JP2000003796A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely operate a no-load detection circuit when input power source is turned on in an no-load state and when a discharge lamp is incompletely mounted and surely perform an intermittent oscillating operation, when emission- less of the discharge lamp is detected by adding a means for varying a detection voltage to the no-load detection circuit and changing detected voltage for a prescribed period. SOLUTION: A no-load detection circuit is provided with a varying means of detected voltage Vc1, and detected voltage is made to be lowered at least for a recharge period. As a result, because a time Tc1 which is the time for voltage Vc1 of a capacitor C1 to reach a reference voltage Vk becomes Tc1<Vk, the no-load detection circuit becomes normal operation and is decided as being at no-load, even if a time constant with resistance R1 and the capacitor c1 is not set to a smaller, oscillation will not start. When discharge lamp load exists, since a reducing degree of detected voltage Vc1 needs to be designed carefully, because Vc1>Vk is required when the precharge period is finished.

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 using an inverter circuit.

[0002]

2. Description of the Related Art FIG. 16 shows a circuit diagram of a conventional example. In the figure,
Vs is a commercial AC power supply, DB is a full-wave rectifier, R1 to R6 are resistors, C1 to C6 are capacitors, T1 is a transformer, L1
Is an inductor, n1 and n4 are primary windings, n2, n3, n
5, n6 are secondary windings, D1 and D2 are diodes, ZD1
Is a Zener diode, LA is a discharge lamp, f1 and f2 are filaments, CP1 is a comparator, 1 is a DC power supply circuit, 2 is an inverter circuit, 3 is a control circuit, 4 is an Emiless detector, and 5 is a no-load detector.

A commercial AC power supply Vs is full-wave rectified by a full-wave rectifier DB, and is supplied to a DC power supply circuit 1 such as a chopper circuit.
To output a DC voltage E. An output terminal of the DC power supply circuit 1 is connected to an inverter circuit 2, and an output terminal of the inverter circuit 2 is connected to a series circuit of a resonance inductor L <b> 1 and a capacitor C <b> 2. A primary winding n1 of a transformer T1 is connected to both ends of the capacitor C2, and a capacitor C3 and a discharge lamp L are connected to a secondary winding n2 of the transformer T1.
A series circuit is connected. Here, an inverter load circuit is configured by the inductor L1, the capacitor C2, the transformer T1, the capacitor C3, and the discharge lamp LA. At both ends of the filaments f1 and f2, capacitors C4 and
It is connected to the secondary windings n5 and n6 of the inductor L1 via C5. This is to supply a current to the filaments f1 and f2 during preheating before the discharge lamp LA is turned on.

Next, the configuration of the no-load detection circuit will be described. The positive output terminal a of the DC power supply circuit 1 is connected to the connection point b between the capacitor C3 and the filament f1 via the resistor R4, and the filament f1, the resistor R3, and the filament f
2 connected to one end of the secondary winding n2 and a connection point c between the filament f2 and a resistor R2.
And a Zener diode ZD1 are connected to the ground via a series circuit. Resistor R2 and Zener diode Z
From the connection point of D1 to the capacitor C via the diode D1
1 and a parallel circuit of a resistor R1 are connected. The voltage Vc1 of the capacitor C1 is input to the comparator CP1 of the no-load detecting section 5 and is compared with the reference voltage Vk. The comparison result becomes a detection output of the no-load detecting circuit.

Next, the configuration of the Emiless detection circuit will be described. One end of a secondary winding n3 of the transformer T1 is connected to the ground, and the other end is connected to a diode D2 and resistors R5 and R6.
Connected to the ground via A capacitor C6 is connected to both ends of the resistor R6, and the voltage of the capacitor C6 is input to the Emiless detector 4. With this configuration, when the discharge lamp LA is in the end-of-life state, it is possible to detect, via the winding n3, that the lamp voltage of the discharge lamp LA is higher than in the normal state.

Next, the inverter circuit 2 and the DC power supply circuit 1
Will be described based on FIG. In the figure, Q1 to Q3 are switching elements, R9 is a resistor, C7 and C8 are capacitors, L2 is an inductor, and D4 and D5 are diodes. In the circuit of FIG. 17, a series circuit of switching elements Q1 and Q2 forms an inverter circuit 2, and a series circuit of a smoothing capacitor C7, an inductor L2, and a diode D4 is connected in parallel with one switching element Q1. Further, a diode D5 is connected between the source terminal of the switching element Q2 and a connection point of the diode D4 and the smoothing capacitor C7. A resistor R is connected between the cathode of the diode D4 and the source terminal of the switching element Q2.
9 and a switching element Q3 are connected in series. Here, a series circuit of the resistor R9 and the switching element Q3 forms an inrush current prevention circuit 6, and a step-down chopper circuit is formed by the inductor L2, the smoothing capacitor C7, the diode D4, the switching element Q2, the capacitor C8, and the diode D5. ing. And the switching element Q
A signal from the control circuit 3 is sent to each gate terminal of 1, Q2 and Q3. Here, a step-down chopper circuit as shown in FIG. 17 is illustrated as a specific example of the DC power supply circuit 1, but a power supply circuit having another configuration may be used.

Next, the operation of the conventional circuit will be described. First, the operation until the DC power supply circuit 1 starts up will be described with reference to FIG. Here, the inrush current prevention circuit 6
When the input AC power supply Vs is supplied in a state where there is no charge and the capacitor C7 has no charge, in order to charge the capacitor C7, a path from the input AC power supply Vs to the inductor L2, the capacitor C7, the diode D4, and the switching element Q2. A large inrush current will flow. Therefore,
In order to prevent the inrush current, an inrush current prevention circuit 6 is added, and the capacitor C7
Until is charged to a predetermined voltage, the control circuit 3 is provided with a timer function so that the switching elements Q1 and Q2 are in the oscillation stop state for a certain period.
Is turned on, from the input AC power supply Vs, the inductor L2, capacitor C7, diode D4, current limiting resistor R
A rush current is prevented by flowing a current to the switching element Q3 via the switching element Q9. The oscillation stop period of the switching elements Q1 and Q2 by the timer function of the control circuit 3, that is, the ON period of the switching element Q3 is hereinafter referred to as a precharge period (Tpc).

Next, FIG. 16 will be described. First, when at least one of the filaments f1 and f2 of the discharge lamp LA is removed and the input AC power supply Vs is turned on in a no-load state, the resistance R4, the capacitor C3, the winding n
2, a current flows through the path of the resistor R2, the diode D1, and the capacitor C1 until the capacitor C3 is completely charged;
As a result, the capacitor C1 is also charged. After that, when the capacitor C3 is completely charged, the capacitor C1 is no longer charged, and starts discharging through the resistor R1. Note that the diode D1 functions to prevent discharge of the capacitor C1. At the end of the precharge period, the comparator CP1 compares the voltage Vc1 of the capacitor C1 with the reference voltage Vk of the no-load detecting unit 5. If the voltage Vc1 of the capacitor C1 is lower than the reference voltage Vk, the no-load detecting unit 5 is determined to be in a no-load state,
The no-load detecting unit 5 outputs a low level, and the control circuit 3 receives the low level and receives the low level.
1 and Q2 are both turned off. That is, the oscillation of the inverter circuit 2 is stopped.

