AC/DC 和 DC/DC 电源转换器的标准电源解决方案和应用

The step-down (buck) converter can convert a higher DC input voltage into a stabilized, but lower, DC voltage at its output. See Figure 1.



The advantage of buck converters is that losses are low, enabling efficiencies of over 97%. The switching frequencies range into the hundreds of kHz. A good power density architecture is achieved using smaller inductors along with a fast transient response capability. During its switching cycle, when the FET switch is disabled, the output level drops to zero. This enables very low no-load power consumption. Taken together, these advantages make the buck regulator an attractive replacement for a linear voltage regulator in a variety of applications.

Buck converters do come with a disadvantage: The Pulse Width Modulation (PWM) regulator feedback circuit needs to have a minimum output ripple to reach proper regulation. This is because the regulation occurs cycle by cycle. In addition, the output ripple depends on the duty cycle, which is a maximum at 50%. In this case, it would not be possible to achieve ripple and noise down to μV levels; this can only be achieved by using linear regulators that are non-switching.

If a designer requires a cleaner power supply, a linear regulator can be placed after a buck regulator, to achieve the best performance of both topologies. This is made possible because the linear regulator Power Supply Rejection Ratio (PSRR) greatly reduces ripple/noise at its output.

A step-up, or boost, converter power design converts a lower input voltage into a stable and solid higher voltage at the output. Figure 2.



The advantage of using a boost converter architecture is that the output voltage can be varied with the mark-space ratio (defined as the ratio between the high time and the low time, or the duty cycle). For example, a 50% duty cycle occurs when the voltage high time is equal to the voltage low time of the PWM signal in order to be equal to, or “boosted” above, the input voltage VIN.

This functionality allows the boost converter, for example, to boost a low battery voltage output to a more useful higher-voltage level. However, a boost ratio that is more than two or three times the input would make feedback stability more difficult to maintain at a solid level. In addition, because the input current pulses would increase proportionally, compared with the boost gain, a converter that triples its input voltage would draw three times its input current. This level of pulsed input current can even lead to increased EMI, and to voltage-drop levels at the battery input leads.

Another disadvantage of the boost converter is that its output cannot be switched off without adding a second switch, placed in series with the input. This is because disabling the PWM controller alone would not disconnect the load from the input.

Power designers should not allow a boost converter’s input voltage to rise above its output voltage. In such a case, the PWM controller could then keep S1, in Figure 3, open continuously. The input and output would be connected directly from L1 and D1 without regulation. Highly damaging currents may flow that could quickly damage the converter along with its load. Designers who cannot avoid this condition must employ a replacement topology that permits both buck and boost operation.

The buck-boost converter (also known as flyback converter) can convert an input voltage to a regulated, negative output voltage, which can go higher or lower than the absolute value level of that input voltage. The image in Figure 3 shows a simplified schematic of the Buck/Boost converter.



The input voltage of a buck-boost converter may be higher or lower than the regulated output voltage. That capability is useful for applications that may require a stabilized voltage output from a battery that can have a terminal voltage between 9V (when discharged) and 14V (fully charged). Buck-boost converters can help stabilize the outputs of photovoltaic cells. Solar cells are able to deliver high voltage and current when in bright sunlight but revert to low voltage and low current when the sunlight is blocked or diminished. As the voltage/current relationship changes in such an example, a buck-boost converter can be quite useful for Maximum Power Point Tracking (MPPT) because the input/output voltage ratio can be continuously adjusted.

The greatest disadvantage of a buck-boost converter is its inverted output voltage. If used with a battery, the output voltage inversion is irrelevant because the battery supply can be left floating and the -VOUT may then be connected to ground in order to yield a positive-going output voltage. Another disadvantage is that the switch S1 is without a ground connection. This means that a level translator is needed in the PWM output circuit, a factor that can quickly add design cost and complexity.

In general, the main requirement for using DC/DC power supplies in automation applications centers on isolation. Isolation would ensure that the power design avoids any interference with other equipment. The DC/DC converter should also be designed into a system, taking care to avoid any ground loops or potential differences that may disturb the operation of the automatic control system.

For example, isolated DC/DC converters might be used in automation to help break up ground loops. This would allow separation of noise-sensitive parts of a circuit from the source of that noise. A regulated and isolated DC/DC converter can help minimize electrical noise using that isolation. The choice of an isolated and regulated DC/DC converter for voltage conversion would help prevent electrical noise isolation, and ensure immunity to line surges and dropout/dips.

