What type of transformers are used for ignition purposes?

The correct choice for the type of transformers used for ignition purposes is step-up transformers. These transformers are designed to increase the voltage from a lower level to a higher level, which is essential for igniting fuel in various applications, particularly in gas appliances and engines.

In ignition systems, higher voltages are necessary to create a spark that can ignite the air-fuel mixture. Step-up transformers achieve this by having more turns of wire in the secondary coil than in the primary coil, resulting in a higher output voltage. This function is critical in automotive ignition systems and other gas-related ignition applications, as a strong spark is required to ensure efficient combustion.

While step-down transformers decrease voltage, isolation transformers provide galvanic isolation without changing voltage levels, and auto transformers are typically used for voltage regulation rather than ignition purposes. Consequently, they do not fit the specific requirement for generating the high voltage needed for effective ignition.