JPH0261996A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To detect the abnormal state of a discharge lamp with a single power source by superimposing the DC voltage with a fixed level to the voltage at the connection point between the discharge lamp and a current limiting element for detection. CONSTITUTION:One end of a discharge lamp la is connected to the positive electrode of a DC power source E, the other end is connected to the negative electrode of the power source E via a current limiting element L2 and a switching element Tr1, the element Tr1, repeats excitation and nonexcitation, thereby an inverter device (L1 and C2) is provided in a discharge lamp la. The DC voltage with a fixed level is superimposed to the voltage Va at the connection point between the discharge lamp la and the element L2, the voltage is detected by a detecting circuit 2, the detected voltage is compared with the voltage with the preset level, and the abnormal state of the discharge lamp la is judged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a discharge lamp lighting device for lighting a discharge lamp at high frequency using an inverter device.

[Conventional technology] FIG. 7 is a circuit diagram of a conventional discharge lamp lighting device.

In this lighting device, the transistor Tr is turned on,
A one-way inverter circuit is used that supplies high-frequency power to the discharge lamp 1a by repeatedly turning it off. A discharge lamp lighting device using an inverter circuit has high circuit efficiency and features that it can be made smaller and lighter.

The circuit configuration will be explained below. Commercial exchange; source V
s is full-wave rectified by a diode bridge DB and smoothed by a capacitor C3 to obtain a DC power source E. A parallel circuit of an inductor L+ and a capacitor C2 is connected to the capacitor C1 between the collector and emitter of the transistor Tr. A diode D is connected in antiparallel between the collector and emitter of the transistor Trl.

The oscillation output of the control circuit 3 is supplied to the base of the transistor Tr. Inductor L and capacitor C2
The power supply side terminals of the filaments L and f2 of the discharge lamp 1a are connected to the parallel circuit through a current-limiting inductor L2. A preheating capacitor C3 is connected in parallel between the non-power supply side terminals of the filaments r+ and rz of the discharge lamp 1a. Filament f2 and inductor L of discharge lamp la
The voltage Va at the connection point 2 is divided by resistors R, , R2 and detected by the control circuit 3. The operating power supply voltage of the control circuit 3 is obtained by charging a capacitor C1 from a capacitor CI via a resistor R4 and regulating the voltage with a Zener diode ZD. In the circuit shown in FIG. 7, the voltage VI)c of the DC power supply E is at most 140
V, and the discharge lamp 1a has a lamp voltage Vi of 40W class.
If a is high, the lamp voltage V is added to the DC voltage VDC.
Voltage V a= V DC+ V Ia when 1a is m tatami
It is not rare for the value to fall below the ground level (0■).

By the way, when the discharge lamp fa is a hot cathode discharge lamp such as a fluorescent lamp, a thermionic emission material called an emitter is coated on the filaments rl and h to facilitate discharge. The state in which the is exhausted is called emitterless (hereinafter referred to as ``emitterless''). Generally, when an emission-free discharge lamp is turned on using an inverter,
Due to half-wave discharge, the l! of the inductor, which is a current-limiting element, In circuits that use 1 sum, L, and C vibrations, vibration disturbances occur,
Abnormal current flows through the switching element, causing heat generation and damage to the element. In this one-way inverter circuit, when the upper filament f is in an emissive state,
Current limiting - transistor Trl due to saturation of inductor L2
An overcurrent flows through the inductor L, causing heat generation in the element, and when the lower filament L is in an emissive state, the saturation of the inductor L causes heat generation in the inductor L. Therefore, in the circuit shown in FIG. 7, the control circuit 3 detects that the discharge lamp 1a has entered the emissionless state, and suppresses or stops the oscillation of the inverter device. This control circuit 3 detects the voltage Va at the connection point between the discharge lamp 1a and the inductor L2. Discharge lamp 1! When a is turned on, a voltage of V a = V DC - V Ia appears at the connection point between the filament r2 and the inductor L2 of the discharge lamp ffa.

FIG. 8 shows the difference in the detected voltage Va when the discharge lamp 1a is in a normal state and when it is in an abnormal state. As can be seen from the figure, since no electrons are emitted from the filament in the emisless state, the discharge lamp 1a has a so-called poor half-wave number electric condition. For example, when the filament rI is in an emissive state, the lamp current is
The flow is caused only by electron emission from the At this time, a lamp voltage V1a is generated due to the lamp current, but
Even if the voltage on the filament r2 side is higher than that on the filament rI side, electron emission from the filament r is poor and no lamp current flows, so the lamp voltage at this time is higher than the lamp voltage Vla during normal lighting. The opposite is true when the filament r2 becomes emisless.

Therefore, in the conventional example, as shown in FIG.
A voltage between the upper limit value ■ and the lower limit value V2 of the detection voltage Va is determined as the normal voltage, and when the voltage Vn is greater than the upper limit value V or smaller than the lower limit value ■2, the discharge lamp 1a is in an abnormal state. It was determined that there was.

