JPH01265498A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To automatically and surely stop the oscillation of an inverter under any abnormal condition and secure positive protection of a device by discriminating a no-load condition, a discharge life end condition, and a normal load condition. CONSTITUTION:When a power source is turned on, no current flows in a series resonance circuit consisting of an inductance element 9 and a capacitor element 10 under the condition of without load and the rectification output current in a secondary coil 9A of the element 9 is zero. In the case a discharge lamp La comes to the life end period and an excessive heat is produced under the condition of without emission, a series resonance condition is maintained and a current greater than that during a normal lighting flows in the element 6. Three kinds of conditions are detected with a single system by setting a threshold value higher than a rectification output voltage of the coil 9A during a normal lighting condition and a threshold value lower than that at the time of lighting start to a discrimination circuit 11. When an abnormal condition is detected, a protection circuit 12 works to stop the oscillation of an inverter 3 to securely protect the device.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides full-wave rectification of commercial alternating current, and uses this pulsating current or smoothed DC power to power a pair of switching elements and a driving transformer. The present invention relates to a device that drives an inverter consisting of a device, etc., and lights a discharge lamp using the high frequency output of the inverter.

<Prior art> A conventional device for lighting this type of discharge lamp at high frequency uses a full-wave rectifier to full-wave rectify the commercial AC from a commercial AC power source, and then supplies the DC power smoothed by a smoothing capacitor to an inverter. A pair of switching elements is alternately controlled on and off by each output of a pair of drive windings of a drive transformer in this inverter, and a high frequency current flows through the discharge lamp.The generation of this high frequency current causes the discharge lamp to The structure is such that a high voltage is generated by series resonance between an inductance element and a capacitance element at both ends, and the discharge lamp shifts to a lighting state.

<Problems to be Solved by the Invention> By the way, in a discharge lamp lighting device equipped with this type of inverter, if an abnormal state occurs in the load during operation, for example, at the end of the discharge lamp's life, the discharge lamp's A large difference arises between the emission effects of the two discharge electrodes, and eventually one electrode becomes so-called "emissionless" and no longer effectively emits electrons, and the discharge lamp continues half-wave discharge. The picture electrode of the discharge lamp is almost in an emissionless state and virtually no discharge occurs, and the lamp continues to be preheated at the end of its life. Then, the loss in the switching elements of the inverter increases, the temperature of the switching elements increases, and eventually the switching elements are destroyed.

Furthermore, heat generation occurs due to power loss in each component of the inverter, or overheating occurs near the electrodes on one side of the lamp, which may sometimes result in disasters such as fire.

In addition, as other load abnormalities, if the discharge lamp is removed while the device is in operation, or if the power is turned on while the discharge lamp is removed, power is wasted. Not only that, but the secondary side of the drive transformer is in a no-load state, and circuit voltage is directly applied alternately to each switching element, eventually leading to damage to the switching elements.

The present invention has been made in view of the above-mentioned problems. To protect equipment by distinguishing between three types of states (preheating state) and normal load state using a single system circuit configuration, and automatically stopping inverter oscillation in any abnormal state. The object of the present invention is to provide a lighting device for a discharge lamp that can perform the following steps.

<Means for Solving the Problems> In the present invention, technical means for achieving the above-mentioned objects are configured as shown in FIG. That is, commercial AC from a commercial AC power source 1 is full-wave rectified by a full-wave rectifier 2, this pulsating current or DC power smoothed from this pulsating current is supplied to an inverter 3, and the high frequency output of this inverter 3 is used to power the discharge lamp La. In the device for lighting up, the pair of drive windings 4B and 4C of the drive transformer 4 are connected between the positive and negative output terminals of the full-wave rectifier 2.
A pair of switching elements 5 and 6 which are alternately controlled on and off by each output, and both switching elements 5 and 6.
A pair of capacitors connected in series in parallel with 7.8
, a discharge lamp La connected between an intermediate connection point between both capacitors 7.8 and an intermediate connection point between both switching elements 5.6, an inductance element 9 and a capacitance element 10 connected in parallel to the discharge lamp. a secondary winding 9A derived from the inductance element 9 or another inductance element interposed and connected to the series resonant circuit in the form of a current transformer, and this secondary winding 9A. The DC voltage obtained by full-wave rectification of the output of the discharge lamp 1. is compared with at least two threshold voltages. A discriminating circuit 11 that detects a total of three states: two types of abnormal states: a no-load state in which lamp a is not installed and a preheating state in which discharge lamp La is emitted without emission, and a normal load state in normal starting or lighting; It is characterized by comprising a protection circuit 12 which stops the oscillation of the inverter 3 in response to the output of an abnormal state detection signal from the inverter 11.

