线性调节器驱动噪声降低

　　线性调节器驱动噪声降低

　　低压差稳压器（LDO）长期以来一直是降压电压转换的选择，不仅在成本是一个问题，但在噪声性能是至关重要的。

　　线性技术公司的创始人Robert Dobkin发明的，他曾在美国国家半导体的构思时，调节器的核心架构是非常简单而有效的。Dobkin把一个固定的电压调整器和适应它的输出可以使用一个分压器的输出进行调整。¹

　　在经典的线性调节器中，晶体管充当电势分配器的一半。它的输出电压是控制一个反馈电路，在MOSFET的情况下控制晶体管的门，这通常是LDO稳压器的情况。通过栅极电压反馈的恒定控制在基准电路设置的电平上提供稳定的输出电压。由于使用了分压器结构，线性调节器只能产生比输入电压低的电压。旧的稳压器电路可能会下降2 V或更多。LDO是设计来提供更容易的控制输出电压和限制这个电压差小于2 V.

　　LDO的主要变化是从一个射极跟随器拓扑到一个集电极开路或开漏拓扑结构，使晶体管能在饱和状态下工作，从而使压降降到最小。

One reason why linear regulators are not used in all cases for buck regulation is that their efficiency is poor compared to that of a switched regulator. Even when the regulator is quiescent, it passes a small amount of current that is dissipated as wasted heat. The LDO attacks the efficiency problem on one front by minimizing the difference between input and output voltage, which helps in situations where the input voltage is reasonably constant. For example, this is often the case when a linear regulator follows a switching regulator and is present primarily to provide a stable voltage to the target circuit. However, designers must account for the quiescent current that remains.