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The Analysis of Processes in the Power Factor Corrector with Unlocking of the Power Transistor at Zero Value of a Throttle's Current


G.A. Belov, A.V. Serebryannikov

On the basis of consideration of the power factor corrector’s (PFC) control microcircuit’s functioning, analysis and calculation of PFC’s quasistationary mode and transients is given. The quasistationary mode is considered in the assumption that the power part works in a boundary mode when a throttle’s current represents sequence of triangular impulses without pauses between them. Then at performance of the additional condition consisting in a constancy of the power transistor’s on-condition time, average value of throttle’s current changes to proportionally PFC’s input voltage in the absence of a special input current’s average value regulation contour. The nonlinear differential equation for average value of the output condenser’s voltage received here as depends on input power and a load’s current, as well as in PFC with a double-circuit control system. This equation shows presence in PFC’s output voltage of the low-frequency pulsations changing with doubled frequency of a power line which can decrease only increase in capacity of output condenser. These pulsations get on an output of voltage regulator and on an input of the pulse-width modulator, causing additional peak modulation of impulses of throttle’s current and additional distortions of PFC’s input current and a power line current. The analytical parities, allowing organizing fast and exact enough calculation of transients, are proved. Results of calculations well illustrate the basic features of PFC’s considered scheme. Switching frequency of the power transistor is maximum in the beginning and in the end of a power line voltage’s half-period where the switching period is minimum and is approximately equal to necessary duration of the power transistor’s on-condition t1 . Changing of time t1 during the power line voltage’s half-period, necessary for maintenance of a output voltage’s constancy, is slightly, as well as is required on conditions of PFC’s normal work. It is provided with that voltage regulator’s output voltage uvr also slightly changes for the power line voltage’s half-period (apparently from the presented curves, in the beginning of a half-period voltage uvr is supported at level 7 V, in the middle of a half-period – at the rate of about 7,25 V, in the end of a half-period – 7,5 V). Time t1 , as well as voltage uvr , changes for the power line voltage’s half-period approximately on 7 %.

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