JPH0820827B2 - Copier power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a copying machine using a fluorescent lamp as a light source for illuminating an original, and particularly to supplying power to the fluorescent lamp and supplying power to a control unit. The present invention relates to a power supply device of a copying machine which performs the above-mentioned operation based on the output of one oscillation circuit.

(B) Conventional technology In a copying machine aiming at downsizing and cost reduction, a fluorescent lamp is used as a light source for illuminating an original, and a common power source section is used for the fluorescent lamp and the control section. I am trying to configure it. In order to make the power supply unit common, the power supply unit is configured by an inverter having an oscillation circuit built therein, the fluorescent lamp is turned on at a high frequency, and a DC output obtained by rectifying the inverter output is supplied to the control unit. In a copying machine equipped with such a power supply device, keeping the fluorescent lamp in a preheated state always shortens the life of the fluorescent lamp. Therefore, it is not necessary to preheat the fluorescent lamp, that is, when the fixing device is preheated (when preheated).
In, there is a method of turning off the power supply to the fluorescent lamp. To turn off the power supply to the fluorescent lamp, turn off the input to the primary side of the oscillation circuit.

The output terminal of the power supply device to the fluorescent lamp is opened.

 Short the output terminals to the fluorescent lamp.

However, the method cannot be used because the power supply to the control unit is also stopped, and the method uses an expensive switching component because the output circuit to the fluorescent lamp is high voltage and large current. There is a problem to be addressed. Also, a ballast is connected in series to this output terminal, and since the inductance of this ballast serves as a switching component, spark noise is generated when the ballast is turned on and off, and an expensive noise absorption capacitor for absorbing the noise. Parts are required. Therefore, in order to turn off the power supply to the fluorescent lamp, the method of the above three is considered to be the most preferable method. FIG. 6 is a diagram for explaining this method. In the figure, an oscillator circuit (not shown) is connected to the primary side of the transformer T1, the ballast L1 is connected to the fluorescent lamp output terminal on the secondary side, and the filament of the fluorescent lamp FL is connected. When the switch S1 connected between the filaments is turned on, the fluorescent lamp is preheated and the switch
When S1 and S3 are off, the high frequency high voltage of the secondary output is applied to both ends of the fluorescent lamp FL to light the fluorescent lamp. Then, in order to turn off the power supply to the fluorescent lamp, the switch S3 is turned on and the secondary side output is short-circuited. With this configuration, the switch can be operated with the load connected.
Since the switch S3 is turned on / off, the switch S3 does not have to be composed of an expensive component having a high breakdown voltage, and spark noise does not occur when the switch S3 is turned on / off.

(C) Problem to be Solved by the Invention However, in the above method, even if the switch S3 is turned on to turn off the power supply to the fluorescent lamp, the magnitude of the output current seen from the power supply side does not decrease. Absent. Therefore, the power consumption of the power supply device is not substantially reduced, and the loss and temperature rise inside the power supply device are not changed. Therefore, especially during preheating of the fixing device, the cooling fan of the main body of the copying machine is often turned off. Therefore, in the case of a small copying machine that does not have enough space for storing the parts, the temperature rise of the copying machine causes the copying operation. There was a problem of becoming higher than.

The object of the present invention is to pay attention to the fact that a ballast is connected in series to the output terminal to the fluorescent lamp, and the output current is reduced by the action of this ballast during preheating of the fixing device, thereby reducing the power consumption. It is to provide a power supply device in which

(D) Means for Solving the Problems The present invention relates to a power supply device for performing power supply to a fluorescent lamp for illuminating a document and power supply to a control unit based on the output of one oscillation circuit. A ballast is connected in series to the lamp output circuit, and switching means for increasing the oscillation frequency of the oscillation circuit when preheating the fixing device is provided.

FIG. 1 shows a configuration diagram of a power supply device according to the present invention.

Power is supplied to the control unit and the fluorescent lamp from one inverter, and one oscillator circuit OS is provided on the primary side of the inverter.
C is connected. Power is supplied to the fixing device from a fixing device drive circuit. Impedances Z1 and Z2, which are circuit elements that determine the oscillation frequency of the oscillation circuit, are connected in parallel to the oscillation circuit OSC included in the inverter, and the oscillation frequency switching circuit SW is connected in series to one of the impedances Z1. ing. When the switching circuit SW is turned on, the impedances Z1 and Z2 are connected in parallel, and when the switching circuit SW is turned off, only the impedance Z2 is connected to the oscillation circuit OSC. The oscillation frequency of the oscillator circuit OSC is lower when the impedances Z1 and Z2 are connected in parallel than when the impedance Z2 is alone. Oscillator circuit
The higher the OSC oscillation frequency, the higher the inverter output frequency. On the other hand, in the power down mode, the control unit outputs the power down mode signal PDM to the fixing device drive circuit and the switching circuit SW. The fixing device drive circuit uses this signal PD
When M is received, the fixing device is put into a preheat state, and the switching circuit SW puts the impedance Z1 into an open state.

