JPH0479119B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a discharge lamp lighting device for lighting a discharge lamp at high frequency.

[Background Art] Fig. 12 is a diagram showing the circuit configuration of a conventional high-frequency discharge lamp lighting device, in which transistors Q ₁ and Q ₂ are connected in series to a DC power supply (including rectified voltage of an AC power supply). Diodes D ₁ and D ₂ are connected in parallel to transistors Q ₁ and Q ₂ with the polarities shown (however, diodes D ₁ and D ₂ are not necessarily required). Capacitor in parallel with transistor _Q1
A series circuit of C ₁ , a resonant circuit A including a discharge lamp l, and a primary winding n ₁ of a drive transformer T ₁ consisting of a saturable transformer is connected. A half bridge type inverter circuit is constructed with such a configuration.
A drive transformer T ₁ with a primary winding n ₁ has a secondary winding
n ₂ , n ₃ , the secondary winding n ₂ is connected to the control resistor R ₁ of the transistor Q ₁ , and the secondary winding n ₃ is connected to the control resistor R ₂ of the transistor Q ₂ . . The resonant circuit A consists of an inductance element L ₁ , a resonant capacitor C ₂ , and a discharge lamp l.

Here, capacitor _C1 is a coupling capacitor, has a sufficiently larger capacity than capacitor _C2 , and is used as a power source for the inverter circuit.

Furthermore, a starting circuit 6 for the inverter circuit is provided. This starting circuit 6 is composed of a resistor R ₃ and a capacitor C ₃ connected in series, and, for example, a diac Q ₃ . The connection point between the resistor _R3 and the capacitor _C3 is connected to one end of the dielectric _Q3 , and the other end is connected to the base terminal, which is the control terminal of the transistor _Q2 . Also, resistor R ₃ , capacitor
The connection point of C ₃ connects to the anode of diode D ₃ ,
The cathode is connected to the collector of transistor _Q2 .

The operation of the circuit described above is as follows. In other words, when the power switch SW is turned on, the capacitor
C ₃ is charged through resistor R ₃ . Then, when the voltage on capacitor _C3 reaches the breakover voltage of diode _Q3 , capacitor _C3 discharges through the base-emitter junction of transistor _Q2 .
This discharge causes transistor _Q2 to conduct for the first time. Therefore, a current flows through the DC power supply E → capacitor C ₁ → resonant circuit A → primary winding n ₁ of drive transformer T ₁ → transistor Q ₂ → DC power supply E to charge the capacitor C ₁ . Since this current flows through the primary winding n ₁ of the drive transformer T ₁ , a voltage is induced in the two secondary windings n ₂ and n ₃ . The induced voltage in the secondary winding _n3 has a polarity (forward voltage) that maintains the conduction state of the transistor _Q2 .

The current flowing through the transistor Q ₂ increases, the current flowing through the primary winding n ₁ of the drive transformer T ₁ also increases,
Eventually, the drive transformer _T1 saturates. Therefore, the polarity of the voltage induced in the secondary windings n ₂ and n ₃ of the drive transformer T ₁ is reversed, and an on signal is sent to the transistor Q ₁ .
An off signal is given to transistor _Q2 . Then, resonant circuit A, the primary winding of drive transformer _T1
A closed circuit is formed between n ₁ and transistor Q ₁ , and current flows through transistor Q ₁ using capacitor C ₁ as a power source. Thereafter, the transistors Q ₁ and Q ₂ are turned on and off alternately due to the saturation of the drive transformer T ₁ , causing current to flow through the resonant circuit A, and applying the voltage of the capacitor C ₂ to the discharge lamp l, thereby lighting the discharge lamp l. .

