3. Passive Devices

• Passive devices will have the same operating characteristics at the same operating points.

3.1 Transformers

• A transformer can be viewed as a converter that can increase voltage and lower current, or vice versa. It only works when using AC.

• The transformer is effectively a magnetic circuit. The transformer has two or more coils of wire wrapped about a common core.


• The ideal relationship is,


• If a transformer has an iron core it will be shown with lines in the centre,


• To deal with a transformer in a circuit analysis we need to pay attention to the polarity of the coils, and we may consider the inductance of each coil at times.

• Consider the example below, from [Nilsson, pg. 450]. We want to find the power delivered to the 1ohm resistor. We will use the mesh current method,