Poe power supply has the following advantages: convenient installation and expansion: network cable transmits signal and power, and there is no need to configure power interface around PD equipment remote management: one PSE device provides power for multiple PD devices, which is convenient for remote power management low cost: signal line and power line are combined into one, eliminating one power line, so network cable is not only the carrier of signal transmission, It also plays the role of power transmission, so the wiring cost is reduced good compatibility: it is not limited by the power grid standards of various countries, and the unified Poe protocol ensures that PD equipment can be compatible with any PSE worldwide
From the perspective of circuit architecture, the PSE on the left transmits DC 44-57v to PD, and the PD on the right cooperates with step-down circuit to convert the power supply into required power. PSE and PD are connected through RJ45 interface and up to 100m twisted pair.
IEEE 802.3af, IEEE 802.3at and
Ieee802.3bt three Ethernet power supply standards. In particular, the IEEE 802.3bt standard was released in 2019, which greatly increased the power supplied by Poe. PSE provides 90W power. After passing through 100m network cable, the received power of PD reaches 71w. This class 8 power level is mainly used in the power supply system of small base stations. Moreover, 802.3bt standard is downward compatible with 802.3af and 802.3at standards; When the 802.3bt PD is connected to the low-power 802.3af and 802.3at PSE, it will work in the low-power state, that is, "degraded".
In this process, the lower power PD is connected to the higher power PSE, and the equipment is not damaged. The following handshake process is mainly experienced when the PSE supplies power to the PD:
Pictures from the Internet
The picture comes from the network, and the chart comes from the inside of shunluo
In the circuit architecture of PD equipment, three parameters are mainly concerned: size, efficiency and EMC. Then how to connect the requirements of PD equipment and the design requirements of transformer.
//3.1 optimized size
key points of design 1: reduce the size of the transformer with high frequency. In a circuit board, it can be seen that the larger the volume is the transformer, so reducing the size of the transformer can save the size of the board. High frequency can reduce the size of transformer and power transmission of transformer, so the frequency from 200 kHz to 300 kHz to 500 kHz can reduce the volume of transformer. Design point 2: CCM working mode reduces device size design point 3: primary side feedback reduces size
Pictures from the Internet
3.2 improving efficiency
EMC measures the interference of noise source on sensitive equipment, including conduction and radiation composition. On the one hand, reduce the interference source, on the other hand, optimize the coupling path.
In order to reduce EMI, first confirm the noise source in the circuit. The noise source is divided into conduction noise source and radiation noise source. The conducted noise source is generally low-frequency noise within 30MHz, which is generated by the change of electric field; The conduction noise source is mainly the switching action of the power tube, which will lead to the sudden change of MOS source level voltage, which will lead to the transformer transmitting the sudden change of voltage to the secondary side. Increasing the driving resistance of MOS can reduce the switching speed, but the driving loss will increase; Or increase the absorption circuit to reduce the high-frequency oscillation. Stray parameters of transformer have a great impact on EMI. For example, transformer CP (primary winding electric field) affects voltage spike and current ripple.
The radiated noise source is the noise above 30m, which is the interference of spatial magnetic field and consists of high-frequency current loop. High frequency loop refers to the primary side loop and secondary side loop of transformer. During PCB layout, the loop path should be reduced to reduce noise, or small capacitance in parallel should be added.
3.3 shunluo electronic transformer
Shunluo electronics has a strong transformer design team. In the transformer design of Poe power supply, it comprehensively optimizes the transformer design from the perspective of size, efficiency and EMC to meet the customized needs of customers. Shunluo electronics has a fully automatic transformer production line to ensure the reliability and consistency of products and short delivery cycle. You are welcome to place an order.
Editing: JQ
Bao’an District Shenzhen City, China
+86 189 3806 5764
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