Next, the filaments f1, f of the discharge lamp LA
2 are connected together, a series circuit of a capacitor C3 and a winding n2 and a series circuit of a filament f1 (capacitor C4), a resistor R3, and a filament f2 (capacitor C5) from a DC power source E via a resistor R4. To charge the capacitor C1. Thereafter, when the capacitor C3 is charged, the DC power source E continues to charge the capacitor C1 through the path of the resistor R4, the filament f1, the resistor R3, the filament f2, the resistor R2, the diode D1, and the capacitor C1. Then, at the end of the precharge period, the voltage Vc1 of the capacitor C1 is compared with the reference voltage Vk. If the voltage Vc1 of the capacitor C1 is higher, the no-load detector 5 determines that the discharge lamp LA is connected. , High
Output level. In response, the control circuit 3 turns on the switching elements Q1 and Q2 of the inverter circuit 2 alternately.
Turn off. That is, the inverter circuit 2 starts oscillating,
After passing through the preheating / starting mode, the discharge lamp LA is led to lighting.

Next, the operation of the Emiless detection circuit of FIG. 16 will be described with reference to FIG. When the discharge lamp LA is in an end-of-life state (Emiless state), it is provided in the transformer T1 by utilizing the fact that the voltage across the discharge lamp when the discharge lamp LA is about to be lit becomes higher than that in a normal discharge lamp. The voltage across the discharge lamp is detected via the secondary winding n3, and if the detected voltage is higher than the reference voltage in the Emiless detector 4, it is determined that the discharge lamp LA is in the Emiless state. After determining that the Emiless state, the Emiless detection section 4 outputs the state to the control circuit 3. The control circuit 3 receives it and
As shown in FIG. 8, the operation of the inverter circuit 2 is intermittently oscillated. If the cycle of the intermittent oscillation operation is Tb, the oscillation operation period is Tb1, and the oscillation stop period is Tb2, Tb = Tb1 + Tb2.

The end-of-life state of the discharge lamp LA includes a break in the filament, and this phenomenon can be detected by the no-load detection circuit. That is, when at least one of the filaments f1 and f2 is broken, there is no loop for charging the capacitor C1 from the DC power supply E. And the no-load detecting unit 5
When the control circuit 3 determines that the filament is broken, it outputs a low level, and the control circuit 3 receives the low level and maintains the inverter circuit 2 to stop the oscillation. At the same time, the operation of the Emiless detection circuit (intermittent oscillation operation) is also stopped.

Thus, when there is no discharge lamp LA,
The inverter circuit 2 keeps the oscillation stopped by the no-load detection operation, and when the discharge lamp LA is in the emiless state, the protection function that the inverter circuit 2 performs the intermittent oscillation operation by the emiless detection operation works, so that the discharge lamp is turned on. Not only can the stress applied to the electronic components in the device be reduced, but also a safe and reliable discharge lamp lighting device can be provided.

[0013]

However, the structure shown in FIG. 16 has two main problems. First, 1
The third problem will be described. The first problem relates to a malfunction of the no-load detection when the input power is turned on in a no-load state. FIG. 19 shows a temporal change of the no-load detection voltage Vc1 after the input power is turned on in the no-load state. As described in the operation of the conventional no-load detection circuit, the no-load detection voltage Vc1 is generated even when the input power is turned on in the no-load state. this is,
This is because even if the filaments f1 and f2 are not present and the DC current loop of the original no-load detection circuit is not established, the capacitor C1 is charged with a charge through the path for charging the capacitor C3. When the charging of the capacitor C3 is completed, the charge of the capacitor C1 starts to be discharged through the resistor R1, and the voltage Vc1 of the capacitor C1 decreases.
If the time Tc1 required for the voltage Vc1 of the capacitor C1 to reach the reference voltage Vk is longer than the precharge period Tpc, the no-load detecting unit 5 ends the precharge period Tpc.
Determines that there is a load in spite of no load, and outputs a High level. As a result, the inverter circuit 2 starts oscillating. When the inverter circuit 2 starts oscillating, a high-frequency voltage is generated on the secondary side of the transformer T1, and a high-frequency current is charged in the capacitor C1 via the diode D1, so that the output of the no-load detection unit 5 is High.
The inverter circuit 2 continues to oscillate while maintaining the h level.
This causes a problem of applying a large stress to the circuit.

The cause of the malfunction in the no-load detection is that it takes a long time to discharge the charge of the capacitor C1 because the time constant of the resistor R1 and the capacitor C1 is large. That is, if the time constant is reduced by lowering the value of the resistor R1 and / or the capacitor C1,
Since the discharge time of one charge is shortened, the above problem may be solved.

However, the resistor R1 and the capacitor C
There is a limit to reducing the value of 1. First, the resistor R
Regarding 1, in determining the constant of the no-load detection circuit, there is a limitation due to the following equation. Vc1 = E · R1 / (R1 + R2 + R3 + R4)> Vk R1> (R2 + R3 + R4) · Vk / (E−Vk) That is, when there is a load, the voltage V of the capacitor C1 is
Since c1 must be higher than the reference voltage Vk, there is a limit even if the resistance R1 is reduced as in the above equation. In addition, if the capacitance of the capacitor C1 becomes small, a problem occurs in the stability of the potential, so that it is not preferable to make the capacitance C1 too small.

As described above, it can be said that the above problem arises because the time constant of the resistor R1 and the capacitor C1 is large. However, there is a limit even if the time constant is made small. I can not say.

Further, as a problem due to the same cause, there is also the following phenomenon. This will be described with reference to FIGS. First, FIG. 20 will be described. In the situation of FIG. 20, when the discharge lamp LA is stably lit with the same circuit configuration as in FIG. 16, the discharge lamp L is removed from the lamp socket on the filament f1 side in order to remove the discharge lamp LA.
This shows a situation where A is pulled out. First, the discharge lamp L
At the moment when A is extracted, the output voltage of the transformer T1 sharply rises, so that the Emiless detection operates and the oscillation of the inverter circuit 2 stops (the oscillation stop period of the intermittent oscillation operation).
When the inverter circuit 2 stops oscillating, the transformer T1
No high-frequency current caused by the high-frequency voltage generated on the next side is charged to the capacitor C1 via the diode D1, and no DC current is supplied from the DC power supply E because there is no filament f1. As a result, the voltage Vc1 of the capacitor C1 decreases, and finally, the no-load detection starts to operate, and the inverter circuit 2 maintains the oscillation stop as it is. At this time, capacitors C3 and C3
When attention is paid to the voltages of C4 and C5, Vc3 ≒ E
(V), Vc4 ≒ E (V), and Vc5 ≒ 0 (V).
That is, the voltage of the DC power supply E is applied to the capacitors C3 and C4 as they are, but almost no voltage is generated for the capacitor C5 because the low-resistance filament f2 exists in parallel with the capacitor C5. And the discharge lamp LA
In order to completely remove the discharge lamp LA, it is assumed that the discharge lamp LA is also pulled out from the lamp socket on the filament f2 side. Even at this stage, the relationship between Vc3 ≒ Vc4 ≒ E and Vc5 ≒ 0 hardly changes.

