JPH07220879A - Fluorescent lamp lighting device and image forming device - Google Patents

Abstract

PURPOSE:To control the preheating voltage to fluorescent lamp filaments with high accuracy and good responsiveness. CONSTITUTION:A power source is turned on or off by an oscillator 1 provided on the primary side to drive a fluorescent lamp lighting inverter transformer T2, and the high-frequency voltage outputted from the secondary side is fed to a fluorescent lamp FL1 via a fluorescent lamp lighting current limiting inductance L1. A diode bridge DB1 and a transistor Q2 are connected to both ends of the fluorescent lamp FL1, and the fluorescent lamp FL1 is turned on or off via the control of the transistor Q2 by a fluorescent lamp control circuit 2. The outputs from the secondary windings S1, S2 of a filament preheating converter transformer T1 are rectified, smoothed, and fed to preheat the filaments 11, 12 of the fluorescent lamp FL1. A transistor Q1 is turned on or off by a preheating voltage control circuit 3 to control the input to the primary winding P1 so that the output detection value from a detecting winding P2 provided on the filament preheating converter transformer T1 is stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a printer,
A fluorescent lamp lighting device suitable for lighting and controlling a fluorescent lamp for irradiating an image forming object provided in various other electronic devices, and a copying machine for irradiating the image forming object with the fluorescent lamp and forming and outputting an image on a recording medium, The present invention relates to an image forming apparatus such as a printer.

[0002]

2. Description of the Related Art In image forming apparatuses such as copying machines and printers, a structure in which an image forming object is irradiated by a fluorescent lamp and an image is formed and output on a recording medium by an electrophotographic method or the like is widely adopted.

FIG. 6 is a circuit diagram showing a prior art example of a fluorescent lamp lighting device provided in an image forming apparatus.

The lighting circuit of the fluorescent lamp FL1 drives the inverter transformer T2 by turning on / off the transistor Q4 by the input from the oscillator provided on the primary side, and the high frequency voltage output from the secondary side is the fluorescent lamp lighting current limiting inductance. Filament 1 at both ends of the fluorescent lamp FL1 via L1
1, 12 are connected. A diode bridge DB1 is connected to both ends of the fluorescent lamp FL1 so that turning on / off of the fluorescent lamp FL1 is controlled by a transistor Q3. Note that T1 is a transformer provided for supplying a preheating current to the filaments 11 and 12 of the fluorescent lamp FL1.

The fluorescent lamp lighting device provided in the image forming apparatus is
It is necessary to accurately control the preheating of the filament in order to instantly turn on the fluorescent lamp and prolong its life.
The conventional fluorescent lamp lighting device has a structure as shown in the circuit diagram of FIG.

That is, the filament 11 of the fluorescent lamp FL1,
The secondary side winding of the preheating transformer T1 is connected to 12 and a sine wave or a rectangular wave is applied to the primary side winding,
And the filaments 11 and 12 are preheated with a sine wave or a rectangular wave. Further, the filament temperature is controlled to an appropriate temperature by controlling the peak value of the waveform applied to the primary side.

[0007]

In the above prior art, since the filament is always preheated by the AC power source, a temperature ripple occurs, the life is shortened, and a circuit for controlling the peak value is required, which is costly. Was a disadvantage to Also,
Preheating with AC voltage makes it difficult to control with high precision.
The filament temperature slows to rise and it is difficult to shorten the preheating time before lighting.

FIG. 7 is a circuit diagram showing an example of a preheating circuit using a DC power source.

Preheating with direct current can completely eliminate the temperature ripple of the filament, extend the life of the fluorescent lamp, realize highly precise control of the preheating voltage, and shorten the preheating time before lighting. The cost was lower than that of the example shown.

However, when it is necessary to control the preheating voltage to a plurality of values as will be described later, the transient response characteristic is poor due to the difference in the time constants of the load and the detection system, resulting in an uncontrollable period and a fluorescent lamp life. There was a problem that it adversely affected.

