Improved inductorless phase control dimmer power stage with semiconductor controlled voltage rise time

Claim 1

Electronic dimming apparatus comprising a semiconductor power controlling means for coupling a lamp load to an alternating current source, and for variable controlling the average power supplied to said lamp load by adjusting the relative proportion of substantially each half-cycle of the alternating current waveform in which said semiconductor power controlling means is in a substantially conductive versus a substantially non-conductive power condition; said semiconductor power controlling means having a control input and adapted to modulate the instantaneous amplitude of the voltage or current supplied to said lamp load under the active control of said control input, said semiconductor power controlling means further having an inherent minimum duration required for a transition between one and the other of its substantially conductive and substantially non-conductive power conditions in response to a stepped change between a value at its control input producing the one and a value producing the other of said power conditions; means for triggering responsive to at least a first input condition corresponding to a desired average power to be supplied to said lamp load and further responsive to the zero-crossing of said alternating current waveform, said means for triggering having at least one output, and producing at least one change in condition at said output substantially corresponding to the phase angle of said alternating current waveform of said half-cycle at which said semiconductor power controlling means must change from one of said power conditions to the other of said power conditions to supply said desired average power to said lamp load; means for transition control responsive to said output of said means for triggering and having an output coupled to said control input of said power controlling means, for controlling the duration of the change between said value at said control input of said power controlling means producing the one and said value producing the other of said power conditions, such that the power condition of said semiconductor power controlling means is gradually changed between one and the other of said power conditions over a period greater than said inherent minimum duration and less than the remaining portion of said half-cycle, whereby the electro-magnetic interference product of said transition is decreased, and wherein the voltage across said lamp load during said transition is controlled to maintain a substantially stable rate of voltage change despite variations in the impedance of said lamp load.