Abstract: In one aspect, an apparatus for charging a device includes a charger and a controller. The charger includes a capacitance and has a charger input and a charger output. The charger input receives an AC input voltage waveform, and the charger output outputs an output voltage waveform and an output current waveform. The controller determines whether an amplitude of the output voltage waveform is within a voltage range. In response to determining that the amplitude of the output voltage waveform is within the voltage range, the controller directs an amplitude of the output current waveform to be substantially proportional to an amplitude of the AC input voltage waveform. In response to determining that the amplitude of the output voltage waveform is not within the voltage range, the controller increases the capacitance of the charger to adjust the amplitude of the output voltage waveform to be within the voltage range.

Abstract: An AC-to-DC power converting apparatus includes a power factor correction circuit generating a DC output voltage based on a rectified voltage obtained through rectifying an AC input voltage and on a PWM signal generated based on an adjustment current and a predetermined ramp signal. A multiplier-divider circuit includes: a ramp generating unit generating a ramp signal based on a clock signal and on a first detection voltage associated with the rectified voltage; a control unit generating a control signal based on the clock signal, the ramp signal, and a detection voltage generated based on the DC output voltage; and an output unit generating an adjustment signal based on an input signal associated with the rectified voltage and the control signal.

Abstract: The converter comprises an inverter and a conversion unit in which a transformer powers a controlled rectifier formed by saturable inductors and power diodes. According to the invention, a series reactive circuit associated with the transformer co-operates with the controlled rectifier for the phase displacement of the voltage applied at the primary of the transformer in relation to the current flowing therethrough. The phase displacement is regulated by a control voltage as a function of the variations in the output voltage of the converter.

Abstract: A power-factor-improving circuit and method for an offline converter block the DC component and obtain the AC component of an input voltage of the offline converter. The AC component is superpositioned onto a DC bias signal to generate a dimming signal for the offline converter to adjust an output current of the offline converter. The offline converter has a high power factor due to the dimming signal with the AC component of the input voltage. In addition, the average of the dimming signal is determined by the DC bias signal, hence the output current can be precisely controlled according to the DC bias signal.

Abstract: A controller for a power converter and method of operating the same employable with a bridge rectifier having first and second synchronous rectifier switches. In one embodiment, the controller includes an amplifier configured to enable a turn-on delay for the first synchronous rectifier switch. The controller also includes a discharge switch having first and second switched terminals coupled to gate and source terminals, respectively, of the first synchronous rectifier switch and configured to discharge a gate-to-source capacitance of the first synchronous rectifier switch to enable a turn off thereof.

Abstract: A resonant converter system includes a first stage having inverter circuitry and resonant tank circuitry configured to generate an AC signal from a DC input signal, a transformer configured to transform the AC signal, and a second stage. The second stage features synchronous rectifier (SR) circuitry including a plurality of SR switches each having a body diode and SR control circuitry. SR control circuitry is configured to generate gate control signals to control the conduction state of the SR switches so that the body diode conduction time is minimized and a negative current across the SR switches is reduced or eliminated. The method includes controlling the conduction state of SR switches to conduct as the body diode associated with the switch begins to conduct and controlling the SR switch to turn off as the current through the switch approaches a zero crossing.

Abstract: An adaptive dead time (ADT) control scheme for use with a switch mode power converter having a full bridge with synchronous rectifiers topology. A controller which implements the control scheme includes an input circuit arranged to receive a signal representative of the converter's output voltage, and an output circuit arranged to operate the converter's switching elements and synchronous rectifiers to produce a desired output voltage. The controller is further arranged such that the converter's “dead time” is adaptively varied in an inverse relationship to the magnitude of the load current. In a preferred embodiment, the signals used to operate the synchronous rectifiers are PWM signals, and the controller adaptively varies the dead time in a linear inverse relationship to the magnitude of the load current by modulating the rising and falling edges of the signals used to operate the synchronous rectifiers.

Abstract: A control method for bidirectional DC-DC converter includes: operating a bidirectional DC-DC converter having a low voltage side including a plurality of low-voltage-side switches, a voltage clamping switch and a voltage clamping capacitor, and a high voltage side including a plurality of high-voltage-side switches in a boost mode; switching the voltage clamping switch with a predetermined duty cycle prior to switching on all of the low-voltage-side switches; adjusting the predetermined duty cycle of the voltage clamping switch to be smaller than a turn-off interval of the low-voltage-side switches to reduce the conduction loss of the low-voltage-side switches and the voltage clamping switch; alternatively, operating the DC-DC converter in a buck mode; and adjusting and extending the duty cycle of the low-voltage-side switches to overlap a turn-off time of the high-voltage-side switches to reduce the conduction loss of the low-voltage-side switches.

