A detailed explanation of the method of designing multi-level industrial power supplies

National Semiconductor has launched a variety of power modules in the SIMPLE SWITCHER® product series. Among them, the LMZ series module is a highly integrated, high-efficiency buck regulator with a new high-performance package. It integrates an inductor and a monolithic synchronous regulator. In addition, National Semiconductor has launched a new online tool WEBENCH® Power Architect, which allows engineers to complete concept design, modeling and solution implementation in a few seconds, thereby quickly designing high-performance multi-output DC/DC power supplies for the entire electronic system, which used to take several hours.

　　This article details how to design an efficient multi-output power supply using the new power module in WEBENCH Power Architect in a typical industrial 24V power supply environment. The industrial 24V power supply converts the power to an intermediate voltage rail in the first stage and finally to a typical load point voltage and load point current. The purpose of this article is to explain the design method of each stage and its easy modification and optimization according to the project requirements.

　　

　　Figure 1 _SS power module PR2290

　　The power supply requirements of various industrial applications are basically the same. The following are the main parameter values ​​required for typical applications such as FPGA power supply. In the fields of motor control, automation network and machine vision, the same design method can be adopted according to this step.

　　The first step is to determine the possible voltage values ​​of the power input:

　　Vin nom operating: 24V

　　Vin operating: 18V~30.5V

　　Vin transient: 36V~42V

　　Tambient operating: -40℃~+85℃ (without external heat sink or fan)

　　The requirements for electrostatic discharge (ESD), burst and surge, and current injection specified by IEC 61132 PLC will be ignored here. Therefore, the power supply can be designed alone without considering the protection circuits to design the system robustness to meet the above test requirements.

　　We used National Semiconductor's WEBENCH Power Architect tool to design the multi-output solution. This innovative online tool can be accessed through www.national.com/analog/webench/power_architect. After launching the tool, on the landing page (configuration step), you will see a panel where you can fill in the input and load specifications. The input load should be named after the load in the actual application.

　　Power supply: "24V industrial voltage rail" VMin: 18V VMax: 42V Tambient: 85℃

　　The "Add Load" button should be used to set the specifications of each load.

　　LOAD_1: "FPGA Core" VLoad: 1.2V ILoadMax: 4A

　　LOAD_2: “Analog power supply” VLoad: 2.5V ILoadMax: 0.5A

　　LOAD_3: “I/O power supply” VLoad: 3.3V ILoadMax: 0.5A

　　LOAD_4: “I/O power supply” VLoad: 1.8V ILoadMax: 0.5A

　　LOAD_5: “General purpose” VLoad: 5V ILoadMax: 1A

　　We can use modules whenever possible and select the "Prefer module solutions" option.

　　Clicking the "Submit Project Request" button will start a complex calculation and optimization process, which will ultimately display multiple solutions via three different design tools. In the first selection it is possible to limit the number of solutions displayed in order to simplify the results.

　　Tables and box diagrams:

　　Each row represents a complete multi-output power supply design and lists the main system parameters. The highlighted row represents the alternative with the best efficiency and cost, and its corresponding block diagram is shown on the right.

　　Graphical chart (Figure 2):

　　

　　Figure 2 Webench PA optimization project phases diagram

　　

　　Figure 3 Webench PA Optimization Project Phases Dial

Each circle corresponds to a row in the table, and you can identify a specific design by moving your mouse over a circle. This graph allows you to easily understand the relationship between footprint (y-axis), efficiency (x-axis), and cost (area size of the circle).

　　The “Optimization Tuning” dial (Figure 3) can be turned toward “Lowest BOM Cost” or “Highest Efficiency.” This will add more design solutions to the graph and table (Figure 2). The yellow circle corresponds to the highlighted design in the table and the actual block diagram displayed. The color difference between the other circles and the background color of the optimization dial scale can be used to understand the relevant optimization strategy.

　　This allows designers to see at a glance the impact that choosing a certain bus voltage or solution architecture will have on cost and efficiency.

　　In the following steps, we will use the design with the best performance highlighted by WEBENCH. The bus voltage is set to 5V. This is to allow the parts working under the 5V voltage rail to obtain the best efficiency and cost performance.

　　Clicking the "View Project Details" button will take you to the next level, where you will see the final block diagram (as shown in Figure 4), the schematics of the selected power modules, and a pie chart showing the proportional relationship between power consumption, price, and footprint for each module (as shown in Figure 5). The colors in the chart correspond to the corresponding modules in the block diagram.

　　

　　Figure 4 _Webench PA_View Project Phases_Diagram 1

　　

　　Figure 5 _Webench PA_View Project Phase_Pie Chart 1

　　At this point we can consider the design complete and the chosen solution brings all the above advantages using only the power module.

　　Power Architect also offers the possibility to further optimize the selected architecture. It allows replacing parts in the selected design. In our example, we noticed that the LMZ14203 module in the first stage is the biggest contributor to power loss (see Figure 6). Click on the device in the window below the pie chart and select "Alternative Solution" (see Figure 7). Sort the devices by efficiency (click on the corresponding column) and select the LM3150, which will increase the total efficiency by 5% to 79%. Another optimization option is the solution cost, and the pie chart shows the huge impact of three modules with a load current of only 0.5A. Therefore, we sort by "BOM $ Cost" and replace these three modules in the "Alternative Solution" with the LM3674, which will keep the total system efficiency high (81%), but at the same time cut the solution cost by more than half.

　　

　　Figure 6 _Webench PA_View Project Phases_Diagram 2

　　

　　Figure 7 _Webench PA_View Project Phase_Pie Chart 2

　　in conclusion

　　Using WEBENCH Power Architect, you can design a multi-output power supply in seconds, which has great design and optimization flexibility when designing multiple industrial standards. The power module provides the highest integration and reliability for these designs. National Semiconductor will release more voltage and power options for power modules, which will greatly increase the design flexibility of such complex power solutions.