Why does an SMPS have a smaller transformer?

Power supplies play a crucial role in our electronic gadgets, ensuring they get the energy they need to function smoothly. When we peek inside these power supplies, we often find transformers that come in different shapes and sizes. Have you ever wondered why the transformer in a Switched-Mode Power Supply (SMPS) is noticeably smaller than its counterpart in a Linear Power Supply, even when they have similar ratings?

Understanding the Basics: let’s grasp the fundamental working principles of both types of power supplies.

  1. Linear Power Supply:
    In a linear power supply, the transformer’s primary job is to step down the voltage from the input to a lower level, making it suitable for powering electronic devices. However, the size of the transformer is determined by the frequency of the AC input power. The higher the frequency, the smaller the transformer can be, but this comes with increased costs.
  2. Switched-Mode Power Supply (SMPS):
    Switched-Mode Power Supplies (SMPS) work by rapidly switching the input voltage on and off at a high frequency, typically tens or hundreds of kilohertz; the main AC supply is first converted to DC using a rectifier and this DC is fed to a High frequency switching device. This switched voltage is then fed through a transformer, which steps it up or down as needed. The output is rectified and filtered to provide a stable DC voltage for electronic devices. This rapid switching allows the transformer in an SMPS to be much smaller compared to its linear counterpart.

The key to the smaller size of an SMPS transformer lies in its ability to operate efficiently at high frequencies. Here are the main reasons:

  1. Reduced Core Size:
    SMPS transformers operate at frequencies far higher than the 50-60 Hz used in linear power supplies. This high frequency allows for a significant reduction in the size of the transformer’s core without sacrificing performance. Smaller cores mean less material and, consequently, a more compact transformer.
  2. Less Copper Winding:
    The high-frequency operation also results in fewer turns of copper winding on the transformer. With fewer turns, the winding takes up less space, contributing to the overall reduction in size. This efficiency in copper usage is a substantial factor in making SMPS transformers compact.
  3. Lighter and More Portable:
    The combination of a smaller core and reduced copper winding not only results in a compact transformer but also makes the entire power supply lighter. This is a significant advantage for electronic devices where portability is key, such as laptops, smartphones, and other gadgets.

The smaller size of an SMPS transformer compared to its linear counterpart boils down to the magic of high-frequency operation. The efficiency gains achieved through reduced core size and copper winding make SMPS a preferred choice for modern electronic devices, enabling them to be both powerful and portable. So, the next time you marvel at the sleek design of your laptop charger or the compact size of your smartphone adapter, remember that the SMPS transformer inside is working its high-frequency magic to keep things small yet powerful.

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