By the way, there is no problem when the discharge lamp l that is lit by high-frequency output is lit normally, but when the discharge lamp l reaches the end of its lifespan, the filaments at both ends of the discharge lamp l become disconnected from each other. This may result in unbalanced DC lighting, or the discharge sustaining voltage may rise, making lighting unstable, resulting in abnormal oscillation. In other words, when looking at a discharge lamp 1, a filament coated with an active substance is provided at both ends of the discharge lamp 1, and the discharge lamp 1 lights up by alternating discharge between the filaments, but at the end of its life, If this happens, the active material on one filament will completely peel off, resulting in "DC lighting" due to discharge in only one direction, as shown in Figure 13, or if only a small amount of active material on one filament remains. In some cases, an imbalance between the left and right sides of the filament causes abnormal lighting, which is slightly different from DC lighting. In this way, when the filament of the discharge lamp L becomes unbalanced, a large current 3 to 4 times the normal current flows through the transistors Q ₁ and Q ₂ , resulting in a very large switching loss, which lasts for a long time. Continuing, transistor Q ₁ ,
There was a risk that Q ₂ would run out of heat and be destroyed.

[Object of the Invention] The present invention has been provided in view of the above-mentioned points, and provides reliable detection of the end of life of a discharge lamp.
A highly reliable discharge lamp lighting device that controls the switching operation of the switching element when the discharge lamp is at the end of its life, reduces the increase in current flowing through the switching element, and does not cause unstable operation. The purpose is to provide the following.

[Disclosure of the Invention] (Configuration) The present invention provides two
Switching elements connected in parallel with one of the switching elements, including a first capacitor, an inductance element, and a discharge lamp, connected in series so that the first capacitor is on one electrode side of the DC power supply. and a second capacitor connected in parallel with the discharge lamp, the discharge lamp lighting device supplies the discharge lamp with a high frequency voltage generated by alternately turning on and off the switching element, wherein the first capacitor A voltage detection circuit section detects the voltage between the non-power supply side terminal of the DC power source and the other electrode of the DC power supply, and the detected voltage of this voltage detection circuit section is used as the detection voltage of the voltage detection circuit section when the discharge lamp is normally lit. a comparison circuit unit that compares the voltage detected by the voltage detection circuit unit with a first reference voltage that is higher than the first reference voltage and a second reference voltage that is lower than the voltage detected by the voltage detection circuit unit during normal lighting of the discharge lamp; The present invention is characterized by comprising an output control section that limits the switching operation output of the switching element based on the output of the comparator circuit section when the reference voltage is higher than the reference voltage or lower than the second reference voltage.

(Example 1) Hereinafter, an example of the present invention will be described with reference to the drawings.
FIG. 2 shows a schematic block diagram, and the DC power source E is constituted by a constant voltage power source obtained by rectifying an AC power source. The drive circuit 2 is for switching the transistors Q ₁ and Q ₂ which are two switching elements, and also connects the non-power supply side terminal of the capacitor C ₁ connected to the positive terminal of the DC power supply E to the non-power supply side terminal of the DC power supply E. The voltage detection circuit section 3 that detects the voltage between the negative electrode and the negative electrode is configured by a voltage dividing circuit using a resistive element or the like having a higher impedance than the load circuit 1 which is the discharge lamp 1. The comparison circuit section 4 compares the detected voltage of the voltage detection circuit section 3 with a first reference voltage that is higher and a second reference voltage that is lower than when the discharge lamp 1 is normally lit, which are set in advance. is sent to the output control section 5, and the output control section 5 controls the output of the drive circuit 2. In addition, the inductance element
The series resonant circuit composed of _L1 and capacitor _C2 is for smooth high frequency conversion.

Next, the basic operation of the present invention will be explained. When the discharge lamp 1 is normally lit, the output of the voltage detection circuit section 3 is at the "E1" level, and this signal is compared by the comparison circuit section 4. This result is further sent to the output control section 5, and the transistors Q ₁ ,
_Q2 is continuously driven, but when the discharge lamp l is at the end of its life, the output of the voltage detection circuit section 3 becomes "E2" or "L level (0)", and this signal is compared in the comparator circuit section 4. This result is further output to the output control unit 5.
to suppress or stop the operation of transistors Q ₁ and Q ₂ . Note that E2 and E1 satisfy E2>E1, and E2≈2E1. This will be discussed later.

