Method and apparatus for determining a target light intensity from a phase-control signal

摘要

A dimmable ballast circuit for a compact fluorescent lamp controls the intensity of a lamp tube in response to a phase-control voltage received from a dimmer switch. The ballast circuit comprises a phase-control-to-DC converter circuit that receives the phase-control voltage, which is characterized by a duty cycle defining a target intensity of the lamp tube, and generates a DC voltage representative of the duty cycle of the phase-control voltage. Changes in the duty cycle of the phase-control voltage that are below a threshold amount are filtered out by the converter circuit, while intentional changes in the duty cycle of the phase-control voltage are reflected in changes in the target intensity level and thereby the intensity level of the lamp tube.

主权项

1. A phase-control-to-DC converter circuit for a load control device for controlling an amount of power delivered to an electrical load, said load control adapted to receive a phase-control voltage characterized by a duty cycle for determining a target amount of power to be delivered to said electrical load, said phase-control-to-DC converter circuit comprising:
a first filter circuit for generating a first filtered voltage in response to said duty cycle of said phase-control voltage, said first filter circuit characterized by a first time constant; and a second filter circuit for receiving said first filtered voltage and generating a second filtered voltage in response to said first filtered voltage, said second filter circuit characterized by a second time constant having a nominal value that is slower than a value of said first time constant of said first filter circuit; wherein, when a difference between magnitudes of said first and second filtered voltages exceeds a predetermined threshold, said second time constant has a fast value that is faster than said nominal value, such that the magnitude of said second filtered voltage quickly changes to be equal to the magnitude of said first filtered voltage.