Abstract: A dual voltage power conversion system with power factor correction (PFC) having a capabilities to adjust a PFC setpoint according to operating conditions. The input signaling levels, for example, may be monitored and used to control adjustments to the PFC setpoint in order to allow the PFC setpoint to dynamically change with any input variation. The PFC setpoint may be adjusted to a PFC setpoint resulting in maximum efficiency.

Abstract: A power supply system and method are disclosed. The system includes a power converter comprising a switching stage to conduct an output current in response to switching signals having a defined duty-cycle. The output current can be provided at an output of the power converter system. The system also includes a current monitor to sense a magnitude of the output current. The system further includes a gate drive controller to generate the switching signals and to control an output impedance of the switching stage based on the sensed magnitude of the output current to control the magnitude of the output current.

Abstract: A control apparatus for regenerative medium voltage inverter is disclosed. The control apparatus controls a switching of a PWM converter unit by generating a voltage compensating a power difference between an input and an output of the PWM converter unit.

Abstract: An off-line power converter includes an integrated circuit power factor controller including a multi-function input terminal, a drive terminal for providing a drive signal to a gate of a drive transistor, a processing circuit coupled to the multi-function input terminal and, based on a signal received from the multi-function input terminal, providing at least one current signal representative of a current conducted in the off-line power converter, and at least one voltage signal representative of a voltage provided to a load, and a controller for providing the drive signal selectively in response to the at least one current signal and the at least one voltage signal.

Abstract: A variable resistance device may be used in a dimmer compatibility circuit to reduce power dissipation in an integrated circuit of the dimmer compatibility circuit. For example, the integrated circuit may include switches coupled to resistors external to the integrated circuit. The integrated circuit may operate the switches to commutate among the external resistors and select a voltage drop that reduces a voltage at a drain voltage of the switches. The reduced drain voltage reduces power dissipation in the switches and instead dissipates the power in the external resistors.

Abstract: A high voltage full wave rectifier and doubler circuit having complementary serially connected low voltage MOSFET stacks to provide high voltage capability. The state of the MOSFETs in the MOSFET stacks is controlled by means of resistors coupled between the circuit's outputs and a time varying input signal. The resistance values of the resistors are selected to maintain operation of the stacked MOSFETs below their breakdown voltages.

Abstract: A bridge-less step-up switching power supply device includes (i) a first and a second reactor having: a first and a second main winding connected to a first and a second input terminal, respectively; and a first and a second auxiliary winding magnetically coupled to the first main winding and connected to the first and second main windings, the first and second auxiliary windings having a first and a second leakage inductance, respectively; (ii) a first and a second diode connected between the first and second auxiliary windings and a first output terminal, respectively; (iii) a first capacitor connected between the first output terminal and a second output terminal; (iv) a second capacitor connected between a connection point of a third switch and a fourth switch, and the first output terminal; and (v) a controller for controlling turning on/off of first to fourth switches.

Abstract: A power supply apparatus and a display apparatus are provided. The power supply apparatus including: a rectifier configured to receive alternating current (AC) power to output a rectified current; a first converter configured to perform a switching operation with respect to the rectified current to output a first output voltage; and a controller configured to control the first converter in order to perform the switching operation so that the first output voltage reaches a first target value in a first period of the input AC current, and not to perform the switching operation in a second period of the input AC power.

Abstract: A controller for estimating a power of a power converter and method of estimating the same has been introduced herein. In one embodiment, the controller includes an analog/digital converter configured to provide samples of a rectified voltage waveform corresponding to a rectified sensed voltage of the power converter. The controller also includes a processor configured to estimate a minimum value of the rectified voltage waveform in accordance with the samples and remove an offset from the rectified voltage waveform to obtain an unbiased rectified voltage waveform in accordance with the estimate of the minimum value. The controller is also configured to obtain an unbiased rectified current waveform corresponding to sensed current of the power converter and provide an average power of the power converter.

Abstract: Methods and systems are described for providing power factor correction for high-power loads using two interleaved power factor correction stages. Each power factor correction stage includes a controllable switch that is operated to control the phasing of each power factor correction stage. The phasing of output current from the second power factor correction stage is shifted 180 degree relative to the output current from the first power factor correction stage.

