Abstract: A pulse frequency modulation (PFM) controller for controlling a switching mode power supply. The controller includes an output terminal for providing a control signal to turn on and off a current in the power supply to regulate an output of the power supply. A first input terminal receives a feedback signal related to the output of the power supply, the feedback signal exhibiting a ringing waveform when the current in the power supply is turned off. The controller also includes a control circuit configured to provide the control signal in response to the feedback signal. The control signal is adapted to turn on the current in the power supply when the feedback signal is substantially at a valley of the ringing waveform of the feedback signal. In an embodiment, such a PFM controller can reduce turn-on transition loss in a power supply and provides frequency dithering to reduce electromagnetic interference.

Abstract: A control circuit is provided for a buck converter that includes at least an inductor coupled to an output of the buck converter. The control circuit includes a power switch configured for coupling to a line voltage and configured for charging the inductor, an input line voltage sampling circuit, and a constant-voltage (CV) and constant-current (CC) control module coupled to the power switch. During a charging period of the inductor, the CV and CC control module is configured to control the power switch to provide a constant output current by maintaining a constant peak inductor current, even when the input line voltage changes. During a discharging period of the inductor, the CV and CC control module is configured to monitor the sensed output voltage to control the power switch to provide a constant output voltage.

Abstract: A synchronous rectification circuit for a power supply includes a power switch for coupling to a secondary winding of a transformer of the power supply and an output capacitor of the power supply. The power switch includes a four-terminal MOSFET having a source, a drain, a gate, and a body. A body diode is formed by a junction between the body and the drain or by a junction between the body and the source. The body diode is coupled in parallel to the source and drain of the power transistor. A control circuit is configured to provide a control signal for controlling an on/off state of the power switch in response to a voltage condition of two terminals of the power switch. When the body diode makes a transition from reverse bias to forward bias, the control circuit causes the MOSFET to turn on, and when the forward bias voltage drops below a reference voltage, the control circuit causes the MOSFET to turn off.

Abstract: A switching mode power supply (SMPS) includes a power transistor coupled to the primary winding of transformer and a resistor coupled between the input power source and a control terminal of the power transistor for triggering a primary current flow through the power transistor for providing startup power. A primary side control circuit is configured to regulate the output of the SMPS. A secondary side control circuit is coupled to the secondary winding and being configured to provide a first electrical signal to the secondary winding when an output voltage of the SMPS is less than a first reference voltage, whereupon an awakening signal is induced in the auxiliary winding and causes the primary side control circuit to provide a turn-on signal to the power transistor. The primary side control circuit is configured to enter a standby mode or a normal operating mode in response to the awakening signal.

Abstract: An apparatus for coupling a switching mode power supply (SMPS) controller to a rectified line voltage. The apparatus includes a high-voltage startup transistor configured to provide a charging current during a startup phase of the SMPS controller and to provide substantially no current during a normal operation phase of the SMPS controller. A switch coupled to the high-voltage startup transistor. The switch receives a control signal from the SMPS controller, for turning off the switch during the startup phase and turning on the switch during the normal operation phase. A biasing device is connected in series with the switch and maintains the startup transistor in an off state when the SMPS controller is in the normal operation phase. A standby current in the apparatus is substantially lower when the SMPS controller is in the normal operation phase than the charging current in the apparatus when the SMPS is in the startup phase.

Abstract: A switching mode power supply (SMPS) includes a rectifying device configured for converting a periodically varying input AC (alternating current) voltage into a DC (direct current) voltage, and a transformer including a primary winding, a secondary winding, and an auxiliary winding. The primary winding is coupled to the rectifying device. An input capacitor is coupled to the rectifying device and the primary winding of the transformer. A first power switch is coupled to the input capacitor. A control circuit is coupled to the first power switch and is configured to control the first power switch based on a phase or amplitude of the input AC voltage. By controlling the charging and discharging of the input capacitor, power is provided to the primary winding during a longer portion of the AC input voltage cycle, allowing the rectifier device to have a larger conduction angle to increase a power factor (PF).

