Abstract: A feedback circuit with feedback impedance modulation according to the present invention comprises a compare circuit, a counter and a switching resistor circuit. The compare circuit receives a feedback signal of a power converter to compare the feedback signal with a threshold signal for generating a control signal. The feedback signal is correlated to a load condition of the power converter. The counter is coupled to the compare circuit and generates a modulation signal in response to the control signal. The switching resistor circuit is coupled to the counter and a feedback loop of the power converter for modulating a feedback impedance of the power converter in response to the modulation signal. The feedback impedance is directly modulated from a lower resistance to a higher resistance when the load condition is reduced from a half/full-load to a no/light-load.

Abstract: A start-up circuit with low standby power loss for power converters according to present invention comprises a first diode and a second diode coupled to an input voltage of the power converter. A start-up resistor is coupled to the join of the first diode and the second diode. A high-voltage switch is coupled to the start-up resistor to generate a power source. A control circuit generates a switching signal for switching a transformer. A detection circuit generates a disable signal in response to the input voltage to disable the switching signal. A winding of the transformer is coupled to the power source to generate the power for the power source. The high-voltage switch is turned off to cut off the start-up resistor for saving the power loss once the voltage of the power source is higher than a threshold.

Abstract: A control circuit with deep burst mode for power converter according to the present invention comprises a load detection circuit and a PWM circuit. The load detection circuit generates a switching control signal in response to a feedback signal. The feedback signal is correlated to a load condition of the power converter. The PWM circuit generates a switching signal to regulate an output of the power converter in response to the switching control signal and the feedback signal. The control circuit performs a deep burst mode to switch the switching signal only one time during each deep burst period when the load condition of the power converter is a very light-load. Therefore, switching loss is reduced so that the power consumption of the power converter is also reduced.

Abstract: The present invention provides a power converter. The power converter includes a transformer, a power switch and a controller. The transformer has a primary winding, a secondary winding and an auxiliary winding. The power switch is coupled to the primary winding of the transformer to regulate the power converter. The controller has an output terminal for generating a driving signal to switch the power switch in response to a switching signal. A thermal resistor is coupled to the output terminal of the controller. The driving signal is adjusted across the thermal resistor during an off-period of the switching signal.

Abstract: A biased current-limit circuit for limiting a maximum output power of a power converter includes an oscillator for generating a pulse signal and an oscillation signal. A waveform generator generates a waveform signal in response to the oscillation signal. A sample-hold circuit is used to sample the waveform signal to generate a hold signal in response to a switching signal. The sample-hold circuit further samples the hold signal to generate a current-limit threshold in response to a second-sampling signal. A current comparator is utilized to compare a current-sensing signal with the current-limit threshold to limit a maximum on-time of 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: The present invention proposes a controller with power saving for a power converter. The controller includes a delay circuit, a detection circuit, an output circuit, a counter circuit, a wake-up circuit and a PWM circuit. The delay circuit determines a delay time. The detection circuit activates the delay circuit whenever an output load of the power converter is lower than a light-load threshold. The output circuit generates a power-saving signal to cease a regulation of the power converter after the delay time ends. The regulation of the power converter is resumed once the output load increases during the regulation of the power converter is being ceased. The counter circuit coupled to the delay circuit is counted by the delay circuit to determine a sleep period. The output circuit generates the power-saving signal to cease the regulation of the power converter after the sleep period ends.

Abstract: A two-switch Flyback power converter is disclosed. The two-switch Flyback power converter comprises a transformer, a first switch, a second switch, and a control circuit. The transformer includes a primary-winding and a secondary-winding. The primary-winding has a first winding and a second winding. The first switch is coupled to switch the first winding. The second switch is coupled to switch the first winding and the second winding. The control circuit generates a first-drive signal and a second-drive signal to control the first switch and the second switch for switching the transformer and regulating an output of the two-switch Flyback power converter. The two-switch Flyback power converter with less capacitance of the bulk capacitor or bulk capacitor-less can reduce the voltage ripples at the output voltage for cost saving.

Abstract: A start-up circuit to discharge EMI filter is developed for power saving. It includes a detection circuit detecting a power source for generating a sample signal. A sample circuit is coupled to the detection circuit for generating a reset signal in response to the sample signal. The reset signal is utilized for discharging a stored voltage of the EMI filter.

Abstract: A start-up circuit to discharge EMI filter is developed for power saving. It includes a detection circuit detecting a power source for generating a sample signal. A sample circuit is coupled to the detection circuit for generating a reset signal in response to the sample signal. The reset signal is utilized for discharging a stored voltage of the EMI filter.

Abstract: A start-up circuit to discharge EMI filter is developed for power saving. It includes a detection circuit detecting a power source for generating a sample signal. A sample circuit is coupled to the detection circuit for generating a reset signal in response to the sample signal. The reset signal is utilized for discharging a stored voltage of the EMI filter.

