The post explains a simple LM317 IC based RGB 3 watt LED color mixer circuit, which can be used for demonstrating the color mixing effects of red, blue, green colors as specified in the standard color charts. The idea was requested by Mr.Praveen.
Technical Specifications
My name is Pravin, I work in school as Physics technician.I need to show kids colour mixing of red green and
blue. I would like to be able to vary the brightness of the three
colours LEDs to show the effect it has on screen. I have 3W RGB LEDs.
Could you please help me to make a circuit . The simple the better.I have tried to make one with LM317 IC.
Regards,
Pravin
Analyzing the RGB LED Specifications
The following image shows a typical 3 watt RGB LED.
According to the datasheet of this LED the three leads on each side correspond with the three leads on the other side on a straight line such that the two straight ends left to right form the terminals of the red, green, blue LEDs embedded respectively inside the package.
Therefore, the upper most left, right end to end leads may form the cathode, anode of the red LED, the center left, right leads may correspond to the green LED, and identically the lower most left, right end to end leads may signify the terminals for the blue LED.
How to Configure the LED Pinouts
Configuring these leads of this RGB LED such that the individual colors can be adjusted separately, is actually quite easy.
The idea is simply to integrate three separate adjustable voltage regulators for these three LEDs, for example by using a LM317 voltage regulator, as shown in the following diagram.
Using LM317 Regulator for the Control Circuit
Referring to the above diagram one can visualize that the three LM317 voltage regulators are in fact exactly identical with their part and wiring configuration.
Each of the modules have the facility of voltage adjustment and are all current controlled through a BC547 transistor and a resistor Rc.
The leads of the 3 watt LED are hooked up individually to the outputs of the 3 LM317 circuits, while the input is fed to all the 3 modules through a common DC source which could be a SMPS adapter rated appropriately for handling the RGB illumination.
The anode, cathode orientation of the LED is also indicated in the diagram which must be carefully and correctly set before connecting them to the 317 outputs.
Once everything is completed, and the power is switched ON, the voltage control feature present in the LM317 modules can be used for setting up the illumination levels of the respective LEDs discretely for creating any of the specified color effects, right from the primary RGB to voilet, indigo, orange, maroon etc etc.
The 10K presets of the 317 circuit can be replaced with 10K pots for enabling an external control for the intended color mixing effects on the LED.
The value of Rc can be calculated by using the following formula:
Rc = 0.6/LED current rating
Simple RGB Color Mixer using Transistors
For color mixing, 3nos of 8050 variable voltage power supply could beuilt and their outputs connected with points A, B and C.
For creating fading effect, fading circuit could be connected to point E
For flashing effect point F could be used for supplying the flashing signal.
3 Color LED Automatic Color Change
Using this circuit, a multicolored LED may gradually mix and shift across 3 colors. The color transition can be from yellow to red to yellow to green before returning to yellow.
This cycle is then continuously repeated. Both the construction and the theory of operation are extremely straightforward.
The IC 556 dual oscillator/two timer's timers are set up for astable functioning with a 50% duty cycle. One timer is programmed to oscillate a lot more quickly than the other.
Each timing capacitor voltage is supplied to two comparators, which then apply a voltage to the multicolored LED with a polarity that depends on which capacitor voltage is higher.
The red and green LED components alternately light up as a result of the voltage of the capacitors fluctuating quickly, creating the appearance of yellow light.
The duty cycle is altered to favor one hue or the other as the average value of the slowly varying voltage from the slower timing capacitor alters.
As a result, the change in color appears to be mixing seamless. Hopefully the automatic RGB mixer effect can be utilized in a variety of ways.
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