I am building a Phase Locked Loop circuit with a power supply -/+ 12v. On this circuit there are mm74c74n & mm74c00n. I looked on the data sheets and they are powered +12 & gnd. But I would normally on other circuits power all opamps -/+ 12v. How should I power these opamps on this circuit??

 

http://www.experimentalistsanonymous.com/diy/Datasheets/MM74C74.pdf

 

You don't have to restrict yourself to only using ±12V to power an opamp.You can use other voltages as long as you meet the minimum requirements and do not exceed the maximum voltage specified in the data sheet. You can power the opamp on 0-12V as long as you provide a common reference point that is half-way between the supply rails. For example, if the supply is 0-12V, create a pseudo-ground at a reference voltage of 6V.

Or you can select an opamp designed to operate on a single supply.

The max supply voltage on 74C00 is 18V.
±12V suppy will kill it whereas 0-12V will be fine.

The circuit you have posted is from this TI LM331 Application Note.
This circuit is a mixed mode circuit with analog and digital components. The opamps are powered from a ±12V suppy. The digital section can be powered from +12V.

 

Thank you, I understand but absolutely to be clear, if I power the opamps at -/+12. The digital chips I power with ground and +12?
Or
The alternative will be to make an extra power rail -/+ 6v to power the digital chips? I could do this with a voltage converter.