How to Select the Power Supply Components You Need

Created: December 14, 2020
Updated: October 10, 2024

Over the years, I’ve broken open a fair share of power supplies, and I was always impressed at the number of components that could be packed into a small benchtop power supply unit. These things were just stepping down and rectifying AC to DC, right? Unfortunately, like most electronics systems, it’s just not that simple, especially when you consider the way real power supply components operate.

Whether you need to design a low-power unit or a high power system with multiple regulation stages, you’ll need a range of power supply components for conversion, filtering, regulation, and control. We’ve compiled a short list of some components you’ll need in your power system, as well as the important specifications to watch for when selecting components.

Important Power Supply Components

All components in a power supply are important, but it’s more important to group components by task within a power regulation system. If you’re working at low power and you just need a regulator IC, then there’s a blog for that. Take a look at this article to see how to select a voltage regulator.

Otherwise, your job is to select the right components that will sit in each stage of the system such that it can operate without thermal or electrical failure. Some components are universally needed (e.g., passives and power MOSFETs) across multiple stages of a power system, so we’ll try to help the newer power system designers reading this informed on these points. Let’s look in order from the input to the output of a larger power supply and conditioning system and some of the components needed in each stage.

Input: Rectification and Filtering

At the input, you’ll need some filtering to remove common-mode noise from propagating through to the output. If you’re planning to run a DC system on an AC power source (e.g., from a generator) or off of AC mains (grid power), you’ll need rectification if you’re powering a DC system. Bridge rectifier ICs are available for mid-range powers (high voltage/low current). Very high current systems can’t run through an IC, so a range of custom components will be needed.

For rectifier diodes and ICs, watch for the forward voltage/current and the reverse breakdown voltage. You want to ensure the input power sufficiently forward biases the diodes in the bridge but does not cause breakdown in reverse bias. For filters, you should look at the common-mode noise reduction ratio (CMRR) and the DC resistance of the leads. You want to ensure IR drop is as low as possible while keeping CMRR sufficiently high.

Conditioning: Power Factor Correction and Regulation Stages

For low power systems, even if they take power off the grid, you’ll want to use a power factor correction (PFC) IC. This is required under IEC standards and will help keep the efficiency of your downstream regulator stages high. High power systems have the same requirements, so they also need a PFC stage, possibly with rectification for AC-DC conversion

The first regulation stage for an AC-DC power system appears after the PFC circuit and provides the first high power conversion stage to the desired output. In AC-DC systems, the 1st regulator stage effectively converts leftover ripple from rectification and exchanges it for high frequency noise on a stable DC output. Downstream regulation stages will then step up or down the power as needed to provide the necessary voltage or current to different subsystems.

Input/output voltage and current values are important here, but so is efficiency.

Example application of the Renesas ISL6731BFBZ-T PFC circuit. Similar circuits can be built from discrete components for high power systems. Taken from the ISL6731BFBZ-T datasheet.

Feedback and Control

This is where power supply design gets very fun. The feedback arm of the system is one area where power needs to be given back to an earlier stage in the regulator or a sensing unit to control conversion. This is all about ensuring the system always outputs stable power as long as the supply voltage is above some minimum. Constructing a feedback and control loop requires isolation as well as a custom driver to adjust the output from any of the regulator stages.

There is a variety of different specs to look at when selecting these components. For components in a feedback loop, where the output needs to be sensed and used to provide precision control, the input voltage/current specs are probably most important. For PWM driver/control circuits, you’ll need to match the PWM frequency to the ideal value for the regulator section. ESD protection ratings are also important here as you need to ensure the system will not fail in the event of a hazardous discharge in the control loop.

The UCC24612 from Texas Instruments used in low-side synchronous rectification. From the UCC24612 datasheet.

Other Power Supply Components

Other components you might need in a power supply include a range of passives, which make an appearance in all the above sections in some way. If you’re laying out a custom power converter/regulator for a high power regulator, you’ll likely end up using dozens of capacitors. In a recent project for an unmanned vehicle, we used well over 100 capacitors in the power regulation section alone to ensure stable output power.

When you need to select power supply components, you need to use a search engine with advanced search and filtration features. Octopart gives you a complete solution for electronics sourcing and supply chain management, and you’ll have access to a range of components for different applications. Take a look at our power management integrated circuits page to find some specialty components you’ll need for your next power regulator.

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