Function> The operation of turning on the power and transitioning to the lighting state is the same as that of existing devices. In the no-load state, no current flows through the series resonant circuit, so that the rectified output current of the secondary winding 9A of the inductance element 9 is 0 ampere. On the other hand, when the discharge lamp La reaches the end of its life and preheating occurs in the emission reflex state, the series resonance state is maintained, and a much larger current flows through the inductance element 9 than in the steady lighting state. . Therefore, as the first threshold voltage of the discrimination circuit 11, the voltage applied to the secondary winding 9 of the inductance element 9 in the emissionless state is
A voltage value lower than the rectified output voltage of A and higher than the rectified output voltage of the secondary winding 9A in the steady lighting state is set as the second threshold voltage. If a voltage value is set that is lower than the rectified output voltage of the secondary winding 9A and higher than the rectified output voltage of the secondary winding 9A in a no-load state, that is, 0 volts, the rectified output voltage of the secondary winding 9A is higher than the first threshold voltage to indicate an emission-free state, lower than the second threshold voltage to indicate a no-load state, and being within the range between the second threshold voltage and the first threshold voltage to indicate a normal state. starting or normal load condition, respectively. That is, three types of load states can be detected using a single circuit configuration. When a preheating state and a no-load state in the emissionless state are detected, the protection circuit 12 is activated by the abnormal state detection signal output from the discrimination circuit, and, for example, the protection circuit 12 is activated to electrolytic capacitor 1
4 is short-circuited, and the oscillation operation of the inverter 3 is stopped.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

In FIG. 2 showing details of FIG. 1, the same parts as in FIG. 1 are given the same reference numerals.

Two electrolytic capacitors 15.14 are connected in series between the positive and negative output terminals of the full-wave rectifier 2, and the intermediate tap of the primary winding 4A of the drive transformer 4 is connected to the intermediate connection point. , one end of this primary winding 4A is connected to the negative output terminal of the full-wave rectifier 2 via an auxiliary switching element 16 consisting of a transistor and a resistor 17, and the other end is connected to the negative output terminal of the full-wave rectifier 2 via a backflow prevention diode 18. It is connected to the negative output terminal of the rectifier 2, and DC current is intermittently supplied from the intermediate tap of the primary winding 4A of the drive transformer 4 by on/off control of the auxiliary switching 16.
A rectangular wave alternating voltage is generated in the next winding 4A.

The oscillation circuit 19 that controls the on/off of the auxiliary switching element 16 uses a model NE555 manufactured by Signetic Co., Ltd. in this embodiment as an oscillation element 13 which is a main component.
A semiconductor integrated circuit is shown in which the oscillation frequency and duty cycle can be arbitrarily varied simply by changing the time constants of capacitors and resistors. In this embodiment, a power supply terminal Vcc and a ground terminal GND are connected to both ends of a power supply electrolytic capacitor 14, and two timing resistors 20 for determining the oscillation frequency are connected in parallel to the electrolytic capacitor 14 and in series with each other. Both timing resistors 20. at 21 and timing capacitor 22.
A discharge terminal DC is connected to the intermediate connection point of 21, and a resistor 21
A threshold terminal TH and a trigger terminal TR are respectively connected to the intermediate connection point between the timing capacitor 20 and the capacitor 22, and the timing capacitor 22 repeats charging and discharging via both timing resistors 20 and 21, thereby performing a self-optical oscillation operation and outputting Output from terminal OUT.

In addition, in order to perform self-oscillation operation, it is necessary that the reset terminal RS is not set to the "0" level, and in this embodiment, the reset terminal R3 is connected to the power supply capacitor 14.
Connect it to the charging positive side.

Additionally, a bypass capacitor 23 is connected to the control voltage terminal C2, and this bypass capacitor 23 eliminates the influence of power supply noise.

Furthermore, the auxiliary switching element 16 is controlled to be turned on or off by inputting the oscillation output from the output terminal OUT to the base of the auxiliary switching element 16 via the base resistor 24.

