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Topic: driving 11v 7 segment led displays (Read 1 time) previous topic - next topic

dhenry

In that case, any of those small signal bjt / mosfet will work.

freakdaddy

Thanks dhenry...  As a novice, I appreciate your knowledge greatly.

MarkT


I need to drive 6 - 3" 7 segment led displays.  Each segment has a forward voltage of 11v.  The approach I would take with a regular 7 segment would be to use a 7447 but since the voltage requirement is higher I am not sure what to do.  Should I use a 7447 to drive transistors that will drive the leds?  Any tips are appreciated!


Just use the SN7447 as normal, it will drive up to 30V - its an open-collector device so only sinks current (upto 40mA per segment).

Note the SN74LS47 has less voltage and current drive (15V, 24mA), but should still handle your displays.
[ I won't respond to messages, use the forum please ]

freakdaddy

I was actually looking through the data sheet today and noticed that.  I didn't realize they went up to 30v.  Thanks!

CrossRoads

The 7447 does not have any latching function. I'd go with 83 cent (avnet.com) TPIC6B595 shift register with high current/high voltage open drain output.
Daisy chain 6 of them, 6 SPI.transfer()s to update the display.
MOSFET outputs will run a lot cooler than 7447 as well.
Create an array with your font, pull that data & write it out.
Code: [Select]

// update display
digitalWrite(SS, LOW);
for (x=0; x<6; x=x+1){
SPI.transfer(fontArray[x]);  // fontArray[] = {B00111111, B00000110, }; etc with 1 = segment on
}
digitalWrite(SS, HIGH);
[code]
[/code]
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
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