JP4103397B2 - Discharge lamp lighting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for reducing an overshoot of a lamp current that occurs at the time of polarity reversal in a high pressure discharge lamp lighting device that supplies an AC lamp current to a high pressure discharge lamp to light the high pressure discharge lamp.
[0002]
[Prior art]
FIG. 9 shows a conventional example of a discharge lamp lighting device (Japanese Patent Publication No. 6-101388, Japanese Patent Publication No. 6-101389). A switching circuit in which switching elements Q1 to Q4 are connected in a bridge shape is connected to a DC power supply E via a current detection resistor R. Diodes D1 to D4 are connected in parallel to the switching elements Q1 to Q4 in the direction opposite to the energizing direction of the switching elements Q1 to Q4, respectively. A series circuit of the choke coil L1 and the capacitor C1 is connected between the connection point of the switching elements Q1, Q4 and the connection point of the switching elements Q2, Q3, and the discharge lamp La and the inductance element L2 are connected in series with the capacitor C1. The circuit is connected. The control circuit 7 is a circuit for controlling the switching elements Q1 to Q4 according to the detection voltage Vla and the detection current Ila.
[0003]
FIGS. 10A to 10D are timing charts showing operations of the switching elements Q1 to Q4, respectively. The switching elements Q3 and Q4 are turned on and off by the control circuit 7 at a frequency suitable for the discharge lamp La in the range of several tens of Hz to 500 Hz. When the switching element Q3 is on, the switching element Q1 has a duty of, for example, 30 KHz (1 / T ₂ ). The variable ratio on / off operation is performed. When the switching element Q4 is on, the switching element Q2 performs the same on / off operation as the switching element Q1. Further, at the time of polarity inversion of the discharge lamp La 4 two switching elements Q1~Q4 is turned off at the same time, having a pause interval T _D. The control circuit 7 changes the on / off duty ratio according to the voltage of the current detection resistor R. Accordingly, a rectangular wave alternating current containing high-frequency ripple flows through the discharge lamp La.
[0004]
Now, the circuit operation of FIG. 9 will be further described with reference to FIGS. 10A to 10D. Between t1 and t2 in FIG. 10, the switching element Q3 operating at a low frequency is turned on as shown in FIG. The switching element Q1 is in an on / off operation state at a high frequency shown in FIG. During this period, the switching elements Q2 and Q4 are in the off state as shown in FIGS. When the switching element Q1 is turned on, the DC power supply E, the switching element Q1, the series circuit of the discharge lamp La and the inductance element L2 and its parallel capacitor C1, the choke coil L1, the switching element Q3, the current detection resistor R, and the DC power supply E are closed. The current flows through the circuit, and the current I _L1 flowing through the choke coil L1 rises linearly with a certain slope. When the switching element Q1 is turned off, the current I _L1 at this time and the value determined by the inductance value of the choke coil L1 are accumulated. The direction in which the energy keeps the current flowing, that is, the direction of the current when the switching element Q1 is on, is the same as the choke coil L1, the switching element Q3, the diode D4, the discharge lamp La, and the inductance element. L2 series circuit and its parallel capacitor C1, Closed circuit energy stored Kukoiru L1 is released, the operation is repeated up to the point of t2.
[0005]
In the period T _D of the next t2 to t3, a both turned off four switching elements Q1 to Q4, this period is not performed power supply from the DC power source E. Further, the period from t3 to t4 is basically the same as the period from t1 to t2, but during this period, the switching elements Q2 and Q4 operate, and the switching elements Q1 and Q3 are in the OFF state. That is, when the switching element Q2 is turned on, the DC power supply E, the switching element Q2, the choke coil L1, the series circuit of the discharge lamp La and the inductance element L2 and its parallel capacitor C1, the switching element Q4, the current detection resistor R, the DC power supply E When the current flows in the closed circuit of the circuit and the switching element Q2 is turned off, the closed circuit of the choke coil L1, the series circuit of the discharge lamp La and the inductance element L2 and its parallel capacitor C1, the switching element Q4, the diode D3, and the choke coil L1. The stored energy is released, and this operation is repeated until time t4.
