The concept of stepping up or down certain values has to do with the number of turns each coil contains, that is, how many loops of wire are within the coil. This is important because the number of turns means that there is more efficiency within the transformer and as a result more influence from the primary coil to the secondary coil. To step up or down a certain value what you need to be aware of is which coil has more turns. This is because if the primary coil has more turns than the secondary coil, result would be an output of more current but less voltage. If the secondary coil has more turns than the primary coil then the output of the transformer would be more voltage but less current.
Current and voltage
To determine what the output of the transformer will be you will need to be aware of the math behind the transformer. Ratios are used when specifying the turns but simple dividing and multiplying are the only tools you will need to determining the output of the transformer and both equations can be seen below.
Ratio = secondary coil turns: Primary coil turns
Output Current = Input current * (Primary coil / Secondary coil)
or
I = I(Cp / Cs)
Output Voltage = Input voltage * (Secondary coil / Primary coil)
or
E = E(Cs / Cp)
Let us say that in the picture above the primary coil that has the AC input has an amperage of 2A input and the secondary coil has 1A output. [1] Since we know that if the primary coil has more turns, then the output will be more current. [2] But the output is less current so it means that the primary coil has less turns then the secondary coil. [3] The output current is exactly half of the input [4] The primary coil has exactly half the turns The ratio would be 2:1
