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 is developed to adaptively operate a power converter at quasi-resonance (QR) and in a continuous current mode (CCM) to achieve high efficiency. The control circuit includes a PWM circuit generating a switching signal coupled to switch a transformer. A signal generation circuit generates a ramp signal and a pulse signal. The pulse signal is generated in response to the ramp signal for switching on the switching signal. A feedback circuit produces a feedback signal according to an output load of the power converter. The feedback signal is coupled to switch off the switching signal. A detection circuit is coupled to the transformer for generating a valley signal in response to the waveform of the transformer. The valley signal is further coupled to generate the pulse signal when the ramp signal is lower than a threshold. The level of the threshold is correlated to the feedback 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 method and an apparatus for detecting a CCM operation of a magnetic device are developed. The method generates a current signal in accordance with a switching current of the magnetic device and generates a first current signal and a second current signal by sampling the current signal. A mode signal is further generated according to the first current signal and the second current signal. The mode signal indicates the magnetic device is operated in CCM or DCM. The apparatus comprises a first sample circuit, a second sample circuit, and an arbiter. The first sample circuit samples the current signal to generate the first current signal. The second sample circuit samples the current signal to generate the second current signal. The arbiter generates the mode signal according to the first current signal and the second current signal for indicating the magnetic device is operated in CCM or DCM.

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: An apparatus for detecting a switching current of the power converter, wherein the apparatus includes a signal generation circuit, a sample-and-hold circuit, and a calculating circuit. The signal generation circuit generates a sample signal in accordance with the pulse width of a switching signal. The sample-and-hold circuit is coupled to receive the sample signal and switching current signal for generating a first current signal and a second current signal. The calculating circuit is coupled to receive the first current signal and the second current signal for generating output signals. The switching signal is used for switching the magnetic device of the power converter, and the switching current signal is correlated to the switching current of the power converter; the output signals are correlated to the value of the switching current of the power converter.

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 is developed to adaptively operate a power converter at quasi-resonance (QR) and in a continuous current mode (CCM) to achieve high efficiency. The control circuit includes a PWM circuit generating a switching signal coupled to switch a transformer. A signal generation circuit generates a ramp signal and a pulse signal. The pulse signal is generated in response to the ramp signal for switching on the switching signal. A feedback circuit produces a feedback signal according to an output load of the power converter. The feedback signal is coupled to switch off the switching signal. A detection circuit is coupled to the transformer for generating a valley signal in response to the waveform of the transformer. The valley signal is further coupled to generate the pulse signal when the ramp signal is lower than a threshold. The level of the threshold is correlated to the feedback signal.

Abstract: A circuit and a method for detecting a voltage of a transformer are provided. The circuit includes a current output circuit coupled to a winding of a transformer to generate a current signal. A current-to-voltage circuit is coupled to the current output circuit to generate a voltage signal in response to the current signal. A sample-and-hold circuit generates an output signal by sampling the voltage signal. An input voltage is applied to the transformer. The output signal is correlated to the input voltage of the transformer.

Abstract: A circuit for detecting an input voltage of a transformer is provided. The circuit includes a current source circuit coupled to a winding of a transformer. A current-to-voltage circuit is coupled to the current source circuit to generate a first voltage in response to a current outputted from the current source circuit. A sample-and-hold circuit generates an output voltage by sampling the first voltage. The transformer is coupled to the input voltage, and the output voltage is correlated to the input voltage of the transformer.

Abstract: A switching control circuit is provided for measuring and regulating an output current of a power converter. The power converter is operated under continuous current mode. A detection circuit generates a continuous-current signal and a peak-current signal by detecting a switching current of an inductive device. An integration circuit generates an average-current signal in response to the continuous-current signal, the peak-current signal and an off time of a switching signal. The switching control circuit generates the switching signal in response to the average-current signal. The switching signal is coupled to switch the inductive device and regulate the output current of the power converter. A time constant of the integration circuit is correlated to the switching period of the switching signal, therefore the average-current signal will be proportional to the output current.

