Abstract: A power conversion circuit, such as a buck converter/regulator, includes a feedback loop operatively coupling the output voltage to the controller for the switching mechanism. The feedback loop includes an analog error amplifier that sources current to the controller when the output voltage falls below a predetermined reference voltage and sinks current from the controller when the output voltage rises above a predetermined reference voltage. The feedback loop further includes at least one of a sinking boost circuit that sinks additional current from the controller when the output voltage falls below a low voltage threshold or a sourcing boost circuit that sources additional current to the controller when the output voltage rises above a high voltage threshold. The boost circuits can include analog amplifiers, digital comparators, or a combination thereof.

Abstract: A power supply with reduced electromagnetic interference (EMI) is described. This power supply includes cascaded stages with switched-mode power-supply circuits that are switched synchronously during operation by switching signals that have a common fundamental frequency. EMI associated with the power supply is reduced by establishing a phase shift between the switching signals in at least two of the stages.

Abstract: This application relates to systems, methods, and apparatus for controlling a switching frequency of a boost or flyback converter to be above an audible frequency range when operating the boost or flyback converter in a pulse frequency modulation (PFM) mode. The boost or flyback converter uses one or more switches for converting power for a display panel. In order to boost the switching frequency when operating in the PFM mode, the boost or flyback converter can selectively implement certain current and/or voltage limits for pulses that are generated as a result of the switching. The current and/or voltage limits can be set according to a load of the boost or flyback converter, and a correspondence between the current and/or voltage limits and the loads can be stored in a lookup table accessible to the boost or flyback converter.

Abstract: Various systems, apparatuses, and methods are disclosed herein, which provide a new power conversion topology for isolated systems that does not include a transformer. Embodiments of the inventive systems comprise: a switching system utilizing high voltage, low leakage switches, e.g., Silicon Carbide (SiC) MOS-FETs; a power source; an inductor and a capacitor operating as a link stage resonant LC circuit; and a load. The switching system may be configured to be controlled in a synchronized ‘four phase’ control loop process, wherein the input switches are prevented from being closed at the same time as the output switches, thereby providing electrical isolation between the input power source and the load—without the use of a transformer. The techniques disclosed herein are applicable to any number of isolated systems that supply power to electronic systems such as: digital cameras, mobile phones, watches, personal data assistants (PDAs), portable music players, displays, and computers.

Abstract: Various systems and methods are disclosed herein, which provide isolated systems with an auxiliary, multi-signal digital feedback loop for reporting a plurality of different potential fault conditions in an output system (e.g., output short circuit, output over-voltage, output under-voltage, output over temperature, etc.) to a Primary Controller in an input system. The signals may be sent according to any desired standardized (or proprietary) data transmission protocols. Use of a digital feedback loop allows the signals to be passed to the Primary Controller more quickly than is allowed by traditional analog feedback paths—and while using only a single optocoupler device for the transmission of all fault conditions. The techniques disclosed herein are applicable to any number of isolated systems that supply power to electronic systems such as: digital cameras, mobile phones, watches, personal data assistants (PDAs), portable music players, monitors, as well as desktop, laptop, and tablet computers.

Abstract: A power conversion circuit, such as a buck converter/regulator, includes a feedback loop operatively coupling the output voltage to the controller for the switching mechanism. The feedback loop includes an analog error amplifier that sources current to the controller when the output voltage falls below a predetermined reference voltage and sinks current from the controller when the output voltage rises above a predetermined reference voltage. The feedback loop further includes at least one of a sinking boost circuit that sinks additional current from the controller when the output voltage falls below a low voltage threshold or a sourcing boost circuit that sources additional current to the controller when the output voltage rises above a high voltage threshold. The boost circuits can include analog amplifiers, digital comparators, or a combination thereof.

Abstract: A power supply with reduced electromagnetic interference (EMI) is described. This power supply includes cascaded stages with switched-mode power-supply circuits that are switched synchronously during operation by switching signals that have a common fundamental frequency. EMI associated with the power supply is reduced by establishing a phase shift between the switching signals in at least two of the stages.

