Discharge lamp lighting apparatus

Abstract

A discharge lamp lighting apparatus includes a DC-DC converter for outputting voltages having respective different potentials from two wirings, a switching circuit having input terminals connected to the two wirings, an output terminal connected to one electrode of a discharge lamp, and a capacitor having one electrode terminal connected to a second electrode of the discharge lamp and a second electrode terminal connected to one of the two wirings of the DC-DC converter. The switching circuit includes a switching element for controlling connections between one of the two wirings and the output terminal. The other wiring is connected to the output terminal.

1 . A discharge lamp lighting apparatus comprising: 
 electric power regulating means for regulating electric power supplied from a power source and outputting voltages having respective different potentials at first and second wirings,    a switching circuit including a switching element having first and second input terminals connected to the first and second wirings of said electric power regulating means, said first input terminal being connected to a first electrode of a discharge lamp, and an output terminal being connected to a second electrode of the discharge lamp, and    a first capacitor connected in series with the discharge lamp in a circuit for making connections to one of said first input terminal of said switching circuit, the discharge lamp, and said output terminal of said switching circuit.    
   
   
       2 . The discharge lamp lighting apparatus as defined in  claim 1 , wherein the discharge lamp is driven with alternating current by repeatedly supplying a current from said electric power regulating means to the discharge lamp and charging said capacitor, and by stopping actuation of said electric power regulating means and supplying a reverse direction current from said first capacitor to the discharge lamp.  
   
   
       3 . The discharge lamp lighting apparatus as defined in  claim 1 , wherein the discharge lamp is operative in periods including 
 a standby period preparing for lighting of the discharge lamp,    an electrode heating period for detecting at least a voltage of said capacitor for heating electrodes of the discharge lamp with a discharge lamp current until the voltage reaches a threshold voltage after the discharge lamp is lighted, and    an AC discharge period for passing an AC current through the discharge lamp to sustain a discharge in the discharge lamp.    
   
   
       4 . The discharge lamp lighting apparatus as defined in  claim 1 , wherein 
 one of said first and second input terminals of said switching circuit is connected to said output terminal through said switching element, and    the other of said first and second input terminals of said switching circuit is directly connected to said output terminal.    
   
   
       5 . The discharge lamp lighting apparatus as defined in  claim 1 , wherein said switching element comprises means for regulating a control voltage so that a discharge lamp current becomes a fixed current.  
   
   
       6 . The discharge lamp lighting apparatus as defined in  claim 1 , including voltage smoothing and initial current supply means for smoothing a voltage output by said electric power regulating means and supplying a current to the discharge lamp upon starting of a discharge.  
   
   
       7 . The discharge lamp lighting apparatus as defined in  claim 1 , wherein operation of the discharge lamp includes a dead period overlaying a period of stopping actuation of said electric power regulating means in an OFF period of said switching element when driving the discharge lamp with AC.  
   
   
       8 . The discharge lamp lighting apparatus as defined in  claim 1 , wherein said voltage smoothing and initial current supply means includes 
 a resistor and a diode connected in parallel in a parallel circuit, said parallel circuit being connected in series with said first capacitor, and    a second capacitor connected in parallel with said parallel circuit.    
   
   
       9 - 14 . (canceled)  
   
   
       15 . The discharge lamp lighting apparatus as defined in  claim 1 , including an igniter circuit.  
   
   
       16 - 17 . (canceled)