PWM LED Light Intensity Controller

The post explains a simple IC 555 based PWM controller circuit which may be used for controlling the intensity of a specified LED bank. The idea was requested by Mr.Rajdeep.

Technical Specifications


Fantastic blog you have got. I learnt many things from your blog.

I have read that dimming LEDs by reducing voltage or current lowers the LED lifespan. Is it correct? And the best way to dim LED is by PWM?

I did some more research on this matter and found out that LEDs don't get damaged, but the colour spectrum of LEDs changes at lower current/voltage.

A 6500K LED will move towards 5000K when dimmed, I found this information on some aquarium forum, I can send you the link if you need. Also, they say LED tends to heatup when current-dimmed.

Anyway, can you do a tutorial on pwm of high power LEDs. I have been searching for a tutorial, but could not find any suitable MOSFETs that will work in 5volt, while carrying 20-30amps.

Most MOSFETs work in 10volts, so is it possible to connect a MOSFET to a bc547 & then to a pwm circuit? Will it work, or it will be slow/inefficient?

Can such huge load be controlled by a 555-pwm?

Another question, will a pwm circuit work with a 'LM317 constant current circuit'?

P.S: I am planning to do a full LED aquarium lighting, so I am making sure it will work. Sorry for a lot of questions, I am not an electrical engineer, so I need your help. Sorry for bothering you... :-)

And will pwm work in series with a 317-constant current driver circuit?
If this works, I am thinking the circuit will be like this:

12V smps --> 555pwm --> 317 current limiter --> LED

Rajdeep.

Solving the Circuit Query


Thanks Rajdeep! What you have learned from the forums could be completely incorrect and misleading, LEDs work most efficiently when driven with minimal currents, although that would mean proportionately lower intensity.

Driving an LED through PWM actually is not difficult....higher duty cycle will produce higher intensity and vice versa, that's the basic principle behind it.

The Design


First let's learn about a 12V LED PWM controller circuit, later at the concluding section of the article we'll see how the same may be implemented using 5V supply and a mosfet.

The following circuit idea shows a simple PWM controller circuit using IC 555 which can be used for controlling LED intensities from 0 to maximum digitally.



In the image above, the supply is acquired from an SMPS unit which applied to the PWM circuit through a LM338 current controller circuit stage.

The pot P1 is used for adjusting the PWM duty cycles to the LED bank for achieving the desired intensity levels.

The resistor R3 determines the limiting current level from the IC LM338, it may be calculated with the following formula:

R3 = 1.25/LED current

The circuit shows a 36 LED (1 watt each) bank being driven by the PWM and the current controller stages.

The LED series resistors are introduced for safeguarding each 3 LED string from over voltage. since the total forward voltage drop of the strings constitute to 3.3 x 3 = 9.9V and the supply voltage 12V that's about 2V higher.

R3 controls the overall current for the entire LED bank, and may be calculated by using the above mentioned formula, for the shown design the result may be calculated as:

R3 = 1.25/0.35 x 12 = 0.29 Ohms

Wattage = 1.25 x 0.35 x 12 = 5.25 watts, here 0.35 is the current through each LED string, 12 is the number of strings, and 1.25 is the fixed reference as specified by the IC LM338 datasheet.

With a little effort you can skip the LM338 stage by modifying your existing SMPS unit to any desired maximum current limit, as per the specs of the LED, the entire procedure may be learned below:

How to make a variable current SMPS circuit

Using PWM Control


In cases where the supply voltage is restricted to 5V, and the intended applications requires a PWM control of the LEDs through a mosfet, the following circuit can be suitably used for the same.


Circuit Diagram




As we can see, the above configuration  is identical to the first one, barring the addition of the voltage booster stage between pin3 of the IC 555 and the mosfet gate.

Here a couple of diodes and capacitors effectively raise the pin3 PWM level from 5V peak to 10V peak, this becomes imperative since a mosfet is being used for the regulations, and mosfets do not respond optimally with gate voltages lower than 9V.

The shown mosfet gate voltage booster stage can be also applied with PWM outputs that may be derived from an Arduino board or other MCUs.

