| 摘要 |
<p>A lamp drive circuit for driving a compact source metal halide discharge lamp (10) comprises a d.c. power supply (18 to 28) coupled to switching means (32 to 36). The switching means supply alternating current to the lamp at a commutation frequency of about 100 to 250 H z. The d.c. power supply includes an a.c. stage (20 to 25) operating at a frequency of the order of 30 to 40 Hz. The a.c. stage determines the internal inductive impedance of the d.c. power supply. The frequency of operation of the a.c. stage is seen to be greater than the frequency of the alternating current supplied to the lamp. Conveniently the d.c. power supply comprises a forward converter, and also includes an R.F. filter (16) and rectifying and smoothing circuit (17). A striker circuit (31) is provided for starting the lamp (10). The switching means may comprise two transistors (32, 33) switched on and off alternately by a switching circuit (36). When the lamp drive circuit is used with a cine film projector or camera, the switching circuit (36) may be synchronised with the pull-down motion of the film transport mechanism by a sensor (40) and control unit (39). </p> |
