JPH0745380A - Discharge lamp lighting unit - Google Patents

Abstract

PURPOSE:To lower the effective value of no load secondary voltage. CONSTITUTION:An inverter circuit 1, which includes switching elements Q1 and Q2 being switched in a high frequency manner, converts DC power E into AC of rectangular waves. This unit is equipped with a filter circuit comprising a capacitor C1, which prevents a high frequency current from flowing to the discharge lamp DL connected to the output of an inverter circuit 1, and an inductor element L2. A switching element Q5 is provided inside the closed loop composed of a capacitor C1, the discharge lamp DL, and an inductance element L2. When a lamp voltage detecting circuit 3 detects no-load condition, a control circuit 2 turns off all the switching elements Q1-Q4 of an inverter circuit 1, in the specified period of the half cycle of the said rectangular wave AC, and also turns off the switching element Q5. Hereby, the said closed loop is broken, and the period of the voltage across the capacitor C1 being applied to the discharge lamp DL is shortened, and the effective value of the no-load secondary voltage is lowered.

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 for lighting a discharge lamp with a rectangular wave and having a closed loop including at least a capacitor and a discharge lamp.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional discharge lamp lighting device for lighting a discharge lamp with a rectangular wave. This discharge lamp lighting device is constituted by a so-called full-bridge inverter circuit 1. The inverter circuit 1 of this full bridge configuration is a DC power source E
Both ends of the switching element Q ₁ to Q ₄ bridge-connected to the inductance elements L _1, L ₂ and the discharge lamp between the connection point of the switching element Q _1, the connection point of Q ₃ and the switching element Q _2, Q ₄ DL is connected in series, and a capacitor C ₁ is connected in parallel at both ends of a series circuit of the discharge lamp DL and the inductance element L ₂ . In addition, diodes D _{1 to} D ₄ are connected in antiparallel to the switching elements Q _{1 to} Q ₄ , respectively.

The above discharge lamp lighting device has a negative electrode of the DC power source E.
Switching element Q connected to the side ₃, Q_Four(Below, low
The switching element on the potential side) is shown in FIG.
As shown in (d), on and off at low frequency (several hundred Hz)
And these switching elements Q₃, Q_FourAgainst
Switching elements Q arranged in diagonal positions₁, Q
₂As shown in FIGS. 8 (a) and 8 (b).
Element Q₃, Q_FourAt high frequency (several tens of kHz) in synchronization with
Turn off.

Now, the switching element Q_FourDuring the on period
The switching element Q₁When turned on, DC power supply
E → Switching element Q₁→ Inductance element L₁→
Capacitor C₁(And discharge lamp DL → inductance element
L₂) → Switching element Q _Four→ Use the DC power supply E route
The flow flows. In addition, the switching element Q₁Is off
Is the inductance element L₁The energy stored in
Therefore, the inductance element L₁→ Capacitor C₁(as well as
Discharge lamp DL → inductance element L₂) → switching
Element Q_Four→ Diode D₃→ Inductance element L₁of
A current flows along the path.

On the other hand, the switching element Q₃During the on period
The switching element Q₂When turned on, DC power supply
E → Switching element Q₂→ Capacitor C₁(And in
Dactance element L₂→ Discharge lamp DL) → Inductance required
Element L₁→ Switching element Q ₃→ Use the DC power supply E route
The flow flows. In addition, the switching element Q₂Is off
Is the inductance element L₁The energy stored in
Therefore, the inductance element L₁→ Switching element Q₃
→ Diode D_Four→ Capacitor C₁(And Inductin
Element L₂→ discharge lamp DL) → inductance element L₁of
A current flows along the path. That is, the transistor Q₃, Q
_FourAs shown in Fig. 8 (f), the polarity changes depending on whether the
An inverted rectangular wave current flows through the discharge lamp DL. In addition,
Dactance element L₁The current flowing in the
So that the switching element Q₁, Q₂On and off
The corresponding high frequency component is superimposed, but the capacitor C₁Is high
By flowing the frequency component, it flows to the discharge lamp DL.
The high frequency component of the current is suppressed. That is, the capacitor
C₁And inductance element L₂Is high frequency in the discharge lamp DL
It functions as a filter circuit that prevents current from flowing.
It In addition, the inductance element L₁Is for current-limiting.

