How to Add a Dimmer Facility to a LED Bulb

In this article we learn how to make a dimmer circuit for LEDs bulbs and LED tubes which are intended to be operated with mains 220V or 120V.

How LED Bulbs Work

We know that our ceiling fans and incandescent bulbs can be easily controlled using triac dimmer switches, and we are quite used to with dimmer switches in our homes installed for controlling such devices.

However with the advent of LED bulbs and tubes, incandescent bulbs are slowly making an exit, and our home bulb holders are getting replaced with LED bulbs.

LED bulbs come with a built in SMPS driver within their holder cabinet, and an SMPS circuit makes it difficult to operate or control through a triac dimmer switches, until and unless its suitably modified for the application.

Because, the SMPS driver inside LED bulbs and tubes strictly employ inductor or capacitive based circuits which are never recommended to be used through triac dimmers, since triac dimmers utilize phase chopping technology for the dimming purpose which unfortunately does not suit inductive/capacitive load control.

If used then the LED bulbs do not dim correctly rather show erratic dimming or brightening behavior, due to an incompatible reaction.

The best method and probably the technically correct approach is the PWM technology which can be effectively used for controlling or dimming LED bulbs or tubes. The figure shows the design may be implemented.


 Dimmer feature to a LED Bulb

How it Works


The idea is actually very simple, thanks to the MOC series opto couplers which make triac control through PWM extremely easy and compatible.

The right side of the figure comprises a standard MOC3063 IC based triac controller circuit which is operated through an IC 555 based PWM circuit shown at the left side of the figure.

The IC 555 is configured as a standard adjustable PWM generator which feeds the desired PWM to the input pin#1/2 of the MOC IC.

The adjustable PWMs are appropriately processed by the IC through its built in zero crossing detector circuit and photo triac which is ultimately used for controlling an external triac BT136 via its output pin#4/6.

The connected LED bulb now responds to the PWM content applied by the 555 circuit and proportionately adjusts its brightness as per the user preference.

The PWM control is executed through the associated 100K pot, which must be suitably insulated, as the whole circuit is not isolated from mains current.

The circuit is not isolated from mains despite of the opto coupler due to fact that the IC 555 requires a DC supply for operating which is supplied from anon-isolated transformerless power supply, this is done in order to keep the design compact and avoid the use of costly SMPS module which could have been otherwise an overkill.

If you have any concerned question regarding the above explained dimmer circuit for LED bulb, you can express them through your comments.

UPDATE:

A Simpler LED Lamp Dimmer Circuit


In the above design we seem to have missed one crucial point. All LED lamps use DC operated circuits and therefore  incorporate an internal bridge rectifier to convert the input AC to DC.

This implies that LED bulbs could be also operated from a DC supply input, and therefore the triac can be replaced with a power BJT stage, as shown in the following figure. This simplifies the design greatly and allows us to use the IC 555 PWM directly with the LED bulb via a the indicated opto-coupler and a BJT.


How to Add a Dimmer Facility to a LED Bulb

Need Help? Please send your queries through Comments for quick replies! And please Bookmark my site :)




