Multi-string LED current balancing circuit with fault detection

1. A lighting device circuit comprising:

a reference light emitting diode (LED) string;

a mirror LED string coupled in parallel to the reference LED string;

an operational amplifier input and a second input, wherein the first input is coupled to a resistor measuring the current through the reference LED string and the second input is coupled to a resistor measuring the current through the mirror LED string; and

a window comparator circuit having an input that is coupled to a fault sense node and adapted to receive a voltage input from the fault sense node, wherein the fault sense node is directly connected to a drain node of a transistor having a gate node coupled to the output of the operational amplifier and to a LED within the mirror LED string.

2. The lighting device circuit of claim 1 , wherein the reference LED string includes a first number of LED components and the mirror LED string includes a second number of LED components, and wherein the first number of LED components is greater than the second number of LED components.

3. The lighting device circuit of claim 2 , wherein the LED components within the reference LED string are connected in series and the LED components within the mirror LED string are connected in series.

4. The lighting device circuit of claim 1 , further comprising an LED driver that is coupled to the reference LED string and the mirror LED string.

5. The lighting device circuit of claim 4 , wherein the LED driver provides a constant current to the reference LED string and the mirror LED string.

6. The lighting device circuit of claim 1 , wherein the window comparator circuit includes a first comparator that is connected to a reference high voltage and the fault sense node.

7. The lighting device circuit of claim 6 , wherein the window comparator circuit includes a second comparator that is connected to a reference low voltage and the fault sense node.

8. The lighting device circuit of claim 6 , wherein the reference low voltage is generated from a voltage divider circuit.

9. The lighting device circuit of claim 1 , wherein the window comparator circuit is directly connected to the fault sense node.

10. An apparatus comprising:

a light generation circuit comprising:

a reference light emitting diode (LED) string;

a resistor directly coupled to the reference LED string;

a mirror LED string coupled in parallel to the reference LED string;

an operational amplifier having a first input and a second input, wherein the first input is coupled to a resistor measuring the current through the reference LED string and the second input is coupled to a resistor measuring the current through the mirror LED string; and

a fault detection circuit that includes a window comparator circuit that receives a voltage from a fault sense node within the light generation circuit, wherein the window comparator circuit does not receive voltage inputs from other nodes within the light generation circuit;

wherein the fault sense node is directly connected to a drain node of a transistor having a gate node coupled to the output of the operational amplifier and a LED within the mirror LED string.

11. The apparatus of claim 10 , wherein the window comparator circuit compares the voltage from the fault sense node to a reference low voltage and a reference high voltage and determines that a failures occurs within the light generation circuit when the voltage exceeds the reference high voltage or is less than the reference low voltage.

12. The apparatus of claim 10 , wherein the reference LED string includes a first number of LED components and the mirror LED string includes a second number of LED components, and wherein the first number of LED components is greater than the second number of LED components.