JPH11162688A - Discharge-lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abnormality-detecting type protection means high in accuracy in judgement of a life-ending stage irrespective of dimming level. SOLUTION: This device is provided with a dimmer lighting circuit 100 capable of adjusting optical output of a discharge lamp 5. Abnormality-detecting protection circuits (34, 41, 42, 301, etc.), are provided for limiting the optical output of the discharge lamp 5 when lamp voltage of the discharge lamp 5 exceeds a fixed threshold value A. A threshold changing means 302 is provided for detecting the status of the optical output of the discharge lamp 5 and changing the threshold value A. A characteristic of the threshold changing means 302 is determined such that the threshold value A becomes smaller when the optical output gets greater and vice versa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting apparatus of a type in which a threshold value of a tube voltage activated by an abnormality detection type protection circuit is varied.

[0002]

2. Description of the Related Art At the end of the life of a discharge lamp, oxide of a filament is consumed, and an excessive discharge state is caused, and the lighting device is overloaded. Therefore, in general, an abnormality detection type protection circuit for limiting the light output of the discharge lamp when the tube voltage of the discharge lamp exceeds a predetermined threshold is used. On the other hand, when dimming the discharge lamp, the tube voltage rises. FIG. 3 is a characteristic diagram showing a tube voltage C and the like of a 40 W fluorescent lamp. The hatched width of the tube voltage C indicates a change due to the influence of the ambient temperature. The tube voltage (ratio) C at the time of all light with 100% light output (at the time of non-dimming or at the time of rated output) is almost 1 and is low. When the light output (%) is decreased and light control is performed, the tube voltage C increases. The tube voltage at the level B is the tube voltage when the oxide is consumed (exactly, the data of the test 40 W fluorescent lamp in which the oxide is not applied to the filament). The threshold value of the abnormality detection type protection circuit is set to a level A slightly lower than the level B.

[0003]

A comparison of the tube voltage C characteristic shown in FIG. 3 with the threshold value A shows that, in the case of dimming, especially in the case of a low temperature where the tube voltage becomes high, despite the fact that the discharge lamp is normal, ,
It can be seen that there is a possibility of being erroneously determined as the end of life. SUMMARY OF THE INVENTION It is an object of the present invention to provide an abnormality detection type protection unit having a high accuracy of the end-of-life determination regardless of the dimming level.

[0004]

SUMMARY OF THE INVENTION The present invention comprises a dimmable lighting circuit capable of adjusting the light output of a discharge lamp. An abnormality detection type protection circuit is provided for limiting the light output of the discharge lamp when the tube voltage of the discharge lamp exceeds a predetermined threshold. In the present invention, the apparatus further comprises threshold changing means for changing the threshold according to the light output state of the discharge lamp, and the characteristic of the threshold changing means is such that the threshold is low when the light output is large and high when the light output is small. Set forth in

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. The discharge lamp lighting device according to the present invention includes a dimmable lighting circuit 10 capable of adjusting the light output of the discharge lamp 5.
0 is provided. An abnormality detection type protection circuit (34, 41, 42, 301, etc.) for limiting the light output of the discharge lamp 5 when the tube voltage of the discharge lamp 5 exceeds a predetermined threshold A is provided. Discharge lamp 5
And a threshold changing unit 302 that changes the threshold A by detecting the light output state. The characteristics of the threshold value changing means 302 are determined so that the threshold value A is low when the light output is large, and high when the light output is small. For convenience of illustration in FIG. 1, the dimming type lighting circuit 100, the abnormality detection type protection circuit, and the threshold value changing means 30
Although the two cannot be clearly separated from each other, this figure does not show the concept of higher or lower levels as constituent elements.

FIG. 1 shows an AC power supply 1 and a rectifying and smoothing circuit 2. The dimming type lighting circuit 100 is a modified half-bridge type inverter type circuit, and receives an output of the rectifying / smoothing circuit 2. The dimming type lighting circuit 100 includes a pair of switching elements, for example, switching transistors 11 and 12 connected in series. 21 and 22 are flywheel diodes connected in anti-parallel with the switching elements 11 and 12, respectively. Reference numeral 4 denotes a drive circuit that controls the switching elements 11 and 12 to turn on and off alternately.
Reference numeral 3 denotes an oscillation control circuit that controls the drive circuit 4. The oscillation control circuit 3 has a function of appropriately varying or stopping the oscillation frequency (inverter output frequency) via the drive circuit 4.

The threshold changing means 302 belongs to or is attached to the oscillation control circuit 3. The threshold changing unit 302 holds the data of the threshold A in FIG. Reference numeral 5 denotes a discharge lamp, more specifically, a fluorescent lamp. The discharge lamp 5, the ballast inductor 31 in series with the discharge lamp 5, and the preheating capacitor 32 in parallel with the discharge lamp 5 constitute an inverter load. An auxiliary capacitor 33 in series with the inverter load assists in inverter operation. 34 is a detecting capacitor, 41 is a detecting resistor, and 42 is another detecting resistor, which forms a detecting circuit for detecting the tube voltage of the discharge lamp 5. This detection circuit is arranged between the connection point between the discharge lamp 5 and the ballast inductor 31 and the negative terminal of the rectifying / smoothing circuit 2. Reference numeral 50 denotes a dimming input terminal, which is connected to the oscillation control circuit 3. By operating a level switch (not shown) connected to the dimming input terminal 50, the necessity of dimming or the dimming level is indicated.

