How to choose a power supply?

Electronic products are inseparable from power supplies. There are many types of power supplies available, which bring convenience to our lives. Power supplies are devices that convert other forms of energy into electrical energy. The power source is based on the principle of "magnetic electricity", which is generated from renewable energy sources such as hydraulic power, wind power, ocean tides, dam water pressure differences, solar energy, etc., as well as burning coal, oil residue, etc. Common power sources are dry batteries (DC) and household 110V-220V AC power.

High-quality power supplies generally have multinational certification marks such as FCC, American UL, and China Great Wall. These certifications are professional standards for power supplies set by certification agencies based on technical specifications in the industry, including production processes, electromagnetic interference, safety protection, etc. Only products that meet certain indicators can use certification marks on packaging and product surfaces after applying for certification. Has a certain authority.

working principle

Generators can convert mechanical energy into electrical energy, and dry batteries can convert chemical energy into electrical energy. Generators and batteries themselves are not charged. They have positive and negative charges at their two poles. Voltage is generated by positive and negative charges (current is formed by the directional movement of charges under the action of voltage). Charges are already present in conductors to generate current. You only need to apply voltage. When the two poles of the battery are connected to a conductor, the positive and negative charges are released in order to generate current. When the charges are dissipated, the charges are discharged (voltage). Dry batteries, etc. are called power sources. A device that converts alternating current into direct current through a transformer and rectifier is called a rectified power supply. An electronic device that can provide a signal is called a signal source. The transistor can amplify the signal sent from the front and transmit the amplified signal to the subsequent circuit. The transistor can also be regarded as a signal source for the subsequent circuit. Rectified power supplies and signal sources are sometimes called power supplies.

A power supply is a device that provides power to electronic equipment, also called a power supply. It provides the power required by all components in the computer. The size of the power supply and whether the current and voltage are stable will directly affect the working performance and service life of the computer.

The computer power supply is a closed independent component installed in the main chassis. Its function is to convert alternating current into stable direct current such as 5V, -5V, +12V, -12V, +3.3V through a switching power supply transformer to supply System components such as system version, floppy disk, hard drive and various adapter expansion cards are used in the main chassis. In layman's terms, if one power supply breaks down, another backup power supply takes its place. Hardware availability can be enhanced by providing battery backup for nodes and disks. HP-supported uninterruptible power supplies (UPS), such as HP PowerTrust, protect against momentary power outages. The disks should be connected to the power supply circuits in such a way that the mirror copies are connected to different power supplies. The root disk and its corresponding node should be powered by the same power circuit. In particular, the cluster lock disk (used as an arbiter when reorganizing the cluster) should have redundant power supplies, or it can be powered by a power source external to the nodes in the cluster.

Your HP representative can provide detailed information about the cluster's power, disk, and LAN hardware layout. Many disk arrays and other rack-mounted systems today contain multiple power inputs, and they should be deployed so that the different power inputs on the device are connected to separate circuit devices with two or three power inputs, so that, generally, whenever If no more than one circuit fails, the system can continue to operate normally. Therefore, if all the hardware in the cluster has 2 or 3 power inputs, it is required to have at least three independent circuits to ensure that there is no single point of failure in the circuit design of the cluster. Generators can convert mechanical energy into electrical energy, and dry batteries can convert chemical energy into electrical energy. Generators and batteries themselves are not charged. They have positive and negative charges at their two poles. Voltage is generated by positive and negative charges (current is formed by the directional movement of charges under the action of voltage). Charges are already present in conductors to generate current. You only need to apply voltage. When the two poles of the battery are connected to a conductor, the positive and negative charges are released in order to generate current. When the charges are dissipated, the charges are discharged (voltage). Dry batteries, etc. are called power sources. A device that converts alternating current into direct current through a transformer and rectifier is called a rectified power supply. An electronic device that can provide a signal is called a signal source. The transistor can amplify the signal sent from the front and transmit the amplified signal to the subsequent circuit. The transistor can also be regarded as a signal source for the subsequent circuit. Rectified power supplies and signal sources are sometimes called power supplies.

