This figure below is from Raymond B. Ridley Dissertation "A New Small-Signal Model for Current-Mode Control".
Here is an except from the document:
The general implementation of hysteretic current-mode control is shown
2.2. The inductor current waveforms are used to control both the turn-on and the turn-off of the power switch of the PWM converter. The
advantages of this kind of circuit are apparent: no clock or timing
function is needed, and the current level is controlled between two
limits. Although this implementation was popular before control
circuits became available, its variable switching frequency, and the
need to sense the inductor current during both the on- and off-times
of the power switch have restricted its use today. This circuit does
not have any problems with instability of the current-feedback loop,
and it is not analyzed in this dissertation.
Can anyone explain why this control method has varibale switching frequency? Also why this is bad?