The present invention solves the above-mentioned problems of the prior art, can control the preheating voltage to the fluorescent lamp filament with high accuracy and good responsiveness, and eliminates the temperature ripple of the fluorescent lamp lighting device and image forming apparatus. It is intended to provide.

[0012]

Therefore, the fluorescent lamp lighting device according to the present invention includes a lighting power source means for supplying a fluorescent lamp with a tube current for lighting the fluorescent lamp, and a filament for preheating the fluorescent lamp. A fluorescent lamp lighting device having a preheating power supply means for supplying a DC current, wherein the preheating power supply means comprises an input winding connected to a drive power supply and a plurality of output windings connected to a filament. A preheating transformer including a detection winding that detects an output voltage, a switching unit that turns on and off an input to the input winding, and a rectifier that smoothes the output from the output winding and supplies it to a filament. Means, comparing means for comparing the output detection value from the detection winding with a predetermined value, and controlling the on / off ratio of the switching means so that the output detection value from the detection winding becomes the predetermined value. Control Means and a resetting means for resetting an output detection value input when the output detection value input to the comparison means exceeds a predetermined value, by the constitution characterized by the above-mentioned, to achieve the above object. is there.

Further, it is an object of the present invention to achieve the above object of the image forming apparatus by providing the fluorescent lamp lighting device having the above structure.

[0014]

With the construction of the above fluorescent lamp lighting device, the fluorescent lamp can be turned on by the power supplied from the lighting power supply means, and the filament can be preheated by the preheating power supply means in accordance with the usage state of the image forming apparatus.

In particular, the waveform of the voltage for preheating the filament is a direct current rectified and smoothed by the rectifying means and can be controlled with high precision by the comparing means and the control means, and a predetermined voltage is supplied to the filament to preheat it. Further, it is possible to eliminate the temperature ripple of the filament and shorten the filament preheating time. Also, the transient response characteristic when the control voltage is changed can be improved.

Since the fluorescent lamp lighting device is provided, the image forming apparatus can use the fluorescent lamp stably and effectively for a long period of time, and can efficiently form an image.

[0017]

EXAMPLES The fluorescent lamp lighting device and the image forming apparatus of the present invention will be described below with reference to examples.

(First Embodiment) FIG. 1 is a circuit diagram of a fluorescent lamp lighting device according to a first embodiment of the present invention for lighting and controlling a fluorescent lamp provided in an image forming apparatus. The same or corresponding parts are denoted by the same reference numerals.

The configuration and operation of the first embodiment will be described with reference to FIG.

The fluorescent lamp inverter transformer T2 is an oscillator 1
Driven to generate a desired high-frequency high-voltage AC waveform defined by the characteristics of the fluorescent lamp FL1 on the secondary side. The output of the transformer T2 is connected to the filaments 11 and 12 at both ends of the fluorescent lamp FL1 via the fluorescent lamp lighting current limiting inductance L1. Generally, a fluorescent lamp is proportional to the length of the fluorescent tube in order to shift from the extinguished state to the lit state,
A voltage that is inversely proportional to the diameter is required, and a low impedance occurs when the state shifts to the lighting state, so that a current limiting element is necessary to limit lighting to a current value that maintains the lighting and obtains the required maximum amount of light. In this embodiment, the inductance L1 is It is connected.

Further, a shunt switch composed of a diode bridge DB1 and a transistor Q2 is connected to both ends of the fluorescent lamp FL1. Transistor Q2 is O
When it is N, the output of the transformer T2 is not applied to the fluorescent lamp FL1, so the fluorescent lamp FL1 is in the off state. When the transistor Q2 is turned off, the output of the transformer T2 is applied to the fluorescent lamp FL1 to turn on the light.

The transistor Q2 is a fluorescent lamp control circuit 2
Thus, for example, PWM control is performed so that the output of a light amount sensor (not shown) becomes a constant value. That is, by changing the ON / OFF duty of the transistor Q2, the lighting / lighting-off of the fluorescent lamp FL1 can be controlled in a timely manner, and operation is performed so that the lighting light amount is maintained at a constant value.

