buck feedback - should trigger what change?

[mikeinfodoc]

if I have a feedback network on a buck circuit (such as a voltage feedback)...

Should/would it generally want to trigger a change in :

• Frequency? ...or...
• Duty Cycle?

In other words, would it be better to adjust duty cycle? or frequency? (of pwm) in order to adjust output voltage?

[David Hess]

Either can be used.  Common switching regulators vary their duty cycle to control the output but constant off-time switching regulators like the old 78S40 instead effectively alter their frequency.  Both methods of operation have their virtues.