Abstract: A DC to DC converter can include a reverse-blocking semiconductor switch that makes a synchronously rectifying MOSFET become parallel-connected with a capacitor that is connected to a power supply of a controller IC for a conventionally used synchronously rectifying circuit. The reverse-blocking semiconductor switch can be driven either by signals for adjusting a voltage of the capacitor within a permitted range of voltage of the power supply of the controller circuit, or by signals that are determined by a signal obtained from voltage across the MOSFET and the signals for adjusting a voltage of the capacitor within a permitted range of voltage of the power supply of the controller circuit.

Abstract: A power factor correction circuit includes a first series circuit, a second series circuit, a smoothing capacitor, and a reactor. The power factor correction circuit further includes an input voltage detector that detects an input voltage of at least one end of an AC power source based on one end on a ground side of the smoothing capacitor, and a current detector that detects a reactor current from the AC power source, the current detector having a transformer in which the reactor is a primary side, and first and second switching elements are controlled based at least partially on a reactor current detection signal that is output in accordance with the reactor current from a secondary side of the transformer to supply a desired DC voltage to a load circuit.

Abstract: A power circuit includes a first and a second switches between a input terminal and a reference power source; an inductor between a output terminal and a node between the first and the second switches, a main capacitor coupled to the output terminal, a main switch between the inductor and the output terminal, a sub capacitor coupled to a node between the inductor and the main switch through a sub switch, and a control circuit. And the control circuit performs: switching operation of the first and the second switches, and suspension operation that maintains an off-state of the first and the second switches after switching operation; the switching operation on the main capacitor by switching on the main switch; the switching operation on the sub capacitor by switching on the sub switch; and the switching operation by switching on the main switch and the sub switch.

Abstract: An apparatus comprises a power converter circuit and a controller. The power converter circuit includes an inductor, a switching circuit, and a digital control loop circuit having an adjustable transfer function, wherein the transfer function includes a zero variable and a signal gain variable. The controller includes a tuning module configured to set a value for the zero variable, set the signal gain variable to a first gain value, determine a control error for the first gain value setting, wherein the control error is a difference between a reference current and a load current at a circuit load, iteratively update the gain value of the signal gain variable and determine the control error for the updated gain value, and set an operating gain value of the signal gain variable to the gain value corresponding to a minimum control error.

Abstract: A power factor correction circuit may include a boost converter circuit in which a plurality of boost circuits including a boost inductor, a rectifying diode, and a boost switch are connected with each other; and a snubber circuit including a snubber inductor and a snubber switch so as to snubber the boost converter circuit. The snubber inductor may be controlled so as to be turned on before the boost inductor is turned on to apply zero voltage to the boost inductor. It is possible to reduce switching loss occurring when the boost switch is turned on and increase efficiency of an AC-DC power supply apparatus.

Abstract: An improved control arrangement is used in a high power rectifier and comprises two or more power controllers ganged together in parallel. Each power controller rectifies an AC voltage signal using zero voltage crossing switching to produce a binary switched signal and each power controller is connected to an independent connectable load. Each power controller includes a fast acting binary power switch that selectively connects the respective independent connectable load to the rectified AC voltage signal. The control arrangement selectively activates the power controllers to define a desired connected load. This high power rectifier and control arrangement is advantageously used to provide fast up down power regulation to a grid by selective storage of thermal energy and deriving power from the thermal energy storage system to add fill in power to the grid.

Abstract: The respective main electrodes of the semiconductor switching elements such as IGBTs, which are respectively mounted on the plurality of insulating boards, are electrically connected to each other via the conductor member. This configuration makes it possible to suppress the occurrence of the resonant voltage due to the junction capacity and the parasitic inductance of each semiconductor switching element.

Abstract: The disclosed embodiments provide an AC/DC power converter that converts an AC input voltage into a DC output voltage. This AC/DC power converter includes an input rectifier stage which rectifies an AC input voltage into a first rectified voltage of a first constant polarity and a first amplitude. The AC/DC power converter also includes a switching resonant stage which is directly coupled to the output of the input rectifier stage. This switching resonant stage converts the rectified voltage into a second rectified voltage of a second constant polarity and a second amplitude. The AC/DC power converter additionally includes an output rectifier stage coupled to the output of the switching resonant stage, wherein the output rectifier stage rectifies the second rectified voltage into a DC voltage output.

