Connect Common Anode RGB LED's to Common Ground RGB LED's





Introduction: Connect Common Anode RGB LED's to Common Ground RGB LED's

During my RGB led fan project I accidently bought common ground rgb leds while my circuit was disigned for controlling common anode rgb leds.
Now that I have run out of common anode RGB leds I tried to come up with a solution to somehow connect common ground to common anode.

After a few tests I came up with the circuit below. Using 3 pnp transistors it inverts the R-, G- and B- to R+, G+ and B+.
In order to create ground for the led's I connected 3 rectifier diodes to R-, G- and B-.
I am very happy with the results of this circuit and the fact that I don't need an additional wire for ground to drive the common ground leds.

I added the eagle files including the circuit and board. (NOTE: on the board I used BEC PNP transistors)



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    46 Discussions

    Was very easy! Thanks a lot :)

    I had already figured on making a waterproof box for it or run it into the car itself. I am just not technically inclined with electronics so am having some trouble. I do know it is a 22" RGB Scanner bar as shown in the website link I posted. It had a separate controller box that plugged into it with a transmitter to change the lights and patterns. I found a better controller though that would run on my phone so that was the initial reason why I wanted to do this. There were 11 wires that ran from the light to the controller box, I figured out which would be my positive and which three would be my R,G,B neg but didn't realize they would be opposite from my new controller. I tried to look for any convertors all over the web but have yet to see anything other than what you had come up with. I don't want to bother you is there a way you could help me figure out what all parts I would need to make something work? I can provide any information about the lightbar you would need. I have someone who can make the board for me as well. I just need a parts list and a diagram. Like I said I am not electronic inclined so talk of mosfets and such makes no sense to me haha. I would really appreciate if you could help me with this as I would like to have my lights up and running again and not have to use the old controller it came with.

    Ok I need some help from someone please. I know this is old post but could use some advice as I am not completely electronic swavy. I have a Oracle WiFi controller used to control led light bars via remote or cell phone in am app. This is a common anode controller. I also have a rgb illumination grill bar for my car. This had a controller box with a remote to control the colors patterns etc. as shown here. I wanted to use the WiFi controller instead which I know I can however after figuring out what wires were my pos and than my r g and b I found out that this is a cathode led bar. So my delima is would this chip that you made work for me? Or what can I make that would go between the two to convert it basically. I don't want to get a different light bar as this is made for the grill being able to be outside and the controller I bought is expensive as was the light bar. Please someone help me as I said I am not that savy with electronics but if I had a part list and how to do it I could have my dad make it for me as he has a electronics degree but don't think he has ever dealt with this before so having diagram and parts would help .Or if someone sells something like this. Please let me know I can also be reached at

    1 reply

    U would need to build a sealed isolated box as this is a car situation so the pcb would be exposed to the elements. For your purpose I think those rgb bars will use quite a bit of current so mosfets would be your best option. I don't know if there is a commercial option that uses my concept but u might look for rgb common anode to cathode converter on ebay maybe now they have made those. When I made this instructable there were none.

    Does anybody know the transistor values and or part numbers for this? Diagram is straight forward but doesn't show values of transistors specifically the t1 t2 and t3

    1 reply

    Values depends on the amount of leds u are controlling. Small TO-92 can handle 200 ~ 1000 ma for more u need large heatsink mountable transistors or mosfets. Current is for each channel.

    Awesome mate, thank you U make it look so simple!!

    OK, because I
    am new to the electronics, and thinking this through, all of these CCTS shown are for LED strip only not direct RGB led like I want to use.

    With the AQ5 it will control the colour output via it's software on those pins, so I need to take these outputs and feed them into my 4 RGB leds. Which will be used to show TEMP in a sort of colour format, RED=HOT, BLUE=COOL etc..and change based on temperature.

    As I want to just use 4 x single RGB LEDS i need some additional changes to prevent damage to the AQ5 since its designed for 1 rgb led.

    1. I just
    add suitable resistors to each RGB driver output/LED based on their data sheet for MAX brighness

    R: (5V-2.2V)/20mA = 140 Ohms
    G: (5V-3.5V)/20mA = 75 Ohms
    B: (5V-3.5V)/20mA = 75 Ohms

    2. I need to control the current and make sure that when all LED are on does not draw more than Imax20mA from the AQ5, so current limiting regulating/transistor would be required?

    3. Since the AQ5 will control the output then these 3 'triggers' will feed into 3 transistors to drive the 3 colours of the RGB leds, just not sure what transistors 2N3904 ?

    4. All RGB leds will be in parallel connected directly to a molex power connector to the 5V rail or could use 7V if required by linking 12+5 together as the Common Anode? Should I use 12V?

    From all this, how difficult would it be to draw up an appropriate diagram and CCT board to be etched out, could you provide a rough cost an payment via paypal?

    Thank you again!


