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

Picture of 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)


MarcSebastian (author)2016-11-17

Was very easy! Thanks a lot :)

kavish laxkar (author)2016-05-12


vestalsin23 (author)2016-02-16

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.

vestalsin23 (author)2016-02-06

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

Err0rC0deX (author)vestalsin232016-02-16

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.

vestalsin23 (author)2016-02-13

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

Err0rC0deX (author)vestalsin232016-02-16

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.

Kostiz (author)2015-01-31

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!


Err0rC0deX (author)Kostiz2015-02-05

I have added schematic and simple board design.
U have to find a fab house yourself I don't manufacture pcb's.

Kostiz (author)Err0rC0deX2015-02-05

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!!



Kostiz (author)2015-01-29

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


Err0rC0deX (author)Kostiz2015-01-30

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.

Kostiz (author)2015-01-29

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!


Err0rC0deX (author)Kostiz2015-01-29

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.

polus23 (author)2014-11-02

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.

Err0rC0deX (author)polus232014-11-10

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.

bzzeigler (author)2013-10-07

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.


Err0rC0deX (author)bzzeigler2013-10-08

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.

Err0rC0deX (author)Err0rC0deX2013-10-08


cpmills1975 (author)Err0rC0deX2014-09-13

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?

Err0rC0deX (author)cpmills19752014-09-17

the TIP3055 is overkill for a 2A channel. Yes the controller is no longer a driver just a signal box that tells which color is on with pwm. The transitors do the actual power switching. U should look at 3 - 4 amp transistors and look up their datasheet. To see what current on the base opens the gate so u can calculate what resistor is required between the signal line from the controller and the base of the the transitor.

ceejaax (author)Err0rC0deX2014-04-07

I just bought the following common anode controller to play around with :

I want to drive 1-2 of these LEDs:

The LEDs are surface mounted to an common cathode FPC and each LED current limited to draw 20mA.

I've been looking for a circuit similar the 2nd one you posted so that I can. Would this work?

Err0rC0deX (author)ceejaax2014-04-08

The main circuit I posted in this instructable is what you want to go with.

The second circuit I posted in the comments here is for common cathode to common anode and thus not what u are looking for.

otterpot (author)Err0rC0deX2013-11-21

Cute little circuit Err0rC0deX. Here in the UK common cathode RGB strips are like rocking horse sh*t! I have some common cathode controllers that I need to use for a project and have spent 2 days searching for RGB strips/floods/spotlights/bulbs that would suit, to no avail. I knocked up your circuit today with some 25 year old transistors I had (a past career!) and it worked like a dream- thanks, and well done. Well.... to be honest, it worked like a dream once I replaced the PNP transistors for NPN having not read the thread correctly :( - as I said, its a long time since I designed circuits. Anyway, my question.... I can see from you design why you comment that the controller doesn't supply current to the lights, in my project the controllers have a 54W (4ish Amp) output, which I believe would be irrelevant in this scenario as the controller is just triggering the transistors (assuming the controller doesn't have a ground track a couple of microns thick of course). So, am I right in thinking that the LED drive capacity is purely down to what the transistors can switch and the 12V PSU? If so, if I want to switch 120W of RGB LEDs (this is a external lighting project) would I just need a 120W 12V supply and transistors capable of switching 10A? As I am so out of touch with components, could you recommend a suitable transistor (I guess the resistor wattage is irrelevant)?
Once again, well done with this cct - got me out of a hole.
Regards, Graham

bzzeigler (author)otterpot2013-11-21

For the circuit Err0rC0deX put together for me the controller doesn't do anything more than provide a trigger signal to the transistors in Err0rC0deX's circuit. If you have a bunch of LEDs to drive then you would just build Err0rC0deX's circuit with higher power transistors and a bigger 12v PSU. in my case, I used small transistors as I had already purchased an RGB repeater to drive the RGB strips... The total package is about 1.5" x 1.5" as you can see here. As you can see, I should have laid the circuit out a bit more before I actually started soldering everything down and I might have saved a bit of room.

otterpot (author)bzzeigler2013-11-22

Thanks for your reply. Yes, pretty much as I thought. I will be driving the LEDs direct, and I have about 10A to switch, so I think I'll need 4A transistors and something beefier than breadboard- which I wouldn't like to put more than 1A through each track.

