Power supply device and image forming apparatus

1. A power supply device comprising:

an auxiliary power supply unit configured to be charged with a direct-current electric power, the auxiliary power supply unit being a second capacitor;

a constant-voltage power supply unit that includes

a charging unit configured to convert an alternating-current electric power from an alternating-current power source into direct-current power,

a third switch, and

a first switching control unit configured to alternate a supply of converted direct-current power between a first load and the second capacitor via the third switch;

a voltage converting unit configured to convert a first voltage of the auxiliary power supply unit into a second voltage, the voltage converting unit including

a second switch, and

a first capacitor,

wherein the voltage converting unit is configured to

control a soft-switching of the second switch that switches on and off a supply of electric power of a second voltage to the first capacitor, and

generate voltage by the soft-switching of the second switch, the voltage converting unit stopping voltage generation when the second switch halts the soft-switching and becomes an open state;

a voltage-conversion control unit configured to control the voltage converting unit;

a voltage determining unit configured to determine whether the second voltage exceeds a predetermined threshold;

a first switch that is arranged between the voltage converting unit and a second load, the first switch switching on and off a supply of an electric power of the second voltage to the second load; and

a second switching control unit that controls the first switch,

wherein when the voltage determining unit determines that the second voltage exceeds the predetermined threshold, the voltage-conversion control unit controls the voltage converting unit to stop converting the voltage, and then the second switching control unit controls the first switch to supply the electric power of the second voltage to the second load,

wherein while an inrush current flows into a second load located in a subsequent stage of an output terminal through the voltage converting unit as a supply of the electric power, only an electric charge charged in the first capacitor flows into the second load, and as a result no high current flows through the voltage converting unit and power loss is reduced.

2. The power supply device according to claim 1 , wherein

the first capacitor is temporarily charged with the electric power of the second voltage, and the voltage converting unit supplies a charged electric power to the second load, and

when the voltage determining unit determines that the second voltage of the charged electric power exceeds the predetermined threshold, the voltage-conversion control unit controls the second switch to stop supplying the electric power of the second voltage to the first capacitor.

3. The power supply device according to claim 2 , wherein when the voltage determining unit determines that the second voltage drops below the predetermined threshold, the voltage-conversion control unit controls the voltage converting unit to resume converting the voltage.

4. The power supply device according to claim 2 , wherein the voltage converting unit converts the first voltage into the second voltage by a soft-switching of the second switch.

5. The power supply device according to claim 1 , wherein the voltage-conversion control unit controls the voltage converting unit to resume converting the voltage in a predetermined time.

6. The power supply device according to claim 1 , further comprising a constant-voltage power supply unit that converts an alternating-current voltage from the alternating-current power source into a direct-current voltage,

wherein the charging unit charges the auxiliary power supply unit with a converted direct-current electric voltage.

7. The power supply device according to claim 1 , further comprising an interface unit that is connected to an external unit to establish a communication with the external unit,

wherein when the power supply device receives a signal from the external unit via the interface unit, the charging unit determines an operation state of the external unit based on the signal, and controls charging of the auxiliary power supply unit depending on the operation state.

8. The power supply device according to claim 7 , wherein when the power supply device receives the signal from the external unit via the interface unit, the voltage-conversion control unit determines the operation state of the external unit based on the signal, and controls the voltage converting unit to convert the voltage depending on the operation state.

9. The power supply device according to claim 1 , wherein the voltage converting unit converts the first voltage into the second voltage by boosting the first voltage.

10. The power supply device according to claim 1 , wherein the second load is a heater.

11. The power supply device according to claim 1 , wherein the second load is a motor.

12. An image forming apparatus comprising:

a power supply device configured to supply an electric power to a second load, the power supply device including

an auxiliary power supply unit configured to be charged with a direct-current electric power, the auxiliary power supply unit being a second capacitor,

a constant-voltage power supply unit that includes

a charging unit configured to convert an alternating-current electric power from an alternating-current power source into direct-current power,

a third switch, and

a first switching control unit configured to alternate a supply of converted direct-current power between a first load and the second capacitor via the third switch;

a voltage converting unit configured to convert a first voltage of the auxiliary power supply unit into a second voltage, the voltage converting unit including

a second switch, and

a first capacitor,

wherein the voltage converting unit is configured to

control a soft-switching of the second switch that switches on and off a supply of electric power of a second voltage to the first capacitor, and

generate voltage by the soft-switching of the second switch, the voltage converting unit stopping voltage generation when the second switch halts the soft-switching and becomes an open state;

a voltage-conversion control unit configured to control the voltage converting unit,

a voltage determining unit configured to determine whether the second voltage exceeds a predetermined threshold,

a first switch that is arranged between the voltage converting unit and a second load, the first switch switching on and off a supply of an electric power of the second voltage to the second load, and

a second switching control unit that controls the first switch,

wherein when the voltage determining unit determines that the second voltage exceeds the predetermined threshold, the voltage-conversion control unit controls the voltage converting unit to stop converting the voltage, and then the second switching control unit controls the first switch to supply the electric power of the second voltage to the second load,

wherein while an inrush current flows into a second load located in a subsequent stage of an output terminal through the voltage converting unit as a supply of the electric power, only an electric charge charged in the first capacitor flows into the second load, and as a result no high current flows through the voltage converting unit and power loss is reduced.