In this post I have explained 2 simple universal current controller circuits which can be used for safely operating any desired high watt LED.
The universal high watt LED current limiter circuit explained here can be integrated with any crude DC supply source for getting an outstanding over current protection for the connected high watt LEDs.
Why Current Limiting is Crucial for LEDs
We know that LEDs are highly efficient devices which are able to produce dazzling illuminations at relatively lower consumption, however these devices are highly vulnerable especially to heat and current which are complementary parameters and affect an LED performance.
Especially with high watt LEds which tend to generate considerable heat, the above parameters become crucial issues.
If an LED is driven with higher current it will tend to get hot beyond tolerance and get destroyed, while conversely if the heat dissipation is not controlled the LED will start drawing more current until it gets destroyed.
In this blog we have studied a few versatile work horse ICs such as LM317, LM338, LM196 etc which are attributed with many outstanding power regulating capabilities.
LM317 is designed for handling currents up to 1.5 amps, LM338 will allow a maximum of 5 amps while LM196 is assigned for generating as high as 10 amps.
Here we utilize these devices for current limiting application for LEds in the most simplest possible ways:
The first circuit given below is simplicity in itself, using just one calculated resistor the IC can be configured as an accurate current controller or limiter.
Calculating the Current Limiter Resistor
The figure shows a variable resistor for setting the current control, however R1 can be replaced with a fixed resistor by calculating it using the following formula:
R1 (Limiting Resistor) = Vref/current
or R1 = 1.25/current.
R1 wattage = R x I2
Current may be different for different LEDs and can be calculated by dividing the optimal forward voltage with its wattage, for example for a 1watt LED, the current would be 1/3.3 = 0.3amps or 300 ma, current for other LEDs may be calculated in similar fashion.
The above figure would support a maximum of 1.5 amps, for larger current ranges, the IC may be simply replaced with an LM338 or LM196 as per the LED specs.
Application Circuits
Making a current controlled LED tubelight.
The above circuit can be very efficiently used for making precision current controlled LED tube light circuits.
A classic example is illustrated below, which can be easily modified as per the requirements and LED specs.
30 watt Constant Current LED Driver Circuit
Assume the LEDs to be 3.3 V, 10 watt, and Supply input to be 12 V
Current of LED becomes = 10 / 3.3 = 3 amps
The LM338 current limiter can be calculated using the formula
R1 = 1.25 / 3 = 0.41 Ohms
Wattage = R x I2 = 0.41 x 3 x 3 = 3.69 watts or 4 watts
The series resistor connected with the three LEDs is calculated by using the following formula:
R = (supply voltage – Total LED forward voltage) / LED current
R(watts) = (supply voltage – Total LED forward voltage) x LED current
R = [12 - (3.3+3.3+3.3)]/3amps
R= (12 - 9.9)/3
R = 0.7 ohms
R watts = V x A = (12 - 9.9) x 3 = 2.1 x 3 = 6.3 watts
Restricting LED Current using Transistors
In case you do not have an access to the IC LM338 or if the device unavailable in your area, then you could simply configure a few transistors or BJTs and form an effective current limiter circuit for your LED.
The schematic for the current control circuit using transistors can be seen below. The design is an example for a 100 watt LED current limiter, with 35V as the input supply and the 2.5 amp as the maximum current limit.
PNP Version of the Above Circuit
How to Calculate the resistors
In order to determine R1 you may use the following formula:
R1 = (Us - 0.7)Hfe/Load Current,
where Us = supply voltage, Hfe = T1 forward current gain, Load current = LED current = 100W/35V = 2.5 amps
R1 = (35 - 0.7)30/2.5= 410 Ohms,
Wattage for the above resistor would be P = V2 / R = 35 x 35 / 410 = 2.98 or 3 watts
R2 may be calculated as shown below:
R2 = 0.7/LED current
R2 = 0.7/2.5 = 0.3 ohms,
wattage may be calculated as = 0.7 x 2.5 = 2 watts
Using MOSFET for Higher Current Applications
MOSFETs are more efficient than BJTs in terms of handling higher current and wattage. therefore, for applications that require high current limiting, for high wattage loads, a MOSFET can be used in place of T1.
The current handling capacity of the MOSFET will depend on its VDS and IDS ratings, with respect to the case temperature. Meaning, the MOSFET will be able to tolerate the amount of current defined by the product of its VDS x IDS, provided the case temperature does not exceed 40 degrees Celsius.
This may appear practically impossible, therefore the actual limit will be defined by the amount of VDS and IDS that allows the device to work below the 40 degrees Celsius mark.
The above BJT based current limit circuits can be upgraded by replacing T1 with a MOSFET as shown below:
The resistor value calculations will remain the same as discussed above for the BJT version
Variable Current Limiter Circuit
We can easily convert the above fixed current limiter into a versatile variable current limiter circuit.
Using a Darlington Transistor
This current controller circuit features a Darlington pair T2/T3 coupled with T1 to implement a negative feedback loop.
The working can be understood as follows. Let's say the input supply the source current I starts rising due to high consumption by the load for some reason. This will result in an increase in the potential across R3, causing the T1 base/emitter potential to rise and a conduction across its collector emitter. This would in turn cause the base bias of the Darlington pair to start getting more grounded. Due to this the current increase would get countered and restricted through the load.
The inclusion of R2 pull up resistor makes sure that T1 always conducts with a constant current value (I) as set by the following formula. Thus the supply voltage fluctuations have no effect on the current limiting action of the circuit
R3 = 0.6 / I
Here, I is the current limit in amps as required by the application.
