JPH09319441A - Power controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power controller which can reduce a noise or a rush current. SOLUTION: A 'PWM' signal generated by a PWM circuit 71 and a 'phase control' signal generated by a phase control circuit 8 are synthesized by an OR circuit 73 of an inverter driving circuit 7. Since switching is performed at a frequency higher than an AC power source by the 'PWM' signal, an input current can be let flow over the full cycle of the AC power source 1. Thus, a power rate is improved and a high frequency current can be reduced. Since the number of times of switching is reduced while depending on the 'phase control' signal, on the other hand, the noise is reduced. By using both the merits, the high frequency current and noise can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power control device, and more particularly to a power control device used in a fixing device such as a copying machine or a printer, or an electromagnetic cooker.

[0002]

2. Description of the Related Art At present, a thermal fixing system is widely used in copying machines and printers. This is to fuse the toner with a heated roller in order to fix the copy image by the toner formed on the transfer paper. This roller has a structure in which a rod-shaped halogen heater is provided inside a hollow roller member, and the surface thereof is kept at a predetermined temperature by controlling the energization time of the halogen heater. The halogen heater has a structure in which a tungsten filament is enclosed in a rod-shaped glass tube together with an inert gas.

A phase control method using a triac is known as a method for controlling the energization time of the halogen heater. This is a method of controlling the trigger point (phase angle) for turning on the triac in synchronization with the zero cross of the AC power supply. According to this method, the load power can be efficiently controlled with a small number of parts by utilizing the commutation characteristics of the triac.

However, in the above method, since it is necessary to control the energization ratio every half cycle of the AC power source, the power factor of the electric power becomes low. Also, a switching element with a large current capacity is required.

For this reason, a fixing heater driving device described in Japanese Patent Laid-Open No. 5-216358 has been proposed. This device rectifies an AC power supply, provides a switch means, and controls an output voltage for energizing a fixing device heater to be substantially constant. According to this apparatus, constant electric power can be supplied to the heater regardless of fluctuations in the AC power source, so that stable fixing characteristics can be obtained.

Further, Japanese Patent Publication No. 6-87432 proposes a technique in which a switching element is connected to an AC power source via a load and a rectifier to switch at a high frequency. This improves the power factor of the power supply and reduces high frequencies.

[0007]

However, the above-mentioned JP-A-5-216358 and JP-B-6-8743.
The device described in Japanese Patent No. 2 has a problem that noise increases because the number of switching times increases. There is also the problem of inrush current.

Therefore, the present invention has been made in view of the above, and an object thereof is to provide a power control device capable of reducing noise and inrush current.

[0009]

In order to achieve the above object, in a power control device according to claim 1, a load, an AC power supply for supplying power to the load, a switching element connected in series to the load, In a power control device having drive signal output means for outputting a drive signal for driving the switching element, the drive signal output means causes the drive signal output means to switch the switching element at a frequency higher than the frequency of the AC power supply. And a second signal for continuously turning on the switching element, so that the half cycle of the AC power supply is divided into a switching period and a continuous on period.

That is, the half cycle of the AC power supply is divided into a switching period and a continuous ON period,
I made use of each advantage. High frequency current can be reduced and power factor can be improved in the switching period.
Noise is generated. Therefore, we set a part of the period as a continuous ON period with less noise. Therefore, it is possible to reduce the high frequency current, improve the power factor and reduce the noise as a whole.

According to a second aspect of the power control apparatus, the power control apparatus (Claim 1) is further provided with load temperature detecting means for detecting the temperature of the load, and the classification is performed based on the temperature of the load. To do.

The load resistance of a load such as a halogen heater or a halogen lamp depends on temperature. Therefore, as described above, the load can be stably driven by performing the classification according to the temperature of the load to control the power factor and the like. For example, it is possible to prevent an overcurrent or an inrush current from flowing at a low temperature when the load resistance is small.

