JPH10133750A - Heater current controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heater current controller which can suppress a rush current when a power is supplied to a heater and suppress the energy consumption of a thermistor. SOLUTION: When the temperature of the heater 2 is low and the resistance value is small, the thermistor 6 is inserted in series to apply an AC power 9 and when the resistance value of the heater 2 becomes larger, since the thermistor 6 is disconnected to apply the AC power source directly, the rush current of the heater 2 is suppressed. Further, since a current is made to flow to the thermistor 6 not always during supplying power to the heater 2, but only at the beginning of electricity feeding to the heater 2 and the thermistor is used only for rush current suppression, the self-heat generation of the thermistor is reduced and the energy consumption of the thermistor 6 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater current control device for a heat fixing device used in a dry copying machine, a laser printer, a facsimile, and the like.

[0002]

2. Description of the Related Art FIG. 4 shows a block diagram of a conventional heater current control device. The heat fixing device 21 includes a heater 22 and a temperature detector 23. As the heater 22, a halogen lamp or the like is used. A switch element 24 for turning on and off the power supply to the heater 22 in series with the heating and fixing device 21 and a thermistor 25 between the heater 22 and the switch element 24 are provided.
It has a temperature control circuit 26 for performing F. The thermistor 25
Uses a so-called negative temperature characteristic in which the resistance value decreases as its temperature rises.

The inrush current when energizing the heater 22 electrically connected in series with the thermistor 25
Even if the resistance value before energization is small, it can be suppressed by the resistance value of the thermistor 25 when the temperature is low. afterwards,
The current flowing through the heater 22 and the thermistor 25 causes the temperature of the thermistor 25 to gradually rise, thereby lowering the resistance value of the thermistor 25. However, the self-heating of the heater 22 causes the resistance value of the heater 22 to increase, and the heater current to rise. The current gradually approaches the rated current of the heater 22. Next, the temperature detector 23 detects the temperature of the heater 22 to operate the temperature control circuit 26, and the temperature control circuit 26
Then, control is performed to turn on and off the switch element 24 so that the temperature of the switch element 2 is always at the fixable temperature.

[0004]

The first problem of the above-described conventional heater current control device is that the rush current to the heater is suppressed when the heater is first energized, but the rush current is reduced when the heater is de-energized after the power is turned off. There is a problem that the current cannot be suppressed. The reason is that a current also flows through the thermistor while the heater is energized, so the thermistor continues to generate heat, and if the thermistor is energized again without cooling, the resistance value of the thermistor decreases, causing a large inrush current. Because it flows.

A second problem is that a current always flows through the thermistor when the heater is energized, and the thermistor consumes energy. SUMMARY OF THE INVENTION It is an object of the present invention to provide a heater current control device capable of suppressing an inrush current even when power is supplied again and reducing the energy consumption of a circuit. The present invention has been made under such a background, and an object of the present invention is to provide a heater current control device capable of suppressing an inrush current when energization of a heater is turned on and suppressing energy consumption of a thermistor.

[0006]

According to the first aspect of the present invention,
A temperature detector for detecting the surface temperature of the heat fixing device, a temperature control circuit for controlling ON / OFF of the first switch element based on the detection result detected by the temperature detector, and a heater for heating the heat fixing device And a second switch element connected in series between the first switch element and the heater, and a thermistor connected in parallel with the second switch element. A heater current control device is provided.

According to a second aspect of the present invention, in the heater current control device according to the first aspect, the first switch element is turned on and the second switch element is turned off within a predetermined time from the start of energization of the heater. To energize the heater,
Control means for turning on the second switch element after a predetermined time has elapsed is provided. The invention according to claim 3 is the heater current control device according to claim 1, wherein the thermistor has a negative temperature characteristic.
According to a fourth aspect of the present invention, in the heater current control device of the first aspect, a fixed resistor is provided instead of the thermistor.

[0008]

FIG. 1 is a block diagram showing a first embodiment of a heater current control device according to the present invention used in a laser printer. In FIG. 1, a heat fixing device 1 includes a heater 2 using a halogen lamp or the like and a temperature detector 3. The heater 2 is a first heater such as a triac.
Is controlled by the switch element 4, the second switch element 5, and the thermistor 6 having a negative temperature characteristic to maintain a predetermined temperature. The energization control is performed by the temperature control circuit 7.
And the switching of the AC power supply 9 by the timer circuit 8.

The first switch element 4 and the second switch element 5 are provided between an AC power supply 9 and the heater 2. The second switch element 5 is provided in series with the first switch element 4, and a thermistor 6 is provided in parallel with the second switch element 5. The temperature control circuit 7 is connected to the timer circuit 8. The timer circuit 8 counts the ON / OFF time of the first switch element 4. The temperature control circuit 7 turns on the first switch element 4 based on the signal from the temperature detector 3 when the temperature is low,
It is determined whether or not the switch element 5 is turned on by the timer circuit 8.
ON of the first switch element 4 counted by
It is determined by the OFF time.

When the OFF time of the first switch element 4 has passed a predetermined time (8 sec) or more, the power supply to the heater 2 turns on the first switch element 4 and turns off the second switch element 5. After the ON time of the first switch element 4 has passed for a predetermined time (300 msec) or more, the second switch element 5 is turned on, and the heating and fixing device 1 is heated until the surface temperature thereof reaches a predetermined temperature. When the temperature reaches a predetermined temperature, the first switch element 4 and the second switch element 5 are turned off. When the OFF time of the first switch element 4 is shorter than a fixed time (8 sec), the current supply to the heater 2 is started by turning on the first switch element 4 and the second switch element 5 and reaches a predetermined temperature. Then, the first switch element 4 and the second switch element 5 are turned off.
F.

