Detailed explanation of application circuits of several intelligent lighting platforms

　　Lighting technologies mainly include mainstream fluorescent lamps, LED lamps and HID technologies, etc. Their wide application makes the topological structure of power drive very different. The common Flyback, Buck, Boost and other extended structures are all being used in large quantities. Whether the product design adopts advanced digital energy-saving control design, whether it supports flexible topological structure applications such as flyback, Buck, Boost, etc., the length of R&D cycle and time to market will determine the success or failure of the product. However, traditional lighting solutions are often implemented with dedicated devices, which are difficult to meet the needs of rapid development. Therefore, an excellent lighting platform solution undoubtedly needs to support flexible topological structure applications and meet the dimming and networking requirements of today's mainstream lighting control solutions such as DALI, DMX512, 0-10V, wireless, infrared, etc.

　　Figure 2 is a reference solution for LED drive control applications. In this solution, three constant current controls can be performed independently by using only the comparator and PWM output linkage functions. Dimming can be achieved by changing the internal reference voltage or PWM output settings. In addition, the MCU supports various sensors and multiple communication interfaces such as DALI, DMX512, and analog input. The appropriate communication control solution can be selected according to the external environment to achieve optimal control.

　　Figure 2-78K0/Ix2 LED driver control

　　The following is an example of the Flyback circuit to illustrate the process of constant current control through a comparator.

　　Figure 3-Flyback circuit constant current control

　　For the switching power supply, the PWM duty cycle determines the output voltage, as shown in Figure 3. After the circuit starts working, the LED current is sampled and added to the MCU built-in comparator port, which is compared with the reference value to generate an interrupt signal to adjust the PWM duty cycle. The change process is shown in Figure 4. For example, when the current is greater than the reference value, the duty cycle is reduced; otherwise, the duty cycle is increased, and finally a state of dynamic stability of the load current is achieved.

　　For dimming, the 78K0/Ix2 series MCU has a variety of ways to achieve it, by changing the comparator reference voltage or using the timer TMH1 and PWM output linkage function. In addition, Shiqiang Telecom's solution can also use the powerful data processing and computing capabilities of this MCU to achieve constant current control through ADC function and embedded algorithm control, while providing sufficient resources for MCU function expansion.

　　Figure 5 shows a smart lighting platform solution embedded with the DALI protocol. This solution uses the communication module with the DALI bus interface built into the MCU, and uses a single MCU to complete the dimming and networking of lamps, thus realizing a high-performance DALI green energy-saving lighting system. It has been used as a reference design by a large domestic lighting manufacturer. The DALI slave system is mainly divided into two parts: the communication module and the LED drive control module, and the peripheral circuit design is simple.

　　Figure 5-DALI slave system structure

The BOOST power supply topology 　　is adopted , and the input voltage is directly driven by the LED lamp after being boosted; the load current is sampled and constant current control is achieved through the embedded algorithm; the MCU has a built-in DALI communication interface, which is connected to the DALI host through the bus to achieve mutual communication with the host and complete the operation control instructions issued by the host computer; the lamp temperature and light intensity sensor signals are added to the MCU port to achieve abnormal detection protection.