DC-DC switching power supply with power factor correction

A switching power supply apparatus comprising:

• a power factor correction converter including a rectifying circuit arranged to perform full-wave rectification on AC input power supply, a switching circuit arranged to perform switching of a voltage output from the rectifying circuit, an inductor arranged to allow a current intermittently supplied from the switching circuit to flow, a rectifying/smoothing circuit arranged to rectify and smooth a voltage output from the inductor, and a peak-current control circuit arranged to drive the switching circuit in a critical mode at a timing when a current supplied to the inductor becomes zero and to control the switching circuit so that a phase of a peak value of the current supplied to the inductor follows a phase of a voltage signal supplied from the AC input power supply;
• and
• an isolated DC-DC converter including a transformer, a switching circuit which is connected to a primary winding of the transformer and arranged to perform switching of an output from the power factor correction converter, and a rectifying/smoothing circuit arranged to rectify and smooth an AC voltage generated in a secondary winding of the transformer and to output the AC voltage to an output terminal;
• wherein
• a digital control circuit arranged to define the peak current control circuit is disposed on a secondary side of the transformer of the isolated DC-DC converter;
• a circuit arranged to transmit a switching control signal output from the digital control circuit to the switching circuit included in the power factor correction converter in an isolated state, a circuit arranged to transmit a signal used to detect a voltage output from the power factor correction converter to the digital control circuit in an isolated state, a circuit arranged to transmit a value of the current supplied to the inductor included in the power factor correction converter to the digital control circuit in an isolated state, and a circuit arranged to transmit a timing when the current supplied to the inductor included in the power factor correction converter becomes zero to the digital control circuit in an isolated state are included;
• a circuit arranged to transmit a voltage signal supplied from the AC input power supply to the digital control circuit in an isolated state is included;
• the circuit arranged to transmit a voltage signal supplied from the AC input power supply in an isolated state includes a circuit arranged to detect a current supplied to the switching circuit included in the power factor correction converter or a current supplied to the rectifying/smoothing circuit included in the power factor correction converter in an isolated state;
• and
• the digital control circuit includes a calculating circuit arranged to detect an instantaneous value of a voltage input to the power factor correction converter in accordance with a difference between a minimum value and a maximum value of the current supplied to the switching circuit included in the power factor correction converter or the current supplied to the rectifying/smoothing circuit in the power factor correction converter, an inductance of the inductor included in the power factor correction converter, and an on-period of the switching circuit included in the power factor correction converter.