Micro transformers are categorized into micro current transformers (including micro current converters) and micro voltage transformers. They are equipment in the power industry, commonly used in various electrical instruments for measurement and protection purposes. Compared to conventional transformers, micro transformers have advantages such as smaller size (which can be as small as a fingernail) and higher accuracy (conventional transformers have four accuracy levels: 0.5, 0.5S, 0.2, and 0.2S, while micro transformers can achieve level 0.1).

A micro voltage transformer is a current-type voltage transformer. In the primary circuit, a resistor is connected in series, while in the secondary circuit, a resistor is connected in parallel. This converts the voltage into current. After the current transformation by the transformer, the primary output current signal is converted into the required voltage through a sampling resistor. Most micro voltage transformers are used by being plugged into a circuit board.

The primary side of a micro current transformer (including micro current transducer) has no resistance. A common micro current transformer is one with a resistor connected in parallel on the secondary side, producing a current output. The micro current transducer within the micro current transformer has a resistor connected in parallel on the secondary side, producing a voltage output. Micro current transformers are available in two types of usage: multi-turn winding type (inserted into a circuit board) and through-core type.