The IoT is consumer-oriented while the IIoT, a subset of the IoT, is industrial-oriented. The IoT and the IIoT are systems of inter-related objects, connected on the Internet, which make it possible to collect, share, and transfer data over wireless networks with virtually no human intervention. These two systems feature distributed intelligence, countless interconnected sensors and actuators, along with decentralized control.

The IIoT is made up of devices that collect large amounts of data compared to IoT devices, which generate a relatively lower volume of data. An IIoT example is a single turbine compressor blade that can generate more than 500Gb of data every day. Beyond connectivity, IoT and IIoT are all about the information these devices can collect, leading to powerful insights. Typically, rugged, isolated DC/DC converters are needed to power IIoT sensors, such as those monitoring the condition of industrial machines. Large power surges may occur with the starting and stopping of heavy machinery. As a result, isolated DC/DC converters with isolation of 3kV to 4kV are required to protect the sensors.

Creating smart spaces, the IoT and the IIoT leverage sensors in environments/objects that can communicate to gain intelligence. IoT examples include a business setting that has lighting with smart capabilities to adjust to ambient light levels, and even to the number of people present. Within the IoT, machines can monitor their own functionality, or adapt to daily routines in homes. The IoT automatically saves energy while providing human comfort. The IoT also needs power designers that choose cost-effective and high-power-density DC/DC power supply modules. In this space, applications include smart offices, which are filled with intelligent sensor nodes. Energy harvesting is another excellent application that leverages DC/DC converters.

Power supplies for the IoT and the IIoT need to be highly efficient, at low and full load levels. DC/DC power supplies designed to handle fast transient and dynamic load currents are best suited for these environments. Such power supplies must be physically compact, reliable, and cost-effective. These DC/DC power supplies will be as ubiquitous as the sensors, processors, radios, and actuators that they are designed to power.

See this video entitled “What is the ‘Internet of Things”.

In industrial applications, fork-lift trucks and other materials-handling equipment use traction batteries rated from 320V to 600V. A series of on-board power supplies can optionally generate 24V or 48V from the high-voltage battery rated at 4kW with high efficiency. A 19-inch-rack product version can be baseplate- or liquid-cooled.

With the availability of fossil fuels decreasing, electric vehicles (EVs) have surged as a solution to reduce fossil fuel dependence and help sustain natural resources.

EV development is characterized by:

• increasing battery capacity
• faster charging
• longer lifespan
• improved power density

As EVs increasingly populate our roads, these cars, buses, and trucks need more charging stations, which are being deployed along major roads and highways as well as in local areas. EV charging stations’ power levels are fast reaching several kW of power. DC/DC converters with increased isolation and high insulation strength are critical to these charging stations. DC/DC converters are used to provide regulated power to the network interface of the EV charger. This component ensures reliable communication between the EV and the charging station, as well as connectivity to the Internet.

A key application for industrial high power DC/DC converters is in railway applications. This sector includes applications for railway rolling stock, on-board and trackside applications, industrial applications, high voltage battery-powered applications, and distributed power supply architectures. Typically, DC/DC converters are used in railway environments to convert DC battery voltages to a lower voltage for use in various control and energy systems. Railway rolling stock designs have a DC power distribution system that uses batteries that are deployed to maintain electrical power in the event a generator fails.

For these applications, DC/DC converters must be designed and constructed in accordance with EN 50155 to ensure that harsh environmental conditions do not affect operation. These DC/DC converters are exposed to extremely tough conditions such as heat, frost, vibration, and mechanical impact, all of which can cause serious damage to electronic components. Engineers require DC/DC converters that can withstand these potentially catastrophic conditions and are certified for railway applications.

The power density of a DC/DC converter is a measure of the output power divided by the volume of the DC/DC converter, expressed as watts of output power per cubic centimeter. A high value, meaning more power for a given volume, is a design advantage.

Low-power, non-isolated DC/DC switching regulators are cost-effective solutions that meet increasing demands for better performance with improved power density. Their packages need to be small so that they can compete with discrete designs. Non-isolated DC/DC designs face the challenge of being highly efficient while maintaining a small form factor. The use of faster switching techniques, such as in wide bandgap designs, helps reduce size while maintaining strong efficiency.

