The progress of Internet of things technology promotes the development of smart home security system, which can provide consumers with security, convenience and energy efficiency. New sensing technologies and wireless protocols, such as wireless local area network (Wi Fi), have created a range of devices to monitor security equipment, access control equipment, household appliances, energy management equipment, power sockets, lighting and entertainment systems. Figure 1 illustrates the breadth of IOT technology supporting smart home.
Smart home security market is a dynamic market. Unit shipments of residential security cameras are expected to increase from 54 million in 2018 to 120 million in 2023. This means a substantial compound annual growth rate (CAGR) of 17%. There are great opportunities for innovation and new products in this market.
Smart home security products need to be highly reliable to win market share. As more and more manufacturers enter the market and the degree of product differentiation is reduced, product quality will become a greater determinant for consumers. Therefore, the product needs to have high reliability against overload and transient. The following paragraphs will provide recommendations for designers of family safety systems to use and select the elements that protect and control their circuits. The components used to protect the following products will be introduced:
Wired and wireless security cameras
Wired doorbell camera
The line security camera system is usually a fixed installation security system, which is used to monitor the area around the house. Figure 2 shows the wired security camera and the recommended elements for protecting and controlling the camera. These cameras are powered by AC lines and are vulnerable to overloads and transients transmitted on AC power lines. In addition, all connections to the external environment will be affected by electrostatic discharge (ESD).
Designers will need to protect their camera circuits from these hazardous conditions. Figure 3 shows a block diagram of a wired security camera and the protection and control elements recommended to ensure product reliability.
The power adapter is connected to the AC power line and needs protection to prevent current surges and voltage transients of the power line. We recommend using fuses for overload protection, metal oxide varistors (MOVs) to protect transient current surges, and Transient Voltage Suppressors (TVS) diodes to protect transient voltages. These three elements and the parameters selected for your design will ensure high reliability of the power adapter against overload and transients.
Select slow fuse to avoid fuse damage due to switching power supply surge current. However, to avoid damaging the power adapter circuit, select a fuse that can respond quickly to continuous overload (e.g. 200% overload in a few seconds). When selecting fuse, please do not ignore other key parameters. Confirm whether the rated voltage of the fuse exceeds the maximum line voltage that the power supply can reach. Also, make sure that the breaking rating is higher than the worst-case current overload that the circuit may encounter.
Proper breaking rating will avoid physical damage to the fuse due to large instantaneous overload of AC line. Due to the limited power space, please find a small fuse that meets the requirements. Finally, UL / IEC certified fuses are used to simplify and accelerate product safety compliance certification.
For example, for large high-energy surge caused by lightning, please use metal oxide varistor (MOV) to protect the power supply. The position of the metal varistor should be as close to the input of the power supply as possible. Mov can absorb surge current up to 10 Ka and peak pulse energy of more than 500 J. Since the MOV is in contact with the power line, please use UL / IEC certified components.
The third protection element you want to consider is the transient voltage suppressor (TVS) diode, which is used to protect the downstream circuit from voltage transients. TVs diodes respond very fast to transients, less than 1ps. When suppressing transients, TVS diode clamps its output at low voltage to protect sensitive circuits. TVs diodes are available in unidirectional and bidirectional versions, with a wide clamping voltage range, up to 10V at the lowest.
