What Type of Transformer do you Need?
There are many kinds of transformers available, from standard laminated core to a range of more specialist types which offer different properties and features. Different types are suitable for different purposes, but it can be hard to know which kind you need for a given electronics project.
Of the main kinds of transformer, the type you need will of course depend on the application and on what exactly you need from it.
Good, General-Purpose Performance
Laminated core transformers are the most common kind and essentially represent the standard transformer. This is because they offer good, reliable performance and are very flexible. They make excellent general-purpose transformers, and are probably the best choice if your needs are essentially straightforward and all you need is a transformer that will do its job effectively.
If you need a transformer that will be as complex as possible, then you may want to consider a toroidal transformer. These offer comparable performance to laminated core transformer types, but are considerably more space efficient than other kinds of transformer of equivalent ratings. They are, however, more expensive than laminated core transformers, as the process of manufacturing them is slower and more complicated. They are also less widely available, though many specialist vendors such as Siga Transformers can supply a variety of toroidal and other specialist transformer types.
Autotransformers are also more compact than many other types of transformer of equivalent power ratings, and unlike toroidal transformers are also a very affordable variety. However, be aware that they are only suitable for use in applications where voltage ratios are under 3:1, and this of course limits their flexibility between different projects. If your voltage ratios are suitable they can be a practical and affordable solution, but otherwise they will simply not be an option that is open to you.
For applications where various voltages will be required at different times, then variable transformers are naturally the way to go. The only alternative would be to use multiple transformers, which are obviously less convenient and would quickly become entirely unworkable if more than a couple of voltages or continuous variation were required. The most common type of variable transformer by far is a kind of autotransformer. This provides easy adjustment of voltage and extremely small increments, offering a near continuous range of output voltage options.