开关电源外文文献翻译

开关电源外文文献翻译

(文档含中英文对照即英文原文和中文翻译)

外文：

Switched-mode power supply

A switched-mode power supply (also switching-mode power supply, SMPS, or simply switcher) is an electronic power supply unit (PSU) that incorporates a switching regulator. While a linear regulator maintains the desired output voltage by dissipating excess power in a pass power transistor, the switched-mode power supply switches a power transistor between saturation (full on) and cutoff (completely off) with a variable duty cycle whose average is the desired output voltage. It switches at a much-higher frequency (tens to hundreds of kHz) than that of the AC line (mains), which means that the transformer that it feeds can be much smaller than one connected directly to the line/mains. Switching creates a rectangular waveform that typically goes to the primary of the transformer; typically several secondaries feed rectifiers, series inductors, and filter capacitors to provide various DC outputs with low ripple.

The main advantage of this method is greater efficiency because the switching transistor dissipates little power in the saturated state and the off state compared to the semiconducting state (active region). Other advantages include smaller size and lighter weight (from the elimination of low frequency transformers which have a high weight) and lower heat generation due to higher efficiency. Disadvantages include greater complexity, the generation of high amplitude, high frequency energy that the low-pass filter must block to avoid electromagnetic interference (EMI), and a ripple voltage at the switching frequency and the harmonic frequencies thereof.

A note about terminology

Although the term "power supply" has been in use since radios were first powered from the line/mains, that does not mean that it is a source of power, in the sense that a battery provides power. It is simply a device that (usually) accepts commercial AC power and provides one or more DC outputs. It would be more correctly referred to as a power converter, but long usage has established the term. Classification

SMPS can be classified into four types according to the input and output waveforms: AC in, DC out: rectifier, off-line converter input stage

DC in, DC out: voltage converter, or current converter, or DC to DC converter

AC in, AC out: frequency changer, cycloconverter, transformer

DC in, AC out: inverter

Input rectifier stage

If the SMPS has an AC input, then the first stage is to convert the input to DC. This is called rectification. The rectifier circuit can be configured as a voltage doubler by the addition of a switch operated either manually or automatically. This is a feature of larger supplies to permit operation from nominally 120 volt or 240 volt supplies. The rectifier produces an unregulated DC voltage which is then sent to a large filter capacitor. The current drawn from the mains supply by this rectifier circuit occurs in short pulses around the AC voltage peaks. These pulses have significant high frequency energy which reduces the power factor. Special control techniques can be employed by the following SMPS to force the average input current to follow the sinusoidal shape of the AC input voltage thus the designer should try correcting the power factor. An SMPS with a DC input does not require this stage. An SMPS designed for AC input can often be run from a DC supply (for 230V AC this would be 330V DC), as the DC passes through the rectifier stage unchanged. It's however

advisable to consult the manual before trying this, though most supplies are quite capable of such operation even though nothing is mentioned in the documentation. However, this type of use may be harmful to the rectifier stage as it will only utilize half of diodes in the rectifier for the full load. This may result in overheating of these components, and cause them to fail prematurely.

If an input range switch is used, the rectifier stage is usually configured to operate as a voltage doubler when operating on the low voltage (~120 V AC) range and as a straight rectifier when operating on the high voltage (~240 V AC) range. If an input range switch is not used, then a full-wave rectifier is usually used and the downstream inverter stage is simply designed to be flexible enough to accept the wide range of dc voltages that will be produced by the rectifier stage. In higher-power SMPSs, some form of automatic range switching may be used.

Inverter stage

The inverter stage converts DC, whether directly from the input or from the rectifier stage described above, to AC by running it through a power oscillator, whose output transformer is very small with few windings at a frequency of tens or hundreds of kilohertz (kHz). The frequency is usually chosen to be above 20 kHz, to make it inaudible to humans. The output voltage is optically coupled to the input and thus very tightly controlled. The switching is implemented as a multistage (to achieve high gain) MOSFET amplifier. MOSFETs are a type of transistor with a low on-resistance and a high current-handling capacity. Since only the last stage has a large duty cycle, previous stages can be implemented by bipolar transistors leading to roughly the same efficiency. The second last stage needs to be of a complementary design, where one transistor charges the last MOSFET and another one discharges the MOSFET. A design using a resistor would run idle most of the time and reduce efficiency. All earlier stages do not weight into efficiency because power decreases by a factor of 10 for every stage (going backwards) and thus the earlier stages are responsible for at most 1% of the efficiency. This section refers to the block marked Chopper in the block diagram.