[Problem to be solved by the invention M1 However, if the wattage of the discharge lamp la used is, for example, 40
In the case of a high wattage such as W, since the lamp voltage VZ & of the discharge lamp 1a is originally high, the power supply voltage VD
When a decrease in C occurs or when the lamp voltage ■ea varies due to variations in the gas pressure of the discharge lamp ea, the detected voltage V a in FIG.
-V DCV 1 a may become a negative potential. In such a case, it is necessary to set the lower limit value (■) of the setting level mentioned above to a negative value with respect to the ground level of the circuit, and it is necessary to use both positive and negative power supplies for the power supply of the control circuit 3. There was a problem of increased costs. In addition, in order to detect negative voltage, there is a method of rectifying the detection voltage using a diode bridge, but since the ground line of the rectified output is different from the ground line of the main circuit, the control circuit uses the rectified output as a detection signal. When returning to the factory, it was necessary to insulate the photocoupler etc., making it difficult to put it into practical use.

The present invention has been made in view of the above, and an object thereof is to provide a discharge lamp lighting device that can detect abnormality π in a discharge lamp using a single power source. be.

[Means for Solving the Problems] In order to solve the above problems, in the discharge lamp lighting device according to the present invention, as shown in FIG. 1 pole (positive pole), and the other end of the discharge lamp 1a is connected to the second pole (negative pole) of the DC power supply E via a current limiting element (inductor L2) and a switching element (transistor T r , ). , includes an inverter device that supplies high-frequency power to the discharge lamp f'a by repeating conduction and non-conduction of the switching element, and superimposes a constant level of DC voltage on the voltage Va at the connection point between the discharge lamp Ia and the current-limiting element. The present invention is characterized by comprising a means for determining an abnormal state of the discharge lamp 1'a by detecting the detected voltage and comparing the detected voltage with a predetermined level of voltage.

[Operation] In the present invention, since the voltage Va at the connection point between the discharge lamp 1a and the current limiting element is detected by superimposing a constant level of DC voltage, the gas pressure of the discharge lamp La is Fluctuations in lamp voltage ■1a due to variations in temperature and fluctuations in tube wall temperature,
Or, due to a drop in the power supply voltage VDC, etc., the discharge lamp 1a
Even if a situation arises in which the voltage Va at the connection point of the current-limiting element and the current-limiting element does not exist between the various potentials of the first and second voltage sources of the DC power source E, due to the superposition of DC voltages at a certain level, the first voltage Va of the DC power source E The detection voltage can be level-shifted between the first and second various potentials, and therefore the detection voltage levels can be easily compared.

[Embodiment] FIG. 1 is a circuit diagram of an embodiment of the present invention. In this embodiment, a constant current circuit 1 is added to the conventional example shown in FIG. The constant current circuit 1 includes a transistor T r 2 ,
A constant current I = (Vcc-
VBF R/Ry is caused to flow, and the same current is also caused to flow through the resistor R2 via the transistor Tr3 and the diode D2. ■8ε is the transistor T r2. T r
This is the base-emitter voltage drop of 3. Resistance R2
, an extra DC constant voltage Vd of rXR2=(Vcc-VBE)XR2/R is generated. This DC constant voltage Vd
According to the principle of superposition, voltage Va is connected to resistors R1 and R
2, the input voltage VR2 to the detection circuit 2 is level-shifted by the DC constant voltage Vd, as shown in FIG.

Therefore, the input voltage to the detection circuit 2 can be set so as not to become negative. In the conventional example, both positive and negative potentials had to be compared in level, so both positive and negative power supplies were required, but in the present invention, it is only necessary to compare the levels on the positive potential side, so the detection circuit 2 is a single one. Can be powered by power,
The circuit configuration can be simplified.

FIG. 3 is a circuit diagram of another embodiment of the present invention.

In this embodiment, a level shift circuit 4 is added to the conventional example shown in FIG. The level shift circuit 4 includes a secondary winding provided in the current limiting inductor L2, rectifies the high frequency voltage generated in the secondary winding with a diode D3, and regulates and smooths the voltage with a Zener diode ZD2 and a capacitor C3. Thus, a constant DC voltage Vd is generated and applied in series to the voltage dividing resistors R, , R2 of the voltage Va of the lower filament r2. Therefore, the voltage dividing resistors R,,R
The voltage at the connection point 2 is the voltage at the resistor R6 in the conventional example shown in FIG.
The voltage VR2 generated in the voltage VR2 is a voltage obtained by multiplying the DC constant voltage Vd by 1i, and the detection circuit 2 only needs to perform level comparison on the positive potential side, which simplifies the circuit configuration.

