JP2002063981A - Heater driver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply an inexpensive small heater driver with suppressed generation of a higher-harmonic current by soft starting at the time of halogen lamp lighting, voltage fluctuation, and flicker, in the header driver of a printer which has two or more halogen lamps for fixing. SOLUTION: A phase control driver drives a small electric power halogen lamp of a printer that has two or more halogen lamps, by a triac or a thyristor. A PWM control driver drives a large electric power halogen lamp by an IGBT or an FET. The heater driver as for the printer has generation of the higher- harmonic current and voltage fluctuation/flicker suppressed below a regulation value of the high-harmonic current and voltage fluctuation/flicker.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater driver, and more particularly to an electrophotographic apparatus such as a copying machine and a laser printer.

[0002]

2. Description of the Related Art An electrophotographic apparatus to which the conventional electrophotographic technology is applied uses a halogen lamp as a heat source of a fixing device for fixing toner, rectifies an AC lighting using a triac or a thyristor, or rectifies an AC power supply to use an FET or an FET. IGB
DC lighting using T has been used to control the power of the halogen lamp. FIG. 10 is a block diagram showing an example of a heater driver using a conventional phase control method.

In a conventional phase control type heater driver circuit, when there are a plurality of halogen lamps, the same number of phase control type heater driver circuits as the halogen lamps are used, and one driver circuit drives one halogen lamp. Phase control type heater driver circuit 3 in heater driver 34
Reference numeral 5 denotes a driver for the low power halogen lamp 3, and a phase control type heater driver circuit 36 is a driver for the high power halogen lamp 5. Each heater driver performs a phase control to prevent an inrush current when each heater is turned on.

FIG. 6 shows the AC power supply input terminal voltage of the phase control and the current of the halogen lamp at the start of halogen lamp lighting. FIG. 8 shows an embodiment of the phase control type heater driver circuit 35 and the phase control type heater driver circuit 36. It is a block diagram of.

The heater driver circuit of the phase control type uses a photo-coupler which receives a signal through a soft start control signal input terminal 10 and a heater-on signal input terminal 9 and a current flowing through a resistor 12 and a photo coupler 14 and a current flowing through the resistor 11 and a photo coupler 13. The signal 14 and the photocoupler 13 transmit a signal to the phase control circuit 16. The phase control circuit 16 to which the signal has been transmitted controls the phase of the triac 17, controls the conduction phase of the triac 17 in synchronization with the voltage phase of the AC power supply input terminal voltage 18, and suppresses the inrush current of the halogen lamp 13. The halogen lamp 15 is heated.
After the halogen lamp 15 is sufficiently heated, when the signal of the soft start control signal input terminal 10 is turned off, the phase control circuit stops the phase control of the triac 17, makes the triac 17 fully conductive, and supplies the halogen lamp 15 with the full phase of the AC power supply. Apply current with.

FIG. 11 is a block diagram showing an example of a conventional PWM control type heater driver.

When the conventional PWM control type heater driver has a plurality of halogen lamps, the same number of PWM control type heater driver circuits as the heaters are used, and one PWM control type heater driver drives one halogen lamp and turns on each halogen lamp. In order to prevent rush current at the time, each heater driver circuit performs PWM control to prevent rush current. The PWM control heater driver circuit 38 in the heater driver 37 is a driver for the low power halogen lamp 3, and the PWM control heater driver circuit 39 is a driver for the high power halogen lamp 5. In order to prevent an inrush current when each heater is turned on, each heater driver performs PWM control to prevent an inrush current.

FIG. 3 shows PWM at the start of lighting of a halogen lamp.
FIG. 9 is a block diagram of the PWM control type heater driver circuit 39 and the PWM control type heater driver circuit 39. FIG.

In the PWM control type heater driver circuit, when a signal is input to the heater-on signal input terminal 31, the reference voltage of the reference voltage generation circuit 27 starts to increase. When the reference voltage of the reference voltage generation circuit 27 rises and reaches the output voltage of the triangular wave oscillation circuit 28, the voltage comparator 29 starts outputting pulses at the oscillation frequency of the triangular wave oscillation circuit 28. The output of the voltage comparator 29 controls the IGBT 25 via the driver 30 by PWM. The duty cycle of the pulse rises as the output voltage of the reference voltage generation circuit 27 rises, and finally reaches 100% duty cycle to make the IGBT 25 fully conductive and stop the PWM operation.

The current detector 19 detects a current flowing through the halogen lamp 22 and controls a rising speed of the reference voltage 27 so that the current of the heater 22 becomes appropriate. During the conduction period of the IGBT 25, the input current of the AC power supply input terminal 33 is rectified by the diode bridge 20, and flows through the path of the halogen lamp 22, the choke coil 21, and the IGBT 25. PWM
During the heater-off period of the control IGBT 25, the energy stored in the choke coil 21 flows through the path of the diode 23 and the halogen lamp 22.

