Lighting circuit for high-pressure discharge lamp for vehicles

In a lighting circuit for a discharge lamp for a vehicle comprising a DC voltage booster circuit for boosting an input voltage from a DC voltage input terminal to provide an output voltage that is converted into an AC voltage to be applied to a high-pressure discharge lamp, the improvement comprising:

• a voltage detector for detecting the output of the DC voltage booster circuit;
• a current detector for detecting an output current of the DC voltage booster circuit;
• a control circuit for applying a control signal corresponding to signals from the voltage detector circuit and the current detector to control the output voltage of the DC voltage booster circuit, the control circuit together with the voltage detector and the current detector constituting a feedback system for the DC voltage booster circuit;
• an igniter circuit comprising a capacitor for lamp-current detection and lamp-current control connected in series with the discharge lamp for supplying a trigger pulse to the discharge lamp until the discharge lamp is lit after reception of a lighting start command;
• an igniter starter circuit for discriminating whether or not the discharge lamp is lit on the basis of a detection voltage from the capacitor and sending a signal to the igniter circuit to stop generation of the trigger pulse when the discharge lamp is lit;
• and
• a high frequency booster circuit for converting the output voltage of the DC voltage booster circuit into an AC voltage, wherein a power supply voltage on an output line of the high frequency booster circuit is supplied to the igniter circuit for applying a trigger pulse to the discharge lamp until the discharge lamp is lit, and to said igniter starter circuit for discriminating whether or not the discharge lamp is lit, said high frequency booster circuit comprising:
• positive and negative input terminals;
• a transformer having a primary winding and a feedback winding;
• a choke coil having a first terminal connected to the positive input terminal and a second terminal connected to a center tap of the primary winding of the transformer;
• a pair of active switching elements, respectively provided between both ends of the primary winding of the transformer and the negative input terminal, for performing mutually opposite switching operations;
• and
• a bias circuit having constant current means, connected to said second terminal of the choke coil, for supplying a predetermined bias voltage based on a potential at a subsequent stage of the choke coil to the active switching elements.

In a lighting circuit for a discharge lamp for a vehicle comprising a DC voltage booster circuit for boosting an input voltage from a DC voltage input terminal to provide an output voltage that is converted into an AC voltage to be applied to a high-pressure discharge lamp, the improvement comprising:

• a voltage detector for detecting the output of the DC voltage booster circuit;
• a current detector for detecting an output current of the DC voltage booster circuit;
• a control circuit for applying a control signal corresponding to signals from the voltage detector circuit and the current detector to control the output voltage of the DC voltage booster circuit, the control circuit together with the voltage detector and the current detector constituting a feedback system for the DC voltage booster circuit;
• and
• a high frequency booster circuit for converting the output voltage of the DC voltage booster circuit into an AC voltage, the high frequency booster circuit comprising:
• positive and negative input terminals;
• a transformer having a primary winding and a feedback winding;
• a choke coil having a first terminal connected to the positive input terminal and a second terminal connected to a center tap of the primary winding of the transformer;
• a pair of active switching elements, respectively provided between both ends of the primary winding of the transformer and the negative input terminals, for performing mutually opposite switching operations;
• and
• a bias circuit having a constant current means, connected to said second terminal of the choke coil, for supplying a predetermined biased voltage based on a potential at a subsequent stage of the choke coil to the active switching elements.