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Designing wide input DC/DC converters for solar inverter applications
[TEXAS INSTRUMENTS SOUND EFFECT] Hello. I am Robert Blattner. I'm an application engineer who works in TI's buck converters and controllers product line. Today, I'm talking about wide VIN converters servicing solar inverters. Shown on the left is a generic schematic for an inverter used in rooftop solar. In this design, we are focusing on the general housekeeping power supply. This supply powers digital circuitry and is often supplied to another isolated supply, which provides control power for the inverter's actual power stage. Key needs for this supply are a long service life, and it must operate in a high temperature environment. TA typically reaches 105 C. This converter is powered by a 24 volt rail. Output rails typically, 5 volts at 2.5 amps, but may also be 12 volts at 1 amp. Summarizing this application's electrical needs and comparing it to another high-reliability end equipment in-cabin automotive and to a low-reliability application-- cell phones. We see that solar inverters need eight to 24 volt input, whereas in-cabin automotive generally requires a wider range of input voltages, and cell phones require primarily low-input voltages. Also, output voltages for solar inverters are higher-- 5 volts or 12 volts-- versus, typically, 3.3 volts and 5 volts for in-cabin automotive. And cell phones only have point-of-load regulators. The current range needed for solar inverters, housekeeping supply is 2 amps or less, while in-cabin automotive applications for body control typically require 3 amps and less. Cell phones have a wide variety of output current requirements. Solar inverters typically require an efficient light-load operation. Automotive applications will often require extremely efficient light-load operation. Typically, only 10 micro amps should be consumed when the converter is unloaded. Solar inverters stand out for their service life. Typically an inverter is expected to last in excess of 25 years. Automotive is also a very high-reliability market. Typically, manufacturers would like their circuitry to last at least 20 years. Cell phones aren't expected to last that long. Solar inverters also operate over a wide variety of temperature conditions. Typically, ambient is specified to go as high as 105 degrees on the outside of the application. In-cabin automotive, typically it's 105 degrees, but at the PCB. Cell phones aren't expected to run above 70 degrees. These reliability requirements lead to solar inverter manufacturers typically requiring leading packages. This improves board-level reliability because the leads can flex. Automotive manufacturers often have very tight specifications for board-level reliability and temperature cycling, typically in excess of 1,000 cycles. They do this rather than requiring leaded package. In cell phones, size is everything, so you won't see many leaded packages in a cell phone. Solar inverters require low price. in-cabin automotive, quality comes above cost, but still, it's a very competitive market. In cell phones, very low cost is typical. As far as quality standards, the automotive industry has the Q100 standards for semiconductors to ensure quality. Since solar inverters are expected to operate at high ambient temperatures, designing with thermal constraints is key. Under these conditions, the junction temperature is the key constraint. Both part efficiency and the thermal resistance of the package and PCI together limit the amount of power that an IC deliver. Note that thermal resistance depends on system parameters, such as PCB size-- shown below-- PSP composition and layout-- discussed later. One good way of getting started on thermal design is to use WEBENCH. WEBENCH can estimate power dissipation and, for some devices, junction temperature. These estimates are a good starting point for device selection in a design. In WebTHERM, assumptions about the PCB copper thickness can be changed to match the application and explore possible application configurations. Another way to proceed with thermal design is using calculations. The app note "AN 2020 Thermal Designed by Insight, Not Hindsight" contains enough information for initial estimates and a start for thermal design for systems. This app note contains quantities to look at, how to estimate thermal conductivity, the effect of board size, the use of thermal vias, optimal layout