The capacitor 24 is a capacitor for absorbing a spike voltage generated by the choke coil 21 at the moment when the IGBT 24 switches from on to off.
2 is a switching noise prevention capacitor of the IGBT.

[0012]

A conventional apparatus having a plurality of halogen lamps has one heater driver circuit for each halogen lamp, and the heater driver circuit uses a phase control method using a triac or thyristor, an IGBT or FE.
There is a PWM control method that performs PWM control using T.
The phase control method heater driver circuit shown in the figure performs phase control when the halogen lamp is turned on to suppress the inrush current when the halogen lamp is turned on.The halogen lamp is heated, the resistance of the halogen lamp filament increases, and the inrush current stops flowing. At this point, the phase control is stopped, the triac is fully turned on, and all power is supplied to the halogen lamp.

Since the phase control is performed at the start of lighting of each halogen lamp, a harmonic current corresponding to the wattage of the halogen lamp is generated at the start of lighting of each halogen lamp,
In the heater driver having a plurality of halogen lamps shown in FIG. 10, the phase control is performed in synchronization with the phase of the AC power supply at the start of lighting of the halogen lamp or when the period of the phase control is overlapped. Overlap,
A higher harmonic current is generated as compared with the higher harmonic current by the phase control at the start of lighting of one heater.

When the phase of a high-power halogen lamp is controlled, a large harmonic current is generated even with a single halogen lamp. Since the phase control method can gradually increase the current, it can prevent inrush current at the start of lighting of the halogen lamp and can cope with voltage fluctuation and flicker, but generates harmonic current.

[0015] Voltage fluctuations and flickers cause a sudden drop in the AC input current of a device, causing a voltage drop or the like of an AC power supply, causing malfunctions or voltage drops in other devices to cause flickering of the lighting device. This may cause overheating of power equipment and malfunction of other equipment.

In the conventional PWM system using an IGBT or FET corresponding to harmonics shown in FIG. 9, the heater control circuit performs PWM control at the start of lighting of the halogen lamp to suppress an inrush current when the halogen lamp is turned on. Is heated and the resistance of the halogen lamp increases,
Stop the WM, make the IGBT fully conductive, and supply all power to the halogen lamp.

Although the generation of harmonic current can be suppressed in the heater driver having a plurality of halogen lamps shown in FIG. 11, the number of PWM control heater control circuits must be equal to the number of halogen lamps, although the circuit is complicated and the number of heat generating components is large. Therefore, there is a problem that circuit components increase, the price becomes high, and the heater driver circuit becomes large.

Although the PWM control system can prevent the occurrence of voltage fluctuations / flickers and harmonic currents, the circuit is more complicated and has more components than the phase control system, and the driver circuit is large and expensive. A device having a large number of halogen lamps requires the same number of PWM control type heater driver circuits as the halogen lamps, and has a drawback that the heater driver becomes large and expensive. In the prior art, it has been difficult to realize a small and inexpensive heater driver that does not generate a harmonic current, which responds to the harmonic current and voltage fluctuations and flicker.

[0019]

SUMMARY OF THE INVENTION In order to solve the problem of the conventional heater control circuit, in a heater control circuit for driving a plurality of halogen lamps, a low power halogen lamp is replaced by a halogen lamp using a conventional triac or thyristor. When the halogen lamp is on, the phase control is performed, and when the halogen lamp is on, the PWM control is performed using a IGBT or FET. Alternatively, a plurality of low-power halogen lamps are used without using a high-power halogen lamp. Each of the plurality of halogen lamps is connected to one phase-control heater driver, and software is provided by controlling the phase at the start of lighting of each halogen lamp. By shifting the start period, the phase control current of each halogen lamp is prevented from overlapping.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When a halogen lamp is used for fixing a toner in a laser beam printer or a copying machine, the temperature is controlled by using a plurality of halogen lamps having different electric powers depending on the paper size and paper thickness. Is common. Conventionally, the same number of heater driver circuits as the number of halogen lamps are mounted, and one heater driver circuit drives one halogen lamp. The filament resistance of a halogen lamp used as a heater is about 2Ω when the filament is cold for a halogen lamp with a rated power of 1500 W and a rated voltage of 200 V, and is about Ω when the filament is cold for a halogen lamp with a rated power of 750 W and a rated power of 200 V. The resistance is about 4Ω. Since the current of the halogen lamp is inversely proportional to the resistance, harmonic current and voltage fluctuation during phase control
Flicker is approximately proportional to the wattage of the halogen lamp.

