Patent ID: 6614192
Filing Date: 2003-09-02
Classification: H05B,Y02B

Abstract:
An electronic gas discharge lamp ballast circuit of the type comprising a control means (22, 23, 25) providing an alternating substantially square current waveform (30) for the electronic gas discharge lamp having a substantially vertical portion (31) providing a substantially instantaneous transition phase and a substantially horizontal peak portion (33) characterized in that the control means (22, 23, 25) comprises:a current value sensor (23) to sense when the vertical portion (31) reaches a pre-set control value; and a microcontroller connected to a digital analogue converter (DAC) to provide at the pre-set value an inclined rising slew portion (32) to form a gradual transition phase between the instantaneous phase and the horizontal peak portion (33) and then toward the end of the half-cycle to provide an inclined falling slew portion (34) from the horizontal peak portion (33) to the pre-set level and in the next half-cycle to cause the microcontroller connected to a digital analogue converter (DAC) to form a mirror image negative current waveform (36).