JPH0426268B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention can be used, for example, as a light source for exposing documents in copying machines, reading devices, etc., or as a light source for electrophotographic optical writing printers, liquid crystal shutters, etc. The present invention relates to a light source device including a fluorescent tube as a light emitting means.

[Conventional technology]

In the above-mentioned device, since it is necessary to immediately light up the fluorescent tube, the device is equipped with means for applying a voltage to the filament in order to preheat the filament in the fluorescent tube when the fluorescent tube is idling in the non-lighting state. Conventionally, this preheating voltage has been applied at a predetermined rated voltage regardless of the temperature of the fluorescent tube during idling.

[Problems with conventional technology]

Generally, the luminous efficiency of a fluorescent tube is determined by mercury vapor pressure and tube current. In particular, since mercury vapor pressure depends on temperature, luminous efficiency is greatly affected by temperature. For example, the luminous efficiency is highest when the tube wall temperature of a fluorescent tube is approximately 40 [℃], and the luminous efficiency decreases if the temperature is higher or lower than this.
generally known. It is also known that the mercury vapor pressure is determined by the temperature at the lowest point of the tube wall temperature (hereinafter referred to as the coldest point). Therefore, when lighting the fluorescent tube, it is desirable to maintain the temperature of this coldest point at approximately 40 [°C].

However, in the above-mentioned conventional device, if the structure is focused on stabilizing the amount of light at low temperatures, the amount of light at high temperatures tends to become unstable. Particularly during idling, as described above, the rated voltage is applied to the filament regardless of whether the tube wall temperature is high or low, so the tube wall temperature near the filament will rise too much in a high-temperature environment. As a result, temperature variations occur throughout the pipe wall, reducing the coldest point to 40 [℃].
As a result, a large unevenness in light intensity of approximately 20% or more occurred immediately after idling.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to provide a light source device that can stabilize the amount of light immediately after idling in a high-temperature environment.

[Key points of the invention]

In order to achieve the above object, the present invention provides a light source device having a fluorescent tube and a voltage applying means for applying a preheating voltage to a filament of the fluorescent tube. and a control means for controlling the voltage applied by the voltage application means based on the output signal from the temperature detection means.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram schematically showing an embodiment of the present invention. In the figure, near the fluorescent tube 1,
A photo sensor 2 is provided to detect the amount of light from the fluorescent tube 1, and on the wall of the fluorescent tube 1,
A thermistor 3 is attached to detect the tube wall temperature near the filament 1a. The light intensity signal output by the photo sensor 2 is converted into a DC voltage level by the amplifier 4, and then sent to the input terminal 5a of the control unit 5.
The output signal of the thermistor 3 is also guided to the input terminal 5b of the control section 5. Further, another input terminal 5c receives an instruction to switch between lighting the fluorescent lamp 1 and preheating the filament 1a, which is output from the main control unit of a copying machine or the like in which the light source device according to the present invention is used. A control signal _S1 is input for this purpose. The operation of the control unit 5 is based on this control signal S ₁
When the fluorescent tube 1 is turned on, the control voltage _V1 for controlling the light intensity of the fluorescent tube 1 to a constant level is applied according to the output signal of the photo sensor 2, and when the filament 1a is preheated, the control voltage V1 is switched to the output signal of the thermistor 3. A control voltage V ₂ for controlling the tube wall temperature to a constant value is output between output terminals 5d and 5e, respectively. These control voltages V ₁ and V ₂ are applied to the ballast 6
is led between the input terminals 6a and 6b of the
The above-described control signal _S1 is input to the two input terminals 6c. The ballast 6 switches between the lighting and preheating based on this control signal _S1 , converts the control voltage _V1 into a high frequency AC voltage to prevent flicker when lighting and supplies it to the fluorescent tube 1, and when preheating The control voltage V ₂ is converted into an alternating current voltage and supplied to the filament 1a. Therefore, when the fluorescent tube 1 is turned on, the amount of light is controlled to be constant based on the output signal of the photo sensor 2, and when it is preheated, the tube wall temperature is controlled to be constant based on the output signal of the thermistor 3.

The control signal 5 and ballast 6 described above will be explained in more detail below.

FIG. 2 specifically shows the control section 5, which is the most characteristic feature of the present invention.

