Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Periodic switch in the primary circuit of the supply...
Patent
1990-03-22
1992-04-07
Pascal, Robert J.
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Periodic switch in the primary circuit of the supply...
315223, 315307, 361 42, 361 45, H05B 3700
Patent
active
051031396
ABSTRACT:
In a power-line-operated power-factor-corrected electronic ballast, a pair of series-connected fluorescent lamps is powered via a tuned L-C circuit that is series-excited by the rectangular-wave 33 kHz voltage output of a half-bridge inverter and parallel-loaded by the fluorescent lamps. Power factor correction is attained via two energy-storing capacitors charged during periods when the instantaneous absolute magnitude of the power line voltage exceeds half of its peak absolute magnitude and discharged when it fails to exceed half of this peak absolute magnitude. As a result, a so-called valley-filled DC voltage is provided to the inverter; which results in the inverter's rectangular-wave output voltage being about 50% amplitude-modulated. In spite of this high degree of amplitude-modulation, the resulting lamp current crest factor is only about 1.8. By control of the symmetry of the inverter's rectangular-wave output voltage, the fluorescent lamp is started and operated in such a manner that maximum available ballast output current is limited to about 30 milli-Ampere (which magnitude of 33 kHz current is considered safe from electric shock hazard) until such time as verification is provided to the effect that this 30 milli-Ampere of 33 kHz current is indeed flowing through both lamps (as opposed to through a ground loop); whereafter the symmetry of the rectangular-wave output voltage is re-controlled such as to provide for the lamp current to increase to some preset level.
REFERENCES:
patent: 4563719 (1986-01-01), Nilssen
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