Another Simple Current Limiter Circuit
This concept uses a simple BJT common collector circuit. which gets its base bias from a 5 k variable resistor.
This pot helps the user to adjust or set the maximum cut off current for the output load.
With the values shown, the output cut off current or current limit can be set from 5 mA to 500 mA.
Although, from the graph we can realize that the current cut-off process is not very sharp, yet its is actually quite enough to ensure proper safety for the output load from an over current situation.
That said, the limiting range and accuracy can be affected depending on the temperature of the transistor.
Adjustable Current Controller Circuit using IC 741
The following IC 741-based arrangement can be used if you want a preset current limit which is adjustable across a wide range.
When R9 is adjusted to zero ohms, the lowest current limit for the components depicted is around 47 mA. Add a suitable fixed-amount resistor in series with R9 if you want to set a specific high current limit.
As you can clearly see, implementing current crowbars offers the excellent method of safeguarding electronics from short circuit destruction.
Hello Mr. Swagatam
I need to build a simple current limiter for a controlled electrolytic process. As my electrolysis proceeds water resistance between electrodes will drop from approx. 150kΩ to 15kΩ. With a supply voltage of 24VDC the load current would thus increase from approx. 0.16mA to 1.6mA.
My intention is to automatically limit the load current to a maximum of 0.25mA irrespective of decreasing water resistance.
Questions:
1. In your circuit “Precision Current Limiter”, if I set R1 = 100kΩ will then the output load current (Iout) be limited to 0.24mA? Would that work in my case?
2. Can LM117/317 regulators even control such low currents accurately?
3. If all this fails, could you please recommend a simple circuitry that would do the job? Thank you much!
Hi Holgar,
0.25mA indeed looks very low and might not allow the lm317 to work properly, in that case why not use just a resistor in series with the supply voltage?
As per Ohm’s law, this Resistor could be:
R = 24/0.00025 = 96000 ohms or 100000 Ohms or 100k Ohms. This will be enough to ensure that the max output current to the water does not exceed 0.25 mA, under any circumstances.
Hi Mr. Swagatam;
I will use 12V 60A car battery but I need about 20A current output for the spot welding purpose circuit.
Is it possibe to use about 4V or 5V buck converter instead of current limiter circuit?
Hi Suat, yes, to get 5V 20 A from a 12V 60A source you can use a buck converter for better efficiency.
I would like to use the MOSFET version to make a heater coil selections of 3.1A, 4.3A, 5.8A and 7.8A. Are the calculations the same as mentioned for Ockie below?
Yes, the calculations will be exactly the same.
Much appreciated Mr. Swagatam.
Want to build a simple 12V 50A current limiter, using a mosfet.
must be adjustable, and does not have to be accurate.
The circuit that you show above should work.
Please can you calculate the limiting resistor for me, being a lay person,
but full of enthusiasm.
Yes, you can try MOSFFET version. MOSFET can be IRF3205.
Current limiting resistor value will be as follows:
R = 0.6 / 50 = 0.012 ohms
Power = 0.6 x 50 = 30 watts
Thanks!!
Can I put a 5k pot (wiper) on the base of T2, and the other 2 legs over the current limiting resistor? So that I can trim the current?
Yes, that looks possible, you can try that…I think a 1k pot will be more suitable.
Thank you for your reply.
The only problem is doing that, I can only increase the current.
So I may use a 0.02 ohm resistor instead for less current, then trim it up,
Even 0.05 ohm should work.
Ons small problem. Where the heck do I find such resistor?
Not your problem. I may find a shunt to work.
Regards.
Ockie.
021 116 1072
You can increase and also decrease the current using the pot.
You can make the resistor by using a calculated number of 0.1 ohm resistors in parallel.
Hello,
My GOBIBLE (www.GoBible.com) uses a single AAA battery which keeps it going for a couple (a few?) hours, the entirety of the book (of books) takes 75 hours to play.
I can not find a converter from 12vdc to 1.5vdc (or even 5vdc to 1.5vdc).
I know dry cells are 1.5v in all sizes and a 9v is just 6 series tiny 1.5s and a 6v is 4 relatively humongous 1.5v cells, how can I current limit enough paralleled 1.5vdc cells so that I don’t have to worry about burning up my little electronic book of books? (And yes, I know that if I would just invest in a 3vdc unit that a converter would be just plenty of easy to come up with. 🙂 )
Hey, thank you very much!
DJ
Hey, thanks for your question.
Why do you need a current limiting circuit? According to me it is not required as long as the voltage is as per the load specifications.
Meaning, if your GOBIBLE is rated to work with a 1.5V supply and you provide the 1.5V supply from any suitable source then the current limiting is absolutely not required, because the load will automatically adjust to the optimal current consumption required for an optimal functioning.
If you restrict the current that might in fact hamper the optimal performance of your device.
Please let me know if you have any further questions.
hello everyone ,
I’m working on a very sensitive temperature sensor with sensing of 0.0001 but having problem that its value continuously changes in a very closed and calm environment even if i use constant resistor to stabilize the the temperature reading but that doesn’t work.
not getting the exact issue, i will be thankful if anyone can help me with this.
here are the components i have used :
Arduino nano
ads1220
ams1117 (to convert 5 v to 3.3 v)
10k ohm NTC thermistor
First your “sensor” does not have any precision by itself, it is a negative coefficient resistor, the precision of the whole system ould come from your analog signal conditioning / front end (at least an op amp, in most case) and the ADC behind it. If you use an “arduino nano”, based on atmega168 a very low end, very old AVR with a poor slow 8bit ADC, you cannot expect any kind of precision, because the discrete steps of this ADC will never be more than 256 values, the ADC precision is low, as its reference voltage source.
