Lossless zero-cross detection in LinkSwitch-TNZ ICs

21st June 2021
Alex Lynn

Power Integrations has announced LinkSwitch-TNZ, a new switching power supply IC that combines offline power conversion, lossless zero-cross detection and, optionally, X-capacitor discharge functions in a compact SO-8C package. The highly efficient LinkSwitch-TNZ IC can be used 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 (HBA) 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 50 to 100 mW of continuous power.”

Devices such as light switches, dimmers, sensors, and plugs connect and disconnect the AC line periodically using a relay or TRIAC. A discrete circuit is typically implemented to detect the AC line zero-crossing to control the turn-on transition of the main power device while reducing switching losses and in-rush current.

This approach requires many components and is very lossy, consuming almost half of the standby power budget in some cases. Similarly, appliances often use a discrete zero-cross detection circuit to control motor and MCU timing. These applications also require an auxiliary power supply for functions such as wireless connectivity, gate drivers, sensors and displays.

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

Optionally, an X-capacitor discharge function can also be included in the package for high power applications, leading to greater PCB space reduction, low BOM count and increased reliability (LNK331x).

LinkSwitch-TNZ switching power supply ICs enable ±3% regulation across line and load, no-load consumption of less than 30 mW with external bias and have an IC standby current of less than 100 µA. Parts are simple to design in, feature an integrated soft start, and work with both isolated and non-isolated topologies.

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