Next, it is assumed that the discharge lamp LA is mounted again from the filament f1 side of the discharge lamp LA in order to mount the discharge lamp LA again. This situation is shown in FIG. At the moment when the discharge lamp LA is mounted on the lamp socket on the side of the filament f1, the voltage of the capacitor C3 does not change at Vc3 ≒ E, but Vc4 changes the electric charge of the capacitor C4 due to the parallel connection of the low-resistance filament f1. Is rapidly discharged through V.sub.c, so that it tries to decrease to Vc4.apprxeq.0 (V). At the same time, the DC power supply E
4, a filament R1, a resistor R3, a capacitor C5, a winding n6, a resistor R2, a Zener diode ZD1 and a current for charging the capacitor C5 through the path of the diode D1 and the capacitor C1. This current also contributes to charging the capacitor C1. The charging of the capacitor C1 is continued until the charging of the capacitor C5 is completed, that is, Vc5 ≒ E.
When the charge of the capacitor C1 is completed, the charge of the capacitor C1 is changed to the resistance R1.
This phenomenon is similar to the above-described phenomenon that the capacitor C3 is charged when the input power is turned on. While the capacitor C1 progresses from charge to discharge, the voltage Vc1 of the capacitor C1
Is longer than the precharge period Tpc when the time Tc1 until the voltage drops to the reference voltage Vk.
Outputs a High level output, and the inverter circuit 2 starts oscillating. That is, the inverter circuit 2 starts oscillating only by mounting the discharge lamp LA only on the filament f1 side, which is a phenomenon that the no-load detection circuit has to erroneously detect.

The above is the first problem. Next, the second problem will be described. The second problem is a malfunction of the no-load detection circuit at the time of Emiless detection, and the operation is shown in FIG. When the discharge lamp LA enters the emiless state, the capacitor C3 is charged with a DC voltage having the polarity shown in FIG.
May be higher than the DC power supply E of This state is likely to occur when the filament f1 enters the emiless state or when the discharge lamp LA (for example, a lamp of 40 W or more) having a high tube voltage originally enters the emiless state. The inverter circuit 2 performs an intermittent oscillation operation by the Emiless detection circuit. In the oscillation stop period (Tb2 in FIG. 18), the DC power supply E is connected to the capacitor C1 of the no-load detection circuit while Vc3> E. Is not supplied. This state continues until the voltage Vc3 of the capacitor C3 is discharged to a voltage lower than the DC power supply E. Then
Since no current is supplied to the capacitor C1, the charge of the capacitor C1 is discharged by the time constant of the capacitor C1 and the resistor R1, and the voltage Vc1 of the capacitor C1 is changed to the reference voltage Vc.
When the value becomes k or less, the no-load detection circuit operates, and the operation of the Emiless detection circuit, that is, the intermittent oscillation operation is stopped to keep the oscillation stopped state. However, after that, when the charge of the capacitor C3 is discharged and Vc3 ≦ E, the charging current flows from the DC power supply E to the capacitor C1 again, and the voltage Vc1 of the capacitor C1 increases. The unit 5 outputs a High level, and the inverter circuit 2 starts oscillating again.

By repeating this state, when the discharge lamp LA is in the emiless state, the oscillation stop period Tb2 is reduced by the operation of the no-load detection circuit, although the intermittent oscillation operation should be performed at the cycle Tb. Very short,
The intermittent oscillation cycle Tb is also shortened, and as a result, the preheating / starting mode in which a high voltage is applied to the discharge lamp LA is repeated in a short cycle, so that stress on components of the inverter circuit 2 and the transformer T1 increases. In addition, there is a problem that heat generation is increased.

The cause of the malfunction of the no-load detection circuit is that the time constant of the resistor R1 and the capacitor C1 is small.
That is, the charge of the capacitor C1 is immediately discharged.

Although the two problems have been described above, considering the causes, it can be understood that the contents are mutually contradictory. In other words, the first problem is caused by the large time constant of the resistor R1 and the capacitor C1, whereas the second problem is caused by the small time constant of the resistor R1 and the capacitor C1. Things. Therefore, it is very difficult to solve both of these two problems with the time constant of the resistor R1 and the capacitor C1.

The present invention has been made in view of the above two problems, and an object of the present invention is to provide a discharge lamp lighting device having the above-mentioned no-load detecting circuit and Emiless detecting circuit, which is capable of operating in a no-load state. When the input power is turned on or when the discharge lamp is incompletely mounted, the no-load detection circuit operates reliably, and when the emitter of the discharge lamp is detected, the intermittent oscillating operation is performed reliably to reduce the stress on the parts. An object of the present invention is to provide a highly reliable discharge lamp lighting device.

[0024]

In order to achieve the above-mentioned object, the present invention provides the above-mentioned no-load detecting circuit, in which means for changing the detected voltage is added so that the detected voltage is changed in a predetermined period. It was done. However, the certain period is at least the precharge period Tpc.
Is the oscillation stop period. Another solution is
The reference voltage level to be compared when the no-load detecting circuit determines the presence or absence of the filament is changed in a predetermined period. Here, the certain predetermined period is at least the precharge period Tpc and / or at least the oscillation stop period during the intermittent oscillation operation based on the Emiless detection.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, as described in the first problem of the conventional example, there is a limit even if the resistance R1 and the capacitor C1 of the no-load detecting circuit shown in FIG.
Therefore, the time constant of the resistor R1 and the capacitor C1 is set so large that the malfunction of the no-load detection circuit due to the decrease of the voltage Vc1 of the capacitor C1 at the time of Emiless detection described in the second problem of the conventional example is eliminated. As a result, the intermittent oscillation operation at the time of Emiless detection operates normally.

The remaining problem 1 is that the no-load detection circuit malfunctions and starts oscillating when the input power is turned on in the no-load state or when the lamp is incompletely mounted after the lamp is removed. is there. To address this issue,
As a means for solving the above-mentioned problem, there is a method of varying the detection voltage Vc1 at least in the precharge period Tpc. The operation will be described with reference to FIG. FIG. 2 shows a temporal change of the no-load detection voltage Vc1 after the input power is turned on in the no-load state. First, to explain once again from the conventional example, when the input power is turned on in a no-load state, the capacitor C1 is also charged through the path for charging the DC cut capacitor C3. When the charging of the DC cut capacitor C3 is completed, the charge of the capacitor C1 is discharged via the resistor R1, so that the voltage Vc1 of the capacitor C1 decreases. At the moment when the precharge period Tpc ends, If Vc1> Vk, it is determined that a discharge lamp load exists, and oscillation starts. In the precharge period Tpc of FIG. 2, the portion where the voltage Vc1 of the capacitor C1 is flat is a predetermined voltage (Vz in the conventional example) at the Zener diode ZD1.
d1 = 2Vk). Further, in the precharge period Tpc, the drain-source voltage Vds of the switching element Q3 (FIG. 17)
3 is zero.

