| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power-supply device having high output-voltage accuracy while enhancing surge breakdown voltage by a simple configuration.SOLUTION: A switching power-supply device comprises: a detection circuit detecting an output voltage of a secondary-side circuit; and a relay circuit feeding back the detection result of the detection circuit to a primary-side circuit with the primary-side circuit and the secondary-side circuit being insulated. The detection circuit has a first light-emitting element emitting light with the amount of light according to the detected output voltage. The relay circuit has a first light-receiving element generating a current according to the amount of light of the light from the first light-emitting element, and a second light-emitting element emitting light of the amount of light according to the magnitude of the current generated by the first light-receiving element. The primary-side circuit has a second light-receiving element generating a current according to the amount of light of the light from the second light-emitting element, and on/off-controls a current of a primary winding on the basis of the magnitude of the current generated by the second light-receiving element. The impedance between the primary-side circuit and the relay circuit is substantially the same as the impedance between the secondary-side circuit and the relay circuit. |
