What Is PoE, and Why Use It for High Power Applications?

The latest standard for Power over Ethernet (PoE) applications is IEEE 802.3bt. Ratified in September 2018, this new standard increases the maximum power device (PD) power available by utilizing all four pairs of wire available in a CAT5e cable.

To learn the ins and outs of this latest technology, we interviewed Swaroop Vaidyanath, Product Manager for PoE products at Wurth Electronics. Here is what Mr. Vaidyanath had to share!

What is PoE?

PoE stands for Power over Ethernet. This technology is used to send both data and power over a single CAT5e ethernet cable. IP phones, security cameras, and wireless access points are some popular examples powered with this technology.

What are the advantages of PoE?

  • It is cost effective. A single PoE cable takes care of both powering and transmitting data to the devices. For example, CAT5e cables could be used in the future to power LED lights in your house, and an electrician would not be needed for its installation.
  • It has fewer limitations. Installation of PoE devices such as security cameras at inaccessible locations is possible and no longer limited to the location of AC mains.
  • It is a mature and growing technology. PoE is very reliable, as power sourcing equipment (PSE) and powered devices (PDs) have current limiters. PSE only delivers and monitors the power requested by the PD.

What are PSE and PD?

PSE stands for power sourcing equipment. These switches or midspans provide source power on the CAT5e cable, as shown in Figure 1.

This power is delivered to a PD, or powered device, such as an IP phone or security camera.

What are the different IEEE standards?

These IEEE standards define the maximum power to be transferred over Ethernet cables, the length of the cable, the max voltage, and the current that can be applied over these cables, etc. As shown in the Figure 1, the BT standard uses all four pairs of the wire in a CAT5e cable to transfer both power and data from PSE to PD.

Why do we need higher power?

With more power, more features can be added, and newer products can be developed for emerging markets.

For example, at 13W to PD, IP phones were introduced, and security cameras were just stationary units. When 25.5W was available, IP phones got video capability (VOIP); and pan, tilt, and zoom capabilities were added to security cameras. Now, with 71W available, developers are adding heating sensors and integrating fans on these cameras.

LED lighting, point-of-sale systems, video conferencing at hospitals, and industrial applications (such as motor control units and brushless drives) are all potential markets as well.

Figure 1

Can you tell us about Wurth Electronics transformers developed for PoE applications?

Sure! As shown in Figure 1, the DC-DC converter is an important block at the PD end. It uses a flyback or a forward transformer topology, depending on the PD’s voltage and current requirements.

The transformer has two important functions:

  • Stepping down the PoE input voltage to deliver power to the PDs
  • Providing isolation between the PD’s interface and the rest of the PoE circuitry

Wurth Electronics has developed a PoE series using our EPW15 package, customized for IEEE 802.3bt applications. Three of these EPW15 transformers are for flyback CCM topology and have outputs of 3.3V/8A, 5V/6A, and 12V/3A. The other three are for active clamp forward topology and have outputs of 3.3V/18A, 5V/14A, and 12V/6A. All of these EPW15 transformers work at telecom input voltage, meet UL60950 with functional insulation, and have a low profile height of 13.5mm.

We also have various PoE transformer sizes/packages customized for PWM controllers from several IC manufacturers. For low profile versions, planar transformers are favored, such as those with a max height of 10.5mm.

On behalf of the Wurth Electronics team and our readers, we’d like to thank Swaroop Vaidyanath for the introduction to PoE and for interviewing with us.

As Mr. Vaidyanath mentioned, if you would like to learn more about Power over Ethernet, please view our PoE products here!

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