一种应用于PD的高精度限流保护调节电路

在POE(PowerOverEthernet)系统的终端受电设备中,限流保护调节电路保证了其稳定可靠工作。根据IEEE802.3af标准规定,受电设备开关电源启动到正常工作的过程中,电流要限制在100mA以内,在正常工作情况下电流要限制在390mA以下。本设计通过栅源比例电阻使采样功率管栅源电压与输出功率管的栅源电压保持一致,采样功率管精确采样输出功率管的电流值,采样电流经栅源比例电阻转换为电压后,调节输出功率管栅源电压,来完成PD(PowerDevice)限流保护。

A high precision current limiting protection control circuit applied in PD

Current-limiting protection circuit ensures Power Device＇ s stable and reliable work in POE （ Power Over Ethernet ） system. According to IEEE802.3af standard, the current of the switching power supply of Power Device should he limited below 100 mA during the process from starlup to normal operation, and lhe current under normal operating conditions should be less than 390 mA. In this design, gate-source ratio resisters are used to keep the gate-source voltage of the sampling and the output power transistors close. The sampling power transistor samples the current value of the output power transistor accurately. After the sampling current being converted to voltage by gate-source ratio resisters, the gate-source voltage of the output power transistor is adjusted to accomplish the function of PD （ Power Device ） current-limiting protection.