POWER SUPPLY UNIT AND IMAGE FORMING APPARATUS

• US 20070212102A1
• Filed: 02/27/2007
• Published: 09/13/2007
• Est. Priority Date: 03/03/2006
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: YANO, Tetsuya
• Granted Patent: US 7,882,371 B2
• Time in Patent Office: Days
• US Class Current: 399/88
• 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 signal generating unit that includes a converting unit that converts a load current flowing in the load into a current signal, the signal generating unit generating a control signal for compensating a shortfall of the load current indicated by the current signal when exceeding an upper limit of an output current of the first power supply;

a capacitor for charging a power; and

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

the first power supply controls an output voltage therefrom in such a manner that a voltage of a power supply line that is closer to the load than a current detection position of the converting unit is made constant at a setting value.

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

a current indicator that generates a current indicator signal obtained by subtracting the upper limit of the output current from a load current detected by the converting unit, 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 converting unit.

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 converting unit is a current detection resistor.

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 signal generating unit that includes a converting unit that converts a load current flowing in the load into a current signal, the signal generating unit generating a control signal for compensating a shortfall of the load current indicated by the current signal when exceeding an upper limit of an output current of the first power supply;

a capacitor for charging a power; and

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

the converting unit converts the load current at a stage prior to a loading position for an output voltage fed back by the first power supply 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 a current indicator signal obtained by subtracting the upper limit of the output current from a load current detected by the converting unit, 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 converting unit.

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 converting unit 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, wherein

the power supply unit includes

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 signal generating unit that includes a converting unit that converts a load current flowing in the load into a current signal, the signal generating unit generating a control signal for compensating a shortfall of the load current indicated by the current signal when exceeding an upper limit of an output current of the first power supply,

a capacitor for charging a power, and

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

the first power supply controls an output voltage therefrom in such a manner that a voltage of a power supply line that is closer to the load than a current detection position of the converting unit is made constant at a setting value.