By the way, in the above discharge lamp lighting device,
When the discharge lamp DL is in a no-load state, as shown in FIG. 8 (g), a rectangular wave voltage (no-load secondary voltage) that alternates the voltage V ₂ of the DC power supply E at both ends of the discharge lamp DL at a low frequency. V _o2 ) is applied. That is, since the capacitor C ₁ is charged up to the voltage V ₂ of the DC power source E, the rectangular-wave unloaded secondary voltage V _o2 is applied by the voltage across the capacitor C ₁ .

When a sinusoidal voltage is applied to the discharge lamp DL, if the peak value is the voltage required for starting the discharge lamp DL, the effective value is 1 / √2 (√2 is the square root of 2) of the peak value. ) (Effective value = peak value / √2), the applied voltage of the discharge lamp DL is a rectangular wave when there is no load, and therefore the effective value equal to the peak value (effective value = Peak value). That is, in this case, the voltage required for starting the discharge lamp DL is applied over almost the entire half cycle. Therefore, the switching element Q of the inverter circuit
Loss increases in ₁ to Q _4, also undesirable on safety.

Therefore, there is a discharge lamp lighting device shown in FIG. 9 which improves this point. In this discharge lamp lighting device, a series circuit of a resistor R and a switching element Q ₅ is connected in parallel to both ends of a capacitor C ₁ (both ends of a series circuit of a discharge lamp DL and an inductance element L ₂ ) and the A lamp voltage detection circuit 3 for detecting a no-load state of the discharge lamp DL, and a control circuit 2 for controlling on / off of the switching elements Q _{1 to} Q _{4 by} the control circuit 2 as well as on / off of the switching element Q _5. Provided, lamp voltage detection circuit 3
When it is detected that the discharge lamp DL is in the no-load state in the control circuit 2, as shown in FIGS.
There are as well as the off period of time all the switching elements Q ₁ to Q ₄ of the low frequency, and turns on the switching element Q ₅ during that period. That is, in the period in which all the switching elements Q _{1 to} Q ₄ are off,
As shown in 0 (f), the charge of the capacitor C ₁ is transferred to the resistor R
No-load secondary voltage V applied to the discharge lamp DL
The effective value of _o2 is made low.

[0009]

However, even in this way, the voltage V ₂ of the DC power source E is applied during the period when the corresponding pair of switching elements Q _{1 to} Q ₄ is on.
Moreover, the resistance R becomes large, which is not an effective method in terms of cost and size. Further, in a no-load state, particularly in a state in which the discharge lamp DL is left unattached, the capacitor C ₁ remains charged, which is preferable for safety when the terminal of the socket for mounting the discharge lamp DL is exposed. There was a problem of not having.

The present invention has been made in view of the above points, and its first object is to reduce the effective value of the no-load secondary voltage without causing problems in cost and size. A second object is to provide a discharge lamp lighting device which is safe under no-load condition, especially when the discharge lamp is left unplugged. It is in.

[0011]

In order to achieve the first object, the invention according to claim 1 is a DC power supply, in which a DC power supply and a switching element including a switching element switched at high frequency are turned on and off. An inverter circuit for converting into a rectangular wave AC, a discharge lamp connected to the output of the inverter circuit, and a filter circuit including a capacitor for preventing high-frequency current from flowing to the discharge lamp, at least a capacitor of the filter circuit In a discharge lamp lighting device in which a closed loop including a discharge lamp is formed, a switch element provided in the closed loop, detection means for detecting a no-load state, and a no-load state detected by this detection means,
There is provided control means for turning off all the switching elements of the inverter circuit and turning off the switch elements during a predetermined period of the half cycle of the rectangular wave alternating current.