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Comments

Raj said…
Thank you very much for this article.
What is the transistor 'T1'?
And is the value of R2 = 10 ohm?
I wanted to control 10Watt LEDs, which are 12V, ~1A. What should I change as per the first circuit? Haw many 10W LEDs can be controlled with a single 555?
Swagatam said…
T1 can be any suitable mosfet rated at above the voltage and current ratings of the LED bank
Swagatam said…
you can as many as you want just by upgrading the power of T1....for example with an IRF540 you would be able to use as many as 150 LEDs in parallel
Raj said…
Will this circuit work?
s18.postimg.org/y8l1m6sp5/5_V_pwm_led_circuit.jpg
Sorry, I had to edit your picture.
IRF540 has a gate voltage of 20 V, will it run on this circuit?
Pritam Bhowmik said…
should not 555 be driven with a supply greater than 5v to operate
Swagatam said…
20 V is too high, it must be blow 15V and above 10V.

your image shows 5V as the gate drive?
Swagatam said…
4.5V is the minimum limit....
Raj said…
Yes, 5V comes from an arduino data pin.
You wrote, "Here a couple diodes and capacitors effectively raise the pin3 PWM level from 5V peak to 10V peak"; so my circuit should work with a 12 V supply...
Swagatam said…
when you said "IRF540 has a gate voltage of 20 V, will it run on this circuit" I misunderstood it and thought that you are asking if 20V could be used at the gate....My above question was in response to this



yes 5V when raised to 10V will be fine for the mosfet
Raj said…
This circuit doesnot work, I tried It out today.
Swagatam said…
did you check the voltages at the various and did you try to find why it's not working?

first try without the voltage booster...
Raj said…
At the first 10uF capacitor, the pwm voltage range drops to from 0-5V (from arduino) to 2-3V (at multimeter).
I tried running the MOSFET with a bc547, it seems the maximum voltage that can be obtained is ~9V at the LED due to loss at the LM317, bc547, IRF540. So, I am thinking of using simple relays instead of this circuit, as there is a lot of complexity, cost, voltage drop in the system.
BTW, the bc547 was very hot when running the MOSFET.
Now I am thinking of a relay circuit through ULN2003.
Does ULN2003 inverts the signal?
Can a relay support 20A current?
Swagatam said…
I have modified the second circuit, you can check it now.

ULN2003 have Darlington transistor arrays, so each input/output set will work exactly as a Darlington transistor configuration would work
Rohit Vij said…
Hello Swagatam Sir,
I am a beginner and hobbyist and i wanted to ask you a general question regarding schematics and circuits design diagrams .I have seen many electronics schematics across the web and find that the voltage of capacitor (polarized and non-polarized)and watt of resistor are not mentioned i.e. C1 0.0082uf and R1 100K . Is there any general rule of thumb for this kind of values? If we do not know the exact values then will it be very difficult to purchase such parts and one could face difficulty in simulation(because simulators does required the value of volt and watt). The exact value may be required for other components also.Sir please sort out my problem.
Swagatam said…
Hello Rohit,

all resistors which are unspecified can be assumed to be 1/4 watt by default.

all capacitors which are non-electrolytic are mostly available with 50V rating in the market, therefore mentioning the voltage rating for these caps is normally ignored since it's already well above the safe level....however if the circuit's supply voltage is above 40V then it must be appropriately upgraded, and needs to be specified.

electrolytic capacitor voltages must be preferably rated at twice the supply voltage

the specs for other parts can be acquired from their respective datasheets.
Abhishek Kumar said…
I want to drive some 5W leds using PWM using above circuit.
The specs for led are:
Vf= 9-12V
If= 750mA
What changes should be made to the above circuit for the leds with above specs.
Also I'll be making three drivers,one for the above led ones and other two for led banks with 3.0-3.4V,750mA and other led bank with 3.0v-3.2V,350mA.
(I asked you about how to drive the above led banks some days back if you remember.But since I'll be using them i aquarium,I need to control brightness too so decided PWM method.)
I'll be highly grateful to you if you tell me the changes to be made in the above circuit to drive 3 led banks separately.

(Please edit the following part as these are my contacts.)
You can even E-mail me on akp.ajinkya@gmail.com or whatsapp me on 9634943246,so that I can discuss with you.
Swagatam said…
You can make the following design which looks more effective than the above

https://homemade-circuits.com/2014/11/150-led-pwm-tubelight-circuit.html

the circuit parts will remain as is, only the LED series resistors will need to be calculated and positioned as per the LED specs.

