JPH0372196B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a lighting device for a discharge lamp that can accurately detect the initial state of transition from normal discharge to half-wave discharge and stop discharge. At the end of a discharge lamp's life, there is a large difference between the emission efficiencies of both discharge electrodes of the discharge lamp.
Eventually, one of the electrodes enters the so-called "emiless" state, effectively no longer emitting electrons, and the discharge lamp is operated in a half-wave discharge state. Continuing to light the discharge lamp in this state not only causes a decrease in the lighting efficiency of the discharge lamp, but also when lighting the discharge lamp with the oscillation output of the inverter, the inverter's oscillation circuit may be configured due to an abnormality in the load. Each component generates heat accompanied by power loss or overheats near the electrodes on one side of the lamp, which may eventually damage the oscillation circuit or cause disasters such as fire. Known countermeasure techniques for this include two oscillation transformers.
In the case of lighting multiple lamps, an additional winding is installed on the secondary side of the balancer, and the DC output voltage obtained by rectifying the output is caused by oscillation caused by the half-wave discharge state of the discharge lamp. There is a method of suppressing the oscillation to a minute level or stopping the oscillation by using this analog signal, which changes based on the waveform change of the output of the secondary side of the transformer. (For example, Utsukai 57-
(Refer to Publication No. 18300 and Publication No. 56-56199)
However, this kind of analog output is sensitive to changes in the load that occur when discharging lamps (part or all of them in the case of multiple lamp lighting) and changes in the oscillation frequency that occur as a result. Due to the influence, the circuit becomes complicated to take countermeasures against it, and stable operation cannot be expected. In addition, the half-wave discharge phenomenon of a discharge lamp differs from a phenomenon in which the change from normal to abnormal occurs instantaneously, such as when an incandescent light bulb breaks, and the discharge emission changes as the lamp's lighting time and number of flashes increases. The substance gradually peels off from the electrode, evaporates, and scatters, and the discharge begins to occur.However, until a complete half-wave discharge state is reached, the electrode of the discharge lamp is heated and the temperature rises. A complicated discharge state occurs, such as repeating half-wave discharge and normal discharge. The process from normal discharge to complete half-wave discharge takes a relatively long period of time ranging from several minutes to several days, but over this long period the impedance of the oscillation transformer of the inverter oscillation circuit changes. A pulse-like pulse is generated, and this pulse applies abnormal stress to the oscillation transformer and oscillation transistor. However, in devices that detect changes in the analog signal of the detection winding provided on the secondary side of the oscillation transformer, such as the devices of the aforementioned Utility Model Application No. 57-18300 and 1987-56199, In the early stages of half-wave discharge, the detection signal is too small to detect it. For example, in the device disclosed in Japanese Utility Model Application Publication No. 57-18300, a differential amplifier detects the level difference between the output voltages of a pair of detection windings with the same number of turns and opposite polarities provided on the secondary side of an oscillation transformer. However, in the early stages of half-wave discharge, the level difference is extremely small and cannot be detected. Therefore, if the amplification factor of the differential amplifier is set to a large value, malfunction will occur due to noise that is generated due to switching of the inverter oscillation circuit or discharge phenomenon of the discharge lamp and circulated to the inverter oscillation circuit side. An object of the present invention is to be able to stop oscillation by reliably detecting half-wave discharge at the early stage of occurrence, without being affected by changes in oscillation frequency, load fluctuations during normal lighting, and changes in oscillation power. An object of the present invention is to provide a lighting device for a discharge lamp. In order to achieve the above object, the present invention provides a control means that determines when the discharge waveform of the discharge lamp has become asymmetric between positive and negative and stops the oscillation of the inverter oscillation circuit.
A digital signal of a predetermined voltage value is output when the instantaneous absolute value of each half cycle of the output voltage on both the positive and negative sides of the detection means that detects and outputs a voltage proportional to the voltage between both electrodes of the discharge lamp exceeds a predetermined level. Two logic circuits, a first and a second, output at the oscillation period of the inverter oscillation circuit, and the output digital signals of each logic circuit are individually smoothed using a time constant longer than the oscillation period and converted into pulse signals. two integrating circuits, a first and second integrating circuit; a third logic circuit that detects and outputs a pulse signal from only one of the integrating circuits; A third integrating circuit outputs a constant DC voltage by smoothing the output pulse using a time constant approximately ten times longer than the AC cycle of the AC power source of the inverter oscillation circuit, and the output DC voltage of this third integrating circuit The device is characterized in that it includes a switching element that is turned on to short-circuit the drive current to the inverter oscillation circuit. Next, embodiments of the present invention will be described based on the drawings.