There is just too much you ignore on the topic to waste any time trying to explain further, provided your limited understand you should certainly use use a digital sensor.
i have circuit which has components:
arduino nano
ads1220
ams1117 (to convert 5 v to 3.3 v)
10k ohm ntc thermistor
i want to control the input voltage and current of ntc to 1.5v and 0.5 mA
I am not good with Arduino coding so unable to help you in this regard.
Is an AC constant current limiting circuit possible with a Triac at 230V? So not a voltage regulator (= Dimmer), or inrush limiter, but current = power maximum controller.
E.g. you can adjust the current is limited to 2A or 4A or 6A.
Connecting a boiler of 2000W or a watercooker of 900W both should result in e.g.
I = 2A; P = 460W.
Cannot find a scheme on Internet.
AC current limiting is possible using capacitors. For example a 10uF/400V non polar capacitor can be used to limit the AC current to 500 mA.
This C introduces a resistance. So current will be dependent on the load.
I want a Triac circuit that gives e.g. constant 2A or 5A, adjustable, independent of the load. A kind of current source (Norton).
You are correct, however I can’t figure out a triac based constant current AC circuit. If you can do it please let me know.
It is this watt controller technique I cannot imagine it functions without TRIAC…… I have to reverse engineer it.
No problem, please reverse engineer it and let use know about the details.
Hello,
This is a remarkable work done by author.
Dear, i have a question. I have 4pv of 165 watt each. I am designing another circuit to monitor the voltage. How can I limit the current to keep safe my circuit.
Regards,
Sarfraz
Thank you Sarfraz,
You can try the MOSFET version of the current controller explained in the above article. Let me know if you have any more questions.
Hi, can i use the last current limiter for my bench power supply from atx pc power supply?
I will be using probably this for 12v line.
And whats the wattage of all those resistors?
Thanks.
Hi, I do not have much information about the 741 based current limiter, but you can try it for your application and test how it works. All the resistors are 1/4 watt rated
Hello friend, your work is excellent, I need to make a lamp with 40 leds of 3.3v 3amp max (CREE xlamp xm-l2, 10w) and control its luminosity, what do you recommend? thank you so much.
Hi Juan, for your LEDs you will require a power supply with current limiting facility, and a PWM controller.
Thank you very much Sir. This is very interesting current limiter. I would like to make one on the 12 V battery which discharges the power to the home (house connected to the grid). Usually, the battery connected from one side to wind turbine through MMPT controller and other side to inverter and further to the house line. In this configuration the battery drains very quickly because it discharges not only for house consumption but to grid as well. If introduce the current limiter let’s say for 30 Amps so, only 360 W*h will be discharged which is enough for house consumption during the nighttime. Can you please give me your comment for this application. Will it work?
Thank you Eugene,
That appears to be a good idea, to restrict the battery from draining excessive current to the grid.
You can try the MOSFET version. Your inverter becomes the “load” in the circuit.
You can upgrade the mosfet power rating, depending on the current requirement of your inverter.
Good morning Sir, thank you very much for answer. Could you please explain: – What is this – Hfe = T1 forward current gain? Also, because my system requires high current of 50-60 Amps, so I will use T1 as IRF 1404. What sort of T2 (transistor) I have to use in this situation?
Kind Regards, Eugene
Hello Eugene,
The hFE indicates the relationship between the current/emitter current and the base/emitter current. With higher hFe the collector current will be high and the base current requirement will be low and vice versa. Meaning as the hFE increases the base switching current decreases. So with higher hFE the base resistor can be higher and with low hFE the base resistor value will need to be lower.
However hFE is only for BJTs not for mosfets.
Yes the IRF1404 is OK for 50 amp current.
T2 can be any transistor such as BC547 or 2N2222, as long as the voltage is lower than 40 V.
I am a final year student and nowadays I am working on my Final Year Project. My FYP is about Battery Management System. My project has the additional feature i-e it limits the output/load current of the BMS and then deliver/transmit it to the controller. So can you please suggest me a proper circuit for this?
I do not have a BMS circuit with me right now. If possible i will try to design it and publish it in this website soon.
Thanks alot. But I am basically in search of a current limiting circuit that will limit the current coming out of the BMS. Basically there are two BMS and each BMS has its own current limiting circuit. And that current limiting circuit will limit the current according to the State of Charge and Health of that particular BMS. Basically this is an efficient system which draws more current from that battery pack which has more SOC and SOH and vice versa
OK, if you are looking for a basic current limiter circuit, then you can try the MOSFET based design explained in the above article! It will do the job very efficiently for you!
Thanks for the assistance
Please, please do not use the term “Wattage”
Its POWER.
Power is measured in Watts.
Technically you are right, however I have used “wattage” so that the common hobbyists and newcomers are able to quickly understand that I am referring to the watt specification of the resistor.
Power is right, but Wattage is not wrong either. It is also a method of addressing power especially when it is real power awhich is expressly in watts as opposed to apparent and reactive power which are not true wattages per se. My humble take.
Wish to design the following circuit
Input 12v 60amps output required 12v 10amps.
Need a current limiting circuit with minimum components
You can use the MOSFET version of the current limiter circuit explained in the above article.
Hello I’m interested in a 10 amp 12 V battery charger I like to build it with all the components could you let me know on some schematics thank you
Fred d.
