| 摘要 |
<p>An electronic ballast circuit for a gas discharge lamp includes a driven inverter (52) the high frequency oscillatory ouput of which is supplied to a gas discharge lamp (164) through a current limited inductor (154) with a capacitor (160) in parallel with the lamp. A protection circuit includes an additional winding (152) on the inductor (154) which monitors the peak voltage and current of the lamp (164). The signal from the additional winding (152) is fed to a threshold detector and latch circuit (170) which operates to remove the drive from the inverter (52) and de-energise the lamp (164) if the voltage across the lamp exceeds a first predetermined value. Additional protection is provided by a voltage clamping circuit (166) which shorts out the additional winding (152) if the voltage across the lamp exceeds a second predetermined value higher than the first before the lamp is de-energised, thereby to damp the resonant circuit of the inductor (154) and capacitor (160). The additional winding (152) also supplies power for a low-voltage stabilised supply for parts of the ballast circuit. The ballast circuit can supply a number of lamps (164, 264, 364, 464) connected in parallel to the driven inverter (52), a respective inductor (154, 254, 354, 454) with additional winding (152, 252, 352, 452), and a respective capacitor (160, 260, 360, 460) being provided for each lamp.</p> |
