Hi everyone, I am trying to run multiple RGB light strips using a TLC5940 and a hand full of transistors. My powersupply is an ATX computer supply and it has a 15 amp 12v rail. I have everything wired up like in the schematic (the setup is the same on out 1 i just omitted the rest of the diagram to make it easier to see). Originally I set this up with PWM from the arduino and had TIP 122 Transistors running everything. I have common anode leds so everything was well in the universe and it worked with the limited PWM channels i had with the mega. When I added the next LED I realized I needed more pwm and ran into using the TLC5940 as a possibility. I am using the code and libraries from the arduino website unmodified. My issue is with this... The last transistor (the TIP3055) I have been switching out everything to and its working. Its a higher frequency transistor and it can keep up with the default switching speeds. I am completely self taught and I apologize if my terminology is off please correct me if it is. The tip 122 is alot slower because of the darlington configuration right? I was wondering if there is a way to slow down the frequency of the TLC5940 so that the tip 122 will work in this setup. The powersupply is making a high pitched squeal when the LEDs light up with the TIP3055s and I think thats because the PSU cant keep up with the rapid changes in power fluctuation. So i need capacitors someplace or to slow it down is what I came up with. Thanks in advance for any help!
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Having got off on the wrong foot:-
So i need capacitors someplace or to slow it down is what I came up with.
No a capacitor will smooth the supply, yes you need one, where is it on that schematic?
Inverting the signal from a TLC5940 will not allow the strip to be turned fully off. This is because normally a TLC5940 never fully turns on fully, there is always a single pulse of off in all that on. However, if you invert it then there is always one pulse on even if the rest is off.
You also need a pull up resistor on the base of all those transistors as the TLC5940 only sinks current, maybe when you do that your TIP122's will work.
I didn't include a cap. I wasn't sure where and what value should work. Which of the transistors could use the pullup?
Use a 0.1uF ceramic cap.
The pull up should go from each output of the TLC chip to +5V.