74hct4020 question

[jack0987]

I don't think there is a TTL part 744020. AFAIK there is no TTL part with an on-board oscillator and counter-divider. You can build the oscillator out of two TTL inverters or inverting gates and drive a string of 7490s with it.

For output drivers, a small-signal NPN transistor with a 4.7K base resistor will work. 2N4401, 3904, 2222, etc.

ak

Thanks so much but I think I will leave this part for another day. It will really be overkill for what I need right now and at the moment I think I have all the info needed and a working circuit.

Thanks to all the others for kicking in also.

 

[jack0987]

TTL is so old that I do not look at it.

LOL. Well, as someone once said - "I'm an eight bitter."

 

[AnalogKid]

Just FYI. The ULN2003 is an awesome, cheap driver chip (and very common). But it's ok 7/8s as awesome as the ULN2803. The same part with an addition channel. For some reason, it doesn't seem as well known.

Back in the day, the 18 pin package made it noticeably more expensive (relative to a 16-pin part) to produce as a component, purchase, design into a product, and manufacture. For example, an 18 pin DIP socket was much more than 1.125 times a 16 pin socket, and socketing this driver was very common.

ak

 

[AnalogKid]

TTL is so old ...

Maybe, but you'll always be older.

ak

 

[schmitt trigger]

Old logic types? Did anyone ever worked with DTL or HTL devices?

I once had to repair an industrial control employing HTL chips.

 

[aardyvarky]

I do not understand. What I am doing has nothing to do with coins. Did I misstate something?

Oops sorry was thinking about a different thread.

 

[audioguru]

Maybe Jack does not understand that a 7490 is a decrepit old TTL with high input currents. But a 74HCT4020 is not TTL, instead it us high speed Cmos with TTL threshold voltages.