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Topic: Circuit Design for Large LED matrix (Read 12786 times) previous topic - next topic

CrossRoads

So logic level MOSFETs are really just useful for N-channel parts going to ground then.
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.

dc42

Yes, and for p-channel parts switching +5v. To switch higher voltages with a p-channel part, you need to level-shift the gate drive, and you can just as easily amplify it at the same time.
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mschn

So, since i'm switching such a large voltage source (relative to logic levels), could I have just as easily used PNP and NPN transistors on the anodes/cathodes instead of the npn+pFET combo on the anodes and npn on the cathodes?

CrossRoads

Take a look at this Maxim application note for the 8x8 matrix drive chip, the MAX7219/7221.
You are setting up to do the same.
http://www.maxim-ic.com/app-notes/index.mvp/id/1196
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.

dc42


So, since i'm switching such a large voltage source (relative to logic levels), could I have just as easily used PNP and NPN transistors on the anodes/cathodes instead of the npn+pFET combo on the anodes and npn on the cathodes?


You could have used a PNP transistor or power darlington, plus one additional resistor, in place of the P-channel mosfet. You would still need an NPN transistor to level shift the drive to the PNP transistor.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

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