I'm want to design a circuit with some 7-segment LED displays driven from a 4511 or some variant. Now, I haven't burned up anything in quite some time. So before I burn anything up, I'm wondering:

Is it okay to put a single current-limiting resistor on the common cathode, or is it a necessity to have a separate current-limiting resistor on each LED segment? Can someone experienced in this give me a hint?

Joe

 

You will need a separate resistor for each segment.

 

I too recommend you go with a resistor per segment. If you try to get away with one resistor, you will find that the brightness of the segments will change as a function of the number of segments you have illuminated at any one time.

hgmjr

 

That's going to be lot of resistors, but I don't want the display to change in intensity. So thanks to all!

Joe

 

If you are multiplexing several digits, you only need one set of segment resistors as only one display is actually drawing current at any time.

 

If you research it they make 7 resistor arrays, in a 14 pin DIP package. Resistors are cheaper though.

 

Yes, I've seen the resistor arrays. I'd rather just solder some 0805 packages. Not hard at all and much cheaper, lots of flexibility in positioning.