A series-parallel circuit has some components in series and others in parallel. The power source and control or protection devices are usually in series; the loads are usually in parallel. The same current flows in the series portion, different currents in the parallel portion. The same voltage is applied to parallel devices, different voltages to series devices. If the series portion is broken, current stops flowing in the entire circuit. If a parallel branch is broken, current continues flowing in the series portion and the remaining branches.

A resistance and lamps may be connected in a circuit as illustrated below. This type of connecting method is called series-parallel connection, and is a combination of series and parallel connections. The interior dash board lights are a good example. By adjusting the rheostat, you can increase or decrease the brilliance of the lights.

Serial and parallel circuit

a. practical view; b. electronical view

The switch has the role to provide current to the circuit so that the other components can function properly. And the power supply has the principal role to generate energy for the circuit.

The combined resistance R₀₂ in this series-parallel connection can be determined in the following order:

· determine combined resistance R₀₁, which is a combination of resistances R₂ and R₃ connected in parallel;

· then, determine resistance R₀₂, which is a combination of resistance R1 and combined resistance R₀₁ connected in series.

 

Total current I flowing in the circuit can be determined from Ohm's law as follows:

The voltage applied to R₂ and R₃ can be found by the following formula: