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      Company News

      PoE power supply option

      source: Shanghai Biaojun Electronic Technology Co., Ltd. time: 2018-08-29

        With the development of technology, many of the cameras currently used support PoE power supply. In network monitoring construction, in order to reduce wiring costs and be more convenient and fast, most engineering companies will consider PoE power supply.

        However, the engineering company who first contacted the PoE power supply may not know much about the PoE switch, and they don't know how to choose it. They don't know how many cameras a PoE switch can supply. Dongguan small ear power supply for PoE switches and PoE power supply, specially organized the following points for everyone to understand.

        Learn about PoE switches

        First, PoE Introduction

        POE (Power Over Ethernet) refers to some IP-based terminals (such as IP phones, WLAN access points APs, network cameras) without any changes to the existing Ethernet Cat.5 cabling infrastructure. When transmitting data signals, it can also provide DC power for such devices. It is a switch that supports Power over Ethernet.

        POE is also known as POL (Power over LAN) or Active Ethernet, and is sometimes referred to as Power over Ethernet. This is the simultaneous transmission of data using existing standard Ethernet transmission cables. The latest standard specification for electrical power and maintains compatibility with existing Ethernet systems and users.

        Second, the work process

        1 Detection: At first, the PoE switch outputs a small voltage on the port until it detects that the cable terminal is connected to a powered-end device that supports the IEEE802.3af standard.

        2PD device classification: After detecting the PD device PD, the PoE switch may classify the PD device and evaluate the power loss required by the PD device.

        3 Start power supply: During the start-up period of a configurable time (generally less than 15μs), the poe switch starts to supply power from the low voltage to the PD device until it supplies 48V DC power.

        4 Power supply: Provides stable and reliable 48V DC power for the PD device to meet the power consumption of the PD device that does not exceed 15.4W.

        5 Power failure: If the PD device is disconnected from the network, the poe switch will stop powering the PD device quickly (usually within 300 to 400 ms) and repeat the detection process to detect whether the cable terminal is connected to the PD device.

        Third, the system constitutes

        A complete POE system includes two parts: Power Sourcing Equipment (PSE) and Powered Device (PD). The PSE device is a device that powers Ethernet client devices and is the administrator of the entire POE Power over Ethernet process. The PD device is a PSE load that accepts power, that is, a client device of the POE system, such as an IP phone, a network security camera, an AP, and a PDA or a mobile phone charger, etc. (actually, any power Devices up to 13W can receive the corresponding power from the RJ45 socket. Based on the IEEE 802.3af standard, the two establish information about the connection status, device type, and power consumption level of the PD of the powered device, and use this as the power supply to the PD through the Ethernet.

        Fourth, the power supply method

        1. A type of "Mid-Span" that uses a separate PoE-powered device that is connected between a switch and a PoE-capable terminal device, typically using unused idleness in the Ethernet cable. Wire pairs to transmit DC power. MidspanPSE is a dedicated power management device that is usually placed with the switch. It has two RJ45 jacks for each port, one is connected to the switch with a short line (here, the traditional switch without PoE function), and the other is connected to the remote device.

        2. Another method is the “End-Span”, which is the outlet of the signal that integrates the power supply equipment into the switch. This type of integrated connection generally provides “dual” power supply for the idle pair and the data line pair. Features. The data line pair uses a signal isolation transformer and uses a center tap to achieve DC power supply. It is foreseeable that End-Span will be quickly promoted, because Ethernet data and transmission use a common line pair, thus eliminating the need to set up a dedicated line for independent transmission, which is only for 8-core cable and matching standard RJ The -45 socket is of great significance.

        Powered by data pin (end crossover method)

        PoE switch selection

        To see how many cameras a PoE switch can power at the same time, there are two aspects to consider: the power supply of the PoE switch and the total power of the PoE switch.

        The power supply of a 1PoE switch can be understood as the single-port power supply of a PoE switch.

        There are two power supply protocols for 2PoE switches, IEEE802.3af and IEEE802.3at.

        The IEEE802.3af standard defines a power supply of 15.4W. The IEEE802.3at standard defines a power supply of up to 30W. The power supply of a single port varies depending on the power supply standard. For example, the camera power is 9W, and the af standard PoE switch can be used; if the camera power is 20W, the at-standard PoE switch needs to be used; if the camera power is 30W or more, it needs to be powered by the dedicated PoE power supply module.

        The total power of a PoE switch is a very important indicator, which is directly related to how many cameras can be brought. Take the small ear STD-POE5203-28 monitoring dedicated POE switch as an example, STD-POE5203-28 output maximum power is 360W, the maximum number of powered cameras = POE maximum output power / camera power, such as camera power is 15W, then STD- POE5203-28 can supply the number of cameras = 24 (360 / 15); if the ball machine power is 25W, the number of ball machines that STD-POE5203-28 can supply = 14 (360 / 25).

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