Switching power-supply

A switching power-supply, comprising:

• a transformer including a primary main winding, a secondary output winding and a feedback winding;
• a switching element, which is connected in series with said primary main winding in a primary DC power-supply and having a control terminal which is connected to one end of said feedback winding;
• a first control element which is connected to a control terminal of said switching element;
• an output stabilization circuit which is connected between the control terminal of said first control element and said feedback winding;
• an overcurrent protection circuit which is connected between the control terminal of said first control element and said feedback winding;
• a secondary DC power-supply and a circuit for rectifying and smoothing the output of said secondary DC power-supply;
• an output voltage detection circuit connected to said secondary DC power-supply;
• an oscillation frequency inhibit circuit having a second control element for controlling a switching frequency of said switching element so that it does not exceed a predetermined frequency;
• and
• an operation switching circuit for causing said oscillation frequency inhibit circuit to operate in response to a light load signal, and for causing said oscillation frequency inhibit circuit to stop operating in response to a heavy load signal.