The working process of the switching power supply is quite easy to understand. In the linear power supply, the power transistor is allowed to work in linear mode. Different from the linear power supply, the PWM switching power supply allows the power transistor to work in the on and off states. In these two states In the state, the volt-ampere product added to the power transistor is very small (when it is turned on, the voltage is low and the current is large; when it is turned off, the voltage is high and the current is small)/The volt-ampere product on the power device is the power semiconductor losses on the device.

Compared with linear power supplies, the more efficient working process of PWM switching power supplies is achieved by "chopping", that is, chopping the input DC voltage into a pulse voltage whose amplitude is equal to the input voltage amplitude. The duty cycle of the pulse is adjusted by the controller of the switching power supply. Once the input voltage has been chopped into an AC square wave, its amplitude can be increased or decreased through the transformer. By increasing the number of secondary windings of the transformer, the output voltage value can be increased. Finally, these AC waveforms are rectified and filtered to obtain the DC output voltage.

The main purpose of the controller is to keep the output voltage stable, and its working process is very similar to the linear form of the controller. This means that the controller's functional blocks, voltage reference, and error amplifier can be designed to be identical to those of a linear regulator. The difference between them is that the output of the error amplifier (error voltage) passes through a voltage/pulse width conversion unit before driving the power tube. There are two main working modes of switching power supply: forward conversion and boost conversion. Although there is little difference in the arrangement of their parts, their working processes vary greatly, and each has its own advantages in specific applications.

Power supply classification

Ordinary power supply

It can also be subdivided into: switching power supply, inverter power supply, AC stabilized power supply, DC stabilized power supply, DC/DC power supply, communication power supply, module power supply, variable frequency power supply, UPS power supply, EPS emergency power supply, purification power supply, PC power supply, Rectified power supply, customized power supply, heating power supply, welding power supply/arc power supply, electroplating power supply, network power supply, power operating power supply, adapter power supply, linear power supply, power supply controller/driver, power supply, other ordinary power supply, inverter power supply, parametric power supply , voltage-regulated power supply, transformer power supply.

Special power supply

Special power supplies can be subdivided into: shore power supplies, security power supplies, high voltage power supplies, medical power supplies, military power supplies, aerospace power supplies, laser power supplies, and other special power supplies.

Special power supply is a special type of power supply. The so-called special is mainly because the technical index requirements for measuring power supplies are different from commonly used power supplies. The main reasons are that the output voltage is particularly high, the output current is particularly large, or the stability, dynamic response and ripple requirements are particularly high, or the power supply output voltage is required. Or the current is pulse or some other requirement. This makes the design and production of this type of power supply have more special and even stricter requirements than ordinary power supplies. Special power supplies are generally designed for special loads or occasion requirements, and are widely used. Mainly include: electroplating electrolysis, anodizing, induction heating, medical equipment, electrical operation, electrical testing, environmental dust removal, air purification, food sterilization, laser infrared, photoelectric display, etc. In national defense and military fields, special power supplies have irreplaceable uses for ordinary power supplies. They are mainly used in: radar navigation, high-energy physics, plasma physics and nuclear technology research, etc.

1. High-voltage power supply for radar transmitter

In modern radar transmitters, traveling wave tubes (TWT) occupy a large proportion as microwave power amplifier components. As a high-power part, its reliability and technical indicators have a direct impact on the radar transmitter and even the entire radar. . The high-voltage power supply (system) supporting the traveling wave tube is even more important. As a high-frequency, high-efficiency power electronics technology, switching power supply technology has developed with the continuous updating of electronic components and products and the replacement of high-power devices. The high-voltage switching power supply for radar traveling wave tubes can adopt the full-bridge resonant PWM modulation method. The high-power switching device adopts advanced IGBT modules and advanced and reliable drive circuits, which makes the power supply have good overall performance, good stability, and has various protection functions. .

