Minolta DI700 Printer Printer Driver Download.The present invention relates to a ballast circuit for a fluorescent lamp which is used as a vehicle lamp or the like.
FIG. 1 is a circuit diagram showing the essential parts of a conventional circuit for an electronic ballast circuit which is used in a fluorescent lamp, and FIG. 2 is a time chart showing the operation of the circuit. The electronic ballast circuit for a fluorescent lamp comprises a circuit board 1, a power supply circuit 2, a current limiting circuit 3, an ignitor circuit 4 and a switching circuit 5. The power supply circuit 2 comprises an ac input circuit 6, a voltage drop circuit 7, a dc converter circuit 8 and a dc-dc converter circuit 9. The current limiting circuit 3 comprises a resistor 10, a capacitor 11, an induction circuit 12 and a choke coil 13. The ignitor circuit 4 comprises a primary coil 14, a switching circuit 15 and a secondary coil 16. The switching circuit 5 comprises a control transistor 17 and a comparator 18. The control transistor 17 has a base connected to a junction between the primary coil 14 and the switching circuit 15, a collector connected to a junction between the current limiting circuit 3 and the switching circuit 5, an emitter connected to a junction between the secondary coil 16 and the switching circuit 5, and a base voltage Vc supplied to the collector of the control transistor 17 from the power supply circuit 2 via the voltage drop circuit 7 and the dc-dc converter circuit 9. The control transistor 17 is turned on when the base voltage Vc is higher than a predetermined voltage, and turned off when the base voltage Vc is lower than a predetermined voltage. When the control transistor 17 is turned on, the current limiting circuit 3 is enabled to set a current at a predetermined level to flow in the secondary coil 16. As a result, the impedance of the secondary coil 16 is set at a predetermined level so that the fluorescent lamp is lighted.
FIG. 3 shows waveforms of various voltages used in the electronic ballast circuit. In the electronic ballast circuit, in order to light the fluorescent lamp, the base voltage Vc is set higher than a predetermined voltage (e.g., 700 V) by adjusting a voltage supplied from the power supply circuit 2 to the power supply circuit 2. Since the switching circuit 5 is set to be turned on when the base voltage Vc becomes higher than the predetermined voltage, the control transistor 17 is turned on. Thus, the current limiting circuit 3 is ac619d1d87
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