Switching power supply device, AC power supply device, and image forming apparatus

A switching power supply device comprising:

• a switching power supply integrated circuit that includes
• a dead time generating unit that generates a high-side drive signal and a low-side drive signal having a dead time based on a pulse width modulation signal,
• a drive signal generating unit that
• includes a current supply, a comparator, an AND circuit, and an OR circuit, and
• generates a first PWM signal and a second PWM signal based on the high-side drive signal, the low-side drive signal, and a voltage of an output terminal of the switching power supply integrated circuit, and
• a driver that includes a high-side switch element driven by the first PWM signal and a low-side switch element driven by the second PWM signal, the high-side switch element having a drain connected to the output terminal and a source connected to a power supply, the low-side switch element having a drain connected to the drain of the high-side switch element and a source connected to ground;
• a filter that is connected to the output terminal and includes a coil for cutting off a high frequency and a capacitor for passing the high frequency;
• a first diode that has a cathode connected to the source of the high-side switch element and an anode connected to the output terminal, the first diode being arranged outside the switching power supply integrated circuit;
• and
• a second diode that has an anode connected to the source of the low-side switch element and a cathode connected to the output terminal, the second diode being arranged outside the switching power supply integrated circuit,
• wherein one of the first diode and the second diode conducts in a period in which both of the high-side switching element and the low-side switching element are turned off,
• wherein the drive signal generating unit generates the first PWM signal for turning on the high-side switching element when the second diode is turned off, and
• wherein the drive signal generating unit generates the second PWM signal for turning on the low-side switching element when the first diode is turned off.