Next, specific examples of the present invention will be described. FIG. 1 shows a specific circuit diagram. Transistors Q ₁ and Q ₂ connected in series are connected in parallel to a DC power supply E via a power switch SW, and a load resistor R is connected between the collector and emitter of the transistor Q ₁ via a capacitor C ₁ . (The load resistance R indicates the resistance when the discharge lamp I is considered as a resistance.) are connected in parallel. This capacitor _C1 has two transistors as described below.
When Q ₁ and Q ₂ are turned on and off alternately, the voltage supplied to the load resistor R can be reversed, or the DC component can be cut and the AC component (high frequency power) can be supplied to the load resistor R.
It acts to supply. Further, a capacitor _C2 is connected in parallel with the load resistor R, and an inductance element _L1 is connected to the connection point between the capacitor _C2 and the load resistor R (on the opposite side of the capacitor _C1 ). Here, the two capacitors C ₁ and C ₂ are C ₁
The relationship 〓C ₂ is satisfied.

The non-load side terminal of the inductance element L ₁ is connected to the connection point of the transistors Q ₁ and Q 2 via the primary winding n ₁ of the drive transformer T 1, and is further connected to the connection point of the transistors Q ₁ and Q ₂ through the primary winding n 1 of the drive transformer T ₁ . ₂ and n ₃ are resistors R ₁ and
It is connected to each of the bases of transistors Q ₁ and Q ₂ via R ₂ . In addition, the drive transformer T ₁ and 2
The polarities of the next windings n ₂ and n ₃ are reversed so that the transistors Q ₁ and Q ₂ are turned on and off alternately, and the drive circuit 2 is configured with this drive transformer T ₁ and its attached circuit. It consists of Connection point of capacitor C ₁ with load resistor R and DC power supply E
A voltage dividing circuit constituted by a series circuit of resistors R ₅ and R ₆ is provided between the negative electrode terminal and the voltage detection circuit section 3 . Here, resistors R ₅ and R ₆ are selected to have high impedance values relative to the load resistance R. Furthermore, the connection point between resistors R ₅ and R ₆ is a Zener diode.
It is connected to the base of transistor Q ₅ via ZD ₁ and resistor R ₇ , and the collector of transistor Q ₅ is connected to the connection point of resistors R ₅ and R ₆ . The emitter of transistor _Q5 is connected to the negative terminal side of DC power supply E. Comparison circuit section 4 with transistor Q ₅ , Zener diode ZD ₁ and its attached circuit
It consists of

Furthermore, the base of the transistor Q ₄ is connected to the collector of the transistor Q ₅ through a resistor R ₈ , the collector of the transistor Q ₄ is connected to the gate terminal of the thyristor SCR through a resistor R ₉ and to the capacitor C ₁ through a resistor R ₄ . connected to the power supply side of the Also,
The emitter of the transistor _Q4 is connected to the negative terminal side of the DC power supply E in common with the cathode of the thyristor SCR. The anode of the thyristor SCR is connected to the power supply side of the capacitor _C1 via a resistor _R3 , and is also connected to one end of the winding _n4 of the drive transformer _T1 and its anode via a diode _D5 . The other end of the winding n ₄ of the drive transformer T ₁ is connected to the negative terminal side of the DC power supply E. The output control unit 5 is composed of the transistor Q ₄ , the thyristor SCR, the winding n ₄ of the drive transformer T ₁ , the diode D ₅ and its attached circuits.

On the other hand, a resistor R ₃ and a capacitor C ₃ are connected in parallel with the DC power supply E, and a capacitor C ₃ and a resistor
A diode D ₃ is connected between the connection point of R ₃ and the connection point of transistors Q ₁ and Q ₂ . This diode D ₃ resists the anode as shown
Connected to the connection point of R ₃ and capacitor C ₃ . A dielectric Q ₃ is provided between the connection point of the resistor R ₃ and the capacitor C ₃ and the base of the transistor Q ₂ , and these constitute a starting circuit 6 of the inverter device. Here, the series circuit of resistor R ₃ and capacitor C ₃ constitutes a trigger circuit for diode Q ₃ , and diode D ₃ connects the current supplied from DC power supply E to resistor R ₃ after diode Q ₃ breaks over. A bypass circuit is formed that leads directly to transistor _Q2 through the transistor Q2. Note that feedback diodes D ₁ and D ₂ are connected in antiparallel to each of the transistors Q ₁ and Q ₂ .

