Abstract: A power converter can include an input PFC stage that receives a rectified input voltage coupled to a flyback stage including a center-tapped primary winding magnetically coupled to a secondary winding and a main switch coupled in series with the primary winding. The output of the PFC stage can be coupled to the center tap of the primary winding, and an output of the power converter can be coupled to the secondary winding of the flyback stage. The converter can further include control circuitry coupled to the main switch and an auxiliary switch in the PFC stage that operates the main switch to regulate an output voltage of the power converter, selectively enables the auxiliary switch responsive to a low line voltage condition at the input of the power converter, and operates the enabled auxiliary switch synchronously with the main switch.

Abstract: A multi-output AC/DC adapter can include a main power stage that receives power from an AC power source and delivers an intermediate output voltage, a plurality of regulator stages each comprising a chopper circuit that receives the intermediate output voltage and produces a regulated output DC voltage for one of the multiple outputs, and a controller. The main power stage can be a flyback converter, and the intermediate output voltage can be derived from a secondary winding of a flyback transformer of the flyback converter. The controller can provide a voltage reference signal and a feedback signal to the feedback loop of the main power stage, and the feedback signal can be an output voltage of one of the regulator stages. The controller can also provide a voltage reference signal to the controller of each of the regulator stages.

Abstract: A multi-output AC/DC adapter can include a main power stage that receives power from an AC power source and delivers an intermediate output voltage, a plurality of regulator stages each comprising a chopper circuit that receives the intermediate output voltage and produces a regulated output DC voltage for one of the multiple outputs, and a controller. The main power stage can be a flyback converter, and the intermediate output voltage can be derived from a secondary winding of a flyback transformer of the flyback converter. The controller can provide a voltage reference signal and a feedback signal to the feedback loop of the main power stage, and the feedback signal can be an output voltage of one of the regulator stages. The controller can also provide a voltage reference signal to the controller of each of the regulator stages..

Abstract: An electronic device may include air input sensors that gather air input from a user's fingers, a stylus, or other object in a volume of air near the electronic device. The air input sensors may include ultrasonic transducers that emit ultrasonic signals towards the volume of air and that detect the ultrasonic signals after the signals reflect from the external object. Using time-of-flight measurement techniques, control circuitry may track the movement of the external object in the volume of air near the electronic device. A display may provide visual feedback of the air input, such as shadows that preview where the input will be directed to on the display. The volume of air where input is detected may be divided into multiple input zones that trigger different actions from the electronic device. The ultrasonic transducers may include acoustic lenses.

Abstract: A power converter can include a magnetic energy storage element, a main switch, a synchronous rectifier switch, and an energy recovery circuit. The energy recovery circuit can include a resonant circuit and an auxiliary switch configured to operate in conjunction with the main and synchronous rectifier switches to store energy in the resonant circuit and deliver energy therefrom to reduce switching losses associated with the main and synchronous rectifier switches. The converter can be a buck, boost, buck-boost, or other converter type. The auxiliary switch may be operated according to a two-pulse control mode or using a conventional buck converter controller with additional delay elements. The resonant circuit inductance may be a discrete inductor or a parasitic inductance, such as a PCB trace, which may be designed to provide a desired inductance value selected to efficiently provide sufficient energy to achieve reduced switching losses of the main and auxiliary switches.

Abstract: A power converter can include a magnetic energy storage element, a main switch, a synchronous rectifier switch, and an energy recovery circuit. The energy recovery circuit can include a resonant circuit and an auxiliary switch configured to operate in conjunction with the main and synchronous rectifier switches to store energy in the resonant circuit and deliver energy therefrom to reduce switching losses associated with the main and synchronous rectifier switches. The converter can be a buck, boost, buck-boost, or other converter type. The auxiliary switch may be operated according to a two-pulse control mode or using a conventional buck converter controller with additional delay elements. The resonant circuit inductance may be a discrete inductor or a parasitic inductance, such as a PCB trace, which may be designed to provide a desired inductance value selected to efficiently provide sufficient energy to achieve reduced switching losses of the main and auxiliary switches.

