Minimize Standby Power in Smoke Detectors, Smart Alarms and Security Systems

To enhance safety, many municipalities now mandate newly constructed buildings to install hardwired smoke/carbon monoxide detectors with battery backup. Powering these devices with AC typically involves a discrete circuit to detect the AC line zero-crossing and control the switching of relays, IGBTs, and TRIACs. This minimizes switching stress from in-rush current.

The discrete approach adds components and consumes up to half of the standby power budget. Power Integrations’ LinkSwitch-TNZ family of switcher ICs provide an accurate signal when the sinusoidal AC line crosses zero volts. This process consumes less than 5 mW and eliminates the need for 10 or more discrete components, which would burn 50 to 100 mW continuously.

LinkSwitch-TNZ Product Family

LinkSwitch-TNZ ICs combine offline power conversion and lossless zero-cross detection in a compact SO-8C package. They can be used for non-isolated buck and buck-boost power supplies with up to 575 mA output current and can provide up to 12 W output for universal input isolated flyback designs.

Devices such as smoke detectors, smart alarms, security systems and plugs connect and disconnect the AC line periodically using a relay or TRIAC. Some applications also require an auxiliary power supply for functions such as wireless connectivity, gate drivers, sensors and displays. LinkSwitch-TNZ based designs are more flexible than discrete implementations, reducing component count by 40% or more.

Key Features

• Lossless zero-cross signal generation
• Supports buck, buck-boost and flyback topologies
• Selectable device current limit
• Allows the use of low-cost off-the-shelf inductors
• Frequency jittering reduces EMI filter complexity
• Enhanced safety and reliability features
• Reduces size and cost of magnetics and output capacitor
• 725 V MOSFET rating for excellent surge withstand
• Enables <150 µA leakage in 2-wire no neutral designs
• Allows designs that easily meets all global energy efficiency regulations

• Up to 92% efficiency
• Up to 40% lower component count compared to traditional solutions
• Greatly reduced BOM with integrated MOSEFET and controller
• Design flexibility and simplicity
• No heat sinks needed
• Full safety and regulatory compliance

PI’s Design Services

• Full schematic design, BOM, transformer design, PCB layout, hardware builds, prototype designing and testing, EMI testing, and all types of pre-compliance testing.
• From simple data sheet questions to complex design challenges, get support directly from our engineers. PowerPros is an online tech support service that enables power-supply designers to talk directly with members of our applications engineering team 24 hours a day, six days a week, anywhere in the world.