Abstract: A power source apparatus includes: a first series circuit that has a first rectifier element, a first switching element, and a third rectifier element; a second series circuit that has a second rectifier element, a second switching element, and a fourth rectifier element; a reactor connected between a connecting point of the first rectifier element and the first switching element and a connecting point of the second rectifier element and the second switching element; and a current detection unit having a first resistor element. The first and second switching elements are controllable based on a first zero current detection signal in accordance with a first current detected in the current detection unit, and a desired direct current voltage is fed to a load circuit.

Abstract: Embodiments of the invention provide a power supply apparatus, including an AC/DC rectifying unit converting an AC voltage into a DC voltage, a power factor correction unit correcting a power factor of the DC voltage, and a DC/DC conversion unit converting the DC voltage having the corrected power factor into a DC voltage having a different magnitude therefrom. According to various embodiments, the power supply apparatus further includes an auxiliary winding connected to a primary side winding of a transformer of the DC/DC conversion unit and generating the DC voltage having a predetermined magnitude, and an internal power generation unit connected to an output terminal of the power factor correction unit and the auxiliary winding and using a voltage of the output terminal of the power factor correction unit and a voltage generated by the auxiliary winding to generate temporary Vcc power and supply the generated temporary Vcc power as internal power of the power factor correction unit.

Abstract: A power conversion device includes a main circuit unit (direct-current main circuit) that converts direct-current power into alternating-current power, and a control unit that controls the direct-current main circuit. The direct-current main circuit includes a voltage detector (detector) that detects a capacitor voltage and a discharge circuit that discharges energy accumulated in a capacitor. The control unit includes a detection circuit that estimates a capacitor voltage during a normal operation based on a voltage transmitted from the voltage detector in a state where the main circuit unit is disconnected from a power supply and that detects a sign that a short circuit fault occurs in the capacitor, and a control circuit that outputs a control signal for controlling the discharge circuit to operate when the control circuit receives a detection signal from the detection circuit.

Abstract: A power detecting circuit for a power supply module is disclosed. The power detecting circuit includes a current detecting module, a micro control unit (MCU), a correcting circuit. The current detecting module is electrically coupled to the power supply module and configured to detect an output current value of the power supply module. The micro control unit (MCU) is electrically coupled to the current detecting module. The correcting circuit is electrically coupled to the MCU and configured to correct the output current value of the power supply module. The MCU is configured to calculate an output power value of the power supply module according to the output current value and a preset output voltage value or a tested output voltage value of the power supply module and display the output power value via a display module.

Abstract: A controller having adjustable frequency-reduction function for a power conversion application, comprising: a threshold voltage sampling unit, having a first node coupled to an external resistor network for generating a threshold voltage at the first node, which is then sampled by the threshold voltage sampling unit; a PWM unit having a second node for receiving a feedback voltage from a load, and a third node for providing a PWM signal of a switching frequency; and a driver unit for driving an external power transistor according to the PWM signal; wherein the switching frequency starts to decrease from a first frequency when the feedback voltage falls below a first threshold voltage, which is a first function of the threshold voltage.

Abstract: According to one embodiment, a power supply device includes a rectifying circuit configured to rectify an alternating-current power supply, a first capacitor configured to smooth a voltage after rectification, and a falling voltage chopper circuit configured to supply electric power to a load. The first capacitor is set to a capacity in which a section where a voltage after smoothing drops to an output voltage to the load is provided in a rectified half period of the alternating-current power supply. The falling voltage chopper circuit includes at least one switching element configured to receive an input of the voltage after smoothing, operate in a section where the voltage after smoothing exceeds the output voltage, and pause in a section of the output voltage and a second capacitor provided on an output side and having a capacity larger than the capacity of the first capacitor.

Abstract: Provided is a power factor correction circuit correcting a power factor of AC voltage. The power factor correction circuit includes: a rectifying unit stopping rectifying the AC voltage in a transient state and generating an rectified voltage by rectifying the AC voltage in a steady state; a power factor correction unit generating a power-factor-corrected voltage by correcting the rectified voltage; a smoothing unit generating a smoothed voltage by smoothing the power-factor-corrected voltage; and an inrush current limiting unit providing a limited current by limiting an inrush current generated by the AC voltage in the transient state and stopping providing a current to the smoothing unit.