Next, the circuit operation of FIG. 1 will be described with reference to FIG. FIG. 2 is a time chart showing the operation of the first embodiment of the present invention, in which each operation of the laser printer is displayed for each case of a warm-up, a printing state, and a standby state. O of the switch element 4 of
N, OFF state, (b): O of the second switch element 5
N, OFF state, (c) is a temperature curve of the heat fixing unit 1,
(D) shows a resistance value curve of the heater 2.

When the laser printer is switched on, the surface temperature of the heat fixing unit 1 is raised to a fixing temperature of 200 ° C. as a warm-up operation. The operation of each switch element in this case is as follows: first, the first switch element 4 is turned on,
Is turned off, and power is supplied to the heater 2 through the thermistor 6. This is because the inrush current is suppressed because the resistance value of the heater 2 before the warm-up is as small as 1.5 ohm. When 300 msec has elapsed since the first switch element 4 was turned on and the resistance value of the heater 2 was increased, the second switch element 5 was turned on, and the thermistor 6 was turned on.
The heater 2 is energized without passing through.

When the surface temperature of the heating and fixing unit 1 of the laser printer reaches 200 ° C., the warm-up is completed, printing is enabled, and printing is started. In the printing state, the first switch element 4 and the second switch element 5 are ON / OFF controlled so that the surface temperature of the heat fixing unit 1 becomes 180 ° C. or more and 200 ° C. or less. In this case, the resistance value of the heater 2 is increased from 9 ohms to 12.5 ohms, and no rush current flows. Therefore, the first switch element 4 and the second switch element 5 are simultaneously turned on.
The current is supplied to the heater 2 without passing through the thermistor 6.

Next, when the laser printer finishes printing and enters a standby state, the temperature is adjusted so that the surface temperature of the heat fixing unit 1 becomes 120 ° C. or more and 140 ° C. or less.
In the standby state, when the temperature of the heat fixing unit 1 of the laser printer is lowered to 120 ° C., the resistance value of the heater 2 becomes 1.5.
Since it has decreased to near ohms, the first switch element 4 is turned on and the second switch element is turned off in the same manner as in warm-up, in order to prevent a rush current from flowing when the next heater 2 is energized. Then, the heater 2 is energized through the thermistor 6 and the first switch element 4 is turned on for 30 minutes.
After the lapse of Omsc, the second switch element 5 is turned on, and current is supplied to the heater 2 without passing through the thermistor 6.

As described above, in order to suppress the rush current to the heater 2 of the heat fixing unit 1 to a predetermined value (42 A) or less,
The inrush current can be suppressed by turning on the first switch element 4 and turning off the second switch element 5 to energize the heater 2 from the state where the resistance value of the heater 2 is small, and energizing through the thermistor 6. Note that the above-described temperature control range of the heater 2, ON of the switch elements 4 and 5,
The OFF time, the resistance values of the thermistor 6 and the heater 2, and the inrush current of the heater 2 are all examples, and are not limited thereto.

Next, FIG. 3 shows a block diagram of a second embodiment of the present invention. When a heater having a low rated power is used, a fixed resistor 4 as shown in FIG. 3 can be used as a material of the rush current suppressing component instead of the thermistor used in the first embodiment. In the case of a thermistor, the resistance value changes due to self-heating, whereas in the case of a fixed resistance, the resistance value is always constant, so that more energy is consumed than the thermistor while the heater current flows. Therefore, it is necessary to use a fixed resistor having a large power rating, and it can be used only when the rated power of the heater is low.

The operation of one embodiment of the present invention has been described above in detail with reference to the drawings. However, the present invention is not limited to this embodiment, and a design change or the like may be made without departing from the gist of the present invention. The present invention is also included in the present invention. For example, the same effect can be obtained when a switch element is not a triac but a relay using another switch semiconductor or a mechanical contact is used.

[0018]

As described above, according to the present invention,
When the temperature of the heater 2 is low and the resistance value is small, the thermistor 6 is inserted in series and the AC power supply 9 is added. When the resistance value of the heater 2 becomes large, the thermistor 6 is disconnected and the AC power supply is directly applied. There is an effect that the rush current of the heater 2 can be suppressed. In addition, the current is supplied to the thermistor 6 only during the energization of the heater 2 and only for the initial stage of the energization of the heater 2 and used only for suppressing the rush current. Reduce
There is an effect that energy consumption in the thermistor 6 can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a heater current control device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing an operation of the first exemplary embodiment of the present invention.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional heater current control device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat fixing device 2 Heater 3 Temperature detector 4 First switch element 5 Second switch element 6 Thermistor 7 Temperature control circuit 8 Timer circuit 9 AC power supply 10 Fixed resistance

Claims (4)

[Claims] A temperature detector for detecting a surface temperature of the heat fixing device; a temperature control circuit for turning on and off a first switch element based on a detection result detected by the temperature detector; A heater current controller including a heater for heating a heater, a second switch element connected in series between the first switch element and the heater, and a second switch element connected in parallel with the second switch element. A current control device comprising: a thermistor; 2. Within a predetermined time from the start of energization of the heater,
Control means for turning on the first switch element, turning off the second switch element and energizing the heater, and turning on the second switch element after a predetermined time has elapsed. The heater current control device according to claim 1. 3. The heater current control device according to claim 1, wherein the thermistor has a negative temperature characteristic. 4. The heater current control device according to claim 1, further comprising a fixed resistor in place of said thermistor.