电源管理几乎在每个电子系统中都起着重要作用，因为它可以控制，调节和分发直流电源在整个系统中。因此，DC电源管理子系统可能会影响相关电子设备的可靠性，性能，成本和上市时间。
电源管理子系统使电子系统能够通过提供和控制其直流电源来正常运行。一个类比是电源管理子系统以类似于人体血管的方式起作用，该血管提供适当的营养以保持人体的生命。同样，电源管理子系统提供并控制了使电子系统保持活力的电源。
The key component of the dc power management system is the power supply that provides dc power for the associated system. The specific type of dc power management subsystem depends on its power input, which includes:
•电池输入（用于便携式设备）- 由于便携式设备的尺寸和重量限制，该电源管理子系统通常与电子系统的其余部分集成在一起。其中一些系统还包括一个交流适配器，AC适配器是一个小动力单元，可插入交流墙插座并提供直流输出电压。通常，交流适配器用于为设备供电，还可以为系统电池充电。
•交流输入– This subsystem employs a power supply that accepts an ac utility power input, rectifies and filters it, then applies the resulting dc voltage to a regulator circuit that provides a constant dc output voltage. There are a wide variety of ac-dc supplies that can have an output voltage from less than 1V to thousands of volts. This dc power management system usually employs a switch-mode power supply, although some linear supplies are available.
•DC输入– This power management subsystem employs a power supply that accepts a dc voltage input, typically 5 V, 12V, 24V, or 48 V and produces a dc output voltage. At the low end, a supply of this type can produce less than1Vdc, whereas other dc-dc supplies can produce thousands of volts dc. This power management subsystem usually employs a switch-mode power supply.
•Ultralow voltage input (energy harvesting)- 能源收集可以提供充电，补充或更换电池的动力。能量收集的关键组件是一个可以使用超低电压输入来运行的电源转换器。在运行中，该电源转换器捕获了微量的能量，积累了它，将其存储，然后将存储的能量保持为电源。低压输入可能来自太阳能，热能，风能或动能。
孤立与非分离
就它们对DC输入的响应而言，有两种类型的DC-DC转换器：隔离和非分离，这取决于是否有从输入到输出的直接DC路径。一个孤立的转换器可在输入电压和输出电压（通常使用变压器）之间进行隔离。在非分离转换器中，有一个从输入到输出的直流路径。
For some applications, non-isolated converters are appropriate. However, some applications require isolation between the input and output voltages. An advantage of the transformer-based isolation converter is that it has the ability to easily produce multiple output voltages.
Linear vs. Switch-Mode Power Supplies
DC电源管理子系统使用两种基本电源配置：线性和开关模式。线性电源始终会导致电流。这两种配置之间的差异包括尺寸和重量，功率处理能力，EMI和调节。
线性调节器的主要组件是通过晶体管，错误放大器和电压参考，如图所示图1-1. The linear regulator maintains a constant output voltage by using the error amplifier to compare a portion of the output voltage with a stable voltage reference. If the output voltage tends to increase, feedback causes the pass transistor to the lower the output voltage and vice versa.
OEM linear supplies can handle several amperes of current. They are usually bulky benchtop or rack-mounted supplies.
在大多数较旧的应用中，高电流线性供应已被开关模式供应取代。显示在图1-2是典型的隔离开关模式电源。在这里，对交流输入电压进行了整流并过滤，以获得其他电源组件的直流电压。一种广泛使用的方法使用开机和关闭时间脉冲宽度调制（PWM）来控制电源开关输出电压。时间与切换期间的比率是占空比。占空比越高，功率半导体开关的功率输出越高。
误差放大器将输出电压反馈的一部分与稳定的电压参考进行比较，以产生PWM电路的驱动器。PWM的最终驱动器控制应用于电源开关的脉冲信号的占空比，这反过来控制了电源DC输出电压。如果输出电压倾向于上升或下降，则PWM会改变占空比，从而使直流输出电压保持恒定。
An isolation circuit is required to maintain isolation between the output ground and the power supplied to the power supplies components. Usually, an optocoupler provides the isolation while permitting the feedback voltage to control the supply’s output.
电感电容器低通输出滤波器将开关电压从开关变压器转换为直流电压。过滤器不是完美的，因此总会有一些残留的输出噪声称为Ripple。涟漪的数量取决于在开关频率下低通滤波器的有效性。电源开关频率的范围在100kHz之间至1MHz以上。较高的开关频率允许在输出低通滤波器中使用较低的值电感器和电容器。但是，较高的频率也可以增加功率半导体损耗，从而降低电源效率。
The power switch is key component in the power supply in terms of power dissipation. The switch is usually a power MOSFET that operates in only two states - on and off. In the off state the power switch draws very little current and dissipates very little power. In the on state the power switch draws the maximum amount of current, but its on-resistance is low, so in most cases its power dissipation is minimal. In the transition from the on state to the off state and off to on the power switch goes through its linear region so it can consume a moderate amount of power. The total losses for the power switch is therefore the sum of the on and off state plus the transition through its linear regions. The actual losses depend on the power switch and its operating characteristics.表1-1比较隔离，AC-DC线性和开关模式电源的特性。
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