| 摘要 |
PROBLEM TO BE SOLVED: To improve power factor and reduce peak factor by subjecting an input current to a specified wave-shaping. SOLUTION: A wave-shaping network 20 and a resistor 27 are constituted so that a peak of a lamp current flowing through an N-channel transistor 29 and a primary winding follows a flat, full-wave-rectified sine wave. When the average of the peal of the current to a lamp resonance circuit varies, the peak amplitude of the flat, full-wave-rectified current flowing from a rectifier bridge 11 also varies. However, such a peak amplitude, if the pulse width of the gate control output of a pulse modulation circuit 25 is constant, is always smaller than a full-wave-rectified sine wave current which would otherwise flow from the bridge 11. Since the current flowing from the rectifier bridge 11 has the full-wave-rectified waveform at a node 104, the power factor of the ballast circuit is improved. Also, such a current wave-shaping reduces the peal factor. |
