Power supply system, image forming apparatus having the same, and control method of the same

A power supply system comprising:

• a switching power supply configured to convert an AC voltage from an AC power supply into predetermined DC voltages, and outputs the DC voltages;
• a switch circuit provided on an AC input line, the switch circuit being configured to be switched on and off and supply AC power to the switching power supply when the switch circuit is turned on, the switch circuit including a switching unit configured to turn on and off the switch circuit;
• a low-capacity power supply circuit connected to the AC input line at a front stage of the switch circuit, the low-capacity power supply circuit including a voltage line that is connected to the switching unit, a first accumulating capacitor that is connected to a first voltage line, a DC-to-DC converter configured to convert a charging voltage of the first accumulating capacitor into another voltage, and a second accumulating capacitor that is connected to a second voltage line on an output side of the DC-to-DC converter, the low-capacity power supply circuit being configured to supply electric power to the switch circuit if the switching power supply is active and supply predetermined electric power if the switching power supply is not used;
• a control device configured, to receive the predetermined electric power from the low-capacity power supply circuit;
• and
• a power detecting circuit configured to detect input of the AC power supply to the AC input line,
• wherein the switching unit is connected to the second voltage line,
• wherein the control device determines whether electric charge necessary for controlling the switch circuit has been accumulated in the low-capacity power supply circuit according to the acquired second line voltage or first line voltage, and turns on the switch circuit if the electric charge necessary for controlling the switch circuit has been accumulated in the low-capacity power supply circuit,
• wherein after detection of input of the AC power supply, if a voltage of the voltage line becomes equal to or higher than a voltage necessary for driving the switching unit, the control device determines that the electric charge has been accumulated, and
• wherein when the switching power supply is not used, the control device turns off the switch circuit to stop supply of the AC power to the switching power supply.

A power supply system comprising:

• a switching power supply configured to convert an AC voltage from an AC power supply into predetermined DC voltages, and outputs the DC voltages;
• a switch circuit provided on an AC input line, the switch circuit being configured to be switched on and off and supply AC power to the switching power supply when the switch circuit is turned on;
• a low-capacity power supply circuit connected to the AC input line at a front stage of the switch circuit, the low-capacity power supply circuit being configured to supply electric power to the switch circuit if the switching power supply is active and supply predetermined electric power if the switching power supply is not used;
• a control device configured, to receive the predetermined electric power from the low-capacity power supply circuit;
• a power detecting circuit configured to detect input of the AC power supply to the AC input line;
• a cutoff detecting circuit configured to detect cutoff of the AC power supply to the AC input line;
• and
• a timer circuit configured to measure the duration of the cutoff, wherein the control device sets the predetermined period to be shorter as the duration decreases;
• wherein when the switching power supply is not used, the control device turns off the switch circuit to stop supply of the AC power to the switching power supply;
• wherein after detection of the AC power supply, if a predetermined period elapses, the control device determines that the electric charge has been accumulated;
• wherein the control device determines whether electric charge necessary for controlling the switch circuit has been accumulated in the low-capacity power supply circuit, and turns on the switch circuit if the electric charge necessary for controlling the switch circuit has been accumulated in the low-capacity power supply circuit.