Power source circuit and ocean-floor optical cable

A power source circuit comprising a plurality of circuit elements each including:

• a current control circuit including
• a DC/DC converter configured to input a predetermined voltage and output a voltage being adjusted based on a control signal for feedback control, to a load to be operated by feeding a predetermined current,
• a voltage dividing resistor configured to generate a reference voltage according to a voltage being output from the DC/DC converter,
• a current detecting resistor configured to generate a current detecting voltage according to a current being fed to the load, and
• a feedback circuit configured to compare the reference voltage and the current detecting voltage with each other and output the control signal indicating a comparison result, to the DC/DC converter;
• and
• one or more Zener diodes being connected in parallel to the DC/DC converter at a terminal for inputting the predetermined voltage, wherein
• a plurality of the circuit elements are connected to one another in series, and
• a system current is supplied from an external power source to a plurality of the circuit elements being connected to one another in series.