As disclosed in Froeschle U.S. Pat. No. 4,456,872, hysteretic current-mode control offers significant advantages for many applications. Hysteretic current-mode control offers the tightest and most accurate control of inductor current, is unconditionally stable regardless of duty cycle, and offers excellent transient response to step loads. It is also inherently load-current limiting. Other advantages include short-circuit-proof operation in buck-derived topologies, easy loop-stability design, absence of subharmonic oscillation, instantaneous peak-to-average inductor-current ratio, and the absence of a need for slope compensation for duty cycles above 50%.
Although hysteretic current-mode control offers many advantages, it has not yet achieved the widespread use which might be anticipated given the advantages it offers. This may be due to the fact that most hysteretic current-mode control circuits of the present state of the art are complex, requiring numerous components, with an accompanying significant cost disadvantage with respect to simpler, non-hysteretic arrangements. A hysteretic current-mode control circuit requiring fewer and simpler components would naturally be less expensive to design and manufacture, and would make the advantages of this mode of control available in more applications.
The present invention recognizes the need for a circuit for achieving hysteretic current-mode control which can be manufactured using a small number of simple components to form a low cost unit suitable for use in applications such as a low cost battery charger, a regulated voltage source in a battery operated electronic device or any other application requiring a low cost DC-to-DC converter, as more fully described below.