In a switching power supply of the present invention, when a voltage output from
start-up means is greater than a driving voltage produced by output means, the
voltage from the start-up means is provided to control means, whereby the switching
power supply can be started up reliably. Furthermore, when the voltage output from
the start-up means is less than the driving voltage produced by the output means,
the current path is blocked in the start-up means so that no voltage is provided
to the control means from the start-up means, whereby it is possible to reduce
the power consumption during the steady operation.
