Multi-string LED drive system

摘要

A multi-string LED drive system for multiple LED strings powered by a common line voltage. A plurality of current control circuits are connected in series with respective LED strings, each of which includes a transistor which causes a desired LED string current to be conducted when a sufficient voltage is applied to the transistor's gate. A “maximum” circuit receives each of the gate voltages at respective inputs and outputs a voltage which is proportional to the greatest of the received voltages. A line regulator circuit receives the output of the maximum circuit and a signal which represents a target gate voltage at respective inputs and generates the common line voltage such that the highest of the gate voltages is approximately equal to the target gate voltage, such that system power efficiency is optimized in cases of imbalance between LED string voltage drops and/or sink device characteristics.

主权项

1. A multi-string LED drive system for controlling the currents conducted by two or more LED strings which are powered by a common line voltage, said system comprising:
a plurality of current control circuits connected in series with respective LED strings, each of said current control circuits including a transistor arranged to cause a desired LED string current to be conducted when a sufficient voltage is applied to said transistor's control input; a maximum circuit which receives the voltages on each of said control inputs at respective inputs and which outputs a voltage which is proportional to a highest said received control input voltages; and a line regulator circuit which receives the output of said maximum circuit and a signal which represents a target control input voltage at respective inputs and which generates said common line voltage such that the highest of said received control input voltages is approximately equal to said target control input voltage, wherein said line regulator circuit further comprises: an error amplifier which provides an output; a voltage regulator which provides an output and an output voltage that varies with the signal received at a feedback input, said feedback input coupled to the output of said error amplifier; and a second amplifier interposed between said error amplifier and said feedback input, said second amplifier receiving the output of said error amplifier and a signal which varies with the output of said voltage regulator at respective inputs and providing an output to said feedback input such that said second amplifier forms a local loop around said voltage regulator.