Lighting apparatus for high-voltage discharge lamp

A lighting apparatus for a high-voltage discharge lamp comprising:

• a DC-voltage input terminal to which a first DC voltage is supplied;
• a DC-DC converter circuit arranged to convert the first DC voltage into a second DC voltage;
• an output-voltage detecting circuit arranged to detect an output voltage of the DC-DC converter circuit;
• a DC-AC inverter circuit arranged to convert the DC voltage output from the DC-DC converter circuit into an AC voltage;
• a lamp-current detecting circuit arranged to detect a lamp current passing through the high-voltage discharge lamp;
• an igniter circuit arranged to operate when lighting of the high-voltage discharge lamp is started and to apply a high voltage to the high-voltage discharge lamp;
• and
• a control circuit arranged and programmed to control the DC-DC converter circuit and the DC-AC inverter circuit;
• wherein
• the igniter circuit, the DC-DC converter circuit, and the DC-AC inverter circuit each include a semiconductor switching element;
• the control circuit is arranged and programmed to control switching of the semiconductor switching element of the DC-DC converter circuit and the semiconductor switching element of the DC-AC inverter circuit in accordance with the output voltage detected by the output-voltage detecting circuit and the lamp current detected by the lamp-current detecting circuit such that ON/OFF timings of the semiconductor switching element of the DC-DC converter circuit and ON/OFF timings of the semiconductor switching element of the igniter circuit are synchronized when the lighting of the high-voltage discharge lamp is started, such that the semiconductor switching element of the igniter circuit is turned on after a predetermined period of time after the semiconductor switching element of the DC-DC converter circuit is turned on, and such that the semiconductor switching element of the DC-DC converter circuit is controlled not to output ON pulses when the voltage detected by the output-voltage detecting circuit changes and drops by a predetermined value or more within a predetermined period of time even when ON/OFF timings for the semiconductor switching element of the DC-DC converter circuit arrive at the semiconductor switching element of the DC-DC converter circuit;
• and
• the control circuit is arranged and programmed to control the DC-DC converter circuit using a pulse width modulation control scheme by setting a switching frequency of the semiconductor switching element included in the DC-DC converter circuit so as to be an integer multiple of a switching frequency of the semiconductor switching element included in the igniter circuit.