BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching control circuit of a step-up converter for power factor control using a soft switching technique. In the related art, a product of a voltage and a current generated when a switching element is turned on or off is a switching loss generated in each element. The current waveforms have a lot of overlapping parts, which leads to a large loss. Especially, due to the loss caused by the reverse recovery characteristic of the diode during switching, the efficiency decreases, and in order to dissipate this loss, it is necessary to use a large heat sink and a large fan. have. Accordingly, in the present invention, the period selector determines the period of the switching element by using the oscillator 27 for outputting a frequency proportional to the signal output from the power factor controller 26 and the output frequency of the oscillator 27. A condition of zero voltage or zero current in order to minimize switching losses of a switch and a diode by using the unit 28 and a switching driver 29 which drives the switching element in response to the output signal of the period selector 28. By supplying a switching control signal to the boost converter to reduce the loss due to the reverse recovery characteristics of the diode during switching, the use of a large heat sink and a large fan volume to dissipate the switching loss It allows you to remove it so that the entire system can be compactly configured.
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