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MOSFET在DC／DC变换器中的主要效率损失
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MOSFET在DC／DC变换器中的主要效率损失
硅MOSFET已成为DC／DC转换器设计中的一个关键部件，它提供了实现高效率、脉宽调制控制策略所需的高速开关和电流处理能力。朝着更高的效率驱动将更强烈要求MOSFET，特别是在有约束的尺寸设计，减少空间的数量，可以在散热器和其他冷却援助。
这种趋势正在推动使用降低RDS（on）的MOSFET，以及通过良好的电荷存储特性提供低开关损耗。本文将讨论典型的DC / DC转换器应用中MOSFET的一些关键参数。
金属氧化物半导体场效应晶体管（MOSFET）已成为功率变换电路的关键部件。与双极电路相比，它的低电荷存储使其成为开关型DC/DC变换器中处理大功率功能的首选元件。
典型的DC / DC转换器采用两个MOSFET。一种是控制或高侧FET，如图1所示为Q1。另一种是同步或低端FET，在图1中被标记为Q2。低端FET的名称来自晶体管将电源轨连接到地上的事实。相反，高侧FET连接输入和输出电源轨。
The high- and low-side FETs are synchronized， which gives the switching converter its commonly used name of synchronous rectifier. Only one switch can be open at any one time and the controller will generally organize switching events to prevent overlap in switching between the two transistors. One transistor will be switched off before the other is allowed to turn on. This behavior prevents losses caused by cross-conduction.
As well as the nominal maximum power that the DC/DC converter can deliver， the two MOSFETs need to handle voltage spikes caused by parasitic inductances and a current level equal to the maximum output current， plus 50 percent of the ripple current. Losses from the two transistors are important. Not only will static losses from the on-resistance through the transistor cause lower efficiency， but so will losses incurred during switching. The switching losses are especially important in DC/DC architectures that employ hard switching; this is where the transistor is exposed to non-zero voltage and current during switching events.
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