Comments

VIJAY AJ said…
What is the maximum pwm frequency from ic??? 555
Swagatam said…
should be set as per the triac's frequency handling specification
VIJAY AJ said…
Sir if ic 555 produces a frequency in the range of kHz. Weather it will affect the triac because triac should be triggered at every cycle when it reaches above the zero of ac to control the voltage..I think optocoupler zero crossing detector will take care of it am I right sir???
Swagatam said…
Vijay, yes the IC is positioned to make sure that the external triac and the load are operated at the most favorable conditions, however the concept could be applied even without a MOC IC according to me, since the most LED bulbs would be already having all the protection measures built-in.
Swagatam said…
the 555 frequency will break the AC mains cycle into pieces, and the average RMS of this chopped AC cycle will determine the intensity level of the LED bulb
Swagatam said…
yes you are right, at every AC cycle the triac will get latched and the PWMs will have no effect....the idea needs to be reassessed
Swagatam said…
...or if the gate voltage from the MOC IC is facilitated to swing across a +/- voltages then the triac would respond and switch OFF/ON in accordance with the PWM during the AC cycles.
VIJAY AJ said…
Tnx for your response sir. Shall I operate 555ic to generate 50hz of duty cycle in astable mode of operation to generate pwm. Or do you have any other simple and most reliable idea than this.
Swagatam said…
thanks Vijay, triacs cannot be controlled through PWM, so it won't work....you can try the last updated deign in the article and let us know how it works.
VIJAY AJ said…
Yes sir. Triac is similar to scr. Once the gate is triggered scr lose it switching property until voltage reaches next half cycle. So I feel that generating high frequency pwm is useless because of this I am looking for a pwm in the range of 50hz.am I right sir??? Shall I use ic 555 to generate pwm for my requirement.
Swagatam said…
Vijay, PWM concept will not work for a triacs no matter what frequency is used,,,the phase chopping method as used in dimmer switches is only option of achieving some kind of PWM like control with a triac circuit.
Hi Swagatam ,
I am a regular visitor of your page for more than 4 years. Thank you for your work with dedication and great interest, you have helped me a lot in refreshing my knowledge , improving and knowing new things.Great keep it up.
I have a 10W LED driver, I am using it for 10 X 1W LED.
My requirement is how could i drive two sets of 10 X 1W LED alternatively so when seen by us should be 20 lights glowing.
Swagatam said…
Thank you Jayaprakash,

you can use a transistor astable multivibrator circuit and connect the LEDs across the two arms of the circuit and oscillate the circuit at a rate that would almost make both the arms appear constant.

a transistorized astable circuit can be studied in this article:

https://homemade-circuits.com/2012/01/how-to-make-any-light-strobe-light.html
kunal talele said…
Dear sir how we can fade in fade out 220v ac lamp using ardiuno? Sir please help
Kesava Raj said…
Sir i need Dc led dimmer circuits...
I already use with 555ic Pwm method by using NPN...working good..When i see the led glowing in camera ..the led glows like sagging ..but in normal works good..when i see in camera its sagging sir....

I bought 1 emergency light with dimmer control...same i see in camera its not sagging....which type of circuit they are using....
Pls guide me sir

Is there any alternate circuit sir...


Swagatam said…
Kesava, you can simply use an emitter follower with pot for the purpose...as shown below:

https://homemade-circuits.com/2012/08/simplest-dc-cell-phone-charger-circuit.html

replace the 220 ohm with a 10K resistor, and replace the zener with a 10K pot
Kesava Raj said…
In the between of pot to negative voltage shall i connect 1 k resistor...
When the pot is fully rotate means the output will direct to transistor base ...

Is needed resistor or no need sir
Swagatam said…
you already have the 10k from positive to base...so any other resistor is not required.
Kesava Raj said…
In base i use 10k resistor not working...but i use 1k resistor in base and 10k pot means working....

Is it correct sir or any idea
Swagatam said…
OK then you can use 1K, it will depend and need to be varied as per the current requirement of the load....
Vadiraj said…
Hi Swagatam,
I tried to implement AC LED dimmer using Arduino. Instead of 555 timer I used Arduino PWM signal. But I found that LED bulb flickers. I tried PWM between 0~255. Please let me know what could be the issue.
Swag said…
Hi Vadiraj, keep the frequency to a higher level, may be at 5kHz or more, this will prevent the LED from flickering.
Vadiraj said…
Hi Swagatam,
Thanks for the suggestion. As you said above 5Khz PWM frequency flickering did not happen.
But I do not see any change in LED intensity. What I observed is, for lower duty cycle bulb, say PWM value below 50, bulb doesn't turn ON. Then above PWM 50 till 255 the LED intensity is almost same. No visible difference in light intensity.

When I use only Triac dimmer, the one used for dimming Incandescent, I observe dimming happening as expected. Please let me know any suggestions.
Swag said…
Hi Vadiraj, I am glad you could solve the flickering issue, however the PWM issue will need to be solved through an oscilloscope.

Because if the PWM is varying correctly then the LEd ust also respond and vary its intensity accordingly. Therefore you may have to confirm this through an oscilloscope.

