Discharging circuit, image forming apparatus having the discharging circuit, and power supply unit

Patent metadata

Field	Value
Publication number	US-9559527-B2
Application number	US-201314013111-A
Country	US
Kind code	B2
Filing date	Aug 29, 2013
Priority date	Aug 30, 2012
Publication date	Jan 31, 2017
Grant date	Jan 31, 2017

Abstract

A discharge circuit, an image forming apparatus having the discharge circuit, and a power-supply unit are disclosed to minimize a standby power generated in a standby mode and improve a discharging speed of a capacitor charged with electricity by the AC power in a power off mode. The discharge circuit connected between AC power input lines receiving an AC power includes a first resistor and a first switch element connected in series between the AC power lines, and a second resistor and a second switch element which are connected in series between the AC power lines, turn off the first switching element upon receiving an electric current during supply of the AC power, and turn on the first switching element in response to cutoff of the AC power to discharge the first capacitor.

First claim

What is claimed is:

1. A discharge circuit connected between AC power input lines receiving an AC power to discharge a first capacitor charged with electricity by the AC power, comprising:
a first resistor and a first switch element which are connected in series between the AC power input lines;
a second resistor and a second switch element which are connected in series between the AC power input lines and which are connected in parallel to the first resistor and the first switch element, to turn off the first switch element upon receiving an electric current during supply of the AC power, and to turn on the first switch element in response to cutoff of the AC power so as to discharge the first capacitor through the first resistor and the first switch element;
a second capacitor charged with electricity through the second resistor during a supply of the AC power to turn on the second switch element; and
a third resistor usable together with the second capacitor to turn off the second switch element by discharging the second capacitor during the cutting off of the AC power,
wherein at least one of the first switch element and the second switch element is directly connected to a neutral terminal of the AC power input lines.

2. The discharge circuit of claim 1 , wherein:
the first switch element is turned on by turning off the second switch element; and
the first switch element is turned off by turning on the second switch element.

3. The discharge circuit of claim 1 , wherein an on/off control terminal of the first switch element is connected between the second resistor and the second switch element.

4. The discharge circuit of claim 1 , further comprising:
a rectifier element connected from the second resistor to the second capacitor in a manner that a current flowing through the second resistor is supplied to the second capacitor.

5. The discharge circuit of claim 3 , wherein:
when a turn-on voltage of the second switch is set to 0.7V and an input voltage is a DC voltage, a resistance value of the first resistor and a capacitance of the second capacitor are determined in a manner that a time constant decided by the first resistor and the second capacitor is less than 8.45.

6. The discharge circuit of claim 3 , wherein the second resistor is a single resistor.

7. The discharge circuit of claim 3 , wherein the second resistor includes a plurality of resistor elements connected in series.

8. The discharge circuit of claim 3 , wherein the second switch element is a bipolar transistor.

9. The discharge circuit of claim 3 , wherein the second switch element is a Metal Oxide Semiconductor Field Effect Transistor (MOSFET).

10. The discharge circuit of claim 1 , wherein the first resistor is a single resistor element.

11. The discharge circuit of claim 1 , wherein the first resistor includes a plurality of resistor elements connected in series.

12. A discharge circuit connected between AC power input lines receiving an AC power to discharge a first capacitor charged with electricity by the AC power, comprising:
a first discharge circuit including:
a first resistor and a first switch element connected in series between the AC power input lines, and
a second resistor and a second switch element which are connected in series between the AC power input lines, turn off the first switch element upon receiving an electric current during supply of the AC power, and turn on the first switch element in response to cutoff of the AC power so as to discharge the first capacitor in a direction of a first polarity through the first resistor and the first switch element; and
a second discharge circuit including:
a third resistor and a third switch element connected in series between the AC power input lines, and
a fourth resistor and a fourth switch element which are connected in series between the AC power input lines, turn off the third switch element upon receiving an electric current during a supply of the AC power, and turn on the third switch element in response to a cutoff of the AC power to discharge the first capacitor in a direction of a second polarity opposite to the first polarity through the third resistor and the third switch element,
wherein a resistance value of the second resistor is higher than a resistance value of the first resistor, and a resistance value of the fourth resistor is relatively higher than a resistance value of the third resistor.

13. The discharge circuit of claim 12 , wherein the first discharge circuit enables the first switch element to be turned on by a turn-off state of the second switch element, and enables the first switch element to be turned off by a turn-on state of the second switch element.

14. The discharge circuit of claim 13 , wherein the first discharge circuit includes:
a second capacitor charged with electricity through the second resistor during the supply of the AC power so as to turn on the second switch element; and
a fifth resistor usable with the second capacitor to turn off the second switch element by discharging the second capacitor during the cutoff of the AC power.

15. The discharge circuit of claim 12 , wherein the second discharge circuit enables the second switch element to be turned on by a turn-off state of the fourth switch element, and enables the fourth switch to be turned off by a turn-on state of the second switch element.

16. The discharge circuit of claim 15 , wherein the second discharge circuit includes:
a second capacitor charged with electricity through the fourth resistor during the supply of the AC power to turn on the fourth switch element; and
a sixth resistor usable with the second capacitor to turn off the fourth switch element by discharging the fourth capacitor during the cutoff of the AC power.

17. The discharge circuit of claim 12 , wherein the first discharge circuit and the second discharge circuit are complementarily discharged according to polarity variation of the AC power.

18. An image forming apparatus including a discharge circuit connected between AC power input lines receiving an AC power to discharge a first capacitor charged with electricity by the AC power, the discharge circuit comprising:
a first resistor and a first switch element which are connected in series between the AC power input lines;
a second resistor and a second switch element which are connected in series between the AC power input lines and which are connected in parallel to the first resistor and the first switch element, to turn off the first switch element upon receiving an electric current during supply of the AC power, and to turn on the first switch element in response to cutoff of the AC power so as to discharge the first capacitor through the first resistor and the first switch element;
a second capacitor charged with electricity through the second resistor during a supply of the AC power to turn on the second switch element; and
a third resistor usable together with the second capacitor to turn off the second switch element by discharging the second capacitor during a cutoff of the AC power,
wherein at least one of the first switch element and the second switch element is directly connected to a neutral terminal of the AC power input lines.

19. An image forming apparatus including a discharge circuit connected between AC power input lines receiving an AC power to discharge a first capacitor charged with electricity by the AC power, the discharge circuit comprising:
a first discharge circuit including:
a first resistor and a first switch element connected

Assignees

• Samsung Electronics Co Ltd

Inventors

• Jeong An Sik

Classifications

• H02J3/00

  Circuit arrangements for AC mains or AC distribution networks · CPC title

• H02J9/005

  using a power saving mode (for copiers G03G15/5004) · CPC title

• H02J7/00 Primary

  Circuit arrangements for charging or discharging batteries or for supplying loads from batteries · CPC title

• G03G15/80

  Details relating to power supplies, circuits boards, electrical connections · CPC title

• G03G15/5004

  Power supply control, e.g. power-saving mode, automatic power turn-off · CPC title