工作原理：将50Hz三相380V通过电网滤波器，经整流及滤波得到500多伏的直流电压，供给串联谐振变换器。由于本电源输出高达20kV，为了减轻变压器的设计难度以及减小高压整流二极管的耐压值、提高电源的可靠性，采用变压器两个次级分别全桥整流，然后叠加输出。全桥变换器由四个IGBT、一个高频变压器及整流电路组成。控制电路提供两对彼此绝缘、相位相差180°的脉冲输入到IGBT驱动电路，控制IGBT的通断。将直流电压变换成为交变的20kHz脉冲电压，经变压器及全桥整流和滤波电路，得到几十kV的电压。

2、电子束焊机用大功率高压电源

电子束焊接因具有不用焊条、不易氧化、工艺重复性好及热变形量小的优点而广泛应用于航空航天、原子能、国防及军工、汽车和电气电工仪表等众多行业。电子束焊接的基本原理是电子枪中的阴极由于直接或间接加热而发射电子，该电子在高压静电场的加速下通过电磁场的聚焦就可以形成能量密度极高的电子束，用此电子束去轰击工件，巨大的动能转化为热量，使焊接处工件熔化，形成熔池，从而实现对工件的焊接。

高压电源是设备的关键技术之一，它主要为电子枪提供加速电压，其性能好坏直接决定电子束焊接工艺和焊接质量。电子束焊机用高压电源与其它类型的高压电源相比，具有不同的技术特性，技术要求主要为纹波系数和稳定度，纹波系数要求小于1%，稳定度为±1%，甚至纹波系数小于0.5%，稳定度为±0.5%，同时重复性要求小于0.5%。以上要求均根据电子束斑和焊接工艺所决定。电子束焊机用高压电源的操作是必须与有关系统进行连锁保护，主要有真空连锁、阴极连锁、闸阀连锁、聚焦连锁等，以确保设备和人身安全。高压电源必须符合EMC标准，具有软起动功能，防止突然合闸对电源的冲击。

这种电源由于功率大(达30kW)，输出电压高(150kV)，工作频率较高(20kHz)，而对稳定精度、纹波及电压调节率均有较高的要求。选用先进的三相全控可控整流技术、大功率高频逆变器，用新型功率器件IGBT作为功率开关。三相全控可控整流和逆变器各自采用独立的控制板，IGBT驱动采用进口厚膜驱动电路，加上输入电网滤波器和平波电抗器及电容组成的滤波电路。使电源的功率变换部分具有较好的技术先进性和良好的功率变换性。

高压部分：高压变压器磁芯采用最新的非晶态材料，采用独特的高频高压绕制工艺，双高压变压器叠加工作。先进的整流和合理的倍压电路以及高压均压技术保证高压电源的高压部分稳定可靠，反馈及高压指示信号用精密的分压器，由高压输出端直接采样，保证电源有很高的稳压精度、电压调整率和准确可信的高压测量精度。采用合理的高压滤波技术，保证电源有良好的纹波。高压部分放在一个油箱内。

3、高压脉冲电源

在雷达导航设备中，其发射部分一般都需要一高电压、窄脉冲、不同重复频率的强功率脉冲源。这种强功率脉冲源一般通过一个高压电源将市电升为几千伏至几十千伏直流高压，然后由一个调制器将直流高压调制为所需脉宽及频率的脉冲源以供发射管使用。

脉冲源主要由高压电源及调制器部分组成，高压电源采用开关稳压电源，调制器采用半导体器件的固态调制器。

使用方给出的触发脉冲是TTL电平的信号，应在输入隔离变压器前增加接口电路，此接口电路一是为了预放大TTL脉冲信号，二是为了与隔离变压器匹配。为了达到隔离的目的，使用方可提供此接口电路的电源，制造方只需提出电源需求并在电路中设计相应的变换、滤波电路即可。