Alternatively you can simply connect a 5mm LED across the PWM output through a 1K resistor and check whether its responding to the PWM variations or not. The same can be done using a DC voltmeter,the voltage must show s gradual change in response to the PWM adjustment.
Swag said…
Hi Vadiraj, since I reply the comments through my website's dashboard I sometimes fail to understand the reference of the comment...sorry about that...

are you referring to the first circuit in the above article?...if you are then I am afraid the assumed concept might not be entirely correct, that's the reason I had to update the warning message at the end of the post.
Vadiraj said…
Hi Swagatam,
I did check the PWM signal, it is varying and also when connected 5mm LED there is variation in brightness. So there is no issues with PWM signal generation w.r.t freq and duty cycle.

When tested with AC 230V LED there is no significant difference in brightness as said earlier.

The reason could be:
1. As the frequency increases the PWM pulse period decreases. If the frequency is above 5Khz and if the PWM duty cycle is lower( ex: <70) then the IGBT will get chance to turn on for very short time in each AC cycle. As a result the LED will not turn ON. If the PWM duty cycle is higher ( 100 ~255) then LED will turn ON but the brightness variation is not observed. The reason could be, the PWM pulse period compared to AC signal is very LOW so the difference in "ON " time for different PWM values becomes insignificant.

2. At lower PWM frequency (Ex: < 1KHZ) the PWM pulse period will be higher. In this case changing PWM values will result into brightness variation. But lower frequency causes flickering.

Let me know your views. What was your test setup and did you notice the above said issues.
Swag said…
Vadiraj, OK that means you are using the PWM with an IGBT and not the design which I suggested in the above diagrams, actually it looks to be a very sensible idea, because LED bulbs do not require an AC anyway, so no need of using triacs.

Therefore according to me involving AC is simply not required...convert the AC to DC using a bridge rectifier, then feed this to the Led via the IGBT. Once this is done, probably all the remaining issues will be automatically taken care of and you will find the LED dimming smoothly...try this and let us know.
Vadiraj said…
Hi Swagatam,
Thanks for your info. I have some clarifications please let me know.
1. The LED bulb I am using is rated for AC 220V. If I supply 220V DC does this work? as it may have some circuit to step down AC to DC as needed. I can give a try, let me know if you have circuit for AC 220V to 220V DC conversion.

2. W.r.t your design the changes I have made is: Instead of 555 timer which generates pulse train I am using Arduino to generate the Pulse with required freq and duty cycle. So logically my circuit should work as yours.
Swag said…
Hi Vairaj, LED bulbs normally use an SMPS for powering the lamp, and since SMPS involve electronic circuitry they have to work with a DC input, so ultimately the mains AC is first converted to DC and then fed to the SMPS.

In my design I have used a triac and an optocoupler which might not work correctly for this application, your idea looks more appropriate.
Ender Duman said…
Hi Swagatam,
Can I use BTA41 in this circuit?

Regards,

Ender
Swag said…
Hi Ender, the last diagram is the recommended one, and you can use a BTA41 in it
Luis said…
Hi, I am not an advanced technician and i need this circuit for a project, so please i would like to know the caracteristics of the Zener and the optocoupler, because as you said "any optocoupler" and the zener reference is missing, i searched the devices datasheet and found that the optocoupler has a maximun voltage of 80V and the Zener only shows Vz, Iz and Pz. The thing here is that i am not sure of connecting the circuit to 120V AC main.

i searched the 1N4742A zener and MOC8050 optocoupler.
Please could you explain better the behavior of the voltages for over the circuit?
Thanks in advance.
Swag said…
Hi, yes the optocoupler needs to be a high voltage opto, I have changed the explanation and added the required number for the optocoupler IC. Also the series resistor with the opto collector is mistakenly shown as 1 K, please use a higher value in the order of 10K to 22K.

The design is not tested, but the concept is perfect according to me and therefore it should work as intended after some minor tweaking, ...and connecting to with 120V should be perfectly safe for the circuit, except to a human touch. Since the circuit is not isolated from mains can be fatal to a human touch without proper precautions.

Contact me for Customized Circuits

Name

Email *

Message *


 Follow on G+  Follow on Facebook   Follow on Tweeter  Follow on G+  Follow on G+

Follow Homemade Circuits