[0006]
The direction of the current I _La flowing through the discharge lamp La and current I _L1 flowing to the choke coil L1 shown in FIG. 9 are those between t1 to t2, the direction of the current I _L1, I _La is between t3~t4 is Vice versa. In this way, a rectangular wave-shaped alternating current containing high-frequency ripple flows through the discharge lamp La. It is known that this high-frequency ripple causes arc instability due to an acoustic resonance phenomenon when the discharge lamp is turned on. Therefore, in order to reduce this high frequency ripple, generally, the capacitance of the capacitor C1 connected in parallel with the discharge lamp La is adjusted to avoid the acoustic resonance phenomenon.
[0007]
The diodes D1 and D2 do not flow current in normal operation, but are for flowing surge current during transition. The period T _D is the switching element Q1, Q2, Q3, Q4 period all are off (t2~t3, t4~5) shows a, which is the switching element Q1, Q4 or Q2, Q3 is turned on at the same time This is a dead time to prevent a lighting device from being destroyed due to a short circuit condition. This simultaneous ON occurs when the storage time becomes longer due to variations in switching elements or due to temperature rise, or due to timing deviation between switching elements.
[0008]
Capacitor C1 is a time corresponding to t2 in FIG. 10 is a polarity shown in FIG. 9, the period T _D in the capacitor C1, the discharge lamp La, closed circuit of the inductance element L2 is formed, the release of the charge of the capacitor C1 Becomes an oscillating current, and I _La flowing in the discharge lamp La reverses polarity in this section while maintaining continuity, and at time t3, the switching element Q2 is turned on to complete the inversion without causing a pause in the current I _La. .
[0009]
[Problems to be solved by the invention]
FIG. 11 shows detailed operation waveforms at the time of polarity reversal (period T _{D from} t2 to t3) in the above-described conventional example. FIG. 4A shows the operation of the switching element Q1, and FIG. 4B shows the operation of the switching element Q2. FIG. 5C shows the input current I1, which corresponds to the current flowing through the switching elements Q1 and Q2. FIG. 4D shows the current I _L1 flowing through the choke coil L1, and FIG. 4E shows the current I _La flowing through the discharge lamp La. In the period T _D of t2 to t3, is released substantially capacitor C1, the discharge lamp La, an operational closed circuit of the inductance element L2, to the discharge lamp La charge of the capacitor C1 through the inductance element L2, this time, the oscillating current Flows at a period according to these circuit constants. At time t3, the polarity of the voltage of the capacitor C1 is as shown in FIG. 9, and when the switching element Q2 is turned on under this condition, the voltage across the DC power supply E and the capacitor C1 becomes polar, and FIG. As shown in Fig. 11 (d), the current I1 flowing in the choke coil L1 and the current _IL1 flowing in the discharge lamp La as shown in Fig. 11 (e) are steep. _La also overshoots. At this time, the capacitance of the capacitor C1 for thereby avoiding acoustic resonance phenomenon as described above is large, the current I _La flowing to the discharge lamp La Immediately after this t3 becomes more excessive, the overshoot problem remarkably occurs To do.
[0010]
In this way, in a discharge lamp lighting device that performs a low-frequency AC lighting operation, if the overshoot of the lamp current increases due to a sharp rise in the lamp current immediately after the polarity reversal, the current that flows to each lamp electrode each time the polarity is reversed. Since it grows instantaneously, it will adversely affect the life of the lamp.
[0011]
The present invention has been made in view of the above points, and in a discharge lamp lighting device for lighting a discharge lamp in a rectangular wave, by reducing the overshoot of the lamp current that occurs every time the polarity of the discharge lamp is reversed, It is an object to suppress the electrode deterioration of the discharge lamp and extend the life of the discharge lamp.
