Abstract: A symmetry control circuit for a trailing edge phase control dimmer circuit for controlling alternating current (AC) power to a load, the symmetry control circuit including: a bias signal generator circuit configured to monitor non-conduction periods of each half cycle of said AC power for an elapsed duration of the non-conduction periods, and generate a bias signal voltage based on the elapsed duration, whereby an amplitude of the bias signal voltage is proportional to the elapsed duration of the non-conduction periods; and a bias signal converter circuit configured to convert the bias signal voltage to a bias signal current, wherein the bias signal current is added to a reference current of a conduction period timing circuit configured to determine said conduction periods, and wherein the conduction period timing circuit is configured to alter one of the conduction periods immediately following one of the non-conduction periods based on the bias signal current when added to the reference current to compensa

Abstract: Dimming system with parallel dimmers each with user interface and dimmer circuit are connected in series with a load and AC source. AC switch in dimmer circuit switches AC to the load at a conduction angle, the AC conducted in ON state and not OFF state; a controller determines the conduction angle to control turn-ON at each half cycle to control switching of ON and OFF states based on user control signal; controller detects zero-crossing of the AC and track conduction angle by detecting change in conduction angle based on zero-crossing of the AC. If the controller of an initiating dimmer determines a new conduction angle based on user signal this controller uses the new conduction angle. The controller of each dimmer except the initiating one detects a change in the conduction angle of the load in response to the new angle and the controller of each dimmer except the initiating one adopts that angle.

Abstract: A zero-crossing detection circuit for a trailing edge phase control dimmer circuit for controlling alternating current (AC) power to a load, wherein the circuit includes: a switching circuit for controlling delivery of AC power to the load by conducting power to the load in an ON state and not conducting power to the load in an OFF state; a switching control circuit for controlling turn-OFF and turn-ON of the switching circuit at each cycle of the AC; and a rectifier for rectifying the AC power in the non-conduction period to generate rectified dimmer voltage to be provided to the dimmer circuit, wherein the zero-crossing detection circuit includes a current sink circuit; wherein the current sink circuit has a low impedance at low instantaneous AC voltages; a comparator circuit configured to detect zero crossings of a first threshold value of the rectified dimmer voltage.

Abstract: A trailing edge phase control dimmer circuit for controlling alternating current (AC) power to a load with short-circuit protection, wherein a switching control circuit includes a zero-crossing detection circuit configured to detect zero crossings of the AC and to detect crossings of a first threshold value and a second threshold value of the rectified dimmer voltage, and wherein the zero-crossing detection circuit is further configured to initiate the switching circuit to commence one of the conduction periods when the rectified dimmer voltage crosses below the first threshold value and to initiate the switching circuit to prematurely terminate one of the conduction periods when the rectified dimmer voltage crosses above the second threshold value to provide short-circuit protection for the trailing edge phase control dimmer circuit.

Abstract: A trailing edge phase control dimmer circuit for controlling alternating current (AC) power to a load, the circuit including: a switching circuit for controlling delivery of AC power to the load by conducting power to the load in an ON state and not conducting power to the load in an OFF state; and a switching control circuit for controlling turn-OFF and turn-ON of the switching circuit at each cycle of the AC to control switching of the ON and OFF states of the switching circuit, wherein the switching control circuit controlling turn-OFF of the switching circuit includes controlling a turn-OFF transition of the switching circuit between the ON state and the OFF state of the switching circuit extending for a selected turn-OFF transition time, and wherein the switching control circuit further includes a dv/dt feedback circuit for controlling a turn-OFF transition profile indicative of a drain voltage of the switching circuit of the turn-OFF transition and the selected turn-OFF transition time by returning at l