Hello everyone,
I am currently working on designing an 8bit microprocessor. I want to display the current values of my different components, like the ALU or RAM, by using some LEDs. Every component containing information should have it's own selectable LED-Array and Line Drivers.
But I have the problem that I can not find a suitable octal (or even) quad line drivers capable of driving 8 LED's at 18-20mA each. All the common one like the SN74HC541 have a maximum rating of only around 8mA output current per pin.
Does anyone know a cuitable driver or other solution?

Thank you for the help in advance.
Tom

 

Welcome to AAC!

But I have the problem that I can not find a suitable octal (or even) quad line drivers capable of driving 8 LED's at 18-20mA each.

If you're using them for indicators, you don't need to operate them at that high of a current. A few mA should be sufficient. I often operate indicator LEDs at a mA or so.

That being said, 74AC04 will sink/source 24mA. Seems like the whole family might. Or you could use ULN2803 which will sink 500mA.

All the common one like the SN74HC541 have a maximum rating of only around 8mA output current per pin.

It sounds like you want to drive the LEDs high side. I'd do it low side so that sink only drivers are an option.

 

I vote for the ULN2003 for a 7 port unit, or the ULN2803 for 8 ports. They can current sink a lot of current, enough to drive all 8 LEDs at the same time, and are all driven by TTL levels on the inputs.
If you need to invert the signals, use some common inverter chip between, or use the UDN2981 which can source current to the LEDs with a high signal (non-inverting)

 

I second thee notion that you should use high-efficiency LED's running on 1 or 2 mA.

You are going to need tons of them anyways, those milliamps add up.

 

Thanks for all the help!

I second thee notion that you should use high-efficiency LED's running on 1 or 2 mA.
You are going to need tons of them anyways, those milliamps add up.

There will only be one single LED-Array powered at a time (the one of the component adressed at that time) so thats not the problem.

I vote for the ULN2003 for a 7 port unit, or the ULN2803 for 8 ports. They can current sink a lot of current, enough to drive all 8 LEDs at the same time

As I am limited to use specific LEDs (which need about 15mA to shine bright enough for my purpose) I will go for the ULN2803 and also use some SN74HC541 because of it's tristate function.