Also, IEC61000-3-2 and IEC
Since the regulated values of the harmonic current, voltage fluctuation and flicker regulated by 61000-3-3 are determined by the total power of the device equipped with the halogen lamp, the harmonic generated by the small power halogen lamp in the device with large power is used. It is possible to make the wave current, voltage fluctuation and flicker less than the regulation value.

The experimental results show that the rated power is 750 W and the rated power is 2
When a halogen lamp with a power of 00V or less is used, the regulation value of the harmonic current of the class A equipment specified in IEC61000-3-2 can be adapted to either the phase control using a triac or thyristor or the PWM method. Has been confirmed by experiments.

The voltage fluctuation and flicker specified by IEC61000-3-3 can be suppressed to a specified value or less by both the phase control method and the PWM method.

FIG. 1 is a block diagram showing one embodiment of the present invention. Reference numeral 1 denotes a heater driver according to the present invention, which includes a phase control heater driver circuit 2 using a triac and a PWM heater driver circuit 4 using an IGBT. The internal blocks of the circuit are the same as the phase control heater driver circuit of FIG. 8 and the PWM heater driver circuit of FIG. The phase control heater driver 2 is for driving a low power halogen lamp, and the PWM control heater driver circuit 4 is for driving a high power halogen lamp 5.

In this embodiment, one heater driver circuit for the phase control system and one heater driver circuit for the PWM system are used, but a plurality of heater driver circuits may be used depending on the number of halogen lamps or heater power.

FIG. 2 is a horizontal sectional view of one embodiment of a heat roll for melting the toner and fixing it on paper.
The cylindrical heat roll 7 for fixing the toner transferred to the paper has a cylindrical cavity at the center, and the small power halogen lamp 3 and the high power halogen lamp 5 which are switched according to the paper size are inside the cavity. I have. The high-power halogen lamp 5 has a filament wound around a portion where sheets of all sizes pass over the heat roll 7. The low-power halogen lamp 3 heats a portion of the high-power halogen lamp 5 where the filament is not wound in a portion where the wide paper passes over the heat roll 7. It is wound.

The low-power halogen lamp 3 is turned on when fixing toner on a wide sheet of paper, and when the high-power halogen lamp 5 alone cannot fix the toner.

When the sheet size is limited, the filaments of the halogen lamp 3 and the halogen lamp 5 are wound around the same position on the heat roll. May be done.

Next, the operation will be described with reference to FIG. When the high-power halogen lamp 5 starts lighting, the PWM heater control circuit 4 performs PWM control to increase the current supplied to the high-power halogen lamp 5 from 0 A. Is turned on and the halogen lamp 5 is turned on. When the lamp is turned off, the halogen lamp 5 can be turned off from the lighting state. To further reduce flicker, the PWM duty of the halogen lamp is changed from 100% to 0% from the lighting state to the light-off state as shown in FIG.
It may be changed up to. When the low-power halogen lamp 3 starts to be lit, the phase control heater driver circuit 2 performs phase control to increase the current flowing through the low-power halogen lamp 3 from 0 A, and the filament of the low-power halogen lamp 3 generates heat. When the rush current stops flowing, the phase control is stopped and the halogen lamp 3 is completely turned on. When the lamp is turned off, it is possible to turn off the halogen lamp 3 from the lighting state. However, in order to further reduce flicker, it is possible to start the phase control from the lighting state as shown in FIG. good.

In the heater driver of FIG. 1, since the high power halogen lamp 5 is of the PWM control type, no harmonic current is generated. Therefore, the harmonic current generated by the low power halogen lamp 3 becomes the harmonic current of the entire device.

The high-current halogen lamp 5 of FIG. 10 is divided into a plurality of low-power halogen lamps, and the low-power halogen lamps 8 and 9 of FIG.
The low power halogen lamp 8 and the low power halogen lamp 9 are driven by a phase control type heater driver circuit 41 and a phase control type heater driver circuit 42, respectively. The phase control heater driver circuit 35, the phase control heater driver circuit 41, and the phase control heater driver circuit 42 are controlled so that the phase control periods do not overlap. Since the phase control of each halogen lamp does not overlap, the harmonic current generated by the heater driver is equal to the harmonic current generated by one low power halogen lamp. In a low-power halogen lamp, the amount of generation of harmonic current and voltage fluctuation / flicker generated during phase control is small, so that the generation of harmonic current and voltage fluctuation / flicker is small unless the phase control periods overlap.

