According to the control of the LED drive current output terminal, it can be divided into three kinds of dimming modes. The control circuit can also be divided into analog control and PWM control. The control circuit is usually realized by a microcontroller.
First, the main dimming technology of LED lamps
The first mode of dimming is to achieve dimming of the LED lamp by adjusting the LED driving current, because the brightness of the LED chip is proportional to the LED driving current.
The second type of dimming is often referred to as analog dimming or linear dimming. The advantage of the dimming mode is that when the driving current is linearly increased or decreased, the influence of the driving current overshoot on the LED chip is relatively reduced, and the control circuit has strong anti-interference. The disadvantage is that the magnitude of the drive current will have a certain effect on the color temperature of the LED chip.
The third mode of dimming is pulse-light modulation (PWM). In this way, the driving current is square wave-shaped by a certain control, and the pulse width is variable. The pulse width is adjusted to change the time during which the LED lamp is continuously lit, and the output power is also changed, thereby achieving the purpose of energy saving. The frequency is generally controlled at 200 Hz to 10 kHz. Due to the retention of human eye vision, the flicker of the light source during the dimming process is not felt. The advantage of this dimming method is that it can improve the heat dissipation of the LED. The disadvantage is that the overshoot of the driving current has a certain influence on the life of the LED chip.
Second, the composition and future development of the dimming system
Perfect intelligent control should have manual control, intelligent control, light control, time control and fault alarm control functions. When the sun goes down, the sky will automatically light up. After 12 o'clock in the morning, the illumination of the lamp can be automatically halved. After dawn, the lamp can be automatically extinguished; in special cases, the person can manually control; in the event of a malfunction of the lamp, the control system Can automatically alarm.
The intelligent dimming system is mainly composed of a server, a central controller, a single-chip controller and a signal detection circuit.
Server: It consists of upper computer and upper computer software, mainly realizes monitoring operation and alarm function. The server is located in a control center such as street lamp management, and its connection with the central controller can be by power carrier, network or wireless.
The central controller is responsible for accepting the signal sent by the server, decoding it and sending it to the unit controller for control, and transmitting the result of the signal detection to the server.
Signal detection circuit: detects ambient brightness, drive power supply voltage, and current. The detected signal is sent to the unit controller or the central controller.
Unit controller: Each LED light is equipped with a unit controller. By receiving the command of the central controller, the LED is dimmed or turned on and off, and the driving voltage and current of the LED light are sent to the signal detection circuit. Central controller. The fault signal is transmitted to the central controller when the LED luminaire fails.
At present, in the field of road lighting, the application of LED is rapidly spreading, and long life and reliability are still the first elements considered at present, but with the development of technology, when the problem of life and reliability has been solved to some extent, LED Lighting applications must move forward toward intelligent dimming systems.
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