In the figure, the output signal of the photo sensor 2 is input to the + terminal of the amplifier 11 for error detection via the amplifier 4, and the output signal of the thermistor 3 is input to the - terminal of the other amplifier 12 for error detection. It has been entered. The transistors 13 and 14 are switch circuits that turn on and off according to the control signal _S1 input from the input terminal 5c, and based on this switch operation, the H level voltage E is applied to the amplifier 11.
and the + terminal of the amplifier 12. The outputs of amplifiers 11 and 12 are connected to two diodes 1
Analog OR (OR) is performed by 5 and 16, and a control signal is sent to the inverting input terminal of comparator 17.
It is applied as S ₂ . A sawtooth PWM (pulse width modulation) signal _S3 is input to the other input terminal of the comparator 17, and the control signal _S2 is pulse width modulated and output. The modulation signal output by the comparator 17 is transmitted to the transistors 18a and 18.
b, a DC-DC converter 1 consisting of a coil 18c, a diode 18d, a capacitor 18e, etc.
8, and this output voltage is input to the output terminals 5d, 5.
It is taken out from between e.

Next, the operation of the control section 5 having the above configuration will be explained. The control signal _S1 is set to H level when preheating the filament 1a, and set to L level when lighting the fluorescent tube 1. First, the control signal S ₁
When is at H level, transistor 13 is turned on and transistor 14 is turned off, so amplifier 1
An H signal due to the voltage E is input to the negative terminal of the amplifier 1 and the positive terminal of the amplifier 12. Therefore, amplifier 1
2 becomes active, and its amplified output signal is sent via diode 16 to comparator 17 as control signal S ₂ . The level of this control signal _S2 becomes smaller as the temperature detected by the thermistor 3 becomes lower. In thermistor 17, the above PWM
The signal S ₃ and the control signal S ₂ are compared, and the lower the level of the control signal S ₂ , the longer the pulse width is output. The DC-DC comparator 18 operates according to this pulse width, and outputs a larger voltage as the pulse width becomes longer. Therefore, when the filament 1a is preheated, the output voltage of the DC-DC converter 18 is taken out from between the output terminals 5d and 5e as the control voltage _V2 , and this control voltage _V2 is detected by the thermistor 3. It changes depending on the temperature, and when the temperature is low, it is set large, and when the temperature is high, it is set small.

On the other hand, when the fluorescent tube 1 is turned on, that is, the control signal S ₁
When is switched to the L level, unlike the above, the transistor 13 is turned off and the transistor 14 is turned on, so that the L signal is input to the - terminal of the amplifier 11 and the + terminal of the amplifier 12. Therefore,
This time, the amplifier 11 becomes active, and its output signal is sent to the comparator 17 via the diode 15 as the control signal _S2 . Thereafter, the comparator 17 and the DC-DC converter 18 perform operations similar to those described above, and the output voltage of the DC-DC converter 18 is taken out from between the output terminals 5d and 5e as the control voltage _V1 . Therefore, this control voltage _V1 also changes depending on the amount of light detected by the photo sensor 2, and is set to be large when the amount of light is small, and set to be small when the amount of light is large.

Next, FIG. 3 shows a more specific configuration of the ballast 6 described above. In the figure, input terminals 6a,
Control voltages V ₁ and V 2 outputted between the output terminals 5d and 5e of the control section 5 are inputted between the terminals 6b _{and 6b} .
DC-AC inverter 2 is connected between input terminals 6a and 6b.
1 and 22 are connected, and the control voltages V ₁ and V ₂ are applied thereto. The DC-AC inverter 21 is used for lighting the fluorescent tube 1, and converts the voltage between the input terminals 6a and 6b into a high-frequency alternating current voltage, which is applied to both ends of the fluorescent tube 1. Another
The DC-AC inverter 22 is used for residual heat of the filament 1a, converts the voltage between the input terminals 6a and 6b into an alternating current voltage, and applies the voltage to each of the filaments 1a. The transistors 23 and 24 are
It is a switch circuit that turns on and off in response to a control signal _S1 inputted from the input terminal 6c, and the signals appearing on the respective collector sides are inputted to the DC-AC inverters 21 and 22 as oscillation control signals _S4 and _S5 . ing. The DC-AC inverters 21 and 22 perform the above operation only when the oscillation control signals S ₄ and S ₅ are at H level, respectively.

The overall operation of the ballast 6 having the above configuration will be described next. First, when the filament 1a is preheated, that is, when the control signal _S1 is at H level, both transistors 23 and 24 are turned off. Therefore, the oscillation control signal _S4 becomes L level, the oscillation control signal _S5 becomes H level, and only the DC-AC inverter 22 operates. At this time, since the control signal S ₁ is at the H level, the control section 5 outputs the control voltage.
V ₁ is output, and this control voltage V ₁ is DC−
It is converted into an alternating current voltage by the AC inverter 22 and applied to the filament 1a as a preheat voltage _V4 ,
Preheating is performed. In this case, the DC-AC inverter 21 stops operating, and the fluorescent lamp 1 is in an unlit state.