(E) Operation In the power supply device shown in FIG. 1 described above, the signal PDM is not output from the control unit during the warm-up state of the fixing device and during the copy cycle. Therefore, the fixing device is controlled to the fixing temperature, and the switching circuit SW is in the ON state. In this state, the oscillation frequency of the oscillator circuit OSC is relatively lower than when the impedance Z2 is connected alone. On the other hand, when the copying machine is in the power down state, such as when a certain time has passed from the ready state, the control unit outputs the power down mode signal PDM to the fixing device drive circuit and the switching circuit SW. When the fixing device drive circuit receives this signal PDM, it controls the fixing device to the preheat state, the switching circuit SW is turned off, and the oscillation circuit OSC is turned on.
Increase the oscillation frequency of. At this time, the impedance of the ballast connected in series to the fluorescent lamp output terminal of the inverter rises, so that the output current output to the fluorescent lamp decreases, which reduces the power consumption of the entire inverter. Generally, the power consumption of the control unit is extremely smaller than the power consumption of the fluorescent lamp, and therefore the reduction in the output current to the fluorescent lamp greatly affects the reduction in the power consumption of the inverter itself. Therefore, when the power down mode is set, that is, when the fixing device is in the preheated state, the power consumption of the inverter is automatically reduced and the heat generation can be suppressed.

(F) Embodiment FIG. 2 shows a concrete circuit diagram of an embodiment of the present invention.

In this embodiment, a self-excited inverter is used as the inverter. The oscillator circuit connected to the primary side of the transformer T1 includes switching transistors Q1 and Q2, and these transistors Q1 and Q2 are alternately turned on / off. The resistors R1 and R2 included in the oscillator circuit correspond to the impedances Z1 and Z2 in FIG. 1, and the oscillation frequency changes depending on the magnitude of the voltage across the resistance. The outline of the operation of this oscillator circuit is as follows.

First, when the power is turned on, the transistor is connected via the resistor R7.
Q2 is biased and transistor Q2 rapidly turns on. With the transition to the ON state, resistors R1 and R
The voltage drop across both terminals 2 also increases, and when the voltage exceeds the threshold voltage for turning on the transistor Q4, the base current of the transistor Q2 is bypassed to the transistor Q4 and the transistor Q2 is turned off. on the other hand,
This time, the transistor Q1 is turned on, and the same operation as above is repeated, so that the transistors Q1 and Q2
Repeats on / off. When the rate of increase of the current flowing through the transistors Q1 and Q2 is constant, the larger the resistance value at both ends of the resistors R1 and R2, the shorter the time until the transistors Q2 and Q1 turn off and the higher the oscillation frequency. Resistance in this example
A switching circuit SW including a switch S2 is connected to R1, and the switching circuit SW is configured to turn off the switch S2 when the power-down mode signal PDM is output from the control unit. The oscillation frequency is higher when the switch S2 is off and the resistor R2 is connected alone than when the switch S2 is on and the resistor R1 and the resistor R2 are combined.

On the other hand, a fluorescent lamp output circuit and a control unit output circuit are provided on the secondary side of the transformer T1, and the control unit output circuit is a diode.
It contains a rectifier circuit consisting of D6, D7 and capacitor C2.
A DC power source rectified by this rectifier circuit is supplied to the control unit. The fluorescent light output circuit includes a ballast L1, which
Output current is supplied to the fluorescent lamp via L1. switch
As will be described later, S1 is set to the ON state by the control unit during warm-up, ready state and power-down state. As shown, in this embodiment, the switch S3 as shown in FIG. 6 is not provided. The AC power is rectified by the diode bridge DB1 and the output is input to the inverter.

