Abstract: In one embodiment, a power factor correction (PFC) circuit can include: (i) a rectifier bridge and a PFC converter coupled to an input capacitor; (ii) a harmonic wave compensation circuit configured to shift a phase of a DC input voltage provided from the rectifier bridge, where the harmonic wave compensation circuit comprises a phase of about ?45° when a corner frequency is about 50 Hz; and (iii) a PFC control circuit configured to control the PFC converter, where the PFC control circuit comprises a first sampling voltage, and the harmonic wave compensation circuit is configured to control a phase of the first sampling voltage to lag a phase of the DC input voltage by about 45°.

Abstract: In one embodiment, a method of controlling a capacitor discharge for a switching power supply, can include: (i) generating a first voltage signal from a voltage at an X capacitor that is coupled between input terminals of the switching power supply; (ii) activating a detection signal in response to the first voltage signal being inactive for a duration of a predetermined time interval, where the detection signal being activated indicates a cut-off of the input terminals; and (iii) at least partially discharging the X capacitor after the cut-off and in response to activation of the detection signal.

Abstract: In one embodiment, a method of compensating for transmission voltage loss from a switching power supply, can include: (i) receiving a sampling signal that represents an output current of the switching power supply; (ii) delaying the sampling signal to generate a delayed sampling signal; (iii) converting the delayed sampling signal to generate a compensation signal; and (iv) regulating an output voltage of the switching power supply based on the compensation signal to compensate for the transmission voltage loss from the output voltage transmission to a load such that a voltage at the load is maintained as substantially consistent with an expected voltage at the load.

Abstract: In one embodiment, an undervoltage protection circuit for a switching power supply can include: (i) an undervoltage detection circuit that determines whether an input voltage of the switching power supply is in an undervoltage state; (ii) a selection circuit configured to select a first or a second control signal to be provided as a main control signal to a control circuit; (iii) the control circuit being configured, in response to the main control signal being the first control signal, to control a switching operation of a power transistor in the switching power supply such that an output voltage of the switching power supply is maintained as substantially stable; and (iv) the control circuit being configured, in response to the main control signal being the second control signal, to control the switching operation of the power transistor to reduce an input power of the switching power supply.

Abstract: In one embodiment, a method of detecting a voltage can include: (i) generating a first current according to a first voltage and a converting resistor; (ii) charging a detection capacitor by the first current during a first time period of a switching cycle of a switching power supply; (iii) charging the detection capacitor by a second current during a second time period of the switching cycle; (iv) detecting a voltage across the detection capacitor to obtain a detection voltage at an end time of the second time period, where the first time period includes a rising portion of a current flowing through the inductor, and the second time period includes a decreasing portion of the inductor current; and (v) determining a state of a present output voltage of the switching power supply according to the detection voltage.

Abstract: In one embodiment, a power factor correction (PFC) circuit can include: (i) a rectifier bridge and a PFC converter coupled to an input capacitor; (ii) a harmonic wave compensation circuit configured to shift a phase of a DC input voltage provided from the rectifier bridge, where the harmonic wave compensation circuit comprises a phase of about ?45° when a corner frequency is about 50 Hz; and (iii) a PFC control circuit configured to control the PFC converter, where the PFC control circuit comprises a first sampling voltage, and the harmonic wave compensation circuit is configured to control a phase of the first sampling voltage to lag a phase of the DC input voltage by about 45°.

Abstract: A silicon-controlled rectifier (SCR) dimming circuit and a dimming control method are disclosed. The SCR dimming circuit includes a SCR element, a rectifier circuit, a filter circuit, a power converter, and a dimming control circuit. The dimmer control circuit includes a phase angle detection circuit, an output current feedback control circuit, an input current control circuit, a maximum operation time detection circuit, and a logic operator. An input current sampling signal fluctuates near a predetermined value after the SCR element is turned off by turning on and off the power converter, so that the input AC current is less than a holding current of the SCR element. The present SCR dimming circuit and the present dimming control method can avoid repeatedly turning on the SCR element in cycles of an operating frequency. Thus, the linearity of dimming is improved and the flicker of an LED lamp is eliminated.

Abstract: In one embodiment, a method of controlling a switching power supply, can include: (i) generating a driving current signal that follows a waveform of a sense voltage signal, where the sense voltage signal is related to a current through a collector of a transistor that is configured as a power switch of the switching power supply, where the collector is coupled to an inductive element of the switching power supply; (ii) providing the driving current signal to a base of the transistor, where the transistor is in a saturated conduction state when a pulse-width modulation (PWM) signal is active; and (iii) releasing charge accumulated on the base when the PWM signal is inactive to turn off the transistor.