In FIG. 5, the high power halogen lamp 5 and the low power halogen lamp 9 shown in FIG.
It is more effective to increase the number of halogen lamps and the number of phase-control heater driving circuits to reduce the wattage per halogen lamp. For example, if a halogen lamp with a rated power of 1500 W is required, it can be configured with two halogen lamps with a rated power of 750 W and two phase control type heater driving circuits, but with three halogen lamps with a rated power of 500 W and a phase control type heater. It is possible to replace even three driving circuits, and a smaller wattage per halogen lamp is more effective in suppressing harmonic current, voltage fluctuation and flicker.

Although not shown, as an electrophotographic apparatus using the heater driver described in the present embodiment, the surface of the photoreceptor is charged by a well-known charger, and is exposed by a signal such as image data. A fixing device for exposing and scanning the surface of the photoreceptor by a device, forming a toner image on the surface of the photoreceptor by a developing device, transferring the toner image on the surface of the photoreceptor to paper by a transfer device, and fixing unfixed toner on the paper With the configuration provided. The heater driver is provided in a heating roller in contact with the unfixed toner image in the fixing device.

[0034]

According to the present invention, the phase control method and the PWM control are selectively used, and the PWM control is performed only for the high power halogen lamp.
By controlling the phase of the low-power halogen lamp, the heater driver can be made small and inexpensive. Alternatively, a high-power halogen lamp is divided into a plurality of low-power halogen lamps, and the timing of phase control for generating a harmonic current is shifted to suppress the occurrence of harmonic currents and voltage fluctuations and flicker, thereby providing a small and inexpensive heater driver. Can be supplied.

[Brief description of the drawings]

FIG. 1 is a schematic view of a heater driver according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view in a horizontal direction of a heat roll.

FIG. 3 is a voltage / current waveform at the start of halogen lamp lighting of a PWM heater driver circuit.

FIG. 4 is a voltage / current waveform at the start of turning off a halogen lamp in a PWM heater driver circuit.

FIG. 5 is a schematic view of a heater driver according to another embodiment of the present invention.

FIG. 6 is a voltage / current waveform at the start of halogen lamp lighting of a phase control type heater driver circuit.

FIG. 7 is a voltage / current waveform at the start of turning off a halogen lamp in a phase control type heater driver circuit.

FIG. 8 is a block diagram of a phase control type heater driver circuit.

FIG. 9 is a block diagram of a PWM control type heater driver circuit.

FIG. 10 is a block diagram of a conventional heater driver that does not comply with harmonic regulation.

FIG. 11 is a block diagram of a conventional heater driver compliant with harmonic regulation.

[Explanation of symbols]

1, 34, 37, 40 ... heater driver, 2, 35, 3
6, 41, 42 ... phase control type heater driver circuit,
3, 8, 9 ... low power halogen lamp, 4, 38, 39 ...
PWM control type heater driver circuit, 5: high power halogen lamp, 6, 33: AC power input terminal, 7: heat roll, 9: heater ON signal input terminal, 10: soft start control signal input terminal, 11, 12: resistance, 13,14
... Photocoupler, 15, 22 Halogen lamp, 16 Phase control circuit, 17 Triac, 18 AC power input terminal, 19 Current detector, 20 Diode bridge
21: choke coil, 23: diode, 24, 32
... Capacitor, 25 ... IGBT, 26 ... Control circuit, 27
... Reference voltage generating circuit, 28... Triangular wave oscillation circuit, 29... Voltage comparator, 30... Driver, 31... Heater-on signal input terminal.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kazuhiko Kawasaki 1060 Takeda, Hitachinaka City, Ibaraki Prefecture Inside Hitachi Koki Co., Ltd. (72) Inventor Tomoaki Takahashi 1060 Takeda Hitachinaka City, Ibaraki Prefecture F-term in Hitachi Koki Co. Reference) 2H033 AA21 AA41 CA23 CA46 3K058 AA27 AA46 AA95 BA18 CA04 CB06 CB07 CB18 CC06 CE23 CE24 CE25 DA02 GA06

Claims (3)

[Claims] 1. A heater control circuit for supplying an alternating current or a rectified direct current to a heater and using the heater as a heat source, wherein at least one phase control type heater driver circuit for performing phase control at the start of lighting of the heater; A heater driver comprising at least one PWM type heater driver circuit for performing PWM control and driving a heater at the start of lighting of a plurality of heaters, and controlling a plurality of heaters. 2. A heater control circuit for supplying an alternating current or a rectified direct current to a heater and using the heater as a heat source, wherein a plurality of phase control type heater driver circuits for performing phase control at the start of heating of the heater are provided. A heater driver characterized by the above-mentioned. 3. An electrophotographic apparatus using the heater driver according to claim 1 in a fixing device.