Patent ID: 7443110

Claim:
A circuit for outputting a succession of positive and negative pulses to energize a discharge lamp, comprising: a pulse generating circuit having a DC power supply unit, and a transformer and at least one semiconductor switch which are connected in series across said DC power supply unit, wherein said pulse generating circuit outputs high-voltage pulses to said discharge lamp; and a control circuit for supplying energizing pulses for turning on and off said semiconductor switch; wherein said transformer has a secondary winding with said discharge lamp connected thereacross; and said control circuit controls said energizing pulses to output said high-voltage pulses at a first frequency to cause said discharge lamp to develop an initial discharge therein during a first period, and controls said energizing pulses to output said high-voltage pulses at a second frequency which is higher than said first frequency to develop a substantially steady discharge in said discharge lamp during a second period subsequent to said first period.