Why are some transformers one sided?

Question

From the schematic point of view, some transistors are one sided (primary only). What's the point in that? Isn't the secondary part (stepped up or down) the output that we are looking for?

In this case there is no secondary. Pin wise, it's either 2 pins or 3 pins (for CT type)

There are some one sided current sense xfmr with center tap.

http://www.pulseeng.com/products/datasheets/P578.pdf
(take a look at schematic 2B)

Answer 1

agrees the above answer by bogdn ,,,, there is a small correction in ur question , it is mentioned about potental type - voltage transformer in you first para. the one u mentioned in second para - CT type - is current transformer or torroid

Answer 2

You encountered an autotransformer. They have no secondary coils, the output you are looking for is obtained from the single coil they have. You probablly noticed one or more wires comming out of the certain positions of the coil. Usually, the imput is applied on the ends of the coil, and the output is obtained from one end of the coil and a point somewhere in the coil. In this case the output voltage is smaller than the input voltage. If you needed a higher voltage, the input voltage were applied to one end of the coil and some point in the middle of the coil, and the output voltage is obtained from the ends of the coil.
I hope this is clear to you now

Answer 3

One example of an autotransformer is a car's ignition coil.

An autotransformer must have at least 3 connections.

The second correspondent's "CT type - is current transformer or torroid" makes no sense at all.

CT, when referring to transformer windings, means centre tap (or tapped) and torroid refers to the construction not to the use.

Answer 4

For Transformer with 2 pins, it's acutally an Inductor. This is also indicated in the brochure you have attached. Inductor is use in e.g LC circuit. So, it's a for a different application than for a Transformer; to step up/down and isolation.