Light control circuit and method

摘要

A system and method for controlling the dimming of a lighting element, or other electrical load, that uses a timer synchronized to the AC waveform is disclosed. The timer is set up to repeatedly count at a rate equal to twice the frequency of the AC waveform. An output from the timer logic is asserted when the timer value exceeds a predetermined value, stored in a compare register. This output is connected to the gate of a triac, which controls the passage of current from the AC power source to the electrical load. A capture register is used to determine the temporal relationship between the restart of the timer and the AC waveform. This system and method reduces the real time requirements of an associated processing unit, and improves consistency, thereby reducing flicker.

主权项

1. A method of controlling a current to a load, where the load is powered by an AC voltage having a frequency and a period, the method comprising:
utilizing timer logic comprising a timer, a reload register, a capture register, a compare register and an output, wherein the timer counts to a value based on a value loaded in the reload register, resets and restarts, and wherein the output is asserted when the value of the timer is greater than a value loaded in the compare register; electrically connecting the output to the gate of a triac, where the triac is disposed between a source of the AC voltage and the load; loading the reload register with a value such that the timer restarts at a rate equal to twice the frequency of the AC voltage; loading the compare register with a value less than the value of the reload register, where the difference between the value of the reload register and the value of the compare register defines a pulse width of the output; calculating a desired temporal relationship between the restarting of the timer and the AC voltage to achieve the desired current, where said relationship can be determined by reading the value of the timer when the AC voltage is at zero voltage by reading the capture register; reading the capture register to determine the actual temporal relationship; determining a difference between the actual temporal relationship and the desired temporal relationship; adjusting the value of the reload register based on the difference; and repeating the reading, determining and adjusting steps.