RECOM achieves high power density with an over-molded “flip-chip-on-lead frame” construction. EMI is reduced due to smaller switching current loops in the design.
To increase power density with 3D Power Packaging, watch the video ‘Big power in small packages’.

The RP and RPA series are board-mounted DC/DC converters with a power rating of 30W to 240W and a power density of up to 4.5W/cm3. This is one of the highest power densities available for this class of DC/DC converters.

A major reason for the excellent power density is that these devices use planar transformers in their design. These transformers reduce the overall package size without compromising efficiency or output power. This construction method supports a fully automated production process, which leads to high reliability and excellent cost-effectiveness. These two series are best for space-constrained industrial, test-and-measurement, transport, railway, and other demanding applications that require a 4:1 input voltage range and even an excellent 10:1 input voltage range.

Medical applications are high risk by nature. Electronic equipment, especially those containing power electronic devices, must meet extremely high standards of safety and reliability. Medical power supplies need to have properties that meet the necessary standards for medical use in hospitals and other medical environments.

Medical-grade DC/DC converters require reinforced isolation with two means of patient protection (2MOPP), low leakage, and a creepage/clearance distance greater than 8mm. Reinforced isolation provides an added level of safety beyond standard isolation, to meet the medical safety standard ES/IEC/EN60601-1 3rd Ed. High isolation and low noise are critical to medical-grade DC/DC converters. Since patients or operators are always involved with equipment containing such devices, they must be protected in the event of a fault.

High-grade medical DC/DC converters are designed to be safe for humans. They meet either type BF (Electrically connected to patient but not directly to heart) or CF (Electrically connected to the heart of the patient) environments. These can be used in incubators, ultrasonic devices, or defibrillators. The power supplies meet the 2MOPP (Means of Patient Protection) spec, which involves high isolation and a robust insulation capability. The internal transformers have reinforced insulation and help limit the leakage current that may reach the patient.

Some medical-grade DC/DC converters are regulated and have a 250VAC working voltage. Additional specifications may include a 5kVAC to 10kVAC/1 minute reinforced isolation and leakage currents as low as 2µA. There may be other options that can reduce standby power to milliwatt levels.

A 1W converter in a very compact SIP-7 package is currently the smallest complete medical supply on the market. Midpower ranges are available, too. These DC/DC converters are cost-effective at 3.5W, 5W, and 6W. They come in an SMD or THT package, with an input voltage range of 2:1, and the output voltage can be 3.3V, 5V, 9V, 12V, 15V, or 24V, depending on the series.

这些 DC/DC 转换器具有增强隔离，250VAC 连续工作电压，爬电距离/电气间隙大于 8mm，并提供 2 x MOPP。它们还配有高达 8kVDC 的扩展增强隔离，适用于高压应用。

这些转换器具有关键医疗应用所需的所有重要功能，同时降低了这些模块化解决方案的成本。它们提供引脚和表面安装设备。

隔离型 DC/DC 转换器可以具有以下优点：

1. 隔离输入和输出之间的接地意味着直流电源的接地方案可以与输出上的负载有所不同
2. 设计人员将能够“映射”输入端（相对于输出端）上各种不同水平的直流电压
3. 如果这些转换器的输出端电容非常低，则可以更容易、更安全地将多个隔离型 DC/DC 转换器并联放置在同一条直流总线上

非隔离型 DC/DC 转换器具有以下优点：

1. 它们的直流输入和输出连接到相同的电位。包括降压、升压或降压-升压 DC/DC 转换器。

双向 DC/DC 转换器在许多新应用（包括汽车、服务器和可再生能源系统）中是一种相对较新的架构。低压双向 DC/DC 转换器通常是非隔离型。

双向 DC/DC 转换器的三个关键应用是汽车、服务器和可再生能源系统。

图 4 中的变压器有两个 115V 初级绕组，通过输入电压选择器开关并联或串联。两个串联的 6V 次级绕组产生额定 12VAC 输出，该输出由桥式整流器 BR 整流，然后由输出电容器 C 进行直流平滑。可以提供大约 14VDC 的典型输出电压。全桥整流器采用四个二极管典型配置。

