No-neutral wireless wall switches for smart-home lighting can be retrofitted

Power Integrations has a new reference design, DER-622, describing a smart wall switch compatible with wiring conditions most commonly found in residential retrofit installations. Smart wall switches offer typically wireless connectivity, occupancy/vacancy sensing and/or voice control require a neutral return wire to power the unit, which is not always available in retrofit situations. No-neutral products are available for legacy incandescent bulbs because the small AC input current that is allowed to leak through the load when the smart-switch is in standby mode is insufficient to heat the filament. However, for LED and compact fluorescent designs, high standby-mode current from the smart-switch’s internal power supply can lead to unacceptable flicker often known as “ghosting,” caused by the leakage energy accumulating in the lamp and initiating intermittent start-up and brief light activation. The device illustrates a Bluetooth LE wall switch consuming less than 500µA in standby mode. The design is based on the company’s LinkSwitch-TN2 offline switcher ICs, which have quiescent consumption of less than 75µA. The ICs’ ultra-low current consumption and high light-load efficiency ensure compatibility with energy-efficient LED bulbs rated down to 3W and are ideal for no-neutral wall switch wiring. Comments Hubie Notohamiprodjo, director of product marketing for LED lighting at Power Integrations: “Lighting control products such as smart wall switches and occupancy sensors play an important role in improving energy efficiency in homes and buildings. Many homes have wiring that is incompatible with available products or require rewiring, which increases cost and discourages product adoption. The simplicity of LinkSwitch-TN2 and its ultra-low current draw enable this elegant line-only smart-switch solution which is compatible with low-power LED bulbs and no-neutral wiring.”