Compared with ordinary street use high-pressure sodium lamps, LED lights are more durable and have a longer life. But there is still room for further improvement possibilities. In order to prolong life, and reduce the design impact on the environment, the brightness sensor can be used to adjust the brightness, and to obtain a constant luminance in the life. To change the brightness of the LED in the case of not changing the color, the use of pulse width modulation scheme.
To this end, a square wave signal is applied to the input terminal of the circuit. When the voltage is higher than 1V, the regulator is disabled, no current flows through the LED string. Voltage is very low, the IC input node will assume the voltage of the shunt resistor reflects effectively making current control, make LED string constant current. This will generate a constant current pulse, followed by a pause, i.e., no current flows through. This will adjust the brightness of the LED in the case of not changing the color.
PFC flyback circuit combination of the above, it is important to not use a visible beat frequency of the PWM modulation signal is generated with the grid frequency. There are many ways to achieve the brightness sensor. For example, use of a phototransistor or photodiode, but they require a portion of the analog circuit, so that their signal is applied to the regulator. Another commercial brightness sensor standardized analog interfaces are in use, the control voltage range of 0 to 10V. In a noisy environment, the signal is also sent to the current loop, for example: 0 to 20mA current.
In addition, the sensor or sensor array combined with the central controller can use the digital interface to achieve brightness adjustment, even redundancy, for example, can compensate for failure lights. This is especially conducive to the inconvenience Setting the lamp replacing, for example: in the semiconductor manufacturing plant.
With such a central controller and the lamp, the adjustment and connected to the operation does not have a negative impact on the life of the lamp, but also can realize more functions, such as the presence or not according to the user adjust the ambient light adjustment, remote control (by telephone or SMS) turn on the lights and turn off the lights.
Conclusion
In the early days, the light output of LED lighting solutions, reliability is poor, these shortcomings hinder its popularity. Subsequently, however, these problems are overcome, LED lighting solutions has been more widely used. Now, with the control circuit and the continuous development of the LED long life characteristics come in handy, its environmental advantages has finally been fully revealed.