Also, in order to achieve the first object, the invention of claim 2 is a power conversion system for converting the power supplied from the DC power supply, which includes a DC power supply and a switching element which is switched at high frequency. Circuit, an inverter circuit that converts the output of the power conversion circuit into a rectangular wave AC, a discharge lamp connected to the output of the inverter circuit, and a filter that includes a capacitor that prevents high-frequency components from being output to the inverter circuit In a discharge lamp lighting device including a circuit, a closed loop including at least a capacitor of a filter circuit and a discharge lamp is formed via a switching element of an inverter circuit, a detection unit that detects a no-load state, and a detection unit that detects When a load condition is detected, the switching elements of the inverter circuit must be switched during the specified period of the half-cycle of the rectangular wave AC. It is provided with a control means for turning off.

In order to achieve the second object, a third aspect of the present invention is to turn the DC power source into a rectangular wave alternating current by turning on and off a DC power source and a switching element including a switching element that is switched at high frequency. A closed loop including an inverter circuit for converting, a discharge lamp connected to the output of the inverter circuit, and a filter circuit including a capacitor for preventing high-frequency current from flowing to the discharge lamp, and including at least the capacitor of the filter circuit and the discharge lamp. In the discharge lamp lighting device in which is formed, a switch element provided in the closed loop, a detection means for detecting an unloaded state, and when the unloaded state continues for a predetermined period or more, all switching elements of the inverter circuit are turned off. In addition, a control means for turning off the switch element is provided.

Also, in order to achieve the second object, the invention of claim 4 is a power conversion system for converting the power supplied from a DC power supply including a DC power supply and a switching element that is switched at high frequency. Circuit, an inverter circuit that converts the output of the power conversion circuit into a rectangular wave AC, a discharge lamp connected to the output of the inverter circuit, and a filter that includes a capacitor that prevents high-frequency components from being output to the inverter circuit In a discharge lamp lighting device including a circuit, a closed loop including at least a capacitor of a filter circuit and a discharge lamp is formed via a switching element of an inverter circuit, a detection unit that detects a no-load state, and a no-load state is predetermined. And a control means for turning off all the switching elements of the inverter circuit when the operation is continued for a period of time or more.

[0015]

According to the invention of claim 1, when configured as described above, all the switching elements of the inverter circuit are turned off and the switch is turned off during a predetermined period of a half cycle of the rectangular wave alternating current in the unloaded state. Turn off the element, cut off the closed loop formed including at least the capacitor of the filter circuit and the discharge lamp, shorten the period in which the voltage across the capacitor is applied to the discharge lamp, and reduce the effective value of the no-load secondary voltage. Lower.

According to the second aspect of the present invention, by the above-mentioned configuration, all the switching elements of the inverter circuit are turned off during a predetermined period of a half cycle of the rectangular wave alternating current in the unloaded state, and the inverter circuit of the inverter circuit is turned off. The closed loop formed including at least the capacitor of the filter circuit and the discharge lamp is disconnected via the switching element, and the period in which the voltage across the capacitor is applied to the discharge lamp is shortened to reduce the effective value of the no-load secondary voltage. Lower.

According to the third aspect of the present invention, the above-mentioned configuration allows the non-loaded state to continue for a predetermined period or more,
Turns off all switching elements of the inverter circuit, turns off the switch element, breaks the closed loop formed including at least the capacitor of the filter circuit and the discharge lamp, and prevents the voltage across the capacitor from being applied to the discharge lamp. .

According to a fourth aspect of the present invention, with the above configuration, when the unloaded state continues for a predetermined period or more,
Turn off all switching elements of the inverter circuit,
The closed loop formed by including at least the capacitor of the filter circuit and the discharge lamp is disconnected via the switching element of the inverter circuit so that the voltage across the capacitor is not applied to the discharge lamp.

[0019]

【Example】

(Embodiment 1) FIG. 1 shows an embodiment of the present invention. This embodiment differs from the conventional discharge lamp lighting device of FIG. 9 in that a switching element Q ₅ is provided in a closed loop formed by a capacitor C ₁ , an inductance element L ₂ and a discharge lamp DL.
Other configurations are the same as those of the discharge lamp lighting device of FIG.