Abstract: An electronic device may be provided with display circuitry that includes a display timing controller, a backlight driver, a light source, and other associated backlight structures. The backlight control circuitry may generate a control signal having an adjustable duty cycle to the backlight driver. The backlight driver may include a boost converter, a current driver, and backlight control circuitry. The current driver may only be activated when the control signal is high. The backlight control circuitry may output an enable signal to the boost converter. The backlight control circuitry may activate the boost converter a predetermined amount of time before each rising clock edge in the control signal by asserting the enable signal for a longer period of time than when the control signal is high. The control signal and the enable signal may be deasserted at around the same times.

Abstract: The embodiments discussed herein relate to systems, methods, and apparatus for executing a pulse frequency modulation (PFM) mode of a boost converter in order to ensure that a switching frequency of the boost converter is a above an audible frequency threshold. In this way, a user operating a display device that is controlled by the boost converter will not be disturbed by audible noises generated at the display device. The PFM mode enforces an audible frequency threshold by using control circuitry designed to increase or decrease the frequency of a pulse signal depending on how the frequency of the pulse signal changes over time. The control circuitry can apply an additional load to the boost converter in order to increase the frequency of the pulse signal when the frequency is approaching the audible frequency threshold.

Abstract: Disclosed embodiments relate to techniques for operating a backlight unit of a display device in a redundant mode and a non-redundant mode in the event of an open circuit condition or short string condition. For instance, in a redundant mode, multiple LED strings are driven to provide a first quantity of light, such that the combined output from all LED strings is capable of providing a total light output corresponding to a maximum brightness setting for the display device. In the case that one of the LED strings fails due to an open circuit condition or short string condition, the remaining LED strings may be driven to provide a second quantity of light that is greater than the first, such that the combined light output from the remaining LED strings provides the same total light output for achieving the maximum brightness setting.

Abstract: Systems, devices, and methods for using a hot plug detect (HPD) signal to reduce turn on time of a backlight of a display are disclosed. The backlight controller may pre-charge the backlight based at least in part on receiving the HPD signal prior to receiving a BL_EN signal to turn on the backlight. The HPD signal may be a multipurpose signal used by components of a system in addition to the backlight driver. The backlight driver may turn on the pre-charged backlight immediately upon receiving the BL_EN signal. The backlight controller may maintain the pre-charge of the backlight while the device is in a sleep state to reduce the turn on time of the backlight from the sleep state. Embodiments of the HPD signal may also power down the display and backlight.

Abstract: This application relates to a dynamic lighting circuit for a keyboard of a computing device. The lighting circuit described herein includes several light emitting diode (LED) drivers having multiple channels for controlling multiple LEDs. The lighting circuit also includes an electrically erasable read-only memory (EEPROM) for storing configuration data for the LED drivers. Each LED is configured to individually illuminate a single key of the keyboard, allowing the lighting circuit to modify the brightness of each key without affecting the brightness of other keys. In this way, more lighting schemes are available for the keyboard, while also providing a thinner mechanical design for the keyboard. Lighting schemes can include illuminating a group or groups of keys at a different brightness level than other keys that are not contained in the group. Additionally, lighting schemes can include animations executed by varying the brightness levels of keys over a period of time.

Abstract: A measured voltage drop across a power-line transistor is used as a sensing element to measure the current and detect an over-current condition for an LED backlight system. An over-current or short condition is detected when the measured voltage drop exceeds a threshold. Accurate detection of the over-current condition is achieved by calibrating the RDS-ON (i.e., internal resistance between drain and source, when transistor is on) of the power-line transistor. In one embodiment, the calibration of RDS-ON is performed by ramping down the threshold from an initial value and using the tripped threshold to determine the actual value for RDS-ON. In another embodiment, the calibration of RDS-ON is performed by using two thresholds, a first threshold to calibrate RDS-ON and a second threshold to detect the over-current condition.