A pair of main switching elements 5 and 6 each consisting of a transistor connected in series between the positive and negative side output terminals of the full-wave rectifier 2 are driven through a base resistor 25.26 and an emitter resistor 27.28, respectively. It is connected to a pair of secondary windings 4B and 4C of the transformer 4, and each main switching element 5.6 is alternately controlled on and off by voltages alternately induced in the corresponding secondary windings 4B and 4C. Ru.

A pair of electrolytic capacitors 7.8 are connected in parallel with each other and in series with the amphibonic switching elements 5 and 6, and an intermediate connection point between the amphibian switching elements 5.6 and an intermediate connection point between both capacitors 7.8. A discharge lamp La, an LC series resonant circuit consisting of a capacitance element 10 and an inductance element 9 connected in parallel to the discharge lamp La, and a primary winding 29A of a filament heating transformer 29 are connected between the A pair of secondary windings 2 of this
9B and 29C are connected to the filaments on both sides of the discharge lamp La through diodes 30 and 31, respectively. Further, a triac 32 is connected in parallel to the filament heating transformer 29 for shorting the primary winding 29A and lighting the discharge lamp La.
A timer circuit 33 is connected to the gate terminal of the circuit, which outputs a gate signal after a certain period of time has elapsed since the power was turned on.
A voltage is input to this timer circuit 33 from the auxiliary winding ki4D wound around the driving transformer 4. Furthermore, as a power supply circuit to the oscillation element 13, a primary winding 34 of a high frequency transformer 34 is connected in parallel to the LC series resonant circuit described above.
A is connected to the secondary winding 34 of this high frequency transformer 34.
The output of B is full-wave rectified by diodes 35 and 36 and is supplied to both ends of the power supply electrolytic capacitor 14.

The inductance element 9 has a secondary winding 9 in the form of a current transformer.
A is provided, and after the output of this secondary winding 9A is full-wave rectified by a diode 37.38, it is connected to a resistor 39.40.
The electrolytic capacitor 41 inputs the signal to the discrimination circuit 11 via an integrating circuit whose time constant is set to a time constant sufficiently longer than the oscillation period of the inverter 3. The discrimination circuit 11 has a first operational lamp 42 for detecting a preheating state in an emissionless state, a second operational amplifier 43 for detecting a no-load state, and a non-inverting input terminal of the first operational amplifier 42 to determine an upper limit value for a normal load state. A resistor 44 and a Zener diode 45 for inputting a first threshold voltage that is , and a resistor for inputting a second threshold voltage that is the lower limit value A in a normal load state to the inverting input terminal of the second operational amplifier 43 . 4 and Zener diode 47, both op amps 42.43
A switching transistor 49 whose switching is controlled by the output of the Nant's gate 48 is input, and when the transistor 49 is turned on, the output terminal of the full-wave rectifier 2 is driven from the positive output terminal of the full-wave rectifier 2 via the resistor 51. The photocoupler includes a light emitting diode 50 and a phototransistor 52.

The protection circuit 12 driven by the discrimination circuit 11 includes a thyristor 53 connected in parallel to the electrolytic capacitor 14 for supplying power to the oscillation element 13 via a resistor 54;
Two resistors 55 and 56 are connected in parallel to the electrolytic capacitor 14 via a phototransistor 52.
The gate of the thyristor 53 is connected to the intermediate connection point between the resistors 55 and 56, and when the thyristor 53 is turned on, the electrolytic capacitor 14 for power supply is short-circuited, and the power supply to the oscillation element 13 is stopped. It is designed to stop the oscillation operation.

To explain other circuit elements, a protective element 57 such as a varistor and a capacitor 58 connected to both ends of the AC power supply 1
, a line filter 59, a capacitor 60, and a capacitor 6 connected between the positive and negative output terminals of the full-wave rectifier 2.
1 is for preventing the incorporation of power supply noise or the transmission of noise from the circuit to the power supply 1 in addition to absorbing external pulses. Further, a Zener diode 62 is connected in parallel to the electrolytic capacitor 14, and the oscillation element 1
The power supply voltage to 3 is stabilized by the zener voltage of the zener diode 62. Furthermore, electrolytic capacitors 15 and 7.8 are provided with discharge resistors 63 and 64.65, respectively.
are connected in parallel.

Furthermore, a diode 66.67 is connected in parallel to each of the amphibonic switching elements 5.6, and each main switching element 5, 6 has a corresponding diode 66.67 connected thereto.
67 absorbs pulsed electromagnetic energy from each of the secondary windings 4B, 4C of the drive transformer 4, the inductance element 9, and the like.