Abstract: An example controller includes a power factor enhancer, an on-time controller, and a switching signal generator. The power factor enhancer is coupled to generate a pre-distortion signal each half-line cycle of an ac input voltage of a PFC converter. The on-time controller ends an on-time of a PFC switch in response to a sensed PFC switch current of the PFC converter multiplied by the pre-distortion signal. The switching signal generator controls an input current waveform of the PFC converter to substantially follow a shape of an input voltage waveform by generating a switching signal in response to the on-time controller to control switching of the PFC switch. The power factor enhancer adjusts the pre-distortion signal to pre-distort the sensed PFC switch current to compensate for distortion in the input current waveform.

Abstract: In one embodiment, a method of driving a load can include: monitoring an AC input to a rectifier circuit in real-time, where the rectifier circuit can include first and second rectifier circuits, and controlling first and second controllable switches based on a state of the AC input is in a first state. For example, a first state can include the AC input being in a positive half cycle and increasing, or the AC input being in the positive half cycle and decreasing while being at least as high as a predetermined threshold value. The AC input can be used to supply power to a load circuit and an output capacitor via the first rectifier circuit when the AC input is in the first state, where the first rectifier circuit can include a first diode and the second controllable switch.

Abstract: A method of operating a power factor correction (PFC) circuit and a corresponding power factor correction circuit include determining an adaptive switching frequency of the PFC circuit related to a current of the boost inductor of the PFC circuit, and operating the PFC circuit at a light load based on the adaptive switching frequency.

Abstract: A semiconductor device includes: a first output unit configured to output a first phase; a second output unit configured to output a second phase different from the first phase, the second output unit being disposed to be stacked on the first output unit; and a controller configured to control the output units.

Abstract: A first error amplification circuit amplifies a difference between a predetermined reference voltage and a first detection voltage that corresponds to the output voltage of a DC/DC converter, so as to generate a second voltage. A voltage level judgment circuit generates a third voltage having a discrete level that corresponds to the amplitude of a first voltage. A multiplying/dividing circuit multiplies the first voltage by the second voltage, and divides the resulting product by the third voltage, so as to generate a fourth voltage. A comparator compares the fourth voltage with a second detection voltage that corresponds to a current that flows through a switching transistor included in the DC/DC comparator. A driving circuit turns on the switching transistor for each predetermined period, and turns off the switching transistor according to the output of the comparator every time the second detection voltage becomes higher than the fourth voltage.

Abstract: A power supply circuit includes: a first switch and a second switch that are connected in series between an input voltage terminal and a reference power supply; a controller that controls the first and second switches to be turned on and off by turns; a comparator that has an inverting input terminal connected to a voltage supply and that has a non-inverting input terminal connected to a first terminal of a capacitor; a third switch that is provided between an output terminal and the non-inverting input terminal of the comparator; a fourth switch that is provided between a connection node of the first and second switches, and a second terminal of the capacitor; and a latch circuit that detects change of output of the output terminal of the comparator and controls the second switch to be turned off.

Abstract: A control device for a transistor of a switching converter rectifier generates a control signal of the transistor and comprises a circuit to measure the conduction time of the body diode of the transistor cycle by cycle. When the conduction time is greater than a first threshold, the off time instant of the transistor is delayed by a first quantity in the next cycles, until the conduction time is less than the first threshold and greater than a second threshold. When the conduction time is between the first and second thresholds, the off time instant is delayed by a fixed second quantity in the next cycles until the conduction time is lower than the second threshold, with the second quantity less than the first quantity. When the conduction time is lower than the second threshold, the off time instant is advanced by the second quantity in the next cycle.

Abstract: A light emitting system includes a series connection of a light emitting unit and a variable current source, and a voltage conversion device that includes a rectifier circuit and an output circuit. The rectifier circuit rectifies an AC voltage to generate a rectified voltage across a first rectifier output coupled to one end of the series connection of the light emitting unit and the variable current source, and a second rectifier output. The output circuit is coupled between the second rectifier output and another end of the series connection of the light emitting unit and the variable current source, and is configured to generate a direct-current (DC) output voltage.

Abstract: An apparatus and a method for wireless power reception include converting a received wireless power to a wireless power for charging using a synchronous rectifier and a direct current/direct current (DC/DC) converter having a structure providing a high efficiency and low heat generation even when a high charging current is supplied.