Hello, you can try the following circuit:
https://www.homemade-circuits.com/wp-content/uploads/2022/02/simple-high-current-battery-charger.jpg
Thank you Sir
When it opens, I have a question about (R8) – there should be a heater. If the heater takes more or less than 6A.
the red LEDs should be displayed. and then after it should be off automatically. is it possible sir?
i.ibb.co/r3CmcF5/Bildschirmfoto-2022-03-09-um-18-49-53.png
Thank you Sir once again.
Abhishek, the LED is already shown across R8 which will light up when a specific amount of current passes through it. You can use the following formula to fix the R8 value so that LED illuminates at 6 amp current through R8.
R8 = 2 / 6 = 0.33 ohms (12 watts)
The 2 indicates the voltage level required for the LED to start glowing.
Thank you Sir
It is a great Idea. Sir
I would like to ask you, can I connect a relay?
if yes, what would be the best way to add there,
Thank you very much Sir
i.ibb.co/MRhJNfV/Screenshot-2022-03-10-140733.png
You are welcome Abhishek, You can connect a relay so that its activates when the current exceeds 6 amps across R8, but you cannot connect the relay directly across R8 because the relay requires high voltage and current to activate. You will have to use an LED/transistor based opto coupler, and replace the R9 LED with the opto LED, and configure the relay coil across the transistor side of the opto coupler.
Thank you Sir
but i have used exactly the same website. and it is opening on my browser.
may i have your E-mail Address Sir.
it would be very nice.
thank you for your supports.
Hi Abhishek, please try the link which I provided you in previous comment, it will definitely work….or use any website from the following link:
Image hosting sites
Thank you for your reply Sir.
now i have created an Account on this website.
i hope that it will open there too.
ibb.co/8Y6qkCv
Thank you Sir
Unfortunately the link is still not opening.
You can try uploading in some other site such as this one
https://imgbb.com/
Hello sir
It’s about short circuit protection and if a fan would be more than 300mA and 24V or short circuit occurred. then it should be displayed red. i have built a circuit with PNP and NPN transistor. It works fine only when it has a complete short circuit, but I want to build it , when the fan would be below 24 volts or more than 330mA, the LED should be displayed completely red.
i hope that you understading my questions
Thank you
Hello Abhishek, If you add an LED in series with the base of T2 in the above transistorized current limiter circuit, then the LED can be used to indicate the 330mA current. Formula for R2 will be.
R2 = LED FWD V + 0.6 / 0.330
For indicating low voltage you will need another LED/transistor circuit as explained in the following article:
Low Battery Indicator Circuit Using Two Transistors Only
Thank you Sir
it helps me.
You are welcome Abhishek!
once again thank you Sir .
could you please check your Email Sir , i have sent to you a circuit diagram. here i cant upload the circuits Photo. It would be great !
Thank you for your Supporting
Hello Abhishek, I checked my email but could not find any email from you.
Alternatively you can upload the diagram in any free image hosting site and provide the link to me. Make sure to remove https while providing the link here:
https://www.google.com/search?q=free+image+hosting+site&oq=free+image+hosting+site&aqs=chrome..69i57j69i65l3j69i60l2j69i61j69i60.4886j0j7&sourceid=chrome&{google:instantExtendedEnabledParameter}ie=UTF-8
Thank you Sir
as you told me, I uploaded the photo and the link is here.
I am in trouble again.
I have built a short circuit protection with MOSFET and comparator.
I wanted to post this picture directly on your website but unfortunately I can’t get it.
So here is a standard short circuit protection.
I need to protect about 6A and 24V output.
I have shorted the circuit but the red LED is not showing.
What should I do sir?
If the load takes more than 6A it should show red, otherwise green.
ibb.co/VtfN47q
thank you very very much Sir .
You are doing really Well
god bless You
great future ahead
You are welcome Abhishek,
However, the link you sent is not opening here. Please check it.
Sorry Sir
I just have copied and paste it .
I have tried once again.
https://ibb.co/2MfLN7f
I hope that it will open .
Thank you for everything.
Abhishek, It is still not opening. Please do not put https, it is not required…if the image link is valid it should open even without https. It seems the link is not valid according to me…or it may be opening only in your browser.
Great article thanks! I’m looking to use your MOSFET circuit for current limiting the charging current to 20A for a 54V 65F super capacitor and when calculating the R values the watt rating of the resistors are massive. Is there a better way to achieve this than just duplicating the circuit 5-6 times at lower current values? Thanks
Thank you, I don’t think the R2 resistor for the MOSFET circuit will be massive for 20 amp current. Here’s the calculation:
R2 = 0.6 / 20 = 0.03 Ohms
Wattage = 0.6 x 20 = 12 watts.
A 12 watt resistor would just be around a 3 inch long wire-wound resistor.
Duplicating the circuit may not be a feasible option.
Hi hi,
I am looking for a simple circuit to limit an electric motor running more than 10mps at 12volts. Would the LM196 be suitable in your opinion and what is the best circuit to drive the motor
Thank you
Hi, the transistor/MOSFET based design looks a better option for your motor current control application. LM196 can get too hot at 10 amps.
Thank you for your suggestion. Stay safe.
Hi Swagatam,
I have Smps with constant output 5v and 35W current capacity (with over voltage and over current protection). I am planning to utilise it as 4 port usb mobile charger.
However i want to limit the current Max upto 3A per usb port, so that it does not harm the mobile incase something goes wrong at mobile internal circuit end.
Is it possible to make such current limiting circuit? Any help regarding this will be highly appreciated. Thank You.
Hi Dharmesh,
All mobile phones have an internal current limiter according to my knowledge, so external current limiting is not required.
As long as your 5V is constant, the current will not have any impact on the mobile phone battery, and it will be charged with optimal current as set internally.
