POWER SUPPLY INCLUDING ZERO-CROSS DETECTION CIRCUIT, AND IMAGE FORMING APPARATUS

• US 20130148998A1
• Filed: 12/10/2012
• Published: 06/13/2013
• Est. Priority Date: 12/12/2011
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Shimura, Yasuhiro
• Granted Patent: US 8,761,631 B2
• Time in Patent Office: Days
• US Class Current: 399/88
• CPC Class Codes: G03G 15/80 Details relating to power supplies, circuits boards, electrical connections
• CPC Class Codes: H02M 1/322 Means for rapidly discharging a capacitor of the converter for protecting electrical components or for preventing electrical shock
• CPC Class Codes: H02M 7/06 using discharge tubes without control electrode or semiconductor devices without control electrode
• CPC Class Codes: H02M 7/217 using semiconductor devices only

Abstract

A power supply includes a first capacitor, a resistor for discharging an electric charge of the first capacitor and for detecting zero crossing of the AC voltage input from the AC power supply, a second capacitor, and a frame ground o and a discharge resistor having a resistance value smaller than the resistor and configured to discharge an electric charge of the second capacitor, and switches between a state where a current to the discharge resistor is cut off and a state where a current flows through the discharge resistor.

Claims

1. A power supply comprising:

a first capacitor provided between lines to which an AC voltage is input from an AC power supply;

a zero-cross detection resistor for discharging an electric charge of the first capacitor and for detecting zero crossing of the AC voltage input from the AC power supply;

a zero-cross detection unit configured to detect the timing of the zero crossing of the AC voltage input from the AC power supply based on a detection signal from the zero-cross detection resistor;

a second capacitor provided between a line to which a voltage obtained by full-wave rectifying the AC voltage that is input from the AC power supply is output, and a frame ground of an image forming apparatus;

a discharge resistor having a resistance value smaller than the zero-cross detection resistor and configured to discharge an electric charge of the second capacitor; and

a first switch configured to switch between a first state where a current to the discharge resistor is cut off and a second state where a current flows through the discharge resistor.

2. The power supply according to claim 1, further having a third state where the current to the discharge resistor is cut off by the first switch, and electric power to be supplied to the zero-cross detection unit is supplied.

3. The power supply according to claim 1, further comprising

a voltage detection unit configured to detect that the AC voltage input from the AC power supply has fallen using the current flowing through the discharge resistor.

4. The power supply according to claim 3, further comprising

a first converter configured to convert the voltage obtained by full-wave rectifying the AC voltage that is input from the AC power supply,

wherein the first converter is stopped when the voltage detection unit detects that the voltage has fallen.

5. The power supply according to claim 3, further comprising

a second switch, and

a second converter configured to convert a voltage obtained by full-wave rectifying or voltage-doubler rectifying the AC voltage that is input from the AC power supply in the succeeding stage of the second switch,

wherein the second converter is stopped by the second switch when the voltage detection unit detects that the voltage has become higher than a threshold value.

6. An image forming apparatus configured to form an image on a recording material and including a fixing unit configured to fix the image formed on the recording material, comprising:

a power supply including a first capacitor provided between lines to which an AC voltage is input from an AC power supply, a zero-cross detection resistor for discharging an electric charge of the first capacitor and for detecting a zero crossing of the AC voltage input from the AC power supply, a zero-cross detection unit configured to detect the timing of zero crossing of the AC voltage input from the AC power supply based on a detection signal from the zero-cross detection resistor, a second capacitor provided between a line to which a voltage obtained by full-wave rectifying the AC voltage that is input from the AC power supply is output, and a frame ground of the image forming apparatus, a discharge resistor having a resistance value smaller than the zero-cross detection resistor and configured to discharge an electric charge of the second capacitor, and a first switch configured to switch between a first state where a current to the discharge resistor is cut off and a second state where a current flows through the discharge resistor;

an electric power supply switch for supplying electric power to the fixing unit; and

an electric power control unit configured to control the electric power supplied to the fixing unit by controlling an operation of the electric power supply switch,

wherein the electric power control unit controls an operation of the electric power supply switch according to a detection result of the zero-cross detection unit.

7. The image forming apparatus according to claim 6, further having a third state where the current to the discharge resistor is cut off using the first switch, and electric power to be supplied to the zero-cross detection unit is supplied.

8. The image forming apparatus according to claim 6, further comprising

a voltage detection unit configured to detect that the AC voltage input from the AC power supply has fallen using the current flowing through the discharge resistor.

9. The image forming apparatus according to claim 8, further comprising

a first converter configured to convert the voltage obtained by full-wave rectifying the AC voltage that is input from the AC power supply,

wherein the first converter is stopped when the voltage detection unit detects that the voltage has fallen.

10. The image forming apparatus according to claim 8, further comprising

a second switch, and

a second converter configured to convert a voltage obtained by full-wave rectifying or voltage-doubler rectifying the AC voltage that is input from the AC power supply, in the succeeding stage of the second switch,

wherein the second converter is stopped by the second switch when the voltage detection unit detects that the voltage has become higher than a threshold value.