Err0rC0deX (author)otterpot2013-11-22

For these High loads(4A) u should use mosfets as main switches and have those triggered by transistors(effectively a Darlington pair) to be able to use low current signals(ttl). Transistors are used for signal applications up to 2A. Anything above should be done with a mosfet with the exception of very fast switching requirements.

With mosfets if u want to expand the drive current (for more leds on each tack) take cooling into consideration when building your circuit.

otterpot (author)Err0rC0deX2013-11-22

Thanks for your reply Err0rC0deX. I understand what you mean by switching loads. The more I think about it, switching very high loads of LEDs is creating unnecessary self-inflicted hassle- not just the circuitry, but heat (as you say), not being able to use prototype board, complicating the circuitry... I think I'll stick to 50W load total and keep it simple! My only other thought would be to consider triacs? Thanks again for a great circuit.

Err0rC0deX (author)otterpot2013-11-22

It is indeed more manageable to have smaller led strips/clusters driven in paralel en control it with single controller to send PWM signals. Instead of one 120 watt load split it to 4 X 40watt circuits.

bzzeigler (author)Err0rC0deX2013-10-13

Hey, Just wanted to follow up and say the circuit works wonderfully, Thanks again!

bzzeigler (author)Err0rC0deX2013-10-10

You sir, are awesome.

prmcguire (author)2014-02-16

I know this is an old thread, but I came across it searching for this exact solution
Knocked up the cct in about 20 minutes and works perfect. Thanks for publishing

isa_olcer (author)2013-08-24


mzuidwijk (author)2012-12-22

Super! This is exactly what I was looking for!!! I have bought 4 of there 3Watt RGB LED stars and wanted a controller for it. Now It seems like I have a common anode controller and a common cathode RGB Led.

Can I add the RGB LED directly to this inverter? Or must there be a resistor between ever channel?

My idea would be:
[PSU]---[controller]---[inverter]---[RGB LED]---[RGB LED]---[RGB LED]---[RGB LED]

I have this RGB LED:
And this controller:

Err0rC0deX (author)mzuidwijk2012-12-23

That is a good idea but u should replace the transistors with mosfet's because your switching quite a large load. Also it would be better to remove the diodes and connect a wire that takes the ground line from leds directly to the V- on the converter because u would need very large fast switching diodes if u want to do it the way I did it. Which I only tested on short led strips which use a lot less current then your power leds.

Err0rC0deX (author)Err0rC0deX2012-12-23

and yes you need resistors else the led, controller and inverter will all blow cause u will create a short circuit since leds and diodes have close to zero resistance. Problem with resistors is that they will get hot and therefore waste quite a lot of energy. U could use 3 watt led driver that u can find on ebay and use 3 of those to drive the 3 color channels of the leds and then use mosfets to allow the controller to control the flow of current to the leds.

if you want I can make some schematics to make it all more clear.

gazz (author)2012-09-27

Excellent little circuit,
Helped me out when i won an ebay auction for 2 x 5 meter strips of RGB tape for a tenner, after finding it with 2 minutes to go,

Got it, and discovered why no one else had bothered with it, they were common cathode tapes, and all controllers available seem to be common anode,

I pulled 3 random pnp transistors from an old pcb, connected them up as shown, and it bloomin well worked..... i didnt bother with the diodes, instead i just connected the negative wire from the strips to the negative input terminal on the controller (where the psu is connected)

Then i tripped over the wire and pulled the legs off 2 of the transistors,
And would you believe it, i cant find any more pnp transistors in the pcb i have to rob for parts,

So ordered some BD442 transistors from the maplins toy shop (remember when they were an electronics shop)
Hope they will work the same with 1k resistors, as i havent learnt how to figure out the resistance needed for a given transistors saturation point yet.

but thanks again for this great circuit.

