Abstract: A power adapter includes a protocol integrated circuit (IC) on a secondary side of a transformer and a controller IC on a primary side of the transformer. The power adapter has an output voltage that changes depending on the charging voltage requirement of an electronic device (e.g., mobile device) connected to receive power from the power adapter. The power adapter includes an adaptive overvoltage protection mode that sets an overvoltage protection threshold to a low level during startup and thereafter sets the overvoltage protection threshold to a higher level after detecting proper operation of the protocol IC.

Abstract: A method for reducing electromagnetic interference in a flyback converter includes activating a first switch to generate a primary current therein. The first switch is deactivated to generate a secondary current from a magnetic flux generated by the primary current. The magnetic flux is removed by the generation of the secondary current. A second switch is activated with a first voltage pulse to limit an excess voltage across the first switch. The excess voltage is generated in response to the deactivation of the first switch. A second switch is activated with a second voltage pulse to limit a voltage oscillation across the first switch. The voltage oscillation occurs after the removal of the magnetic flux. A first pulse width of the first voltage pulse is increased by a first jitter delay. A second pulse width of the second voltage pulse is increased by a second jitter delay.

Abstract: An active clamp flyback controller includes first and second input terminals, a clamp voltage detection circuit, and an overvoltage protection circuit. The first input terminal is adapted to be coupled to a terminal of a clamp capacitor. The second input terminal receives a feedback signal proportional to a voltage across an auxiliary winding of a flyback transformer. The clamp voltage detection circuit is coupled to the first and second input terminals, and detects a clamp voltage as a difference between a voltage at the first input terminal and an input voltage, the clamp voltage detection circuit calculating the input voltage using a signal from the second input terminal. The overvoltage protection circuit is coupled to the clamp voltage detection circuit for comparing the clamp voltage to a threshold and triggering a protection operation if the clamp voltage is greater than the threshold.

Abstract: A method for reducing electromagnetic interference in a flyback converter includes activating a first switch to generate a primary current therein. The first switch is deactivated to generate a secondary current from a magnetic flux generated by the primary current. The magnetic flux is removed by the generation of the secondary current. A second switch is activated with a first voltage pulse to limit an excess voltage across the first switch. The excess voltage is generated in response to the deactivation of the first switch. A second switch is activated with a second voltage pulse to limit a voltage oscillation across the first switch. The voltage oscillation occurs after the removal of the magnetic flux. A first pulse width of the first voltage pulse is increased by a first jitter delay. A second pulse width of the second voltage pulse is increased by a second jitter delay.

Abstract: An active clamp flyback converter includes a low-side switch that serves as a power switch and a high-side switch that serves as a clamp switch. The high-side switch is operated in one of two active clamp switching modes, which is selected based on load condition. In a complementary active clamp mode, the switching frequency of the low-side switch is decreased as the load increases. In a modified active clamp mode, the high-side switch is turned on in a same switching cycle first by zero voltage switching (ZVS) and second by quasi-resonant switching (QRS), with a QRS blanking time being increased as the load decreases. A ZVS delay time and dead time between switching are adaptively set based on a duty cycle of the low-side switch. The output voltage of the active clamp flyback converter is sensed from an auxiliary voltage of an auxiliary winding of the transformer.

Abstract: A method for reducing electromagnetic interference in a flyback converter includes activating a first switch to generate a primary current therein. The first switch is deactivated to generate a secondary current from a magnetic flux generated by the primary current. The magnetic flux is removed by the generation of the secondary current. A second switch is activated with a first voltage pulse to limit an excess voltage across the first switch. The excess voltage is generated in response to the deactivation of the first switch. A second switch is activated with a second voltage pulse to limit a voltage oscillation across the first switch. The voltage oscillation occurs after the removal of the magnetic flux. A first pulse width of the first voltage pulse is increased by a first jitter delay. A second pulse width of the second voltage pulse is increased by a second jitter delay.

Abstract: A method for controlling a resonant converter includes maintaining an output current equal to an output power of the converter divided by an output voltage of the converter in response to a secondary current of a transformer being greater than or equal to a maximum output current. The output power is maintained at a constant output power in response to the output power being greater than or equal to a maximum output power, and the secondary current being less than the maximum output current. Maintaining the output current ratio and the constant output power each comprises changing the duty cycle of a primary-side switch configured to gate a primary current of the transformer. The output voltage is limited to a maximum output voltage in response to the secondary current being less than the maximum output current, and the output power being less than the maximum output power.

Abstract: An active clamp flyback controller includes first and second input terminals, a clamp voltage detection circuit, and an overvoltage protection circuit. The first input terminal is adapted to be coupled to a terminal of a clamp capacitor. The second input terminal receives a feedback signal proportional to a voltage across an auxiliary winding of a flyback transformer. The clamp voltage detection circuit is coupled to the first and second input terminals, and detects a clamp voltage as a difference between a voltage at the first input terminal and an input voltage, the clamp voltage detection circuit calculating the input voltage using a signal from the second input terminal. The overvoltage protection circuit is coupled to the clamp voltage detection circuit for comparing the clamp voltage to a threshold and triggering a protection operation if the clamp voltage is greater than the threshold.

Abstract: An active clamp flyback converter includes a low-side switch that serves as a power switch and a high-side switch that serves as a clamp switch. The high-side switch is operated in one of two active clamp switching modes, which is selected based on load condition. In a complementary active clamp mode, the switching frequency of the low-side switch is decreased as the load increases. In a modified active clamp mode, the high-side switch is turned on in a same switching cycle first by zero voltage switching (ZVS) and second by quasi-resonant switching (QRS), with a QRS blanking time being increased as the load decreases. A ZVS delay time and dead time between switching are adaptively set based on a duty cycle of the low-side switch. The output voltage of the active clamp flyback converter is sensed from an auxiliary voltage of an auxiliary winding of the transformer.

Abstract: A power adapter includes a protocol integrated circuit (IC) on a secondary side of a transformer and a controller IC on a primary side of the transformer. The power adapter has an output voltage that changes depending on the charging voltage requirement of an electronic device (e.g., mobile device) connected to receive power from the power adapter. The power adapter includes an adaptive overvoltage protection mode that sets an overvoltage protection threshold to a low level during startup and thereafter sets the overvoltage protection threshold to a higher level after detecting proper operation of the protocol IC.