JP2001244093A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device that can surely detect an inverter circuit operating in a lead phase without complicating the circuit configuration. SOLUTION: The inverter circuit 2 inverts the DC voltage from a rectifier/ filter circuit 1 into a high frequency wave to supply to the load circuit 3. The load circuit 3 possesses a series circuit of an inductor L1 and a capacitor C1 connected between the output terminals of the inverter circuit 2 through a DC blocking capacitor C2 and a discharge lamp La connected in parallel with the capacitor C1. A first and a second impedance detector elements 4 and 5 detect respectively impedance changes of the condenser C1 and the inductor L1 as voltage changes and the current phase detector circuit 6 detects the phase of the lamp current based on the output of the first and the second impedance detector elements 4 and 5 to find out if the inverter circuit 2 is operating in the lead phase or not.

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 device.

[0002]

2. Description of the Related Art Conventionally, as shown in FIGS. 18 and 19, a rectifying and smoothing circuit 1 for rectifying and smoothing an AC voltage of a commercial power supply AC, and a load circuit for converting a DC voltage of the rectifying and smoothing circuit 1 to a high frequency. 3 is provided with an inverter circuit 2 for supplying the discharge lamp 3 to the discharge lamp 3 (see, for example, Japanese Patent Application Laid-Open No.
1997797).

The rectifying and smoothing circuit 1 includes a rectifier DB composed of a diode bridge for rectifying an AC voltage of a commercial power supply AC input through a filter circuit F, an inductor L2 connected between the DC output terminals of the rectifier DB, and a switching device. It comprises a series circuit of an element Q3, a diode D1 having an anode connected to a connection point between the inductor L2 and the switching element Q3, and a smoothing capacitor C3 connected between both ends of the switching element Q3 via the diode D1. Here, inductor L2, switching element Q
3, a diode C1 and a smoothing capacitor C3 constitute a boost chopper, and the switching element Q3 is controlled on / off by a chopper control circuit 1a. The filter circuit F includes a line filter LF1 and a capacitor C8.
And provided to reduce noise returning to the power supply line.

[0004] The inverter circuit 2 has a half-bridge type circuit configuration, and is composed of a series circuit of a pair of switching elements Q1 and Q2 connected between both ends of a smoothing capacitor C3. The switching elements Q1 and Q2 are inverter control circuits. It is turned on / off alternately by 2a. The switching elements Q1 and Q2 are capable of flowing a current in both directions when turned on, and can flow a current in the opposite direction when turned off. For example, a diode is connected in anti-parallel to a collector-emitter of a transistor. A MOSFET that is connected to form a current path when the diode is off or a MOSFET can be used. In the case of a MOSFET, a body diode formed from the structure serves as a current path at the time of off.

The load circuit 3 includes an inductor L1 connected between the output terminals X and Y of the inverter circuit 2 via a DC cut capacitor C2 and an LC of the capacitor C1.
It comprises a series resonance circuit and a discharge lamp La such as a fluorescent lamp connected in parallel to the capacitor C1. The capacitor C1 is connected to the non-power supply side of both filaments F1 and F2 of the discharge lamp La.

FIG. 20 is a diagram showing the relationship between the oscillation frequency f of the inverter circuit 2 and the voltage VC1 across the capacitor C1, and FIG. 20A shows the resonance curve when the discharge lamp La is not lit. FIG. 20B shows a resonance curve when the discharge lamp La is lit.

Next, the operation of this circuit will be described. When the commercial power supply AC is turned on and the rectifying and smoothing circuit 1 starts operating, the smoothing capacitor C3 is charged to a constant voltage obtained by boosting the power supply voltage of the commercial power supply AC. On the other hand, in the inverter circuit 2, a current flows to the capacitor C1 via both the filaments F1 and F2 of the discharge lamp La in accordance with ON / OFF of the switching elements Q1 and Q2, and the filaments F1 and F2
2 and a resonance voltage is applied to both ends of the discharge lamp La.

When the discharge lamp La is preheated, the inverter control circuit 2a controls the oscillation frequency f of the inverter circuit 2 to a frequency sufficiently higher than the resonance frequency f01 of the series resonance circuit composed of the capacitor C1 and the inductor L1,
The voltage VC1 across the capacitor C1 is lowered, and the discharge lamp L
A preheating current is supplied to the filaments F1 and F2. When the discharge lamp La is started and lit, the inverter control circuit 2a lowers the oscillation frequency f of the inverter circuit 2 to f2 and approaches the resonance frequency f01, and increases the voltage VC1 across the capacitor C1 to release the discharge. After the filaments F1 and F2 of the electric lamp La are sufficiently preheated, they are turned on.

When the discharge lamp La is turned on, a resonance circuit is constituted by a parallel circuit composed of the capacitor C1 and the discharge lamp La and an inductor L1 connected in series with the parallel circuit, depending on the lamp impedance of the discharge lamp La. The resonance frequency changes from f01 to f03 (f03 <f0
1), the resonance curve of the resonance output VC1 changes from the resonance curve shown in FIG. 20A to the resonance curve shown in FIG. At this time, the inverter control circuit 2a outputs the resonance output VC
The oscillation frequency f of the inverter circuit 2 is controlled to, for example, f1 (f03 <f1 <f01) such that 1 becomes a predetermined voltage value, and the lighting state of the discharge lamp La is maintained.

By the way, at the end of the life of the discharge lamp La, thermionic emission material (emitter) applied to the filament scatters and evaporates, so that thermionic emission from the filament stops being performed, and the discharge lamp La is only in one direction. An abnormal discharge (half-wave discharge) occurs so that no current flows. Such a state is called an Emiless state, and when the Emiless state occurs, the resonance system collapses, and the lamp voltage of the discharge lamp La abnormally increases as compared with the normal lighting. As the Emiless state progresses, the impedance of the discharge lamp La changes in the increasing direction, so that the resonance curve of the resonance circuit gradually approaches the resonance curve at the time of no load (when the discharge lamp goes out), and finally, both filaments The emitters applied to F1 and F2 are completely consumed and cannot be discharged, and have a resonance curve when there is no load (when the discharge lamp goes out).

In order to detect such an abnormal rise of the lamp voltage in the Emiless state, as shown in FIG. 21, a resonance voltage VC1 generated between both ends of the capacitor C1 is divided by resistors R1 and R2. When the voltage exceeds a predetermined threshold voltage V10 and the divided voltage Va is equal to the threshold voltage V
There has also been provided a discharge lamp lighting device that performs a protective operation such as determining that the output voltage of the inverter circuit 2 is stopped when the reference voltage corresponding to the reference voltage exceeds 10 is detected.
The threshold voltage V10 for detecting the Emiless state
Is higher than the output voltage when the discharge lamp La is normally lit (that is, when the oscillation frequency f of the inverter circuit 2 is f1) and when the discharge lamp La is started (that is, when the oscillation frequency f of the inverter circuit 2 is f2). ) Is set to a value lower than the output voltage in (1). In order to prevent erroneous detection of the end-of-life state at the time of preheating and starting the discharge lamp La, the detection operation is generally prohibited during this period.

Conventionally, as shown in FIG.
8, the capacitor C1a is connected between the power supply side terminals of both filaments F1 and F2 of the discharge lamp La.
And a discharge lamp lighting device in which a capacitor C1b is connected between the non-power-supply-side terminals of both filaments F1 and F2. In this circuit, a capacitor for resonance is connected to a capacitor C1a connected to the power supply side of the discharge lamp La;
Since the preheating current of the filaments F1 and F2 is obtained by the capacitor C1b connected to the non-power supply side of the discharge lamp La and the capacitor C1b connected to the non-power supply side, the capacitor C1b is connected when the discharge lamp La is turned on. By reducing the current flowing through both filaments F1 and F2, the power loss due to the filament current can be reduced, the life of the discharge lamp La can be prolonged, and the capacitance of the resonance capacitor can be increased. Accordingly, the starting voltage of the discharge lamp La can be increased. In this circuit, FIG.
By using the same configuration as that of the circuit described above, it is possible to detect an abnormal rise in the lamp voltage at the time of Emiless.

