signal proportional to it a fifth resistor r 5 a third capacitor c 3 and a fourth capacitor c 4 that form the feedback of the second operational amplifier amp 2 compares the voltage signal with the output voltage of the first operational amplifier amp 1 to operate and output a voltage difference accordingly the higher the primary winding current ip a lower value is outputted to the contrary the lower the primary winding current ip a higher value is outputted the third operational amplifier amp 3 that is a stage next to the second operational amplifier amp 2 receives the output voltage of the second operational amplifier amp 2 through a negative terminal u2212 also the third operational amplifier amp 3 receives a sawtooth wave having a certain frequency for example 50 khz through a positive terminal the third operational amplifier amp 3 compares the sawtooth wave with the output voltage of the second operational amplifier amp 2 to operate according to the voltage difference here the third operational amplifier amp 3 does not have a feedback connection and thus it operates in a saturation region therefore when the output voltage of the second operational amplifier amp 2 is greater than the sawtooth wave a positive saturation voltage value is outputted but when the output voltage of the second operational amplifier amp 2 is.