Therefore, in the present invention, a variable means of the detection voltage Vc1 is provided in the no-load detection circuit, and the detection voltage is reduced at least during the precharge period Tpc. Then, even if the time constants of the resistor R1 and the capacitor C1 are not set small, the voltage V
The time Tc1 until c1 reaches the reference voltage Vk is Tc
1 <Tpc, and after the elapse of the precharge period Tpc, Vc1 <Vk, the no-load detecting circuit operates normally, and it is determined that there is no load, so that oscillation does not start.
If there is a discharge lamp load, the precharge period T
Since Vc1> Vk must be satisfied at the end of pc,
It is necessary to carefully design the degree of reduction of the detection voltage Vc1. Further, after the start of the oscillation after it is determined that there is a load after the elapse of the precharge period Tpc, at least when the oscillation continues after the start mode, the voltage V
It is necessary to return c1 to the original level. This is because when the discharge lamp LA is in the emiless state, if the voltage Vc1 of the capacitor C1 remains at a low level, the voltage Vc1 of the capacitor C1 immediately falls below the reference voltage Vk, and the second problem of the conventional example occurs. is there.

In addition, the same effect can be obtained with respect to the problem that the oscillation starts at the time of incomplete mounting after the discharge lamp has been attached / detached. As described above, the first problem of the conventional example can be solved, and a safe and reliable discharge lamp lighting device can be provided. Hereinafter, specific circuit examples will be described in the embodiments.

(Embodiment 1) FIG. 1 is a circuit diagram of Embodiment 1 of the present invention. The circuit configuration is the same as the conventional circuit diagram (FIG. 16) except for the following points. Between the connection point b of the resistor R4 and the filament f1 and the ground, that is, the resistance R
The point is that a series circuit of a resistor R10 and a switch SW is newly provided in parallel with the series circuit of R1, R2 and R3.

When comparing the voltage Vb at point b when the switch SW is off and when the switch SW is on, the switch S
When W is on, the resistor R10 is connected to the resistors R1, R2, R
3 in parallel with the series circuit of FIG.
The voltage Vb at the point is lower than when the switch SW is off. Therefore, the level of voltage Vc1 of capacitor C1 also decreases. Utilizing the above, the switch SW is turned on at least during the precharge period Tpc, and the level of the voltage Vc1 of the capacitor C1 is reduced. Further, at least at the time of oscillation after the start mode, the switch SW is turned off, and the voltage Vc of the capacitor C1 is turned off.
Try to raise the level of 1. As described above, the two problems of the conventional example can be solved, and a safe and reliable discharge lamp lighting device can be provided without applying great stress to circuit components.

(Embodiment 2) FIG. 3 is a circuit diagram of Embodiment 2 of the present invention. The circuit configuration is obtained by adding the following circuit to the circuit diagram of the first embodiment shown in FIG. A diode D is connected between the connection point between the winding n3 and the diode D2 and the ground.
3. A series circuit of resistors R7 and R8 is connected, and resistors R7 and R8 are connected.
The discharge lamp attachment / detachment detection unit 7 is connected to the connection point 8.
The output of the discharge lamp attachment / detachment detection unit 7 is input to the control circuit 3. Here, the diode D3, the resistors R7 and R8, and the discharge lamp detachment detection unit 7 constitute a discharge lamp detachment detection circuit. The role and circuit operation of the discharge lamp detachment detection circuit will be described below.

First, the role of the discharge lamp attachment / detachment detection circuit is at least one of the filaments f1 and f2 of the discharge lamp LA.
When one filament is removed during the inverter oscillation operation (during lighting), that is, when the discharge lamp is attached / detached, it is detected earlier than the Emiless detection circuit, and the oscillation of the inverter circuit 2 is stopped. The circuit operation is very similar to the Emiless detection circuit, and the discharge lamp LA is lit while the inverter circuit 2 is oscillating and the discharge lamp LA is lit.
Is removed, using the fact that the voltage across the winding n2 becomes higher than when the discharge lamp is turned on, a voltage rise is detected via the secondary winding n3 provided in the transformer T1, and the detected voltage is If the voltage is higher than the reference voltage set inside the discharge lamp attachment / detachment detecting section 7, it is determined that the discharge lamp LA is attached / detached, and the oscillation of the inverter circuit 2 is stopped via the control circuit 3.

Here, the difference between discharge lamp detachment detection and Emiless detection will be described with reference to FIG. FIG. 4 shows the generated voltage Vn3 of the winding n3 in the normal lighting state, the Emiless state, and the no-load state. Note that the horizontal axis is the oscillation frequency f of the inverter circuit 2. F0 is the natural oscillation frequency of the inductor L1 and the capacitor C2.
The generated voltages Vn3 of the winding n3 in the normal lighting state, the Emiless state, and the no-load state at the oscillation frequency f = f1 (when lighted) of the inverter circuit 2 are point A, point B, and point C, respectively. What can be said here is that the magnitude relation is point A <point B <point C, but point A and point B are relatively close values, whereas point C has a considerably high voltage. is there. That is, the voltage Vn3 generated by the winding n3 in the normal lighting and the Emiless state is higher in the Emiless state than in the Emiless state.
In both cases, since the discharge lamp LA is in a discharge state,
Not a big difference. However, since the equivalent resistance of the discharge lamp is infinite under no load, the pure inductor L1
And the resonance voltage of the capacitor C2 is generated, and the generated voltage Vn3 of the winding n3 also becomes a considerably high voltage. From the above, in the Emiless detection circuit, it is necessary to connect a capacitor C6 for voltage stabilization in parallel with the resistor R6 in order to accurately determine whether the circuit is in the Emiless state or during normal lighting. However, the connection of the capacitor C6 causes a time for charging the capacitor C6 to occur as a detection delay. Therefore, in order to quickly detect the attachment / detachment of the discharge lamp, a detection circuit in which only the capacitor C6 is removed from the configuration of the Emiless detection circuit is required separately. Needless to say, the setting of the partial pressure ratio between the resistors R7 and R8 is not detected in the Emiless state, but must be detected and detected only when the discharge lamp is attached or detached.

From the above, the new installation of the discharge lamp detachment detection circuit shortens the time until the oscillation stops when the discharge lamp is detached and attached, and performs high-speed and reliable protection in a no-load state regardless of whether or not the inverter circuit oscillates. Now you can do it.

Next, this is the main subject of the present embodiment. The ON period of the switch SW is not limited to the precharge period Tpc of the first embodiment, but the entire period in which the discharge lamp stops oscillating under no load condition. We will include the period. This corresponds to a period in which the oscillation is stopped by the detection of the detachment of the discharge lamp and the oscillation is stopped by the detection of no load. Further, at least at the time of oscillation after the start mode, the switch SW is turned off.

As described above, the two problems of the conventional example can be solved similarly to the first embodiment. In addition, the capacitors connected in parallel to the filaments f1 and f2 when no load is applied (the capacitors in FIG. 3). Since the DC voltage applied to C4 and C5) is not the voltage E from the DC power supply but the voltage Vb at the point b divided by the resistors R4 and R10, the withstand voltage of the capacitors C4 and C5 can be reduced. . Another effect is that the voltage between the point b and the point c in FIG.
Instead, the voltage can be reduced to the voltage Vb at the point b divided by the resistors R4 and R10.