However, if still you want to attach an external current limiter you can easily do it using an LM338 IC configured in the same manner as the LM317, which is shown at the start of the above article.
Hay it’s me again. New project. I have and LCD TV that had a cracked screen. I found out that they make great over head lighting. I don’t want to use the TV guts so this is what I have 40 LED’s in series. Now what I know is the supply voltage is 115 volts dc and guessing each LED needs 20 ma to work at full brightness. So 115 volts dc at 800ma. I want to pull this in the wall at 120 volts AC. Do you have a circuit for this voltage and current. I made a voltage divider but it get so hot even with heatsinks it burns up over time. Thanks
Hi,
If each LED is rated at 20 mA, then the whole series will also consume 20 mA.
To limit this current, you can use a high watt series resistor. The value can be calculated using the following formula:
R = Input Supply – Total LEd FWD drop / LED Current(20mA)
R = 120 – Total LED FWD drop / 0.02
This resistor might dissipate a lot of heat, therefore you can also use a capacitive power supply
https://www.homemade-circuits.com/wp-content/uploads/2021/09/stabilized-transformerless-power-supply-circuit.jpg
Make sure to replace C1 with a 0.33uF/400V capacitor, and the zener voltage can be equal to the total forward drop of the LED series.
I have an interesting situation. I am building a machine to do a precise task in 3 locations. To accomplish this, I’m proposing to use a NEMA 23 Unipolar Stepper Motor to drive an ACME thread lead screw. The
‘nut’ of the Lead Screw will be attached to a Turret arm. The total movement is -30°, stop, do a task, move to 0°, stop, do a task, move to +30° angle, do a task. Then the Fixture will move an increment, and the process will reverse. The effector will do a task, continue to the next stop point, do a task, continue to the next stop point, do a task, and then the motion process will repeat in an oscillatory motion.
I have chosen an appropriate Stepper Motor, and I have a personally-designed Stepper Motor controller.
Why, personally-designed? Because in all my research I could not find a Stepper Motor Controller which
offers direct BCD-coded ‘Step input’. My controller accepts BCD-coded steps from Thumbwheel switches, and activates a square wave generator, with a comparitor circuit. When the number of Motor steps equals the set point on the switches, an active low ‘DONE’ signal is sent. Each time this circuit receives a START pulse from the PLC controlling the overall action of the machine, this circuit activates the Stepper motor through 4 IGFETS in quadrature format. The circuit has been tested many times, and works perfectly.
However, here is my current problem. The machine has only two DC voltages available …. 12 & 24. The motor is rated at 8.6 volts for 1 ampere coil current. I know that IF the actual coil voltage is higher, the motor will develop more dynamic torque. However, I’ve been advised that I should include a current-limiting circuit to limit the current to 1 ampere, I’m a little bit unsure about how to proceed in this regard.
Any comments would be greatly appreciated. Thank you.
Thank you for the detailed explanation. I would advise using the LM317 circuit which is shown at the beginning of the article. It is an extremely reliable and accurate design for all applications requiring current limiting within 1 amp range
In the formula to find the resistance value, for the value of hfe of the TIP32C you have entered 30.
How did you find him?
The hFE value for a transistor may have a wide range, I have selected the approximate average value. For TIP32, the hFE may be between 15 and 50.
Thanks Mr.Swagatam iam 60 years old ritred man required your complete help for laser diode driver circuit use for experiment medical use
Hello Mr. Zafar, Please ask your question, I will try to help!
Good evening Swagatam Ji. I am glad to see your posts and schematics very interesting. The social forum is intending to reform the society through various sociological, psychological, philosophical and scientific attributes and aspects. in this regard i need bit help from you. I want to talk with you over phone. kindly give me your no. or have a conversation with me on my cell no. xxxxxxxxxx. Thanks while awaiting your quick response.
Pankaj.
Odisha.
Thank you Pankaj, I appreciate your kind words. I will surely try to help you, however a phone chat may not be possible….you can share your thoughts through comments here, if possible I will try to solve them them quickly.
Sir this is not a personal matter to help me. the things to discuss about is to help people through reformative measures in different sectores out of that one can be possible with you. the thing is that to provide electronic ideas through writings to be circulated through paper media. so we have to discuss through talkings i feel. if you do have any problem to converse over phone that’s ok.
Thank you.
Hello Pankaj, I am sorry, I provide help only through this site’s commenting platform, so if you have any doubts you can comment under a related post, I will try to help!
Sir,
I will sure comment and ask my problems related to circuits if required in future. But right now I was talking about a matter separate than this. That was about giving Circuit ideas and articles on electronic projects to be published in one free paper which has aimed to reach people to reform their humanic attitudes along with some practical scientific ideas out of which this would be one subjeat. one paper we are going to print in the name ” Samajik Sanskar” and distribute free of cost to the educational institution and Govt./private offices wherein there would be many factual and truthfull sociological, psychological and philosophical aspects along with some practical scientific ideas like project report, how things works, practical health tips and business & financial management ideas. In this connection I need help of you, that I was mentioned. If you would be interested to provide anything related, well. Otherwise that’s OK. Thanks.
Hello Pankaj, I understand the noble cause that you want me participate in, however due to lack of time it may not be possible for me to help you in this regard. I can help only for solving circuit related issues through comments in this website!
Nevertheless, you can feel free to use my articles for publishing and distributing the work to the masses.
