Compact switcher reduces components for smart appliance applications

Power Integrations has released the LinkSwitch-TNZ, a new switching power supply IC that links offline power conversion, lossless zero-cross detection and, optionally, X-capacitor discharge functions in a compact SO-8C package. The highly efficient IC can be utilised for non-isolated buck and buck-boost power supplies up to 575mA output current and provides up to 12W output for universal-input isolated flyback designs.

Adnaan Lokhandwala, product marketing manager at Power Integrations, said: “The new LinkSwitch-TNZ ICs provide an accurate signal indicating that the sinusoidal AC line is at zero volts. This signal is used by smart home and building automation products and appliances to control the switching of relays, IGBTs and TRIACs to minimise switching stress and system in-rush current. LinkSwitch-TNZ’s detection of the zero-cross point consumes less than 5mW, allowing systems to reduce standby power losses versus alternative approaches that require ten or more discrete components and burn 50mW to 100mW of continuous power.”

Devices including light switches, sensors, dimmers, and plugs connect and disconnect the AC line periodically utilising a Relay or TRIAC. A discrete circuit is generally implemented to detect the AC line zero-crossing to control the turn-on transition of the main power device while decreasing switching losses and in-rush current. This approach needs many components and is extremely lossy, consuming nearly half of the standby power budget in many cases. Similarly, appliances often employ a discrete zero-cross detection circuit to control motor and MCU timing. These applications also need an auxiliary power supply for wireless connectivity, gate drivers, sensors and displays.

These ICs offer best-in-class light-load efficiencies, facilitating more system features to be powered while satisfying stringent standby regulations such as the European Commission standard for home appliances (1275), which needs equipment to consume no more than 0.5W in standby or in off mode; ENERGY STAR’s version 1.1 for Smart Home Energy Management Systems, which limits standby consumption of smart lighting control devices to 0.5W; and China’s GB24849, which limits the off-mode power consumption in microwave ovens to 0.5W. The ICs also lessen component count by 40% or more when compared to discrete designs.

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