Abstract: A switching mode power supply (SMPS) includes a transformer having a primary winding, a secondary winding for providing an output voltage, and an auxiliary winding. The SMPS also includes a power switch coupled to the primary winding. A first control circuit is coupled to the secondary winding, and is configured to provide a first electrical signal to the secondary winding when the output voltage of the SMPS is less than a reference voltage during a discontinuous time, whereupon a second electrical signal is induced in the auxiliary winding. A second control circuit is coupled to the auxiliary winding and the power switch. The second control circuit is configured to regulate the output of the SMPS by controlling the power switch in response to a feedback voltage signal from the auxiliary winding, and is further configured to turn on the power switch in response to the second electrical signal.

Abstract: A synchronous rectification circuit for a power converter includes a power switch coupled to a transformer and an output capacitor and a switching control circuit configured to provide a control signal to the power switch in response to a first state and a second state of the voltage across the power switch. In the switching control circuit, the second state is determined prior to the first state is determined. In an embodiment, the switching control circuit includes a voltage comparing unit configured to act in response to the first and second inputs. The voltage comparing unit is also configured to output a logic signal according to the voltage difference between the sensed voltage drop across the power switch and a reference threshold voltage. A logic processing circuit is coupled to the voltage comparing unit and configured to provide the first state and the second state of the voltage across the power switch.

Abstract: A power supply controller is provided for providing a drive current to a control terminal of a power transistor in three time intervals. The controller includes control circuits configured to control the drive current in multiple stages. During a first time interval, first drive current includes a current spike for turning on the power transistor in response to a start of the control signal pulse. During a second time interval, a second drive current includes a ramping current substantially proportional to a magnitude of a current through the power transistor. During a third time interval, current flow to the power transistor is at least partially turned off before an end of the control signal pulse.

Abstract: A switching mode power supply (SMPS) includes a power transistor coupled to the primary winding of transformer and a resistor coupled between the input power source and a control terminal of the power transistor for triggering a primary current flow through the power transistor for providing startup power. A primary side control circuit is configured to regulate the output of the SMPS. A secondary side control circuit is coupled to the secondary winding and being configured to provide a first electrical signal to the secondary winding when an output voltage of the SMPS is less than a first reference voltage, whereupon an awakening signal is induced in the auxiliary winding and causes the primary side control circuit to provide a turn-on signal to the power transistor. The primary side control circuit is configured to enter a standby mode or a normal operating mode in response to the awakening signal.

Abstract: A switching mode power supply (SMPS) includes a transformer having a primary winding, a secondary winding for providing an output voltage, and an auxiliary winding. The SMPS also includes a power switch coupled to the primary winding. A first control circuit is coupled to the secondary winding, and is configured to provide a first electrical signal to the secondary winding when the output voltage of the SMPS is less than a reference voltage during a discontinuous time, whereupon a second electrical signal is induced in the auxiliary winding. A second control circuit is coupled to the auxiliary winding and the power switch. The second control circuit is configured to regulate the output of the SMPS by controlling the power switch in response to a feedback voltage signal from the auxiliary winding, and is further configured to turn on the power switch in response to the second electrical signal.

Abstract: A switch mode power supply (SMPS) system includes a rectifying circuit for coupling to an AC input voltage and a transformer having a primary winding for coupling to the rectifying circuit and a secondary winding coupled to the primary winding. The system also has a power switch coupled to the primary winding and a control circuit coupled to the power switch. The control circuit is configured to control current flow in the primary winding such that an envelop waveform formed by peak points of current pulses are in phase with the magnitude of the AC input voltage. Moreover, the SMPS system is configured to provide a constant average output current.

Abstract: Circuits and method for sensing a system output voltage change and transmitting an electrical signal to an auxiliary winding on the primary side. In an embodiment, a primary side controller detects the electrical signal and turns a power switch on and off to transfer energy from a primary winding to a secondary winding. A secondary side controller generates a voltage pulse at a terminal of the secondary winding when the system output voltage is below a reference voltage. The secondary side controller includes an input terminal connected to a system output, an output terminal connected to a terminal of the secondary winding, and a ground terminal connected to a ground potential of the system output.