Further, in the power control device according to claim 3, the power control device (claim 2) is further provided with a classification changing means for changing the classification according to the temperature.

By thus changing the division according to the temperature, the load can be driven more stably. That is, the power factor and the like can be efficiently improved while preventing the above-mentioned overcurrent and inrush current.

According to a fourth aspect of the power control apparatus, the power control apparatus (Claim 1) is further provided with a division changing means for changing the division according to an elapsed time of energization of the load.

Since the temperature of the load is substantially proportional to the elapsed time of energization, the same effect as described above can be obtained even if the above-mentioned classification is performed according to the elapsed time of energization. Furthermore, when a load is installed in a device having a large heat capacity, a difference often occurs between the temperature of the load and the temperature of the load temperature detecting means. Since it is not affected by the difference, the above classification can be appropriately performed.

[0017]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. The present invention is not limited to this embodiment.

(Embodiment 1) FIG. 1 is a block diagram showing a power control apparatus of the present invention. This power control device 100
In, the load 3 and the switching element 4 are connected to the AC power source 1 via the rectifier 2. For load 3,
A temperature detector 5 is provided. Furthermore, the temperature detection unit 5
The whole machine control unit 6 is connected to the. The entire machine control unit 6 controls the entire machine (such as a copying machine) in which the power control device 100 is incorporated. An inverter 9 is composed of a switching element 4, an inverter drive circuit 7 and a phase control circuit 8.

The inverter drive circuit 7 includes a PWM circuit 71 for generating a drive signal for the switching element 4 in response to a "temperature control" signal input from the overall machine control unit 6, and a "load" input from the overall machine control unit 6. An on / off circuit 72 for controlling on / off of the load 3 by intermittently driving the drive signal supplied to the switching element 4 in accordance with the "on / off" signal.
It consists of and.

Further, the phase control circuit 8 has a continuous ON circuit 81 for generating a signal for continuously turning on the switching element 4 in accordance with a "reference value" signal inputted from the entire machine control section 6, and the switching element 4 And a power supply voltage detection circuit 82 for detecting the timing of turning on the switch in accordance with the instantaneous value of the power supply voltage.

Now, at the timing of operating the load 3, the entire machine control unit 6 causes the inverter 9 to "turn on the load.
The “off” signal is input, and a signal for driving the switching element 4 is supplied to the switching element 4.

There are two types of signals for driving the switching element 4. One is a "PWM" signal for switching the switching element 4 at a frequency much higher than the frequency of the AC power supply 1 (for example, 20 KHz),
The other is a "phase control" signal for continuously turning on the switching element 4.

The "PWM" signal is generated by the PWM circuit 71 and outputs a duty corresponding to the "temperature control" signal. The “temperature control” signal is a voltage corresponding to the difference between the temperature detected by the temperature detection unit 5 and the set temperature, and is output from the machine overall control unit 6.

For example, as shown in FIG. 2, when the temperature of the load 3 is lower than the set value, the duty is increased, and when the temperature is high, the duty is decreased. Furthermore, FIG.
As shown in, the upper limit of the duty is set according to the temperature of the load 3.

FIG. 4 shows the waveform of the load voltage by the "PWM" signal. FIG. 5 is an enlarged view of the time axis of the waveform of switching by the "PWM" signal. When the switching element 4 is turned on, due to the inductance of the wiring from the AC power supply 1 to the load 3, the current flowing through the load 3 increases with a slope like the broken line. Thus, load 3
When the resistance is low, the duty of the "PWM" signal is reduced to suppress an abnormal increase in load current.

FIG. 6 shows the waveform of the load voltage due to the "phase control" signal. The “phase control” signal is generated by the phase control circuit 8. This "phase control" signal is output when the power supply voltage detected by the power supply voltage detection circuit 82 and the "reference value" signal are compared by the continuous ON circuit 81 and the power supply voltage is equal to or lower than the voltage corresponding to the "reference value". To be done. Therefore, in FIG. 6, the switching element 4 is continuously turned on when the power supply voltage is lower than the voltage Vr set as the “reference value” signal. As a result, the load 3 is energized twice in a half cycle.

