Systems and methods for driving light-emitting diodes

Abstract

At least some embodiments include a LED driver system. The system includes multiple branches of series-coupled LEDs, multiple current sources, and control logic. Each of the current sources is coupled to a separate branch of series-coupled LEDs. The control logic is coupled to the current sources, and is configured to regulate current through each branch based at least in part on a feedback voltage measured at a node in one of the branches.

1 . A light-emitting diode (“LED”) driver system, comprising
 a plurality of branches of series-coupled LEDs;   a plurality of current sources, each of the plurality of current sources coupled to a separate branch; and   control logic coupled to the plurality of current sources, the control logic configured to regulate current through each of the plurality of branches based at least in part on a feedback voltage measured at a node in one of the plurality of branches.   
   
   
       2 . The LED driver system of  claim 1 , wherein the control logic is configured to regulate current through the plurality of branches using the plurality of current sources. 
   
   
       3 . The LED driver system of  claim 1 , wherein the control logic is configured to regulate current through the plurality of branches using a boost converter. 
   
   
       4 . The LED driver system of  claim 1 , further comprising a plurality of pins, the plurality of pins outnumbering the plurality of branches by one. 
   
   
       5 . The LED driver system of  claim 1 , wherein at least one branch comprises less LEDs than another branch, the at least one branch comprising a resistor. 
   
   
       6 . The LED driver system of  claim 1 , wherein each particular branch out of the plurality of branches is configured to have the current in the particular branch adjustable independently of currents in other branches out of the plurality of branches. 
   
   
       7 . The LED driver system of  claim 1 , wherein the control logic comprises a finite state machine configured to select the one of the plurality of branches comprising the node. 
   
   
       8 . The LED driver system of  claim 7 , wherein the finite state machine is configured to select a branch with a non-zero current magnitude as the one of the plurality of branches. 
   
   
       9 . The LED driver system of  claim 7 , wherein the finite state machine is configured to select a branch that requires a highest voltage drop as the one of the plurality of branches. 
   
   
       10 . The LED driver system of  claim 7 , wherein the finite state machine is configured to select a branch that contains the most LEDs as the one of the plurality of branches. 
   
   
       11 . The LED driver system of  claim 7 , wherein the control logic further comprises an open circuit detector configured to preclude selection of an open branch as the one of the plurality of branches. 
   
   
       12 . The LED driver system of  claim 1 , wherein the LEDs comprise white LEDs in a mobile electronic device. 
   
   
       13 . The LED driver system of  claim 1 , wherein the node is located after a final LED, in the direction of current travel, in the one of the plurality of branches. 
   
   
       14 . The LED driver system of  claim 1 , further comprising:
 a plurality of digital-to-analog converters (“DACs”) coupled to the control logic, each of the plurality of DACs corresponding to a separate current source out of the plurality of current sources;   wherein the control logic loads a digital value into a DAC;   wherein the DAC generates a reference voltage proportional to the digital value; and   wherein the corresponding current source regulates current in the branch coupled to the current source based on the reference voltage.   
   
   
       15 . A driver system, comprising:
 means for regulating current through each branch of a plurality of branches comprising series-coupled components, the plurality of branches coupled in parallel; and   means for providing a feedback voltage, the means for regulating current regulating current based at least in part on the feedback voltage;   wherein the feedback voltage is measured at a node located after a final component, in the direction of current travel, in one of the plurality of branches.   
   
   
       16 . The driver system of  claim 15 , wherein the means for regulating current is configured to regulate current through the plurality of branches using a plurality of current sources. 
   
   
       17 . The driver system of  claim 15 , wherein the means for regulating current is configured to regulate current through the plurality of branches using a boost converter. 
   
   
       18 . The driver system of  claim 15 , further comprising a plurality of pins, the plurality of pins outnumbering the plurality of branches by one. 
   
   
       19 . The driver system of  claim 15 , wherein the means for regulating current comprises a means for selecting the one of the plurality of branches comprising the node. 
   
   
       20 . The driver system of  claim 15 , wherein the means for selecting the one of the plurality of branches selects a branch that requires a highest voltage drop as the one of the plurality of branches. 
   
   
       21 . A method of driving light-emitting diodes (LEDs) comprising:
 measuring voltages at a plurality of nodes in a plurality of branches comprising one or more series-coupled LEDs, the plurality of branches coupled in parallel, one node per branch;   selecting one branch out of the plurality of branches;   regulating current through each of the plurality of branches based at least in part on the voltage measured at the node in the selected branch.   
   
   
       22 . The method of  claim 21 , wherein selecting the one branch comprises selecting a branch with a non-zero current magnitude as the one of the plurality of branches. 
   
   
       23 . The method of  claim 21 , wherein selecting the one branch comprises selecting a branch that requires a highest voltage drop as the one of the plurality of branches. 
   
   
       24 . The method of  claim 21 , wherein selecting the one branch comprises selecting a branch that contains the most LEDs as the one of the plurality of branches. 
   
   
       25 . The method of  claim 21 , wherein selecting the one branch comprises precluding selection of an open branch as the one of the plurality of branches.