[0013]

Among the above-described discharge lamp lighting devices, in the former discharge lamp lighting device, when the discharge lamp La is lit at the frequency f1, the discharge gas sealed in the bulb is discharged. When an abnormality such as leakage (slow leak) occurs and the discharge lamp La goes out, the resonance curve of the resonance output changes from the resonance curve when the discharge lamp is turned on (b in FIG. 20) to the resonance curve when no load is applied (FIG. 20). The resonance voltage VC1 rises to the voltage C rapidly. Here, when the voltage C is lower than the above-described threshold voltage V10, the inverter circuit 2 does not shift to the protection operation and continues the oscillating operation, and the frequency f1 becomes equal to the resonance frequency f01 of the resonance circuit at no load. If the frequency is set to a lower frequency, the switching operation is performed in a so-called advanced phase region, so that the switching elements Q1 and Q2 of the inverter circuit 2 are simultaneously turned on, a through current flows, and excessive stress is applied to the switching elements Q1 and Q2. Was added.

Further, in the latter discharge lamp lighting device, even when the discharge lamp La is disconnected or the filaments F1 and F2 are disconnected, the capacitor C1a and the inductor L1 keep the L.
Since the C series resonance circuit is formed, a resonance voltage is generated between both ends of the capacitor C1a, and an excessive voltage may be generated at the connection terminal of the discharge lamp La. At this time, the resonance output VC
The resonance curve 1 'is the resonance curve when the discharge lamp is turned on (FIG. 2).
3) to a resonance curve (c in FIG. 23) when there is no load (when the discharge lamp La is not mounted or when the filament is broken). Here, the resonance frequency f02 of the LC series resonance circuit formed by the capacitor C1a and the inductor L1 is higher than the resonance frequency f01 of the LC series resonance circuit formed by the parallel circuit of the capacitors C1a and C1b and the inductor L1. Therefore, when the inverter circuit 2 oscillates when the discharge lamp La is not attached or when the filament is broken, the oscillation frequency f1 of the inverter circuit 2 becomes lower than the resonance frequency f02, and the switching operation is performed in a so-called advanced phase region.
The switching elements Q1 and Q2 of the inverter circuit 2 are simultaneously turned on and a through current flows, and the switching elements Q1 and Q2
There is a problem that excessive stress is applied to the device. In order to solve such a problem, the filaments F1, F2
A separate detection circuit is required to detect the presence or absence of a disconnection and a disconnection, resulting in a problem that the number of components increases and the cost increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to provide a system which can reliably detect the operation of the inverter circuit in the phase advance region without complicating the circuit configuration. An object of the present invention is to provide a lighting device.

[0016]

According to a first aspect of the present invention, there is provided an inverter circuit for converting an output of a DC power supply to a high frequency by switching with a switching element, a resonance inductor, and a resonance circuit. A resonance circuit consisting of a series circuit of capacitors and connected between the output terminals of the inverter circuit, a discharge lamp connected in parallel with the resonance capacitor, an inverter control circuit that controls the output of the inverter circuit, and an impedance change of the resonance capacitor , A second impedance detecting means for detecting a change in impedance of the resonance inductor, and a current phase for detecting the phase of the lamp current from the detection results of the first and second impedance detecting means. And an oscillation frequency of the resonance frequency. The impedance of the resonance inductor becomes dominant in the lag region higher than the number, and the impedance of the resonance capacitor and the discharge lamp becomes dominant in the lag region where the oscillation frequency is lower than the resonance frequency. Then, it can be easily detected from the detection results of the first and second impedance detection means whether or not the inverter circuit is operating in the phase advance region. In the current phase detection circuit, the phase of the lamp current is detected by detecting the impedance of the resonance inductor and the resonance capacitor, so that the operation in the early phase region is ensured without complicating the circuit configuration. Can be detected.

According to a second aspect of the present invention, in the first aspect of the present invention, the resonance capacitor includes a first capacitor connected between output terminals of an inverter circuit via a resonance inductor.
And a second capacitor connected to the non-power supply side of the discharge lamp connected in parallel to the first capacitor, and whether or not the discharge lamp is mounted, or a filament Since the configuration of the resonance circuit changes depending on whether or not the wire is broken, the resonance frequency changes. Therefore, it is necessary to detect an abnormality such as disconnection of the discharge lamp or breakage of the filament from the detection results of the first and second impedance detecting means. As compared with a case where a circuit for detecting the presence or absence of a filament is separately provided, the number of components is reduced, and cost can be reduced.

According to a third aspect of the present invention, in the first or second aspect of the present invention, when the discharge lamp is turned on, the inverter circuit has a resonance frequency higher than the resonance frequency of the resonance circuit formed by the discharge lamp, the resonance inductor and the resonance capacitor. When the oscillation frequency of the inverter becomes low, the inverter control circuit shifts the operation of the inverter circuit from a normal oscillation operation to a protection operation for lowering the output. When the operation in the phase advance region is detected, the operation of the inverter circuit is shifted to the protection operation, so that stress on circuit elements such as switching elements can be prevented.

According to a fourth aspect of the present invention, when the oscillation frequency of the inverter circuit becomes lower than a predetermined frequency upper limit value higher than the resonance frequency of the resonance circuit in the first or second aspect of the invention, the inverter control circuit becomes the inverter circuit. The operation is shifted from a normal oscillation operation to a protection operation for lowering the output.In addition to the case where the inverter circuit is operating in the phase advance region, the output of the inverter circuit becomes higher than a predetermined voltage. Also in this case, since the inverter control circuit shifts the operation of the inverter circuit to the protection operation, it is possible to prevent the stress on the circuit elements such as the switching elements.

According to a fifth aspect of the present invention, in the third or fourth aspect of the present invention, the protection operation includes an operation for stopping the switching operation of the inverter circuit, or a period for performing the switching operation and a period for stopping the switching operation. The operation is either alternately provided or an operation of increasing the oscillation frequency of the switching element to weaken the resonance of the resonance circuit, and has the same effect as the invention of claim 3 or 4.

According to a sixth aspect of the present invention, in the fourth aspect of the invention, the frequency upper limit value is a frequency at which the output of the inverter circuit at that frequency is higher than a voltage at which the discharge lamp can be started. The inverter control circuit protects the operation of the inverter circuit when the output of the inverter circuit is higher than the starting voltage of the discharge lamp, in addition to the case where the inverter circuit is operating in the phase advance region. , It is possible to prevent stress on circuit elements such as switching elements.

According to a seventh aspect of the present invention, in the fourth aspect of the present invention, when the oscillation frequency of the inverter circuit becomes higher than a predetermined lower frequency limit lower than the resonance frequency of the resonance circuit, the inverter control circuit operates. The operation is shifted to the protection operation, and the same operation as the invention of claim 4 is achieved. In addition, a frequency upper limit value and a frequency lower limit value are provided in a frequency range in which the inverter control circuit performs the protection operation. Therefore, frequency control can be performed with high accuracy.

According to an eighth aspect of the present invention, in the seventh aspect of the present invention, the lower limit value of the frequency is a frequency at which the output of the inverter circuit at the frequency is the lowest, and When operating at a frequency lower than the lower limit, the output of the inverter circuit is sufficiently low and there is no need to perform a protection operation. Therefore, the inverter circuit operates in a frequency range higher than the lower frequency limit and lower than the upper frequency limit. By doing so, stress applied to circuit components of the inverter circuit can be reduced.

According to a ninth aspect of the present invention, in the first to eighth aspects, the current phase detecting means compares the detected output of the first impedance detecting means with the detected output of the second impedance detecting means. And comparing the level of the detection output of the first and second impedance detection means with a simple circuit configuration by detecting the phase of the lamp current from the comparison result of the comparison unit. An operation in the fast-phase region can be detected.

According to a tenth aspect of the present invention, in the first to eighth aspects, the current phase detecting means detects a difference between a detection output of the first impedance detecting means and a detection output of the second impedance detecting means. It is characterized by detecting the phase of the lamp current from the output of the difference detection unit, and the output of the difference detection unit is inverted before and after the resonance frequency. Can be detected, and the output of the difference detection unit decreases as the oscillation frequency of the inverter circuit approaches the resonance frequency. Therefore, the oscillation frequency of the inverter circuit approaches the resonance frequency, and the output of the inverter circuit becomes abnormal. A rising frequency range can also be detected.

In the eleventh aspect, the first to tenth aspects are provided.
In the invention described above, the inverter control circuit controls the operation of the inverter circuit irrespective of the output of the current phase detection means from the time when the power is turned on until the inverter circuit starts the oscillating operation. Thus, it is possible to prevent the influence of erroneous detection or non-operation of the current phase detection circuit from being eliminated.

