How to Design a Switch-Mode Power Supply



Switch-mode power supplies represent a popular choice to supply power to low voltage equipment, both for industrial and domestic applications. Nowadays, more and more modern equipment requires a low voltage supply. A power supply also simplifies the task of maintaining safety isolation in wet or polluted environments.

For this reason, in many circumstances, it makes perfect sense to use extra-low voltage relays, even if what’s being controlled runs on mains voltage. However, while the benefits of using a SMPS are often clear, it is also important to review how to design such type of power module. Below we will review where to start in the design of a switch-mode power supply.

How to Design a Switch-mode Power Supply

Switch-mode power supplies are needed to take an unsuitable voltage and convert it to a suitable voltage required for the specific low-voltage application. SMPSs help provide isolation by keeping the low voltage equipment separated from the higher mains voltage. They also help regulate the output current and output voltage, keeping the voltage constant and preventing short circuits from damaging the power supply and other equipment.

Several factors need to consider when designing a switching power supply, including topology, output current, switching frequency, etc. We review some of these important factors in more detail as follows.

1. Determine the topology

About 13 SMPS topologies exist for switching power supplies, each with specific advantages and disadvantages. Therefore, the first and most important decision you must make is determining which topology is best for your project needs. We typically choose between three popular SMPS topologies: buck, boost, and buck-boost. You must envision the scenario around the device you want to power and decide if the topology is optimal over time.

2. Output current

The output current determines the amount of current supplied through the voltage regulator, and it is important to confirm whether this value meets the requirements of the load. In the design case, you must ensure that the ratings of the components match the output current requirements. Although it’s accurate in most cases, adding a safety margin is still a wise choice. The maximum current draw will always be lower than the specified figures in the datasheet.

3. Output voltage

Switch-mode power supplies typically have variable output voltages. But no matter fixed or variable output voltages, ensure the power supply is rated for your application needs. Lower, higher, or unstable voltages can damage any device or circuit connected to the power source.

4. Input voltage

Whether the type of topologies, the power supply must be designed with a specific input voltage range while considering its effect on the output voltage. For example, with a boost converter, the regulator will provide a stable voltage at the output even if the input voltage is low. However, the situation is different with a buck converter because the voltage at the input must be higher than the needed output voltage. It is closely related to the decisions you made about topology.

5. Energy efficiency requirements

Some applications have low power efficiency expectations, which may be overlooked, while others, especially based on battery or inverter, require optimal power efficiency. Therefore, from component topology to component selection and layout, you must ensure that every decision increases rather than reduces the system’s efficiency.

Besides the above factors, other factors need to be considered when designing switch-mode power supplies, such as EMI verification, the temperature range of operation, the expected in-rush current, the switching frequency, and so on. Therefore, designing switch-mode power supplies is a complicated job. That is why it is crucial to conduct comprehensive research on the topic, just as it is essential to rely on an experienced manufacturer of electrical components. This way, it will be easier to design a more reliable and efficient SMPS for any intended application.

MORNSUN’s Switch-mode Power Supplies

Designing a sufficient SMPS power supply for your equipment’s power system is a time-consuming and difficult task requiring specific techniques and plenty of time to market. In addition, designers are under competitive pressure to reduce cost, time, and size. At the same time, the power supply should have high efficiency and meet certain electromagnetic compatibility (EMC) requirements.

The power supply must maintain efficiency and performance over a wide range of AC (and sometimes DC) input voltages and operate under a wide range of temperatures. The power supply should ensure the safety of devices and users by output short-circuit protection and overcurrent protection. Such power requirements significantly prolong system design and verification, delaying time to market. Considering the above restrictions, designers can choose an off-the-shelf SMPS power supply that meets safety regulations.

One of the major advantages of switch-mode power supplies is their higher efficiency. To fully take advantage of this benefit, it is recommended to invest enough time and resources in careful component selection. MORNSUN is dedicated to providing you with the greatest power supply options as a reputable SMPS manufacturer. From 15W to 1000W module offerings, MORNSUN has a large assortment of AC/DC enclosed switching power supplies.

Our products are perfect for various industries, including industrial automation, instrumentation, charging stations, LED, street light management, electric power, smart homes, IoT, medical, etc. They also feature a wide working temperature range and outstanding EMC performance. Our AC/DC enclosed SMPS is more sophisticated and offers a great conformal coating to ensure protection from humidity and air pollutants, in addition to fulfilling the most recent technical requirements of the industry.


LMF350-23BxxUH is the latest ultra-thin series of fanless and semi-potted encapsulation produced by MORNSUN. It is the hospital of the MORNSUN 305RAC family, with an input range of 85-305VAC. It’s suitable for industrial and outdoor applications where the environment is particularly harsh.

MORNSUN’s power supply solutions focus on providing you with professional, safe, and efficient SMPS power supplies, which are affordable and widely used. If you are looking for a reliable SMPS power supplier, feel free to contact us.

For more information, please visit www.mornsun-power.com

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