In this embodiment, the discharge lamp detachment detection is detected from the lamp voltage at both ends of the discharge lamp. However, it may be detected from the resonance voltage or the resonance current, or the lamp current or the filament current. .

(Embodiment 3) Although the present embodiment has the same circuit configuration as that of FIG. 3, the ON period of the switch SW is added to the precharge period Tpc and the oscillation stop period at the time of no load in the second embodiment, and Include time periods. That is, a period during which the inverter oscillates in a light load state (preheating and starting mode) before the discharge lamp LA is turned on in a stable state is also included in the ON period of the switch SW. It should be noted that, from the time when the start mode ends and the mode shifts to the lighting mode, the switch SW
To turn off.

The effect obtained by this is the effect described in the second embodiment, that is, the two problems of the conventional example are solved, and when there is no load, each filament f1, f2
In addition to reducing the applied voltage of the capacitors C4 and C5 connected in parallel with each other, and also reducing the secondary voltage in the no-load state, the DC power supply voltage may be excessively boosted when the discharge lamp is lightly loaded. In a DC power supply circuit (for example, a power supply circuit in which a boosting chopper circuit is provided in a stage preceding a smoothing capacitor), an effect of reducing the boosting action is also added. That is, the power loss consumed by the conventional no-load detection circuit is P = IV = V ²
/ R = E ² / (R1 + R2 + R3 + R4) (W) In this embodiment, since the resistor R10 is connected in parallel with the series circuit of the resistors R1, R2 and R3, the resistance value of the entire no-load detection circuit is obtained. Becomes smaller, and accordingly, the power consumption becomes larger than that of the conventional example. Thereby, an effect of reducing an excessive boost of the DC power supply E is produced.

(Embodiment 4) FIG. 5 is a circuit diagram of Embodiment 4 of the present invention. In this embodiment, the detection voltage Vc of the no-load detection circuit is used.
This is an example of a circuit in which the DC power supply voltage E of the no-load detection circuit is changed to E1 and E2 as means for making 1 variable. The circuit configuration is such that the DC power supply circuit 1 is a series circuit of smoothing capacitors C9 and C10 in the circuit diagram of FIG.
The terminals are taken out from the high voltage side of the capacitors C10 and C9, respectively, and connected to the terminals a1 and a2 of the switch SW. The terminal a of the switch SW is connected to the resistor R4 of the no-load detection circuit.
Connect to The circuit operation is performed at least during the precharge period T
The switch SW is connected to the terminal a1 during pc, and is connected to the terminal a2 at least after the start mode ends.
E1 is a DC voltage across the series circuit of the capacitors C9 and C10, E2 is a DC voltage across the capacitor C10, and naturally E1> E2. Thereby, the same effect as in the first embodiment can be obtained. Also, as in the second and third embodiments, a discharge lamp detachment detection circuit is added, and the connection period of the switch SW to the terminal a1 is set as in the second or third embodiment, thereby adding the second or third embodiment. The objective effect can also be obtained.

(Embodiment 5) FIG. 6 is a circuit diagram of Embodiment 5 of the present invention. The circuit configuration is such that the DC power supply circuit in the circuit of FIG. 5 is changed to a double voltage power supply circuit. With one polarity of the AC power supply Vs, the capacitor C9 is charged via the diode D6, and with the other polarity, the capacitor C10 is charged via the diode D7. As in the circuit of FIG. 5, terminals are respectively drawn from the high voltage sides of the capacitors C10 and C9 and connected to the terminals a1 and a2 of the switch SW, and the terminal a of the switch SW is connected to the resistor R4 of the no-load detection circuit. The circuit operation of the switch SW is the same as that of the fourth embodiment, and the effect is the same as that of the fourth embodiment.

(Embodiment 6) FIG. 7 is a circuit diagram of Embodiment 6 of the present invention. The circuit configuration is the same as that of FIG. 5 except that the voltage input from the DC power supply circuit 1 to the inverter circuit 2 is changed to E2 instead of E1. First, the resonance inductor L1 and the capacitor C2 connected to the primary side of the transformer T1 are eliminated, and instead, the transformer T1 also serves as the inductor L1 as a leakage transformer, and the capacitor C2 is connected to both ends of the discharge lamp LA. Connected to the transformer side for secondary side resonance. Capacitors C4 and C5 were connected to both ends of the filaments f1 and f2, respectively, as measures against arc discharge during loose contact. The no-load detection circuit also has a resistor R4 and a filament f.
1 and the connection point c between the resistor R2 and the filament f2 are changed from the secondary winding side of the transformer T1 to the non-secondary winding side. Conversely, the resistor R3 is connected from the non-secondary winding side to the secondary winding side. Changed to the next winding side.

The terminals a1 and a2 of the switch SW are connected to the high voltage side of the capacitors C10 and C9, respectively. The operation of the inverter circuit 2 is different from that of the fourth or fifth embodiment in that the primary resonance of the transformer T1 is changed to the secondary resonance, and the supply of the filament current to the filaments f1 and f2 during preheating is performed by the inductor L1. Except that the supply from the secondary winding is changed to the resonance current to the capacitor C2,
It is basically the same. The circuit operation of the switch SW is the same as that of the fourth embodiment, and the effect is the same as that of the fourth embodiment.

(Embodiment 7) FIG. 8 is a circuit diagram of Embodiment 7 of the present invention. In this embodiment, the detection voltage V of the no-load detection circuit is used.
This is a circuit example in which the voltage dividing element in the no-load detection circuit is made variable as means for making c1 variable. The circuit configuration is obtained by changing the following points from the circuit diagram of FIG. First, the resonance inductor L1 and the capacitor C2 connected to the primary side of the transformer T1 are eliminated, and the transformer T1 also serves as an inductor L1 as a leakage transformer, and the capacitor C2 is connected to both ends of the discharge lamp LA. Connected to the transformer side for secondary side resonance.
In the no-load detection circuit, a parallel circuit of the resistor R10 and the switch SW was inserted between the connection point b between the filament f1 and the capacitor C3 and the resistor R4.

In the switching operation of the switch SW, the switch SW is turned off at least during the precharge period Tpc.
W is turned on. When the switch SW is off, the level of the detection voltage Vc1 becomes lower because a resistor R10 is newly added to the conventional no-load detection circuit. Also,
When the switch SW is turned on, the level returns to the level of Vc1 as in the conventional example.

As described above, the two problems of the conventional example can be solved, and a safe and reliable discharge lamp lighting device can be provided without applying great stress to circuit components. The parallel circuit of the resistor R10 and the switch SW is inserted from the connection point a with the DC power supply to the diode D
1, may be inserted anywhere in the no-load detection circuit loop up to the connection point of the zener diode ZD1.