Good day Swagatam, please what value of choke resistor in terms of wattage and ohms can I use to limit grid Ac current by 10%. Thanks
Hello Seun, I don’t have the calculations for that, You may have to test it through some practical trial and error. You can use a transformer primary winding for the experimentation
OK Sir, please what size of trafo can I use for the trial and error. Thanks
You can use any small transformer, and connect a load in series with its primary to check the current level limited by the trafo winding. If it is more than 10%, then you can try reducing the number of turns to increase the current proportionately. Or alternatively you an take an iron bolt, wind the 1000 turns of 30 SWG wire and check what result it gives….the experiment is not difficult just depends on what type of winding you want to start with.
Thanks Sir, Swag. Can the 30swg handle 100w load.
Yes it will be able to handle a 100 watt load
Hello Swagatam,
I need a current limiting circuit to power a small resistive heater in an automotive application. The heater is for the carburetor choke, which uses a bimetallic coil to pull the choke rod. The car is a 12V system with common ground (earth) which provides the negative side of the heater’s circuit (the heater is riveted to a plate bolted to the engine); as such there is only one wire to it. Since I can only manipulate V, I, R on the positive side, am I correct in thinking the PNP version of the limiter is my solution? Is there a better one?
The original circuit that operated this arrangement was a bimetallic thermal “snap switch” and a wirewould resistor. The snap switch worked as a timer and the resistor limited current to the heater. Both items were failure prone so I’m trying a more elegant solution. I have simulated the approximate average “timing” of the snap switch with a simple 555 circuit; when it switches off I would like to limit current to the heater to ~500mA, just enough to keep the choke fully open. The limiter will be in constant operation once the initial timing event has passed, so any ideas you might have that would make the circuit more robust are certainly appreciated!
Hello Dr Jass, If you are able manipulate only the positive side of the circuit, in that case a PNP type current limiter can be the only solution. So, you can try the PNP version of the current limiter as indicated the diagram
Thank you so much sir, for this article. I am learning very interesting electronics stuff because of you.
After getting this I think I can use directly Led with (above mentioned current limiters) in solar wind hybrid charger circuit instead of including battery in all these …Am I correct sir? If not plzz correct me..
Thank you so much for your quick reponse.
Thank you Zeel, yes you are correct, you can use the above circuits directly with solar, wind energy source to drive an LED safely.
Hi Swagatam,
Thank you for your time writing this article, But could you explain better the R1 and R2 calculation for the MOSFET use in esfesific you mention the formulas are the same as the BJT transistor”
R1 = (Us – 0.7)Hfe/Load Current
But what is exactly the HFE value for a MOSFET I can’t find ir anywhere in the datasheet of the IRF540?
or in the case of the MOSFETS what terminology should be used instead of the HFE of the BJTs?
Thanks
Raul V.
Hi Rahul,
MOSFETs are like ON/OFF switches similar to mechanical switches, they do not have current gain. They are either fully ON or OFF, since they are voltage driven devices and not current driven
R1 calculation for the MOSFET will be based on the collector current handling capacity of the T2 only. So R1 can be any value between 10K and 1 Meg, because for a MOSFET current is immaterial, and the gate can work even with minimal current from a high resistor such as 1 Meg.
So to calculate R1 for the mosfet, consider the current handling capacity of the T2, and select a resistor such that its current is at a level which can be easily handled by the collector of the T2.
Hi Swagatam,
Thanks very much for your article!
I am trying to drive a 700mA IR LED (1.5v forward voltage) from a 5v power source. With a simple current-limiting resistor, I would need a resistor of R = V/I. This = (5-1.5)/0.7 = 5 ohms. And P = IV = 0.7*(5-1.5) = 2.45 watts. I only have 1/4 watt resistors, so want a more efficient circuit.
Using your “Transistors” circuit, do I still need resistors > 1/4 watt? Can you include the resistor power calculation in your article? I have BC337 and 2N222 transistors available. I also have AMS1117 voltage regulator or a variable buck converter, if these would help.
Thank you,
Andrew
Hi Andrew, yes, for the transistorized circuit also current sensing resistors will be required, albeit with much lower wattage value compared to resistor without transistors. I have added the wattage calculations formula in the relevant sections.
Thanks Swagatam, for your quick response!
Ah, yes I see now. For my case, R1 = (5-0.7)*30/0.7 = 184 ohms. So P = V^2 / R = 5^2/184 = 0.14 watts. So a 1/4W resistor will be fine.
How do I find value for Hfe? You use 30. I have bc337 or 2n2222 transistors. When I search for “hfe bc337” I find “Current Gain (hFE), 100 to 630”. Which value do I use?
In your transistors example there may be a mistake. Your schematic shows +12v voltage source, but you use +35v in your calculation (R1 = (35 – 0.7)30/2.5= 410 Ohms).
Thanks again!
Andrew
No problem Andrew, The R1 resistor is for the base of T1, but the actual current limiter is the resistor R2, at the base of T2. So in your case R2 = 0.7/0.7 = 1 Ohm and its wattage is 0.7 x 0.7 = 0.49 watts
You can assume the gain to be 200 for BC337.
Actually the mistake was in the diagram, it is supposed to be a 35 V circuit example for controlling a 100 watt 35V LED module.
Excuse me the problem may be me and my ignorance.
How did you find the HFE (200)?
You can get the average value from the datasheet of the device, or you can practically measure it with a mulltimeter.
With regard to your mosfet circuit version, above:
I still have a bunch of the Fairchild BS170 (rated to handle 500ma in a to92 case) mosfets I’d mentioned in a previous message.