[0008] A general operation will be briefly described. When the switching element 11 is on, the auxiliary capacitor 33
Charge. When the switching element 12 is on, it discharges it. Repeat it. In the process, high-frequency power is supplied to the discharge lamp 5 and the like. The oscillation control circuit 3 has a dimming input terminal 5
An inverter frequency corresponding to the level of the dimming signal input from 0 is selected. If the inverter frequency is high, the ballast inductor 31 functions as a high impedance, and appropriately limits the light output of the discharge lamp 5.

FIG. 2 is a characteristic diagram similar to FIG. The threshold value A is also described therein, but the value changes according to the light output (%). B shown in FIG. 2 is a tube voltage level at the end of life. The tube voltage B at the end of life also changes according to the light output (%). Since the tube voltage B at the end of life is complicated to measure, it is actually data obtained using the test 40 W fluorescent lamp (5). At the end of life, the tube voltage B increases as the light output (%) decreases. In the present invention, a threshold A curve obtained by shifting the curve of the tube voltage B at the end of life slightly downward is adopted. A threshold A according to the light output (%) is selected from the threshold A curve, and when the actual tube voltage exceeds the threshold, it is determined that the end of life is reached. In FIG. 1, the DC component voltage generated at the detection capacitor 34 is subtracted from the potential at one end of the discharge lamp 5, and the remaining voltages are subtracted from the detection resistors 41.4.
Divide pressure by 2. The result is taken into the judgment means 301 attached to the oscillation control circuit 3 to judge whether or not the threshold value A is exceeded. If it exceeds the threshold value A, it is determined that it is the end of life, and the light output of the discharge lamp 5 is limited to a level that does not overload. A slightly special example of the restriction is forced light-off, and another special example is intermittent lighting. These points are the same as before.

In the present invention, the threshold value A is appropriately selected by the threshold value changing means 302 attached to the oscillation control circuit 3 and transferred to the judgment means 301. The threshold changing unit 302 stores the threshold A curve of FIG. 2 with an appropriate roughness, and selects a threshold A that matches a command signal input from the dimming input terminal 50. By the way,
If the command signal has a light output (%) of 75%, the threshold value A corresponds to the light output (%) of 75%. As a result, an appropriate drop (margin) is secured between the actual tube voltage of the normal discharge lamp 5 and the selected value of the threshold A, and the possibility of erroneous determination is reduced. If the discharge lamp 5 is used for a long time, the tube voltage, which was in the range of the hatched area C in the normal state, rises and gradually approaches the B level. In the process, the threshold value A level is exceeded, the end of life is determined, and the light output limiting function (protection function) is activated. Threshold changing means 30
The data referred to when selecting the threshold value A of 2 is an optical output signal, which is either a dimming command signal or an actual measurement value, and either of them may be used in the present invention. In the latter case, whether or not a new change in the light output limit should be taken in with the result of the end-of-life determination is a temporary problem, but since the determination unit 301 does not repeatedly perform the end-of-life determination, it is a matter of concern. do not have to.

[0011]

The present invention comprises threshold changing means for changing a threshold according to the light output state of the discharge lamp. The characteristics of the threshold changing means are such that when the light output is large, the threshold is low, and when the light output is small, the threshold is high. The main feature is that it is determined to be. According to this, regardless of the dimming level, an excellent discharge lamp lighting device with high end-of-life determination accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a discharge lamp lighting device according to the present invention.

FIG. 2 is an explanatory diagram for explaining the threshold characteristic.

FIG. 3 is a special diagram illustrating a change in a tube voltage of a discharge lamp.

[Explanation of symbols]

 100: Dimming type lighting circuit 1: AC power supply 2: Rectifying smoothing circuit 11 ・ 12: Switching element 21 ・ 22: Flywheel diode 3: Oscillation control circuit 31: Ballast inductor 32: Preheating type capacitor 301: Judging means 302: Threshold value Changing means 33: Auxiliary capacitor 4: Drive circuit 41: Detection resistor 42: Detection resistor 34: Detection capacitor 5: Discharge lamp 50: Dimming input terminal A: Threshold or threshold level B: Tube voltage or tube voltage level at end of life C: tube voltage or tube voltage level at normal time

Claims (1)

[Claims] 1. An abnormality detection type protection circuit comprising a dimming type lighting circuit capable of adjusting a light output of a discharge lamp, and limiting a light output of the discharge lamp when a tube voltage of the discharge lamp exceeds a predetermined threshold. A discharge lamp lighting device comprising: a threshold changing unit that changes the threshold in accordance with a light output state of the discharge lamp. When the light output is large, the threshold is low, and the characteristic of the threshold changing unit is low. A discharge lamp lighting device characterized in that it is sometimes set to be high.