Apparatus and method for trimming an output parameter of an electronic ballast

1. An electronic ballast, comprising a microprocessor which is programmed to:

read an external voltage value from an adjustable external voltage source;

output a pulse width modulation (PWM) signal which controls an amount of power outputted by the electronic ballast to a high intensity discharge lamp;

compare the external voltage value to an internal reference value to determine a difference between the external voltage value and the internal reference value; and

adjust a duty cycle of the PWM signal based upon the difference between the external voltage value and the internal reference value, so as to adjust the amount of power outputted to the high intensity discharge lamp.

2. An electronic ballast according to claim 1 , wherein the external voltage source comprises a power supply and a voltage divider.

3. An electronic ballast according to claim 1 , wherein the microprocessor is programmed to determine whether to operate in a trimming mode or in a normal mode.

4. An electronic ballast according to claim 3 , wherein the microprocessor is programmed to determine whether to operate in the trimming mode or the normal mode based upon the external voltage value.

5. An electronic ballast according to claim 4 , wherein the microprocessor is programmed to operate in the normal mode when the electronic ballast is not connected to the external voltage source.

6. An electronic ballast according to claim 4 , wherein the microprocessor is programmed to operate in the trimming mode when the electronic ballast is connected to the external voltage source.

7. An electronic ballast according to claim 3 , wherein the microprocessor is programmed to trim the amount of power outputted by the electronic ballast to a load by adjusting the signal based upon the difference between the external voltage value and the internal reference value, and to store a result of the adjustment, when the microprocessor operates in the trimming mode.

8. The electronic ballast according to claim 7 , wherein the load comprises a resistor corresponding to an impedance of the high intensity discharge lamp.

9. The electronic ballast according to claim 7 , wherein the microprocessor is programmed to output the signal which controls the amount of power outputted by the electronic ballast to the high intensity discharge lamp in accordance with a voltage corresponding to the electronic ballast output and a result of the adjustment performed in the trimming mode, when the microprocessor operates in the normal mode.

10. An electronic ballast according to claim 1 , wherein the microprocessor is programmed to adjust the duty cycle of the PWM signal by applying a duty cycle offset to a prior duty cycle of the PWM signal.

11. An electronic ballast according to claim 10 , wherein the microprocessor is programmed to adjust the duty cycle offset based upon the difference between the external voltage value and the internal reference value.

12. An electronic ballast according to claim 10 , wherein the duty cycle offset is a value representing a percentage, and the microprocessor is programmed to apply the duty cycle offset by multiplying the duty cycle offset with the prior duty cycle of the PWM signal.

13. A method for controlling an electronic ballast, comprising:

reading an external voltage value from an adjustable external voltage source, by a microprocessor;

outputting a pulse width modulation (PWM) signal, from the microprocessor, which controls an amount of power outputted by the electronic ballast to a high intensity discharge lamp;

comparing, by the microprocessor, the external voltage value to an internal reference value to determine a difference between the external voltage value and the internal reference value; and

adjusting a duty cycle of the PWM signal, by the microprocessor, based upon the difference between the external voltage value and the internal reference value, so as to adjust the amount of power outputted to the high intensity discharge lamp.

14. A non-transitory computer-readable medium which stores a program which is executed by a microprocessor to control an electronic ballast, the program comprising:

code for reading an external voltage value from an adjustable external voltage source;

code for outputting a pulse width modulation (PWM) signal which controls an amount of power outputted by the electronic ballast to a high intensity discharge lamp;

code for comparing the external voltage value to an internal reference value to determine a difference between the external voltage value and the internal reference value; and

code for adjusting a duty cycle of the PWM signal based upon the difference between the external voltage value and the internal reference value, so as to adjust the amount of power outputted to the high intensity discharge lamp.