Abstract: System and method for regulating a power conversion system. A system controller for regulating a power conversion system includes a first controller terminal and a second controller terminal. The system controller is configured to receive at least an input signal at the first controller terminal, and generate a gate drive signal at the second controller terminal based on at least information associated with the input signal to turn on or off a transistor in order to affect a current associated with a secondary winding of the power conversion system. The system controller is further configured to, if the input signal is larger than a first threshold, generate the gate drive signal at a first logic level to turn off the transistor.

Abstract: The present invention describes systems and methods for harvesting energy from an alternating magnetic field. An exemplary embodiment can include a flux concentrator having an open core coil wherein a first current with a first voltage is induced in the flux concentrator when placed proximate an alternating magnetic field. Additionally, the system can include a transformer, having a first and second winding, connected to the flux concentrator and inducing a second current in the second winding, wherein the second current has a second voltage higher than the first voltage and a threshold voltage of a first and second diode. Furthermore, the system can include a converter, connected to the secondary winding for charging the leakage inductance of the secondary winding by creating a short circuit between the secondary winding and the converter; and the diodes connected to the secondary winding and the converter for discharging the leakage inductance.

Abstract: The switching power supply circuit includes a full-wave rectifier (1) which full-wave rectifies alternating power-supply voltage to output a pulsating current, and an inductor (3) connected to the full-wave rectifier (1). A level conversion circuit (20) includes a plurality of resistors connected in series, and converts inductor current detection voltage to a first current level signal and a second current level signal (S1 and S2) which are different in voltage level and which are proportional to inductor current. A continuous control setting circuit (30) generates a reference potential signal a phase of which is approximately the same as a phase of alternating input voltage from the first current level signal (S1) and compares a voltage level of the reference potential signal with a voltage level of the second current level signal (S2) to output a second set pulse (S8) that specifies timing at which a switching element (4) turns on.

Abstract: A converter control device comprises: a voltage-zero-cross detection unit detecting zero cross of the alternate-current voltage and outputting a voltage zero-cross signal; a power-source-current detection unit detecting a power source current of the alternate-current power source; a bus-line-voltage detection unit detecting a bus-line voltage between terminals of the smoothing capacitor; a PWM-signal generation unit generating a PWM-signal for on/off-controlling the switching unit, based on the power-source current, the bus-line voltage and a bus-line-voltage command value as a target voltage of the bus-line voltage; a power-source voltage-state detection unit detecting a signal state of the alternate-current voltage based on the voltage zero-cross signal; and a fundamental-switching-frequency selection unit selecting a fundamental switching frequency of the PWM-signal based on the signal state of the alternate-current voltage.

Abstract: A second control circuit is configured to switch a pulse signal to a level which turns off a second switching transistor when a coil current that flows through a primary winding reaches a predetermined threshold current. The second control circuit is configured to start a switching operation when a power supply for an electronic device is turned on, to set the threshold current to a first value when an intermediate voltage is higher than a predetermined level, and to set the threshold current to a second value that is lower than the first value when the intermediate voltage is lower than a predetermined level. A first control circuit is configured to start a switching operation upon receiving an instruction from a microcontroller to start operating.

Abstract: Methods and systems are described for providing power factor correction for high-power loads using two interleaved power factor correction stages. Each power factor correction stage includes a controllable switch that is operated to control the phasing of each power factor correction stage. The phasing of output current from the second power factor correction stage is shifted 180 degree relative to the output current from the first power factor correction stage.

Abstract: A timing controlled converter for converting a time varying input signal to a regulated DC output voltage for application to a load circuit. A feedback loop is employed as a control means for switchably coupling the time varying input signal to the load circuit for controlled periods of time in a manner so as to provide an average load voltage equal to a reference voltage. The duration of the controlled periods of time is a function of: the difference between the time varying input signal and the output voltage; and the integral of the difference between the output voltage and the reference voltage.

Abstract: An active power factor correction (PFC) circuit for calibrating a power factor of an AC-to-DC converter when the active PFC circuit is coupled with the AC-to-DC converter is disclosed including: a piecewise linear gain circuit, an error amplifier, a PWM controller, and a PWM signal generator. The piecewise linear gain circuit is for receiving a feed forward signal and generating a corresponding gain signal, wherein the gain signal and the feed forward signal have a broken line relation with respect to magnitude. The error amplifier is for generating an error signal according to an output voltage of the AC-to-DC converter. The PWM controller is for generating a control signal according to the gain signal and the error signal. The PWM signal generator is for generating a PWM signal for controlling a power switch of the AC-to-DC converter according to the control signal.