[0012]
[Means for Solving the Problems]
According to the invention of claim 1, in order to solve the above-mentioned problem, as shown in FIG. 1, at least one or more DC power supply E and the output of the DC power supply E are intermittently switched at a high frequency. A chopper circuit 1 including a switching element S and an inductance L, and a bridge circuit composed of at least two or more switching elements S1 to S4 that invert the output polarity from the chopper circuit 1 to the discharge lamp La at a low frequency. In the discharge lamp lighting device, as shown in FIGS. 2B and 2C, the switching elements S1 to S4 operating at the low frequency reverse the polarity of the output to the discharge lamp La for a certain period immediately after the polarity reversal. while maintaining the output polarity and the same polarity after operation child at the frequency higher than the low frequency so that the peak value of the output current of the chopper circuit 1 is reduced The one in which the features.
[0013]
As described above, the switching elements S1 to S4 operating at a low frequency of the bridge circuit are operated at a high frequency immediately after the polarity inversion, thereby reducing the overshoot of the lamp current at the time of the polarity inversion. Here, the switching elements S1 to S4 of the bridge circuit and the switching element S of the chopper circuit may be synchronized or asynchronous. Moreover, it does not matter whether all or part of the switching elements S1 to S4 of the bridge circuit are shared as the switching elements S of the chopper circuit or provided separately.
[0014]
According to a second aspect of the present invention, in the first aspect, the on-time of the switching element S of the chopper circuit is narrowed immediately after polarity inversion.
According to a third aspect of the present invention, in the first aspect, the frequency of the switching element S of the chopper circuit is increased immediately after the polarity inversion.
[0015]
According to the invention of claim 4, in any one of claims 1 to 3, as shown in FIG. 1, there is one switching element S of the chopper circuit, and switching elements S1 to S1 of the bridge circuit operating at a low frequency. S4 is constituted by four.
According to the invention of claim 5, in any one of claims 1 to 3, as shown in FIG. 5, there are two switching elements Q <b> 6 and Q <b> 7 of the chopper circuit, and switching elements Q <b> 5 and Q <b> 8 that operate at a low frequency. The four switching elements Q6, Q7 and Q5, Q8 constitute a full bridge circuit.
[0016]
According to a sixth aspect of the present invention, in any one of the first to third aspects, the bridge circuit is a half-bridge circuit. Here, the half-bridge circuit is a circuit in which a series circuit of two switching elements and a series circuit of two capacitors are connected in parallel, and a load is connected between the connection point of the two switching elements and the connection point of the two capacitors. When the two switching elements are operated at a high frequency to be shared with the switching elements of the chopper circuit, and the two switching elements are operated at a low frequency to operate between the DC power source and the bridge circuit at a high frequency. And a case where a switching element of the circuit is provided separately.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
FIG. 1 is a circuit diagram of Embodiment 1 of the present invention, and FIG. 2 is an operation waveform diagram thereof. In the present embodiment, the voltage supplied from the DC power source E is stepped down by the down converter 1 including a step-down chopper circuit, and the voltage is stored in the capacitor C. Then, a high-pressure pulse is applied to the discharge lamp La by the high-pressure generation circuit IG, causing dielectric breakdown between the electrodes and starting discharge. Thereafter, the current stored in the capacitor C flows into the discharge lamp La at once. Thereafter, the voltage detection circuit 2 and the current detection circuit 3 detect the voltage and current of the discharge lamp La, the power calculation circuit 4 calculates the power supplied to the discharge lamp La, and feeds back to the down converter 1 via the PWM control circuit 5. Then, the pulse width of the down converter 1 is controlled to supply power to the discharge lamp La. The capacitor C is a smoothing capacitor for reducing the high-frequency ripple current caused by the down converter 1. In addition, the control circuit 6 controls the polarity inversion unit configured by a bridge circuit including the switching elements S1 to S4, detects the peak current flowing through the choke coil L, and also controls the frequency.