In the twelfth aspect of the present invention, the first to eleventh aspects
In the invention described in the above, an end-of-life detection circuit for detecting the end-of-life state of the discharge lamp from any of the detection output of the first impedance detection means or the detection output of the second impedance detection means is provided. When the end-of-life detection circuit detects the end of life of the discharge lamp, the inverter control circuit shifts the operation of the inverter circuit from a normal oscillating operation to a protection operation that lowers the output. Since the voltage rises abnormally, the end-of-life state of the discharge lamp can be detected from the detection output of the first or second impedance detecting means, and
Alternatively, since the detection output of the second impedance detecting means is also used as the detection signal of the end-of-life state, the number of components can be reduced as compared with a case where a circuit for detecting the end-of-life state is separately provided.

According to a thirteenth aspect of the present invention, in the twelfth aspect, the inverter control circuit causes the protection operation to be performed with priority given to the detection result of the current phase detection means over the detection result of the end-of-life detection circuit. As a feature, the protection operation at the time of load abnormality can be reliably performed, and the reliability of the detection circuit is improved.

[0029]

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

(Embodiment 1) FIG. 1 is a schematic circuit diagram of a discharge lamp lighting device according to the present embodiment. Since the basic configuration of this circuit is the same as that of the circuit shown in FIG. 18 described above, the same components are denoted by the same reference numerals and description thereof will be omitted.

In this embodiment, in the circuit of FIG. 18 described above, a first impedance detecting section (first impedance detecting means) 4 for detecting a change in impedance of the resonance capacitor C1 as a voltage change, and a resonance inductor L1 A second impedance detecting section (second impedance detecting means) 5 for detecting a change in impedance of the lamp as a voltage change, and a phase of a lamp current based on detection results of the first and second impedance detecting sections 4 and 5. And a current phase detection circuit 6 for performing the operation.

The first impedance detecting section 4 comprises a series circuit of resistors R1 and R2 connected between the high-potential terminal of the capacitor C1 and the ground of the circuit, and detects the voltage VC1 across the capacitor C1 by the resistor R1. , R2 and outputs the voltage Va to the current phase detection circuit 6.

The second impedance detector 5 comprises a series circuit of resistors R3 and R4 connected between one end of a secondary winding n1 magnetically coupled to the inductor L1 and the ground of the circuit. The other end of the winding n1 is connected to the ground of the circuit, and the second impedance detecting unit 5 supplies a voltage Vb obtained by dividing the voltage between both ends of the secondary winding n1 by the resistors R3 and R4 to the current phase detecting circuit 6. Output.

FIG. 2 is a specific circuit diagram of the current phase detecting circuit 6. The voltages Va 'and Vb' are obtained by rectifying and smoothing the voltages Va and Vb input from the first and second impedance detecting sections 4 and 5, respectively. Rectifying / smoothing units 6a and 6b for generating
The rectifying / smoothing units 6a and 6b are configured with a comparator CP1 for comparing the levels of the output voltages Va 'and Vb'.

In the rectifying / smoothing unit 6a, the voltage Va input from the first impedance detecting unit 4 is divided by the voltage dividing resistors R5 and R5.
6, the DC component is cut by the capacitor C4, and then rectified by the diodes D2 and D3.
5, and the smoothed voltage Va 'of the capacitor C5 is input to one input terminal of the comparator CP1. The capacitor C5 has a resistor R7 constituting a discharge path.
And the Zener diode ZD1 are connected in parallel, and the Zener diode ZD1 prevents overvoltage from being input to the comparator CP1.

The rectifying / smoothing unit 6b has a circuit configuration similar to that of the rectifying / smoothing unit 6a.
8, R9, the DC component is cut by the capacitor C6, rectified by the diodes D4 and D5, smoothed by the capacitor C7, and smoothed by the capacitor C7.
b ′ is input to the other input terminal of the comparator CP1. Note that a resistor R10 forming a discharge path and a Zener diode ZD2 are connected in parallel to the capacitor C7, and the Zener diode ZD2 prevents an overvoltage from being input to the comparator CP1.

The comparator CP1 includes a rectifying / smoothing unit 6a,
6b comparing the output voltages Va ′ and Vb ′.
The output signal Vc of the comparator CP1 is input to the inverter control circuit 2a.

The method by which the current phase detection circuit 6 detects the phase of the lamp current will be briefly described below. FIG. 3 shows the detection voltage V of the first and second impedance detection units 4 and 5 when the discharge lamp La is not lit (when no load is applied).
3 shows the relationship between a and Vb and the oscillation frequency f of the inverter circuit 2. Here, in this circuit, at the frequency at which the impedance of the capacitor C1 and the impedance of the inductor L1 become equal, that is, at the resonance frequency f01 of the resonance circuit at the time of no load, the detection voltages Va,
The resistance values of the resistors R1 to R4 are set such that Vb is equal to each other. Here, in a frequency region (slow region) in which the oscillation frequency f is higher than the resonance frequency f01, the impedance of the inductor L1 becomes more dominant than the impedance of the capacitor C1, so that the voltage Vb is higher than the voltage Vb.
a (Va <Vb). Conversely, in a frequency region where the oscillation frequency f is lower than the resonance frequency f01 (phase advance region), the impedance of the capacitor C1
, The voltage Va becomes higher than the voltage Vb (Va> Vb).

FIG. 4 shows the relationship between the detected voltages Va and Vb and the oscillation frequency f of the inverter circuit 2 when the discharge lamp is turned on. When the discharge lamp La is turned on, the capacitor C
1 and the parallel circuit of the discharge lamp La and the inductor L1
Since a series resonance circuit is formed, the resonance frequency changes from f01 to f03 depending on the impedance of the discharge lamp La. Even at the resonance frequency f03, the impedance of the inductor L1 is equal to the impedance of the parallel circuit of the capacitor C1 and the discharge lamp La. The resonance frequency f
03, the detection voltages Va and Vb become substantially equal. Then, in the late phase region, the impedance of the inductor L1 becomes more dominant than the impedance of the parallel circuit of the capacitor C1 and the discharge lamp La, so that the voltage Vb is higher than the voltage Va (Va <Vb). On the other hand, in the phase advance region, the impedance of the parallel circuit of the capacitor C1 and the discharge lamp La becomes more dominant than the impedance of the inductor L1, so that the voltage Va is higher than the voltage Vb (Va>).
Vb).

The current phase detection circuit 6 detects the operation of the inverter circuit 2 in the phase advance region by utilizing the magnitude relation between the detection voltages Va and Vb as described above. Here, when the inverter circuit 2 performs the switching operation in the late phase region,
The voltage Va ′ becomes lower than the voltage Vb ′ (Va ′ <V
b ′), and when the inverter circuit 2 performs the switching operation in the phase advance region, the resistance values of the resistors R5 to R10 are set so that the voltage Va ′ becomes higher than the voltage Vb ′ (Va ′> Vb ′). I have. Therefore, when the inverter circuit 2 performs the switching operation in the phase advance region, the comparator C
The voltage level of the output signal Vc of P1 becomes H level, and when the inverter circuit 2 performs the switching operation in the delay region, the voltage level of the output signal Vc of the comparator CP1 becomes L level.

The output signal Vc of the comparator CP1 is input to the inverter control circuit 2a, and if the voltage level of the output signal Vc is L level,
“a” determines that the inverter circuit 2 is operating in the in-phase or late-phase region, and performs a normal switching operation.
On the other hand, when the voltage level of the output signal Vc becomes H level,
The inverter control circuit 2a determines that the inverter circuit 2 is performing a switching operation in the early phase region, and shifts to a protection operation in which the output of the inverter circuit 2 is reduced. Can be prevented. The protection operation by the inverter control circuit 2a includes a state in which the switching operation by the switching elements Q1 and Q2 is stopped, and a state in which a period during which the switching operation is performed and a period during which the switching operation is stopped are alternately provided (that is, the switching operation is intermittent). The operation of the inverter circuit 2 is shifted to one of the states in which the oscillation frequency of the switching elements Q1 and Q2 is increased and the resonance of the resonance circuit is weakened.

When the current phase detection circuit 6 detects the switching operation in the early phase region as described above, the inverter control circuit 2a shifts the operation of the inverter circuit 2 to the protection operation, and the discharge lamp La is turned on. In the absence state (at the time of no load), the frequency range lower than the resonance frequency f01 at the time of no load (the range WA in FIG. 3) corresponds to the inverter circuit 2.
In the state where the discharge lamp La is lit, the frequency range lower than the resonance frequency f03 when the discharge lamp is lit (the range WB in FIG. 4) corresponds to the inverter circuit 2. This is the frequency range in which the switching operation is shifted to the protection operation.