Abstract: This disclosure describes a gate driver with voltage boosting capabilities. In some embodiments, the gate driver may comprise a charge pump that includes capacitor(s) and switch(es). Responsive a logic low input signal, the gate driver may bypass the capacitor(s) to allow the input digital signal to drive the gating signal directly. Conversely, responsive to a logic high input signal, the gate driver may couple the capacitor(s) in series with the input digital signal to generate a boosted gating signal. In some embodiments, the gate driver may comprise an inductor-capacitor resonant circuit to create a doubled output gating signal with respect to the input digital signal. In some embodiments, the resonant gate driver may include an additional voltage boosting capability that can be selectively enabled to compensate for a voltage drop during the signal transfer from the input to the output.

Abstract: A transformer-based switching power converter can include a slew rate limiter coupled to the switching stage and configured to limit rate of change of voltage across one or more switching devices of the switching stage, thereby reducing voltage spikes appearing on the secondary winding. The slew rate limiter may be configured to selectively operate to limit rate of change of voltage across one or more switching devices of the switching stage during startup of the switching stage, upon waking from burst mode, or at any time when zero voltage switching of the one or more switching devices is unavailable. The slew rate limiter can include at least one circuit element configured to selectively alter a time constant of a gate drive circuit of at least one switching device in the switching stage to increase a turn-on transition time of the at least one switching device.

Abstract: This disclosure describes a flyback converter with a series-parallel mode (SPM) active clamp. The active clamp, coupled in parallel with the primary coil, may include a clamp switch, two or more snubber capacitors, and associated diodes. The active clamp may be configured to absorb and retain the leakage energy from the leakage inductance of the flyback converter. The clamp switch may be turned on selectively as the primary switch approaches one of a plurality peak values to adjust frequencies of the switching devices. With the active clamp circuit, the flyback converter may first re-capture the leakage energy in the active clamp circuit and then recover it back to the power source.

Abstract: A direct feedback isolated power converter can include a transformer with primary, secondary, and bias windings. A main switch can selectively enable and disable current flow through the primary winding. A controller coupled to the bias winding may be configured to generate a gate drive signal for the main switch responsive at least in part to free ringing of the transformer. The controller may detect the free ringing via the bias winding. An auxiliary switch coupled across the secondary winding may be configured to selectively short circuit the secondary winding, responsive to feedback circuitry, to control when free ringing is established. The feedback circuitry may include a proportional, proportional integral, or proportional-integral-derivative control loop, a hysteretic control loop, or other controller type. The controller may operate at a variable or fixed frequency. The direct feedback isolated power converter may be a flyback converter or other type of isolated converter.

Abstract: A leakage energy steering circuit for a flyback converter can include a leakage energy steering capacitor and a leakage energy steering diode configured to be coupled between a first output terminal and a first secondary winding terminal of a flyback converter. The leakage energy steering circuit can further include a reset circuit having an impedance element and a diode configured to be coupled between a junction of the leakage energy steering capacitor and the leakage energy steering diode and a junction of a second secondary winding terminal and a second output terminal of the flyback converter. The impedance element may be a resistor or an inductor.

Abstract: A direct feedback isolated power converter can include a transformer with primary, secondary, and bias windings. A main switch can selectively enable and disable current flow through the primary winding. A controller coupled to the bias winding may be configured to generate a gate drive signal for the main switch responsive at least in part to free ringing of the transformer. The controller may detect the free ringing via the bias winding. An auxiliary switch coupled across the secondary winding may be configured to selectively short circuit the secondary winding, responsive to feedback circuitry, to control when free ringing is established. The feedback circuitry may include a proportional, proportional integral, or proportional-integral-derivative control loop, a hysteretic control loop, or other controller type. The controller may operate at a variable or fixed frequency. The direct feedback isolated power converter may be a flyback converter or other type of isolated converter.

Abstract: This disclosure describes a gate driver with voltage boosting capabilities. In some embodiments, the gate driver may comprise a charge pump that includes capacitor(s) and switch(es). Responsive a logic low input signal, the gate driver may bypass the capacitor(s) to allow the input digital signal to drive the gating signal directly. Conversely, responsive to a logic high input signal, the gate driver may couple the capacitor(s) in series with the input digital signal to generate a boosted gating signal. In some embodiments, the gate driver may comprise an inductor-capacitor resonant circuit to create a doubled output gating signal with respect to the input digital signal. In some embodiments, the resonant gate driver may include an additional voltage boosting capability that can be selectively enabled to compensate for a voltage drop during the signal transfer from the input to the output.