Err0rC0deX (author)gazz2012-09-27

glad it was usefull.
The doides were added because I didn't want to have a additional wire.
For most switching circuits 1k is sufficient for transistors you only need to calculate a spefic value if u are going to do very accurate switching like audio amplification or going to switch large currents.

ajpepe72 (author)2012-03-26

This is the controller 12v 10a

I think the easier option to use controller as signal generator would be better for novice, i have had the controller open and its easy to remove the board once i know what im looking for to find the ground plain. thanks for your help.
i will do some more research. What components will i need just to build the signal generator and what would I connect to the ground plain (once ive found it).

Err0rC0deX (author)ajpepe722012-03-26

if u have it open make an photo of both sides of the pcb and send them to me I can easily mark ground for you.

The option of using the audiocontroller as signal generator is indeed easier but not necessery as your controller is high rated so it should be able to drive the load u want it to power.

I see that the controller has 2 groups meaning u need to make 2 converters with half of the rates I jusr calculated as each group will drive only 75 leds.

By signal generator I mean using the controller to drive power transistors that power the led strip in this way the current driven by the controller is many times smaller then your actual output current.

ajpepe72 (author)2012-03-26

thanks for the advise, my strip is 5m long, although i have cut it down to 2 2.5 strips.
there are a total of 150 smd rgb leds (75 each 2.5m strip).
My local electronics store ( would have all the bits i'd imagaine, its just how they all go together and is the actual green board specific for the components or just a generic board.
As you can tell, ive never attempted anything like this before, soldering wires together has been my limit.

Err0rC0deX (author)ajpepe722012-03-26

150 * 20 = 3000 mA = 3A minimum for transistor
150 * 20 * 3 = 9000 mA = 9A minimum for rectifier diodes

Transistor you need to look for is something like this:
Rectifier diodes should be 10A + like this one:

The pcb I used is a double layer prototype board but u can use any prototype board.

However u should check the soundcontroller maximum output cause 12v * 9A = 108 watt of power if your not sure it would be much better to go with other circuit that uses your controller only as signal generator and not as a driver.
This circuit is also easy te build.

ajpepe72 (author)2012-03-26

Hi, how hard would this be to make, im ok with a soldering iron, but have never made a circuit before.
my problem is i ordered an rgb led strip and a separate led sound controller.
while the sound controller has a positive + line and ground r g and b lines, it turns out the actual strip is ground on the + line and positive on the r g b lines.
wouold this circuit solve my issue ? thanks.

Err0rC0deX (author)ajpepe722012-03-26

Yes this circuit was designed for this problem. In my circuit sv1 would be your sound controller and sv2 your led strip. Making this circuit is easy but there are a few things u need to keep in mind. Depending on the length of the strip u need to select higher rated components. If its only 1 meter 1amp rectifier diodes and 500mA rated pnp transistors should be enough. 3meter or 5 meters of led strip would require higher rated parts.

To calculate the amps, count the nummer of segments your strip has. Ussualy they are marked with a scissor icon. Each segment uses about 20ma for each color. This means the pnp rated mA should be higher then (number of segments * 20). the rectifier diodes should be rated higher then the total mA consumed by the strip so (number of segments * 20 * 3).

if u don't mind having a 5th wire u could also directly connect the ground of your strip to ground of sound controller but this means opening it up and finding the ground plane. When u start soldering be sure too keep the datasheet of the transistor nearby to make sure u use the right pins. Not doing so could harm the led strip, the controller and the circuit your are building.

if you don't now what parts u need or need help leave a comment and ill help you as much as I can.

diy_bloke (author)2012-02-12

Nifty, but I think I would have opted to get new RGB LED's but a clever solution nevertheless

Err0rC0deX (author)diy_bloke2012-02-12

thx, I didn't want to wait 2+ weeks for new leds to arrive from china so thats why I came up with this solution.

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