Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Silicon controlled rectifier ignition
Patent
1992-03-16
1995-08-29
Neyzari, Ali
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Silicon controlled rectifier ignition
315219, 315DIG7, H05B 4136
Patent
active
054463475
ABSTRACT:
A power-line-operated half-bridge inverter is powered from a constant DC voltage and provides an AC output voltage that is--in contrast with the usual squarewave voltage--describable as being a sinusoidal waveform with the tops clipped off at some fixed magnitude; or, described differently, a waveform composed of truncated sinusoidal waves; or, described still differently, a waveform having trapezoidally shaped half-cycles. The DC voltage is derived via voltage-doubling from the power line voltage. The AC voltage is applied across the primary winding of a so-called reactance transformer, whose loosely coupled secondary winding is connected across a gas discharge lamp. The internal inductive reactance of the secondary winding constitutes a lamp ballasting means by way of limiting the magnitude of the resulting lamp current to a pre-established desired level. Potentially damaging parasitic resonances--which are very likely to occur under actual operational circumstances with an unloaded secondary winding when the primary winding is supplied with a squarewave voltage--are avoided because of the truncated sinusoidal waveshape of the AC voltage; which truncated sinusoidal shape is efficiently attained by a combination of three factors: (i) using rapidly switching transistors in the inverter; (ii) having the transformer's primary winding exhibit a substantial shunt inductance; and (iii) providing for a slow-down capacitor coupled directly across the primary winding, thereby to substantially slow down the rise time of the inverter's output voltage as compared with what it would have been if it were to have been determined solely by the high switching speed of the transistors.
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