Control transformers are generally used in electronic circuits that require constant voltage or
constant current with a low power or volt-amp rating. Various filtering devices, such as
capacitors, are used to minimize the variations in the output. This results in a more constant
voltage or current.
The auto transformer is generally used in low power applications where a variable voltage is
required. The auto transformer is a special type of power transformer. It consists of only one
winding. By tapping or connecting at certain points along the winding, different voltages can
be obtained (Figure 8).
Figure 8 Auto Transformer Schematic
Isolation transformers are normally low power transformers used to isolate noise from or to
ground electronic circuits. Since a transformer cannot pass DC voltage from primary to
secondary, any DC voltage (such as noise) cannot be passed, and the transformer acts to isolate