The transformer T1 is a flyback converter transformer for filament preheating. As described above, in order to quickly switch the fluorescent lamp from the extinguished state to the lit state and to secure a long life, the electron emitting substance coated on the filament surface is made to emit thermal electrons easily, and the electron emitting substance is also made. To minimize the scattering and consumption of
It is necessary to keep the filaments 11 and 12 at a predetermined temperature. Therefore, the power applied to both ends of the filament is controlled and output by the transformer T1.

One end of the primary winding P1 of the transformer T1 is connected to the power supply voltage Vcc, and the other end is connected to the collector of the transistor Q1 which is a switching element. The emitter of the transistor Q1 is grounded. The secondary windings S1 and S2 of the transformer T1 are diodes D1 and D
2. The capacitors C1 and C2 are rectified and smoothed to form a DC voltage, the diodes D3 and D4 prevent backflow, and they are respectively connected to the filaments 11 and 12 of the fluorescent lamp FL1.

Further, the transformer T1 is provided with a detection winding P2, the output of which is rectified and smoothed by a diode D5 and a capacitor C3 and converted into a DC voltage as a detection output Vsns. The resistor R1 adjusts the loop response characteristic of control. The detection output Vsns is the secondary winding S
The generated voltage of S1 and S2 can be accurately reflected,
The voltage generated in the secondary windings S1 and S2 is controlled by PWM control of the transistor Q1 so that the preheating voltage control circuit 3 stabilizes this voltage value to a predetermined value.
The filament preheating DC voltage rectified and smoothed by D3, D2, C2 and D4 can be controlled to a desired value with extremely high accuracy.

The relationship between filament preheating and lighting control will be described in more detail. Prior to the start of lighting, a preheating voltage for applying a filament temperature that allows stable lighting start is applied (referred to as full preheating). Further, in the completely extinguished state, some preheating voltage is applied in order to shorten the time required to reach the filament temperature (referred to as half preheating).

Further, during lighting, the fluorescent lamp control circuit 2 duty-controls the transistor Q2 so that the light amount becomes a predetermined amount as described above, so that the light is turned on / off repeatedly in a microscopic manner. The filament temperature is stabilized by applying a preheating voltage (referred to as lighting preheating). Although the optimum value of the preheating voltage during the lighting control strictly varies depending on the lighting duty, a constant value is usually sufficient within the latitude range of the optimum value. That is, the preheating voltage control circuit 3 must control at least three values (at least two values if it is not necessary to shorten the time), and yet change the control voltage instantaneously. However, the filament load is about several Ω, and especially when shifting from full preheating to lighting preheating, even if the control target value is changed by the time constant of the detection output, preheating is stopped during the period when the detection output falls to the control target value. Will result in Therefore, in this embodiment, when the response improvement circuit 4 changes the control target value in a decreasing direction, the control value is instantaneously changed by rapidly discharging the capacitor C3.

The preheating voltage control circuit 3 and the response improving circuit 4 of the transformer T1 are constructed as shown in the circuit diagram of FIG. 2, for example. The same components as those described above are designated by the same reference numerals.

The detection output Vsns is compared with the control target value Vcont by the error amplifier IC1 and amplified. IC1
The output of is compared with the ramp waveform by IC2, and as a result, IC
The output of 2 drives the transistor Q1 as a PWM waveform. Further, the transistor Q4 is configured to drive the transistor Q1 by the signal from the fluorescent lamp control circuit 2 only during the fluorescent lamp off period.

