Power supply unit and image forming apparatus

• US 7,882,371 B2
• Filed: 02/27/2007
• Issued: 02/01/2011
• Est. Priority Date: 03/03/2006
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Yano, Tetsuya
• Primary Examiner(s): Lee; Thomas
• Assistant Examiner(s): Kinsey; Brandon
• Application Number:
  US11/679,522
• Publication Number:
  US 20070212102A1
• Time in Patent Office: 1,435 Days
• Field of Search: 219/200, 713/300, 399/88
• US Class Current: 713/300
• CPC Class Codes: G03G 15/5004 Power supply control, e.g. power-saving mode, automatic power turn-off

Abstract

A first power supply of a constant-voltage output supplies a power to a load by using an external power. A signal generating unit generates a control signal for compensating a shortfall of a load current when exceeding an upper limit of an output current of the first power supply. A second power supply of a constant-current output supplies a power to the load based on the control signal by using a power from a capacitor. An output voltage of the first power supply is controlled so that a voltage of a power supply line that is closer to the load than a current detection position of a converting unit that converts the load current into a current signal is made constant.

Claims

1. A power supply unit comprising:

a first power supply of a constant-voltage output to supply a power to a load by using a power supplied from an external source as an input source;

a capacitor for charging a power;

a second power supply of a constant-current output to supply a power to the load based on a control signal by using the power from the capacitor as an input source; and

a signal generating unit including a current detector disposed at a position between the load and an output from the first power supply and an output from the second power supply, and a converting unit that converts a load current detected by the current detector flowing in the load into a current signal, wherein the signal generating unit generates the control signal which controls the second power supply to supply the power to the load to compensate for a shortfall of the load current indicated by the generated current signal when the load current exceeds an upper limit of an output current of the first power supply,

wherein the first power supply includes a voltage detector which detects a voltage at a position between the current detector and the load which is fed back into a constant-voltage controller of the first power supply which controls an output voltage therefrom and to maintain, at a set value, a voltage of a power supply line that is provided at a position between the load and the current detector.

2. The power supply unit according to claim 1, wherein the signal generating unit includes

a current indicator that generates the current signal obtained by subtracting the upper limit of the output current from the load current detected by the current detector, and

an output-current control unit that generates the control signal for allowing the second power supply to output a current indicated by the current indicator signal.

3. The power supply unit according to claim 1, wherein the first power supply includes a load-current detecting unit including the current detector.

4. The power supply unit according to claim 1, wherein the first power supply includes the converting unit.

5. The power supply unit according to claim 1, wherein the current detector is a current detection resistor.

12. The power supply unit according to claim 1, wherein the first power supply supplies a power to a second load and the upper limit of the output current of the first power supply is lowered when the first power supply supplies the power to the second load.

13. The power supply unit according to claim 1, wherein the constant-voltage controller compares the detected voltage with a reference voltage to control the output voltage therefrom and to maintain, at the set value, the voltage of the power supply line.

14. The power supply unit according to claim 1, wherein the external source supplies a constant level of power to the power supply unit, and wherein the external source supplies the power for charging the capacitor.

15. The power supply unit according to claim 1, wherein the voltage detector detects the voltage at the position between the current detector and the load on a supply line such that no additional elements are provided on the supply line between the current detector and the load.

6. A power supply unit comprising:

a first power supply of a constant-voltage output to supply a power to a load by using a power supplied from an external source as an input source;

a capacitor for charging a power;

a second power supply of a constant-current output to supply a power to the load based on a control signal by using the power from the capacitor as an input source; and

a signal generating unit including a current detector disposed at a position between the load and an output from the first power supply and an output from the second power supply, and a converting unit that converts a load current detected by the current detector flowing in the load into a current signal, wherein the signal generating unit generates the control signal which controls the second power supply to supply the power to the load and to compensate for a shortfall of the load current indicated by the generated current signal when the load current exceeds an upper limit of an output current of the first power supply,

wherein the converting unit converts the load current at a stage prior to a loading position for a voltage detector which detects an output voltage at a position between the current detector and the load which is fed back by the first power supply to a constant-voltage controller to control the constant-voltage output into the current signal.

7. The power supply unit according to claim 6, wherein the signal generating unit includes

a current indicator that generates the current signal obtained by subtracting the upper limit of the output current from the load current detected by the current detector, and

an output-current control unit that generates the control signal for allowing the second power supply to output a current indicated by the current indicator signal.

8. The power supply unit according to claim 6, wherein the first power supply includes a load-current detecting unit including the current detector.

9. The power supply unit according to claim 6, wherein the first power supply includes the converting unit.

10. The power supply unit according to claim 6, wherein the current detector is a current detection resistor.

11. An image forming apparatus comprising:

an image forming unit that forms an image on a recording medium; and

a power supply unit that supplies a power to an electrical load of the image forming unit, the power supply unit including

a first power supply of a constant-voltage output to supply a power to the load by using a power supplied from an external source as an input source,

a capacitor for charging a power;

a second power supply of a constant-current output to supply a power to the load based on a control signal by using the power from the capacitor as an input source; and

a signal generating unit including a current detector disposed at a position between the load and an output from the first power supply and an output from the second power supply, and a converting unit that converts a load current detected by the current detector flowing in the load into a current signal, wherein the signal generating unit generates the control signal which controls the second power supply to supply the power to the load and to compensate for a shortfall of the load current indicated by the generated current signal when the load current exceeds an upper limit of an output current of the first power supply,

wherein the first power supply includes a voltage detector which detects a voltage at a position between the current detector and the load which is fed back into a constant-voltage controller of the first power supply which controls an output voltage therefrom and to maintain, at a set value, a voltage of a power supply line that is provided at a position between the load and the current detector.