FIG. 1 shows the circuit of this embodiment. In FIG. 1, a portion surrounded by a dashed line is an inverter oscillation circuit 1 equivalent to that used in an existing discharge lamp lighting device. However, the diode 6, the winding 5 of the base current energizing transformer 4, and the winding 3 of the oscillation transformer 2 are additionally inserted or wound based on this embodiment. The winding 5 is for the power supply of the circuit section added in this embodiment. Winding 3 outputs a voltage between its terminals 7 and 9 that is proportional to the voltage between the lamp discharge electrodes. The midpoint terminal 8 of this winding is connected to the common reference potential line of the circuit, and the outputs of terminals 7 and 9 to terminal 8 are connected to resistors 10, 11 and 10a, 11, respectively.
a and logic circuits 13 and 13, respectively.
It is input to the first input terminal of a. The second input terminals of the logic circuits 13 and 13a are connected to the circuit's common reference line via resistors 12 and 12a, respectively (or may be directly connected to the circuit's common reference line), and their input states are always It is kept at “O”. Here, the above logic circuits 13, 13
a and the logic circuits 16 and 27 described below are all
It is an Ex-OR (exclusive OR) circuit, and its truth table is as shown below.

[Table] In this table, A is the state of the first input, B is the state of the second input.
The input state and f indicate the output state. In the above, when the discharge lamp is in the normal lighting state, the voltage between the discharge electrodes of the discharge lamp is symmetrical on both the positive and negative sides, and shows a waveform as shown in Figure 2a, and the voltage of this waveform is the voltage of the winding 3. It is also output between terminals 7 and 9. Therefore, a voltage having a waveform as shown in FIG. 2b is input to the first input terminals of the logic circuits 13 and 13a, and its maximum value is the value necessary to set the input state of the logic circuit to "1". If it is set lower, the input states of both logic circuits will be in the "0", "0" state since the second input terminal is always kept at "0", and the output from the truth table will be Both states are "0". Therefore, the input/output states of the logic circuit 16 driven by these outputs are also all "0", and the transistor 23 switched by the output of this logic circuit 16 is kept in a cut-off state. Therefore, no current flows through the resistor 25, and both inputs of the logic circuit 27, which is connected to the power supply line 24 through the resistors 25 and 26, remain in the state "1", and in this case as well, the truth table is According to this, the output state is "0". Therefore, the thyristor 28 driven by this output is kept in a cut-off state, and the bases of the oscillation transistors 31 and 32 of the inverter are
The bias circuits 29 and 30 are not affected and oscillation continues. Even if the oscillation level increases for some reason, as long as the discharge lamp is in a normal discharge state, the input states of the logic circuits 13 and 13a will both be "1" and "0", and both outputs will be in the state "1". Therefore, the input state of the logic circuit 16 becomes "1", "1", and its output state remains "0", and oscillation does not stop in this case as well. Next, when the discharge lamp enters a half-wave discharge state, the voltage between the discharge electrodes of the discharge lamp and the voltage between the terminals 7 and 9 of the winding 3 have vertically asymmetrical waveforms as shown in FIG. 2c. This tendency increases as the half-wave discharge state progresses. Therefore, the potentials of terminals 7 and 9 of winding 3 with respect to terminal 8 are as shown in FIGS. 3a and b.
The waveform will be like this. Which output of terminals 7 and 9 corresponds to a and b in the figure is:
It depends on which discharge electrode of the discharge lamp the electron emission efficiency has decreased. Here, suppose the output of terminal 7 is a
Assume that the output of terminal 9 corresponds to b. These voltages are applied to the resistors 10 and 1 as described above.
1 or divided by voltages 10a and 11a and input to the first input terminals of logic circuits 13 and 13a, respectively. At this time, the input/output state of the logic circuit 13a to which the waveform shown in FIG. 3b is input does not change, and the output state is still in the "0" state.
On the other hand, in the logic circuit 13, depending on the progress of the half-wave discharge state of the discharge lamp, the voltage across the resistor 11 corresponding to the level indicated by the dotted line in FIG. If the value to be set to "1" has been reached, the first input of the logic circuit 13 will be in the state "1" and the state corresponding to the oscillation frequency only during the period where the dotted line in FIG. 3a intersects with the waveform envelope. Repeat “0”.