Next, the operation of the above embodiment will be explained. When the power is turned on, the commercial AC from the commercial power source 1 is full-wave rectified by the full-wave rectifier 2, and this pulsating current is passed through the resistor 63 and electrolytic capacitor 15.
is supplied to the power supply terminal VCC of the oscillation element 13, and at the same time the oscillation element 13 starts oscillating and the auxiliary switching element 16 is controlled on/off, a small amount of charge is also generated in the electrolytic capacitor 14. Accumulated. Due to the switching operation of the auxiliary switching element 16, a direct current flows intermittently between the intermediate tap and one end of the primary winding 4A of the drive transformer 4, so that a rectangular wave alternating voltage is applied to the primary winding 4A. Occur. Therefore, voltages are alternately induced in the pair of secondary windings 4B and 4C of the drive transformer 4, and the pair of main switching elements 5.6 are connected to the drive circuit (not shown).
It is turned on and off alternately via . At the same time, a voltage is also induced in the auxiliary winding 4D of the drive transformer 4, and a current due to this induced voltage is input to the timer circuit 33, which starts timing operation. When the power is turned on, the triac 32 is in the off state and the filament heating transformer 2
9 is in the connected state and the impedance of the primary winding 29A is relatively high, so LC series resonance does not occur.

At the moment when one of the main switching elements 5 is turned on, the output terminal of the full-wave rectifier 2 is connected to one of the main switching elements 5, one of the filaments of the discharge lamp La, the capacitance element 10, and the discharge lamp La. A current flows to the negative output terminal of the full-wave rectifier 2 via the other filament, the inductance element 9, the primary winding 29A of the filament heating transformer 29, and the other capacitor 8.

Next, when the other main switching element 6 is turned on, one capacitor 7, the primary winding 29A1 of the filament heating transformer 29, the inductance element 9, the other filament of the discharge lamp La, the capacitance element 10,
A current flows to the negative output terminal of the full-wave rectifier 2 through one filament of the discharge lamp La and the other main switching element 6, and a high-frequency current is thus generated by driving the inverter 3.

As the high frequency current flows through the primary winding 29A of the filament energizing transformer 29, the pair of secondary windings 29B
, 29C also begins to flow a current according to its turns ratio, and these currents are half-wave rectified by diodes 30 and 31 and supplied to each filament of the discharge lamp La, and each filament is forcibly preheated sufficiently. . On the other hand, when a high frequency current flows, this high frequency current also flows to the primary winding 34A of the high frequency transformer 34 connected in parallel to the LC series resonant circuit, and the secondary output of this high frequency transformer 34 is connected to the diode 35.36. The full-wave rectified power is applied to both ends of an electrolytic capacitor 14 for supplying power to the oscillation element 13, and power is accumulated in the electrolytic capacitor 14 to permanently supply energy to the load. After the oscillation circuit 19 starts its oscillation operation, most of the power is supplied to the oscillation element 13 from the high frequency transformer 34 via the diodes 35 and 36.

Then, when the timer time of the timer circuit 33, which is set to the time necessary for the discharge lamp La to be sufficiently preheated after the power is turned on, has elapsed, a gate signal is output from the timer circuit 33 and the triac 32 is turned on. The primary winding 29A of the filament heating transformer 2 is shorted. Therefore, LC° series resonance occurs between the inductance element 9 and the capacitance element 10, and this series resonance current generates a high voltage across the discharge lamp La, so that the discharge lamp La immediately shifts to the lighting state. In this lighting state, the primary winding 29A of the filament heating transformer 29 is short-circuited, so no power loss occurs due to the transformer 29.

By the way, when we actually measured the value of the current flowing through the inductance element 9 under various load conditions, we found that, to give an example, it was 0 ampere when there was no load with the discharge lamp La removed, 0.31 ampere when lighting started, and 0 ampere during steady lighting. .5
9 amperes, and 0.75 amperes when the discharge lamp La was in an emissionless preheating state at the end of its life. Therefore, the first threshold voltage at point A, which is the upper limit value of the normal load state that should be input to the non-inverting input terminal of the first operational amplifier 42 of the discrimination circuit 11, is applied to the inductance element 9 by the aforementioned 0.75 ampere. and a voltage value that is intermediate between the voltages that occur at the 0 point when a current of 0.59 amperes flows, for example, the voltage value that occurs at the 0 point when it is assumed that a current of 0.65 amperes flows through the inductance element 9. Set to . Further, the second threshold voltage at point B, which is the lower limit value of the normal load state to be input to the inverting input terminal - of the second operational amplifier 43, is applied to the inductance element 9 by the aforementioned 0.3.
If a current of 1 A flows and if no current flows at all (0 ampere), the voltage value is intermediate between the respective voltages generated at the 0 point, for example, when a current of 0.2 ampere flows through the inductance element 9. Set to the voltage value that occurs at the 0 point when assumed.

