Electrical element, circuit board, and switching power supply

An electrical element, comprising:

• a first magnetic core and a second magnetic core disposed opposite to each other, wherein the first magnetic core and the second magnetic core enclose a space for accommodating a winding;
• and
• a third magnetic core located in the space enclosed by the first magnetic core and the second magnetic core, wherein
• the third magnetic core is configured to wind the winding, the third magnetic core is fixedly connected to at least one of the first magnetic core or the second magnetic core, an air gap is disposed in at least one of the first magnetic core or the second magnetic core,
• at least one of the first magnetic core or the second magnetic core comprises a groove configured to receive a respective end portion of the third magnetic core, wherein the air gap is arranged between the groove and the respective end portion of the third magnetic core which is inserted in the groove,
• wherein the air gap comprises an insulation layer, and the respective end portion of the third magnetic core is fixedly connected to the groove using the insulation layer, and a thickness of the insulation layer is smaller than a gap between a side wall of the groove and a side wall of the third magnetic core.