AC/DC 转换器适用于许多关键应用，在本节中，将讨论 AC/DC 转换器的主要应用领域。

如果电子设备不直接与患者接触并且仅由训练有素的操作者进行处理，则归入 MOOP（对操作者的防护措施）类别，表示这类电子设备通常只需要满足 60950-1 和 62368-1 ITE 标准规定的实验室环境下的要求。

医疗电子设计使用患者保护措施 (MOPP)，这是由全球标准组织制定的电气安全标准 IEC60601-1；这些组织包括美国国家标准协会 (ANSI)、加拿大标准协会和欧盟委员会。MOPP 安全标准规定了医疗电气设备的基本安全要求。

AC/DC 电源 的医疗应用，通过电源供电医疗应用的 2 x 患者保护措施 (MOPP) 安全认证。最高级别的安全保护源于使用 2 x MOPP。请注意，一些电源制造商通常会强调其电源符合医疗批准，但未说明设备符合 1 MOPP 还是 2 MOPP。

这些紧凑型医疗级电源具有通用交流输入电压范围、4kVAC 隔离、低待机功耗、有源 PFC (> 0.95)，并且不需要最小负载。

查看此 播客 了解更多详细信息

功率密度是一个用于衡量单位体积功率输出的指标。该指标在电源中非常重要，尤其是在空间有限的区域。

效率是功率电子设备领域的首要问题。提高电源效率可以达到提高功率密度的目的。提高功率密度的一个可靠方法是减小组件尺寸。设计者应尽可能选择小尺寸电容器、电感器、变压器和散热器，以满足设计需求。

高端服务器和电信设备需要最高效率（约 99%）和高功率密度 (73 W/in3)。在此类应用中使用 AC/DC 转换器。

现代工业需要 AC/DC 转换器的尺寸更小、占用空间更少和功率密度更高。随着开关控制器、拓扑结构和组件技术的进步，使得 AC/DC 电源的功率密度翻倍。新设计必须提高安全性、可靠性、效率和性能，才能具有竞争力。

设计者必须清楚 AC/DC 转换器支持的输入电压范围。在西半球国家的大多数行业中，交流电源的输出范围从标称 100VAC 到 277VAC，以便在全球范围内使用。

至关重要的是，AC/DC 转换器在整个负载范围（从满负载到轻负载，甚至到空载）都能有效工作。

大多数 AC/DC 转换器都已通过 UL/IEC/EN 标准的国际安全认证，并附有认证机构 (CB) 报告。节能对客户来说至关重要，许多应用都会自动切换到待机状态，以降低功耗。

在测试和测量领域，设备的应用范畴可以从桌面产品到服务器机架安装。此类系统需要交流输入电压，该电压可以从标称 90VAC 到 277VAC，对于某些工业应用，所需电压通常要高出几倍。

经常将功率范围为 3W 至 20W、安装在 PCB 上的低功率 AC/DC 转换器设计到这些系统中。如需更大功率，例如从 40W 到 550W，设计者可以选择机箱安装。

在 测试和测量 环境中，在没有风扇环境的情况下运行通常具有挑战性。针对这种环境选择的所有 AC/DC 转换器解决方案都必须能够在高温环境下提供有效功率而无需强制风冷。

我们推出了新增基板冷却功能的 230W 和 550W 产品。

根据 IEC/EN 61010、IEC/EN 62368、IEC/EN 60601 和 EN 60335 的要求，可获得不同终端应用环境的安全认证。

优质 AC/DC 转换器需要在不使用任何附加组件的情况下满足电磁兼容性 (EMC) 标准。所有 AC/DC 设备都需要具有低电源泄漏电流，这一点在测试和测量应用中至关重要，尤其是在医疗环境中。需要灵敏测量的应用将需要低输出噪声 AC/DC 电源，对于许多测试和测量系统的设计者而言，我们的产品具有显著优势。

假冒电源组件 会对设计领域造成严重破坏。这些设备可能出现故障，甚至完全失效。即便可以工作，仍然有可能造成人身伤害甚至引发火灾。这将严重损害供应商的声誉。

强烈建议买家从知名制造商的全球分销商处购买他们的产品。

睿智的设计者和采购人员都知道，通过值得信赖的分销商和制造商购买电子组件和电源将是最佳途径，以确保功能完备、可靠安全的最终设计。

(1) 第 1 章 降压、升压和降压/升压转换器简介， RECOM DC/DC 知识手册
(2) 第 2 章 线性 AC/DC 电源， RECOM AC/DC 知识手册