Isolated DC/DC converter and AC/DC converter

An isolated direct current to direct current converter for generating a secondary side voltage on a secondary side from a primary side voltage on a primary side by using a power transformer having a primary side winding and a secondary side winding insulated from each other, the isolated direct current to direct current converter comprising:

• a primary side control circuit that is disposed on the primary side and switches a switching element connected in series with the primary side winding;
• a secondary side control circuit that is disposed on the secondary side and generates a control signal including first control information and second control information on a basis of the secondary side voltage;
• and
• an insulated transmission circuit that transmits, in an insulated manner, each piece of control information included in the control signal to the primary side control circuit;
• the primary side control circuit controlling a switching frequency of the switching element on a basis of the first control information, and controlling a peak value of a primary side current flowing through the primary side winding through the switching element on a basis of the second control information.