Cost and Energy Saving Solution of LED Lighting Control System
According to the US Department of energy, LEDs will account for 75% of all lighting product sales by 2030. It goes without saying why LEDs have great advantages over incandescent lamps and compact fluorescent lamps (CFL). The main point is that the power consumption is reduced by more than 80%.Because they lose less energy through thermal radiation, their life is also improved. Size is another factor. LEDs are much smaller than traditional lighting solutions, allowing them to be used in more applications, such as cars. High output power LED lighting is also entering industrial applications.Developing lighting applications requires expertise in power management. Many LED lighting applications will also be more intelligent than their previous products. People can use wired or wireless protocols to remotely control it as part of a larger lighting network. Adding this level of "intelligence" will require embedded software development and microcontrollers. Now there is a new solution to combine all these elements.Different from the traditional incandescent bulbs and more energy-efficient compact fluorescent lamps that have been replaced in recent years, LEDs need a stable DC power supply to achieve the best working state. This inevitably requires the use of a rectified AC power supply that obtains electrical energy from the main grid. Although this may make them slightly more complex than existing solutions, the benefits in terms of energy efficiency and service life usually far exceed any initial installation cost.Because of these advantages, turning to LED lighting has become a general trend, and perhaps the most obvious change has taken place in the industrial field. However, the applicability of LED is not limited to the commercial field, and its application diversity is also increasing. The automotive industry may be the latest example, but its application in the field of architectural lighting is becoming more and more popular, and solutions for general consumers and homes are emerging in endlessly.There are a large number of variant products of various LED lighting lamps in the market, and various control methods are provided. However, basically speaking, LEDs have specific requirements in power supply and driver circuits. In response to this growing demand, the semiconductor industry is now dealing with these two requirements.At present, there are mainly two methods to generate and provide the DC current required to drive the LED. The first method uses the constant current and constant voltage method to convert the AC power supply into DC and apply it directly to the LED. The second is to use the distributed method, using the primary regulated DC power supply converted from AC input to power multiple subsequent DC-DC converters to provide regulated power supply to LEDs.Other important aspects of this topology technology include current isolation between AC and DC components, ensuring high conversion efficiency, increasing power factor correction to comply with regulations, and circuit protection (overvoltage / undervoltage, short circuit).Dimmable LEDAnother important aspect of LED lighting is the ability to adjust the output to meet various requirements. The LED light adjustment can be realized by changing the applied power, which can be realized by reducing the driving current in continuous (Analog) mode or discontinuous (digital) mode. For the nonlinear output of LED in the power supply current range, it is necessary to realize the analog method, and if you want to provide the best constant current, you need to use the digital method usually using pulse width modulation (PWM).Ncl30186 provided by on semiconductor is an example of LED driver that can adopt these two dimming modes at the same time, and can also provide PFC with high conversion efficiency. This is a combination of PFC boost controller and quasi resonant controller optimized for off-line LED lighting solutions. Figure 1 shows a schematic diagram of a typical application example using ncl30186.Figure 1: typical off-line LED lighting solution using ncl30186 of on semiconductor.Microcontroller based general-purpose devices are also aimed at this application field, such as pic12hv752 of microchip technology. This low-cost 8-pin device integrates many peripherals, so it is an ideal choice for power conversion applications and LED driver circuits. Specific peripherals include complementary output generator (COG) and hardware limit timer (HLT). When using pic12hv752 to build triac dimmable LED driver, both peripherals will work, as shown in Figure 2.Figure 2: Microchip's low-cost 8-bit pic12hv752 MCU includes many peripherals for power conversion and LED control.Cog provides PWM signal to drive MOSFET, and its rising edge is controlled by HLT. The primary side control realizes PFC through feedforward method and peak current mode control.The device also integrates DAC, ADC and comparator. The firmware required to create an application is relatively simple, mainly focusing on the initialization of peripherals.Networked lightingLike many things today, electric lights have become "smarter". In fact, professional lighting equipment has been intelligent for some time, using Dali protocol to centrally control distributed lamps. The same technology has now been used in LED lighting and achieved good results.Dali is the English abbreviation of digital addressable lighting interface, which is standardized as iec-62386. It is mainly used to provide remote interface for electronic ballast, and therefore can be used to control LED, fluorescent lamp, mercury lamp and other electronic discharge lamps.With the addition of microcontrollers, this provides greater flexibility for the development of LED driver solutions. Even some manufacturers further provide special MCU series for this application field, and take this opportunity to increase application specific interfaces, such as Dali.For example, the stlux series launched by STMicroelectronics is a product series dedicated to lighting and power conversion. Typical applications are shown in Figure 3.Figure 3: STMicroelectronics' stlux series devices have a dedicated and configurable state machine for time critical applications such as power conversion, including LED control.Stlux385a has Dali module, but what really distinguishes the device from other devices is that it implements a dedicated and autonomous state machine to control six independent PWM outputs with a resolution of 1.3 ns.State machine is also called smed (state machine, event driven). Smed is configured using an integrated microcontroller. Once configured, smed has a reaction time as low as 10.4 ns, so it is suitable for time critical operations. Smed has four states during operation, and idle and hold states are added. Each of the four states is configurable, and developers can define which system events are triggered by transitions between each state. The PWM output level can be updated during conversion.Some devices in the stlux series have up to 6 smeds. Each smed works independently, but they can be grouped to form a more powerful state machine. The integrated microcontroller adopts stm8 CISC core, with 21 internal registers, 20 addressing modes and 80 instructions.Total solutionMore and more people want to integrate power management and connectivity into a single mature solution. This has prompted semiconductor manufacturers to invest in reference design solutions that include many of their products. 100W, 0.1% dimmable DC-DC LED driver is one of these designs, including the solar collection and wireless connection design launched by Texas Instruments.As shown in Figure 4, the design contains a large number of TI products, the most obvious of which are tps92640 / 41 LED lighting driver and cc2650 Multi Standard 2.4 GHz Wireless MCU. The final design can use the intensity adjustment function based on analog or PWM to control high-power and high-efficiency dimmable LED lamps. In addition, due to the use of wireless MCU, it can provide control of low-power wireless interface.Figure 4: this reference design of Ti contains a large number of devices especially for general power conversion and LED control.The no-load time between the high-voltage side and low-voltage side grid drivers has been optimized to achieve maximum efficiency over a wide input operating voltage and output power range.Cc2650 is a dual core device using arm Â® Cortex Â®- M3 processor, as its main CPU, uses arm Cortex-M0 processor to manage the RF core of the device. The firmware of ble controller and IEEE 802.15.4 MAC is embedded in the ROM of the device and partially executed on the arm Cortex-M0 processor. This enables higher system level efficiency and ensures that flash memory is used for advanced application software.Both PWM and analog dimming signal sources can be generated by cc2650, depending on the requirements of the application. With the addition of digital ambient light sensor, the application can monitor the constant lumen output and adjust it according to the amount of natural sunlight, so as to achieve further energy saving.conclusionLED lighting has realized its potential to significantly reduce costs and save energy consumption. It can be said that its application will continue to deepen, but some people believe that it still faces the challenge of completely penetrating the consumer market.The most common problem is opposition to using it at home due to uncertainty about light quality and concerns about installation costs. Through further technology development and continuous introduction of more advanced and more integrated solutions, it is believed that these two problems will be successfully solved.Now the potential earnings of companies entering the LED market may increase, because the demand is bound to grow in the next few years. The global goal of reducing greenhouse gas emissions will promote the growth of demand, and in addition to global environmental benefits, consumers can now obtain immediate benefits, including better control of their environment.