[0018]
Hereinafter, the operation of the circuit of FIG. 1 will be described. The voltage supplied from the DC power source E is stepped down by the down converter 1 and the four switching elements S1 to S4 are controlled by signals from the control circuit 6 to light the discharge lamp La. 2A shows the operation waveform of the switching element S, FIG. 2B shows the operation of the switching elements S1 and S3 during steady lighting, and FIG. 2C shows the operation of the switching elements S2 and S4 during steady lighting. (D) shows the current waveform flowing through the choke coil L, and (e) shows the current waveform flowing through the discharge lamp La. The current I _L ammeter FIG 1 ▲ 1 ▼ is flowing through the choke coil L, also ammeter ▲ 2 ▼ has detected a current I _La flowing through the discharge lamp La, respectively. When the switching element S is turned on, the current flowing through the choke coil L increases to the right. When the peak current value defined by the control circuit 6 is reached, the switching element S is turned off and the current in the choke coil L is Decrease in decline. When the current value of the choke coil L becomes zero, the control circuit 6 detects it, turns on the switching element S again, and this is repeated. Capacitor C acts as a smoother. Each of the switching elements S1 to S4 is a general full bridge circuit that operates at a low frequency with a pair of the switching elements S1 and S3 and the switching elements S2 and S4 every half cycle.
[0019]
In the present embodiment, when switching elements S1 and S3 (or switching elements S2 and S4) are turned on during polarity reversal, by operating either or both of switching elements S1 and S3 at high frequency, The overshoot of the current flowing through the discharge lamp La is reduced, electrode deterioration of the discharge lamp La is suppressed, and the life of the discharge lamp is improved.
[0020]
In the circuit of FIG. 1, the bridge circuit is configured by a full bridge circuit including four switching elements S1 to S4. For example, the switching elements S1 and S4 may be replaced with capacitors, or the switching elements S2 and S2 may be replaced. S3 may be replaced with a capacitor, and a half-bridge circuit in which a series circuit of two switching elements and a series circuit of two capacitors are connected in parallel may be used.
[0021]
(Embodiment 2)
FIG. 3 is an operation waveform diagram according to the second embodiment of the present invention. FIGS. 3A to 3E show the same waveform as in FIGS. 2A to 2E. The circuit diagram is the same as that of the first embodiment, and detailed description thereof is omitted. As shown in FIG. 3, by reducing the ON time of the switching element S at each polarity reversal, the overshoot of the current flowing through the discharge lamp La at the time of polarity reversal is reduced, and the electrode deterioration of the discharge lamp La is suppressed. In addition, the life of the discharge lamp can be improved. Note that the frequency of the switching element of the chopper circuit may be increased immediately after the polarity inversion, instead of narrowing the ON time of the switching element of the chopper circuit immediately after the polarity inversion.
[0022]
(Embodiment 3)
FIG. 4 is an operation waveform diagram according to the third embodiment of the present invention. 4 (a) to 4 (e) show waveforms at the same portions as those in FIGS. 2 (a) to 2 (e). The circuit diagram is the same as that of the first embodiment, and detailed description thereof is omitted. As shown in FIG. 4, the ON time of the switching element S at each polarity inversion is narrowed, and when the switching elements S1, S3 (or the switching elements S2, S4) are turned ON, either one of the switching elements S1, S3 or By operating both at a high frequency, it is possible to further reduce the overshoot of the current flowing in the discharge lamp La at the time of polarity reversal, suppress electrode deterioration of the discharge lamp La, and improve the life of the discharge lamp. Instead of reducing the ON time of the switching elements of the chopper circuit and the bridge circuit immediately after the polarity inversion, the frequency of the switching elements of the chopper circuit and the bridge circuit may be increased immediately after the polarity inversion.
