74122 IC as a monostable multivibrator    



Can CD4098 replace CD74HCT221 for +12V operation? For gate generator?



t can be, but I caution using a retriggerable monostable multivibrator.  I have many SN74HCT123A chips and found out the hard way what their limitation is.



It can be, but I caution using a retriggerable monostable multivibrator.  I have many SN74HCT123A chips and found out the hard way what their limitation is.

The original VIC circuit has a 74122 IC as a monostable multivibrator, same as the 74123, to adjust the gate.

It would be helpful to know what the limitation is, and propose a better solution.


The difference being retriggerable versus non-retriggerable.  The non-retriggerable variant I find to be more useful for deterministic pulse generation because it delays a predictable amount of time regardless of incoming trigger signals--only the first trigger matters.  Granted in a looped dual configuration like used here in this driver board, either method works fine since you are guaranteed to only get one trigger.  But in other applications, you may not have this guarantee, so the pulse width or pulse delay may get extended when the chip gets multiple triggers that fire before the time delay has expired.  When you see this on the scope for the first time, you'll question whether your duration time is working as you have set it.  The answer is yes, it is, but is now non-deterministic because you have multiple triggers.

Bottom line:

  • Retriggerable -- uses the last trigger seen; looks at every subsequent trigger as a restart until the cycle is able to complete.

  • Non-retriggerable -- uses the first trigger seen; ignores any triggers after this until the cycle completes.

Depends on what you want to do.  In my experience the non-retriggerable one-shot is more useful overall.v




What is direct replacement for cd74hct221 from CD 4000 series , for 12V supply operation?
Thank Matt

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