| 摘要 |
In a power supply apparatus which is used for an image forming apparatus, even when a resonance frequency extremely changes due to an influence by an inductance load just after a fluorescent lamp was lit on and after completion of the stabilization after the light-on, the apparatus can immediately follow such a change and can generate a stable voltage. The apparatus is constructed by a comparator for comparing an output value of a secondary winding of a transformer and a predetermined value, first and second U/D counters in which counting up/down (U/D) operations can be switched by an output of the comparator, a selector for selecting outputs of the counters, a synchronous detecting circuit for generating a sync pulse in accordance with an output of another primary winding of the transformer, a down counter for loading the output of the U/D counter selected by the selector at a timing of the sync pulse, and a control circuit constructed by first and second digital comparators for comparing an output of the down counter and predetermined values X and W. A driver decides a conducting timing of a switching device of a driving winding on the primary side of the transformer in accordance with an output of the comparator. The selector determines the U/D counter to be selected in accordance with an output of the comparator.
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