In the discharge lamp lighting device of this embodiment, the switch
Element Q_FiveSwitching element Q ₃, Q_FourOne of
Control circuit 2 controls to turn on when is on
I do. Then, the discharge lamp DL may be in a no-load state.
When detected by the lamp voltage detection circuit 3, the discharge lamp of FIG.
As in the case of the lighting device, it is shown in Figs. 2 (a)-(d).
Sea urchin, switching element Q₁~ Q_FourAll off
Set a period. Therefore, as shown in FIG.
Touching element Q₃, Q_FourWhen off, the switching element
Child Q_FiveIs also turned off, which causes the capacitor C₁, Inn
Dactance element L₂, The closed loop of the discharge lamp DL is broken,
Capacitor C₁Voltage of both ends is not applied to the discharge lamp DL
Become. That is, in the case of this embodiment, the discharge lamp DL has no load.
Next voltage V _o2Is as shown in FIG. For this reason,
In the case of FIG. 10, the capacitor C is connected via the resistor R.₁Charging power
Period of load consumption, that is, switching element Q₁~ Q
_FourWhen all are off, no voltage is applied to the discharge lamp DL.
No load secondary voltage V_o2Lower the effective value of
be able to.

Here, the voltage V ₂ of the DC power source E is, for example, 3
When the voltage is ₀₀ V or more, the effective value of the no-load secondary voltage V _o2 can be 300 V or less. Also in this case, since the peak value of the no-load secondary voltage V _o2 is 300 V or more, sufficient starting performance can be obtained. As described above, in the present embodiment, the effective value of the no-load secondary voltage V _o2 can be reduced, and the resistor R is not required as shown in FIG. 9, so that there is no problem in cost and size. .
The switching element Q ₅ is turned on switching elements Q _3, Q _4, on the basis off, it is only necessary to turn off, for example, the switching element Q _3, a switching element control output of the Q ₄ via a respective diode Q if so added to _5, in particular the switching element Q to the control circuit 2
There is also an advantage that it is not necessary to provide a circuit for ₅ .

By the way, the DC power source E is a step-up chopper circuit.
If it was created with a power circuit that has
Is the voltage V of the DC power supply E₂Can be changed freely. There
So, when there is no load, the voltage V₂To
Higher and non-negative with a peak value effective for starting the discharge lamp DL
Load secondary voltage V_o2May be applied. Figure 3
The voltage V of the DC power supply E is shown in (a) when the lamp is on and when there is no load.₂To
The case where it is not changed is shown, and in the same figure (b) there is no load than when lighting
DC power supply voltage V at the time₂Shows the case of increasing. Figure 3
In (b), the switching element Q₃, Q_FourOne of
Period T₁And switching element Q₁~ Q_FiveAll
Off period T₂By changing the ratio with
(Period T₁Shorten period T₂By lengthening
R), no-load secondary voltage V _o2Set the effective value of
I have decided. In addition, the unloaded secondary voltage V _o2Fruit
Effective value is period T₁, T₂The ratio can be set freely.

In the above case, the case where the no-load state is detected from the lamp voltage has been described, but it goes without saying that it may be detected from the lamp current or the light output of the discharge lamp DL. (Embodiment 2) FIG. 4 shows another embodiment of the present invention. In this embodiment, an inverter circuit 1 having a full bridge configuration is shown in FIG.
As shown in (c) to (f), the transistors Q _{1 to} Q ₄ are both turned on and off at a low frequency (several hundred Hz).
A switching element Q ₀ is turned on at a high frequency between the inverter circuit 1 and the DC power source E as shown in FIG.
A step-down chopper circuit 4 that is turned off is provided. The step-down chopper circuit 4 is a basic one including a switching element Q ₀ , an inductance element L ₀ , a capacitor C ₀ and a diode D _0, and an inductance element inserted between the step-down chopper circuit 4 and the inverter circuit 1. L ₃
Is for high frequency blocking that prevents high frequency components generated in the step-down chopper circuit 4 from being supplied to the inverter circuit 1, and constitutes a filter circuit together with a capacitor C ₀ that bypasses the high frequency components. Therefore, the inverter circuit 1
Is the inductance element L ₂ and the capacitor C ₁ in FIG. 1 that prevent a high frequency current from flowing in the discharge lamp DL.
Is no longer needed. The inductance element L ₃ also has a current limiting function instead of the inductance element L ₁ .

