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Chapter 7. Project: A simple adjustable DC power supply

The transformer

In this project we use all the components we've learned about in the previous lessons. The only new component is a transformer. A transformer transforms high voltages to low voltages (or vice versa). It basically consists of two coils of wire wrapped around a soft-iron core. When you connect one of the coils to an AC voltage source, it produces an alternating magnetic field in the soft-iron core. This magnetic field also flows in the core of the second coil. This causes an alternating current flow in the second coil.

The coil connected to the source is called the primary coil; the second coil, connected to the load, is called the secondary coil.

The voltage ratio is equal to ratio of the number of turns of each coil:


The current ratio is equal to: is:ip=Np:Ns

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