As the current drawn from a power supply unit increases, the output voltage drops. The fall in voltage between the value at no-load and at the rated current expressed as a percentage of the no-load voltage is termed the regulation. In Figure 1 the upper line (1) shows the voltage curve of a typical power supply unit and the lower line (2) that of a typical battery charger having the same current capacity. The fall in voltage of the battery charger is deliberately made much steeper in order to ovoid overload when con nected to a flat battery. Battery chargers are a convenient and relatively cheap means of obtaining a dc power supply unit and are built to high safety standards, but because of their poor regulation it is best to use one with a current output of between 1.5 to 2 times that of a purpose designed power supply unit (line 3).


Figure 1. Typical regulation curves.