In each of the embodiments described above, the emissionless state of the upper filament r can be detected in the same manner as in the conventional example by increasing the upper limit value I of the detection voltage by the amount of the superimposed DC constant voltage Vd. Regarding the detection of the emissionless state of the lower filament r2, it goes without saying that the lower limit value (2) of the detection voltage is increased by the amount of the superimposed DC constant voltage Vd.

In addition, in the operation waveform diagram of FIG. 2, the lower filament f2
The level of the constant DC voltage Vd is set so that the input voltage of the detection circuit 2 becomes a positive potential when the discharge lamp 4a is in an emissionless state. In the case of potential, when the lower filament ``2'' is in the emisless state, the input voltage of the detection circuit 2 becomes a negative potential, so that the emisless state can be detected.

In the above embodiment, a one-way inverter circuit was illustrated, but
As shown in FIG. 4, similar effects can be obtained even when the present invention is applied to a series resonant type inverter circuit. This circuit is
In place of the parallel circuit of the inductor and capacitor C2 in the one-way inverter circuit shown in FIG. 1 or FIG. 3, a circuit in which a diode D4 is connected in anti-parallel to the transistor Tr is connected. A capacitor C8 for the DC component is connected in series with an inductor L2, and a series resonant circuit is formed by the inductor L2 and the capacitor C5. Since capacitor C9 has a larger capacity than capacitor C3, it does not contribute to resonance.

A drive current is supplied to each transistor T r 4 and T r 1 from the control circuit 3 via a driver 5.6,
High frequency power is supplied to the discharge lamp 1a by turning on the transistors T r l and T r 4 alternately.

Further, in the circuit example shown in the embodiment, the upper filament r of the discharge lamp 1a is connected to the positive electrode of the DC power source E,
In the lower filament f2 of the discharge lamp 1a, Va = V D
A voltage of C-V 1m is generated, and this voltage Va becomes a negative potential at power supply voltage ■. . was low and the lamp voltage V1m was high, but as shown in Figure 5, the discharge lamp I
! When one end of a is connected to the negative terminal of the DC power supply E, that is, to the ground line side, the voltage of the upper filament f1 of the discharge lamp Na oscillates in both positive and negative directions as shown in FIG. It is necessary to determine whether the side filament f2 is in an emissive state by comparing the level at a negative potential.5If the present invention is applied, even in such a case, by superimposing a DC voltage, it can be determined that the side filament f2 is in an emissive state by comparing the level at a negative potential. This makes it possible to detect.

[Effects of the Invention] According to the present invention, as described above, one end of the discharge lamp is connected to the first pole of the DC power supply, and the other end of the discharge lamp is connected to the first pole of the DC power supply through the current limiting element and the switching element. In a discharge lamp lighting device that includes an inverter device that is connected to the second pole and supplies high-frequency power to the discharge lamp by repeating conduction and non-conduction of the switching element, the voltage at the connection point between the discharge lamp and the current-limiting element is kept constant. Since the abnormal state of the discharge lamp is determined by superimposing and detecting a DC voltage of a certain level and comparing the detected voltage with a predetermined level of voltage, in the pot 6 which originally used a discharge lamp with a high lamp voltage, Even if there are fluctuations in lamp voltage due to variations in gas pressure or fluctuations in tube wall temperature, or a drop in power supply voltage, abnormal conditions in the discharge lamp can be reliably determined. It has the advantage that there is no need to use both positive and negative power supplies as power sources for circuits and control circuits, and it can be constructed at low cost.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of one embodiment of the present invention, Fig. 2 is an operation waveform diagram of the same as above, Fig. 3 is a circuit diagram of another embodiment of the present invention, and Fig. 4 is a circuit diagram of an embodiment of the present invention.
The figure is a circuit diagram showing another example of the discharge lamp lighting device to which the present invention can be applied, FIG. 5 is a circuit diagram showing still another example of the discharge lamp lighting device to which the present invention can be applied, and FIG. 6 is the same operation as above. FIG. 7 is a circuit diagram of a conventional example, and FIG. 8 is an operational waveform diagram of the same as above. 1 is a constant current circuit, 2 is a detection circuit, 3 is a side control circuit, E is a DC power supply, T r + is a transistor, 1a is a discharge lamp, ■
, 2 is an inductor.

Claims (1)

[Claims] (1) One end of the discharge lamp is connected to the first pole of the DC power supply,
The other end of the discharge lamp is connected to a second pole of a DC power source via a current-limiting element and a switching element, and the switching element repeatedly turns conductive and non-conductive, thereby comprising an inverter device that supplies high-frequency power to the discharge lamp, The voltage at the connection point between the discharge lamp and the current limiting element is detected by superimposing a constant level of DC voltage,
A discharge lamp lighting device comprising means for determining an abnormal state of a discharge lamp by comparing a detected voltage with a predetermined level of voltage.