Feedback-controlled circuit and method for powering a high intensity discharge lamp

摘要

A circuit and method for powering a high intensity discharge lamp, such as a high pressure sodium lamp (HPSL) are disclosed. Feedback control is used to achieve a nearly constant lamp power despite considerable variations in lamp impedance resulting from aging of the lamp or other causes. The feedback control also achieves a nearly constant amplitude of lamp current so as to attain nearly constant lamp color in a HPSL, and further accommodates considerable variations in a.c. line voltage. The circuit, which shares some features with the method, includes a circuit to supply a d.c. bus voltage and first and second feedback-controlled circuits. The first feedback-controlled circuit regulates on a conductor supplying bus current the bus voltage in response to a first error signal in such manner as to minimize the first error signal. The first error signal is substantially proportional to the difference between (1) a dynamic signal substantially proportional to peak lamp current and (2) a set point signal for peak lamp current. The second feedback-controlled circuit drives the lamp in response to a second error signal in such manner as to minimize the second error signal and thereby regulate power in the lamp. The second error signal is substantially proportional to the difference between (1) a dynamic signal substantially proportional to average bus current and (2) a dynamic set point signal substantially proportional to the difference between (i) a dynamic signal substantially proportional to the regulated bus voltage and (ii) a set point signal relating to lamp power.