I'm using a CD4026BE decade counter/7-segment driver
to drive a seven segment display.
The datasheet for this part specs VOH at 4.95 volts min
with VDD of 5V.
I measure 5V VOH with no load but as soon as I use this
output drive a segment through a 330 OHM resistor the
voltage drops to about 2.7 volts measured to ground.
It drives the segment OK but I also want to use this to
drive the input of a CD4082BE Quad AND gate. Unfortunately
the datasheet for the 4082 specs the VIH at 3.5 volts min
with a VDD of 5V.
Measuring just across the resistor I get .99V and just
across the segment diode I get 1.7V. The datasheet
doesn't say anything about load or no-load conditions
so I don't understand I why I don't get the full 5V VOH.
That shows typical output levels of 4.6 V with a 1 mA load, or 2.5 V at 3.2 mA. That is just about what you are getting.
The 4000 range are not capable of producing a lot of current, especially with a low supply voltage of 5 V.
You need some other type of amplifier to boost the signal. You could amplify the current so that nearly the full 5 V is available with more current, but you might get the brightness of one segment different from the other ones.
Thanks for the replies. I understand the problem now.
The 4026 is driving the 7 segment display just fine it just
won't also drive the 4082 Quad AND gates. Can I replace the
4082 with a TTL Quad AND that only requires 2V VIL?