Allegro Microsystems, LLC

Nai-Chi Lee

Vijay Mangtani

Pranav Raval

Gregory Szczeszynski

Bassem Alnahas

Tseng-Nan Tsai

John Humenick

An LED driver includes a voltage detector and a controller. The voltage detector is configured to couple to an LED string comprising a plurality of series-coupled LEDs and to detect a voltage across the LED string to generate a feedback signal. The controller is configured to control an amount of current provided to the LED string in response to the feedback signal, with an amount of power provided to the LED string being substantially constant. The voltage detector can be coupled in parallel with the LED string, and may be a resistor divider. The controller is further configured to couple to a DC-DC converter comprising a switch controlled by the controller and configured to generate an output current and an output voltage coupled to the LED string to provide the amount of power to the LED string.

Constant power light emitting diode (LED) driver

A driver coupled to a configurable load includes a first switch coupled between an intermediate node of the load and a converter supply voltage and a second switch coupled between the converter supply voltage and a reference potential. A slew rate control circuit is responsive to a command input signal and to a feedback voltage across the first and second switches and is configured to generate switch control signals with a controllable slew rate for coupling to control terminals of the first and second switches. In an embodiment, the command input signal includes a load configuration command and a converter mode command.

Apparatus and methods for converter mode and load configuration control

In one aspect, an integrated circuit (IC) is configured to receive an input signal and includes a boost duty cycle control circuit configured to provide duty cycle control to a power conversion stage configured to drive a load. The power conversion stage is configured to receive an input voltage. The IC also includes a current control circuit configured to control current of a first current source coupled to the first load and an inverter configured to provide an output signal comprising a negative of the input voltage, the output of the inverter configured to be coupled to the boost duty cycle control circuit.

Compensating for voltage changes in driver circuits

An LED driver for driving a plurality of series-coupled LEDs includes a bypass switch having first and second terminals coupled across a portion of the LEDs and a control terminal. A slew rate control circuit is responsive to a command input signal and to a feedback voltage associated with the bypass switch and is configured to generate a bypass switch control signal with a controllable slew rate. The slew rate control circuit is further configured to detect a rate of change of the switch feedback voltage and establish the bypass switch slew rate in response to the detected rate of change. Also described is method for controlling a bypass switch coupled across a portion of a plurality of series-coupled LEDs including detecting a rate of change of a voltage associated with the bypass switch and generating a control signal for the bypass switch in response to a command input signal and to the detected rate of change of the voltage.

Apparatus and methods for LED control

In one aspect, an integrated circuit (IC) is configured to receive an input signal. The IC includes a boost switch driver configured to provide a switching operation to a boost converter to drive a string of light emitting diodes (LEDs), a current sink driver connected to a current source and configured to provide a current signal to the string of LEDs, and a delay module configured to delay the current signal to the string of LEDs with respect to the input signal.

Controlling dimming ratio and output ripple voltage

An LED driver circuit selects a regulated voltage value for use in driving one or more LEDs based on dimming duty cycle. In some embodiments, the regulated voltage value may be selected in accordance with a function that decreases monotonically with increasing dimming duty cycle. In this manner, LED current accuracy can be achieved at lower dimming duty cycles, while still achieving enhanced operational efficiency at higher dimming duty cycles.

Driver circuit using dynamic regulation and related techniques

A driver circuit for driving one or more loads in a controlled manner includes multiple operational modes. In one mode, bypass switching may be used to adjust a drive signal applied to the one or more loads. In another mode, a DC-DC converter may be used to adjust the drive signal applied to the one or more loads. In at least one embodiment, the driver circuit is a light emitting diode driver circuit.

Method and apparatus for driving loads using a DC-DC converter

Control circuits and techniques are provided for use with DC-DC converters. The circuits and techniques may, in some implementations, be used with LED driver systems. In some embodiments control circuits are provided that rely on multiple different feedback paths to adjust a duty cycle of a DC-DC converter. In some embodiments, control circuits are provided that switch between multiple capacitors to provide as duty cycle control signal for use with a DC-DC converter.

Method and apparatus to control a DC-DC converter

In one aspect, a circuit includes a plurality of comparators. Each comparator is configured to receive a first input from a corresponding load of a plurality of loads and to receive a second input as a regulation voltage. The circuit also includes an amplifier configured to receive signals provided by the plurality of comparators, a pulse-width modulation (PWM) circuit configured to receive a control signal from the amplifier and to provide a signal to a primary switch to control voltage provided to the loads and an output switch sequencer coupled to each of the comparators and configured to provide control signals to control switches coupled to the primary switch enabling one control switch to be active at a time. Each control switch provides a voltage increase to a respective load of the plurality of loads if enabled.

Circuitry to drive parallel loads sequentially

A capacitor charging circuit is provided with a primary side output voltage sensing circuit including an RC network having an RC time constant with a predetermined relationship to the RC time constant of the output capacitor. Once the capacitor voltage reaches a fully charged level, the charging mode is terminated. The output voltage is continuously detected by measuring the voltage across the primary side RC network that decays at a predetermined rate with respect to the output capacitor and the charging mode is commenced once the RC voltage falls to a predetermined level. According to a further aspect of the invention, a switch control circuit in a flyback converter controls the switch off time in response to detection of a change in the slope polarity of the voltage at a terminal of the switch.

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Nashua, NH, United States of America

Nai-Chi Lee