With this setting, the voltage at the 0 point is such that the current in the range of 0.31 to 0.59 amperes flows through the inductance element 9 at the time of normal lighting start of the discharge lamp La or under the normal load condition of the normal lighting state. Since the voltage value corresponds to that when the current flows and is within the range of the first threshold voltage and the second threshold voltage, the outputs of both operational amplifiers 42 and 43 are at high level, and the output of the Nant gate 48 is The low level is maintained, the transistor 49 is turned off, and the thyristor 53 of the protection circuit 12 is turned off. Therefore, power is supplied to the oscillation element 13 from the electrolytic capacitor 14.

When a no-load state occurs, the voltage at point 0 becomes lower than the second threshold voltage at point B, which is the lower limit. On the other hand, when no emission occurs, the voltage at point 0 becomes lower than the second threshold voltage at point B, which is the lower limit. It becomes higher than the first threshold voltage at point A, which is the upper limit value. Therefore, when an abnormal load condition occurs, such as a no-load condition or an emissionless preheating condition, the output of either one of the operational amplifiers 42 or 43 becomes a low level, and the output of the Nant gate 48 becomes a high level. The transistor 49 is turned on, the photocoupler is driven, and the phototransistor 52 is turned on. That is, the abnormal state detection signal is outputted from the discrimination circuit 11 to the protection circuit 12, and current flows to the phototransistor 52 via the two resistors 55 and 56, and both resistors 55 and 55
．． The gate voltage of the thyristor 53 increases due to the current flowing through the thyristor 56, and the thyristor 53 turns on and short-circuits the electrolytic capacitor 14. Therefore, the power supply to the oscillation element 13 is stopped and the oscillation operation is stopped, thereby preventing excessive damage to the circuit elements. Prevent damage due to added load.

FIG. 3 shows another embodiment of the present invention, in which a second embodiment of the present invention is shown.
Components that are the same as or equivalent to those in the figures are given the same reference numerals. The only difference from FIG. 2 is the configuration of the discrimination circuit 11A, and this discrimination circuit ffA is provided with an exclusive OR circuit constituted by four Nant gates 68 to 71 as comparison means, and a resistor 72 and The rectified output of the secondary winding 9A of the inductance element 9, which is input through an integrating circuit consisting of an electrolytic capacitor 73, is connected to three resistors. 4,75
The voltage is divided by .degree.76, and the intermediate connection points between the resistors 74, 75, and 76 are inputted to the exclusive OR circuit via input resistors 77 and 78, respectively.

That is, the lower limit value and the upper limit value 2 [! A threshold voltage is set so that the point D is at a high level and the point E is at a low level when the load is in a normal state. Therefore, in the preheating state with no emissions, both points D and E are at high level, and when there is no load, both points are high and point E are at low level, and in any of these abnormal load states, the output signal of the exclusive OR circuit is low. This level is inverted by the transistor 79 and the switching transistor 49 is switched off.

FIG. 4 shows still another embodiment of the present invention, in which the same or equivalent parts as in FIGS. 1 to 3 are given the same reference numerals. The difference from the one in FIG. 3 is that in addition to the inductance element 9 of the series resonant circuit,
An inductance element 8 is connected in series with the capacitance element 10.
0 is inserted and connected, a secondary winding BOA is derived from this inductance element 80 like a current transformer, and the output of this secondary winding BOA is full-wave rectified with a diode 37, 38, and then a resistor 8
8 and a capacitor 89, and threshold voltages at points D and E, which are the input terminals of the exclusive OR circuit in the discrimination circuit 11B, are connected to separate resistors. 81.82 and 84,85
．． 86 and capacitors 83 and 87.

