and a thermal sensing device the energy storing device is coupled to an input power source and controlled by the power switch to increase or decrease the power therein the power switch has a control terminal connected to the driving circuit for switching the thermal sensing device is connected to the control terminal of the power switch and powered by the driving circuit when sensing an operation temperature exceeding a predetermined range the thermal sensing device disables the driving circuit application_number US 48425309 A description to facilitate a further comprehension of objectives characteristics and advantages of the present invention the following paragraphs bring out preferred embodiments in conjunction with accompanying drawings for detailed explanation for ease of explanation same or similar functions will be represented by the same element symbol therefore the same symbols in different embodiments do not necessarily mean that two elements are completely the same the scope of the present invention is dependent on the limitations recited in the claims fig2 is a diagram of a switching power supply 80 according to an embodiment of the present invention switching power supply 80 is a flyback power converter converting energy inputted by the ac power source v ac into an output power source v out all the same or similar elements represented by the same symbol in fig1 and fig2 are explained in the prior art and therefore further description will be omitted here for brevity unlike the conventional configuration shown in fig1 thermistor 86 and resistor 88 in this embodiment are connected in series between the control terminal of power switch 72 and the electrical ground gnd the connecting point between thermistor 86 and resistor 88 is connected to.