With the above operation, the preheat voltage is the control target value Vco.
The voltage is controlled according to nt. As described above, an appropriate resistor R1 is a capacitor C3 for the purpose of adjusting the stability of control.
Although it is inserted in parallel with the above, it is only an effect of ensuring stability when the control reaches the target value, and a discharge effect in a transient state cannot be expected. Therefore, when the control target value is decreased as in the case where Vcont is changed from full preheating to lighting preheating, the filament load has a low resistance in the circuit shown in FIG. , C2 are discharged in a short time, while the charges accumulated in the capacitor C3 are discharged only through the resistor R1, the output of IC1 remains High until the detection signal Vsns falls to the control target value Vcont. As a result, the PWM signal is stopped, and as a result, the preheat is not applied to the desired value for a relatively long time.

Therefore, the emitter for inputting the detection output Vsns is connected to the + input of the error amplifier IC1, the base is connected to the − input of the error amplifier, and the collector is connected to the ground via the resistor R2. A response improving circuit is constituted by a protection diode D6 connected in the opposite direction to the emitter-base direction of.

In the steady state in which the control value is controlled to the target value, the +/- input of the error amplifier IC1 is in an imaginary short-circuit state, and the added response improving circuit does not function at all and the original preheating voltage control circuit does not operate. It does not interfere with the operation. Therefore, when Vcont is changed from the full preheat state to the lighting preheat state, the filaments have low impedance as described above, and thus the capacitors C1, C
The electric charge stored in 2 is discharged in an extremely short time. On the other hand, the electric charge of the capacitor C3 is discharged through the resistor R1 and slowly decreases, so that it hardly changes momentarily and the error amplifier IC1 enters a saturated state and the PWM signal stops, but the potential difference between Vcont and Vsns is reduced by the transistor Q3. When Vbe is exceeded, the transistor Q3 is turned on and is grounded via the resistor R2 having a value sufficiently lower than the resistor R1 and not exceeding the maximum rating of the transistor Q3. Therefore, the electric charge of the capacitor C3 is rapidly discharged, and the detection signal Vsns rapidly approaches the control target value Vcont.

Further, the control target value Vcont and the detection signal V
When the potential difference of sns becomes equal to or lower than Vbe of the transistor Q3, the transistor Q3 is turned off, and thereafter the capacitor C
The charge of 3 is again discharged through the resistor R1, and when Vsns and Vcont become approximately the same potential, the error amplifier IC1 goes out of the saturation state and shifts to the control state to generate the PWM signal.

As described above, the period during which the PWM signal is stopped exists in principle in this embodiment as well, but the period can be made short enough not to affect the life of the filament, and the constant is optimized. When set to, the voltage waveform itself applied to the filament has a unique time constant. Therefore, when observed with the filament, it does not look like the waveform affected by the PWM stop period as in the conventional case shown in FIG. Instead, it becomes possible to smoothly shift the applied voltage as shown in FIG.

As described above, the predetermined potentials can be rapidly and smoothly switched and stably supplied to the filament of the fluorescent lamp in response to full preheating, half preheating, and lighting preheating, thereby improving the utilization efficiency of the fluorescent lamp. It can be improved and the life can be extended.

(Second Embodiment) FIG. 4 is a circuit diagram of a main part showing a filament preheating power supply control portion of a second embodiment of a fluorescent lamp lighting device for lighting and controlling a fluorescent lamp provided in an image forming apparatus, The same or corresponding parts as in the first embodiment are designated by the same reference numerals.

The other parts have the same structure and operation as those of the first embodiment, and therefore the description thereof will be omitted. The characteristic structure and operation of the second embodiment will be described with reference to FIG.

Similar to the first embodiment, the output of the detection winding P2 is rectified and smoothed by the diode D5 and the capacitor C3, and is DC.
Be converted. This DC voltage value is divided by the resistors R3 and R4 and input to the error amplifier IC1 as a detection signal Vsns.