(Eighth Embodiment) FIG. 9 is a circuit diagram of an eighth embodiment of the present invention. The circuit configuration is different from that of FIG. 8 in that the connection position of the resistor R10 and the switch SW is changed to form a series circuit of the resistor R10 and the switch SW, which is connected to both ends of the resistor R2. The switching operation of the switch SW lowers the level of the detection voltage Vc1 of the no-load detection circuit by turning off the switch SW at least during the precharge period Tpc. In addition, at least after the start mode ends, the switch S
When W is turned on, the combined resistance is reduced by connecting the resistors R2 and R10 in parallel, and the level of the detection voltage Vc1 is returned to the level as in the related art. The effects obtained from the above are the same as in the seventh embodiment. The connection position of the series circuit of the resistor R10 and the switch SW is not limited to both ends of the resistor R2, but may be located at both ends of the resistor R3 or R4.

(Embodiment 9) FIG. 10 is a circuit diagram of Embodiment 9 of the present invention. The circuit configuration changes the connection position of the resistor R10 and the switch SW from FIG.
And is connected to the low voltage side of the resistor R3, that is, between the connection point of the resistor R3 and the filament f2 and the ground. The switching operation of the switch SW is performed at least during the precharge period Tpc.
W is turned on to lower the level of the detection voltage Vc1 of the no-load detection circuit. Further, at least after the start mode ends, the switch SW is turned off to return the level of the detection voltage Vc1 to the level as in the conventional example. The effect obtained from the above is the seventh embodiment.
Is the same as Note that the non-ground side of the series circuit of the resistor R10 and the switch SW is not limited to the low voltage side of the resistor R3, but point b (the embodiment in FIG. 1), the high voltage side of the resistor R3, the point c (high voltage side of the resistor R2), It may be connected to R2 low voltage side.

(Embodiment 10) FIG. 11 shows Embodiment 1 of the present invention.
0 is a circuit diagram of FIG. The circuit configuration is the same as that of the resistor R1 shown in FIGS.
0 and the switch SW, a Zener diode ZD2
A series circuit of the switch SW and the Zener diode ZD1
Are connected to both ends. Zener diode ZD
1 and ZD2 to Vzd1 and Vzd, respectively.
If Vzd1> Vzd2, the switch SW
Switching operation at least in the precharge period Tp
By turning on during c, the detection voltage V of the no-load detection circuit
C1 is controlled by Vzd2, and the level of the detection voltage Vc1 is lowered. Further, at least after the start mode ends, the switch SW is turned off, and the detection voltage Vc1 of the no-load detection circuit is set to Vz.
By dominating with d1, the level of the detection voltage Vc1 is increased.

When Vzd1 <Vzd2, the switching operation of the switch SW is turned off at least during the precharge period Tpc, so that the detection voltage Vc1 of the no-load detection circuit is controlled by Vzd1, and the level of the detection voltage Vc1 is controlled. make low. The switch SW is turned on at least after the start mode ends, and the detection voltage Vc1 of the no-load detection circuit is turned on.
Is controlled by Vzd2, thereby increasing the level of the detection voltage Vc1. The effects obtained as described above are the same as in the seventh embodiment.

(Embodiment 11) FIG. 12 shows Embodiment 1 of the present invention.
1 is a circuit diagram of FIG. The circuit configuration is obtained by changing the following points from the circuit diagram of FIG. That is, a parallel circuit of the Zener diode ZD2 and the switch SW is inserted between the anode side of the Zener diode ZD1 and the ground. The switching operation of the switch SW turns on the switch SW at least during the precharge period Tpc,
By controlling the detection voltage Vc1 of the no-load detection circuit only by Vzd1, the level of the detection voltage Vc1 is reduced.
Further, at least after the start mode ends, the switch SW is turned off, and the detection voltage Vc1 of the no-load detection circuit is changed to Vzd1 +
By dominating with Vzd2, the level of the detection voltage Vc1 is increased. The effects obtained as described above are the same as in the seventh embodiment.

(Embodiment 12) FIG. 13 shows Embodiment 1 of the present invention.
2 is a circuit diagram of FIG. Hereinafter, the circuit configuration will be described. The commercial AC power supply Vs is connected to an AC input terminal of the full-wave rectifier DB. A capacitor C11 is connected to the DC output terminal of the full-wave rectifier DB, and a capacitor C8 and diodes D6 and D7 are connected in series to both ends of the capacitor C11. A capacitor C is connected between both ends of the diode D6.
9 are connected in parallel. A series circuit of switching elements Q1 and Q2 is connected in parallel to both ends of the capacitor C8. A series circuit of the capacitor C10 and the primary winding n1 of the transformer T1 is connected between the connection point of the switching elements Q1 and Q2 and the connection point of the diodes D6 and D7. A capacitor C3 and a series circuit of discharge lamps LA1 and LA2 are connected to the secondary winding n2 of the transformer T1 as a load circuit, and the secondary winding n2 of the series circuit of the discharge lamps LA1 and LA2 is connected to the opposite side (non-power supply). Side), a capacitor C2 is connected in parallel. Here, transformer T1, capacitor C
2. An inverter load circuit is constituted by the discharge lamps LA1 and LA2, and the switching elements Q1 and Q2 are alternately turned on and off at a high frequency, that is, by oscillating.
The discharge lamps LA1 and LA2 light up.

A series circuit of an inductor L1 and a diode D5 inserted in the opposite direction to the capacitor C7 is connected between both ends of the capacitor C8, and a connection point between the capacitor C7 and the diode D5 and a connection between the switching elements Q1 and Q2. The diode D4 is inserted between the point and the forward direction. Thereby, the switching element Q2 and the diode D
4, D5, inductor L1, and capacitors C7, C8 form a step-down chopper circuit. Further, a series circuit of a resistor R10, a diode D8, and a switching element Q3 is connected between the source terminal of the switching element Q2 and the cathode terminal of the diode D4. Here, a rush current prevention circuit (corresponding to the circuit 6 in FIG. 17) is configured by the resistor R10, the diode D8, and the switching element Q3.

A capacitor C is connected to the winding n3 of the transformer T1.
4, a series circuit of filaments f2 and f3 is connected. This allows a filament current to flow through the filaments f2 and f3 during preheating before the discharge lamps LA1 and LA2 are turned on. One terminal of the winding n4 is connected to the ground, and the other terminal is connected to the anode terminals of the diodes D2 and D3. A series circuit of resistors R6 and R7 is connected between the cathode terminal of the diode D2 and the ground, and a capacitor C5 is connected in parallel with the resistor R7 to form an Emiless detection circuit. A resistor R8 is connected between the cathode terminal of the diode D3 and the ground.
And R9 are connected in series to form a discharge lamp detachment detection circuit. Further, a resistor R is applied from the high voltage side of the full-wave rectifier DB.
5, filament f1, resistance R4, filament f2
By connecting f3, resistor R3, filament f4, resistor R2, zener diode ZD1, diode D1, resistor R1, and capacitor C1, a no-load detection circuit is configured. A resistor R11 is connected between the low voltage side of the resistor R5 and the connection point between the resistor R10 and the diode D8 and the switching element Q3. The control circuit 3 controls on / off operations of the switching elements Q1, Q2, Q3.

