Method and apparatus for controlling a DC-DC converter change the switching
frequency of the switching devices and the on-off ratio of the switching devices.
The on-off ratio can be changed in response to the output voltage and the switching
frequency can be changed in response to the input voltage supplied by the DC power
supply. Alternatively, the switching frequency can be changed while the on-off
ratio is fixed at a certain value, and the on-off ratio can be changed while the
switching frequency is fixed at a predetermined value after the switching frequency
has reached the predetermined value, thereby preventing the switching frequency
from exceeding the predetermined value.
