PURPOSE: To save the electric power as well as to realize a miniature size and light weight for the converter circuit, by obtaining the error voltage equivalent to the difference voltage between the supplied voltage and the reference voltage, converting the error voltage into the current value via the switching element and then varying the duration of the clock pulse according to the current value.

CONSTITUTION: Error voltage detector part 5 compares the supplied voltage V0 with the reference voltage which is set previously in order to detect the error voltage equivalent to the difference voltage. Then transistor Tr7 uses this error voltage as the control signal to insert switching diodes 8....10 between the base voltage and the earth potential as well as to connect the anode side to the base electrode and resistance 6. The detected error voltage is then converted (13) to the current, and the duration of the clock pulse is changed according to the converted current and via the pulse duration changing part. In this way, the power can be saved, also realizing a miniature size and light weight for the converter circuit