Abstract: A silicon-controlled rectifier (SCR) dimming circuit and a dimming control method are disclosed. The SCR dimming circuit includes a SCR element, a rectifier circuit, a filter circuit, a power converter, and a dimming control circuit. The dimmer control circuit includes a phase angle detection circuit, an output current feedback control circuit, an input current control circuit, a maximum operation time detection circuit, and a logic operator. An input current sampling signal fluctuates near a predetermined value after the SCR element is turned off by turning on and off the power converter, so that the input AC current is less than a holding current of the SCR element. The present SCR dimming circuit and the present dimming control method can avoid repeatedly turning on the SCR element in cycles of an operating frequency. Thus, the linearity of dimming is improved and the flicker of an LED lamp is eliminated.

Abstract: In one embodiment, method of signal processing can include: (i) determining a high level sampling pulse amount by counting a number of pulses of a first clock signal during a high level portion of a period of a first PWM; (ii) generating a first pulse signal based on a second clock signal and the high level sampling pulse amount; (iii) determining a low level sampling pulse amount by counting a number of pulses of the first clock signal during a low level portion of the period of the first PWM signal; (iv) generating a second pulse signal based on the second clock signal and the low level sampling pulse amount; and (v) generating a second PWM signal based on the first and second pulse signals.

Abstract: In one embodiment, a method of detecting a voltage can include: (i) generating a first current according to a first voltage and a converting resistor; (ii) charging a detection capacitor by the first current during a first time period of a switching cycle of a switching power supply; (iii) charging the detection capacitor by a second current during a second time period of the switching cycle; (iv) detecting a voltage across the detection capacitor to obtain a detection voltage at an end time of the second time period, where the first time period includes a rising portion of a current flowing through the inductor, and the second time period includes a decreasing portion of the inductor current; and (v) determining a state of a present output voltage of the switching power supply according to the detection voltage.

Abstract: In one embodiment, a power factor correction (PFC) circuit can include: (i) a rectifier bridge and a PFC converter coupled to an input capacitor; (ii) a harmonic wave compensation circuit configured to shift a phase of a DC input voltage provided from the rectifier bridge, where the harmonic wave compensation circuit comprises a phase of about ?45° when a corner frequency is about 50 Hz; and (iii) a PFC control circuit configured to control the PFC converter, where the PFC control circuit comprises a first sampling voltage, and the harmonic wave compensation circuit is configured to control a phase of the first sampling voltage to lag a phase of the DC input voltage by about 45°.

Abstract: In one embodiment, method of signal processing can include: (i) determining a high level sampling pulse amount by counting a number of pulses of a first clock signal during a high level portion of a period of a first PWM; (ii) generating a first pulse signal based on a second clock signal and the high level sampling pulse amount; (iii) determining a low level sampling pulse amount by counting a number of pulses of the first clock signal during a low level portion of the period of the first PWM signal; (iv) generating a second pulse signal based on the second clock signal and the low level sampling pulse amount; and (v) generating a second PWM signal based on the first and second pulse signals.

Abstract: In one embodiment, a method of compensating for transmission voltage loss from a switching power supply, can include: (i) receiving a sampling signal that represents an output current of the switching power supply; (ii) delaying the sampling signal to generate a delayed sampling signal; (iii) converting the delayed sampling signal to generate a compensation signal; and (iv) regulating an output voltage of the switching power supply based on the compensation signal to compensate for the transmission voltage loss from the output voltage transmission to a load such that a voltage at the load is maintained as substantially consistent with an expected voltage at the load.

Abstract: In one embodiment, a method of controlling a capacitor discharge for a switching power supply, can include: (i) generating a first voltage signal from a voltage at an X capacitor that is coupled between input terminals of the switching power supply; (ii) activating a detection signal in response to the first voltage signal being inactive for a duration of a predetermined time interval, where the detection signal being activated indicates a cut-off of the input terminals; and (iii) at least partially discharging the X capacitor after the cut-off and in response to activation of the detection signal.

Abstract: In one embodiment, an undervoltage protection circuit for a switching power supply can include: (i) an undervoltage detection circuit that determines whether an input voltage of the switching power supply is in an undervoltage state; (ii) a selection circuit configured to select a first or a second control signal to be provided as a main control signal to a control circuit; (iii) the control circuit being configured, in response to the main control signal being the first control signal, to control a switching operation of a power transistor in the switching power supply such that an output voltage of the switching power supply is maintained as substantially stable; and (iv) the control circuit being configured, in response to the main control signal being the second control signal, to control the switching operation of the power transistor to reduce an input power of the switching power supply.