POWER SUPPLY CIRCUIT AND IMAGE FORMING APPARATUS

• US 20170277108A1
• Filed: 03/16/2017
• Published: 09/28/2017
• Est. Priority Date: 03/23/2016
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Masaki, Takuya
• Granted Patent: US 10,018,955 B2
• Time in Patent Office: Days
• CPC Class Codes: G03G 15/0283 Arrangements for supplying power to the sensitising device
• CPC Class Codes: G03G 15/80 Details relating to power supplies, circuits boards, electrical connections
• CPC Class Codes: H03F 2200/432 Two or more amplifiers of different type are coupled in parallel at the input or output, e.g. a class D and a linear amplifier, a class B and a class A amplifier
• CPC Class Codes: H03F 2200/51 Capacitor in positive feedback circuit of an amplifier circuit to bootstrap a resistor
• CPC Class Codes: H03F 2200/78 A comparator being used in a controlling circuit of an amplifier
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers
• CPC Class Codes: H03F 3/2171 with field-effect devices H03F3/2173 - H03F3/2178 take precedence
• CPC Class Codes: H03F 3/2173 of the bridge type

Abstract

A half bridge circuit of a class-D amplifier outputs a voltage in accordance with switching of a first switching element and of a second switching element, to a load. A high side gate drive circuit and a low side gate drive circuit respectively drive the first and second switching elements. A bootstrap capacitor connected between the high side gate drive circuit and an output terminal of the half bridge circuit is charged by a charging current from a second direct-current power supply while the first switching element is off. An inductance component for noise suppression, and a voltage limit element that is connected in parallel with the inductance component and is for limiting a voltage that occurs at the inductance component are provided on a path in which the charging current flows.

Claims

1. A power supply circuit, comprising:

a bridge circuit having a first switching element connected to a first direct-current power supply and a second switching element connected in series with the first switching element, and configured to output a voltage, in accordance with switching of the first switching element and of the second switching element, to a load;

first and second drive circuits configured to respectively drive the first and second switching elements so that the first and second switching elements alternatingly enter an on state in accordance with an input pulse signal;

a capacitor connected between the first drive circuit and an output terminal of the bridge circuit, and configured to generate a charge voltage used for driving of the first switching element by the first drive circuit, in accordance with charging by being supplied with a charging current from a second direct-current power supply while the first switching element is in an off state;

an inductance component for noise suppression provided in a path in which the charging current flows; and

a voltage limit element connected in parallel with the inductance component, and configured to limit a voltage that occurs at the inductance component.

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

the inductance component is provided between the capacitor and the output terminal;

and

the voltage limit element operates to limit the voltage that occurs at the inductance component when the first switching element switches between the on state and the off state.

3. The power supply circuit according to claim 1, wherein

the voltage limit element is a diode arranged in a direction in which a current from the second direct-current power supply is caused to pass, and

the voltage that occurs at the inductance component is limited to a voltage that does not exceed a threshold voltage that is a voltage at which the diode enters a conductive state.

4. The power supply circuit according to claim 3, wherein the diode is a Schottky barrier diode.

5. The power supply circuit according to claim 1, wherein

a voltage obtained by adding the charge voltage to a voltage of the output terminal is inputted to the first drive circuit, and

the first drive circuit outputs the inputted voltage to the first switching element as a driving voltage, when the first switching element switches from the off state to the on state.

6. The power supply circuit according to claim 1, wherein a bootstrap circuit for outputting, to the first drive circuit, a voltage obtained by adding the charge voltage to a voltage of the output terminal is configured by a diode, for which an anode terminal is connected to the second direct-current power supply and a cathode terminal is connected to the first drive circuit and the capacitor, and the capacitor.

7. The power supply circuit according to claim 6, wherein

the first and second switching elements are connected in series between the first direct-current power supply and ground, and the output terminal is provided at a connection point between the first switching element and the second switching element, and

when the first switching element enters the off state and the second switching element enters the on state, the diode of the bootstrap circuit enters a conductive state by a potential of the output terminal becoming equivalent to the ground, the charging current is supplied from the second direct-current power supply to the capacitor via the diode, and the charge voltage is input to the first drive circuit.

8. The power supply circuit according to claim 7, wherein

when the first switching element enters the on state and the second switching element enters the off state, the diode of the bootstrap circuit enters a non-conductive state by the potential of the output terminal becoming equivalent to the first direct-current power supply, and a voltage obtained by adding the charge voltage to the output voltage of the first direct-current power supply is input to the first drive circuit.

9. The power supply circuit according to claim 1, wherein, while the first switching element is in the off state, the charging current flows in a path from the second direct-current power supply to ground via the capacitor, the output terminal, and the second switching element that is in the on state.

10. The power supply circuit according to claim 1, wherein the second drive circuit is connected to the second direct-current power supply and outputs, to the second switching element, a voltage input from the second direct-current power supply as the driving voltage when the second switching element switches from the off state to the on state.

11. An image forming apparatus, comprising:

an image formation unit configured to form an image on a recording material; and

a power supply circuit configured to supply a voltage to the image formation unit,

wherein the power supply circuit comprises;

a bridge circuit having a first switching element connected to a first direct-current power supply and a second switching element connected in series with the first switching element, and configured to output a voltage, in accordance with switching of the first switching element and of the second switching element, to a load;

first and second drive circuits configured to respectively drive the first and second switching elements so that the first and second switching elements alternatingly enter an on state in accordance with an input pulse signal;

a capacitor connected between the first drive circuit and an output terminal of the bridge circuit, and configured to generate a charge voltage used for driving of the first switching element by the first drive circuit in accordance with charging by being supplied with a charging current from a second direct-current power supply while the first switching element is in an off state;

an inductance component for noise suppression provided in a path in which the charging current flows; and

a voltage limit element connected in parallel with the inductance component, and configured to limit a voltage that occurs at the inductance component.

12. The image generating apparatus according to claim 11, wherein

the image formation unit includes an image carrier and a charging unit configured to charge the image carrier, and

the power supply circuit supplies the charging unit with a voltage for charging the image carrier.