An LED driver for controlling the intensity of an LED light source includes a power converter circuit for generating a DC bus voltage, an LED drive circuit for receiving the bus voltage and controlling a load current through, and thus the intensity of, the LED light source, and a controller operatively coupled to the power converter circuit and the LED drive circuit. The LED drive circuit comprises a controllable-impedance circuit coupled in series with the LED light source. The controller adjusts the magnitude of the bus voltage to a target bus voltage and generates a drive signal for controlling the controllable-impedance circuit. To adjust the intensity of the LED light source, the controller controls the magnitudes of both the load current and the regulator voltage. The controller controls the magnitude of the regulator voltage by simultaneously maintaining the magnitude of the drive signal constant and adjusting the target bus voltage.

Load Control Device for a Light-Emitting Diode Light Source

An adaptive switch mode LED driver provides an intelligent approach to driving multiple strings of LEDs. The LED driver determines an optimal current level for each LED channel from a limited set of allowed currents. The LDO driver then determines a PWM duty cycle for driving the LEDs in each LED channel to provide precise brightness control over the LED channels. Beneficially, the LED driver minimizes the power dissipation in the LDO circuits driving each LED string, while also ensuring that the currents in each LED string are maintained within a limited range. A sample and hold LDO allows PWM control over extreme duty cycles with very fast dynamic response. Furthermore, fault protection circuitry ensures fault-free startup and operation of the LED driver.

Adaptive Switch Mode LED Driver

Electronic circuits provide an error signal to control a regulated output voltage signal generated by a controllable DC-DC converter for driving one or more series connected strings of light emitting diodes.

Electronic circuits for driving series connected light emitting diode strings

Power management in a light emitting diode (LED) system having a plurality of LED strings is disclosed. A voltage source provides an output voltage to drive the LED strings. An LED driver monitors the tail voltages of the active LED strings to identify the minimum, or lowest, tail voltage and adjusts the output voltage of the voltage source based on the lowest tail voltage. The LED driver can adjust the output voltage so as to maintain the lowest tail voltage at or near a predetermined threshold voltage so as to ensure that the output voltage is sufficient to properly drive each active LED string with a regulated current in view of pulse width modulation (PWM) performance requirements without excessive power consumption.

LED driver with dynamic power management

A light emitting element drive apparatus that drives light emitting elements reduces power loss caused by variability between forward voltage drops of the light emitting elements. A plurality of voltage applying sections (1, 32 and 33; and 2, 34 and 35) generate application voltages based on a detection voltage determined based on a maximum forward voltage drop among the forward voltage drops of the light emitting element arrays (11 to 14), and apply the generated application voltages to the light emitting elements (11 to 14). Switching sections (30 and 31) switch between a plurality of voltage applying sections (1, 32 and 33; and 2, 34 and 35) to which the light emitting element arrays (11 to 14) individually connect. Controlling sections (40 to 42) control the switching sections (30 and 31) to switch connection to minimize the difference between forward voltage drops of light emitting element arrays (11 to 14).

Light emitting element drive apparatus, planar illumination apparatus, and liquid crystal display apparatus

Techniques for dynamic headroom control in a light emitting diode (LED) system are disclosed. An output voltage is provided to drive a plurality of LED strings. A feedback controller monitors the tail voltages of the LED strings to identify the minimum tail voltage and adjusts the output voltage based on the lowest tail voltage. The LED strings grouped into subsets and the feedback controller is segmented such that, for a certain duration, a minimum tail voltage is determined for each subset. The minimum tail voltages of the subsets are used to determine the overall minimum tail voltage of the plurality of LED strings for the certain duration so as to control the output voltage in the following duration. The segments of the feedback controller can be implemented in separate integrated circuit (IC) packages, thereby facilitating adaptation to different numbers of LED strings by integrating the corresponding number of IC packages.

Led driver with segmented dynamic headroom control

A voltage source provides an output voltage to drive a plurality of light emitting diode (LED) strings. A LED driver adjusts the level of the output voltage so as to maintain the lowest tail voltage of the LED strings at or near a predetermined threshold voltage so as provide sufficient headroom voltages for current regulators for the LED strings. The LED driver operates in an operational mode and a calibration mode, which can be implemented in parallel with, or part of, the operational mode. During the calibration mode, the LED driver determines, for each LED string, a code value representative of the level of the output voltage necessary to maintain the tail voltage of the corresponding LED string at or near the predetermined threshold voltage. In the operational mode, the code values from the calibration mode are used to control the voltage source to provide an appropriate level for the output voltage.

LED driver with dynamic headroom control

Power management in a light emitting diode (LED) system having a plurality of LED strings is disclosed. A voltage source provides an output voltage to drive a plurality of LED strings. An LED driver implements a feedback mechanism to monitor the tail voltages of the active LED strings to identify the minimum tail voltage and adjust the output voltage of the voltage source based on the lowest tail voltage. A loop calibration module of the LED driver calibrates the feedback mechanism of the LED driver based on a relationship between a digital code value used to generate a particular output voltage and another digital code value generated based on the minimum tail voltage resulting from the particular output voltage.

Led driver with feedback calibration

A PWM generation module generates a PWM data signal used to control a light emitting diode (LED) driver for one or more strings of LEDs of a display device. The PWM data signal is synchronized with the frame boundaries of the video content being displayed. The PWM generation module can configure the PWM data signal such that a new PWM cycle is initiated at the start of each successive frame, and further whereby those PWM cycles that would be prematurely terminated at frame boundaries are instead driven at a constant reference level until the frame boundary. With this configuration, a substantially linear average light intensity can be achieved across frames, thereby reducing or eliminating display distortion that is often present in other PWM cycle synchronization techniques. The PWM generation module can use a self-learning process to make adjustments to the expected number of completeable PWM cycles per frame in response to dynamic changes in the frame rate, PWM frequency, or other related display parameters.

Andrew M. Kameya

Papers

LED driver with dynamic power management

Led driver with segmented dynamic headroom control

LED driver with dynamic headroom control

Led driver with feedback calibration

Frequency synthesis and synchronization for led drivers