Switching power supply circuit with reduced noise and potential stabilization of stable potential nodes

A switching power supply circuit, comprising:

• a transformer in which a primary side and a secondary side are insulated and separated and power is transmitted to the secondary side;
• a switching field effect transistor which performs switching of power in the primary side of the transformer;
• and a rectifier element which rectifies power in the secondary side of the transformer, wherein
• one end of a primary-side terminal of the transformer is connected to a primary-side high-voltage stable potential node,
• the other end of the primary-side terminal of the transformer is connected to a drain of the switching field effect transistor,
• a source of the switching field effect transistor is connected to a primary-side low-voltage stable potential node,
• one end of a secondary-side terminal of the transformer is connected to an anode of the rectifier element,
• a cathode of the rectifier element is connected to a secondary-side high-voltage stable potential node,
• the other end of the secondary-side terminal of the transformer is connected to a secondary-side low-voltage stable potential node,
• a low-voltage node capacitor is connected between the primary-side low-voltage stable potential node and the secondary-side low-voltage stable potential node,
• a high-voltage node capacitor is connected between the primary-side high-voltage stable potential node and the anode of the rectifier element,
• a capacitance value of the low-voltage node capacitor is 5 times or more and 18 times or less of a capacitance value of the high-voltage node capacitor,
• a noise filter is provided on the primary side, and
• a capacitance value of the high-voltage node capacitor is equal to or more than 25 pF and equal to or less than 100 pF by which an inductance value of the noise filter is reduced by half.