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In the home, connected, energy-efficient LED lighting can generate huge energy savings and personalize living spaces. Take advantage of our secure wireless platform, that offers a high temperature tolerance, and our broad portfolio of certified wireless protocol stacks , including Zigbee, Z-Wave, Thread, and Bluetooth.
Adding smart wireless connectivity to an LED light bulb presents a few design challenges:
LED light bulbs have an electronic ballast which typically includes a PMIC and high voltage discrete components. The electronic ballast typically drives the LEDs with a constant current to achieve a constant brightness that does not vary with input voltage or temperature. The PMIC auxiliary supply can also power a microcontroller (MCU), wireless system-on-a-chip (SoC) or RF module, but the supply is typically poorly regulated of 10 to 15 volts, thus a linear regulator is required to lower this voltage and provide a well-regulated 3 V or 1.8 V supply.
One method adds a MOSFET between the LED cathode and ground for the MCU to switch off or dim the LED. This presents some issues if the PMIC was originally designed for constant load. Disabling the PMIC would also disable the auxiliary supply and is not an option. Energy efficiency standards, such as the EPA's ENERGY STAR program and California Energy Commission’s (CEC) Title 20 Appliance Efficiency program, have strict requirements for standby current and to be CA Title 20 compliant the bulb need to consume less than 200 mW in standby mode. The challenge is to convert the AC line voltage down to the RF transceiver voltage efficiently. The auxiliary supply needs to provide about 50 mW to the RF module with an efficiency of better than 50% and a quiescent current of less than 100 mW.
Basic LED bulbs often have a metal shield around the ballast board minimizing electromagnetic interference from the switching converter. Smart LED bulb designs need to shield the ballast and also provide a good antenna for the RF. A simple PCB antenna on the RF module might work if the module is positioned vertically near the top of the bulb. However, this might interfere with the light transmission and will put the smart semiconductors close to the LED heat source. Designers should carefully consider how RF performance will impact the usability of their bulbs. It is important to consumers to have a reliable connection.
Ideally the RF module should be placed far from heat generating LEDs and ballast electronics, but this is not always practical. The product reliability can be enhanced by monitoring the temperature of the LEDs and the wireless SoC. Dimming the LEDs can limit the heat generation. A thermistor placed near the LEDs can monitor the LED temperature, while the wireless SoC may have an on chip temperature sensor.