Next, the operation will be explained.

<Operation during normal lighting> In the case of normal lighting, the equivalent basic circuit can be drawn as shown in Figure 3. In this case, the voltages e _{1 and e 2 appearing across the transistors Q 1 and Q 2} due to the switching operation of the transistors Q ₁ and Q ₂ are the fourth voltages e ₁ and e _{2 ,} respectively.
The voltage becomes a rectangular wave as shown in Figures b and c, and the voltage across the series resonant circuit is a voltage e ₃ as shown in Figure 4 e, with the DC component removed by the capacitor C ₁ .
is supplied. Incidentally, FIG. 4a shows the DC power supply voltage E. Here, the capacitance of capacitor _C1 is sufficiently larger than that of capacitor _C2 , and
It operates as a power source for the inverter circuit. The voltage ec ₁ across the capacitor C ₁ is determined by ec ₁ =e ₁ −e ₃ and becomes E/2 as shown in FIG. 4d.
Although a slight ripple is included in FIG. 4, this ripple can be reduced by increasing the value of the time constant C ₁ ·R of the circuit including the capacitor C ₁ and the load resistor R. Furthermore, the voltage e ₄ applied to the voltage detection circuit section 3 is determined by e ₄ = e ₀ - ec ₁ and has the waveform shown in FIG. 4f,
e ₄ =E/2 is found.

Therefore, in the case of normal lighting, the voltage _e4 generated in the voltage detection circuit section 3 is E/2. This voltage is divided by the voltage dividing resistors R ₅ and R ₆ shown in FIG. Then, in the comparator circuit section 4, the Zener voltage V _ZD1 of the Zener diode ZD ₁ is set as V _ZD1 >E1, so the transistor Q ₅ is turned off. Therefore, the voltage at the output terminal a of the comparator circuit section 4 becomes "H level". This signal is further sent to the output control section 5, and by turning on the transistor _Q4 , no current flows through the gate of the thyristor SCR, so that the thyristor SCR is turned off.
In this case, the winding n ₄ of the drive transformer T ₁ is replaced by the winding n ₂ ,
It is designed not to affect the voltage fed back to n ₃ , so that transistors Q ₁ and Q ₂ can operate normally, and the oscillation operation of the inverter circuit continues.

Next, the oscillation operation of this inverter circuit will be explained.

Figure 4 shows the schematic circuit of Figure 3 (Figure 1), e ₁ ,
The diagram shows the operation waveform diagram (a diagram that makes it easier to see the relationship between e ₂ , e ₃ , e ₄ , and ec ₁ ), and shows the self-excited oscillation operation of the inverter circuit. Explain the oscillation operation (vibration). In other words, when the power switch SW is turned on, capacitor C ₃ connects to resistor R ₃
is charged via. Then, when the voltage on capacitor _C3 reaches the breakover voltage of diode _Q3 , capacitor _C3 discharges through the base-emitter junction of transistor _Q2 . This discharge causes transistor _Q2 to conduct for the first time.

Therefore, a current flows through the DC power supply E → capacitor C ₁ → resonant circuit A → primary winding n ₁ of drive transformer T ₁ → transistor Q ₂ → DC power supply E to charge the capacitor C ₁ . This current is the driving transformer
Since it flows through the primary winding n ₁ of T ₁ , the two secondary windings
Voltage is induced in n ₂ and n ₃ . The induced voltage in the secondary winding _n2 has a polarity (forward voltage) that maintains the conduction state of the transistor _Q2 . After that, the current flowing through the transistor Q ₂ increases, and the current flowing through the primary winding n ₁ of the drive transformer T ₁ also increases, so the drive transformer
T ₁ is saturated, and the secondary windings n ₂ , n ₃ of the drive transformer T ₁
The voltage induced in the transistor _Q1 is turned on and the transistor _Q2 is turned off. When the transistor _Q1 is turned on, a closed circuit is formed between the resonant circuit A, the primary winding _n1 of the drive transformer _T1 , and the transistor _Q1 , and current begins to flow using the capacitor _C1 as a power source. Due to this saturation of the drive transformer T ₁ , the transistors Q ₁ and Q ₂ are turned on and off alternately, allowing current to flow through the resonant circuit A. As described above, the oscillating current due to charging and discharging of capacitor _C1 causes the transistor to
Q ₁ and Q ₂ are not turned on and off, but are driven on and off by the saturation of the drive transformer T ₁ .