[0023]
(Embodiment 4)
FIG. 5 is a circuit diagram of Embodiment 4 of the present invention, and FIG. 6 is an operation waveform diagram thereof. In this embodiment, a switching circuit in which switching elements Q5 to Q8 are connected in a bridge shape is connected to a DC power source E, and a diode D5 is connected to the switching elements Q5 to Q8 in a direction opposite to the energizing direction of the switching elements Q5 to Q8, respectively. D8 are connected in parallel, and a series circuit of a choke coil L3 and a capacitor C4 is connected between the connection point of the switching elements Q5 and Q8 and the connection point of the switching elements Q6 and Q7, and the discharge lamp is connected in parallel with the capacitor C4. A series circuit of La and an inductance element L4 is connected. The capacitors C5 and C6 in the circuit diagram may be omitted. Further, the control circuit of the switching elements Q5 to Q8 and the current detection resistor are not shown.
[0024]
FIG. 5 and FIG. 6 will be briefly described below, but this time a case where the capacitors C5 and C6 are not provided will be described. The circuit configuration is the same as that of the conventional example (FIG. 9), and the switching elements Q5 to Q8 and the diodes D5 to D8 have the same basic operation as the switching elements Q1 to Q4 and the diodes D1 to D4 of the circuit of FIG. However, in the circuit of FIG. 9, the switching elements Q1 and Q2 that switch at a high frequency are on the positive side of the power supply, and the switching elements Q3 and Q4 that switch at a low frequency are on the negative side of the power supply. The circuit of FIG. 5 is different in that switching elements Q7 and Q6 that switch by high frequency are provided in series on the choke coil L3 side, and switching elements Q5 and Q8 that switch by low frequency are provided in series on the discharge lamp La side. . 6A shows the operation of the switching element Q7, FIG. 6B shows the operation of the switching element Q6, FIG. 6C shows the operation of the switching element Q8, and FIG. 6D shows the operation of the switching element Q5. (E) shows the current waveform flowing through the choke coil L3, and (f) shows the current waveform flowing through the discharge lamp La.
[0025]
In the circuit of FIG. 5, when the switching element Q7 is turned on, the DC power supply E, the switching element Q5, the series circuit of the discharge lamp La and the inductance element L4 and its parallel capacitor C4, the choke coil L3, the switching element Q7, and the DC power supply E are closed. When current flows through the circuit and the switching element Q7 is turned off, current flows through the choke coil L3, the diode D6, the switching element Q5, the series circuit of the discharge lamp La and the inductance element L4, the parallel capacitor C4, and the closed circuit of the choke coil L3. . When the switching element Q6 is turned on, a current is passed through the DC power supply E, the switching element Q6, the choke coil L3, the series circuit of the discharge lamp La and the inductance element L4 and its parallel capacitor C4, the switching element Q8, and the closed circuit of the DC power supply E. When the switching element Q6 is turned off, a current flows through the choke coil L3, the series circuit of the discharge lamp La and the inductance element L4 and its parallel capacitor C4, the switching element Q8, the diode D7, and the closed circuit of the choke coil L3. The diodes D5 and D8 are for flowing a surge current at the time of transient, although no current flows in normal operation.
[0026]
In the present embodiment, at the time of polarity reversal, by operating at high frequency when switching elements Q5 and Q8 that switch at low frequency are turned on, the overshoot of the current flowing through the discharge lamp La at the time of polarity reversal is reduced, The electrode deterioration of the discharge lamp La can be suppressed and the life of the discharge lamp can be improved.
[0027]
In the circuit of FIG. 5, the bridge circuit is configured by a full bridge circuit including four switching elements Q5 to Q8. However, the two switching elements Q5 and Q8 (and their antiparallel diodes D5 and S5) that switch at a low frequency are used. D8) may be replaced with a capacitor, and a half-bridge circuit in which a bridge circuit is configured by two switching elements Q6 and Q7 that switch at high frequency and two capacitors may be used.
[0028]
(Embodiment 5)
FIG. 7 shows each waveform of the fifth embodiment. FIGS. 7A to 7F show waveforms at the same portions as those in FIGS. 6A to 6F. The circuit diagram is the same as that of the fourth embodiment, and a detailed description is omitted. In this embodiment, as shown in FIG. 7, the on-time of the switching elements Q6 and Q7 that switch at high frequency at the time of polarity inversion is narrowed, thereby reducing the overshoot of the current flowing through the discharge lamp La at the time of polarity inversion. Thus, electrode deterioration of the discharge lamp La can be suppressed and the life of the discharge lamp can be improved.