As described above, the first and second impedance detectors 4 and 5 detect the impedance change of the capacitor C1 and the inductor L1 as a voltage change, and the current phase detector 6 detects the first and second impedance detectors. 4,
5, the switching operation in the phase advance region is detected by comparing the levels of the output voltages va and Vb. Since the detection circuit 6 is configured, the switching operation in the fast-phase region can be reliably detected without complicating the circuit configuration.

In this embodiment, the half-bridge type inverter circuit 2 has been described as an example. However, the present invention is not intended to limit the inverter circuit 2 to the above-described configuration. It goes without saying that a format can be used. Further, the circuit configuration of the rectifying / smoothing circuit 1 and the load circuit 3 as the DC power supply is not intended to be limited to the above-described configuration. For example, a plurality of load circuits 3 may be connected in parallel to the output terminal of the inverter circuit 2. The load circuit 3 may have a circuit configuration in which a plurality of discharge lamps La are connected in series or in parallel.

(Embodiment 2) FIG. 5 is a circuit diagram of a discharge lamp lighting device according to this embodiment. Since the configuration other than the load circuit 3 is the same as that of the discharge lamp lighting device of the first embodiment, the same components are denoted by the same reference numerals and description thereof will be omitted.

In this embodiment, a load circuit 3 having a circuit configuration similar to that of the above-described circuit of FIG. 22 is used, and the first impedance detection unit 4 is connected to the power supply side of the discharge lamp La. It comprises a series circuit of resistors R1 and R2 connected between the high-potential terminal of the capacitor C1a and the ground of the circuit, and a voltage VC across the capacitor C1a.
A voltage Va obtained by dividing 1 ′ by the resistors R1 and R2 is output to the current phase detection circuit 6. Further, the second impedance detecting unit 5 includes a resistor R connected between one end of the secondary winding n1 magnetically coupled to the inductor L1 and the ground of the circuit.
3 and R4, the other end of the secondary winding n1 is connected to the ground of the circuit, and the second impedance detector 5 separates the voltage across the secondary winding n1 by the resistors R3 and R4. The compressed voltage Vb is output to the current phase detection circuit 6.

Here, as in the first embodiment, the resistance R is set so that the detection voltages Va and Vb are equal at the resonance frequencies f01 and f03 when no load is applied and when the discharge lamp is lit.
Since the resistance values of 1 to R4 are set, the voltage Vb is higher than the voltage Va in the phase advance region (Va <Vb),
In the late phase region, the voltage Va is higher than the voltage Vb (Va> Vb). Therefore, by comparing the levels of the detection voltages Va and Vb of the first and second impedance detection units 4 and 5 with the current phase detection circuit 6, the switching operation of the inverter circuit 2 in the early phase region can be detected. When the current phase detection circuit 6 detects the switching operation in the phase advance region, the inverter control circuit 2
Since a switches the switching operation of the inverter circuit 2 to the protection operation, the stress applied to the switching element can be reduced.

Further, in this circuit, the discharge lamp La is removed or the filaments F1 and F2 are disconnected while the discharge lamp La is lit at the oscillation frequency f1 at which the switching operation of the inverter circuit 2 is in the delay region. When an abnormality occurs, an LC series resonance circuit is formed by the inductor L1 and the capacitor C1a, and the resonance frequency f02 of the resonance circuit is
Is the resonant circuit (ie, inductor L
23, which is higher than the resonance frequency f01 of the resonance circuit (a resonance circuit composed of C1a and capacitors C1a and C1b) (FIG. 23).
), The switching operation of the inverter circuit 2 is an operation in the phase advance region.

At this time, the detection output Vb of the second impedance detector 5 is higher than the detection output Va of the first impedance detector 4 (Va <Vb). The switching operation in the fast-phase region can be detected from the detection outputs Va and Vb of the first and second impedance detection units 4 and 5. When the current phase detection circuit 6 detects the switching operation in the phase advance region, the inverter control circuit 2a shifts the switching operation of the inverter circuit 2 to the protection operation, thereby reducing the stress applied to circuit elements such as switching elements. can do. In this circuit, there is no need to separately provide a detection circuit for detecting the presence / absence of a filament or disconnection, so that the number of components can be reduced and the cost can be reduced.

(Embodiment 3) FIG. 6 shows a circuit diagram of a discharge lamp lighting device according to the present embodiment in which a part thereof can be omitted. In FIG. 6, the main circuit is omitted. Since the configuration other than the current phase detection circuit 6 is the same as that of the first or second embodiment, the same components are denoted by the same reference numerals and description thereof will be omitted.

In the discharge lamp lighting device of the first or second embodiment, the frequency range lower than the resonance frequency is set to the frequency range in which the switching operation of the inverter circuit 2 is shifted to the protection operation. A frequency range (f <fα) lower than the frequency upper limit value fα is set as a frequency range in which the switching operation of the inverter circuit 2 shifts to the protection operation. Here, the frequency fα is a frequency higher than the resonance frequency by a predetermined frequency Δfα, the resonance output Vα at the frequency fα is equal to or higher than the voltage V11 at which the discharge lamp La can be started, and the capacitor C1
The frequency is set such that the voltage becomes lower than the maximum withstand voltage V12 of the circuit component such as b (see FIG. 8).

In the current phase detection circuit 6, the rectifying / smoothing unit 6
a and 6b are the first and second impedance detectors 4,
5 are rectified and smoothed outputs Va and Vb, and the detection outputs Va ′ and
Vb ′, and the detection outputs Va ′ and V ′ at the resonance frequency f01 or f02 as in the first or second embodiment.
The resistance values of the resistors R5 to R10 are set so that b 'is equal (see FIG. 7). Therefore, in the frequency range higher than the resonance frequency f01, the detection output Vb 'is higher than the detection output Va' (Va '<V
b ′), at the frequency fα, the detection output Vb ′ is higher by the voltage α than the detection output Va ′.

Therefore, in this circuit, the negative electrode of the reference power supply Vref1 for generating the difference voltage α at the frequency fα is
a, and the positive terminal of the reference power supply Vref1 is connected to the non-inverting input terminal of the comparator CP1.
The detection output V of the rectifying / smoothing unit 6a is calculated by the comparator CP1.
a ′ and the voltage α of the reference power supply Vref1 (Va ′ +
α) and the detected output Vb ′ of the rectifying / smoothing unit 6b are compared. Thus, the oscillation frequency f of the inverter circuit 2
Becomes higher than the frequency fα, and the detection output Vb ′ becomes higher than the voltage (Va ′ + α).
Output Vc attains the L level. On the other hand, when the oscillation frequency f of the inverter circuit 2 becomes lower than the frequency fα and the detection output Vb ′ becomes lower than the voltage (Va ′ + α), the voltage level of the output Vc of the comparator CP1 becomes H
Become a level.

The output Vc of the comparator CP1 is input to the inverter control circuit 2a. If the voltage level of the output Vc is L level, the inverter control circuit 2a operates the inverter circuit 2 at a frequency higher than the frequency fα. And performs a normal switching operation. On the other hand, when the voltage level of the output Vc becomes H level, the inverter control circuit 2a determines that the inverter circuit 2 is operating at a frequency lower than the frequency fα, and performs an inverter protection operation to reduce the output of the inverter circuit 2. The switching operation of the circuit 2 is shifted. Therefore, in this circuit, not only the inverter circuit 2 performs the switching operation in the early phase region but also the protection operation for reducing the output of the inverter circuit 2 when the resonance output of the inverter circuit 2 abnormally increases. The switching operation of the circuit 2 can be shifted, and the stress applied to circuit components such as switching elements can be reduced.

(Embodiment 4) In the discharge lamp lighting device of Embodiment 3 described above, in the discharge lamp lighting device of Embodiment 1 or 2, a reference power supply Vref1 is connected between the rectifying / smoothing unit 6a and the comparator CP1. Detection output V of rectifying / smoothing unit 6a
a ′ is added to the voltage α of the reference power supply Vref1 and the detection output Vb ′ of the rectifying / smoothing unit 6b is compared with a comparator C
By comparing at P1, when the inverter circuit 2 is operating at a frequency lower than the frequency fα, the operation is shifted to the protection operation. In the present embodiment, however, in the discharge lamp lighting device according to the first or second embodiment, As shown in FIG. 9, the resistance values of the resistors R5 to R10 are set such that the detection output Va 'of the rectifying / smoothing unit 6a and the detection output Vb' of the rectifying / smoothing unit 6b substantially match at the frequency fα.