FIG. 5 shows a waveform diagram of each part of the inverter circuit, where a shows the collector-emitter voltage VQ ₁ of the transistor Q ₁ , and b and c show the current IQ flowing through the transistors Q ₁ and Q ₂ , respectively. ₁ , IQ ₂ , and d in the figure is the current In ₁ flowing through the primary winding n 1 _of the drive transformer T ₁ . In the same figure, e is the drive transformer T ₁
is the voltage Vn ₃ induced in the secondary winding n ₃ of . In the figure, f and g are base currents In ₂ and In ₃ of transistors Q ₁ and Q ₂ , respectively.

To further explain the waveforms in FIG. 5, when the transistor Q ₂ is on, the current IQ ₂ increases, and when the drive transformer T ₁ is saturated, the secondary winding n ₃ flows as shown in FIG. Transistor _Q2 is off (transistor
_Q1 has an on signal). At this time, the oscillating current In ₁
To maintain continuity, diode _D1 turns on,
Current ID ₁ flows through the loop of capacitor C ₁ → resonant circuit A → primary winding n ₁ of drive transformer T ₁ → diode D ₁ , and capacitor C ₁ . Here, the oscillating current In ₁ has a positive direction from the right to the left of the inductance element L ₁ . After this, transistor Q ₁ turns on and current IQ ₁
flows. Further, after the transistor Q ₁ is turned off, a current ID ₂ flows through the loop of the capacitor C ₁ → DC power supply E → diode D ₂ → the primary winding n ₁ of the drive transformer T ₁ → the capacitor C ₁ . After this, transistor Q ₂ turns on, and current IQ ₂ flows from DC power supply E to capacitor C ₁
→ Resonant circuit A → Primary winding n ₁ of drive transformer T ₁ →
Transistor Q ₂ → Flows in the loop of DC power supply E.
Note that the current IQ ₁ flowing through the transistor Q ₁ flows in a loop of the capacitor C ₁ → the transistor Q ₁ → the primary winding n ₁ of the drive transformer T ₁ → the resonant circuit A → the capacitor C ₁ .

The self-excited oscillation operation is performed as described above, and the voltage waveforms at each part become as shown in FIG.

<Operation at the end of discharge lamp life> As explained above, when a discharge lamp reaches the end of its life, the active material on one filament is completely peeled off, resulting in "DC lighting" due to discharge in only one direction, and depending on the polarity, the The basic circuit is shown in Figure 6 a and b.
become that way. Here, capacitors C ₁ and C ₂ are C ₁ ,
Since the relationship of C ₂ is satisfied, capacitor C ₂ has little effect on operation.

(a) In the case of the operation shown in Fig. 6a: When the transistor _Q2 is turned on, a loop current flows, and the capacitor _C1 is charged all at once in the direction shown in the figure up to the voltage E of the DC power supply E. Next, when transistor Q ₁ turns on, the discharge current of capacitor C ₁ flows slightly through capacitor C ₂ as shown by the broken line, but since C ₁ ≫ C ₂ , the potential of capacitor C ₁ remains at E. maintain. Here,
Since the voltage e ₄ across the voltage detection circuit section 3 is determined by e ₄ =e ₀ −ec ₁ , the voltage at e ₄ becomes 0 level. Therefore, the output of the voltage detection circuit section 3 also becomes 0 level, and this 0 level corresponds to the above-mentioned L level. Therefore, the output terminal a of the comparator circuit section 4 is also 0.
level, and the transistor Q ₄ of the output control section 5
is turned off. Then the thyristor SCR is connected to the resistor R ₄
By applying a gate current through _R9 and turning it on, the winding _n4 of the drive transformer _T1 is short-circuited, so that the inverter circuit stops oscillating.

