help needed with powering 8*8*8 led cube

i am building a 8*8*8 led cube but the thing is that i decided to make a lighting fixture out of it
so the idea is to turn it on to light up the room and then turn on the effects when i need to impress someone.
i decided to control the cube with an Arduino board connected to 4 daisychained tlc5940's for the columns and 8 i/o ports controlling the layers.
the thing is that if i just fill the whole cube in the normal way that it's done in such cubes (shifting between layers) every led lights up only 1/8 of the time and it won't give enough light, so in lighting mode i have to be able to turn on all of the leds at the same time to give enough light.
my idea was that since the tlc5940's work as current sink i would source every layer threw a p-channel mosfet controlled individually by an i/o port of the arduino.
in effect mode every column of the cube will be connected to a tlc channel and it will be set to sink the current of one led, and in lighting mode all of the columns will be connected (threw a 1w resistor for every column) to one n-channel mosfet that will sink all of the cubes current and it (the mosfet) will be controlled by a pwm channel of the arduino. so basically what i get in lighting mode (for every column) the i have 8 leds in parallel and they are all current limited by a single 1w resistor.

i attached a schematic that illustrates how a column will be controlled, please take note that the p-channel mosfets (layer control) are for a whole layer 64 leds and the n-channel mosfet sinks the whole cube.



what do you think about this setup? would it work? is there something that needs changing? or am i just stupid?!

i think that IRLZ44N mosfet will be a good choice for the n-channel mosfet but i don't really have any ideas as to what to use for the p-channel mosfets, please advice me what logic level p-channel mosfets i can use

The idea should work. As long as the bottom side FET is turned off well before you turn on the tlc5940.

And since you decided on using P-fets for the high side, no need for bootstrapping either so that keeps that pretty simple. Main point of attention would then be to make sure the gate driver for the P-channel mosfet is able to turn it ON/OFF fast enough. And another thing is that you will have to switch the tlc5940 during the "turn off fet for layer A, turn on fet for layer B" period.

I vaguely recall reading a thread on this subject I think on the TI forums. And some guys had ghosting issues between layers, which is what you get when you don't use some sort of blanking period when switching between layers.

But short version is: yeah looks good. Just make sure your arduino is going to be able to do the switching fast enough.

Also, you may want to check out some other ICs as well. I can guess why you ended up with the 5940. They seem to be pretty popular in Arduino country. But there's a few other cheap and interesting IC's out there that might do an even better job. IMO the TLC5943 is better in every respect, and a little cheaper too. The only reason to go with the tlc5940 I can think of would be the package. The 5940 is available in DIP, the 5943 is not. Another nice one is the TLC59461.

any advice regarding what mosfets to use?
i was thinking of IRLZ44N for the n-channel
and for the p-channel i was thinking of one of these:
Si4425DY
FDS4435
IRF9540N

and i'm leaning towards the FDS4435 because of the smaller gate charge
though maybe i should choose the Si4425DY because of the lower on resistance (IRF9540N is my least favorite mosfet)

i'm open to other mosfet sugestions

by the way
i'm planning on using a switching power supply (something like this: 100W 5V DC 20A Regulated Switching Power Supply [K013] | eBay)
could there be a problem with voltage spikes? (for the mosfets as well as the arduino (atmega328 chip))