At this time, the oscillation frequency f of the inverter circuit 2
Is higher than fα, the detection output Vb ′ is higher than the detection output Va ′ (Va ′ <Vb ′),
The voltage level of the output Vc of the comparator CP1 becomes L level. On the other hand, in the frequency range where the oscillation frequency f is lower than fα, the detection output Va becomes higher than the detection output Vb (Va> Vb), and the voltage level of the output Vc of the comparator CP1 becomes H level. In the inverter control circuit 2a, when the voltage level of the output Vc of the current phase detection circuit 6 becomes H level (that is, when the oscillation frequency f of the inverter circuit 2 becomes lower than the frequency fα), the inverter circuit 2a
Because the switching operation of this is shifted to the protection operation,
In the same manner as in the third embodiment, the inverter circuit 2 performs a switching operation in the early phase region, and also performs a protective operation to reduce the output of the inverter circuit 2 when the resonance output of the inverter circuit 2 abnormally increases. The switching operation of the circuit 2 can be shifted, and the stress applied to circuit components such as switching elements can be reduced.

(Embodiment 5) FIG. 10 is a circuit diagram in which a part of the discharge lamp lighting device of the present embodiment can be omitted. Note that the main circuit is not shown in FIG.
The other configuration is the same as that of the first embodiment, and thus the same components are denoted by the same reference numerals and description thereof will be omitted. FIG. 11 shows the relationship between the oscillation frequency f of the inverter circuit 2 and the detection outputs Va 'and Vb' of the rectifying / smoothing sections 6a and 6b. FIG. 12 shows the resonance curves at no load and at the time of lighting the discharge lamp (FIG. (A) shows a resonance curve when no load is applied, and (b) in the figure shows a resonance curve when the discharge lamp is turned on.)

In the discharge lamp lighting device according to the first embodiment, the frequency range lower than the resonance frequency is set in the inverter circuit 2.
Is a frequency range in which the switching operation is shifted to the protection operation. In the present embodiment, a frequency range (fβ <f <fα) lower than the predetermined frequency fα and higher than the predetermined frequency fβ is set to the inverter circuit 2. The switching operation is performed in a frequency range in which the operation is shifted to the protection operation.

Here, the frequency fα is a frequency higher than the resonance frequency by a predetermined frequency Δfα, and the resonance output Vα at the frequency fα is a voltage V1 at which the discharge lamp La can be started.
The frequency is set to be 1 or more and to be lower than the maximum withstand voltage V12 of the circuit component such as the capacitor C1b. The frequency fβ is a frequency lower than the resonance frequency by a predetermined frequency Δfβ,
As shown in FIG. 12, the resonance output Vβ at the frequency fβ is such an oscillation frequency that the resonance operation of the resonance circuit becomes a weak oscillation state when the output of the inverter circuit 2 has the lowest resonance output, that is, during the protection operation. The resonance output at f3 is set.

In this circuit, in the discharge lamp lighting device of the first embodiment, diodes D6 and D7 each having an anode connected to the output terminal of the rectifying / smoothing unit 6a, and anodes each connected to the output terminal of the rectifying / smoothing unit 6b. Diodes D8 and D9
A reference power supply Vref1 having a negative electrode connected to the cathode of the diode D6, a reference power supply Vref2 having a negative electrode connected to the cathode of the diode D9, and a reference power supply Vref connected to one input terminal.
The comparator CP1 having the positive terminal of ref1 connected thereto and the other input terminal connected to the cathode of the diode D9.
And a comparator CP2 having one input terminal connected to the cathode of the diode D7 and the other input terminal connected to the positive electrode of the reference power supply Vref2.

The comparator CP1 compares the voltage (Va ′ + α) obtained by adding the voltage α of the reference power supply Vref1 to the output Va ′ of the rectifying / smoothing unit 6a with the output Vb ′ of the rectifying / smoothing unit 6b, and compares the level of the comparator CP2. Compares the level of the output Va ′ of the rectifying / smoothing unit 6a with the voltage (Vb ′ + β) obtained by adding the voltage β of the reference power supply Vref2 to the output Vb ′ of the rectifying / smoothing unit 6b. Output V
c and Vd are input to the inverter control circuit 2a, respectively.

Here, the voltage α of the reference power supply Vref1 is set to the difference voltage (Vb′−Va ′) between the detection output Vb ′ and the detection output Va ′ at the frequency fα, so that the oscillation frequency of the inverter circuit 2 When f becomes higher than the frequency fα, the output Vb ′ becomes higher than the voltage (Va ′ + α),
The signal level of the output signal Vc1 of the comparator CP1 is L
Become a level. On the other hand, when the oscillation frequency f becomes lower than the frequency fα, the output Vb ′ becomes lower than the voltage (Va ′ + α), and the signal level of the output signal Vc1 of the comparator CP1 becomes H level.

Since the voltage β of the reference power supply Vref2 is set to the difference voltage (Va′−Vb ′) between the detection output Va ′ and the detection output Vb ′ at the frequency fβ, the oscillation frequency f Becomes higher than the frequency fβ, the output Va ′ becomes lower than the voltage (Vb ′ + β),
The signal level of the output signal Vc2 of the comparator CP2 is L
Become a level. On the other hand, when the oscillation frequency f becomes lower than the frequency fβ, the output Va ′ becomes higher than the voltage (Vb ′ + β), and the signal level of the output signal Vc2 of the comparator CP2 becomes H level.

In the inverter control circuit 2a, when the signal level of the output signal Vc of the comparator CP1 goes high and the signal level of the output signal Vd of the comparator CP2 goes low, the operation of the inverter circuit 2 shifts to the protection operation. Let me. That is, the inverter circuit 2
Is operating in a frequency range higher than the oscillation frequency fβ and lower than the oscillation frequency fα, the inverter control circuit 2a shifts the operation of the inverter circuit 2 to the protection operation. When the switching operation is performed in the phase region or when the resonance output of the inverter circuit 2 abnormally rises, the operation can be shifted to the protection operation for lowering the output of the inverter circuit 2 and the stress applied to the circuit components such as the switching element can be reduced. Can be reduced. In the frequency range where the oscillation frequency f of the inverter circuit 2 is lower than fβ, the operation of the inverter circuit 2 is in the phase advance region, but the output of the inverter circuit 2 is lower than the output during the protection operation. In the embodiment, the switching operation is performed without changing the operation of the inverter circuit 2 to the protection operation.

As described above, in the present embodiment, the upper limit value and the lower limit value are provided in the frequency range in which the protection operation is performed by the inverter control circuit 2a, and the upper limit value and the lower limit value of the frequency range are determined by the voltage values of the reference power supplies Vref1, Vref2. Since the value can be set to an arbitrary value, an abnormal state can be detected with high accuracy.

FIG. 13 shows a resonance curve in the case where the circuit configuration of the load circuit 3 is the same as that of the second embodiment. FIG. 6 shows a resonance curve (in this case, an LC series resonance circuit is formed by the parallel circuit of the capacitors C1a and C1b and the inductor L1). In FIG. FIG. 9 shows a resonance curve (in this case, an LC series resonance circuit is formed by the capacitor C1a and the inductor L1) when the filament is disconnected and no load is applied. 9 shows a resonance curve at the time. In this circuit, the output of the inverter circuit 2 has the lowest resonance output (the lowest resonance output means that the inverter circuit 2 is operated at a frequency sufficiently higher than the resonance frequency during the protection operation to weaken the resonance of the resonance circuit. When the oscillation frequency f of the inverter circuit 2 at the time of the resonance output becomes f3 (f01 <f3 <f
02), the frequencies in the fast region where the resonance output VC1 becomes substantially equal to the resonance output Vβ at the frequency f3 are fβ and fβ ′. Further, the resonance output VC1 is the discharge lamp L
fα and fα ′ are the frequencies in the delay region in which a is equal to or higher than the voltage V11 at which a can be started and is substantially equal to the predetermined voltage Vα lower than the withstand voltage V12 of the circuit component. Accordingly, when the discharge lamp La is turned off and the load becomes a no-load state, the oscillation frequency of the inverter circuit 2 becomes f
When the frequency is in the frequency range of β or more and fα or less (fβ ≦ f ≦ fα), the protection operation is performed by the inverter control circuit 2a, and the discharge lamp La comes off or the filament is disconnected, and the load is not applied. In this case, the protection operation is performed by the inverter control circuit 2a when the oscillation frequency of the inverter circuit 2 is in a frequency range (fβ ′ ≦ f ≦ fα ′) equal to or higher than fβ ′ and equal to or lower than fα ′.