Accordingly, in response to this input signal, the output of the logic circuit 13 also repeats the states "1" and "0", and outputs a digital signal as shown in FIG. 3c. This digital signal is smoothed by an integrating circuit 15 having a time constant sufficiently longer than the oscillation period, and is sent to a first input terminal of a logic circuit 16 as a pulse signal as shown in FIG. 3d. Since the second input terminal of this logic circuit 16 (the input terminal related to the output of the logic circuit 13a) is in the state "0", the output terminal is in the state "0" and "0" in response to the pulse shown in FIG. Repeat 1”. This output passes through an integrating circuit 22 whose time constant is set to a long time on the order of 10 times or more than the AC cycle of the oscillator AC power supply 33, becomes a virtually constant DC voltage, and is input to the base of the transistor 23. This input makes the transistor 23 conductive and a voltage drop occurs across its output resistor 25, so that the logic circuit 27 has its input states "1" and "0" and outputs the state "1". This output makes the thyristor 28 conductive, and the base bias circuits 29 and 3 of the oscillation transistors 31 and 32
0 is shorted and oscillation stops. What is important here is that even if the thyristor 28 conducts, its conduction resistance does not become completely zero, and a slight voltage remains at both ends.If the diode 6 were not inserted, the oscillation circuit would be weak. This means that the oscillation state is maintained. The rising voltage of diode 6 suppresses this effect. In the above explanation, the time constant of the integrating circuit 22 is selected to be a large value because the device responds to voltage abnormalities between the discharge electrodes that may occur after the power is turned on until the discharge lamp reaches a steady lighting state. This is to prevent the oscillation from stopping. As described above, according to the discharge lamp lighting device of the present invention, the positive and negative voltages proportional to the voltage between the electrodes of the discharge lamp are converted into digital signals and processed by at least three logic circuits. Ensures the initial state of half-wave discharge phenomenon without being affected by fluctuations in oscillation frequency, fluctuations in load during steady lighting, changes in oscillation power, and noise caused by switching of the inverter oscillation circuit and discharge of the discharge lamp. It is possible to detect this and stop the oscillation. However, even if a digital integrated circuit made up of several logic circuits is used in this type of noisy device, the oscillation period can be determined after the detection signal from the detection winding is waveform-shaped by the first and second logic circuits. Since smoothing is performed using an integrating circuit with a longer time constant than the above, the influence of noise can be excluded. It goes without saying that the Ex-OR (exclusive OR) circuit can also be made from a combination of other logic circuits such as an AND circuit, an OR circuit, and a NOT circuit.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of this embodiment, Figures 2 and 3 are
The figure is a diagram showing voltage waveforms at various parts of the circuit of this example. 1... Inverter oscillation circuit, 2... Oscillation transformer, 3... Winding that outputs power proportional to discharge voltage, 4... Base current energizing transformer, 5...
...Power supply winding, 6...Diode, 7, 8, 9...
...Terminals of winding 3, 10, 11, 12, 10a, 1
1a, 12a, 25, 26...Resistance, 13, 13
a, 16, 27...Logic circuit, 15, 15a, 2
2...Integrator circuit, 24...Power line, 28...
Thyristor, 29, 30...Base bias circuit, 32, 31...Transistor, 33...AC power supply.

Claims (1)

[Claims] 1. An inverter oscillation circuit that lights the discharge lamp using the secondary output of the oscillation transformer, and a detection winding wound around the oscillation transformer to detect positive and negative voltages proportional to the voltage between the electrodes of the discharge lamp. A discharge lamp lighting device comprising: a detection means for outputting an output; and a control means for determining from the output of the detection means that the discharge waveform of the discharge lamp has become asymmetric between positive and negative, and stopping the oscillation of the inverter oscillation circuit, A first and a first circuit, wherein the control means outputs a digital signal of a predetermined voltage value at the oscillation period of the inverter oscillation circuit when the instantaneous absolute value of each half cycle of the positive and negative output voltages of the detection means exceeds a predetermined level. a second two logic circuits, and two first and second integration circuits that individually smooth the output digital signals of each of the logic circuits using time constants longer than the oscillation period and convert them into pulse signals. and a third logic circuit that detects and outputs a pulse signal from only one of the integration circuits, and outputs the output pulse of the third logic circuit to the AC power supply of the inverter oscillation circuit. a third integrating circuit that outputs a constant DC voltage by smoothing it with a time constant that is about ten times longer than the AC cycle; and a third integrating circuit that is turned on by the output DC voltage of the third integrating circuit to drive the inverter oscillation circuit. A lighting device for a discharge lamp, comprising a switching element that short-circuits current.