converting pos to neg (rgb controller)

Hi all,
I recently bought an rgb led controller,only to find that the leds i installed were the wrong ones,common anode instead of cathode,is there a way to convert the voltages,as i have already spent too much money on led strips,i tried max232 but maybe wired it wrong,can i use 4049 hex inverter,
Thanks for any help.
Ctesla75

A CD4049 has a limited amount of output current that is even less when the supply voltage is low.
If you want its outputs to go positive to light the LEDs then its output current is very low.
But you did not mention the voltage nor the current and did not mention if your LEDs light when driven positive or driven negative.

If you have common anode, you will only need to pull the cathodes low to turn on the LED's, so you won't need a device that has a push-pull output (drive the line low AND high). I imagine a simple NPN transistor per LED chip would suffice. Provided you work out the LED strings voltage drop, and required current, you may need to add a series resistor, and this should also help you pick a transistor which can handle said current.

N channel FET's are also an option, although driving them at high frequencies may require a driver.

A max232 is designed to level shift and invert RS232 signals. Its output is limited to <3mA. A CD4049, being a CMOS device also has very low current output. If you are after using a single 'chip' to invert your signals, then perhaps a darlington transistor array such as the ULN2003, with a max current of 500mA. We really need more info about your setup, voltages/currents to be more specific.

Hi All,
Thanks for the replies,my computer was down again ,so just seen them now,i checked my controller,i made a mistake i have a common cathode controller,and common anode led strip,the controller can output max 3a,and interchanges the color of leds, pwm maybe?,the leds have a resistor built in for each led so they can be run directly on 12vdc.
the led strips have four wires ,
black - negative
red - positive red led
blue - positive blue led
green - positive green led

the controller has four wires
black - positive (it's connected directly to the +12v power input of the controller)
red - negative red led
blue - negative blue led
green - negative green led

hope this is clearer.I will try some transistor designs out and see if i can get it going

If your LED's are common anode, then you would require a way to provide a 'high' level voltage (+12V if thats your supply) when your PWM controller outputs a low. This means you need a PNP transistor (PNP for high side, NPN would be used for low side). Or, for MOSFET's, a P channel.

Sounds like your PWM controller has built in drivers for the LED's. As their output can be up to 3A, these could easily pull a P channels gate low, very quickly, but as I imaginge the output of the PWM is open collector, the MOSFET's gate would need to be drive high when the PWM is off, probably by a resistor.

I would recommend that, provided you can't replace the LED string with common cathode, that you use three P-channel MOSFET's, designed to switch > 5A. Ones that are designed for high speed would make it more efficient (you're looking for low gate capacitance, and low switch on/off times).

What LED's are you using? If they use less than 1Amp, it would be easier and cheaper for you to use PNP transistors instead of mosfets. Eaiser to drive, cheaper, and generally nicer to work with, but not as efficient for switching high current as a P channel MOSFET.