Power over Ethernet (PoE) is already a common concept and is used in products such as Internet telephony, security monitoring systems, and cash registers. In this way, small network devices can be powered through the Ethernet connection and do not need to use an AC power outlet on the wall. This greatly simplifies the wiring and reduces the cost of network infrastructure construction. In addition, the local area network power supply through UPS backup can also protect the network equipment from the impact of the power failure of the power grid. For example, traditional telephones can still operate in the event of a power outage. This article will introduce the current various technologies in detail and analyze how to obtain more power from Power over Ethernet (PoE).
1. Descent Method
The descent method is a technology commonly used in DC/DC parallel power supplies. If the output voltage of the parallel power supply decreases and the load current increases, the parallel power supply will share the current. This method does not require communication between power supplies, and does not cause a single error to fail, and requires very few additional parts. If current mode control is used, only the DC gain of the control loop needs to be limited, and the output voltage drop that is proportional to the increase or decrease of the load current can be generated.
If these power supplies are connected in parallel, the output voltage will generally be adjusted by the highest output power supply when there is no load. If the power supply uses diode regulation as shown in Figure 1, the power supply with the lowest output will not output any current. As the load current increases, the output voltage begins to drop. The power supply with the highest output voltage provides all current until the output value drops to 5.25V. Then the second-highest power source starts to provide current. As the load current increases further, the first power supply may reach its limit. The remaining two power supplies are responsible for increasing the current to complete the full-power operation.
2. Staggered Flyback
The staggered method is similar to the descent method. The difference between it and the drop method is that the interleaved power stages (or phases) share a common primary side controller. This method can reduce costs. Each power stage can also be in the out of phase. Synchronize. Synchronization can reduce the ripple current of the output capacitor. So we can use a smaller output filter. In the interleaving method, all power inputs must share the same loop.
3. Use Secondary Side Load Sharing Controller to Share Power
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