Transformers are handy devices used in many electronic circuits to obtain the right voltage, among other applications. Transformers are found in all sorts of electronic equipment, including TVs, radios and home computers. Another common household application of transformers is found in decorative lighting fixtures, where small bulbs are commonly used. Most of these devices require low voltages, around 5-50 volts and/or DC voltages instead of the AC 110 volts delivered from the wall outlet. Other devices, such as the TV, may require much higher voltages than that obtained from the outlet.
Transformers can be used to either step-down voltage or step-up voltage to whatever is required. The earliest transformers were all magnetic, using a common iron core with two sets of wires wrapped around either side (called primary and secondary). The voltage gain in the transformer is adjusted by changing the ratio of the number of secondary to primary turns in the wire. Magnetic transformers are available in a wide variety of sizes and shapes, including the very large transformers often seen on power lines and for industrial applications.
An electronic transformer operates in a similar fashion to a magnetic transformer. The electronic transformer still uses a common iron core and two sets of wires, but it also has an inverter that operates at much higher frequencies than the magnetic transformer. Current in the electronic transformer operates at about 20,000 to 40,000 Hz compared to the wall outlet 50-60 Hz current used by the magnetic transformer. Because of the high frequency of the current in the electronic transformer, the device can be much smaller than a mechanical transformer. Due to its small size, the electronic transformer can often be directly incorporated into a light fixture or other electronic device instead of being attached as a separate piece of equipment. Magnetic transformers tend to be bulky and hard to hide; even if an electronic transformer can't be integrated into directly into a product, the small size often makes it easier to hide.
However, magnetic transformers still have their uses, even in home applications. Magnetic transformers are usually more rugged than electronic transformers and they are also often cheaper and can be operated over a wider range of conditions. To decide which type of transformer is best for a particular circuit, examine the requirements of that circuit, including its location and expected operating procedures.
In addition to simply stepping up or down voltage, both electronic and magnetic transformers can also be used in other applications. For example, a transformer can be used as part of a dimmable switch, to help protect a circuit or to smooth out power. This last application can be particularly useful when building circuits that may require operation from noisy power sources such as emergency generators.