| 摘要 |
PROBLEM TO BE SOLVED: To control overcurrent without the need for high manufacturing cost by forming a drive circuit as a power supply control circuit which controls a polarity switching circuit, based on a current value detected by a current detecting circuit. SOLUTION: A drive circuit 10 is formed so as to turn on and off the gates of change-over switches Q1 , Q4 and the change-over switches Q2 , Q3 through a reverse phase switching signal generated from a clock generating circuit. When power supply 1 is tuned on/off, electric power is converted into a DC power by a rectifier 2 and a smoothing capacitor 3, converted into a high frequency pulse by a switching circuit 4. The output from a transformer 6 is converted to DC power by a rectifier 7 and a smoothing capacitor 8, and an electrode is periodically inverted by a polarity switching circuit 9 to supply AC power to a discharge lamp 14. The alternating current is supplied to a discharge lamp 14 by causing on/off switchings to be made alternately between the change-over switches Q1 ,Q4 and the change-over switches Q2 ,Q3 . It is thus possible to control overcurrent without the need for high manufacturing cost. |