Abstract: Systems and methods for inaudible enhanced pulse width modulation (PWM) backlight dimming are provided. By way of example, an electronic display backlight system according to the present disclosure may include a backlight element and backlight driver circuitry. The backlight driver circuitry may drive the backlight element at various brightness levels using at least two individual duty cycles that occur immediately after one another. The backlight driver circuitry may vary the individual duty cycles such that none will ever reach 100% unless all are 100%, thereby preventing the occurrence of audible noise that might otherwise arise if an “on” PWM period from one individual duty cycle continued into the next.

Abstract: Disclosed embodiments relate to techniques for operating a backlight unit of a display device in a redundant mode and a non-redundant mode in the event of a shorted LED failure condition. For instance, in a redundant mode, multiple LED strings arranged in an end-to-end configuration are each driven to provide a first quantity of light, such that the combined output from all LED strings is capable of providing a total light output corresponding to a maximum brightness setting for the display device. In the case that an LED on one of the strings fails due to a shorted LED failure condition, the remaining functional LEDs of the affected string may be driven to provide a second quantity of light, such that the combined output from the affected strings and the non-affected strings may still provide the same total light output for achieving the maximum brightness setting. The second quantity of light is greater than the first quantity.

Abstract: The embodiments discussed herein relate to systems, methods, and apparatus for executing a pulse frequency modulation (PFM) mode of a boost converter in order to ensure that a switching frequency of the boost converter is a above an audible frequency threshold. In this way, a user operating a display device that is controlled by the boost converter will not be disturbed by audible noises generated at the display device. The PFM mode enforces an audible frequency threshold by using control circuitry designed to increase or decrease the frequency of a pulse signal depending on how the frequency of the pulse signal changes over time. The control circuitry can apply an additional load to the boost converter in order to increase the frequency of the pulse signal when the frequency is approaching the audible frequency threshold.

Abstract: The embodiments discussed herein relate to systems, methods, and apparatus for synchronizing a pulse width modulation (PWM) dimming clock signal with a frame rate signal, line sync signal, and/or a horizontal sync signal of a display device. The PWM dimming clock signal can be generated by a synchronization block having a programmable offset/delay. The programmable offset/delay can control the offset or phase difference between an input and an output clock signal of the synchronization block. Depending on the clock rate of PWM dimming and/or panel resolution, the phase/offset delay can be adjusted to achieve the optimum front of screen performance. Additionally, an input clock generator/missing pulse detection block can output a programmed clock signal to the synchronization block in case of a missing external clock, or insert a pulse when there is a missing pulse detected, thereby providing an un-interrupted input clock signal to the PWM generator.

Abstract: A system may include a processor, a graphics controller, and a display. The graphics controller may generate video data to be presented on the display. The display may include a display panel, a backlight unit for providing the display panel with backlight, and a display timing controller for communicating with the graphics controller. The display may be used in non-movie mode and movie mode. The backlight unit may be operated in fixed backlight mode during the non-movie display mode and may be operated in dynamic pixel backlight (DPB) mode during the movie display mode. Backlight level adjustments may be sloped only during the non-movie mode. Backlight level sloping can be handled internally within the backlight unit, can be controlled using pulse width modulation with the display timing controller, and implemented using incremental backlight level adjustments with the processor.

Abstract: Systems and methods for light-load efficiency in displays may include a backlight driver circuit that may adjust a gate drive voltage provided to a gate of a metal-oxide-semiconductor field-effect transistor (MOSFET) in the boost converter based on the load conditions of light-emitting diodes used to illuminate the display panel. The backlight driver circuit may also switch between two different voltage sources to further broaden a range of gate drive voltages available to drive the gate of the MOSFET in the boost converter. As a result, the backlight driver circuit may decrease gate drive losses associated with the MOSFET, thereby increasing the efficiency of the boost converter.

Abstract: One embodiment of a display backlight driver integrated circuit can be configured for operation in at least two different ways. A first method transfers data from an EEPROM to hardware registers prior to regular operation. A second method also transfers data from an EEPROM to registers. However, hardware registers can be overwritten with data accepted from a control bus, prior to regular operation. A keyboard driver IC can detect the presence or absence of a cable to an LED. If the cable is absent, the driver IC will not supply power for the LED. One embodiment of a keyboard and display backlight control system can be configured to allow substantially independent operation.