I want to drive some 700ma UV LEDs, though (ten of them, intended to make a 30W 365nM lamp for curing photo-activated polyester and epoxy resins) . Can I simply parallel 2 or more of the BS170’s to get safe and predictable results with the current split between them? I’m not familiar enough with mosfets to know whether or not doing so might result in some non-obvious (to me, anyway) interaction between them. If it can’t be done “simply” (because of some such interaction) is there a “not-so-simple” approach (perhaps using diodes to block them from interacting with each other?)?
[with electronic stores near me still closed due to the pandemic, it’s not so easy to cheaply get parts in small quantities, or without paying more for shipping than the parts themselves, so I’ve been trying to make do with what I already have, when i can ]
Yes you can use BS170 in parallel without any further modifications to the shown design. Just join their respective leads together and put them on a single common heatsink, that’s all
Hi sir, Please clarify bit more under heading , Using Mosfet for current limiting , How to calculate R1,R2 values and Working ,how much current we can limit ?
Hello Anushree, I have added the required information under the specified section!
The calculations will be exactly similar to the previous versions in the article.
I have a 5V 18A desktop computer power supply and I want to build a multiple port charging station where more than 10 handsets (phones) can safely charge without over current issues.
Do I need to build the current limiter for each of the output that will be connected to the handsets?
You can try the first concept from the above article for each channel separately, using IC LM317. If you find the IC heating up, you can try using LM338
A 12 volt power(AC/DC), if it’s output is short, a bulb of 12 volt should light up and when the short section is normal, the bulb should turn off and the power should be back to normal. How is this possible?
Add a low value series resistor with the line, connect a suitable bulb across the resistor. The bulb will light up as soon as the output is shorted
Sir,
I have a proublem. Transformer out put current after 10amp bridge rectifier is 7amp.when directly connected to DMM. I connected 2.2ohm 5watt resister and the current reduced to 3amp. But after lm338 voltage controler circuit, I am getting only 1.15 amp when connected to DMM in series. Since I need 2.5 amp for a battery charger I removed above 2.2 ohm resister. But current still reduced to 0.9amps. Please sir, solve my proublem.
Thanking you sir,
Leelesh.
Leelesh, there can be only two reasons behind this issue, either your LM338 is a duplicate or faulty, or your connections are not fully correct.
A good LM338 will produce a guaranteed 5 amps provided the input is rated higher than 5 amps and the IC is mounted on a large heatsink.
Thanks a lot sir.
Current limiter precision diagram:
I would like to measure the current intensity that I have at the output of the circuit by means of an ammeter when the value of the potentiometer varies, since when I regulate the
output current with the potentiometer I don’t know what exact current value I’m getting at the output of the circuit without a current measuring device. and if possible
Please, where should I connect the ammeter safely so that it works correctly, thank you very much for your attention, I await a reply please through
by e-mail to HNF1975@gmail.com.
You can easily do it by connecting the ammeter directly across the output of the limiter. However, remember doing this will heat up the current regulator, so you must take the readings quickly for the necessary calibration.
Hi Swagatam,
Will the circuit work with 3 volts to power standard 3mm 15-20mA LEDs?
I’ve bought a similar current controlled circuit but it’s minimum of 4 volts and I need the smaller battery size. Is the voltage drop always going to be too large to power LEDs with 3v forward voltage?
Hi Jennifer, the transistorized circuits shown at the bottom section of the article will easily work with 3V supplies.
HI Swagatam,
Thanks very much, so the one with the BJT 2N3054 circuit at the bottom?
If you want to fix the current to say 15mA what is the calculation for a fixed resistor (rather than the variable one)?
And I would this be suitable for any number of LEDs off the output or is there an upper limit?
Hi Jennifer, sorry, I was actually referring to the first transistorized circuit using two transistors, the one which shows the big square LED.
Forgot to tell you that you simply don’t need any special current controller for smaller LEDs with 15mA, 20mA current specs, just a resistor is enough for the job for these low current devices.
A specialized current limiter becomes crucial only for those LEDs that are rated with over 100mA current and have the tendency of becoming hot themselves.
Using the above circuit would be an overkill for your 15 ma LED.
You can read the following article for getting further details about the connections and the calculations:
https://www.homemade-circuits.com/how-to-calculate-and-connect-leds-in/
Hi Swagatam,
I didn’t want to say too much on an open forum but what I need is a way to control current so I can connect multiple LEDs to the same microchip IC output without needing a resistor for each individual LED. I have bought a tiny unit that does this with fixed mA output but it needs minimum of 4volts (4-24v) and I wanted to know if it was possible to successfully run say 5 LEDs off a single IC output at only 3volts using a current control circuit with 10-15mA output. It needs to be a small footprint so it can fit on a small PCB and a 3v battery.
I hope that explains it better.
Hi Jennifer, In this situation, at 4V, the LEDs will need to be connected in parallel across the source, and the 15mA will be shared across all the 5 LEDs, which means each LED will get just 3 mA. At 3 mA each of the LEDs will look very dimly lit.
Hi Swagatam,
Found the datasheet – is there an alternative to the 2N3054 in a more standard small surface mount package? That BJT is too large and expensive for my application but the simple circuit is perfect. I can’t have too many components as it needs to fit onto a very small PCB.
Hello. Great site. I need a simple current limiting circuit for a 12v solenoid valve on a sailboat hyrdraulic steering system. Cannot live with the power consumption of 2 amps to hold the solenoid open and it is not necessary. One user has wrtitten “I designed a current controller using $5 worth of parts that you can get from Radio Shack. The current controller allows full 2 amp current during “pull-in”. 400 milliseconds later it falls off to a modest “hold-in” current of 800 milliamps.”
