Power supply application design is a distinct part of any electronic system development. A separate team of experts works on the power management part in systems ranging from simple appliances such as mobile phones and music headsets to advanced satellite equipment. That’s because power management in itself is a complex entanglement of simple electronics.
The first stage of power management starts with a market survey and coming up with proper specifications that a power converter must satisfy. For example, automotive-grade power converters are expected to work at higher temperatures of the order of 150°C and space applications must work at temperatures way below -40°C. A USB application should work for 2.5 V to 6.5 V DC input, while a charging adapter should work at 85 V to 265 V RMS AC input.
Once these specifications are set, the design team comes up with the design specifications to which the power converter can be designed. What can and cannot be incorporated inside the IC. What external programmability can be supported and so on. After IC is acquired, it’s time to design a board that will cater to specific applications such as a digital TV, battery chargers, and industrial and car audio power supplies. Designing these boards for specific applications is what can be summarized as application design.
Power supply application design has the following steps in general.
- Redesigning the schematic which the IC design team has developed for a specific application with details described in datasheet.
- Deriving and referring to datasheet and application note equations for calculating values of external components such as inductance, capacitance, and resistance.
- Setting appropriate safety margins on values of these external components with other parameters such as parasitic resistance, current ratings, and voltage ratings.
- Selecting closer value of external components (BOM) based on calculations outlined in point b and within the margins decided in point c.
- The chosen BOM placement is carried out on PCB by referring to schematic diagram.
- Testing and tuning to verify if the specifications are met.
Need for online tools
Many companies located across the world that design, develop, manufacture, and sell more than several hundred thousand varieties of consumer electronic equipment. Power management lies at the heart of all this equipment. To cater to these designs, it is impossible to build 10 to 20 sample boards for every specification.
Imagine you have an online design tool with information about every power supply IC that a company manufactures, along with proper schematics for each IC. It has information of all external components—including resistors, inductors, capacitors, MOSFETs, diodes, and so on—along with information provided by the components distributor. Power system engineers provide input-output requirements and get a complete design to support their needs with appropriate BOM, manufacturer, and distributor information. They can modify and simulate the circuit and analyze the performance at the click of a button using online design tools.
Power supply design using online tools
Take the example of car audio power supplies, where the output power requirement is 10 W and the available input voltage is around 12 V DC. For this specific application, we should choose a DC-DC converter that can be powered by the car battery. While choosing power converters, there are many other key performance parameters that an application designer must consider. That includes higher efficiency, lower footprints, low cost, and stable output performance for given input specifications.
There are specific online design tools that help engineers choose converters based on optimum performance parameters and also help them design a specific application by providing initial reference design that can be modified if required. That includes WEBENCH Power Designer by TI, Web Designer+ by ON Semiconductor, and EE-Sim by Maxim Integrated. Input specifications can be directly fed to these tools to generate the list of solutions. Engineers can choose the design that is optimum in terms of performance parameters.
For instance, for car audio power supplies, let’s assume the requirement is Vin = 8-12 V, Vout = 5 V, Iout = 2 A, and efficiency requirement is higher than 90%. Solutions generated from one of the automated tools are shown below.
Figure 1 WEBENCH Power Designer supports various power systems and subsystems for applications ranging from battery management to LED lighting and processor to FPGA power. Source: Texas Instruments
Any power converter that is closer to the required specification can be chosen for further evaluation. The reference design schematic shows the external components that are already available in the BOM options. Design can be further scrutinized with the help of electrical simulations and available charts displayed in the tool. One example that we considered is shown below.
Figure 2 Power system designers can run simulations, print a design report, and start a new design. Source: Texas Instruments
After these evaluations, engineers can select the design and create the PCB. Some of these tools also support the reference PCB designs for a given application in gerber files—providing all information required to manufacture a PCB. These designs can be exported and modified across different PCB design tools. It will also help engineers in prototyping application design.
Figure 3 Engineers can create a PCB after necessary evaluations. Source: Sankalp Semiconductor
Anatomy on online design tools
A lot of background work goes into building online design tools. A database for all the parts, active and passive components with parameters is properly specified. Then there are mathematical equations for external component selection, operating values such as efficiency, and phase margin. These equations are normally written in platforms such as Python, Java, and Angular2 that support HTML.
- Eliminate the need for building first cut PCB.
- Modifications can be done at the click of a button without hassle of PCB issues.
- All information—including performance graphs, simulation results, and PCB layout—is available in one place.
- No need to contact manufacturing team until end customer is satisfied with the design.
- Several design options are available at the same time.
- Saves lot of time, reducing time to market.
- No need for complex lab work.
- A large number of external components is available with a click.
- A person with minimal knowledge in power electronics can come up with first cut designs using these automations.
- Thorough testing is done for standard input/output conditions.
- The automation results and performance might be a little off with the actual board because of modeling limitations such as modelling parasitics and aging effects.
- Due to limitations of running the automation operations—such as large servers and disk space to dump the data—it’s not possible to validate all possible design combinations of inputs. And that may portray bad design as good designs.
- It’s not possible to compare designs from different manufacturers directly.
- If automation is not user-friendly, people with no design background might not be able to use it with full potential.
- In current scenario results, schematic and BOM generated from automation cannot be given directly to mass production due to modelling limitations mentioned above. It must be tested thoroughly; otherwise, it may lead to catastrophic results if bugs are encountered at a later stage in production.
When it comes to automation in the field of power supply application design, the implementation process may vary from one manufacturing company to another. However, the overall methodology discussed in this article remains relevant.
Vishwanath D Tigadi, Raghavendra Chavan and Bhushan Waghmare are design engineers at Sankalp Semiconductor, an HCL Technologies company.
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