A dimming circuit for a fluorescent lamp 13 powered from an AC supply, includes a solid state switch 11, such as a triac. Upon operation of a control switch 20, a gating circuit 19 provides one, or preferably several, gating pulses to the triac switch during each half cycle of the supply. The phase angle at which the pulses are provided is progressively advanced, e.g. from 90o to 0o, over a number of half cycles. The lamp filaments are supplied by a transformer 14 having a primary winding 15 in a circuit with the triac switch and at least one secondary winding 16 supplying the filaments. An associated high pass filter 17 passes only harmonics of the triac switch current to the filaments.
|IPC||H05B 39/02,H05B 41/23|
|Publication status||Published - 9 Jul 1993|