This transformerless mains power supply circuit will allow flashing of a Bi-color 100 LED string, in an alternately switching red, green effect.
Using 2-pin Bi-color LEDs
The proposed circuit can be used as a Bi-color LED flasher, for generating an alternate red, green flashing effect over a string of 100 LEDs.
Bi-color LEDs are available in 3-pin and 2-pin variations, in our project we use the 2-pin Bi-color LED option for keeping things compact and much efficient.
Circuit Operation
Looking at the design shown above, we can see a simple configuration using a push-pull clock generator IC 4047.
The IC is used for generating an alternately switching pair of outputs, from the shown pinout#10 and 11 of the IC.
The frequency of these alternately conducting outputs can be set by appropriately adjusting the pot P1 and by selecting the desired range with C1.
The switching outputs can be seen configured with two oppositely wired SCRs, which are in turn hooked up with the Bi-color LED string across the mains input through a dropping high voltage capacitor C3.
The circuit also incorporates a transformerless power supply stage consisting of C2, D1, C4, Z1, for powering the IC with the required low voltage DC.
When the proposed 2 pin Bi-color LED flasher circuit is switched ON, the IC starts oscillating at the set rate across its pin#10 and pin#11 alternately, driving the SCRs at the same alternating rate.
The SCRs respond to these pulses and conduct accordingly, enabling the Bi-color LED string to illuminate through an alternately green and red color flashing effect.
Caution: The above circuit is not isolated from mains, therefore is extremely dangerous to touch in an uncovered and switch-ON positioned.
Parts list
R1, R2, R3 = 1K
C1, C4 = 100uF 25V
C2, C3 = 0.33uF/400V
Z1 = 12V 1 watt zener
D1 = 1N4007 diode
SCRs = 2nos BT169G
LEDs = 100nos (for 220V input), 50nos (for 110V input) of 2pin, Hi-bright RED, Green Bi-color LEDs
Input: 220V/110V
Correction Update
The design shown above has a serious flaw in it. The SCR1 is configured wrongly and might not conduct as proposed in the explanation.
The following diagram using an DPDT relay appears to be the correct approach for implementing the above discussed Bi-color LED flashing operations:
Sunil says
Hi Swagatam,
One of my friend request me to repair his bi-color (26 nos) LED series. It is china mfg low cost lighting operated in AC current through 4 diodes. Also there is Resistor attached with each LED. How the thing are working on that High voltage using only 4 diodes and resistors?
Swagatam says
Hi Sunil, may be the resistor values are very high, could you tell me what value resistors are used? or you can investigate a little more and check what exactly are used in addition to the 4 diodes to step down the input current.
Abdulbasit says
Hello sir i have 4 pin 8mm led full color sir i wanted to run 300 leds of that so u have any circuit for that
Swagatam says
Hello Abdul, you can try the following concept
https://www.homemade-circuits.com/2014/04/simplest-100-watt-led-bulb-circuit.html
make 3 strings of 100 LED each, and connect them in parallel.
calculate the value of the input capacitor as per the current specs of the LED
satheesh k Nalluswamy says
Sir ,
I did the test twice, i have use bicolour but only shining red color. What will be my fault in this? I'm waiting for your advice.
Swagatam says
Hi Satheesh, yes, SCR1 is incorrectly configured in the first circuit, therefore the circuit might not work, I have designed another one which is shown at the end of the article, you can try that….or alternatively you can try using a 3-pin Bicolor LED with the first circuit by inverting the SCR1 and a few other minor modifications.
satheesh k Nalluswamy says
Sir,
Good day to you I looked at doing this. However, only shining red color. Not two-color fluorescence What is the solution? So please provide you suggestion I have used c1 20k pot
Swagatam says
satheesh, did you connect the ground of the circuit with the SCR ground?
and make sure both the outputs of the IC are oscillating.
and if possible first check the LED series manually by changing the supply polarity with an external DC power supply and check whether or not the LEDs illuminate with their specified twin colors?
Daniel Boulanger says
Me again,
What type of modification could be applied to the circuit so that the leds are fading from one color to the other instead of switching ?
Swagatam says
fading effect will require further stages to be included, which can make the design complex.
Daniel Boulanger says
Hi, I'm assuming that this circuit is designed for main AC voltage of 220 V, right ? (Roughly 2V per led, 100 of them).
What is the value of the potentiometer P1 ? As per the provided values, the switch between red and green would occur roughly 2.2 times a second, assuming P1 is at the zero mark. Putting a 10K pot would max out the switching rate to roughly once every 5 seconds or so. Which value are you using or tested with ?
How much current will this deliver to the leds and how do you calculate it ?
Isn't connecting the main ac neutral to the circuit ground a risky practice ? What if the mains AC neutral and line wire are reversed ? Wouldn't that expose the user to potential risks ?
It should be CLEARLY stated that the ground shown on your drawing ISN'T the earth ground from the mains otherwise if the mains wires are swapped, there will be a good surprise when the user will connect his project. It will flash indeed, but not the expected way.
Swagatam says
I have presented the concept only, rest can be investigated by the interested users.
I am happy that most people here are courteous and respectful to me for my contributions and I acknowledge their immense love and trust and am thankful to them
you can refer to the datasheet of the IC 4047 for finding the correct values of the pot and the capacitor.
the ground in any electronic circuit refers to the negative of the circuit, that's an understood fact.
I have provided enough warnings in this site regarding the consequences of playing with electronics and electricity without adequate knowledge and ignorance, so that makes everything clear.
basit momin says
Hello sir……if I want to run 50 led Series and another 50 leds series in parallel total 100 leds then it will work
Swagatam says
Hello Basit, yes it will work, just connect a 100 ohm resistor with each series.