On the other hand, when the fluorescent tube 1 is turned on, that is, when the control signal _S1 is switched to L level, the transistors 23 and 24 are both turned on. Therefore, the oscillation control signal _S4 is at H level, and the oscillation control signal
_S5 becomes L level, and only the DC-AC inverter 21 operates this time. At this time, the control signal _S1 is L
level, the control signal section 5 outputs the control voltage.
V ₂ is output, and this control voltage V ₂ is DC−
It is converted into a high frequency alternating current voltage by the AC inverter 21 and applied as a tube voltage V ₃ to both ends of the fluorescent tube 1.
Lighting is performed.

Next, the timing of the level changes of the tube voltage V ₃ and residual heat voltage V ₄ with respect to the level changes of the control signal S ₁ is shown in FIG. 4a. As is clear from the figure, when the control signal S ₁ is at H level, the residual heat voltage V ₄
is applied to the filament 1a to preheat it,
When the control signal S ₁ becomes L level, the tube voltage V ₃ is applied to the fluorescent tube 1 and lighting starts. Tube voltage V ₃ ,
The voltage level of the residual heat voltage _V4 is determined by the control unit 5.
The control voltages V ₁ and _{V 2 are} determined by the detection signal levels of _the photo sensor 2 and thermistor 3 as described above. Therefore, the voltage levels of the tube voltage V ₃ and residual heat voltage V ₄ are set to be small when the amount of light from the fluorescent tube 1 is large or when the temperature of the tube wall is high, and to be large when the opposite is the case. The light intensity and tube wall temperature are controlled to be constant.

Alternatively, as shown in FIG. 4b, a sequence may be adopted in which the preheat voltage V ₄ is applied at a high level for a time T when the control signal S ₁ rises, and then the tube voltage V ₃ is applied. In this way, the tube voltage
By applying a sufficient preheat voltage V 4 immediately before V ₃ is applied, that is, immediately before lighting, the preheat voltage V ₄ can be reduced _.
It is possible to prevent the fluorescent tube 1 from becoming black due to insufficient brightness.

The thermistor 3 is installed at the fluorescent tube 1.
It can be placed anywhere on or around the pipe wall as long as it does not block the effective light from the first
It is more preferable to be near the filament 1a as shown in the figure or near the coldest point.
Further, as long as the temperature of the fluorescent tube 1 can be detected, the temperature sensor is not limited to the thermistor 3 described above, but may be a temperature sensor such as a thermocouple.

〔Effect of the invention〕

As explained above, according to the present invention, by controlling the preheating voltage of the filament according to the temperature state of the fluorescent tube, the tube wall temperature can be maintained constant even in a high temperature environment during idling. , can prevent abnormal heating of the tube wall. Therefore, the present invention reduces the unevenness of light intensity by 5% immediately after idling.
At the same time, there is almost no decrease in luminous efficiency, and furthermore, it is possible to save power consumption, which is an extremely excellent effect.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram schematically showing an embodiment of the present invention, Fig. 2 is a circuit diagram specifically showing a control section according to the embodiment, and Fig. 3 is a circuit diagram specifically showing a ballast according to the embodiment. The circuit diagram shown in FIG. 4 is a time chart showing the relationship between the control signal _S1 , the tube voltage _V3 , and the preheating voltage _V4 according to the same embodiment. 1... Fluorescent tube, 1a... Filament, 2...
Photo sensor, 3...Thermistor, 5...Control unit, 6...Ballast, 11, 12...Amplifier for error detection, 17...Comparator, 18...DC
-DC converter, 21, 22...DC-AC inverter.

Claims (1)

[Scope of Claims] 1. A light source device comprising a fluorescent tube and a voltage applying means for applying a preheating voltage to a filament of the fluorescent tube, comprising: a temperature detecting means for detecting a tube wall temperature of the fluorescent tube; A light source device comprising: control means for controlling a voltage applied by the voltage application means based on an output signal from the temperature detection means. 2. Claim 1, characterized in that the temperature detection means is provided near the coldest point of the fluorescent tube.
The light source device described in Section 1. 3. The light source device according to claim 1, wherein the temperature detection means is provided near the filament of the fluorescent tube.