If an appropriate voltage that can be directly input to the error amplifier can be set without the above voltage division configuration, the first
Although it can be configured as in the embodiment, it is often difficult due to the relationship between the control target value Vcont or the output and the turn ratio of the detection winding.
With the configuration according to the present embodiment, the circuits can be set relatively freely by the resistors R3 and R4. Further, the smoothed output is discharged through a discharge resistor R2 to a transistor Q5 which is a discharge switch
, The emitter of the transistor Q5 is grounded, and the base is grounded via a resistor R6. The detection signal Vsns is connected to the emitter of the PNP transistor Q3, and the collector of the transistor Q3 has a resistor R5.
Is connected to the base of the discharge switch Q5 via the input terminal, the base is connected to the control input (-input) of the error amplifier IC1, and the protection diode D6 is connected in the reverse direction between the base and emitter of the transistor Q3.

As in the first embodiment, in the steady state in which the control value is controlled to the target value, the +/- input of the error amplifier IC1 is in an imaginary short state, and the added response improving circuit does not function at all. Without disturbing the original operation of the preheat voltage control circuit. Therefore, when the control target value Vcont is changed from the full preheating state to the lighting preheating state, the electric charge stored in the capacitors C1 and C2 on the output side is extremely short time because the filament has low impedance as described above. Is discharged.

On the other hand, the charge of the capacitor C3 on the control side is discharged through the combined resistance of the resistors R3 and R4 and slowly decreases, so that it hardly changes instantaneously and the error amplifier IC1 becomes saturated and the PWM signal becomes Stop but
When the potential difference between the control target value Vcont and the detection signal Vsns exceeds Vbe of the transistor Q3, the transistor Q3 is turned on and the base current is supplied to the transistor Q5 through the resistor R5 to turn on the transistor Q5. Then, the smoothed output is grounded through the resistor R2 having a value sufficiently lower than the combined resistance of the resistors R3 and R4 and having a value set so as not to exceed the maximum rating of the transistor Q3. Therefore, the electric charge of the capacitor C3 is rapidly discharged, and the detection signal Vsns rapidly approaches the control target value Vcont.

Further, when the potential difference between Vcont and Vsns becomes less than Vbe of the transistor Q3, the transistor Q3
Is turned off, and as a result, the transistor Q5 is also turned off. After that, the charge of the capacitor C3 is discharged again through the combined resistance of the resistors R3 and R4, and when the detection signal Vsns and the control target value Vcont become approximately the same potential, the error amplifier IC1
Goes out of the saturation state and shifts to the control state to generate the PWM signal.

That is, in the first embodiment, the transistor Q3 functionally functions as a comparator having a dead zone of Vbe and also as a discharge switch, whereas in the second embodiment, the transistor Q3 is a comparator having a dead zone of Vbe and is a transistor. The function is divided such that Q5 corresponds to a discharge switch.

As described above, it is possible to switch the predetermined potentials to the filament of the fluorescent lamp in correspondence with full preheating, half preheating, and lighting preheating more quickly and smoothly than in the first embodiment, and to supply stably. The utilization efficiency of the fluorescent lamp can be improved and the life can be extended.

(Third Embodiment) FIG. 5 is a circuit diagram of a main part showing a filament preheating power source portion of a third embodiment of a fluorescent lamp lighting device for lighting and controlling a fluorescent lamp provided in an image forming apparatus. The same or corresponding parts as those in the first or second embodiment are designated by the same reference numerals.

The other parts have the same structure and operation as those of the first embodiment, and therefore will not be described. The characteristic structure and operation of the third embodiment will be described with reference to FIG.

In the first embodiment, the transformer T1 for filament preheating having the input winding P1, the output windings S1 and S2, and the detection winding P2 is configured in the flyback type regulator mode. The third embodiment is configured in the forward regulator mode. The circuit operation is the same as that of a normal forward type regulator, and the control operation / effect and the like are the same as those in the first embodiment.

In the present embodiment, the main parameter of the transformer design is the turns ratio in the case of an application of relatively low power due to the forward type, and in comparison with the forward type, it is necessary to consider the primary inductance. In addition, the characteristics of the transformer are less likely to affect the output, and the control stability can be increased.

