| 摘要 |
A controller generates a load control signal for pulse-width modulation control for changing the duty factor of switching transistors so that the ON period of the switching transistors is elongated when said controller determines based on an error detection amplification signal that the load-side output direct current has increased, and the ON period of the switching transistors is shortened when said controller determines based on the error detection amplification signal that the load-side output direct current has decreased, in the condition in which the switching frequency is kept constant. A driver selecting portion selects, according to the load-light/heavy detection signal, at least one switching transistor to be activated, from among the plurality of switching transistors, and supplying the load control signal to the thus-selected at least one switching transistor.
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