A switching power supply apparatus (200) for controlling the operation
of
a switching FET (225) adapted for switching a rectified smoothed output
of a primary side rectifying smoothing circuit (215) by a switching controlling
circuit (230) having a hysteresis low-voltage mistaken operation prohibiting
circuit. An output of a ternary winding (220C) of a converter transformer
is rectified and smoothed by a rectifying smoothing circuit (238) to drive
the switching controlling circuit (230). An output voltage of the ternary
winding (220C), varied in dependence upon the load state on the secondary
side of a converter transformer (220) is set so as to be lower than a low
voltage protective voltage in case the voltage is lower than a design load and
so as to be higher than the low voltage protective voltage in case the voltage
is higher than the design load, in order to carry out an intermittent operation
during standby time. Thus, the switching operation during standby time may be carried
out intermittently to minimize the power consumption to realize the energy saving
during standby time, simply by adjusting the values of respective key devices,
without appreciably changing the pre-existing circuitry.