[0029]
(Embodiment 6)
FIG. 8 shows each waveform of the sixth embodiment. FIGS. 8A to 8F show waveforms at the same portions as those in FIGS. 6A to 6F. The circuit diagram is the same as that of the fourth embodiment, and a detailed description is omitted. In this embodiment, as shown in FIG. 8, the on-time of the switching elements Q6 and Q7 that are switched by a high frequency at the time of polarity inversion is narrowed and the switching elements Q5 and Q8 that are switched by a low frequency are turned on. By operating at a high frequency, it is possible to further reduce the overshoot of the current flowing through the discharge lamp La at the time of polarity reversal, suppress electrode deterioration of the discharge lamp La, and improve the life of the discharge lamp.
[0030]
【The invention's effect】
According to the present invention, a switching element operating at a low frequency responsible for polarity reversal is operated at a high frequency immediately after polarity reversal, or a switching element operating at a high frequency responsible for power control is shortened immediately after polarity reversal. Thus, by suppressing the current flowing to the discharge lamp immediately after the polarity reversal, the overshoot of the lamp current can be reduced, the electrode deterioration of the discharge lamp can be suppressed, and the life of the discharge lamp can be improved.
[Brief description of the drawings]
FIG. 1 is a circuit diagram according to a first embodiment of the present invention.
FIG. 2 is a waveform diagram for explaining operations of the first embodiment of the present invention.
FIG. 3 is a waveform diagram for explaining the operation of the second embodiment of the present invention.
FIG. 4 is a waveform diagram for explaining operations of the third embodiment of the present invention.
FIG. 5 is a circuit diagram of Embodiment 4 of the present invention.
FIG. 6 is a waveform diagram for explaining operations of the fourth embodiment of the present invention.
FIG. 7 is a waveform diagram for explaining the operation of the fifth embodiment of the present invention.
FIG. 8 is a waveform diagram for explaining the operation of the sixth embodiment of the present invention.
FIG. 9 is a circuit diagram of a conventional example.
FIG. 10 is a waveform diagram for explaining the operation of a conventional example.
FIG. 11 is a detailed waveform diagram at the time of polarity inversion in a conventional example.
[Explanation of symbols]
La discharge lamp E DC power source S Switching element (chopper circuit)
S1 to S4 Switching element (bridge circuit)

Claims (6)

DC power supply,
A chopper circuit including at least one switching element and an inductance that intermittently switches the output of the DC power source at a high frequency;
In a discharge lamp lighting device comprising a bridge circuit composed of at least two or more switching elements that invert the output polarity from the chopper circuit to the discharge lamp at a low frequency,
The switching element operating at the low frequency reduces the peak value of the output current of the chopper circuit while maintaining the output polarity to the discharge lamp at the same polarity as the output polarity after the polarity inversion for a certain period immediately after the polarity inversion. the discharge lamp lighting apparatus characterized by operating at a higher frequency than the lower frequency as. 2. The discharge lamp lighting device according to claim 1, wherein the ON time of the switching element of the chopper circuit is narrowed immediately after the polarity inversion. 2. The discharge lamp lighting device according to claim 1, wherein the frequency of the switching element of the chopper circuit is increased immediately after polarity inversion. 4. The discharge lamp lighting device according to claim 1, wherein the switching element of the chopper circuit is one and the switching element of the bridge circuit operating at a low frequency is composed of four. In any one of Claims 1-3, there are two switching elements of a chopper circuit, two switching elements which operate | move at low frequency, and these four switching elements comprise the full bridge circuit. A discharge lamp lighting device characterized. 4. The discharge lamp lighting device according to claim 1, wherein the bridge circuit is a half bridge circuit.

Images