Abhishek Kumar said…
Took a look at the circuit,seems like transistor can only handle current about 5A,but i'd be requiring more than 10A to drive them...i.e will be using 14 of the above said leds of 5w so 750x14=10.5A....is that correct?
So Which transistor or mosfet can i use for such high current?
Also I'll be driving the led and circuit from a pc smps(a hacked one) with 24A on 12V rail.Also would it be a good idea to drive both led bank and 555 ckt with the same supply i.e pc smps.
Apologies for asking too many questions.
Swagatam said…
for 10 amp you can try a 2N3055 transistor with a 2N2222 to form a Darlington pair.

a mosfet can work but its full gate supply will need to be 5V higher than the LED operating voltage for getting maximum illumination.

same supply can be used for the LeD and the circuit
Abhishek Kumar said…
Many thanks bro..will try it.Will contact again if i have some doubt :)
Abhishek Kumar said…
Tried the circuit from the link you gave above with a darlington pair of 2n2222 and 2n3055,but leds doesn't attain their full brightness,the dimming action is there but they just don't light up like when i power them directly.I am powering the circuit using a hacked pc smps and all leds are connected in parallel.I also tried powering 555 ckt using another supply and transistor-bypass ckt(2n3055) using the pc smps for led but to no avail.
Should I try directly connecting pwm output of 555 to 2n3055(i.e without 2n2222 in between)?
Swagatam said…
May be you did not make the Darlington correctly, or may be one of the transistor is faulty, otherwise it's impossible.... because in the Darlingtom mode the current gain should be extremely high making the LEDs almost fully bright, when the PWM is set at the full width.

make sure the average voltage at pin#3 is almost equal to the supply when the PWM is maximum or if this is not happening then it's the fault of the PWM generation
Swagatam said…
without 2N2222 attached or without a Darlington configuration, the gain could be 1000 times less...still you can try that
Abhishek Kumar said…
Don't know why the configuration didn't work,I tried the same ckt with a single 10W led,it worked good(although with a smps based 12v,2A adapter),seems like smps is limiting supply current.
Abhishek Kumar said…
Are you on whatsapp bro?
Swagatam said…
but if the LEDs are working without the PWM circuit then the SMPS cannot be the issue. Is your 2N3055 heating up a lot? this transistor could be the culprit and causing insufficient current for the LEDs.

sorry bro whatsapp will not be possible because I have 100s of readers and all might start requesting this facility...so it won't be possible.
Abhishek Kumar said…
Oh..yeah,I can understand about the whatsapp issue.
The 2n3055 remains at room temperature 'cause the ckt isnt drawing much current(only about 600-800 mA).Should I go ahead and try 2n3055 directly fed with pwm output?
Swagatam said…
you can try it, if it works then the problem is in your 2N2222 transistor...make sure to use a low value resistor at the base....you can calculate it using the following formula

R = (supply V - 0.7) x 30 divided by LED current
Harimel said…
Hello Swagatam Majumdar, i saw your circuit project and i was thinking of using you project to create an LED lamp. I just want to ask is it possible to increase the number of columns from 12 to 20? Also how can i choose the value of T1? Thank you in advance..
Swagatam said…
Hello Harimel,

yes you can put as many parallel columns as you may want, simply by adding the required number of LED strings with their specified series resistors, but please make sure that the supply current is also appropriately upgraded for enabling proper illumination on the LEDs.

the mosfet just like the supply specs should match the LED voltage and the current.....preferably it should be twice of the LED series fwd voltage value and the total LED ampere value. Mosfest having higher values than this will have no problems but it should not be lower than the LeD power specs.
Unknown said…
Hi swagatam i love your article am having a problem with my lg plasma tv it screen lights keep on blicking for every 2sec Can I use this circuit you posted here to control it screen lights
Swagatam said…
Thanks for liking my articles, A plasma screen is supposed to be working with an SMPS supply, so I am not sure how you would be associating the above circuit with your plasma screen, since the circuitry of the screen would be extremely complex and sophisticated...I wouldn't recommend doing any kind of modifications to it..
Ramesh Adhikari said…
Hi, this helped a lot, thanks for sharing. Is there any post that talks about PWM using arduino for controlling AC power (using fast switching device/IGBT)? The explanation of arduino programming for this concept would be very useful for students like us. Thanks again and we hope for such project from swagatam.
Swag said…
Hi, I am glad it helped you, I have one Arduino based circuit which you can find below, hope this one fulfills your requirement

https://www.homemade-circuits.com/arduino-pwm-signal-generator/

https://www.homemade-circuits.com/high-current-motor-control-using-arduino/
nitin chaudhari said…
Sir, can I run a pwm circuit on mobile battery 3.7v??
Any cheap solution?
Swag said…
Nitin, the IC 555 will not work correctly with 3.7V, you can try the following circuit instead:


https://www.homemade-circuits.com/how-to-make-any-light-strobe-light/

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