(b) In the case of the operation shown in Fig. 6b In the case of Fig. 6b, when the switch SW is closed, the capacitor C ₁ passes through the impedance R ₀ of the voltage detection circuit section 3 in the direction shown by the loop. charged (voltage ec ₁ ). Capacitor C ₁
is charged with a time constant determined by C ₁ and R ₀ ,
Since the impedance R ₀ of the voltage detection circuit section 3 is selected to have a very high impedance value compared to the resistive load R, the inverter device starts oscillating immediately and the transistor Q ₁ turns on.
Current flows through the loop and capacitor _C1 discharges in the direction shown. At this time, since the impedance r of the discharge lamp l is extremely low, the capacitor _C1 is discharged all at once in the direction shown in the figure until the voltage reaches zero.

Here, as shown in FIG. 6b, capacitor C ₁
tries to be charged by the loop, but since the impedance R ₀ of the voltage detection circuit section 3 is a very high impedance compared to the discharge lamp load R, the capacitor C ₁ is hardly charged. Therefore, when the transistor _Q1 is turned on, the slightly charged charge is transferred to the discharge lamp l at the end of its life.
In the forward direction, it discharges quickly due to its low impedance. On the other hand, in the case of Fig. 4 (normal lighting), capacitor C ₁ is sufficiently charged through the discharge lamp load R (R≪Ro) when transistor Q ₂ is turned on, and the voltage of capacitor C ₁ is approximately 1 Since the voltage has increased to /2E, even if transistor _Q1 is turned on, it will not be charged to 0 immediately.

Next, when the transistor _Q2 is turned on, a current tries to flow in a loop, but since the discharge lamp 1 is lit with direct current using the polarity shown, this loop does not actually exist. Furthermore, the transistor
Capacitor C ₁ is slightly charged by the loop between Q ₂ turning off and transistor Q ₁ turning on, but as soon as transistor Q ₁ turns on, the large current in the loop causes capacitor C 1 to charge up.
C ₁ discharges in the direction shown until the voltage is almost zero.
In this way, in the case of FIG. 6b, the voltage ec ₁ across the capacitor C ₁ becomes almost zero, and the voltage e ₄ generated across the voltage detection circuit section 3 is the voltage ec ₁ added to the voltage E of e ₀ . , e ₄ =E. Here, since the voltage E ₂ of the detection voltage dividing resistor R ₆ in FIG.
If the Zener voltage V _ZD1 of ZD ₁ is selected as E ₂ > V _ZD1 > E ₁ (E ₂ ≒ 2E ₁ ), the Zener diode ZD ₁
turns on, and transistor _Q5 also turns on. When the transistor _Q5 is turned on, the output terminal a of the comparator circuit section 4 goes to L level, so the transistor _Q4 of the output control section 5 is turned off. Then, as mentioned above, the thyristor SCR turns on, so
Winding n ₄ of drive transformer T ₁ is shorted and the inverter circuit stops oscillating.

Next, a supplementary explanation will be given of the operation of the discharge lamp 1 shown in FIGS. 6a and 6b at the end of its life. At the end of the life of the discharge lamp l shown in Figures 6a and b, one direction is almost equal to the no-load state (state without the discharge lamp l) with only the capacitors C ₁ and C ₂ and the inductance element L ₁ , so the following is shown. The no-load state will be explained below. DC power supply E is turned on by power switch SW, and transistor Q ₂ is turned on by starting circuit 6. When transistor Q ₂ turns on, DC power supply E → capacitor C ₁ → capacitor C ₂ → inductance element
Resonant current flows through L ₁ → primary winding n ₁ of drive transformer T ₁ → transistor Q ₂ → DC power supply E.
When current flows through the primary winding n ₁ of the drive transformer T ₁ ,
A voltage is induced in the secondary winding _n3 . Since the voltage induced in the secondary winding n ₃ forward biases the transistor Q ₂ , the conduction of the transistor Q ₂ continues.
Eventually the current flowing through transistor _Q2 increases,
The drive transformer T ₁ is saturated and the voltages induced in the secondary windings n ₂ and n ₃ are reversed, providing a voltage that reverse biases the transistor Q ₂ and forward biases the transistor Q ₁ . Thereafter, this operation is repeated and oscillation continues.

