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Topic: Led cube efficiency (Read 6008 times) previous topic - next topic

CrossRoads

I can't recommend those Darlington parts.
TIP125 drops 2V Vce for instance. At 1.28A, that's 2.556W dissipated in the transistor.
Would rather see Logic level, Low Rds, P-Channel MOSFET
This one for example
http://www.digikey.com/product-detail/en/NDP6020P/NDP6020P-ND/1055922http://www.digikey.com/product-detail/en/NDP6020P/NDP6020P-ND/1055922
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

PaulRB

Good suggestion CrossRoads, I was concerned about the voltage drop of the tip125. As well as the power dissipation problem, it would also have limted the choice of leds to those with a low forward voltage. I remember the op had some leds in mind with Vff over 3V, which would have been out.

So a pull-up (down?) resistor will be needed on the gate (10K?) and a low series resistor (100R?).

Another option for driving these fets would be to abandon the 9th shift register and use Arduino outputs directly, if 8 are available.

Paul

CrossRoads

P-channel, so a 10K pullup to keep them turned off during reset times.
I'd just just use another TPIC6B595 to pull the gates low. 100 ohm would be fine.
You know, this board I have I think would  be ideal to drive a cube like this. Need 81 column drives 9 gate drives, and 96 are available when fully populated.
I have been contemplating a 9x9x9 even, just not enough time available to right now to get around to soldering the cube up.
http://www.crossroadsfencing.com/BobuinoRev17/
Bare boards $5, I should get the schematic & PL posted. Pretty straightforward, basically an arduino and 12 shift registers with decoupling caps.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

henkiej

Thanks for all your support, I am trying to get things straight but i think i will be able to sort things out with the help of your comments above.

I will post my final result

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