Abstract: This disclosure describes a gate driver with voltage boosting capabilities. In some embodiments, the gate driver may comprise a charge pump that includes capacitor(s) and switch(es). Responsive a logic low input signal, the gate driver may bypass the capacitor(s) to allow the input digital signal to drive the gating signal directly. Conversely, responsive to a logic high input signal, the gate driver may couple the capacitor(s) in series with the input digital signal to generate a boosted gating signal. In some embodiments, the gate driver may comprise an inductor-capacitor resonant circuit to create a doubled output gating signal with respect to the input digital signal. In some embodiments, the resonant gate driver may include an additional voltage boosting capability that can be selectively enabled to compensate for a voltage drop during the signal transfer from the input to the output.

Abstract: This disclosure describes a flyback converter with a series-parallel mode (SPM) active clamp. The active clamp, coupled in parallel with the primary coil, may include a clamp switch, two or more snubber capacitors, and associated diodes. The active clamp may be configured to absorb and retain the leakage energy from the leakage inductance of the flyback converter. The clamp switch may be turned on selectively as the primary switch approaches one of a plurality peak values to adjust frequencies of the switching devices. With the active clamp circuit, the flyback converter may first re-capture the leakage energy in the active clamp circuit and then recover it back to the power source.

Abstract: A current fed active clamp forward boost (CAFB) converter can include a primary coil coupled to an input voltage and a main switch, an input choke serially coupled with the primary coil, and a clamp switch coupled to the primary coil, input choke, and a clamp capacitor. The main switch may operate to regulate an output voltage of the converter. The clamp switch may operate alternately with respect to the main switch, and the auxiliary switch may selectively couple a DC bus voltage to the primary coil. The converter can be operated in a CAFB mode if the input voltage is greater than the boost voltage threshold or in a current fed active clamp forward (CAF) mode if the input voltage is not greater than the boost voltage threshold.

Abstract: Disclosed herein are a system, method and non-transitory program storage device that are intended to provide a control system with quick response for a multi-level power converter. The control system may regulate an output voltage of the power converter based on one or more feedback signals. The feedback signals may be generated based on a differential between the output voltage and a reference voltage. The control system may further include one or more feed-forward signals representative of either the output voltage or transients of the output voltage. The control system may further include one or more switches in parallel with the one or more capacitors to selectively enable and/or disable direct feed-forward and capacitive feed-forward responsive to the output voltage at different levels.

Abstract: This disclosure describes a circuit, a method, and a system to mitigate common mode noise in a power converter. The converter may include a transformer that isolates input and output terminals with primary and secondary windings. The transformer may further include an auxiliary winding coupled in anti-parallel with a secondary winding. The auxiliary winding may inject a common mode current through a compensation capacitor and a Y-capacitor to cancel a common mode current induced at the secondary side to the primary side. The converter may include a coupler circuit that provides a varying impedance at different frequencies to facilitate the current injection and allocate voltages between the compensation capacitor and the Y-capacitor. A voltage clamping circuit may be employed to protect a coupler capacitor from overvoltage.

Abstract: A current fed active clamp forward boost (CAFB) converter can include a primary coil coupled to an input voltage and a main switch, an input choke serially coupled with the primary coil, and a clamp switch coupled to the primary coil, input choke, and a clamp capacitor. The main switch may operate to regulate an output voltage of the converter. The clamp switch may operate alternately with respect to the main switch, and the auxiliary switch may selectively couple a DC bus voltage to the primary coil. The converter can be operated in a CAFB mode if the input voltage is greater than the boost voltage threshold or in a current fed active clamp forward (CAF) mode if the input voltage is not greater than the boost voltage threshold.

Abstract: This disclosure describes a circuit, a method, and a system to mitigate common mode noise in a power converter. The converter may include a transformer that isolates input and output terminals with primary and secondary windings. The transformer may further include an auxiliary winding coupled in anti-parallel with a secondary winding. The auxiliary winding may inject a common mode current through a compensation capacitor and a Y-capacitor to cancel a common mode current induced at the secondary side to the primary side. The converter may include a coupler circuit that provides a varying impedance at different frequencies to facilitate the current injection and allocate voltages between the compensation capacitor and the Y-capacitor. A voltage clamping circuit may be employed to protect a coupler capacitor from overvoltage.