Abstract: A flyback power converter includes a primary side controller circuit for controlling a primary side switch; and a secondary side controller circuit for generating an SR (Synchronous Rectification) signal to control an SR switch. The SR signal includes an SR pulse and a ZVS (Zero Voltage Switching) pulse. The SR pulse controls the SR switch for synchronous rectification at the secondary side. The secondary side controller circuit samples and holds a voltage at a first end of the SR switch as a first voltage at a timing between the end of the ZVS pulse and the beginning of the SR pulse, and determines a length of the ZVS pulse so as to control the SR switch to be conductive for a ZVS time period, whereby the primary side switch achieves ZVS. The first voltage is proportional to an input voltage.

Abstract: A switching controller circuit for controlling a flyback power converter includes: a power transformer, a primary side controller circuit and a secondary side controller circuit. The power transformer is coupled between the input voltage and the output voltage in an isolated manner. The primary side controller circuit controls a primary side switch of the flyback power converter. The secondary side controller circuit generates a synchronous rectification (SR) signal, to control an SR switch of the flyback power converter. The SR signal includes an SR pulse and a soft switching (SS) pulse. The SR pulse controls the SR switch to be ON for an SR period, to achieve synchronous rectification at the secondary side. The SS pulse controls the SR switch to be ON for an SS period, to achieve soft switching of the primary side switch.

Abstract: An LED (Light Emitting Diode) drive circuit includes a magnetic device, a power transistor, a current-sense resistor, and a controller. The magnetic device has a first terminal for receiving an input voltage derived from an input of the LED drive circuit, and a second terminal. The magnetic device generates an output current to drive at least one LED. The power transistor has a drain coupled to the second terminal of the magnetic device, a control terminal, and a source. The current-sense resistor has a first terminal coupled to the source of the power transistor for forming a current input signal, and a second terminal coupled to ground. The controller generates a switching signal coupled to control the power transistor to switch current through the magnetic device based on both a programmable signal derived from the input of the LED drive circuit, and the current input signal.

Abstract: A flyback power converter circuit includes: a transformer; a primary side switch, for controlling a primary winding to convert an input voltage to an output voltage and an internal voltage; a primary side control circuit, which is powered by the internal voltage; the primary side control circuit generates a switching signal according to a feedback signal, to operate the primary side switch; a secondary side control circuit, which generates the feedback signal according the output voltage; and a dummy load circuit, which is coupled to the output voltage, wherein when the output voltage drops to or is lower than a predetermined threshold, the dummy load circuit generates a dummy load current, to determine the feedback signal, so that the internal voltage is not undesirably low. When the output voltage exceeds the predetermined threshold, the dummy load circuit adjusts the dummy load current to zero current.

Abstract: A switching controller circuit for controlling a flyback power converter includes: a power transformer, a primary side controller circuit and a secondary side controller circuit. The power transformer is coupled between the input voltage and the output voltage in an isolated manner. The primary side controller circuit controls a primary side switch of the flyback power converter. The secondary side controller circuit generates a synchronous rectification (SR) signal, to control an SR switch of the flyback power converter. The SR signal includes an SR pulse and a soft switching (SS) pulse. The SR pulse controls the SR switch to be ON for an SR period, to achieve synchronous rectification at the secondary side. The SS pulse controls the SR switch to be ON for an SS period, to achieve soft switching of the primary side switch.

Abstract: A flyback power converter includes a primary side controller circuit for controlling a primary side switch; and a secondary side controller circuit for generating an SR (Synchronous Rectification) signal to control an SR switch. The SR signal includes an SR pulse and a ZVS (Zero Voltage Switching) pulse. The SR pulse controls the SR switch for synchronous rectification at the secondary side. The secondary side controller circuit samples and holds a voltage at a first end of the SR switch as a first voltage at a timing between the end of the ZVS pulse and the beginning of the SR pulse, and determines a length of the ZVS pulse so as to control the SR switch to be conductive for a ZVS time period, whereby the primary side switch achieves ZVS. The first voltage is proportional to an input voltage.

Abstract: A flyback power converter circuit includes: a transformer; a primary side switch, for controlling a primary winding to convert an input voltage to an output voltage and an internal voltage; a primary side control circuit, which is powered by the internal voltage; the primary side control circuit generates a switching signal according to a feedback signal, to operate the primary side switch; a secondary side control circuit, which generates the feedback signal according the output voltage; and a dummy load circuit, which is coupled to the output voltage, wherein when the output voltage drops to or is lower than a predetermined threshold, the dummy load circuit generates a dummy load current, to determine the feedback signal, so that the internal voltage is not undesirably low. When the output voltage exceeds the predetermined threshold, the dummy load circuit adjusts the dummy load current to zero current.

Abstract: An LED (Light Emitting Diode) drive circuit includes a magnetic device, a power transistor, a current-sense resistor, and a controller. The magnetic device has a first terminal for receiving an input voltage derived from an input of the LED drive circuit, and a second terminal. The magnetic device generates an output current to drive at least one LED. The power transistor has a drain coupled to the second terminal of the magnetic device, a control terminal, and a source. The current-sense resistor has a first terminal coupled to the source of the power transistor for forming a current input signal, and a second terminal coupled to ground. The controller generates a switching signal coupled to control the power transistor to switch current through the magnetic device based on both a programmable signal derived from the input of the LED drive circuit, and the current input signal.

Abstract: An LED drive circuit includes a controller, generating a switching signal to switch a magnetic device that receives an input voltage derived from an input of the LED drive circuit, for generating an output current to drive at least a LED. The controller includes an input circuit receiving a programmable signal correlated to the input of the LED drive circuit to generate a programmable current, the programmable current modulating a current input signal correlated to a switching current of the magnetic device to form a modulated current input signal, and a comparison circuit comparing a signal sourced from an oscillator and a voltage potential generated in response to the modulated current input signal for generating a current control signal. The switching signal is controlled in response to the current control signal for regulating the output current, and a level of the output current is correlated to the current control signal.