触发脉冲经过脉冲变压器隔离后经过预调器脉冲整形，功率放大后去触发调制板和截尾板工作。由预调器产生的激励脉冲经过变压器隔离去驱动调制板的每一只场效应管，此时调制板导通高压电源送到微波三极管的阳极，微波三极管的阴极电子开始发射，微波三极管将送入输入端的小功率高频信号放大成大功率的高频信号。当脉冲结束时，由预调器产生的截尾脉冲去触发截尾板，截尾板导通后将微波三极管的分布电容释放，所以可以得到很好的脉冲后沿。

电源IC特点

电源IC 种类繁多，共同特点有：

工作电压低：一般的工作电压为3.0～3.6V。有一些工作电压更低，如2.0、2.5、2.7V 等;也有一些工作电压为5V，还有少数12V 或28V 的特殊用途的电压源。

工作电流小：从几毫安到几安都有，但由于大多数嵌入式电子产品的工作电流小于300mA，所以30～300mA 的电源IC在品种及数量上占较大的比例。

封装尺寸小：近年来发展的便携式产品都采用贴片式器件，电源IC 也不例外，主要有SO 封装、SOT-23 封装，μMAX 封装及封装尺寸最小的SC-70 及最新的SMD 封装等，使电源占的空间越来越小。

完善的保护措施：新型电源IC 有完善的保护措施，这包括：输出过流限制、过热保护、短路保护及电池极性接反保护，使电源工作安全可靠，不易损坏。

耗电小及关闭电源功能：新型电源IC 的静态电流都较小，一般为几十μA 到几百μA。个别微功耗的线性稳压器其静态电流仅1.1μA。另外，不少电源IC 有关闭电源控制端功能(用电平来控制)，在关闭电源状态时IC 自身耗电在1μA 左右。由于它可使一部分电路不工作，可大大节省电能。例如，在无线通信设备上，在发送状态时可关闭接收电路;在未接收到信号时可关闭显示电路等。

有电源工作状态信号输出：不少便携式电子产品中有单片机，在电源因过热或电池低电压而使输出电压下降一定百分数时，电源IC 有一个电源工作状态信号输给单片机，使单片机复位。利用这个信号也可以做成电源工作状态指示(当电池低电压时，有LED 显示)。

输出电压精度高：一般的输出电压精度为±2～4%之间，有不少新型电源IC 的精度可达±0.5～±1%;并且输出电压温度系数较小，一般在±0.3～±0.5mV/℃，而有一些可达到±0.1mV/℃的水平。线性调整率一般为0.05%～0.1%/V，有的可达0.01%/V;负载调整率一般为0.3～0.5%/mA，有的可达0.01%/mA。

新型组合式电源IC：升压式DC/DC 变换器的效率高但纹波及噪声电压较大，低压差线性稳压器效率低但噪声最小，这两者结合组成的双输出电源IC 可较好地解决效率及噪声的问题。例如，数字电路部分采用升压式DC/DC 变换器电源而对噪声敏感的电路采用LDO 电源。这种电源IC 有MAX710/711，MAX1705/1706 等。另一种例子是电荷泵+LDO 组成，输出稳压的电荷泵电源IC，例如MAX868，它可输出0～-2VIN 可调的稳定电压，并可提供30mA 电流;MAX1673稳压型电荷泵电源IC 输出与VIN 相同的负压，输出电流可达125mA。

1 电源评测主要看哪些

目前市场中大部分电源的拓扑结构相同，一款电源往往由5部分组成，分别是电源市电接入口的设计叫做一级EMI，在一级EMI旁边的是二级EMI，电容一次的部分是一次侧设计(高压滤波电路)，在电源的中间是变压器部分，在电源的最右边是电源输出电路设计这里叫做二次侧(低压滤波部分)。玩家们使用的电源大部分都是采用了这样的结构设计，下面我们来具体聊聊有关电源内每一处的设计。

In fact, the most important thing in the design of these components of the power supply is filtering. The MWI design of the power supply is the first filtering effect on the mains power. The main purpose is to filter out high-frequency clutter and interference signals. If there is no EMI filtered power supply, this pair of power supplies will cause electromagnetic radiation and affect the use of the entire platform. At the same time, we know that the electromagnetic waves of the power supply can also cause harm to the human body. The EMI design in the power supply can actually prevent electromagnetic radiation from leaking to the outside.