Therefore, the operation is almost the same as that in FIG. 3, and the truth table of the exclusive OR circuit in each load state is also the same. When we actually measured the current value flowing through the inductance element 80 under various load conditions in this embodiment, we found that the current value is 0 ampere when there is no load and 0.14 ampere when the lighting is started.
0.25 ampere flowed during steady lighting, and 0.8 ampere flowed during preheating state with no emissions. Therefore, in the same way as explained in FIG.
The threshold voltage at point and point E is set by each resistor 81, 82, 84°8
By appropriately setting according to 5.86, three states can be distinguished: two types of abnormal load states, a preheating state and a no-load state with no emissions, and a normal starting or normal load state.

FIG. 5 shows a part of the configuration when two lamps are connected in parallel, and in this figure, the same or equivalent parts as in FIGS. 1 to 4 are given the same reference numerals.

In addition, in this embodiment, in addition to the inductance element 9 of the series resonant circuit, the connection point of both lamps La and the inverter 3
An inductance element 90 is inserted and connected between the inductance element 88, a secondary winding 90A is derived from the inductance element 88 like a current transformer, and the output of the secondary winding 90A is connected to the diode 37.
38 is used for full-wave rectification and input to a discriminating circuit (not shown), but by selecting appropriate values for the two types of threshold voltages of the discriminating circuit, the same effect as in each of the above-mentioned embodiments can be obtained. .

It should be noted that the present invention is not limited only to the above-described and illustrated examples, and may include various modifications without departing from the scope of the claims. For example, although the inverter 3 is shown as a passive half-bridge type, a self-excited type can also be used. It can also be applied to full bridge type, stone-carved inverters. In addition, although a tritic is shown as an AC switch, a combination of a diode bridge and a transistor may also be used. Furthermore, although the protection circuit 12 is configured to open the power supply circuit to the oscillation element 13 and stop the oscillation operation of the inverter 3, it may also be configured to short-circuit the reset terminal R3 of the oscillation element 13 to the ground terminal, for example. .

<Effects of the Invention> Since the present invention is configured and operates as described above, it produces the following effects. That is, according to the discharge lamp lighting device of the present invention, by comparing the voltage corresponding to the current flowing through the inductance element, which is a component of the series resonant circuit, with two types of threshold voltages, the no-load state and the discharge lamp state are determined. The inverter's oscillation operation can be accurately stopped in any abnormal state by using a single system circuit configuration to distinguish between three states: an emission-free preheating state at the end of its life, and a normal starting or normal load state. It is possible to prevent the occurrence of fire or destruction of circuit elements.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is an electric circuit diagram of FIG. 1, FIG. 3 is an electric circuit diagram of another embodiment of the present invention, and FIG. Electrical circuit diagram of still another embodiment FIG. 5 is a partial electrical circuit diagram of still another embodiment of the present invention. 1......Commercial AC power supply 2...Full wave rectifier. 3...Inverter 4...Drive transformer 4B, 4C...Secondary winding (drive winding'!a)5.
6... Switching element 7.8...
... Capacitor 9.80.88 ... Inductance element 9A, 80
A, 90A/secondary winding 10... Capacitance element 11, II
A, IIB/Discrimination circuit 12...Protection circuit patent applicant Kyoshin Electric Seisakusho Co., Ltd. Agent
Patent Attorney Nishi 1) Arata

Claims (1)

[Claims] (1) In a device for full-wave rectifying commercial alternating current with a full-wave rectifier, supplying this pulsating current or smoothed DC power to an inverter, and lighting a discharge lamp with the high-frequency output of this inverter, A pair of switching elements are connected between the positive and negative output terminals of the wave rectifier, and are alternately controlled on and off by each output of the pair of drive windings of the drive transformer, and a pair of switching elements are connected in parallel to both the switching elements. Consisting of a pair of capacitors connected in series, a discharge lamp connected between the intermediate connection point of both capacitors and the intermediate connection point of both switching elements, and an inductance element and a capacitance element connected in parallel to the discharge lamp. A series resonant circuit, a secondary winding derived from the inductance element or another inductance element interposed and connected to the series resonant circuit in a current transformer manner, and the output of this secondary winding is full-wave rectified. The DC voltage is compared with at least two types of threshold voltages, and the two types of abnormal conditions are a no-load condition in which the discharge lamp is not installed and a preheating condition in which the discharge lamp does not emit emissions, and a normal load condition in which the discharge lamp is started or lit. A lighting device for a discharge lamp, comprising: a discrimination circuit that detects three states; and a protection circuit that stops oscillation of the inverter by outputting an abnormal state detection signal from the discrimination circuit.