    2 replies

    WOW Mate this is awesome! Shoot me your paypal mate I can make a contribution as this is very generous of you!

    Let me know if you have my email, please feel free to send me a message!

    This will help me out a lot, appreciate it mate!!



    Hello Friend Thank you for the reply.!!

    There was one solution by another person Jeaks from the AC forums who was able to make something similar however it seems they are no longer made or available, so I never got a change to buy. The owners of AC are now making there won version however when I enquired about one to buy they wanted $35 EURO just to ship something so small

    By looking at this design, do you think you could mock up a diagram to build one it does look very simple but my electronic days vanished along with my poor eye site?

    Really keen to get this going so appreciate you taking the time to reply

    Thank you


    1 reply

    Added reverse engineered circuit of what he is using.

    parts: IRLR024N mosfets, 1.6M resistors (brown, blue, green gold : color code), molex socket, 3 x 4pin fan header & 1x 3pin fan header.

    This is designed to drive common anode led rgb strips.


    Gday from AUS mate!

    I see a similar question that has been asked before around the AQ5 device

    I got some RGB Leds from ebay and ordered both Common Anode & Common Cathode but they are all mixed together and I do not know how to tell them apart as they look identical. I think seller sent the same as the leg lengths match each other and so do when looking through the LED its self.

    This item

    I believe the AQ5 used common cathode from memory so then I need to reverse your excellent design to be able plug in either one of my RGB LEDS, if I am to use the common cathode, how difficult is it to be able plug either or RGB LED?

    Because I would like to connect 4 X RGB LEDS to this connector on the AQ5 but not sure if I also need to add resistors to each legs of the RGB leds or plug directly to the port.

    If I'm to split in into 4 LEDS what method should I use to get MAX brightness

    Would it be possible to purchase a suitable solution from you to drive my 4 RGB LEDS and plug this into the AQ5?

    Many Thanks!


    1 reply

    Hi Kosti,

    if u look at the connecter is specifies: VCC led1, VCC led2, GND, VCC led3 (so yes its common cathode) and the important tiny letters Imax 20ma, vcc 3-4v.

    This means u can only can connect 1 rgb led directly if u want more u need to power them from different power source (in pc molex would be best).

    This is because vcc is between 3-4v which is enough voltage to lid one led (typical forward voltage is 3~4v for leds hence its same). With multiple leds u need to either parallel (increases current) or series (increases voltage). Either way that goes outside of specs what that AQ5 can deliver.

    Solution would be to use molex as power source and the connector as signals then take transistors to switch the leds.

    Resistors are always needed since leds are diodes the have "no resistance" hence connecting them without is a short-circuit unless they are mounted on the controller board but if that is the case it would be specified.

    Hi !

    I'm looking for solutions on my problem and found your circuit !

    But I'm not really sure it is made for my configuration.

    here is my problem : I'm using a WS2811 driver to generate a PWM signal. The WS2811 is working with common anode.

    datasheet for ws2811 :

    I'm planning to use the PWM signal with a 3W LED driver that supports PWM/

    datasheet for 3W LED DRIVER :

    So I think I need to get common cathode output on the WS2811 to get the PWM signal compatible with the input of the 3W LED Driver. something like the drowing would work ? Thanks for your help.

    1 reply

    first off sorry for the late reply.

    Here my thoughts on your drawing:
    I would remove the 4004 diodes from my circuit and simply tie grounds together. The circuit u gave should work but im not sure whether the constant current circuit will interfere with the transistors. I only have the ws2812 else I could check. U should make the circuit on breadboard and measure the levels at the right output (where u draw the blue lines) to verfy u get a clean pwm output.

    I like how simple this circuit is, would it be possible to make a small change to this circuit so I could go from a common cathode source to a common anode RGB LED? It is far harder to find common cathode RGB strips than common anode, and the Aquacomputer Aquaero 5's RGB LED driver I wish to use to control the RGB strip in my cpmputer case is common cathode.


    3 replies

    Thx for the comment.

    It is possible to control common anode with a common cathode controller using 3 beefy NPN transistors depending on length of the leds strip. The problem is powering the comman anode strip cause the anode from from the controller is split. Solution for this would be to power the strips by using molex (since its inside a compter) wich has 12v pin that is same voltage as used by led strips. In that way u can also have more strips depending on NPN transistors as the controller is only controlling the strips not driving them. I will make a new schematic to show what I mean tonight.

    This looks like exactly what I need. I am looking to control approximately 5M of common anode strip from a common cathode controller. The strip comes with a 12V supply beefy enough for its needs (2Amps per colour). If I understand this correctly, the only load on the controller will be NPN transistors. I have pretty much zero electronics design knowledge so would you be able to help me size the components I will need to do this? I was thinking I'd need TIP3055 transistors to handle the 2A per colour? What size resistors would I need on the base of the transistors to drop the 12V control voltage down to the required input voltage of the transistors?