POE4W2X12

更新时间： 2024-11-28 12:58:43

品牌	Logo	应用领域
库柏 - COOPER		变压器 SMPS变压器开关以太网
页数	文件大小	规格书
4页	313K
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POE4W2X12 数据手册

Power-over-Ethernet (PoE) Application Notes

PoE - the Cost-Effective Means of Power Supply

In addition to data communications between the two devices, Power-

over-Ethernet (PoE) enables an Ethernet Switch/Hub to power a

remote device over an existing LAN cable. Without PoE, any remote

device needs to be powered independently. Typically, device power is

derived from an AC-DC adapter or at board level inside the device.

This adds cost and requires locating the device near a source of AC

power.

Device installation is further complicated by different safety codes,

AC voltages and wall plugs around the world. PoE avoids these

problems by supplying low-voltage DC power directly to the Powered

Device (PD) from the Power Sourcing Equipment (PSE) that is located

in the Ethernet Switcher or mid-span Hub and eliminates the

complexity of AC power sources.

Converter Topology Choices: Flyback Vs. Forward

To ensure that all equipment is protected and devices operate

Flyback or forward converter topologies are normally used in a

properly when connected, the IEEE established a universal standard

powered device DC-DC converter, depending on the PD’s voltage and

current requirements.

(IEEE802.3af). This specifies the power requirements of the PSE and

the PD, and the communication protocol between the two -

regardless of manufacturer or configuration.

Flyback Topology (See Figure 1)

Traditional Power-over-Ethernet

Benefit: Lowest cost for <6A output currents.

The 12.95W power limit was adequate for IP telephony when

IEEE802.3af was initially approved in 2003. Network cameras, were

initially the most prevalent application enabled by the Power-over-

Ethernet standard.

When to Use: Typically for output voltages greater than 2.5V.

Recommended for multi-output, voltages (>12V) and for applications

requiring lowest cost.

Advantages:

However, the popularization of WLAN applications triggered

developers’ and marketers’ inventiveness for creating more power-

hungry derivative devices, such as Video IP Phones, Multi-channel

WLAN Access Points (like the ones in the IEEE802.11n upcoming

MIMO standard) and Pan-Tilt-Zoom IP Cameras.

• Output isolated from input.

• No output inductor required.

Disadvantages:

Higher output ripple current results in higher output capacitor cost

and medium efficiency due to higher peak and rms currents.

All these devices typically require between 13W and 30W - more

than the normally available 13W.

Enhancing Power-over-Ethernet

Input

Output

In December, 2004, the IEEE802 established a PoEPlus group to

study the market needs and possible technical solutions to address

higher power applications while maintaining backward compatibility

with the original standard. In September, 2005, the group set and

approved, as binding, objectives for the IEEE802.3at Power-over-

Ethernet Enhancements. One of the main objectives was providing

maximum power to PDs as allowed within practical limits of at least

30W.

Vin

Figure 1. Transformer Flyback Topology

12 3 4

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与POE4W2X12相关器件

型号	品牌	获取价格	描述	数据表
POE4W2X12-R	COOPER	获取价格	Power-over-Ethernet (PoE) Application Notes
POE4W3X3.3	COOPER	获取价格	SMPS Transformer, 4W
POE4W3X3.3-R	COOPER	获取价格	Power-over-Ethernet (PoE) Application Notes
POE4W3X5.0-R	COOPER	获取价格	Power-over-Ethernet (PoE) Application Notes
POE-4x18i	LSTD	获取价格	Remote networking equipment
POE-4x24i	LSTD	获取价格	Remote networking equipment
POE-4x48	LSTD	获取价格	Remote networking equipment
POE-4x48i	LSTD	获取价格	Remote networking equipment
POE-4X48I-AF	LSTD	获取价格	Remote networking equipment
POE-4x48i-AFI	LSTD	获取价格	Remote networking equipment

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