technique, and multiple heat sources on a board. Calculations based on this app note have been used as a starting point for part selection in solar applications. Even once a part has been selected, not all applications are the same. The thermal conductivity of the PCB is a function of layer stack up and fill-- how traces are laid out. Moving heat from the part to play in layers efficiently is important. This can be accomplished using thermal vias. The position on the part on the PCB is also important. If a part is near heat-sinking structures, such as connectors and mounting hardware, the part will run cooler. If it is near other heat-producing components, it will run hotter. Once a design has been prototyped, a lot of information can be gathered rapidly using thermal imaging. Thermal imaging cannot only assess the device's temperature, but also show thermal paths from the device, other heat sources, as well as heat sinks in the design. The picture in the lower right shows a thermal image of an LMR33630 converting 24 volts to 5 volts. It shows that the inductor is also a heat source. On the left is a plot of temperature versus time, showing that the part reaches thermal steady state after about 10 minutes. Summarizing the advantages of the LMR33630, when used as a housekeeping power supply in rooftop solar inverters, the LMR33630 comes in a pleated leaded, which affords excellent board-level reliability, expected in the solar industry. This package also has low thermal resistance. In addition, the part is highly efficient, generating less heat, allowing operation at high ambience. The LMR33630 also meet BOM cost requirements, as well as solution size requirements. In order to find out more about the LMR33630, it may be searched on TI's website. WEBENCH can also be searched up on TI's website. In order to find out more about solar inverters, please go to ti.com's applications web page, click on Industrial, then Grid Infrastructure, then Micro Inverter. Thank you for watching this video today on the LMR33630 in solar inverters. This is Robert Blattner from the buck converters and controllers product line. [德州仪器生效] 你好。 我是Robert Blattner。 我是TI的降压转换器和控制器产品线的 应用工程师。 今天,我会谈论为太阳能逆变器 提供服务的宽VIN转换器。 左侧显示的是用于屋顶太阳能的 逆变器的通用示意图。 在这个设计中,我们专注于一般的家政 电源。 该电源为数字电路供电,通常 提供给另一个隔离电源, 为逆变器的实际功率级提供控制电源。 这种供应的关键需求是使用寿命长, 并且必须在高温环境中运行。 TA通常达到105℃。该转换器 由24伏铁轨供电。 输出轨通常在2.5安培时为5伏, 但在1安培时也可为12伏。 总结该应用的电气需求,并将其 与其他高可靠性终端设备车载汽车 和低可靠性应用 - 手机进行比较。 我们看到太阳能逆变器需要8到24伏输入, 而机舱内汽车通常需要 更宽范围的输入电压, 而手机主要需要低输入电压。 此外,太阳能逆变器的输出电压更高-- 5伏或12伏 - 相比之下,通常为3.3伏和5伏的 车内汽车。 手机只有负载点调节器。 太阳能逆变器所需的电流范围, 家用电源为2安培或更低, 而用于车身控制的车内汽车应用 通常需要3安培或更少。 手机具有各种各样的输出电流要求。 太阳能逆变器通常需要 有效的轻载操作。 汽车应用通常需要 极其高效的轻载操作。 通常,卸载转换器时 应仅消耗10微安。 太阳能逆变器因其使用寿命而脱颖而出。 通常,逆变器预计 将持续超过25年。 汽车也是一个非常高可靠性的市场。 通常,制造商希望他们的电路 可以使用至少20年。 手机预计不会持续那么久。 太阳能逆变器还可在各种 温度条件下运行。 通常,环境指定在 应用程序外部高达105度。 车内汽车,通常是105度, 但在PCB上。 手机预计不会超过70度。 这些可靠性要求导致 太阳能逆变器制造商通常 需要前导封装。 这提高了板级可靠性, 因为引线可以弯曲。 汽车制造商通常对板级可靠性 和温度循环的规格非常严格, 通常超过1,000次循环。 他们不会要求含铅包装。 在手机中,尺寸就是一切, 所以你不会在手机中看到很多含铅包装。 太阳能逆变器需要低价格。 车内汽车,质量高于成本, 但仍然是一个非常有竞争力的市场。 在手机中,通常成本非常低。 就质量标准而言,汽车行业 拥有半导体Q100标准 以确保质量。 由于预计太阳能逆变器 将在高环境温度下运行, 因此设计热限制是关键。 在这些条件下,结温是 关键的约束条件。 封装和PCI的部件效率和热阻 一起限制了IC提供的 功率。 请注意,热阻取决于系统参数, 例如PCB尺寸 - 如下所示 - PSP组成和布局 - 稍后讨论。 开始使用热设计的一个好方法 是使用WEBENCH。 WEBENCH可以估算功耗, 对于某些器件,可以估算结温。 这些估计值是设计中 器件选择的良好起点。 在WebTHERM中,可以更改关于PCB铜厚度的 假设以匹配应用 并探索可能的应用配置。 进行热设计的另一种方法 是使用计算。 应用笔记“AN 2020 Thermal by Insight, Not Hindsight”包含足够的 初始估计信息和系统 热设计的开始。 此应用笔记包含要查看的数量, 如何估算导热系数,电路板尺寸的 影响,热过孔的使用,最佳布局 技术以及电路板上的多个热源。 基于此应用笔记的计算 已被用作太阳能应用中 部件选择的起点。 即使选择了一个部件, 并非所有应用程序都是相同的。 PCB的导热性是层叠和 填充的函数 - 如何布置迹线。 从部件移动热量以有效地分层运行 非常重要。 这可以使用散热通孔来完成。 PCB上的部件上的位置也很重要。 如果部件靠近散热结构,例如连接器 和安装硬件,则该部件将运行后会变得更冷。 如果它靠近其他发热部件, 它会更热。 一旦设计成为原型, 就可以使用热成像 快速收集大量信息。 热成像不仅可以评估 设备的温度,还可以显示设备, 其他热源以及设计中的散热器的 热路径。 右下方的图片显示了LMR33630的 热图像,其转换为24伏至5伏。 它表明电感器也是一种热源。 左边是温度与时间的关系图, 表明该部件在约10分钟后 达到热稳定状态。 总结LMR33630的优点, 当用作屋顶太阳能逆变器的 家用电源时, LMR33630采用褶状引线, 可提供出色的板级可靠性, 适用于太阳能行业。 该封装还具有低热阻。 此外,该部件高效, 产生的热量更少,可在高度环境下运行。 LMR33630还满足BOM成本要求以及 解决方案尺寸要求。 有关LMR33630的更多信息, 可在TI网站上进行搜索。 也可以在TI的网站上搜索WEBENCH。 要了解有关太阳能逆变器的更多信息, 请访问ti.com的应用程序网页, 单击Industrial,然后单击Grid Infrastructure, 然后单击Micro Inverter。 感谢您今天观看有关太阳能逆变器 LMR33630的视频。 我是Robert Blattner,来自降压转换器和控制器 产品线。
Description
April 5, 2019
What you need to know about wide input DC/DC converters when designing solar inverter systems
Additional information
Learn more about LMR33630
Learn more about solar inverters
Start your WEBENCH design
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