Abstract: In a power supply unit, if a dimmer rate is changed within a range of k1, k2, . . . k7 by a dimmer signal k of a dimmer signal generator, light-emitting diodes are controlled to be lighted by a constant current characteristic in an area where the dimmer rate is small according to a load characteristic corresponding to the dimmer rates k1, k2, . . . k7. As the dimmer rate becomes larger, a tendency of a constant voltage characteristic is gradually strengthened from a constant current characteristic so that the light-emitting diodes are lighted at the larger dimmer rate.

Abstract: In a power supply unit, if a dimmer rate is changed within a range of k1, k2, . . . k7 by a dimmer signal k of a dimmer signal generator, light-emitting diodes are controlled to be lighted by a constant current characteristic in an area where the dimmer rate is small according to a load characteristic corresponding to the dimmer rates k1, k2, . . . k7. As the dimmer rate becomes larger, a tendency of a constant voltage characteristic is gradually strengthened from a constant current characteristic so that the light-emitting diodes are lighted at the larger dimmer rate.

Abstract: In a power supply unit, if a dimmer rate is changed within a range of k1, k2, . . . k7 by a dimmer signal k of a dimmer signal generator, light-emitting diodes are controlled to be lighted by a constant current characteristic in an area where the dimmer rate is small according to a load characteristic corresponding to the dimmer rates k1, k2, . . . k7. As the dimmer rate becomes deeper, a tendency of a constant voltage characteristic is gradually strengthened from a constant current characteristic so that the light-emitting diodes are lighted at the deeper dimmer rate.

Abstract: The present invention provides an improved power factor and lower harmonic distortion in the power supply circuit of a high frequency discharge lamp. An "extra" circuit path is provided so that the driving power to the lamp will "see" a load that significantly reduces the harmonic distortion and tends to cause the power factor to approach "1". In a preferred embodiment of the invention this is accomplished by providing a third capacitor with which the load circuit forms an in-series resonance circuit with the discharge lamp and its associated current-limiting inductance. The new circuit arrangement provides a high frequency current passage not provided in known lighting circuits of this type that raises the power factor and lowers harmonic distortion.