Current sourcing for 16 RGB leds

Hi! My RGB matrix is going to be similar to this http://www.thebox.myzen.co.uk/Hardware/Mini_Monome_files/4%20X%204%20RGB%20LED%20Matrix.pdf using TLC5940, but without the switches. I'd like to source anodes with PNP transistors or some current sourcing IC.

Would a 2N3906 be suitable for this? What would be a good resistor value for base voltage? 4K7? Is there anything similar to MIC2981 in a DIP case? Anything else I could use?

Thanks!

I can't be precise without knowing how many LEDs each transistor will switch and what current each on will take. 2n3906 is probably just about OK but has a rather high saturation voltage and low gain at the sort of currents it's likely to be be switching. BC327 is better. 4k7 as a base drive resistor will supply less than 1mA base current, which may well be too low. 1K is probably about right unless you have a lot of LEDs.

Mmmasa: Is there anything similar to MIC2981 in a DIP case?

MIC2981BN is in a DIP case, however it has quite a high voltage drop (up to 2.2v @ 350mA) so it isn't suitable for driving LEDs unless the supply voltage is quite a bit more than 5v.

My leds will be wired just like the linked schematic shows and I need to be able to switch on any color at any time on every led. I just need something that can source enough current and I dont want to use those surface mount FETs.

So each transistor needs to drive up to12 LEDs, which will draw up to about 120mA total (at 10mA per LED) or 240mA total (at 20mA per LED). BC327 transistors with base drive resistors of about 330 or 470 ohms should do the job, although the voltage drop will be a little higher than for the mosfets in the original circuit. Alternatively, just about any logic-level P-channel power mosfet should do.

Thanks! If I choose a mosfet, what would you recommend? I searched digikey p-channel mosfets in a 8 DIP package, would this be ok: http://search.digikey.com/us/en/products/AOP605/785-1140-5-ND/1855912?

Yes, the P-channel mosfets in that package would be suitable. You get an N-channel mosfet in each package too, which maybe you can find a use for.

In general, Rds On (Max) @ Id, Vgs, are these the values I should look at when choosing fets? What kind of values should there be? Is it better to have rds ohm value as low as possible? What else should I look at when choosing fets?

Mmmasa:
In general, Rds On (Max) @ Id, Vgs, are these the values I should look at when choosing fets? What kind of values should there be? Is it better to have rds ohm value as low as possible? What else should I look at when choosing fets?

Yes, those are usually the most important parameters to consider, along with ensuring that the absolute maximum Vds rating is higher than the voltage you are switching. When switching an unclamped inductive load, the avalanche rating is important too.

Rds(on) needs to be low enough so that the voltage drop is low enough for the application (e.g. for switching LEDs from a 5v supply I would aim for not more than 0.3v) and so that the power dissipated in the FET is sufficiently low that you do not need any heatsinking beyond what you are prepared to provide. The FET you referred to has Rds(on) max of 43 milliohms at logic level drive and up to 6A Ids, so if you do the sums, you will find that it’s already much better than you need.