Constant Current Source Circuits Tutorial
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- Опубліковано 24 сер 2024
- Part 1 of series on using constant current source with LEDs and resistive sensors, power control.
Constant Current Source Tutorial
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LM317 Constant Current Source Circuits
• LM317 Constant Current...
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LM334 CCS Circuits with Thermistors, Photocells
• LM334 CCS Circuits wit...
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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
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!
This is also the reason, that the current will be not stable with respect to different operating voltages, because of self heating of the transistor. I would never make a circuit which relys on the current gain of a transistor. Btw: you can make very good constant current sources by use of voltage regulators.
thank you for refreshing my memories of circuits I played around with about 40 years ago.
thank you so much! you have no idea how hard is was to find this specific and very well explained information
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).
Constant Current Sources well summarized. thank you !
5K POT SOUNDs NICE! DEFF WORTH HITTIN' IT!
I like the information and the way you presented it in the video. Very well done sir! thanks! Already subscribed to see more.
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.
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.
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?
The LM334 circuit is not dependent on transistor hfe other than the transistor must have enough hfe to work at the low current of the LM334. In fact I have used Darlington transistor configuration, works the same. Note: use real darling transistors not the TIP125, etc.
@@LewisLoflin , For the circuit at 5:00 - let me propose a simple experiment here: let's put an ammeter in series with the load (LED), and then swap transistor for a different (yet very similar) type. The current will change, actually it will change even if you take transistors from the same batch. And then imagine you wanted to run a production batch of these. You'll go out of business pretty soon ;)
Yes, this circuit exhibits some characteristics of a current source. No, this circuit is not a practical one.
Wow, thanks for sharing this to us.
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.
thank u very much sir,iam using 5white led and what should be the pnp transistor value
thank you. very well explained and helpful to me.
Well done, easy to follow.
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?
This is an example circuit, not a finished product. I have explained that elsewhere, but you bring up a valid point. I've said before, don't use a 19-volt supply for a single LED.
Great video, thanks!
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.
The load resistance doesn't effect the current unless the voltage drop (based on resistance) comes within 2V of the source. So you are correct.
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).
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?
nice tutorial thank you!
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.
Hi, great video thak you very much! Can this circuit manage a 12VDC 800mA (10W LED) courrent led? Thanks again!
Iván Relota If you using a transistor (MJ2955) the rating is around 10 amps. Most of the current is though the transistor so if it can handle 1 amp then yes. See time 12:33 in the video.
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.
+Mathieu Bacquet That is what I measured on my transistor checker.
+Mathieu Bacquet These are general rules - all silicon PNPs operate the same based on beta, Ic, etc.
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.
To me the same thing. A current limiter is set to a particular current.
@@LewisLoflin Thank you...🙏😊
I love your videos and reminds me about 80's, when I liked electronics as a hobby. Where the power supply still uses a large and heavy transformer and It used to be very difficult to get references/information like the ones on your channel. Around that times, I was very happy to get a 12V 2A switching mode power supply (SMPS) with CT (Center Tap?), there is +12V and -12V, quite small and light for its time. I still keep it to this day.
Thank's again... your video reminds me of the happiest times of my life.
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
240V is AC, the circuit is for DC. You'll need a 240VAC to 12VDC power supply AND the circuit
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
That's two differing circuits one for voltage another for current. The info on each is at my website
www.bristolwatch.com/index.htm
Thank you
Fix your noisy powersupply...
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
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.
+valveman12 Yes it is. Change the load within range the voltage will vary but the current stays the same.
+Lewis Loflin Yes you are correct my bad. Ib Controls the Current. Thanks Lewis.
Your welcome thanks for the input.
I also doubted the same for the first circuit but after experimenting by myself, I accept the inference.
Thank all of you for your input.
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.
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
This is a constant current source. The voltage across the load depends on the current supplied times the resistance. The excess voltage drop is across the transistor.
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!
The PNP ist the "muscle" of the circuit to handle the 150mA for the power LED that is driven. OpAmps usually drive loads in the lower mA-range. The 4-20mA in your example might be a current that the OA can actully source. The max-values can usually be derived from the datasheet. If you look for "output voltage swing" you'll see the max. +/- voltage the OA can handle at a given load. The 741 e.g. has an OVS of +/-13V at a 2k load, yielding a guaranteed current over that swing of +/-6.5mA. This, of course, varies with OVS and Rload. Another datasheet-value of interest is "output short circuit current", which in the case of the 741 is around 25mA. At least that's how I understand it :)
Thank you! That clarifies a lot. I'll look up the data sheet of my op-amp ASAP.
From experience or reliability point of view, would you recommend adding a transistor if the op-amp is capable of handling the output current of 20ma? :)
OpAmps for sure can source and sink current, not much, but they can. I, personally, hardly ever drive anything directly from an OA, unless I use the OA as a buffer for a subsequent stage. But that's more based on habit than any particular consideration :) I have piles of BJTs, they are super cheap and even the smallest ones drive much higher loads than your average OA. But as I said: that's more of a habit of mine. Datasheet-wise you are pretty safe to source currents of 20mA through an OA. For higher currents there are even special Opamps.
Yes you need the PNP or it won't work.
Thank you.
LM334!!!! WOOO WOOO WOOOO WOOOO
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.
See www.bristolwatch.com/ccs/LM334_sensors.htm
Thank you very much
Can I remove ADC? because I don't need it.
Sorry I may ask basic question. Iam chemical engineer and I need to make a circuit for my research
Can this be used to drive precision 405nm laser diodes?
If the current level is correct. These diodes are often pulsed.
@@LewisLoflin I hear two different stories about powering laser diodes. One says to use constant current other says to use pulsed powering.
@@ShopperPlug I have used pulsed myself but see no problem with CCS.
Will the second circuit work if I will put the NPN transistor and connect the feedback to the emitter?
No. The current from the collector is controlled by the B-E current.
Thank you for the response. My intuition (or lack of education) tells me that there should be a way to implement this idea with NPN transistor, am I wrong? I am curious because NPN transistor are easier to find.
Yes, but instead of leading I(b) to ground, you take that current from Vcc.
is this how they make "Driverless" LEDs?
Yes. The current is limited regardless of load - within reason.
HOW do you get the Vref?
Current though the 20K pot.
In the circuit at 4:33, what does RE mean?
+1994fishcake Emitter resisotr.
Easier? No! It just they decided to keep it that way.
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 ?
It can get hot so use a heat sink.
Suppose power lost in transistor would be volt drops of 2 junctions times current. Transistor specs tells max power dissipation
What?
The power dissipated in the transistor will be the product of the C-E voltage and the current.
Yes.
Can you please tell me the transistor you are using
Also the r1 and r2 values for the lm334 circuit
MJ2955
Nice
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 : )
Where do you refer to in the video?
Paused at 11:00 The resistor right by the green pnp on the rh side of the breadboard.
It looks like it's in the emitter circuit likely a 10 ohm in case of a short circuit I think.
Thanks. One more question. All I have right now are darlingtons. When I try to use the circuit, it just burns out the led. I have some pnp's on the way but I am guessing that the darlingtons will not work for this application?
Darlingtons have so much gain they can't be controlled.
Sir,kindly give us a good quality hpf led driver circuit of 09 watt useing most common ic,available in local market.thanks.
👍
Hi I have a very important question
plz
Hfe varies from transistor to transistor and is very temperature sensitive.
Depending on the multiplication of Hfe*Ib for Ic is poor circuit design.
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
didnt understand shit
New video high power LM317 current source ua-cam.com/video/n94xqPMhmTo/v-deo.html