Smart thermostats require a reliable temperature detection device to maintain steady room temperature. A built-in NTC temperature sensor, also known as NTC thermistor, is ideal for smart thermostat temperature detection because it is sensitive to ambient temperature change. A surface mount type NTC thermistor (TSM series) with short response time is recommended to save PCB space. For some customers, epoxy coating type NTC temperature sensor is preferred for its small size, flexible lead wire length and easy installation.
To protect the power supply circuit from current overload and transient surges, THINKING recommends the use of Metal Oxide Varistor (MOV) and Polymeric Positive Temperature Coefficient (PPTC) resettable fuse. The PPTC resettable fuse will reset itself after the fault condition being modified. To minimize consumption of PCB space, both devices are available in surface mount package. The suggested MOV (TVM-B series) is capable of absorbing high surge currents, and the PPTC (KMC series) is with fast trip time.
A rechargeable battery package can be the main power supply or a back-up power of smart thermostat. An NTC thermistor is required to monitor the li-ion battery cell temperature during charging, and to prevent overheats caused by abnormal current condition. Epoxy type, insulation film type, and surface mount type NTC thermistors are available to meet the design requirements. Also, it is critical to protect the battery pack against overcurrent events such as battery cell failure, by using a resettable surface mount PPTC device.
To protect the USB interface from the damage or risk caused by overcurrent, it is advised to utilize a SMD type PPTC resettable fuse (KMC series), especially for USB type-C ports. The USB circuit also needs to prevent damage from ESD threats and we recommend using an ESD suppressor (LCP series or ESD TVS) to protect the fragile components. The recommended ESD suppressors are with ultra-low capacitance to maintain signal integrity and are ideal for high-speed application. THINKING’s ESD suppressors are available with a wide range of working voltage and package types.
Wireless interface allows the smart thermostat to communicate with HVAC appliances and other devices; while user interface receives commend from users’ voice or direct touch. Both the wireless interfaces and user interfaces are threatened by ESD and recommended to protect by ESD suppressors (LCP series or ESD TVS).