Next, the circuit operation will be described. This discharge lamp lighting device can be roughly divided into an inverter circuit and a step-down chopper circuit. First, the operation of the inverter circuit will be described. At the time of lighting, when the switching element Q1 is on and the switching element Q2 is off, the capacitor C8, the switching element Q1, the capacitor C10, the transformer T1 (winding n1), and the capacitor C
A current flows through the path of C9 and C8, and the capacitor C9 is charged. Also, from the input side, a full-wave rectifier DB, a switching element Q1, a capacitor C10, a transformer T1 (winding n
1) A current flows through the path of the diode D7 and the full-wave rectifier DB. The condition for this current to flow is that the capacitor C
The current flows when the sum of the voltage across the capacitor 8 and the voltage across the capacitor C9 is lower than the voltage across the full-wave rectifier DB. Next, when the switching element Q1 is off and the switching element Q2 is on, the capacitor C9 and the transformer T
1 (winding n1), a capacitor C10, a switching element Q2, and a capacitor C9. By this operation, the capacitor C9 is discharged. When the discharge is completed, a current flows through the diode D6, and the diode D6,
A loop current of the transformer T1 (winding n1), the capacitor C10, the switching element Q2, and the diode D6 flows. By operating in this way, a high-frequency voltage is generated across the primary side of the transformer T1, and the discharge lamps LA1, L
A2 lights up.

Next, the operation of the step-down chopper circuit will be described. At the time of lighting, when the switching element Q2 is on (during energizing operation of the diode D6), the full-wave rectifier D
B, inductor L1, capacitor C7, diode D
4. A current flows through the path of the switching element Q2, the diodes D6 and D7, and the full-wave rectifier DB. This operation charges the capacitor C7. Also, the switching element Q
2 is on (during discharging capacitor C9), capacitor C8, inductor L1, capacitor C7, diode D
4. A current flows through the path of the switching element Q2 and the capacitor C8. By this operation, the capacitor C7 is charged by the capacitor C8. Next, when the switching element Q2 is turned off, a current flows through a path of the inductor L1, the capacitor C7, the diode D4, the (reverse diode built in the switching element Q1), and the inductor L1.
This operation releases the energy of the inductor L1. By the above operation, a voltage by the step-down chopper circuit is generated at both ends of the capacitor C7.

The operation of the inrush current prevention circuit by the resistor R10, the diode D8 and the switching element Q3 and the operation of the Emiless detection circuit from the time when the commercial AC power supply Vs is turned on are the same as those of the conventional example. The operation of the circuit is the same as that of the second embodiment, and the description is omitted.

Next, with respect to the no-load detection circuit which is the main subject of this embodiment, means for varying the level of the detection voltage Vc1 include a resistor R11 and a switching element Q3.
Is used. In other words, utilizing that the switching element Q3 is turned on to charge the capacitor C7 only during the precharge period Tpc, a series circuit of the resistor R11 and the switching element Q3 can be added to the original no-load detection circuit. As a result, the voltage Vb at the point b can be lowered, and the level of the detection voltage Vc1 can also be lowered. After the end of the precharge period Tpc, the switching element Q3 is turned off. Therefore, the voltage Vb at the point b is determined according to the original resistance division ratio of the no-load detection circuit, and the level of the detection voltage Vc1 also increases to the original voltage. . The diode D8 is connected to the resistors R5 and R5 from the power supply E when the switching element Q2 is turned on during the inverter oscillation operation.
11, R10, a switching element Q2, and a diode for preventing a current from flowing through the path of the power supply E.

As a result, the two problems of the conventional example can be solved, and a safe and reliable discharge lamp lighting device can be provided. In addition, a discharge lamp detachment detection circuit is also provided, and when the discharge lamp is detached at the time of lighting, the oscillating operation of the switching elements Q1 and Q2 is immediately stopped. At this time, the switching element Q3 is also switched on from off. If this is done, the voltage Vb at point b drops during the oscillation stop period in the no-load state. Therefore, the voltage between the points b and c, that is, the no-load secondary voltage can be reduced.
With a circuit configuration in which a capacitor is connected to both ends of the filaments f1 and f4, the withstand voltage of the capacitor can be reduced.

(Embodiment 13) FIGS. 14 and 15 are conceptual diagrams of Embodiment 13 of the present invention. The circuit configuration of the present embodiment is the same as that of the conventional example.
Is variable, thereby solving the two problems of the conventional example. First, FIG. 14 is a time chart showing a change in the no-load detection voltage Vc1 after the input power is turned on in a no-load state. As described in the problem of the conventional example, in the conventional example, the capacitor C1 is also charged in the path for charging the DC cut capacitor C3 connected in series to the discharge lamp LA, and when the charging of the DC cut capacitor C3 is completed. Although the charge of the capacitor C1 is discharged via the resistor R1 and the detection voltage Vc1 of the no-load detection circuit also decreases, when Vc1> Vk after the end of the precharge period Tpc, the discharge lamp despite no load is present. There is a problem that the inverter circuit 2 oscillates when it is determined that a load exists. Therefore, in this embodiment, means for changing the reference voltage Vk is added so that the level of the reference voltage Vk becomes higher than that of the conventional example at least during the precharge period Tpc. By doing so, it is possible to ensure that Vc1 <Vk at the end of the precharge period Tpc, and the problem as in the conventional example can be solved.

In FIG. 14, the period Tvk during which the level of the reference voltage Vk is shifted high is the precharge period Tp.
c, but preferably at the level of the conventional reference voltage Vk, the detection voltage Vc of the no-load detection circuit.
It is better to set the period Tvk to be longer than the time Tc1 until 1 reaches the reference voltage Vk. In addition, the above-mentioned thing has the same effect also about the subject which starts oscillation at the time of incomplete mounting after discharge lamp attachment / detachment.

FIG. 15 is a time chart showing a change in the no-load detection voltage Vc1 when the discharge lamp is in the Emiless state. First, in the conventional example, intermittent oscillation should be performed at the period Tb. However, when the oscillation is performed in the Emiless state, a voltage higher than the DC power supply is generated in the DC cut capacitor C3, and the DC cutoff is performed during the intermittent oscillation oscillation stop period. Capacitor C3
Until the voltage of the DC power supply becomes equal to or less than the voltage of the DC power supply, the DC power supply stops charging the capacitor C1.
<Vk, and there is a problem that the period of intermittent oscillation becomes shorter than Tb due to the operation of no-load detection.

Therefore, in this embodiment, means for making the reference voltage Vk variable is added, and the level of the reference voltage Vk is lower than that of the conventional example at least during the oscillation stop period during the intermittent oscillation operation by Emiless detection. Therefore, even if the no-load detection voltage Vc1 may decrease, Vc1>
Vk. As a result, the above-described problems of the conventional example can be solved.

The means for increasing the reference voltage Vk or decreasing the reference voltage Vk described in the present embodiment may be implemented by both means, or the capacitor C1 and the resistor R1 may be used.
In consideration of the time constant, only one of them may be adopted.

