POWER SUPPLY DEVICE, HEATING UNIT USING SAME, AND IMAGE FORMING APPARATUS USING SAID HEATING UNIT

• US 20110116823A1
• Filed: 11/02/2010
• Published: 05/19/2011
• Est. Priority Date: 11/17/2009
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Suda, Takeyuki
• Granted Patent: US 8,401,417 B2
• Time in Patent Office: Days
• US Class Current: 399/88
• CPC Class Codes: G03G 15/2039 with means for controlling the fixing temperature
• CPC Class Codes: G03G 15/80 Details relating to power supplies, circuits boards, electrical connections
• CPC Class Codes: H02M 1/0048 Circuits or arrangements for reducing losses using snubbers H02M1/34
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

The invention reduces loss produced when a power supply device supplies power to a fixing unit of a copier, thereby contributing to a reduction in size, a saving in terms of energy and lower cost. To achieve this, it is arranged so that it is possible to vary the capacitance of a resonant capacitor C200 that constructs a resonant circuit together with a coil 71 through which a high-frequency current flows in order to produce an induced electromotive force in an electrically conductive heating element. In an interval in which a tail current flows after closure of an IGBT 401 that switches the coil current, the capacitance of the resonant capacitor C200 of a switching element SW402 is increased, thereby suppressing a rise in voltage Vce of the IGBT 40 over a fixed interval of time. As a result, loss ascribable to the tail current is reduced.

Claims

1. A power supply device for passing a high-frequency current into an inductive load, comprising:

a generating circuit configured to generate a DC voltage;

a first switch element connected in series with the inductive load and configured to switch the DC voltage generated by said generating circuit;

a driving controller adapted to turn said first switch element on and off;

a variable-capacitance capacitor constructing a resonant circuit together with the inductive load; and

a capacitance controller configured to control the capacitance of said variable-capacitance capacitor;

wherein said capacitance controller controls the capacitance of said variable-capacitance capacitor in such a manner that over a predetermined interval from the moment said first switch element is turned off, the capacitance will exceed the capacitance that prevailed prior to turn-off of said first switch element.

2. The device according to claim 1, wherein said first switch element has a characteristic such that a tail current is produced over a fixed period of time after said first switch element is turned off;

and

said capacitance controller exercises control in such a manner that the capacitance of said variable-capacitance capacitor increases over a predetermined interval that includes at least the period of time in which the tail current is produced.

3. The device according to claim 1, wherein said variable-capacitance capacitor includes a first capacitor, a second capacitor connected in parallel with said first capacitor, and a second switch element connected in series with said second capacitor;

and

said capacitor controller increases the capacitance of said variable-capacitance capacitor by turning on said second switch element, and decreases the capacitance of said variable-capacitance capacitor by turning off said second switch element.

4. The device according to claim 3, further comprising a voltage detector for detecting voltage across terminals of said first switch element;

wherein in a case where said voltage detector detects that the voltage across the terminals of said first switch element exceeds a predetermined voltage value over a predetermined period of time, said capacitance controller turns on said second switch.

5. The device according to claim 3, further comprising a current detector for detecting current flowing into said first switch element;

wherein in a case where said current detector detects that the current flowing into said first switch element exceeds a predetermined current value over a predetermined period of time, said capacitance controller turns on said second switch.

6. The device according to claim 2, wherein said first switch element is an insulated-gate bipolar transistor.

8. The device according to claim 6, further comprising a voltage detector configured to detect voltage across terminals of said first switch element, or a current detector configured to detect current flowing into said first switch element;

wherein in a case where said voltage detector detects that the voltage across the terminals of said first switch element has exceeded a predetermined voltage value over a predetermined period of time, or in a case where said current detector detects that the current flowing into said first switch element has exceeded a predetermined current value over a predetermined period of time, said capacitance controller turns on said second switch.

9. A heating unit comprising:

the power supply device as set forth in claim 1;

an inductive load into which a high-frequency current flows owing to said power supply device; and

an electrically conductive heating element placed opposite said inductive load.

10. An electrophotographic image forming apparatus that uses the heating unit set forth in claim 9 as a fixing unit.

7. A power supply device for passing a high-frequency current into an inductive load, comprising:

a rectifying circuit configured to rectify an alternating current;

a first switch element connected in series with the inductive load and configured to switch the current that has been rectified by said rectifying circuit;

a driving controller adapted to turn said first switch element on and off;

a variable-capacitance capacitor constructing a resonant circuit together with the inductive load, said variable-capacitance capacitor including a first capacitor, a second capacitor connected in parallel with said first capacitor, and a second switch element connected in series with said second capacitor; and

a capacitance controller configured to control the capacitance of said variable-capacitance capacitor by turning said second switch on and off;

wherein in a case where voltage across terminals of said first switch has exceeded a predetermined voltage value over a predetermined period of time, said capacitance controller turns on said second switch element.