In relation to a starting circuit for supplying a DC supply voltage to the gate
of a main switching device at a power-on to start a switching operation, a holding
circuit for holding a starting voltage obtained in the starting circuit is provided.
The potential at the gate of the main switching device is increased immediately
from a turn-off to turn on the main switching device repeatedly, realizing a smooth
transition to the steady oscillation state. This allows the switching power supply
to readily start even under the condition of a low supply voltage and a heavy load.
This makes it possible to improve the starting characteristic and to allow for
lower power consumption.