(Embodiment 6) FIG. 14 is a circuit diagram in which a part of the discharge lamp lighting device of this embodiment can be omitted. In FIG. 14, the main circuit is not shown. Since the configuration other than the current phase detection circuit 6 is the same as that of the first embodiment, the same components are denoted by the same reference numerals and description thereof will be omitted.

This circuit uses the operational amplifier OP1 instead of the comparator CP1 in the circuit of FIG. 2 described above, and detects the detection outputs Va 'and Vb' of the rectifying / smoothing units 6a and 6b.
Is input to the operational amplifier OP1, and the detection outputs Va ′,
The output signal Ve of the operational amplifier OP1 proportional to the difference voltage of Vb 'is output to the inverter control circuit 2a.

Here, the resistances R5 to R5 are set so that the detection outputs Va 'and Vb' become substantially equal at the resonance frequency of the resonance circuit.
Since the resistance value of R10 is set, the closer the oscillation frequency f of the inverter circuit 2 is to the resonance frequency, the more the detection output V
The difference between a 'and Vb' becomes smaller, and the magnitude of the output signal Ve of the operational amplifier OP1 becomes smaller. Then, in the inverter control circuit 2a, the output signal Ve of the operational amplifier OP1 is output.
Is lower than a predetermined threshold, the operation of the inverter circuit 2 is shifted to the protection operation.

In this circuit, when the magnitude of the differential output Ve of the operational amplifier OP1 becomes equal to or smaller than a predetermined threshold, the inverter control circuit 2a shifts the operation of the inverter circuit 2 to the protection operation. The frequency range in which the protection operation is performed can be set to an arbitrary frequency range by setting the threshold value. Further, since the magnitude of the differential output Ve increases or decreases according to the difference between the detection outputs Va ′ and Vb ′, the protection operation is performed by shifting the oscillation frequency of the inverter circuit 2 to a frequency sufficiently higher than the resonance frequency, for example. In this case, the protection operation may be performed by increasing the oscillation frequency stepwise or continuously according to the magnitude of the differential output Ve. Since the polarity of the output signal Ve of the operational amplifier OP1 is inverted before and after the resonance frequency, the polarity of the output signal Ve is determined. When the oscillation frequency of the inverter circuit 2 reaches the frequency at which the polarity is inverted, the operation of the inverter circuit 2 is started. May be shifted to the protection operation.

(Embodiment 7) FIG. 15 is a circuit diagram in which a part of the discharge lamp lighting device of this embodiment can be omitted. In FIG. 15, the main circuit is omitted. The configuration other than the current phase detection circuit 6 is the same as that of the first or second embodiment.
The same components are denoted by the same reference numerals and description thereof will be omitted.

In this circuit, the voltage V3 of the reference power supply Vref3 is applied to the output terminal of the rectifying / smoothing unit 6b via the diode D6 in the circuit of FIG. A voltage V3 is given as an initial voltage. In the current phase detection circuit 6, the inductor L1 and the capacitor C1 during the oscillation operation of the inverter circuit 2
(Or the capacitors C1a and C1b) are detected as voltage changes, so that the detection output V is detected when the oscillation operation of the inverter circuit 2 is not performed.
Both a ′ and Vb ′ become 0 V, and there is a possibility that malfunction or non-operation of the current phase detection circuit 6 occurs.

Therefore, the current phase detection circuit 6 of the present embodiment
In this case, the signal level of the output signal Vc is forcibly set to the L level immediately after the inverter circuit 2 starts the oscillating operation by giving the voltage V3 of the reference power supply Vref3 as the initial value to the detection output Vb '. If the signal level of the output signal Vc is at the L level, the inverter control circuit 2a sets the signal level of the output signal Vc to the L level immediately after the start of the oscillation operation because the operation of the inverter circuit 2 is a normal switching operation. By doing so, the detection operation by the current phase detection circuit 6 is stopped, and malfunction or non-operation of the current phase detection circuit 6 can be prevented. When the inverter circuit 2 starts oscillating, the rectifying / smoothing unit 6b
The voltage value of the voltage V3 is set so that the detection output Vb 'of the reference power supply Vref3 becomes higher than the voltage V3 of the reference power supply Vref3. Therefore, the comparator CP1 compares the levels of the detection outputs Va' and Vb 'to determine the lamp current. , And the operation of the inverter circuit 2 in the phase advance region can be reliably detected.

(Embodiment 8) FIG. 16 is a circuit diagram of a discharge lamp lighting device according to the present embodiment, which can partially omit. In FIG. 16, the main circuit is not shown. Since the configuration other than the end-of-life detection circuit 7 is the same as that of the first or second embodiment, the same components are denoted by the same reference numerals and description thereof will be omitted.

In this circuit, an end-of-life detection circuit 7 comprising a comparator CP3 for comparing the level of a detection output Va 'detected by the rectifying / smoothing section 6a with a predetermined reference voltage Vref4 is provided. It is also used as the end-of-life signal of the discharge lamp La. That is, at the end of the life of the discharge lamp La, the lamp voltage of the discharge lamp La abnormally rises compared to the normal lighting, so the end of life detection circuit 7 detects the end of the life of the discharge lamp La from the abnormal rise of the detection output Va '. , An abnormality detection signal Vf is output to the inverter control circuit 2a. At the end of the life of the discharge lamp La, the detection output V
a ′ becomes higher than the reference voltage Vref4, the output (abnormality detection signal) Vf of the comparator CP3 becomes H level, and when the discharge lamp La is normally lit, the detection output Va ′ becomes equal to or lower than the reference voltage Vref4. The output (abnormality detection signal) Vf becomes L level.

As in the first embodiment, the inverter control circuit 2a detects the switching operation of the inverter circuit 2 in the leading phase region based on the output Vc of the current phase detection circuit 6, and outputs the output of the end-of-life detection circuit 7 (Abnormality detection signal)
When Vf becomes H level, it is determined that the discharge lamp La is at the end of life, and the switching operation of the inverter circuit 2 is shifted to the protection operation. Here, the protection operation is
A state in which the switching operation is stopped, a period in which the switching operation is performed and a period in which the switching operation is stopped are alternately provided (that is, the switching operation is performed intermittently), or the oscillation frequency of the switching elements Q1 and Q2 is increased. Transfer the operation of the inverter circuit 2 to one of the states in which the resonance of the resonance circuit is weakened. In this embodiment, the voltage Va 'is used as the end-of-life signal of the discharge lamp La. However, the voltage Vb' may be used.
Since b ′ also increases, the discharge lamp La
The end-of-life state can be detected.

When the inverter control circuit 2a detects the operation of the inverter circuit 2 in the phase advance region from the output Vc of the current phase detection circuit 6, it shifts the operation of the inverter circuit 2 to the protection operation and detects the end of life. When the end-of-life state of the discharge lamp La is detected from the output Vf of the circuit 7, the operation of the inverter circuit 2 is shifted to the protection operation. In the inverter control circuit 2a, the protection by the output Vc of the current phase detection circuit 6 is performed. The operation is terminated by the end-of-life detection circuit 7.
Of the protection operation by the output Vf.

FIG. 17 shows a resonance curve when the circuit configuration of the load circuit 3 is the circuit configuration of the second embodiment.
Note that a in FIG. 17 represents a resonance curve when the discharge lamp La is extinguished or the like and no load occurs (in this case, an LC series resonance circuit is formed by the parallel circuit of the capacitors C1a and C1b and the inductor L1). In the drawing, C represents a resonance curve when the discharge lamp La comes off or the filament breaks, resulting in a no-load state (in this case, the LC is formed by the capacitor C1a and the inductor L1). A series resonance circuit is formed.), And B in the figure indicates a resonance curve when the discharge lamp is turned on.

The following three load conditions (discharge lamp L
The operation state of the inverter circuit 2 at each frequency point in a no-load state due to the extinguishing of a, a no-load state due to the non-attachment of the discharge lamp La or a broken wire, and a lighting state of the discharge lamp La will be described.

