Methods and apparatuses for phase-cut dimming at low conduction angles

#The present invention relates to integrated circuits in general and, in particular, to phase-cut control circuits.

#Phase-cut dimmer circuits are common circuits used in many commercial and residential applications for dimming and power control. For example, phase-cut dimmers are used to control light or heat output, motor speed, etc. They may be typically located inside standard wall receptacles (e.g., to interface with standard wall switches and outlets), or integrated with line cords or controlled equipment (e.g., a variable speed drill).

#It is generally desirable to connect a phase-cut dimming circuit directly to the load it intends to control (e.g., the light bulb or heating element). A number of modern electronics applications, however, use integrated switching power circuitry. The switching power circuitry may cause the phase-cut dimming circuit to be unable directly to see the load. The indirect connection between the phase-cut dimmer and the load may provide undesirable or sub-optimal results, and may even permanently damage the load or other components.

#A further understanding of the nature and advantages of the present invention may be realized by reference to the following drawings. In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

#FIG. 1 shows a simplified block diagram of an exemplary system for providing dimming control using a dimming controller, according to embodiments of the invention.

#FIG. 2A shows a simplified circuit diagram of an exemplary phase-cut dimmer controlling the intensity of a load operated from an input voltage.

#Many typical dimmer circuits used in commercial and residential applications include phase-cut dimmer circuits. The phase-cut dimmer receives a sinusoidal input voltage (e.g., typically mains line voltage), and “cuts” the waveform at some phase angle set by the dimmer control. This effectively switches the power being delivered to a connected load, thereby reducing the average power being seen by the load. Where the load is directly connected to the dimmer circuit, the reduced average power may directly result in a reduced load output (e.g., reduced brightness of a light bulb). However, where the load is switched (e.g., indirectly connected to the dimmer circuit), the switching circuitry may typically be incompatible with the dimming circuitry. For example, certain compact fluorescent bulbs, and other loads connected to switched power supplies or controllers may not work with typical phase-cut dimmers.

#Phase-cut dimming circuits are typically based on circuit elements, like triacs, that fire upon some threshold input current, and maintain a conduction path as long as the input current remains above some holding level. When certain loads are directly connected to the dimming circuit, they continuously try to draw current over the entire half-cycle of the input voltage waveform. As such, the triac (or other similar element) may be fired at substantially any phase angle within the half-cycle and will maintain a current path to the load substantially for the remainder of the half-cycle. This may allow the load (e.g., a resistive light bulb) to be controlled over almost the entire range of phase angles from 0° to 180°.

#Switched loads may create various undesirable scenarios for using phase-cut dimming. In one scenario, a controller switching the load may only operate within a certain range of rectified input voltages. As such, the usable output of the phase-cut dimmer may be limited only to the small range of voltages sufficient to drive the controller, and the phase-cut dimming may only work for a subset of phase angle selections (e.g., only from 90° to 180°). This may not provide a desirable level of dimming for the application. In other scenarios, equipment may even be permanently damaged by the switching load's incompatibility with the phase-cut dimmer.