Abstract: An apparatus for detecting a switching current of the power converter, wherein the apparatus includes a signal generation circuit, a sample-and-hold circuit, and a calculating circuit. The signal generation circuit generates a sample signal in accordance with the pulse width of a switching signal. The sample-and-hold circuit is coupled to receive the sample signal and switching current signal for generating a first current signal and a second current signal. The calculating circuit is coupled to receive the first current signal and the second current signal for generating output signals. The switching signal is used for switching the magnetic device of the power converter, and the switching current signal is correlated to the switching current of the power converter; the output signals are correlated to the value of the switching current of the power converter.

Abstract: A switching regulator includes a switching device to switch a transformer from a primary-side to secondary side. A control circuit generates a switching signal for regulating output of the switching regulator. The control circuit includes a first circuit to generate a first signal and a timing signal by measuring a reflected signal of the transformer. A second circuit produces a second signal by integrating a current signal with the timing signal. The current signal represents a primary-side switching current of the transformer. A first feedback circuit produces a first feedback signal in response to the first signal and the reference signal, in which the reference signal is varied in response to the change of the second signal. Furthermore, a second feedback circuit generates a second feedback signal in response to the second signal. A switching control circuit generates the switching signal in response to the feedback signals.

Abstract: The present invention provides a method and apparatus for detecting a continuous current of a switching current. A current signal is produced in response to a switching current of the magnetic device. By sampling the waveform of the current signal in response to the enabling of a switching signal, a first current signal and a second current signal are generated. A continuous current signal is produced according to the first current signal and the second current signal. The continuous current signal is corrected to the continuous current of the switching current.

Abstract: A switching control circuit is provided for measuring and regulating an output current of a power converter. The power converter is operated under continuous current mode. A detection circuit generates a continuous-current signal and a peak-current signal by detecting a switching current of an inductive device. An integration circuit generates an average-current signal in response to the continuous-current signal, the peak-current signal and an off time of a switching signal. The switching control circuit generates the switching signal in response to the average-current signal. The switching signal is coupled to switch the inductive device and regulate the output current of the power converter. A time constant of the integration circuit is correlated to the switching period of the switching signal, therefore the average-current signal will be proportional to the output current.

Abstract: A control circuit for detecting the reflected voltage of a transformer is provided. A detection circuit is developed for sampling the reflected voltage. Because the pulse width of the reflected voltage is narrower at light load, a bias circuit is utilized for producing a bias signal to help the reflected voltage detection. Furthermore, a blanking circuit ensures a minimum pulse width of the reflected voltage.

Abstract: A transistor drive circuit of a power converter is developed for operating in a wide voltage range. It includes an N-type high-side transistor, a P-type high-side transistor and an N-type low-side transistor. A voltage clamp device is connected to the gate of the N-type high-side transistor to limit the maximum output voltage. A detection circuit is coupled to detect the supply voltage of the transistor drive circuit to generate a disable signal in response to the voltage level of the supply voltage. The disable signal is coupled to disable the P-type high-side transistor once the voltage level of the supply voltage is higher than a threshold voltage.

Abstract: The present invention provides a method and apparatus for detecting a continuous current of a switching current. A current signal is produced in response to a switching current of the magnetic device. By sampling the waveform of the current signal in response to the enabling of a switching signal, a first current signal and a second current signal are generated. A continuous current signal is produced according to the first current signal and the second current signal. The continuous current signal is corrected to the continuous current of the switching current.

Abstract: The present invention provides a power converter having a phase lock circuit for quasi-resonant soft switching. The power converter includes a first circuit coupled to the feedback signal to generate a switching signal for switching a switching device and regulating the output of the power converter. A second circuit is coupled to an auxiliary winding of the transformer for generating a voltage signal in response to the voltage of the transformer. A phase lock circuit generates a control signal to enable the switching signal in accordance with the voltage signal. The switching signal further turns on the switching device in response to a valley voltage across the switching device.

Abstract: The present invention provides a switching control circuit having a valley voltage detector to achieve the soft switching and improve the efficiency of a power converter. The switching control circuit includes a control circuit coupled to the feedback signal to generate a switching signal. Through an output circuit, the switching signal drives a switching device for switching a transformer and regulating the output of the power converter. The valley voltage detector is coupled to an auxiliary winding of the transformer for generating a control signal in response to the voltage of the transformer. The control signal is used for enabling the switching signal. The switching signal further turns on the switching device in response to a valley voltage across the switching device.