"The switch mode controllers (e.g., Sipex SP6652 and National Semiconductor LM3407) have an enable input signal (e.g., Enable signal EN or V.sub.EN) that is pulsed for PWM operation. Ideally, a desired amount of charge for each active time period for LED current I.sub.LED is desired to be provided to the LED system. However, due to limitations of quantizing charge in discrete time, providing an ideal desired amount of charge for an active time period for LED current I.sub.LED to an LED system is very hard or impossible to achieve. Such non-idealities are in itself due to the nature of charge quantization (e.g., charge quantizing cycles). The inherent problem of quantizing cycles of charge is that it is limited to the exactness of the amount of charge of LED current I.sub.LED being provided to the LED system due to the fact that charge is quantized in discrete amounts based on discrete time. For example, the geometric points in time of when LED current I.sub.LED ramp-up (e.g., slope 502) and ramp-down (e.g., slope 602) and the cycle rate at which the LED current I.sub.LED fluctuates at an average peak current value in accordance with the values of pulses of a control signal limit the exactness of the amount of charge being provided. Also, temperature variations, power supply variations, LED aging, etc. also impact the accuracy of the amount of charge being delivered to an LED system.
"Also, too slow of a PWM operation frequency (e.g., below 200 Hz) for pulsing the enable input signal can be perceived as a flicker of the LED of a dimmable LED lighting system. Furthermore, operation below a PWM frequency of 20 kHz for pulsing the enable input signal has the potential to create audio tones due to acoustic behavior of magnetic material, which is undesirable and can lead to higher cost to ameliorate the sound path.
"On the other hand, an overly fast PWM operation frequency for pulsing the enable input signal runs into a problem with the start-up and shut down of the current controller. For example, it may take 0.1 milliseconds to 1 millisecond to turn on and off the current. At high PWM operation frequencies, many other negative effects that the dimmable LED lighting system may encounter are the non-uniform dimming control, unpredictable control, and non-linear behavior. In applications with multiple LED colors, the balance between a slow and fast PWM operation frequency is important to the resulting color, and these issues severely limit the ability to provide a desired resulting color.
"There are also other modes of dimming that modify the intensity in ways other than by PWM operation that have desirable characteristics. One of the ways includes the use of delta-sigma modulation. However, the use of delta-sigma modulation would be impractical with the slow behavior of the controller. Thus, a control system that can operate linearly across wide dimming frequency ranges while maintaining high efficiency is desired and needed."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventor's summary information for this patent: "In one embodiment of the present invention, a light emitting diode (LED) lighting system includes an LED controller to control a current in an LED system. The LED controller includes components to calculate, based on the current and an active time period of an LED current time period, an actual charge amount delivered to the LED system and utilize the actual charge amount to modify and provide a desired target charge amount to be delivered during a future active time period of the LED current time period. The LED system can also have components to compare the actual charge amount to a desired charge amount for the active time period and compensate, for a difference between the actual charge amount and the desired charge amount during the future active time period.
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