Smart home lighting: The hardware

Article By : Aman Jha, Ranajay Mallik, Raunaque Mujeeb Quaiser, Jitendra Jain

Engineers at STMicroelectronics' NOIDA, India, facility setup a smart home lighting system. This part describes the hardware and gives you the schematic.

In today’s world where energy management and conservation is a talked about subject and smartphones are reshaping our lives, smart home lighting is one such area that is gaining lot of attention from the lighting industry. Major advancement in this field is Bluetooth Low Energy (BLE) for connectivity and remote control.

The LED is already a winner in terms of high efficiency, long lifetime, better light quality and reliability and adding smartness to LED lights further boosts superiority. Selective turn on/turn off and brightness control results in increased system life and reduced energy consumption.

However, as input is from an AC source and LEDs represent constant current DC load, power quality is an area of concern that needs to be taken care. The recommended harmonic norms IEC61000-3-2 Class C, EMI limits (CISPR 15) and Energy Star (standby consumption) are also imposed for LED lighting. So, a diode bridge rectifier followed by bulk capacitor is not recommended to power LED lighting. Here, we propose a smart home light based on a monolithic, offline LED driver, which takes care of all the issues, and a BLE module that is controlled by an Android application.

[STMicroelectronics SmartHomeLightingRefDesign Figure1 cr]
Figure 1: The functional block diagram of the BLE-based smart home lighting system.

[STMicroelectronics SmartHomeLightingRefDesign Figure2 (cr)]
*__Figure 2:__ The actual hardware of the smart home lighting system.*

The actual hardware of the system is shown in figure 2. The LED driver is based on offline AC-DC converter working on quasi resonant flyback mode with high power factor (PF) and low total harmonic distortion (THD). Power conversion is based on HVLED815PF, monolithic off-line primary sensing constant current LED driver. For low cost and low power applications, it is an ideal candidate as primary side regulation does not need an optocoupler for LED current feedback. It helps in saving cost as well as PCB area.

It meets the IEC61000-3-2 Class C harmonic norms recommended by International Electrotechnical Commission (IEC) for lighting system. The LED driver has an efficiency of >84% for the entire EU range and has a standby power consumption of <0.5W.

Although dedicated pulse width modulation (PWM) dimming dedicated pin is not available on the HVLED815PF IC, PWM dimming becomes possible in this design. The depth of dimming is at 2.5% level of output power. The board communicates with utility even at switch OFF condition thanks to the offline auxiliary power supply design, which works even in LED OFF condition. The SPBTLE-RF (Bluetooth Low Energy, v4.1, network processor module with integrated RF section and FCC certified) and STM32L051 MCU take care of the connectivity and features, such as remote control, ON and OFF with the help of Android application.

There are several other features, including multiple board control using a single interface. For a typical home, installed with several LED light fixtures, it is important to save on electricity bills. Table 1 shows the specification of smart home lighting system and figures 3-8 show the test results of the LED driver.

[STMicroelectronics SmartHomeLightingRefDesign Table1 (cr)]
Table 1: Specifications of the smart home lighting system.

[STMicroelectronics SmartHomeLightingRefDesign Figures3-4 cr]
Figures 3-4: Power factor value with input voltage variation (figure 3, left); THD value with input voltage variation (figure 4, right).

[STMicroelectronics SmartHomeLightingRefDesign Figures5-6 cr]
Figures 5-6: Current regulation with input voltage variation (figure 5, right); Efficiency variation with input voltage (figure 6, right).

[STMicroelectronics SmartHomeLightingRefDesign Figures7-8 cr]
Figures 7-8: Harmonic current measurement plot (figure 7, left); LED current linearity in dimming (figure 8, right).

[STMicroelectronics SmartHomeLightingRefDesign Schematic Figure9 cr]
Figure 9: Overall schematic diagram of the smart home lighting system to which the hardware was built.

Next: Smart home lighting: Android app demo »

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