Abstract: A switched mode power supply (SMPS) includes a transformer with a primary winding, a secondary winding, an auxiliary winding, and a power switch coupled to the primary winding. During one switching cycle, the auxiliary winding provides a feedback signal which includes a first voltage pulse that is induced after the power switch is turned on and a second voltage pulse that is induced after the power switch is turned off. A control circuit includes a circuit for generating a sampling signal for sampling the second voltage pulse in a switching cycle at a time that is determined based on the first voltage pulse in the same switching cycle. A sample-and-hold circuit is configured for sampling and storing the second voltage pulse in response to the sampling signal. A switching signal generating circuit is configured to generate a switching signal for controlling the power switch based on an output of the sample-and-hold circuit.

Abstract: A controller for a switching mode power supply includes two semiconductor chips. The first semiconductor chip has a high-voltage startup transistor coupled to a high voltage supply input terminal and configured to provide a charging current in a startup phase or protection mode of a switching mode power supply (SMPS) and to provide substantially no current in a normal operation phase of the SMPS. The second semiconductor chip has a control circuit for controlling the switching mode power supply. The second semiconductor chip also has first and second on-chip high-voltage resistors coupled to the high-voltage supply input terminal and the high-voltage startup transistor in the first semiconductor chip. The first and the second on-chip high-voltage resistors are configured to provide a voltage and a current related to a voltage at the high-voltage supply input terminal.

Abstract: A power supply controller is provided for providing a drive current to a control terminal of a power transistor in three time intervals. The controller includes control circuits configured to control the drive current in multiple stages. During a first time interval, first drive current includes a current spike for turning on the power transistor in response to a start of the control signal pulse. During a second time interval, a second drive current includes a ramping current substantially proportional to a magnitude of a current through the power transistor. During a third time interval, current flow to the power transistor is at least partially turned off before an end of the control signal pulse.

Abstract: A synchronous rectification circuit for a power converter includes a power switch coupled to a transformer and an output capacitor and a switching control circuit configured to provide a control signal to the power switch in response to a first state and a second state of the voltage across the power switch. In the switching control circuit, the second state is determined prior to the first state is determined. In an embodiment, the switching control circuit includes a voltage comparing unit configured to act in response to the first and second inputs. The voltage comparing unit is also configured to output a logic signal according to the voltage difference between the sensed voltage drop across the power switch and a reference threshold voltage. A logic processing circuit is coupled to the voltage comparing unit and configured to provide the first state and the second state of the voltage across the power switch.

Abstract: Circuits and method for sensing a system output voltage change and transmitting an electrical signal to an auxiliary winding on the primary side. In an embodiment, a primary side controller detects the electrical signal and turns a power switch on and off to transfer energy from a primary winding to a secondary winding. A secondary side controller generates a voltage pulse at a terminal of the secondary winding when the system output voltage is below a reference voltage. The secondary side controller includes an input terminal connected to a system output, an output terminal connected to a terminal of the secondary winding, and a ground terminal connected to a ground potential of the system output.

Abstract: A controller for a switching mode power supply includes two semiconductor chips. The first semiconductor chip has a high-voltage startup transistor coupled to a high-voltage supply input terminal and configured to provide a charging current in a startup phase or protection mode of a switching mode power supply (SMPS) and to provide substantially no current in a normal operation phase of the SMPS. The second semiconductor chip has a control circuit for controlling the switching mode power supply. The second semiconductor chip also has first and second on-chip high-voltage resistors coupled to the high-voltage supply input terminal and the high-voltage startup transistor in the first semiconductor chip. The first and the second on-chip high-voltage resistors are configured to provide a voltage and a current related to a voltage at the high-voltage supply input terminal.

Abstract: An apparatus for coupling a switching mode power supply (SMPS) controller to a rectified line voltage. The apparatus includes a high-voltage startup transistor configured to provide a charging current during a startup phase of the SMPS controller and to provide substantially no current during a normal operation phase of the SMPS controller. A switch coupled to the high-voltage startup transistor. The switch receives a control signal from the SMPS controller, for turning off the switch during the startup phase and turning on the switch during the normal operation phase. A biasing device is connected in series with the switch and maintains the startup transistor in an off state when the SMPS controller is in the normal operation phase. A standby current in the apparatus is substantially lower when the SMPS controller is in the normal operation phase than the charging current in the apparatus when the SMPS is in the startup phase.