Power Integrations has announced a new reference design, the DER-622, which describes a smart wall switch compatible with the wiring conditions most commonly found in residential retrofit installations.Typically, smart wall switches with wireless connectivity, occupancy/vacancy detection, and/or voice control require a neutral return wire to power the unit, which isn't always available in retrofit situations. Neutral-free products are available for older incandescent bulbs because the small AC input current allowed through the load when the smart switch is in standby mode is insufficient to heat the filament. However, for LED and compact fluorescent designs, the high standby current of the smart switch's internal power supply can cause flickering, often unacceptable, known as "ghosting." This is caused by leakage energy accumulating in the lamp, initiating intermittent and brief light activation.
DER-622 illustrates a low-power (LE) Bluetooth® wall switch that consumes less than 500 µA in standby mode. The design is based on Power Integrations' LinkSwitch™-TN2 offline switching integrated circuits, which have an idle current draw of less than 75 µA. The ICs' ultra-low current draw and high light-load efficiency ensure compatibility with energy-efficient LED bulbs rated up to 3 W and are ideal for wiring wall switches without a neutral wire.
The LinkSwitch-TN2 devices can be configured to support flyback or buck topologies and deliver high-precision results, providing voltage regulation of less than ±3%. The ICs enhance system reliability by incorporating numerous safety features, including input and output overvoltage protection, overtemperature protection, and output short-circuit protection, along with a robust 725V power MOSFET. In the DER-622, the LinkSwitch-TN2 power supply IC is used in a non-isolated flyback topology and employs half-wave AC input rectification to reduce the solution's cost. The power supply provides two outputs: a 12V rail for controlling a relay and a 3.8V rail for powering a Bluetooth LE controller.
According to Hubie Notohamiprodjo, product marketing manager 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 requires rewiring, which increases costs and discourages product adoption. The simplicity of the LinkSwitch-TN2 and its ultra-low current draw enable this elegant smart switch solution to be compatible with low-wattage LED bulbs and wiring without a neutral wire.".
Key applications include wireless lighting control, occupancy and void sensors, motion detectors, wall dimmers, and shading controls. DER-622 is available as a free download at http://www.power.com/der-622.