The “PWM” signal and the “phase control” signal are combined by the logical sum circuit 73 of the inverter drive circuit 7 and supplied to the switching element 4. Here, of the two signals, the signal that turns on the switching signal is preferentially output.

From the above, the load voltage has a waveform as shown in FIG. That is, when the power supply voltage is higher than the voltage Vr, switching is performed, and when it is low, the voltage is continuously applied.

As described above, this power control device 1
00 is characterized in that it combines the advantages of both the "PWM" signal and the "phase control" signal.

That is, when the "PWM" signal is used, switching is performed at a frequency higher than that of the AC power supply, so that the input current can flow over the entire period of the cycle of the AC power supply. As a result, the power factor is improved and the high frequency current can be reduced. In particular, when the output (load current) is varied, a greater effect is obtained compared to the conventional method using a thyristor (even if varied, it flows for the entire period).

On the other hand, when using the "phase control" signal,
The waveform of the load current is applied twice in a half cycle as compared with the conventional method using a thyristor. For this reason, even if the load 3 is energized at the same conduction angle as in the conventional case, a double current can be made to flow, so that the rise of the load 3 can be accelerated. Also, since the number of switching times is small, there is little noise.

As described above, as a result of combining the advantages of both, high frequency current and noise can be reduced.

(Embodiment 2) Further, a region ("PWM" signal) for switching the switching element 4 and a region ("phase control" signal) for continuously turning on the switching device 4 are switched according to the temperature of the load 3. May be. This is because the load resistance depends on the temperature, so that an overcurrent or an inrush current does not flow especially when the load resistance becomes small at a low temperature.

FIG. 8 shows the relationship between the load temperature and the power supply voltage. Further, FIG. 9 shows the waveform of the load 3. Similar to the first embodiment, when the instantaneous value of the power supply voltage supplied to the load 3 is equal to or lower than the "reference value", the heater is continuously energized by the "phase control" signal, and when the instantaneous value is equal to or higher than the "reference value", the "PWM The signal energizes the heater.

Further, as shown in FIG. 9, the "reference value" is switched by the entire machine control unit 6 according to the temperature of the load 3. For example, until the temperature of the load 3 reaches 80 ° C., the “phase control” signal is turned off until the power supply voltage reaches about 5V. At this time, most of one cycle of the AC power supply 1 is switched by the "PWM" signal.

On the other hand, when the temperature is 120 ° C. or higher, the switching element 4 is continuously turned on up to the power supply voltage of about 70 V, and when the temperature of the load 3 is between 80 ° C. and 120 ° C. Switch to linear according to.

As described above, when the temperature is high, the period during which the power is continuously turned on is lengthened, and conversely, when the temperature is high, it is shortened.

In the above power control device, when the power supply voltage (instantaneous value) supplied to the load 3 is equal to or higher than the "reference value", the load 3 is loaded.
In addition to switching the energization of, the "reference value" is switched according to the temperature of the load 3. That is, the switching element 4 is continuously turned on and switched according to the temperature of the load 3, so that an overcurrent or an inrush current to a load such as a halogen heater having a low load resistance at low temperature start-up can be prevented. Can be suppressed.

(Embodiment 3) Further, the area for switching the switching element 4 ("PWM" signal) and the area for continuously turning on ("phase control" signal) are switched according to the energization time of the load 3. You may this is,
This is to stably drive the load 3 whose load resistance depends on temperature. In particular, when the load 3 is incorporated in a device having a large heat capacity to control the temperature, the temperature of the temperature detecting unit 5 and the load 3
This is to prevent the overcurrent and the inrush current from flowing by switching the area accurately even if the temperature difference occurs.