(Example of Image Forming Apparatus) In the example of the image forming apparatus according to the present invention, the fluorescent lamp for illuminating the image forming object is controlled to be turned on by the fluorescent lamp lighting device of the above example, and the image forming object is formed. An image forming apparatus such as a copying machine or a printer that irradiates an object to form an image on a recording medium and outputs the image, and the fluorescent lamp is in a print standby state, image forming start, image forming by the action and effect of filament heating of the fluorescent lamp lighting device. Since it is possible to quickly and easily shift to the operating state or the like, the image forming apparatus of this embodiment can stably use the fluorescent lamp effectively for a long period of time and efficiently form an image.

[0050]

As described above, according to the present invention,
By changing the preheating voltage waveform to direct current, the preheating voltage can be controlled with high accuracy and the temperature ripple of the filament is completely eliminated.
In addition, the peak voltage applied to the filament is reduced, glow discharge at both ends of the filament is less likely to occur, preheating time can be shortened, and transient response characteristics when the control voltage is changed can be improved, extending the life of the fluorescent lamp. It becomes possible to do. Further, in the conventional method, the preheating voltage control circuit has a configuration such as a chopper power supply and the circuit is complicated and the number of parts is very large. However, according to the present invention, the number of parts can be reduced, so that the cost can be reduced. Can be measured.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment.

FIG. 2 is a primary side circuit diagram of a transformer T1 according to a first embodiment.

FIG. 3 is a filament voltage waveform comparison diagram between the first embodiment and the conventional example.

FIG. 4 is a circuit diagram of a main part of a second embodiment.

FIG. 5 is a circuit diagram of a main part of a third embodiment.

FIG. 6 is a circuit diagram of a conventional fluorescent lamp lighting device.

FIG. 7 is a circuit diagram of a conventional fluorescent lamp lighting device.

[Explanation of symbols]

 1 Transmitter 2 Fluorescent lamp control circuit 3 Preheating voltage control circuit 4 Response improvement circuit 11,12 Filament DB1 Diode bridge FL1 Fluorescent lamp L1 Fluorescent lamp lighting current limiting inductance Q2, Q3 Transistor S1, S2 Secondary winding P1 Primary winding P2 Detection winding T1 Filament preheating transformer T2 Fluorescent lamp lighting transformer

Claims (5)

[Claims] 1. A fluorescent lamp lighting device having a transformer, which comprises a lighting power source means for supplying a fluorescent lamp with a tube current for lighting, and a preheating power source means for supplying a direct current for preheating to a filament of the fluorescent lamp. In the device, the preheating power supply means includes a preheating transformer including an input winding connected to a drive power supply, a plurality of output windings connected to a filament, and a detection winding for detecting an output voltage,
A switching means for turning on / off the input to the input winding; a rectifying means for rectifying and smoothing an output from the output winding to supply the filament to the filament; and an output detection value from the detection winding and a predetermined value. Comparison means for comparing, control means for controlling the on / off ratio of the switching means so that the output detection value from the detection winding becomes the predetermined value, and the output detection value input to the comparison means has a predetermined value. A fluorescent lamp lighting device, comprising: a reset unit that resets an output detection value that is input when the value exceeds. 2. The preheating power source means rectifies and smoothes the output from the detection winding to obtain an output detection value to be input to the comparison means, and sets the output winding and the detection winding in a flyback mode. The fluorescent lamp lighting device according to claim 1, which is configured to be driven. 3. A preheating power supply means rectifies and smoothes an output from the detection winding to obtain an output detection value to be input to a comparison means, and drives the output winding and the detection winding in a forward mode. The fluorescent lamp lighting device according to claim 1, wherein the fluorescent lamp lighting device has the following configuration. 4. The fluorescent lamp lighting device according to claim 1, wherein the rectifying means has a backflow preventing function for preventing a backflow current to the filament. 5. The fluorescent lamp lighting device according to any one of claims 1 to 4 is used to illuminate an image forming object with a fluorescent lamp whose lighting and preheating are controlled to output an image on a recording medium. Image forming apparatus.