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Transformer versus switch-mode power supply: Advantages of transformers

What are the advantages and disadvantages of transformers and switch-mode power supplies? Why is a transformer the better choice for long-life, premium and safety-relevant products or applications, such as those used in the medical sector? We have weighed the pros and cons for you and summarized them as follows.

The answer to the question as to the right choice of power supply for an electrical device – transformer or switch-mode power supply – would seem obvious on initial consideration: switch-mode power supplies, which due to their predominantly electronic design are generally lighter and smaller than transformers with comparable performance. They are less expensive to manufacture and are therefore used primarily in mass products with low power requirements and a shorter life expectancy.

That already defines the area of application for switch-mode power supplies. Due to the use of numerous electronic components they are much more likely to fail and have a lower life expectancy than a transformer, and they are also very susceptible to fluctuations in temperature and humidity. The danger of fire is also higher.

Transformers, on the other hand, are much less sensitive to current and voltage fluctuations, and to current and voltage peaks from the power grid. The output voltage is a very clean sinusoidal voltage with optimal power quality, as opposed to the high-frequency operation of switch-mode power supplies, which often causes problems in sensitive applications such as amplifiers. Interference from nearby electrical devices is not a problem with transformers. In addition, transformers offer safe isolation due to the greater thickness of the materials used for their construction.

Switch-mode power supplies are not suitable for high power requirements, unless one is willing to accept a substantial increase in weight and volume. But that would eliminate their main advantages. A transformer causes no EMC interference or emissions and is insensitive to high-frequency irradiation. A switch-mode power, supply on the other hand, requires preventive and protective measures, in addition to inspections.

On the whole, long-life transformers are clearly preferable for premium applications in which trouble-free operation and reliability are essential. A transformer is much more robust in quality and operates more reliably than a switch-mode power supply. That also makes it the more economical solution in the medium term. The costs and uncertainties associated primarily with Asian supply chains for switch-mode power supplies are not a factor with ISMET transformers, since they are manufactured exclusively in Central Europe.

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