FIG. 10 shows the relationship between the load temperature and the power supply voltage. In this way, the “reference value” signal output from the entire machine control unit 6 is switched according to the energization time of the load 3. For example, the switching element 4 is continuously turned on until the power supply voltage reaches 5 V during the energization time of the load 3 for up to 1 second, and switching is performed in a voltage range higher than that. After that, according to the energization time, the voltage is switched to 70V after 3 seconds every 1 second (as a result, the waveform becomes similar to that in FIG. 9).

In the above power control device, when the power supply voltage (instantaneous value) supplied to the heater is equal to or more than the "reference value", the energization of the heater is switched and the "reference value" is set according to the energization time of the heater. I tried to switch. That is, the region in which the switching element 4 is continuously turned on and the region in which the switching element is switched are switched according to the energization time of the load 3. By doing so, it is possible to suppress an overcurrent or an inrush current to a load such as a halogen heater, which has a low load resistance at low temperature startup.

[0042]

As described above, according to the power control device (claim 1) of the present invention, the half cycle of the AC power supply is
It is divided into a switching period and a continuous ON period so that the advantages of each are utilized. Therefore, it is possible to reduce the high frequency current, improve the power factor and reduce the noise as a whole.

Further, according to the power control device of the present invention (claim 2), a load temperature detecting means for detecting the temperature of the load is further provided, and the classification is performed based on the temperature of the load. . Therefore, the load can be driven stably.

Further, according to the electric power control device of the present invention (claim 3), further, the division changing means for changing the division according to the temperature is provided. Therefore, the load can be driven more stably.

Further, according to the electric power control device of the present invention (claim 4), further, there is provided a division changing means for changing the division according to the elapsed time of energization of the load. Therefore, even when a load is installed in a device having a large heat capacity, the classification can be appropriately performed, and high frequency current can be reduced, power factor can be improved, and noise can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a power control circuit according to a first embodiment of the present invention.

FIG. 2 is a graph showing the relationship between PWM duty and temperature difference.

FIG. 3 is a graph showing a relationship between PWM duty and load temperature.

FIG. 4 is a graph showing a waveform of a load voltage according to a “PWM” signal.

FIG. 5 is a graph diagram in which a time axis of a waveform of switching by a “PWM” signal is enlarged.

FIG. 6 is a graph showing a waveform of a load voltage according to a “phase control” signal.

FIG. 7 is a graph showing a waveform of a load voltage generated by a “PWM” signal and a “phase control” signal.

FIG. 8 is a graph showing the relationship between load temperature and power supply voltage according to the second embodiment of the present invention.

FIG. 9 is a graph showing a waveform of a load voltage generated by a “PWM” signal and a “phase control” signal.

FIG. 10 is a graph showing the relationship between load temperature and power supply voltage according to the third embodiment of the present invention.

[Explanation of reference numerals] 100 power control device 1 AC power supply 2 rectifier 3 load 4 switching element 5 temperature detection unit 6 entire machine control unit 7 inverter drive circuit 71 PWM circuit 72 ON / OFF circuit 8 phase control circuit 81 continuous ON circuit 82 power supply Voltage detection circuit 9 Inverter

Claims (4)

[Claims] 1. A power control device comprising a load, an AC power supply for supplying electric power to the load, a switching element connected in series to the load, and drive signal output means for outputting a drive signal for driving the switching element. In, the drive signal output means outputs a first signal for switching the switching element at a frequency higher than the frequency of the AC power source and a second signal for continuously turning on the switching element, and the AC signal A power control device characterized by dividing a half cycle of a power supply into a switching period and a continuous ON period. 2. The power control device according to claim 1, further comprising a load temperature detecting means for detecting a temperature of the load, and performing the classification based on the temperature of the load. 3. The power control apparatus according to claim 2, further comprising a classification changing unit that changes the classification according to the temperature. 4. The power control device according to claim 1, further comprising a classification changing unit that changes the classification according to an elapsed time of energization of the load.