In this embodiment, for example, the switching element Q
_{When 1} and Q ₄ are on and switching elements Q ₂ and Q ₃ are off and switching element Q ₀ is on, DC power supply E → switching element Q ₀ → inductance element L
₀ → capacitor C ₀ (and inductance element L ₃ → switching element Q ₁ → discharge lamp DL → switching element Q
₄ ) → When a current flows through the path of the DC power supply E and the switching element Q ₀ is off, the inductance element L ₀ → the capacitor C ₀ (and the inductance element L ₃ → the switching element Q ₁ → the discharge lamp DL → the switching element Q ₄ ) →
A current flows in the path from the diode D _{0 to the} inductance element L ₀ .

Although not described, when the switching elements Q ₂ and Q ₃ are on and the switching elements Q ₁ and Q ₄ are off, the discharge lamp DL has the above-mentioned structure as shown in FIG. 5 (g). Current flows in the opposite direction to the case. Here, the high frequency component is removed by the capacitor C ₀ and the inductance element L ₃ described above, and a substantially DC rectangular wave current is passed through the inverter circuit 1.

In the case of this embodiment, the lamp current detection circuit 3 detects the no-load state of the discharge lamp DL from the voltage across the capacitor C ₀ . Here, in the case of the present embodiment, when there is no load, a closed loop is formed between the capacitor C ₀ , the inductance element L ₃ and the discharge lamp DL via the switching elements Q ₁ and Q ₄ or the switching elements Q ₂ and Q _3. The voltage across the capacitor C ₀ , which is formed, that is, the alternating rectangular wave unloaded secondary voltage V _o2 is applied to the discharge lamp DL.

Therefore, in this embodiment, the discharge lamp DL is non-negative.
When the load is present, all the inverter circuit 1 switches
Itching element Q₁~ Q_FourBy turning off
Itching element Q₁, Q_FourOr switching element Q
₂, Q₃Capacitor C via₀, Inductance element
L₃And so as to break the closed loop formed by the discharge lamp DL
I am doing it. Accordingly, even in the case of this embodiment, substantially
Is the switching element Q in the first embodiment._FiveTurn off
Similarly to the case, the no-load secondary voltage V_o2Lower the effective value of
I am doing it. In other words, in the case of this embodiment,
Switching element Q_FiveFunction as a switching element
Child Q₁, Q_FourOr switching element Q ₂, Q₃Cum in
It becomes the shape used. Therefore, in the inverter circuit 1,
Switching element Q individually_FiveNeed not be provided. Na
The switching element Q in FIG. ₁, Q_FourOr
Switching element Q₂, Q₃Period T is on₁When,
Switching element Q₁~ Q_FourT is all off
₂By changing the ratio of_o2
The effective value of can be set arbitrarily.

(Embodiment 3) In this embodiment, it is safe to leave the discharge lamp DL unattended, especially if the discharge lamp DL is left unmounted. The construction is the same as that shown in FIG. Occasionally, in the same manner as described in the first embodiment, the unloaded secondary voltage V _o2
Operates to lower the effective value of. However, in the case of the present embodiment, all of the switching elements Q _{1 to} Q ₄ are turned on and off when the above-mentioned no-load state continues for a predetermined feedback or more. Therefore, at the same time, the switching element Q ₅ also turns off. That is, when the no-load state continues, particularly when the discharge lamp is left unplugged, the switching element Q ₅ is turned off to form the capacitor C ₁ , the discharge lamp DL, and the inductance element L _2. The closed loop is cut off so that the voltage across the capacitor C ₁ is not applied across the discharge lamp DL. In this way, even if the terminals of the socket in which the discharge lamp DL is mounted are exposed, no electric shock will occur and it is safe.

(Embodiment 4) In this embodiment, too, no load condition
Made safe even if left without the discharge lamp DL
The configuration is the same as that of the second embodiment of FIG.
If the state continues, switching element Q₁~ Q_Fourof
It is designed to stop all on and off. This
In the same manner as in the third embodiment, the switch
Element Q₁~ Q_FourBy turning off the capacitor C₀, Discharge
Lamp DL and inductance element L ₃Closed with
And disconnect the condenser C on both ends of the discharge lamp DL.₀Both ends of
Ensure safety by not applying voltage.

