What is the function and possible applications of a center-tap primary coil transformer?

  • \$\begingroup\$ Is that an AC power, Audio, or RF transformer? \$\endgroup\$ Aug 21, 2014 at 15:07

1 Answer 1


Basically, have a tap in the primary of the transformer, allows you to adjust the output voltage to possible varying conditions of input voltage. This applies, for example, to power distribution transformers, which usually have 3, 5, 7 taps and a rotary switch to select between them.

Moreover, a center tap, is often found in transformers which are used in two different line voltages. The connection between one end and the center tap corresponds to the lowest voltage (eg 120 V), while the connection between one end and the other corresponds to higher voltage (eg 240 Vac).

  • \$\begingroup\$ Secondarily it can also be helpful if you wish to use certain types of rectifiers, such as the "Center-Tapped Full Wave Rectifier". \$\endgroup\$
    – DylanM
    Aug 21, 2014 at 12:58
  • \$\begingroup\$ @DylanM Yes. I did not include this description in the answer, since the question explicitly says "primary coil" but it is a good consideration. \$\endgroup\$ Aug 21, 2014 at 13:06
  • \$\begingroup\$ It can also be used as an auto-transformer (see en.wikipedia.org/wiki/Autotransformer) \$\endgroup\$ Aug 21, 2014 at 13:10
  • \$\begingroup\$ @JImDearden Yes, it's possible, but why use the primary coil of a transformer as an auto-transformer? I think it is not economical ... Furthermore, in an auto-transformer, the cross section of the coil conductor varies according to the number of turns and the connecting point (on the same auto-transformer), to optimize cost. \$\endgroup\$ Aug 21, 2014 at 13:18
  • \$\begingroup\$ @Tinchito I suggested it as a 'possible application' (as asked for in the OQ but not covered in your answer.) Such transformers are not just limited to low frequency power supplies. \$\endgroup\$ Aug 21, 2014 at 13:32

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