Patent ID: 8004204

Claim:
A power circuit for supplying electric power to a first load circuit driven with a first driving current and a second load circuit driven with a second driving current that is larger than the first driving current, the power circuit comprising a transformer, a constant current circuit, and a current adding circuit, wherein the transformer includes a first winding and a second winding; wherein the constant current circuit includes a voltage generating circuit, a current detecting circuit, and a controlling circuit, and supplies the first driving current to a series load circuit formed by electrically connecting the first load circuit and the second load circuit in series; wherein the current adding circuit obtains energy from electric current flowing through the second winding and supplies electric current having a current value corresponding to a difference between the first driving current and the second driving current to the second load circuit; wherein the voltage generating circuit obtains energy from electric current flowing through the first winding and generates voltage to be applied to the series load circuit; wherein the current detecting circuit treats either of the first load circuit and the second load circuit as a current detection target circuit and detects driving current flowing through the current detection target circuit; and wherein the controlling circuit controls the voltage generating circuit so that the driving current detected by the current detecting circuit becomes a predetermined current value.