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Topic: 12V 7 segment LED display (Read 12330 times) previous topic - next topic


Hi, I have been looking around for a nice solution to driving 3no. large 7 LED segment displays @ 12V and came across this thread: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1212882269/15 - the last post in the thread is very neat so happy to have found a good solution I headed out to find some Allegro 6278EAT chips for the project..... only to find they are out of production :-(????? ??? ????????? ????? ?????????? ????????? ????? ????? ????? ????? ??? ????? ?????????? ???????? ???????? automasys.wordpress.com ????? ?????????????? ???????? ???? ????? ?????? AVR ARM LPC STM32 PIC dsPIC 8051 8086 z80 ????? ???????? ? ?????? ??ARM AVR PIC MicroController Electronic Project GPRS GSM USB BlueTooth Ethernet Network CAN I2C SPI RS485 Automation PLC ????? ????????? ??????????? ??? 8051 ???? ?????? ???????? Interface ???????? ?????? ??????? Visual Studio 2010 C# VB.Net Protel DXP Altium Eagle PCB SPICE PSPICE HSPICE ADS OrCAD Silvaco
I'm wondering if anyone can suggest an alterntive chip or an equally nice solution to the problem....

I suggest using ULN or UDN drivers or for better performance MBI LED driver series.

CrossRoads

Lower the resistance on the PNP gate pullups - that should turn the current off better.
What are you using now?
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.

point5

Thanks - my first attempt was 1K, just tried 560R which had a similar result - how low can I go before I break something?

point5

A quick update... now reduced the pullups down to 220R... things are improving but not there yet... just not sure if I will cause damage if I go too low?

CrossRoads

Post your current schematic, lets review.
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.

point5

Hi, here is what I have at the moment....

CrossRoads

Okay, that Schematic as drawn will not work.
You need PNP's wired up like this:
http://www.mayothi.com/transistors.html
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.

point5

Cheers CrossRoads..... is this how it should go?

CrossRoads

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.

point5

I'm getting there slowly with your help :-)  I have also just ordered Electronics for Dummies.....

I have the circuit breadborded out as per the last schematic but with 1K pullup resistors - it all seems to work great with the exception that the shift register IC gets too hot very quickly.  Is there anything I can do to solve this?

CrossRoads

Why is it hot?
12V/1K = 12mA, * 7 worst case = 84mA, shoudn't be hot from that.
The TPIC6B595 is powered from 5V?
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.

point5


CrossRoads

Try an experiment - with no LEDs on (all outputs high), does it get hot also?
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.

point5

Hi there.... well this in now finally working :-)...  so here is the circuit to help guide others in a similar position.

Only got joy with the N type MOSSFET, the bit I was missing for a while was a pullup resistor from 12V to Gate.

Thanks for all the help, it is very much appreciated :-)

CrossRoads

Part # is MOSFET, picture is NPN.
Yes, need the pullup to turn the P_channel MOSFET off.
6B595 output going low turns it on.
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.

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