Maxim MAX5974A PoE应用参考设计

Maxim公司的MAX5974A/MAX5974B/ MAX5974C/MAX5974D是宽输入电压的电流模式正向电源转换器，主要用于PoE的受电设备（PD）。MAX5974A/MAX5974C适合通用或电信输入电压，而MAX5974B/ MAX5974D输入电压低到10.5V，器件内部提供1%的误差放大器，可编开关频率从100kHz到600kHz，主要用在PoE IEEE® 802.3af/at受电设备，大功率PD(Beyond the 802.3af/at Standard)，有源箝位的正向DC/DC转换器，IP电话，无线接入点，安检照相机。本文介绍MAX5974A/B/C/D主要特性，方块图，典型应用电路图，以及PoE应用参考设计指标和电路图。

The MAX5974_ provide control for wide-input-voltage, active-clamped, current-mode PWM, forward converters in Power-over-Ethernet (PoE) powered device (PD) applications.

The MAX5974A/MAX5974C are well-suited for universal or telecom input range, while the MAX5974B/ MAX5974D also accommodate low input voltage down to 10.5V.

The devices include several features to enhance supply efficiency. The AUX driver recycles magnetizing current instead of wasting it in a dissipative clamp circuit. Programmable dead time between the AUX and main driver allows for zero-voltage switching (ZVS). Under lightload conditions, the devices reduce the switching frequency(frequency foldback) to reduce switching losses.
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