V oltage converter and output rectifier

If the output is required to be isolated from the input, as is usually the case in mains power supplies, the inverted AC is used to drive the primary winding of a high-frequency transformer. This converts the voltage up or down to the required output level on its secondary winding. The output transformer in the block diagram

serves this purpose.

If a DC output is required, the AC output from the transformer is rectified. For output voltages above ten volts or so, ordinary silicon diodes are commonly used. For lower voltages, Schottky diodes are commonly used as the rectifier elements; they have the advantages of faster recovery times than silicon diodes (allowing low-loss operation at higher frequencies) and a lower voltage drop when conducting. For even lower output voltages, MOSFETs may be used as synchronous rectifiers; compared to Schottky diodes, these have even lower conducting state voltage drops.

The rectified output is then smoothed by a filter consisting of inductors and capacitors. For higher switching frequencies, components with lower capacitance and inductance are needed.

Simpler, non-isolated power supplies contain an inductor instead of a transformer. This type includes boost converters, buck converters, and the so called buck-boost converters. These belong to the simplest class of single input, single output converters which utilize one inductor and one active switch. The buck converter reduces the input voltage in direct proportion to the ratio of conductive time to the total switching period, called the duty cycle. For example an ideal buck converter with a 10 V input operating at a 50% duty cycle will produce an average output voltage of 5 V. A feedback control loop is employed to regulate the output voltage by varying the duty cycle to compensate for variations in input voltage. The output voltage of a boost converter is always greater than the input voltage and the buck-boost output voltage is inverted but can be greater than, equal to, or less than the magnitude of its input voltage. There are many variations and extensions to this class of converters but these three form the basis of almost all isolated and non-isolated DC to DC converters. By adding a second inductor the ?uk and SEPIC converters can be implemented, or, by adding additional active switches, various bridge converters can be realised.

Other types of SMPSs use a capacitor-diode voltage multiplier instead of inductors and transformers. These are mostly used for generating high voltages at low currents (Cockcroft-Walton generator). The low voltage variant is called charge pump. Regulation

A feedback circuit monitors the output voltage and compares it with a reference voltage, which is set manually or electronically to the desired output. If there is an error in the output voltage, the feedback circuit compensates by adjusting the timing with which the MOSFETs are switched on and off. This part of the power supply is called the switching regulator. The Chopper controller shown in the block diagram

serves this purpose. Depending on design/safety requirements, the controller may or may not contain an isolation mechanism (such as opto-couplers) to isolate it from the DC output. Switching supplies in computers, TVs and VCRs have these opto-couplers to tightly control the output voltage.

Open-loop regulators do not have a feedback circuit. Instead, they rely on feeding a constant voltage to the input of the transformer or inductor, and assume that the output will be correct. Regulated designs compensate for the parasitic capacitance of the transformer or coil. Monopolar designs also compensate for the magnetic hysteresis of the core.

The feedback circuit needs power to run before it can generate power, so an additional non-switching power-supply for stand-by is added.

Transformer design

SMPS transformers run at high frequency. Most of the cost savings (and space savings) in off-line power supplies come from the fact that a high frequency transformer is much smaller than the 50/60 Hz transformers formerly used.

There are several differences in the design of transformers for 50 Hz vs 500 kHz. Firstly a low frequency transformer usually transfers energy through its core (soft iron), while the (usually ferrite) core of a high frequency transformer limits leakage. Since the waveforms in a SMPS are generally high speed (PWM square waves), the wiring must be capable of supporting high harmonics of the base frequency due to the skin effect, which is a major source of power loss.

Power factor

Simple off-line switched mode power supplies incorporate a simple full wave rectifier connected to a large energy storing capacitor. Such SMPSs draw current from the AC line in short pulses when the mains instantaneous voltage exceeds the voltage across this capacitor. During the remaining portion of the AC cycle the capacitor provides energy to the power supply.

As a result, the input current of such basic switched mode power supplies has high harmonic content and relatively low power factor. This creates extra load on utility lines, increases heating of the utility transformers and standard AC electric motors, and may cause stability problems in some applications such as in emergency generator systems or aircraft generators. Harmonics can be removed through the use of filter banks but the filtering is expensive, and the power utility may require a business with a very low power factor to purchase and install the filtering onsite.

In 2001 the European Union put into effect the standard IEC/EN61000-3-2 to set limits on the harmonics of the AC input current up to the 40th harmonic for equipment above 75 W. The standard defines four classes of equipment depending on its type and current waveform. The most rigorous limits (class D) are established for personal computers, computer monitors, and TV receivers. In order to comply with these requirements modern switched-mode power supplies normally include an additional power factor correction (PFC) stage.

Putting a current regulated boost chopper stage after the off-line rectifier (to charge the storage capacitor) can help correct the power factor, but increases the complexity (and cost).

