your noisy powersupply...

Sir,kindly give us a good quality hpf led driver circuit of 09 watt useing most common ic,available in local market.thanks.

What is that 4th resistor for? The one by the green pnp transistor? Also, what value trim pot did you use with the lm344? Thanks : )

is this how they make "Driverless" LEDs?

In the circuit at 4:33, what does RE mean?

Can you please tell me the transistor you are using

Nice

👍

Hi I have a very important question plz

Easier? No! It just they decided to keep it that way.

Hfe varies from transistor to transistor and is very temperature sensitive. Depending on the multiplication of Hfe*Ib for Ic is poor circuit design.

didnt understand shit