Figure 7 shows the resonant current In ₁ and each transistor Q ₁ ,
It shows how current flows through Q ₂ , diodes D ₁ and D ₂ .

In Figure 8a, the discharge lamp l is connected to the capacitor C ₂ with no load.
The figure shows the no-load secondary voltage, and b in the figure shows the resonant current at no-load. Here, the oscillation frequency X ₁ of the inverter circuit is determined by the inductance element L ₁ , capacitor C ₂ ,
Resonant circuit A consisting of resistive load R and drive transformer
This oscillation frequency X ₁ is determined by T ₁ , and the inductance element
It is set lower than the oscillation frequency X ₀ determined by L ₁ , capacitor C ₂ , and drive transformer T ₁ . In this case, the load on the inverter circuit becomes capacitive. In the opposite case, it is inductive. Now, when there is no load, in order to start and light the discharge lamp l, a high secondary voltage (capacitor
The voltage across _C2 ) is obtained. Therefore, the resonant current also increases, and the transistors Q ₁ ,
The current flowing through Q ₂ also increases. If this state continues for a long time, transistors Q ₁ and Q ₂ will be destroyed. Also,
Since the load becomes lighter at the end of the discharge lamp's life or when the filament breaks, the operation is almost the same as when there is no load.

Next, the above-mentioned E1 and E2 levels will be explained.
The E1 level indicates the voltage across the resistor _R6 in Figure 1 when the discharge lamp l is operating normally, and the E2 level indicates the resistance when operating as shown in Figure 6b (at the end of its life).
Indicates the voltage across _R6 . Therefore, the relationship between E1 and E2 is expressed by the following equation.

E1≒E/2×R ₆ /R ₅ +R ₆ E2≒E×R ₆ /R ₅ +R ₆ Therefore, E2≈2E1.

Further, the L level is a ground level (zero level).

(c) In the case of multiple lamp lighting In the case of multiple lamp lighting, for example, two discharge lamps l ₁ and l ₂ reach the end of their life at the same time, and when DC lighting occurs, a situation as shown in FIG. 9 may occur. At this time, two discharge lamps l ₁ ,
When the polarity of l ₂ is as shown in Figure 9 a or b, no current flows through the discharge lamp load R, so it does not light up, and the voltage across capacitor C ₂ is the same as with no load, and the transistor Q ₁ , a large current will also flow through _Q2 , leading to destruction. In this case, in the configuration of the present invention, since the impedance of capacitor C ₂ is extremely large compared to the impedance of capacitor C ₁ , the output terminal can be regarded as open, and the equivalent basic circuit can be further written as shown in Figure 10. be done. At this time, the current flows in a loop, the capacitor _C1 is charged to E in the direction shown in the figure, and the voltage _e4 across the voltage detection circuit section 3 becomes 0 level. Therefore, the inverter circuit stops its oscillation operation as in the case of FIG.

(Embodiment 2) FIG. 11 shows another embodiment, and the feature of this embodiment is that a diode D ₄ is provided in series with resistors R ₅ and R ₆ . With this configuration, noise components such as surge voltages generated during operation of the inverter circuit are absorbed, and the operation of the inverter circuit is stabilized. Also, resistance
A smoothing capacitor _C4 is connected in parallel to _R6 ,
This capacitor _C4 absorbs surge voltages and ripples to ensure reliable operation of the comparator circuit section 4.

In the above-mentioned embodiment, the output control unit 5 only stops the operation of the transistors Q ₁ and Q ₂ at the end of the life of the discharge lamp, but the present invention is not limited to this. It's not something you can do. For example, at the end of a discharge lamp's life, a transistor
It may be possible to perform the operation of Q ₁ and Q ₂ intermittently or to forcibly reduce the current during switching to below a predetermined value.In short, at the end of the discharge lamp life, the output is controlled and the transistors Q ₁ and Anything that suppresses the current in _{step 2} is fine.

