I'm gonna be using some shift registers to PWM some sets of RGB LEDs using an arduino shiftPWM library. There will be five different sets of LEDs, three colors for each and three series of three LEDs that I wish to power from 12v. So that will be 15 channels of 12v, 60mA each. Should I use a bunch of 3904 and 3906 transistors, or should I use some ULN2003 chips? Can the ULN2003 operate at arduino PWM frequency? Would it get too hot at 420mA per chip?

If I used regular transistors, I can just sink the cathode of the LEDs with a 3904, pulled high, right? Would that be a better idea than trying to use the chip?

What would you do here?

Thanks

 

2003's are good and save space. I use them to drive 7 seg displays up to 600mA (total, per chip), and have no problems.

Dan.

 

If you're using shift registers anyway, you might want to look at serial-to-parallel sinking or sourcing driver ICs or serial-to-parallel constant current sinking driver ICs (no LED current limiting resistors required).

The Micrel MIC5891 serial-to-parallel sourcing driver IC has separate VCC and VBB inputs which help reduce circuit complexity for driving segments with multiple LEDs in series at a higher voltage. For example, the following circuit uses my MacMux method to drive sixteen 12-volt channels using only three I/O pins.

Good luck on your project.

Cheerful regards, Mike

 

I agree with MMcLaren - try using display drivers.

Transistors would work, but for ease of construction I would use drivers.

 

I need to drive the cathodes. Another forum suggested the use of a TPIC6B59 which is the 595 and MOSFETs built in for up to 500mA per chip I think. Is that a similar idea? I need whatever I use to be compatible with the 74HC595 because the library I am depending on uses it.

 

I need to drive the cathodes.

Just curious... Why wouldn't you have the choice of driving anodes or cathodes? Among the features listed on the ShiftPWM web page is;

Outputs can be inverted for common anode RGB LED’s

 

Because I already have the LEDs and they are common anode

 

Because I already have the LEDs and they are common anode

Ok. Sorry! I suspect that if you had described them as "five common anode RGB LEDs" in your first post you could have saved us both some time.

 

Look at the TLC5916 constant-current driver.
/mike