[0065]

As described above, the effect of the present invention is that only when the input power is turned on with no load or when the discharge lamp is detached while the discharge lamp is lit, and then the discharge lamp is incompletely mounted. The no-load detection circuit detects the problem that the inverter circuit starts oscillating and the problem that the no-load detection operates due to the charging voltage of the DC cut capacitor during operation of the Emiless detection circuit and shortens the original intermittent oscillation cycle. The above two problems can be solved by making the voltage variable at least during the precharge period. In addition, the level of the detection voltage of the no-load detection circuit can be changed not only during the precharge period, but also during the period in which the oscillation stops in the no-load state and the period in which the inverter oscillates when the discharge lamp is in the light-load state. This reduces the withstand voltage of the capacitor connected in parallel with the filament, reduces the no-load secondary voltage,
Then, there is an effect that the DC current excessive boosting at the time of light load of the discharge lamp is reduced. Also, regarding the above two conventional problems,
The problem can also be solved by making the reference voltage level of the no-load detection circuit variable. As described above, not only can the erroneous detection of the no-load detection circuit be eliminated, but also the component stress of the inverter circuit can be reduced, and a safer and more reliable discharge lamp lighting device can be provided.

[Brief description of the drawings]

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

FIG. 2 is an operation explanatory diagram of the first embodiment of the present invention.

FIG. 3 is a circuit diagram according to a second embodiment of the present invention.

FIG. 4 is an operation explanatory diagram of a second embodiment of the present invention.

FIG. 5 is a circuit diagram according to a fourth embodiment of the present invention.

FIG. 6 is a circuit diagram of a fifth embodiment of the present invention.

FIG. 7 is a circuit diagram according to a sixth embodiment of the present invention.

FIG. 8 is a circuit diagram of a seventh embodiment of the present invention.

FIG. 9 is a circuit diagram of an eighth embodiment of the present invention.

FIG. 10 is a circuit diagram of a ninth embodiment of the present invention.

FIG. 11 is a circuit diagram of a tenth embodiment of the present invention.

FIG. 12 is a circuit diagram of an eleventh embodiment of the present invention.

FIG. 13 is a circuit diagram according to a twelfth embodiment of the present invention.

FIG. 14 is an explanatory diagram of an operation when power is turned on in Embodiment 13 of the present invention.

FIG. 15 is an explanatory diagram of an operation at the end of life of a thirteenth embodiment of the present invention.

FIG. 16 is a circuit diagram of a conventional example.

FIG. 17 is a circuit diagram showing a configuration of a main part of a conventional example.

FIG. 18 is an operation explanatory diagram of a conventional example.

FIG. 19 is a waveform chart for explaining a first problem of the conventional example.

FIG. 20 is a circuit diagram showing a state in which one filament is detached in a conventional example.

FIG. 21 is a circuit diagram showing a state in which the other filament is detached in the conventional example.

FIG. 22 is a waveform chart for explaining a second problem of the conventional example.

[Explanation of symbols]

 Reference Signs List 1 DC power supply circuit 2 Inverter circuit 3 Control circuit 4 Emiless detector 5 No-load detector SW switch

Claims (11)

[Claims] 1. A DC power supply circuit for converting an AC power supply to a DC power supply, and an inverter circuit for converting the DC power supply to a high frequency and supplying a high frequency power to a load circuit comprising a series circuit of a DC cut capacitor and a discharge lamp. The presence or absence of a filament of the discharge lamp is determined by the presence or absence of a DC current from a DC voltage source including the DC power supply, and when it is determined that there is no filament, a DC detection circuit for stopping oscillation of the inverter circuit is provided. And a timer for stopping the oscillation of the inverter circuit for a certain time when the discharge lamp is mounted when the power is turned on or in a state where the power is turned on and the no-load detection circuit determines that there is a filament. In a discharge lamp lighting device having a control circuit having a function, a means for varying the detection voltage of the no-load detection circuit is added, A discharge lamp lighting device wherein the detection voltage is changed in a certain predetermined period. 2. The discharge period according to claim 1, wherein the predetermined period is a period during which the control circuit stops oscillation of the inverter circuit when at least the no-load detection circuit determines that there is a filament. Lighting device. 3. The predetermined period includes a period in which the control circuit stops oscillation of the inverter circuit when the no-load detection circuit determines that there is a filament, and a period in which the no-load detection circuit determines that there is no filament. 2. The discharge lamp lighting device according to claim 1, wherein the period includes all periods in which oscillation stops in a no-load state, including the oscillation stop period. 4. The predetermined period includes a period in which the control circuit stops oscillation of the inverter circuit when the no-load detecting circuit determines that there is a filament, and a period in which the no-load detecting circuit determines that there is no filament. In addition to the period during which oscillation stops in a no-load state, including the period during which oscillation stops, the period during which the inverter circuit oscillates at a light load before the discharge lamp is turned on in a stable state The discharge lamp lighting device according to claim 1, comprising: 5. The discharge lamp lighting device according to claim 4, wherein the light load state is a time of preheating and a time of starting. 6. The means for varying the detection voltage of the no-load detection circuit is a means for changing the DC voltage of a DC voltage source of the no-load detection circuit. The discharge lamp lighting device according to any one of the above. 7. The means for varying the detection voltage of the no-load detection circuit is means for varying the voltage division ratio of a voltage dividing element in the no-load detection circuit.
The discharge lamp lighting device according to any one of claims 1 to 5. 8. A DC power supply circuit for converting an AC power supply to a DC power supply, an inverter circuit for converting the DC power supply to a high frequency and supplying a high frequency power to a load circuit comprising a series circuit of a DC cut capacitor and a discharge lamp. The presence or absence of a filament of the discharge lamp is determined by the presence or absence of a DC current from a DC voltage source including the DC power supply, and when it is determined that there is no filament, a DC detection circuit for stopping oscillation of the inverter circuit is provided. And a timer for stopping the oscillation of the inverter circuit for a certain time when the discharge lamp is mounted when the power is turned on or in a state where the power is turned on and the no-load detection circuit determines that there is a filament. A control circuit having a function and an end-of-life state of the discharge lamp are detected, and the inverter circuit starts and stops oscillating at predetermined cycles. And a non-load detecting circuit for detecting the no-load while the DC voltage charged in the DC cut capacitor is discharged during the oscillation stop period during the intermittent oscillation operation at the end of life of the discharge lamp. In the discharge lamp lighting device having a configuration in which the intermittent oscillation cycle of the inverter circuit is shorter than the predetermined cycle by the operation of the circuit, the reference voltage to be compared when the no-load detection circuit determines the presence or absence of the filament. A discharge lamp lighting device comprising means for changing a level in a predetermined period. 9. The predetermined period according to claim 8, wherein the predetermined period is a period during which the control circuit stops oscillation of the inverter circuit when the no-load detection circuit determines that there is a filament, or an intermittent period due to the Emiless detection circuit. A discharge lamp lighting device during an oscillation stop period during an oscillation operation. 10. The DC power supply circuit has a voltage at which the inverter circuit can operate stably before the inverter circuit starts oscillating by the control circuit having the timer function. 10. The discharge lamp lighting device according to any one of claims 9 to 9. 11. The no-load detection circuit includes a first resistance from the DC voltage source, a second resistance connected in parallel with the discharge lamp, and a DC detection circuit including a diode, a capacitor, and a third resistance. 11. The method according to claim 1, wherein the presence or absence of a filament is detected by detecting a DC voltage of the capacitor and comparing a magnitude relationship with a reference voltage. Discharge lamp lighting device.