器件名称: DI-70
功能描述: PoE Detection and Classification (Class 0) Interface Circuit
文件大小: 348.21KB 共2页
简 介:Design Idea DI-70 DPA-Switch PoE Detection and
Application PoE/VoIP Device DPA424P Power Output 12.94 W Input Voltage 34-57 VDC
Classication (Class 0) Interface Circuit
Output Voltage 5 V / 7.5 V / 20 V Topology Forward
Design Highlights
Simple, low-cost, discrete PoE interface circuit Low cost bipolar pass-switch: 87% efcient (Figure 5) MOSFET pass-switch: 97% efcient (Figures 2 and 5) Fully compliant with IEEE 802.3af
to identify the device class (Class 0 species 0 mA to 4 mA). This is again accomplished by resistor R51.
Bipolar Transistor Pass-Switch
In the third phase, the bipolar pass-switch (Q51 in Figure 1) connects the input voltage to the power supply at voltages above approximately 30 VDC (28 V + VR52). Zener diode VR51 conducts, driving current through resistor R52 to the base of Q51. Resistor R53 prevents turn-on under other conditions. Once the power supply has started, components D51, D52, C51 and R54 enhance the base-current drive by coupling power from the power supply bias winding.
Operation
Power over Ethernet (PoE) is becoming widely adopted for networking and (VoIP) telecom applications. A typical PD solution is shown in Figure 1, having a PoE interface circuit and a DPA-Switch DC-DC converter block (see DI-69 for full details of operation of the DC-DC converter). The PoE specication requires the PD to provide three functions: detection, classication, pass-switch connection. When an input voltage is rst applied to the PD, it must present the corr……
