Toroidal core transformers indeed offer high power conversion efficiency, making them desirable in various applications. However, their advantages come with certain drawbacks, and it's essential to consider these factors when deciding on their usage.

The primary disadvantage of toroidal core transformers lies in the complexity of their processing and manufacturing. The toroidal shape makes winding the coil around the core more challenging compared to other transformer configurations. This complexity can increase production costs and limit the widespread adoption of toroidal transformers.

Furthermore, the small size advantage of toroidal core transformers becomes less apparent when operating at lower frequencies. At lower frequencies, the cross-section of the toroidal core needs to be increased to prevent magnetic saturation. This phenomenon occurs because the ring core can easily reach magnetic saturation at lower frequencies, necessitating a larger cross-section to maintain optimal performance.

The efficiency of toroidal core transformers, however, remains consistently high regardless of the operating frequency. The design characteristics that contribute to high efficiency, such as reduced magnetic flux leakage, still hold when the transformer operates at lower frequencies.

Despite their efficiency, toroidal core transformers face limitations in certain applications. They are highly brittle, possess low thermal expansion capacity, and are prone to breakage. These factors make them less suitable for applications requiring robustness and durability, particularly in comparison to traditional silicon steel transformers.

While toroidal core transformers may not be ideal for power supply voltage transformation due to their brittleness and low thermal expansion capacity, they find applications in audio equipment, lighting systems, and other scenarios where compact size and high efficiency are paramount.

In conclusion, the advantages of toroidal core transformers, such as high efficiency and compact size, are most pronounced at higher operating frequencies. However, challenges in processing, manufacturing, and limitations in robustness make them less suitable for certain applications, especially those involving power supply voltage transformation. Careful consideration of these factors is crucial when determining the optimal use of toroidal core transformers in different scenarios.