A PFM-type voltage regulator circuit converts an unregulated input voltage
into a regulated output voltage using a first transistor controlled by a
pulse control circuit and a second transistor controlled by a linear
regulator circuit. The linear regulator circuit controls the second
transistor when the regulated output voltage falls to a predetermined
minimum target voltage level, thereby maintaining the regulated output
voltage at the minimum target voltage level. The pulse control circuit
detects the current passing through the second transistor, and in
response generates a pulse signal having a predetermined duration that
fully turns on the first transistor. The voltage through the first
transistor is converted to an increasing inductor current that refreshes
the regulated output voltage to a maximum target voltage level. When the
pulse signal ends, the regulated output voltage again begins to fall
toward the predetermined minimum target voltage level, and the cycle is
repeated.