FIG. 3 is a diagram showing an operation sequence of a copying machine provided with the above power supply device. This figure shows the correspondence between the modes of the copying machine body, the states of the fluorescent lamps, and the states of the switches S1 and S2. When the power is turned on, the main body of the copying machine enters the warm-up mode and power is supplied to the fixing device. At this time, the switch S1 is turned on and the fluorescent lamp is in the preheating A mode. Preheat A mode indicates a state in which the fluorescent lamp is preheated with a sufficient current. Since the fluorescent lamp is in the preheating mode, the switch S1 is set to the ON state, and the switch S2 is also set to the ON state. Ie switch S2
Is turned on, the oscillation frequency of the oscillation circuit is set to a low frequency. Since the oscillation frequency is set low, the current suppression due to the impedance of the ballast L1 does not significantly act, so that a sufficient preheating current is supplied to the fluorescent lamp. When the copy start is started, the copying machine body shifts to the copy cycle mode, but at this time, the switch S1 is turned off. Then, since a high voltage is applied between the electrodes at both ends of the fluorescent lamp, the fluorescent lamp is lit at a high frequency.
When copying is completed, the main body of the copying machine becomes ready. At this time, the switch S1 is turned on again to execute the preheating A mode for the fluorescent lamp. That is, the fluorescent lamp is preheated with a sufficient current. In the copying machine of the present embodiment, the ready state is automatically switched to the power-down mode after a lapse of a predetermined time after the copying is completed. In the power down mode, the temperature control for the fixing device is switched to the preheated temperature control. As a result, the power consumption of the entire copying machine is greatly reduced, and the power supply to the fan motor is stopped. In this power down mode, the fluorescent lamp is in the preheat B mode. This preheat B mode means that the switch S1 is on and the switch S2 is off. As described above, in the power down mode, the control unit outputs the signal PDM, which turns off the switch S2 of the switching circuit SW. When the switch S2 is turned off, the oscillating frequency of the oscillating circuit increases, and the frequency of the output current to the fluorescent lamp output circuit also increases. As the frequency of the output current increases, the output current becomes relatively small due to the impedance of the ballast L1. Therefore, the power consumption of the power supply circuit itself is also reduced. At this time, since the switch S1 is turned on, the preheating current flows to the fluorescent lamp, but the current value is small, so that the life of the fluorescent lamp is not affected.

In the above operation, FIG. 4 (A) shows the waveform of the current flowing through the switching transistors Q1 and Q2 when the switch S2 is on, and FIG. 4 (B) shows the current flowing through the transistors Q1 and Q2 when the switch S2 is off. The waveform is shown. As shown in the figure, when the switch S2 is off, the switching frequency (oscillation frequency) increases and the current value decreases. FIG. 5 is a table showing a comparison between the present embodiment and the prior art. The figure (A) shows the variate in each mode, and the figure (B) shows the comparison of the variate in the prior art and the embodiment. Fluorescent lamp output current I in power-down mode as shown
_It can be seen that the power loss at that time decreases in proportion to the square of the current because _L3 decreases. Therefore, by properly selecting the oscillation frequency, the power loss in the power down mode can be made extremely small.

(G) Effect of the Invention As described above, according to the present invention, since it is possible to supply power to the fluorescent lamp and the control unit with one power supply device, it is possible to realize miniaturization and a fluorescent lamp output circuit. It is not necessary to provide an expensive switch circuit for switching the open state to an open state, and the power consumption of the power supply device can be suppressed at the time of preheating of the fixing device simply by providing a simple switching circuit. Moreover, even if a preheating current is passed through the fluorescent lamp during preheating, the current value is small, so that the life of the fluorescent lamp is not shortened.

[Brief description of drawings]

FIG. 1 shows a block diagram of the present invention. FIG. 2 shows a circuit diagram of an embodiment of the present invention, FIG. 3 is an operation sequence diagram of the copying machine, FIGS. 4 (A) and 4 (B) are views for explaining the operation of the power supply device, and FIG. (A), (B) is a comparison diagram of a prior art and the said Example. FIG. 6 shows a partial circuit diagram of a conventional power supply device. SW …… Switching circuit, Z1, Z2 …… Impedance (circuit element of oscillation circuit), OSC …… Oscillation circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-202494 (JP, A) JP-A-62-6237 (JP, A) Actually developed JP-A-55-76565 (JP, U)

Claims (1)

[Claims] Claim: What is claimed is: 1. A power supply device for a copying machine, wherein a fluorescent lamp for illuminating a document and a control section are supplied with power based on the output of one oscillating circuit. While connecting in series,
A power supply device for a copying machine, comprising switching means for increasing the oscillation frequency of the oscillation circuit during preheating of the fixing device.