DC-AC converter with feedback signal control circuit utilizing power supply voltage, controller IC therefor, and electronic apparatus utilizing the DC-AC converter

A DC-AC converter, comprising:

• a transformer having a primary winding and at least one secondary winding;
• a semiconductor switching circuit arranged to allow electric current to flow from a DC power supply through the primary winding in a first or a second direction;
• a current detection circuit arranged to detect the current flowing through a load connected to the secondary winding to output a current detection signal;
• a voltage detection circuit arranged to detect the voltage applied to the load to output a voltage detection signal;
• a current-error signal generating arranged to generate a current-error signal based on the current detection signal and a current reference signal;
• a voltage-error signal generating circuit arranged to generate a voltage-error signal based on the voltage detection signal and a voltage reference signal;
• a feedback signal formation circuit arranged to provide a feedback signal in accordance with the magnitudes of the current-error signal and voltage error signal;
• a switch drive circuit arranged to provide a drive signal that switches the semiconductor switching circuit on and off in accordance with the feedback signal;
• and
• a feedback signal control circuit arranged to change the feedback signal to reduce the electric power supplied to the load when the DC power supply voltage of the DC power supply sharply rises;
• wherein
• the feedback signal formation circuit includes:
• a current-error control transistor having a control input arranged to receive the current-error detection signal;
• and
• a voltage-error control transistor having a control input arranged to receive the voltage-error detection signal;
• the voltage-error control transistor is connected in parallel with the current-error control transistor to output the feedback signal from a node where the voltage-error control transistor is connected in parallel with the current-error control transistor;
• the feedback signal control circuit includes:
• a sharp-voltage-change detection circuit arranged to receive the DC power supply voltage and arranged to generate a sharp-voltage-change signal by differentiating the DC power supply voltage, the sharp-voltage-change detection circuit including a capacitor and a first resistor;
• and
• a reduction circuit including a transistor switch arranged to receive the sharp-voltage-change signal and a second resistor, the second resistor being connected in series between the transistor switch and the current-error control transistor and in series between the transistor switch and the voltage-error control transistor.