[Effects of the Invention] As described above, the present invention includes two switching elements connected in series to both ends of a DC power supply, and a first capacitor, an inductance element, and a discharge element connected in parallel to one of the switching elements. A series circuit including a lamp is connected such that a first capacitor is connected to one electrode side of a DC power source, and a second capacitor is connected in parallel with the discharge lamp, and the switching element is turned on and off alternately. In a discharge lamp lighting device that supplies a discharge lamp with a high-frequency voltage generated by the above-described voltage, a voltage detection circuit unit detects a voltage between the non-power supply side terminal of the first capacitor and the other electrode of the DC power supply; The voltage detected by the voltage detection circuit section is set to a first reference voltage higher than the detection voltage of the voltage detection circuit section during normal lighting of the discharge lamp, and a first reference voltage lower than the detection voltage of the voltage detection circuit section during normal lighting of the discharge lamp. a comparison circuit section for comparing with the reference voltage of No. 2;
and an output control section that limits the switching operation output of the switching element using the output of the comparison circuit section when the detected voltage of the voltage detection circuit section is equal to or higher than the first reference voltage or lower than the second reference voltage. Therefore, it is possible to reliably detect that the discharge lamp has reached the end of its lifespan, and when the discharge lamp is at the end of its lifespan, the output of the inverter circuit is limited by the output control section, thereby preventing excessive current from flowing through the switching element. It is possible to prevent the switching element from being destroyed, thereby improving the reliability of the device, and also having the effect of suppressing wasteful power consumption. Furthermore, since the voltage detection circuit section uses a method of detecting voltage and does not employ a current detection method of detecting load current, it has the effect of reducing the influence on the operation of the inverter circuit.

[Brief explanation of drawings]

Figure 1 is a specific circuit diagram of one embodiment of the present invention, Figure 2 is a specific circuit diagram of an embodiment of the present invention.
The figure is a block diagram of the same as above, Fig. 3 is an equivalent basic circuit diagram of the above discharge lamp during normal lighting, Fig. 4 is an operating waveform diagram of the same as the above, Fig. 5 is an operating waveform diagram of the same as the above, and Fig. 6 a, b is an equivalent basic circuit diagram at the end of the life of each of the above discharge lamps, Fig. 7 is an operation waveform diagram of the above, Figs. Fig. 9b is an equivalent basic circuit diagram of the above discharge lamp, Fig. 10 is an equivalent basic circuit diagram of the above multi-lamp lighting case, and Fig. 11 is an equivalent basic circuit diagram of the above-mentioned discharge lamp. FIG. 12 is a specific circuit diagram of a conventional example, and FIG. 13 is a circuit diagram showing an equivalent circuit as a part of the same. 1 is a load circuit, 2 is a drive circuit, 3 is a voltage detection circuit section, 4 is a comparison circuit section, 5 is an output control section, l
is a discharge lamp, E is a DC power supply, and Q ₁ and Q ₂ are transistors.

Claims (1)

[Claims] 1 Two switching elements connected in series to both ends of a DC power supply, a first capacitor connected in parallel to one of the switching elements, an inductance element, and a discharge lamp, the first capacitor being connected to one side of the DC power supply. and a second capacitor connected in parallel with the discharge lamp, the device supplies the discharge lamp with a high-frequency voltage generated by alternately turning on and off the switching element. The discharge lamp lighting device includes a voltage detection circuit section that detects the voltage between the non-power supply side terminal of the first capacitor and the other electrode of the DC power supply, and a voltage detection circuit section that detects the voltage detected by the voltage detection circuit section. a comparison circuit unit that compares a first reference voltage higher than the voltage detected by the voltage detection circuit unit during normal lighting and a second reference voltage lower than the voltage detected by the voltage detection circuit unit during normal lighting of the discharge lamp; and an output control section that limits the switching operation output of the switching element using the output of the comparison circuit section when the detected voltage of the voltage detection circuit section is equal to or higher than the first reference voltage or lower than the second reference voltage. A discharge lamp lighting device characterized by: