741 Op Amp into CMOS logic problem

[Les Wilk]

I have connected the output pin of a 741 op amp into a 74HC04 directly
The 74HC04 output sadly doesn't invert the output against input
I have daisy chained all 6 of the gates in the 74HC04 so as to avoid problems with floating inputs.
As this is bread board project so far, by isolating I have proven that the 74HC04 inverts through all of its gates perfectly, it is working fine.
The 741 output pin swings High / Low perfectly according to it's inputs, so it too is fine.
But when I connect 741 into 74HC04 it fails to work as hoped

What is the correct interface between 741 and a 74HC04 ?

Any ideas will be greatly appreciated
Many Thanks
Les

 

[crutschow]

What is the output voltage swing of the 741? "swings High / Low perfectly according to it's inputs" doesn't tell me anything.
Why are you connecting an analog signal to a digital input?

 

[Les Wilk]

My power supply is set to 10v my 741 output goes from 1.7v to 9.6 v according to changing inputs
I need to go from analog output to a digital as further down in circuit there are latches to set/reset according to analogue input thresholds being crossed
Thanks

 

[ronsimpson]

Your 74hc04 probably is on a 5V supply. It won't like getting a 9.6 volt signal. (741 driving 74HCxx)
Use two equal resistors to make a voltage divider. That way the 1.7 to 9.6V signal will be .85 to 4.8V

 

[Les Wilk]

You are right, I had believed that the cmos versions of 74 series were good for up to 12v but that is not the case they are 7v max.
Cranked down my PSU from 10v to 7v and all behaves well, lucky I didn't blow the ic.
Many Thanks from Les in Thailand

 

[ronsimpson]

There is 12V CMOS.
4000 series. OR 14000

 

[Les Wilk]

Thanks for the assistance
Case gratefully closed

 

[crutschow]

You should not operate the 74HC ICs at there maximum rating for best reliability. They are designed to operate at a nominal 5V.