Problem Sinking Current 140mA through a Logic Gate

[weegee]

Hi there, im new to these forums, but Hi to everyone: anyway on to the problem:

I have designed a circuit that will be run from a pic processor:

**broken link removed**

The circuit that you will se is the multiplexing part, my problem is with the sinking of the Common Cathode on the display's, eg when a display is lit, the current is sinked through the 4-16 line decoder, how can I rewire this so that the output from the decoder switches the cathode to ground, rather than sinking the current directly?

any help would be greatly apprecited

Also is a PIC16F84A Running @ 4 MHz likely to be fast enough to update the display, using 7 lines as a parallel output, and 1 output as a strobe, whice counts on the binary counter, which updates the 4-6 decoder.

BTW: the 7 wires at the bottom of the diagram are the 7 parallel data outputs.

Thanks

WeeGee

 

[Russlk]

You could use the MAX4147, a dual noninverting driver, and parallel the outputs for 200 mA drive capability. Or, use this circuit which pulls down to within about .8 volts of ground:

 

[weegee]

Thanks,

This looks exactly like what I want, using the Transistor that you have specified, Will it sink the current when the base is High, or Low?

Thanks

 

[Sebi]

Since this is a PNP transistor, it sink when the base is low.