[0030]

As described above, the invention of claim 1 includes a DC power supply and an inverter circuit for converting the DC power supply into a rectangular wave AC by turning on and off a switching element including a switching element that is switched at high frequency. A discharge lamp connected to the output of the inverter circuit, and a filter circuit including a capacitor for preventing high-frequency current from flowing to the discharge lamp, and a closed loop including at least the capacitor of the filter circuit and the discharge lamp is formed. In the light lighting device,
A switching element provided in the closed loop, a detecting means for detecting an unloaded state, and a switching element of an inverter circuit during a predetermined period of the half cycle of the rectangular wave alternating current when the unloaded state is detected by the detecting means. Is provided with a control means for turning off all of the switching elements, and when there is no load, all the switching elements of the inverter circuit are turned off during a predetermined period of a half cycle of the rectangular wave AC. In addition to turning off the switch element, it is possible to break the closed loop formed including at least the capacitor of the filter circuit and the discharge lamp, and shorten the period in which the voltage across the capacitor is applied to the discharge lamp, thereby reducing the load. The effective value of the secondary voltage can be reduced.

As described above, the invention of claim 2 is a DC power supply, a power conversion circuit that includes a switching element that is switched at high frequency and that converts the power supplied from the DC power supply, and the output of this power conversion circuit. Of the inverter circuit for converting the AC into a rectangular wave AC, a discharge lamp connected to the output of the inverter circuit, and a filter circuit including a capacitor for preventing high frequency components from being output to the inverter circuit, and switching of the inverter circuit. In a discharge lamp lighting device in which a closed loop including at least a capacitor of a filter circuit and a discharge lamp is formed through an element, a detection unit that detects a no-load state, and a non-load state is detected by this detection unit, Control means is provided to turn off all switching elements of the inverter circuit during a prescribed period of a half cycle of rectangular wave AC. Therefore, when no load is applied, all the switching elements of the inverter circuit are turned off during a predetermined period of a half cycle of the rectangular wave AC, and at least the capacitor of the filter circuit and the discharge lamp are connected via the switching element of the inverter circuit. It is possible to break the closed loop formed by including the voltage, and to shorten the period in which the voltage across the capacitor is applied to the discharge lamp, thereby reducing the effective value of the no-load secondary voltage.

As described above, the invention of claim 3 is a DC power supply, an inverter circuit for converting the DC power supply into a rectangular wave AC by turning on and off a switching element including a switching element that is switched at high frequency, and an inverter. Discharge lamp lighting including a discharge lamp connected to the output of the circuit and a filter circuit including a capacitor for preventing high-frequency current from flowing to the discharge lamp, and forming a closed loop including at least the capacitor of the filter circuit and the discharge lamp In the device, a switch element provided in the closed loop, a detection means for detecting an unloaded state, and when the unloaded state continues for a predetermined period or more, all switching elements of the inverter circuit are turned off, and the switching element is Since the control means for turning it off is provided, when the unloaded state continues for a predetermined period or longer, the It is possible to turn off all the switching elements of the data circuit, turn off the switching elements, and break the closed loop formed by including at least the capacitor of the filter circuit and the discharge lamp. Even when the terminals of the socket for mounting the discharge lamp are exposed, the electric shock does not occur and the safety is ensured.

As described above, the invention of claim 4 includes a DC power supply, a power conversion circuit that includes a switching element that is switched at high frequency, and that converts the power supplied from the DC power supply, and the output of this power conversion circuit. Of the inverter circuit for converting the AC into a rectangular wave AC, a discharge lamp connected to the output of the inverter circuit, and a filter circuit including a capacitor for preventing high frequency components from being output to the inverter circuit, and switching of the inverter circuit. In a discharge lamp lighting device in which a closed loop including at least a capacitor of a filter circuit and a discharge lamp is formed via an element, a detection unit that detects a no-load state and an unloaded state of the inverter circuit Since there is a control means for turning off all the switching elements, the no-load state has continued for a predetermined period or longer. Come, and all the switching elements of the inverter circuit off, via the switching elements of the inverter circuit can be cut off a closed loop which is formed and a capacitors of at least the filter circuit discharge lamp,
Therefore, the voltage across the capacitor is not applied to the discharge lamp,
Even if the terminals of the socket to which the discharge lamp is attached are exposed, no electric shock will occur and it will be safe.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an operation when there is no load in the above.