Quasiresonant ZCS/ZVS

A quasiresonant ZCS/ZVS switch (Zero Current/Zero V oltage) is a design where "each switch cycle delivers a quantized 'packet' of energy to the converter output, and switch turn-on and turn-off occurs at zero current and voltage, resulting in an essentially lossless switch."

Efficiency

Higher input voltage and synchronous rectification mode makes the conversion process more efficient. Higher switch frequency allows component size to be shrunk, but suffer from radio frequency (RF) properties on the other hand. The power consumption of the controller also has to be taken into account.

Applications

Switched-mode PSUs in domestic products such as personal computers often have universal inputs, meaning that they can accept power from most mains supplies throughout the world, with rated frequencies from 50 Hz to 60 Hz and voltages from 100 V to 240 V (although a manual voltage range switch may be required). In practice they will operate from a much wider frequency range and often from a DC supply as well. In 2006, at an Intel Developers Forum, Google engineers proposed the use of a single 12 V supply inside PCs, due to the high efficiency of switch mode supplies directly on the PCB.

Most modern desktop and laptop computers already have a DC-DC converter on the motherboard, to step down the voltage from the PSU or the battery to the CPU core voltage, as low as 0.8 V for a low voltage CPU to 1.2-1.5 V for a desktop CPU as of 2007. Most laptop computers also have a DC-AC inverter to step up the voltage from the battery to drive the backlight, typically around 1000 Vrms.

Certain applications, such as in automobile industry where ordinary cars often use 12 V DC and in some industrial settings, DC supply is chosen to avoid hum and interference and ease the integration of capacitors and batteries used to buffer the voltage. Most small aircraft use 28 V DC, but larger aircraft like Boeing-747 often use up to 90 kV A 3-phase at 200 V AC 400 Hz, though they often have a DC bus as well. Even fighter planes like F-16 use 400 Hz power. The MD-81 airplane has an 115/200 V 400 Hz AC and 28 V DC power system generated by three 40 kV A AC generators. Helicopters also use the 28 V DC system. Some submarines like the Soviet Alfa class submarine utilized two synchronous generators providing a variable three-phase current, 2 x 1500 kW, 400 V, 400 Hz. The space shuttle uses three fuel cells generating 30 - 36 V DC. Some is converted into 400 Hz AC power and 28 V DC power. The International Space Station uses 120 V DC power. Larger trucks uses 24 V DC.

See also: Avionics, Airplane ground support

In the case of TV sets, for example, one can test the excellent regulation of the power supply by using a variac. For example, in some models made by Philips, the power supply starts when the voltage reaches around 90 volts. From there, one can change the voltage with the variac, and go as low as 40 volts and as high as 260 (known such case that voltage was 360), and the image will show absolutely no alterations.

Terminology

The term switchmode was widely used until Motorola trademarked SWITCHMODE(TM), for products aimed at the switching-mode power supply market, and started to enforce their trademark.

翻译：

开关模式电源

开关模式电源（也开关式电源，开关电源，或只是交换机）是一种电子电源供应器（电源），包含了开关稳压器。虽然线性稳压保持理想的输出电压超过电源的耗散在通过功率晶体管的开关模式电源开关功率晶体管饱和度之间，并断开（完全关闭），可变占空比是其平均理想的输出电压。它的开关在一个非常高的频率（几十甚至几百千赫）比交流的频率要高，相当于变压器，可充当远距离传输电源。创建一个矩形开关波形，通常涉及到的主要的变压器;通常几个二级整流器，一系列电感、电容和滤波提供各种直流输出低纹波。

主要利用这一方法提高效率，因为开关晶体管功耗小、功率大，半导体为关闭状态（有源区）。其他优势包括更小的尺寸和较轻的重量（从消除低频变压器具有高体重）和低热量的产生，还有更高的效率。缺点包括更大的复杂性，产生高振幅，高频率能量，必须加低通滤波器，以避免电磁干扰（ EMI ）之类，和纹波电压的开关频率和谐波频率不足。

有关术语的说明

虽然“电源一词”开始出现于无线电的供电线路/主干线，这并不意味着它是力量的源泉，而是作为一个电池提供电源。这是一个这直接由公网交流供电，提供一个或多个直流输出的设备。更确切地可将其称为电源转换器，但可长时间不间断使用。