Any suggestions how to do that with LM338? I am thinking some sort of an RC network to control a mosfet that gives path to one resistor when first energized, then a path to the second resistor value when the capacitor voltage decays, but not sure how to approach that.
Hi, thanks, the following idea should accomplish the intended slow start current limit application:
The R3 develops the required switch ON voltage for the BC547 transistor base whenever the current limit exceeds the maximum tolerable threshold.
But due to the presence of the 470uF cap, the BC547 is unable to trigger quickly allowing the full current to pass, at the onset. However, as soon as the 470uF is fully charged, the BC547 activates and becomes functional for controlling the current limit…
Thank you so much, but I do not completely understand.
For a maximum operating current limit (after capacitor delay) of 0.8A, do I use R3=0.6/0.8 = 0.75 ohms?
Does the value of R1 or the setting of the P1 pot matter?
Yes your calculations are correct, but since a diode is also included, the “0.6” will now become 1.2V, therefore R3 = 1.2 / 0.8 = 1.5 ohms, Wattage = 1.2 x 0.8 = 0.96 watts or 1 watt.
other resistors determine the voltage control parameter of the output. R1 and R2 are interdependent, and R2 has to be set to match the load voltage specs.
you can use the following software for calculating R1, R2 values precisely:
https://www.homemade-circuits.com/lm317-lm338-lm396-calculator-software/
Fantastic!!
Thanks Again. Hugely helpful.
Glad to help!
Hi! In my project I need a 10A current limiter, thus LM196 would be the right choice. But it is 24 VDC and according to its datasheet I cannot exceed 15V. So, what is the best IC in my case. I haven’t found a good one.
Do you have any tip?
Tks
Eduardo
Hi, you can try the second last circuit from this article;
https://www.homemade-circuits.com/ic-lm338-application-circuits-explained/
Hello, I am looking to replace some indicator lamps in an old JVC A-X9 amplifier, but there are no specs in the service manual, so I am trying to figure out the circuit diagram. There are two pnp transistors connected at their bases in parallel at the beginning of the light bulb circuits, and each transistor feeds a different circuit. Circuit one has 5 bulbs in series with various switches, and circuit two has 7 bulbs in series with various switches and also RC circuits.
My question is would the pnp transistors act as current limiters for these circuits? I tried to build a simple model in iCircuit, and the current was always the same no matter what bulb characteristics I chose.
Hello, Without checking the schematic practically I cannot suggest much. If the LEDs are 20 mA type then current limiting can be done with series resistors, transistor current limiting is normally required only for power LEDs, with current higher than 100 mA
The original circuit used incandescent bulbs, not LEDs. I would like to change to LEDs, so I am trying to figure out what the circuit will require for modification. Can I send a pic of the schematic?
If they are incandescent lamps then definitely the PNPs are not limiting current, they are probably used as switches. If you use 20 mA LEDs which will be much brighter compared to the incandescent lamps, then appropriate resistors can be used for the current limiting. Images can be sent by uploading to a free image hosting site and providing the link here.
https://photos.app.goo.gl/ViT82BJekkvEDB9L8
Here are the schematics of the indicator lamp circuits
Yes those are incandescent lamps and don’t require current limiting, you can replace them with individual LED/resistor assembly
Thank you. Can you determine the type of bulb from the schematic? The PWR and SPK-1 lamps are seeing 14.6V in series, so they have a voltage drop of 7.3 each. But for the lamps in the series with REC, TAPE MON, etc, I don’t understand how the RC circuits affect the voltage, so I can’t spec the lamp. My ultimate goal is to tell the gentleman who is building the LED replacements for me what the voltage of the bulbs being replaced is.
Swagatam, i have a need to do DC current limiting on a much larger scale. Say we had a 24VDC system with capability of 350A continuous. To prevent battery overheating during charging, we want to do current limiting to 40A on a leg of the circuit. What is a commercial solution that we can apply?
Dave, you can try applying the second last design by upgrading the MOSFET with 5 to 6nos of IRF540 in parallel. Also, to further reduce the dissipation on the MOSFET and the limiting resistor you can use the 24 V in pulsed form. Make sure to put all the MOSFETS over a common heatsink.
i have a collection of 50’s/60’s model trains which work fine until i try to use a modern transformer/controller 0 to 12 v dc @ 2.5 amps. the controller “see’s” a large inrush current and before the locomotive can move and trips the overload circuit in the controller. i need to limit start up current but also retain the torque to get it moving i was looking at the lm 317 circuit but this would need to cope with reverse polarity to make the loco change direction also it needs to be small to fit inside the loco approx space 2cm x 1.5cm x 1cm there is a capasator and a resistor already in circuit assuming capasator is for radio interfearance suppression (wired across brushes) and resistor for current limitation
I don’t think it’s the current that needs to be restricted because if current is restricted then the torque will also get affected. The idea should to slowly increase the voltage instead of applying it at once.
You can try the “Slow Turn ON Output Power Supply” concept presented in the following article, this may probably solve the issue for your application
https://www.homemade-circuits.com/ic-lm338-application-circuits-explained/
Swagtam, I’m trying to use the the Darlington Transistor schematic to limit current to 5volts.
I calculated R1 value to be 169 ohms ( R1=((8.4-0.7)*(110))/5) and R3 to be .12Ohms (R3=0.6/5). My load resistor is set to .0001 ohms. Proteus circuit simulator shows my load drawing 3.10 amps. Battery voltage is 8.4V (LiPo). How can I achieve the full 5 amps I designed it for?
Hi Gary, I won’t be able to judge the proteus results, but according to me the formula results are quite reasonable and can be relied on for achieving the desired conditions.