When the discharge lamp La is extinguished and the like and becomes a no-load state (resonance curve shown in a of FIG. 17),
When the discharge lamp La is not mounted or the filament is disconnected due to the disconnection of the filament (resonance curve indicated by B in FIG. 17), the detection output Va ′ becomes higher than the detection output Vb ′ or the reference voltage Vref4. At such frequency points A and E (Va ′> Vb ′, Va ′> Vref4), the output of the comparator CP3 becomes H level, but the inverter control circuit 2a gives priority to the detection output of the current phase detection circuit 6 Then, the inverter circuit 2 is shifted to the protection operation (leading operation protection). Further, at frequency points B and F (Va '>Vb', Va '<Vref4) where the detection output Va' is higher than the detection output Vb 'and lower than the reference voltage Vref4, the inverter control circuit 2a operates in the phase advance region. Is determined as the switching operation, and the inverter circuit 2 is shifted to the protection operation (leading operation protection). Further, frequency points C and G (Va '<Vb', Va ') where the detection output Va' is lower than the detection output Vb 'and higher than the reference voltage Vref4.
> Vref4), the inverter control circuit 2a sets the discharge lamp La
Is in the end-of-life state, and the inverter circuit 2 is shifted to the protection operation (Emiless protection). Further, frequency points D, H (Va '<Vb', Vf ') where the detection output Va' becomes lower than the detection output Vb 'and the reference voltage Vref4.
When Va ′ <Vref4), the inverter control circuit 2a determines that the lighting state of the discharge lamp La is normal, and sets the inverter circuit 2 to a normal lighting operation.

On the other hand, when the discharge lamp La is normally lit,
At the frequency point I (Va '>Vb', Va '<Vref4) where the detection voltage Va' becomes lower than the reference voltage Vref4 and the detection voltage Va 'becomes higher than the detection output Vb', the inverter control circuit 2a It is determined that the switching operation is in the phase advance region, and the inverter circuit 2 is shifted to the protection operation (phase advance operation protection). On the other hand, the frequency point J (V) at which the detection voltage Va 'becomes lower than the detection output Vb'.
If a ′ <Vb ′, Va ′ <Vref4), the inverter control circuit 2a determines that the switching operation is in the late phase region, and sets the inverter circuit 2 to the normal lighting operation.

As described above, in the inverter control circuit 2a, the protection operation by the output of the current phase detection circuit 6 is given priority over the protection operation by the output of the end-of-life detection circuit 7, so that protection in the event of a load abnormality is performed. The operation can be performed reliably, and the reliability of the detection circuit is improved.

Incidentally, at the time of preheating or starting the discharge lamp La, the end-of-life detecting circuit 7 may erroneously detect it.
Although the detection operation by the end-of-life detection circuit 7 is prohibited during this period, if a load change (for example, disconnection of the discharge lamp) occurs during this period, the detection operation is performed by the current phase detection circuit 6 and the inverter circuit 2 can be shifted to the protection operation.

[0084]

As described above, the invention of claim 1 comprises an inverter circuit for converting the output of a DC power supply to a high frequency by switching with a switching element, and a series circuit of a resonance inductor and a resonance capacitor. A resonance circuit connected between output terminals of the circuit, a discharge lamp connected in parallel to the resonance capacitor, an inverter control circuit for controlling an output of the inverter circuit, and a first impedance for detecting a change in impedance of the resonance capacitor Detecting means; second impedance detecting means for detecting a change in impedance of the resonance inductor;
And current phase detection means for detecting the phase of the lamp current from the detection result of the second impedance detection means, wherein the impedance of the resonance inductor is set in a lagging region where the oscillation frequency is higher than the resonance frequency. Becomes dominant, and the impedance of the resonance capacitor and the discharge lamp becomes dominant in the phase advance region where the oscillation frequency is lower than the resonance frequency, so that the current phase detection means detects the first and second impedance detection means. From the result, it is possible to easily detect whether or not the inverter circuit is operating in the phase advance region. In the current phase detection circuit, the phase of the lamp current is detected by detecting the impedance of the resonance inductor and the resonance capacitor, so that the operation in the early phase region is ensured without complicating the circuit configuration. There is also an effect that can be detected.

According to a second aspect of the present invention, in the first aspect of the present invention, the resonance capacitor includes a first capacitor connected between output terminals of an inverter circuit via a resonance inductor. And a second capacitor connected to the non-power supply side of the discharge lamp connected in parallel to the capacitor, depending on whether the discharge lamp is mounted or whether the filament is broken. Since the configuration of the resonance circuit changes and its resonance frequency changes, abnormalities such as disconnection of the discharge lamp and breakage of the filament can be detected from the detection results of the first and second impedance detection means, and the presence or absence of the filament can be detected. As compared with a case where a separate circuit is separately provided, the number of parts is reduced, and the cost can be reduced.

According to a third aspect of the present invention, in the first or second aspect of the present invention, when the discharge lamp is turned on, the inverter circuit has a resonance frequency higher than the resonance frequency of the resonance circuit composed of the discharge lamp, the resonance inductor and the resonance capacitor. When the oscillation frequency of the inverter becomes low, the inverter control circuit shifts the operation of the inverter circuit from a normal oscillation operation to a protection operation for lowering the output. When the operation in the phase advance region is detected, the operation of the inverter circuit is shifted to the protection operation, so that there is an effect that stress is prevented from being applied to circuit elements such as switching elements.

According to a fourth aspect of the present invention, when the oscillation frequency of the inverter circuit becomes lower than a predetermined frequency upper limit higher than the resonance frequency of the resonance circuit, the inverter control circuit becomes the inverter circuit. The operation is shifted from a normal oscillation operation to a protection operation for lowering the output.In addition to the case where the inverter circuit is operating in the phase advance region, the output of the inverter circuit becomes higher than a predetermined voltage. In this case, the inverter control circuit shifts the operation of the inverter circuit to the protection operation.
There is an effect that stress can be prevented from being applied to a circuit element such as a switching element.

According to a fifth aspect of the present invention, in the third or fourth aspect of the present invention, the protection operation includes an operation for stopping the switching operation of the inverter circuit, or a period for performing the switching operation and a period for stopping the switching operation. The operation is either alternately provided or operation of increasing the oscillation frequency of the switching element to weaken the resonance of the resonance circuit, and has the same effect as the invention of claim 3 or 4.

According to a sixth aspect of the present invention, in the fourth aspect of the present invention, the frequency upper limit value is a frequency at which the output of the inverter circuit at that frequency is higher than a voltage at which the discharge lamp can be started. The inverter control circuit protects the operation of the inverter circuit when the output of the inverter circuit is higher than the starting voltage of the discharge lamp, in addition to the case where the inverter circuit is operating in the phase advance region. The effect is that the stress can be prevented from being applied to circuit elements such as switching elements.

According to a seventh aspect of the present invention, in the fourth aspect of the present invention, when the oscillation frequency of the inverter circuit becomes higher than a predetermined frequency lower limit lower than the resonance frequency of the resonance circuit, the inverter control circuit operates. The operation is shifted to the protection operation, and the same effect as the invention of claim 4 is obtained. In addition, a frequency upper limit value and a frequency lower limit value are provided in a frequency range in which the inverter control circuit performs the protection operation. Therefore, there is an effect that frequency control can be performed with high accuracy.

The invention according to claim 8 is the invention according to claim 7, characterized in that the frequency lower limit value is a frequency at which the output of the inverter circuit at the frequency is the lowest, and When operating at a frequency lower than the lower limit, the output of the inverter circuit is sufficiently low and there is no need to perform a protection operation. Therefore, the inverter circuit operates in a frequency range higher than the lower frequency limit and lower than the upper frequency limit. This has the effect of reducing the stress applied to the circuit components of the inverter circuit.

According to a ninth aspect of the present invention, in the first to eighth aspects, the current phase detecting means compares the level of the detection output of the first impedance detecting means with the level of the detection output of the second impedance detecting means. And comparing the level of the detection output of the first and second impedance detection means with a simple circuit configuration by detecting the phase of the lamp current from the comparison result of the comparison unit. There is an effect that an operation in the early phase region can be detected.

According to a tenth aspect of the present invention, in the first to eighth aspects, the current phase detecting means detects a difference between a detection output of the first impedance detecting means and a detection output of the second impedance detecting means. Having a difference detection unit,
It is characterized by detecting the phase of the lamp current from the output of the difference detection unit, and the output of the difference detection unit is inverted before and after the resonance frequency, so that it is possible to detect the operation in the early phase region with a simple circuit configuration. And, as the oscillation frequency of the inverter circuit is closer to the resonance frequency, the output of the difference detector becomes smaller, so that the oscillation frequency of the inverter circuit is closer to the resonance frequency,
There is also an effect that a frequency range where the output of the inverter circuit rises abnormally can be detected.