2 Better EMI filtering effect

The EMI design of the power supply is essential. At present, the EMI design of the mainstream power supply is directly welded on the circuit. We can see the circuit connecting the power cord and the power supply through the picture. Many power supplies here use yellow squares and blue components. The blue ones are the X and Y capacitors, and the copper coil inductor. This starts The function is the first filtering.

After talking about the first-level EMI, there is the second-level EMI. The second-level EMI is often composed of two Y capacitors and one X capacitor, a fuse and some differential mode inductors and common mode inductors. The functions of these two types of inductors are better filtering and anti-interference. When it comes to common mode inductors and differential mode inductors, some players are not sure. Common mode inductors are wound with double wires, while differential mode inductors are wound with single wires.

The most common use of a power rectifier bridge is to correct AC alternating current into DC current. The mainstream rectifier bridges we see currently use four discrete diodes.

3 PFC is a must-have design for PC power supply

The full English name of PFC is "Power Factor Correction", which means "power factor correction". Power factor refers to the relationship between effective power and total power consumption (apparent power), that is, effective power divided by total power consumption. Quantity (apparent power) ratio. Basically, power factor can measure the degree to which electricity is effectively utilized. The larger the power factor value, the higher the electricity utilization rate. There are three types of PFC we can see at present, namely passive PFC, active PFC and interleaved PFC.

The passive PFC circuit structure is relatively simple. It is actually a huge and heavy inductor. This inductor is generally located on the power wall around the main PCB board perpendicular to the power supply, and is usually tied with yellow tape. At the same time, the passive PFC circuit also has standard high-voltage filter capacitors for power reserve.

The inductor of active PFC is much more effective than the inductor of passive PFC. There will be a relatively large PFC input filter film capacitor. At the same time, we can see that the active PFC power supply has a PFC capacitor, which is called the PFC output capacitor. If it is not the power supply of the active PFC, this capacitor is called the main capacitor. The main function of this capacitor is to store electrical energy for the active PFC.

Interleaved PFC is actually an active PFC, a type of active PFC, and can be regarded as an upgraded and evolved product of active PFC. The difference between interleaved PFC and ordinary active PFC is that it is composed of two large inductors. When working, interleaved PFC works in parallel. This parallel connection can lower the operating current and save losses, and at the same time, the input and output current frequency of the PFC can be doubled.

Interleaved PFC circuits use smaller components, reduce costs, improve thermal performance, provide power density, and reduce conduction losses, thereby improving power supply system efficiency.

4 Mature half-bridge and common forward structures

Topology mainly affects the conversion efficiency, dynamic capabilities, stability and other aspects of the power supply. However, there is no fixed relationship between the topology and the power of the power supply. And the topological structure is very detailed in classification, just like a tree diagram, broadly divided into forward, full bridge, and half bridge.

The half-bridge topology is an old power supply structure. The half-bridge structure is easier to judge. Generally speaking, the transformer in the middle part of the power supply can easily tell whether it is a half-bridge topology power supply. The power supply of the half-bridge topology has one large transformer and two small transformers. The large transformer is the main transformer, and the two small ones are the driving transformer and the auxiliary transformer. Often half-bridge topology will appear with passive PFC.

The forward structure can be divided into single-tube forward, dual-tube forward and active clamp forward. Active clamp forward often appears in FSP's power products. This is also an upgraded version of the forward topology. We can see that there are two types of active clamps: single tube and double tube. The forward topology is the structure used by mainstream power supplies today. The forward power supply has a large transformer and a small transformer. The large transformer is the main transformer, and the small transformer is the auxiliary transformer.