分类

开关电源可分为四种类型根据输入和输出波形：

交流——直流：整流器，离线转换器输入级

直流——直流：电压转换器，或电流转换器，或直流对直流转换器

交流——交流：变频器，变频，变压

直流——交流：逆变器

输入整流器阶段

如果有一个开关电源AC输入，然后在第一阶段把交流变成直流输出。这就是所谓的整流。整流电路可配置一个电压倍增，增加了一个开关操作手动或自动。这是一个较大的特点，这类产品允许用电范围从120V到240V。整流器产生稳压直流电压，然后通过一个大型滤波电容器。目前从电源的这一整流电路中出现的短脉冲交流电压峰值来看。这些脉冲产生重大的高频能量，从而降低了功率因数。特别控制技术可以采用下列开关电源，以迫使平均输入电流跟踪正弦形状的交流输入电压，因此，设计师应设法纠正功率因数。一个开关电源与DC输入并不需要这个阶段。一个开关电源设计的AC输入然后变为直流供电（将230V交流变为330V直流），直流经过整流阶段不变。这是可取的协商，但该手册在尝试此动作，尽管大多数供应是有相当的能力等操作，即使没有提到的文件中。然而，这种类型的使用可能有害整流阶段，因为它只能利用二极管整流的满负荷的一半。这可能导致器件过热，并导致电源受到损害。

如果开关电源在输入范围内使用，整流器阶段通常配置一个电压补偿作业时的低电压（~120VAC）范围和作为直整流作业时的高电压（~240VAC）的范围。如果开关电源没有在输入范围内使用，而是为了有足够的灵活性采用全波整流的下游逆变阶段，以通过整流器产生广泛的直流电压。在高功率开关模式电源，有些可以作为自动开关来使用。

逆变阶段

逆变直流转换阶段，无论是直接输入或从整流阶段输入，要变为交流需要通过一个电源振荡器，其输出变压器有很少的绕组，频率为几十或几百千赫（ kHz ）。频率通常选择将超过20千赫，使人们察觉不到。输出电压是光耦合输入，从而可以非常严格的控制。开关是实施一个多倍放大能力（以实现高增益）的MOSFET。 MOSFET的是一种有低导通、高电流能力的晶体管。因为只有最后一个阶段有一个大的占空比，可在前几个阶段实施双极晶体管导致大致相同的效率。第二个最后阶段需要一个相辅相成的设计，在一个晶体管后接一个相同的MOSFET和一个放电MOSFET的。设计使用一个电阻可以运行大部分的空闲时间，降低效率。所有早期阶段不能达到很好的效率，因为每一个阶段功耗都会降低了10倍，从而早期阶段负责最多产生1％的效率。

电压转换器和输出整流器

如果输出要与输入分开，常常作为工作电路提供主电源。逆变交流是用来驱动主要绕组的高频变压器。这种转换的电压上升或下降到所需的输出电平可在其二次绕组。

如果需要输出直流，纠正变压器输出的交流。输出电压为10伏或10V以上的话，常用普通硅二极管。对于较低的电压，肖特基二极管时常用的整流元件;它的优势，恢复时间比硅二极管更快（允许低损耗运行在更高的频率）和可以在电压下降时进行。甚至输出电压更低的MOSFET可作为同步整流器;与肖特基二极管相比，它们可将电压控制在较低范围。

经过整流后的电压输出较平滑，然后通过一个电感器和电容器组成的过滤器。对于更高的开关频率，较低的电容和电感元件是必要的。

简单的说，非隔离式电源包含一个电感，而不是变压器。这种类型的电源包括升压转换器，降压转换器，以及所谓的升压转换器。这些属于最简单的一类单输入，单输出转换器，它利用一个电感器和一个有效的开关。降低的降压转换器的输入电压的比率传导时间与总开关期间成正比，这就是所谓的占空比。例如，一个理想的降压转换器与输入为10 V运行在50 ％占空比，将产生平均输出为5V电压。反馈控制回路是用来调节输出电压，通过改变占空比来弥补投入的变化电压。输出电压的升压转换器总是大于输入电压的升压输出电压反转，但可能大于，等于或小于其规模输入电压。这一类的转换器有许多的变化和扩展，但是这三种形式都是基于几乎所有的隔离和非隔离式DC直流转换器。通过增加第二个电感的CUK和SEPIC整流器，或者通过增加额外的积极开关，各种桥变换器可以实现。

其他类型的开关模式电源是使用电容二极管电压倍增而不是电感器和变压器。这些都是主要用于产生高电压低电流（克罗夫特-沃尔顿发电机）。低电压变异被称为电荷泵。

条例

监测反馈电路的输出电压，并与它的参考电压相比较，期望设置手动的或电子的输出。如果有一个错误的输出电压，反馈电路补偿调整的时机与该MOSFET 的是接通或关断。这部分的电力供应被称为开关稳压器。根据安全设计的要求，控制器可能不会只包含一个孤立的隔离机制（如光耦合器）直流输出。电脑，电