A transformer with two leads connected to the primary and three to the secondary is called what?

The designation of a transformer with two leads connected to the primary and three leads connected to the secondary is described as a center-tapped secondary transformer. This setup indicates that the secondary winding is split into two equal halves, allowing for a center tap, which can be used for various applications, such as providing two different voltages (one at the center tap and the other at either end of the winding).

In a center-tapped configuration, the center tap serves as a neutral point, which enhances the versatility of the transformer for producing dual voltages. This is often used in power supplies for devices that require both positive and negative supply voltages.

The other types mentioned in the options refer to transformers with specific voltage transformation characteristics or purposes. A step-up transformer increases voltage from primary to secondary, while a step-down transformer decreases voltage. An isolation transformer is designed primarily to isolate different sections of a circuit for safety or noise reduction but does not inherently imply a center tap in its design.

Therefore, the correct identification of the transformer type as a center tapped secondary transformer helps to highlight its unique purpose and configuration in electrical engineering.