Abstract: An LED drive circuit includes a controller, generating a switching signal to switch a magnetic device that receives an input voltage derived from an input of the LED drive circuit, for generating an output current to drive at least a LED. The controller includes an input circuit receiving a programmable signal correlated to the input of the LED drive circuit to generate a programmable current, the programmable current modulating a current input signal correlated to a switching current of the magnetic device to form a modulated current input signal, and a comparison circuit comparing a signal sourced from an oscillator and a voltage potential generated in response to the modulated current input signal for generating a current control signal. The switching signal is controlled in response to the current control signal for regulating the output current, and a level of the output current is correlated to the current control signal.

Abstract: A LED drive circuit according to the present invention comprises a controller and a programmable signal. The controller generates a switching signal coupled to switch a magnetic device for generating an output current to drive a plurality of LEDs. The programmable signal is coupled to regulate a current-control signal of the controller. The switching signal is modulated in response to the current-control signal for regulating the output current, and the level of the output current is correlated to the current-control signal.

Abstract: A LED drive circuit according to the present invention comprises a controller and a programmable signal. The controller generates a switching signal coupled to switch a magnetic device for generating an output current to drive a plurality of LEDs. The programmable signal is coupled to regulate a current-control signal of the controller. The switching signal is modulated in response to the current-control signal for regulating the output current, and the level of the output current is correlated to the current-control signal.

Abstract: A LED drive circuit according to the present invention comprises a controller and a programmable signal. The controller generates a switching signal coupled to switch a magnetic device for generating an output current to drive a plurality of LEDs. The programmable signal is coupled to regulate a current-control signal of the controller. The switching signal is modulated in response to the current-control signal for regulating the output current, and the level of the output current is correlated to the current-control signal.

Abstract: A controller for a power converter includes a clamping circuit, a switching circuit and a pulse generator. The clamping circuit is coupled to an input terminal of the controller for detecting a detection signal from a transformer. The switching circuit generates a switching signal to switch the transformer in response to the detection signal for regulating the power converter. A maximum level of the detection signal is clamped to be under a level of a threshold voltage during an off-period of the switching signal. Since the maximum level of the detection signal is clamped and the oscillating energy of the reflected signal is discharged, the speed of detecting the detection signal is increased. Therefore, the regulation of the primary-side controlled power converter can be improved accordingly.

Abstract: A LED drive circuit according to the present invention comprises a controller and a programmable signal. The controller generates a switching signal coupled to switch a magnetic device for generating an output current to drive a plurality of LEDs. The programmable signal is coupled to regulate a current-control signal of the controller. The switching signal is modulated in response to the current-control signal for regulating the output current, and the level of the output current is correlated to the current-control signal.

Abstract: A LED drive circuit according to the present invention comprises a controller and a programmable signal. The controller generates a switching signal coupled to switch a magnetic device for generating an output current to drive a plurality of LEDs. The programmable signal is coupled to regulate a current-control signal of the controller. The switching signal is modulated in response to the current-control signal for regulating the output current, and the level of the output current is correlated to the current-control signal.

Abstract: A control circuit for power converter according to the present invention comprises a PWM circuit generating a switching signal coupled to switch a transformer of the power converter. A feedback input circuit is coupled to an output of the power converter for generating a feedback signal. The feedback signal is coupled to turn off the switching signal. A detection circuit is coupled to the transformer for generating a valley signal in response to a waveform of the transformer. A frequency-variation circuit is coupled to receive the feedback signal and the valley signal for generating a frequency-variation signal. The frequency-variation signal is coupled to turn on the switching signal. A burst circuit is coupled to receive the feedback signal for generating a burst signal to disable the switching signal.

Abstract: A control circuit of a power converter for light-load power saving according to the present invention comprises a first feedback circuit coupled to an output voltage of the power converter to receive a first feedback signal. A second feedback circuit is coupled to the output voltage to receive a second feedback signal. A control circuit generates a switching signal for switching a transformer of the power converter and regulating the output voltage of the power converter in response to the first feedback signal and the second feedback signal. The switching signal is generated in accordance with the first feedback signal when an output load is high. The switching signal is generated in accordance with the second feedback signal during a light-load condition.

Abstract: A control circuit of a LED driver according to the present invention comprises an output circuit, an input circuit and an input-voltage detection circuit. The output circuit generates a switching signal to produce an output current for driving at least one LED in response to a feedback signal. The switching signal is coupled to switch a transformer. The input circuit samples an input signal for generating the feedback signal. The input signal is correlated to the output current of the LED driver. The input-voltage detection circuit generates an input-voltage signal in response to an input voltage of the LED driver. The input circuit will not sample the input signal when the input-voltage signal is lower than a threshold. The control circuit can eliminate the need of the input capacitor for improving the reliability of the LED driver.

Abstract: A control circuit of a LED driver according to the present invention comprises an output circuit, an input circuit and an input-voltage detection circuit. The output circuit generates a switching signal to produce an output current for driving at least one LED in response to a feedback signal. The switching signal is coupled to switch a transformer. The input circuit samples an input signal for generating the feedback signal. The input signal is correlated to the output current of the LED driver. The input-voltage detection circuit generates an input-voltage signal in response to an input voltage of the LED driver. The input circuit will not sample the input signal when the input-voltage signal is lower than a threshold. The control circuit can eliminate the need of the input capacitor for improving the reliability of the LED driver.