Abstract: A switching controller for power converter comprises a current-sense circuit and a PWM circuit. The current-sense circuit receives high-voltage signal across a first switch to generate a current-sense signal. The PWM circuit generates a switching signal to control the first switch in response to the current-sense signal. The switching controller further comprises a delay circuit. The delay circuit receives the switching signal to generate a delayed switching signal. The current-sense signal and the high-voltage signal ramp up with the same slope during the delayed switching signal is enabled. The current-sense signal will be pulled down to a level of a ground reference during the delayed switching signal is disabled. A delay time provided by the delay circuit avoids the high-voltage signal at the instance which the first switch is being turned off being conducted to a first comparator and a second comparator via a second switch.

Abstract: A power supply with an open-loop protection according to the present invention comprises a transformer, a switch, a signal generation circuit, a feedback detection circuit, a brown-out detection circuit, and a delay circuit. The transformer receives an input voltage. The switch is coupled to the transformer for switching the transformer. The signal generation circuit generates a switching signal to control the switch. The feedback detection circuit generates a pull-high signal in response to a feedback signal of the power supply. The brown-out detection circuit generates a delay signal in response to the pull-high signal and the input voltage. The delay circuit counts a delay time in response to the delay signal for generating a disabling signal coupled to the signal generation circuit to latch the switching signal. The brown-out detection circuit is utilized to detect whether the input voltage is in the brown-out condition for determining whether the open-loop protection is executed.

Abstract: This invention provides a control circuit for burst switching of a power converter comprising: an adaptive circuit generating an adaptive threshold in response to a feedback signal correlated to an output load of the power converter; and a switching circuit generating a switching signal to switch a transformer of the power converter in accordance with the adaptive threshold and the feedback signal for regulating an output of the power converter.

Abstract: The present invention provides a power converter. The power converter includes a transformer, a power switch and a controller. The transformer has a primary winding, a secondary winding and an auxiliary winding. The power switch is coupled to the primary winding of the transformer to regulate the power converter. The controller has an output terminal for generating a driving signal to switch the power switch in response to a switching signal. A thermal resistor is coupled to the output terminal of the controller. The driving signal is adjusted across the thermal resistor during an off-period of the switching signal.

Abstract: A biased current-limit circuit for limiting a maximum output power of a power converter includes an oscillator for generating a pulse signal and an oscillation signal. A waveform generator generates a waveform signal in response to the oscillation signal. A sample-hold circuit is used to sample the waveform signal to generate a hold signal in response to a switching signal. The sample-hold circuit further samples the hold signal to generate a current-limit threshold in response to a second-sampling signal. A current comparator is utilized to compare a current-sensing signal with the current-limit threshold to limit a maximum on-time of the switching signal.

Abstract: A start-up circuit with low standby power loss for power converters according to present invention comprises a first diode and a second diode coupled to an input voltage of the power converter. A start-up resistor is coupled to the join of the first diode and the second diode. A high-voltage switch is coupled to the start-up resistor to generate a power source. A control circuit generates a switching signal for switching a transformer. A detection circuit generates a disable signal in response to the input voltage to disable the switching signal. A winding of the transformer is coupled to the power source to generate the power for the power source. The high-voltage switch is turned off to cut off the start-up resistor for saving the power loss once the voltage of the power source is higher than a threshold.

Abstract: A biased current-limit circuit for limiting a maximum output power of a power converter includes an oscillator for generating a pulse signal. A waveform generator generates a waveform signal in response to a switching signal and a second-sampling signal. A sample-hold circuit is used to sample the waveform signal to generate a hold signal in response to a first-sampling signal. The sample-hold circuit further samples the hold signal to generate a current-limit threshold in response to the second-sampling signal. A current comparator is utilized to compare a current-sensing signal with the current-limit threshold to limit a maximum on-time of the switching signal.

Abstract: A power supply with an open-loop protection according to the present invention comprises a transformer, a switch, a signal generation circuit, a feedback detection circuit, a brown-out detection circuit, and a delay circuit. The transformer receives an input voltage. The switch is coupled to the transformer for switching the transformer. The signal generation circuit generates a switching signal to control the switch. The feedback detection circuit generates a pull-high signal in response to a feedback signal of the power supply. The brown-out detection circuit generates a delay signal in response to the pull-high signal and the input voltage. The delay circuit counts a delay time in response to the delay signal for generating a disabling signal coupled to the signal generation circuit to latch the switching signal. The brown-out detection circuit is utilized to detect whether the input voltage is in the brown-out condition for determining whether the open-loop protection is executed.

Abstract: A switching controller for power converter comprises a current-sense circuit and a PWM circuit, The current-sense circuit receives high-voltage signal across a first switch to generate a current-sense signal. The PWM circuit generates a switching signal to control the first switch in response to the current-sense signal. The switching controller further comprises a delay circuit. The delay circuit receives the switching signal to generate a delayed switching signal. The current-sense signal and the high-voltage signal ramp up with the same slope during the delayed switching signal is enabled. The current-sense signal will be pulled down to a level of a ground reference during the delayed switching signal is disabled. A delay time provided by the delay circuit avoids the high-voltage signal at the instance which the first switch is being turned off being conducted to a first comparator and a second comparator via a second switch.