5 Efficient LLC resonant structure

LLC resonance is a necessary structure for mainstream high-end high-wattage power supplies. The biggest feature of LLC resonance is that it can achieve very good conversion efficiency of the power supply. The circuit of such a structure contains a resonant inductor and a resonant capacitor. Like the plate bridge structure, the LLC resonant structure has one large transformer and two small transformers. The large one is the main transformer, and the small ones are the standby transformer and the resonant circuit driving transformer.

Netizens who know about power supplies must know that LLC resonant structure power supplies will appear together with DC-DC modules. Compared with ordinary transformer output, DC-DC module output can maintain a very stable output under high loads and load differences. DC-DC modules are easy to identify. Most DC-DC modules are in the secondary side circuit part of the power supply and are placed vertically with two PCB boards.

Speaking of the secondary side, in fact, the secondary side is the low-voltage filtered output of the power supply. This is also the circuit that ensures the final output of the power supply. The current is filtered through the internal conversion of the power supply to ensure that the power supply provided by the internal hardware of the host is pure. The most important thing on the secondary side is the filter capacitor. Here we can see that some power supplies use electrolytic capacitors, and some use solid capacitors. Solid capacitors can have better filtering effects.

In addition, the power supply will be designed with a protection chip, which is essential for power supply protection. The protection chip can monitor the output of +12V, +5V and +3.3V to realize UVP (under voltage protection), OVP (over voltage protection), OCP (over current protection) and SCP (short circuit protection) of each output, while also partially The control chip also provides OTP (over-temperature protection) or -12 V UVP (under-voltage protection) functions. When the on-chip set value is exceeded, it will automatically stop working to protect the operation of accessories and components inside the power supply and on the platform. , the internal design has overload protection and lightning protection functions to ensure the stable operation of the entire power supply.

Power supply selection guide

1. Output type: Power supply is the most common instrument that electronic engineers come into contact with. To choose a power supply, you first need to select the type of power supply: DC power supply, AC power supply, variable frequency power supply, special high-voltage power supply, etc.

2. Output voltage: the voltage range that the power supply can output. At the same time, you need to choose whether constant voltage output and over-voltage protection are required.

3. Output current: the current range that the power supply can output. At the same time, you need to choose whether constant current output and overcurrent protection are required.

4. Output power: The maximum power value that can be output when the power supply is fully loaded.

5. Number of channels: the number of output power supply interfaces.

6. Ripple: Since the DC stable power supply is generally formed by the AC power supply through rectification and voltage stabilization, it is inevitable that there is some AC component in the DC stable quantity. This kind of ripple is superimposed on the DC stable quantity. The AC component is called ripple. The smaller the ripple, the smaller the impact will be on the circuit's operation.

7. Load regulation: When the input voltage remains unchanged and the load changes from zero to rated value, the change in output voltage. Usually expressed as a percentage.

8. Output voltage programming accuracy: the deviation between the programmable power supply set value and the actual output value.

Main brands of power supplies:

AMTEK

TDK-lambda

KIKUSUI

HAMEG

Enap (NF)

Chroma

ITECH

GWINSTEK

Power supply accessories selection:

1. Communication interface: Because many high-power power supplies are now installed in certain specific systems, the specific communication interfaces required by the system must be communicated and confirmed in the early stage of purchase.

Selection considerations:

When selecting a power supply, be sure to consider the purpose of the power supply. For example: for capacitor aging, as long as the ripple is not too large, it will generally not affect the quality of capacitor aging, so ordinary power supply will suffice. For high-speed digital circuits, when ripple and noise reach a certain amplitude, they will interfere with the normal operation of digital logic circuits, causing false triggering and logic errors. At this time, the choice of power supply should be a high-precision, low ripple and noise power supply. The above are some tips on power supply selection. I hope they will be helpful to everyone.