According to an eleventh aspect of the present invention, in the first to tenth aspects of the present invention, the inverter control circuit operates independently of the output of the current phase detecting means from when the power is turned on until the inverter circuit starts oscillating. It is characterized in that the operation of the circuit is controlled, and there is an effect that it is possible to prevent the influence of erroneous detection or non-operation of the current phase detection circuit at the start of the oscillation operation.

According to a twelfth aspect of the present invention, in any one of the first to eleventh aspects, a detection output of any one of the detection output of the first impedance detection means and the detection output of the second impedance detection means is used. An end-of-life detection circuit that detects the end-of-life state of the discharge lamp is provided.When the end-of-life detection circuit detects the end of life of the discharge lamp, the inverter control circuit lowers the output of the inverter circuit from normal oscillation operation. At the end of the life of the discharge lamp, the lamp voltage rises abnormally.
Alternatively, the end-of-life state of the discharge lamp can be detected from the detection output of the second impedance detection means, and the detection output of the first or second impedance detection means is also used as a detection signal of the end-of-life state. Therefore, there is an effect that the number of parts can be reduced as compared with a case where a circuit for detecting the end-of-life state is separately provided.

According to a thirteenth aspect, in the twelfth aspect, the inverter control circuit causes the protection operation to be performed by giving priority to the detection result of the current phase detection means over the detection result of the end-of-life detection circuit. As a feature, the protection operation at the time of a load abnormality can be reliably performed, and the reliability of the detection circuit is improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a discharge lamp lighting device according to a first embodiment.

FIG. 2 is a specific circuit diagram in which part of the above is omitted.

FIG. 3 is a diagram showing a relationship between an oscillation frequency and an output voltage of first and second impedance detectors at the time of no load in the embodiment.

FIG. 4 is a diagram showing a relationship between an oscillation frequency and output voltages of first and second impedance detectors at the time of steady lighting according to the first embodiment.

FIG. 5 is a circuit diagram of a discharge lamp lighting device according to a second embodiment.

FIG. 6 is a specific circuit diagram in which a part of the discharge lamp lighting device according to the third embodiment is omitted.

FIG. 7 is a diagram showing the relationship between the oscillation frequency and the output voltages of the first and second impedance detectors when there is no load in the above.

FIG. 8 is a diagram showing a relationship between an oscillation frequency and a resonance output at the time of no load and at the time of steady lighting according to the first embodiment.

FIG. 9 is a diagram showing the relationship between the oscillation frequency of the discharge lamp lighting device according to the fourth embodiment when there is no load and the output voltages of the first and second impedance detectors.

FIG. 10 is a specific circuit diagram in which a part of the discharge lamp lighting device according to the fifth embodiment can be omitted.

FIG. 11 is a diagram showing the relationship between the oscillation frequency and the output voltages of the first and second impedance detectors when there is no load in the above.

FIG. 12 is a diagram showing a relationship between an oscillation frequency and a resonance output at the time of no load and at the time of steady lighting according to the first embodiment.

FIG. 13 is a diagram showing a relationship between an oscillation frequency and a resonance output at the time of no load and at the time of steady lighting according to the first embodiment.

FIG. 14 is a specific circuit diagram in which a part of the discharge lamp lighting device according to the sixth embodiment can be omitted.

FIG. 15 is a specific circuit diagram in which a part of the discharge lamp lighting device according to the seventh embodiment is omitted.

FIG. 16 is a specific circuit diagram in which a part of the discharge lamp lighting device according to the eighth embodiment is omitted.

FIG. 17 is a diagram showing a relationship between an oscillation frequency and a resonance output at the time of no load and at the time of steady lighting according to the first embodiment;

FIG. 18 is a block diagram of a conventional discharge lamp lighting device.

FIG. 19 is a specific circuit diagram of the above.

FIG. 20 is a diagram showing a frequency characteristic of a resonance voltage generated in the resonance circuit of the above.

FIG. 21 is a main part circuit diagram showing another discharge lamp lighting device of the above.

FIG. 22 is a block diagram of still another discharge lamp lighting device of the above.

FIG. 23 is a diagram showing frequency characteristics of a resonance voltage generated in the resonance circuit according to the first embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rectifier smoothing circuit 2 Inverter circuit 3 Load circuit 4 1st impedance detection part 5 2nd impedance detection part 6 Current phase detection circuit C1, C2 Capacitor L1 Inductor La Discharge lamp

Claims (13)

[Claims] An inverter circuit for converting an output of a DC power supply to a high frequency by switching with a switching element, a resonance circuit comprising a series circuit of a resonance inductor and a resonance capacitor and connected between output terminals of the inverter circuit. A discharge lamp connected in parallel to the resonance capacitor, an inverter control circuit for controlling the output of the inverter circuit, first impedance detecting means for detecting a change in impedance of the resonance capacitor, and detecting a change in impedance of the resonance inductor A discharge lamp lighting device comprising: a second impedance detecting means for detecting a phase of a lamp current from detection results of the first and second impedance detecting means. 2. The resonance capacitor includes a first capacitor connected between output terminals of an inverter circuit via a resonance inductor, and a non-power supply side of a discharge lamp connected in parallel to the first capacitor. The discharge lamp lighting device according to claim 1, comprising a second capacitor connected to the discharge lamp lighting device. 3. When the oscillation frequency of the inverter circuit is lower than the resonance frequency of the resonance circuit including the discharge lamp, the resonance inductor and the resonance capacitor when the discharge lamp is turned on, the inverter control circuit operates the inverter circuit. 3. The discharge lamp lighting device according to claim 1, wherein the operation is shifted from a normal oscillation operation to a protection operation for lowering the output. 4. When the oscillation frequency of the inverter circuit becomes lower than a predetermined frequency upper limit value higher than the resonance frequency of the resonance circuit, the inverter control circuit changes the operation of the inverter circuit from a normal oscillation operation to a protection operation for lowering the output. The discharge lamp lighting device according to claim 1, wherein the discharge lamp lighting device is shifted. 5. The protection operation may be an operation of stopping a switching operation of the inverter circuit, an operation of alternately providing a period for performing the switching operation and a period for stopping the switching operation, or increasing the oscillation frequency of the switching element. 5. The discharge lamp lighting device according to claim 3, wherein the operation is any one of an operation of weakening the resonance of the resonance circuit. 6. The frequency upper limit value is a frequency at which the output of the inverter circuit at that frequency is equal to or higher than the voltage at which the discharge lamp can be started.
The discharge lamp lighting device as described in the above. 7. The inverter control circuit according to claim 1, wherein when the oscillation frequency of the inverter circuit becomes higher than a predetermined lower frequency lower than the resonance frequency of the resonance circuit, the operation of the inverter circuit is shifted to the protection operation. Item 5. The discharge lamp lighting device according to Item 4. 8. The discharge lamp lighting device according to claim 7, wherein the lower frequency limit is a frequency at which the output of the inverter circuit becomes the lowest at that frequency. 9. The current phase detecting means has a comparing section for comparing the detected output of the first impedance detecting means with the detected output of the second impedance detecting means, and determines the lamp current based on the comparison result of the comparing section. 9. The discharge lamp lighting device according to claim 1, wherein a phase of the discharge lamp is detected. 10. The current phase detection means has a difference detection part for detecting a difference between a detection output of the first impedance detection means and a detection output of the second impedance detection means. 9. The discharge lamp lighting device according to claim 1, wherein a phase of a current is detected. 11. The inverter control circuit controls the operation of the inverter circuit irrespective of the output of the current phase detecting means from when the power is turned on until the inverter circuit starts oscillating. 10. The discharge lamp lighting device according to 10. 12. An end-of-life detection circuit for detecting the end-of-life state of a discharge lamp from one of the detection output of the first impedance detection means and the detection output of the second impedance detection means. 12. The method according to claim 1, wherein when the end-of-life detection circuit detects the end of life of the discharge lamp, the inverter control circuit shifts the operation of the inverter circuit from a normal oscillation operation to a protection operation for reducing the output. Discharge lamp lighting device. 13. The discharge lamp lighting device according to claim 12, wherein the inverter control circuit causes the protection operation to be performed with priority given to the detection result of the current phase detection means over the detection result of the end-of-life detection circuit.