Constant current switching power supply

A switching power supply circuit which is configured to receive a voltage from a direct current voltage source and supply a direct current power to a load part, the switching power supply circuit comprising:

• a switching element;
• a current detection circuit which is serially connected to the switching element, and which is configured to convert a current flowing in the switching element into a voltage and detect the voltage;
• a control circuit which is configured to output a switch driving signal to the switching element to control an ON/OFF operation of the switching element such that a current flowing in the load part becomes constant;
• a reference voltage generation circuit which is configured to generate a reference voltage proportional to an ON duty of the switch driving signal;
• and
• an error amplification circuit which is configured to output error information between a voltage output from the current detection circuit and the reference voltage, to the control circuit,
• wherein the control circuit is configured to adjust the ON duty of the switch driving signal based on the error information.