FIGS. 9 and 10 are examples of auxiliary DC/DC converters 7, incorporating therein a ringing choke converter. As transistor Q10 is activated by starting resistor RS, a positive feedback is made through a closed loop starting and ending with coil N1 past coil N2, base current iB, and collector current iC, thereby triggering an oscillation, and, consequently, generating an AC voltage in coil N3 or N4. The output AC voltage is rectified and smoothed to become DC voltages E01 and E02.