| 摘要 |
A method and apparatus for providing a rectified voltage to a flyback switch-mode supply circuit with power factor correction is disclosed and claimed. The invention comprises a rectifying bridge and a charge path for charging a capacitor from the rectified voltage obtained from the output of the bridge. The degree of power factor correction is achieved by selecting a time at which either the rectifying bridge output or the capacitor provides a voltage to the supply circuit. The input to the supply circuit is a primary winding having n1 turns between an upper and intermediate tap, and n2 turns between an intermediate and lower tap. The capacitor is connected to the upper tap via a diode, a first rectifying bridge output is connected to the intermediate tap via a diode, and a second rectifying bridge output is connected to the lower tap via a controllable switch. When the rectified voltage is greater than a threshold voltage related to the peak rectified voltage by the ratio n2/(n1+n2), the rectifying bridge outputs provide the voltage to the supply circuit. When the rectified voltage is lower than this threshold voltage, the capacitor provides the voltage to the supply circuit. In this manner, the timing of sources providing voltage to the supply circuit and hence the degree of power factor correction is determined by the ratio of the primary winding turns n1 and n2.
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