FIG. 3 is an explanatory diagram in the case where the voltage applied to the discharge lamp is made higher when there is no load than when lighting.

FIG. 4 is a circuit diagram of another embodiment.

FIG. 5 is an explanatory diagram of an operation in the above steady state.

FIG. 6 is an explanatory diagram of an operation when there is no load in the above.

FIG. 7 is a circuit diagram of a conventional example.

FIG. 8 is an explanatory diagram of the above problem.

FIG. 9 is a circuit diagram of another conventional example.

FIG. 10 is an explanatory diagram of an operation when there is no load in the above.

[Explanation of symbols]

First inverter circuit 2 control circuit 3 lamp voltage detection circuit 4 step-down chopper circuit E DC power source Q ₁ to Q ₅ switching element DL discharge lamp C _0, C ₁ capacitor L _2, L ₃ inductance element

Claims (4)

[Claims] 1. A DC power supply, and a switching element including a switching element that is switched at high frequency, turned on,
An inverter circuit that converts a DC power supply into a rectangular wave AC when it is off, a discharge lamp connected to the output of the inverter circuit, and a filter circuit that includes a capacitor that prevents high-frequency current from flowing to the discharge lamp, and at least a filter In a discharge lamp lighting device in which a closed loop including a circuit capacitor and a discharge lamp is formed, a switch element provided in the closed loop, a detection means for detecting a no-load state, and a no-load state is detected by this detection means. In this case, the discharge lamp lighting device is provided with a control means for turning off all the switching elements of the inverter circuit and turning off the switching elements for a predetermined period of the half cycle of the rectangular wave alternating current. . 2. A DC power supply, a power conversion circuit that includes a switching element that is switched at high frequency and that converts the power supplied from the DC power supply, and an inverter that converts the output of this power conversion circuit into a rectangular wave AC. Circuit, a discharge lamp connected to the output of the inverter circuit, and a filter circuit including a capacitor that prevents high-frequency components from being output to the inverter circuit, and at least the capacitor of the filter circuit via the switching element of the inverter circuit. In a discharge lamp lighting device in which a closed loop including a discharge lamp and a discharge lamp is formed, detecting means for detecting an unloaded state, and when the unloaded state is detected by this detecting means, a predetermined period of the half cycle of the rectangular wave AC And a control means for turning off all switching elements of the inverter circuit. Lighting device. 3. A DC power supply and a switching element including a switching element which is switched at high frequency, and
An inverter circuit that converts a DC power supply into a rectangular wave AC when it is off, a discharge lamp connected to the output of the inverter circuit, and a filter circuit that includes a capacitor that prevents high-frequency current from flowing to the discharge lamp, and at least a filter In a discharge lamp lighting device in which a closed loop including a circuit capacitor and a discharge lamp is formed, a switch element provided in the closed loop, a detection means for detecting a no-load state, and a no-load state for a predetermined period or more A discharge lamp lighting device, comprising: a control means for turning off all switching elements of the inverter circuit and turning off the switching elements. 4. A DC power supply, a power conversion circuit that includes a switching element that is switched at high frequency, and that converts the power supplied from the DC power supply, and an inverter that converts the output of this power conversion circuit into a rectangular wave AC. Circuit, a discharge lamp connected to the output of the inverter circuit, and a filter circuit including a capacitor that prevents high-frequency components from being output to the inverter circuit, and at least the capacitor of the filter circuit via the switching element of the inverter circuit. In a discharge lamp lighting device in which a closed loop including a discharge lamp and a discharge lamp is formed, a detection unit that detects an unloaded state, and a control unit that turns off all switching elements of an inverter circuit when the unloaded state continues for a predetermined period or longer. And a discharge lamp lighting device.