| 摘要 |
A method of dimming a plurality of LEDs (100) includes generating a first pulse-width modulated (PWM) waveform (150) and generating a plurality of second PWM waveforms (155, 160, 165), each of the PWM waveforms (100, 155, 160, 165) having a duty cycle. The duty cycle of the first PWM waveform (100) and the duty cycle of each of the second PWM waveforms (155, 160, 165) begin at approximately the same time. The periods of each of the second PWM waveforms (155, 160, 165) end before the end of the first PWM duty cycle. In the method, and in disclosed circuits and devices, a first switch (135) is closed in response to the duty cycle of the first PWM waveform (100), and each of a plurality of second switches (105, 110, 115) connected between the first switch (135) and a corresponding plurality of LEDs (100) is closed in response to the respective duty cycles of each second PWM waveform (155, 160, 165), so that each LED (100) connected between each second switch (105, 110, 115) and a power source (145) is energized when the first switch (140) and the corresponding second switch (105, 110, 115) are closed and not energized when either the first switch (135) or the corresponding second switch (105, 110, 115) is open. In this way, the chormaticity of each LED (100) is not affected by the length of the duty cycle of the dimming PWM. |
