Methods to simplify switching power supply design

Take the First Step

The first step in an online power supply design is to define the power supply requirements, including the voltage range, output voltage, and load current . Possible solutions are automatically evaluated and one or two recommendations are presented to the user. This is also the first place where the designer may run into trouble: if the requirements are not expressed correctly (for example, if the actual input voltage range is higher or lower than the input value), unsuitable solutions will also be displayed. The user can try multiple sets of requirements, but must have a clear idea of ​​the system requirements.

Once the regulator solution is selected, the components for the circuit can be determined. The tool will display the component number. The user can change to a preset replacement or enter a custom part. There are guidelines for component values ​​and all key parasitic values. If a custom component is used that deviates significantly from the recommended values, performance may be degraded.

Performance Evaluation

Once the circuit components have been selected, it is time to evaluate the performance. Generally, performance is evaluated by looking at frequency response values ​​(crossover frequency and phase margin), peak current and voltage, and thermal performance values ​​(efficiency, junction temperature, and component temperature). Although these calculations are based on models, the simulation results match the bench data very well.

Electrical and Thermal Simulation

Electrical simulation supports some solutions. These simulators display the logic diagram, and the user can further change components and run tests on the regulator circuit. Available tests include Bode plot, steady state, line transient, load transient, and start-up. (Note that Bode plots are only available for circuits that use fixed-frequency regulator ICs.) To make in-circuit testing most useful, the user should carefully check all test conditions. Input voltage and load current may change for each test, and the default values ​​may not match the user's system. The user must first estimate what the results should be, and if the simulation results are different, find out why.

Thermal simulation can be used for many scenarios. The online tool evaluates the voltage regulation circuit implemented on a PCB using a reference design layout . Results for component and board temperatures are displayed in full-color graphics and tables. Since thermal simulations run quickly (results are available in minutes), they are not as accurate as a detailed CFD (computational fluid dynamics) simulation that can take hours. However, temperature estimates are generally within 20°C of the actual value. This is sufficient to identify hot spots on the board or components to prevent overheating.

Testing the prototype

The final step before designing a switching regulator for production is to build a prototype for bench testing. Some solutions include support for custom designs, while others come with reference design boards. Given the power of online tools, you may be tempted to skip this step – don’t! Most designs will work fine, but some require careful layout to get the best performance. Actual components may not exactly match simulation results, especially when their parasitics are taken into account, and actual performance (including board layout effects) will differ slightly from simulation results.