The Overview of Ethernet Network
Ethernet network is the most commonly used LAN at present. The transmission rate of Fast Ethernet is 100 Mbit/s, while the transmission rate of Gigabit Ethernet is up to 1000 Mbit/s. Ethernet has the remarkable advantages of high flexibility, relatively simple and easy to implement. Its transmission medium mainly includes twisted pair, coaxial cable, optical fiber and radio. Now it has become the most important local area network.
Basic Functions of PoE Products
1.Recognition of signal impedance. When an input voltage is applied to the device, it must present the correct identification signal impedance within the specified voltage range. When an Ethernet power equipment requests power supply, it first sends a 2.5V~10V voltage signal to ethernet. When the voltage signal is detected by the power equipment, a 23750~26250 ohm resistance is placed on the power supply circuit, and the current will change with the input voltage. By detecting the current, it is confirmed that there is an effective power supply device in the Ethernet cable terminal. If the resistance is placed in the range of 1200-23750 ohms or 26250-45000 ohms, it is considered that the Ethernet electrical equipment is effective but does not need power supply. Resistance values in other ranges mean that the detected Ethernet power devices are invalid.
2. There are different types of electrical equipment, each type corresponding to a certain current. For example, the current of a "0" type electrical device is 0.5 to 4 mA. When the powered device detects a valid signal, it is classified. The specific method is to raise the voltage sent to the network link to 15.5V~20.5V, so that the Ethernet power device obtains a fixed current, and then completes the classification of the power device according to the current range.
3. There are two main types of switches for connecting Ethernet power (POE power). One is a bipolar crystal switch, which has high power efficiency and low cost. The other is a MOSFET switch, which is extremely efficient and can approach 100%.