Perhaps a simple problem

[Electronics4you]

Hi there

I have build a simple 7-segment circuit of a CD4028 (4-to-10 line converter) and two LED segments. My VDD is 5V and so is all the input. Turning on the first transistor and input the binary number 0b0001 should light up the "b"-segment, but it only appears very weak. The voltage across is only 0.2V and the output from the CD4028 is only 0.9V.

I have tried to change chip a few times, shorted the resistors to give more current but it still doesn't help - annoying, need help.

 

[eng1]

I think that the 4028 can't source enough current out of each pin. It is a decoder without an output power stage, if I remember correctly. The 4511 might be better?

 

[audioguru]

The output current of an ordinary Cmos IC like the CD4028 when it has only 5V for its supply is only about 1mA. The 390 ohm resistors additionally reduce the output current to about 0.8mA. Very dim.

The CD4028 is not a 7-segment driver anyway. It is a BCD to Decimal decoder. Only one output goes high at one time.

Your voltage measurements don't make sense. Each segment that is activated will have about 1.8V across it. Then the output voltage of the IC will be about 2.1V.

 

[Nigel Goodwin]

A fine example of using completely the wrong chip for the job!. As eng1 says, the 4511 is probably what he's really looking for?.

 

[Electronics4you]

I used the wrong chip - caught me...!