JPH0750633B2 - Discharge lamp lighting device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device in which a discharge lamp is lit by an inverter equipped with a switching element that intermittently converts the output of a DC power supply into AC.

[Prior art]

As a discharge lamp lighting device of this type, for example, a circuit configuration as shown in FIG. 4 is known. That is, AC power supply
AC is full-wave rectified by the rectifier DB, the output of the rectifier DB is smoothed by the smoothing capacitor C, and a DC power supply for generating a DC power supply voltage V ₀ is provided. The output of this DC power supply is provided by the inverter 1 having a switching element. It is intermittently converted into alternating current, and the discharge lamp is turned on by the output voltage of the inverter 1. The inverter 1 is configured so that the DC power supply voltage V ₀ is interrupted by the _four switching elements Q _{1 to} Q ₄ , and the discharge lamp 2 is supplied with power via the current limiting inductance L. In addition, the discharge lamp 2 has a high-frequency bypass capacitor C ₁
Are connected in parallel. That is, the four switching elements Q _{1 to} Q ₄ are connected in series, two each (Q ₁ and Q ₃ , Q ₂ and Q ₄ ), and each series circuit is connected between both ends of the DC power supply. Therefore, the series circuit of the current limiting inductance L and the discharge lamp 2 is connected between the connection points of the switching elements Q ₁ , Q ₃ , Q ₂ , and Q ₄ of each series circuit. Further, diodes D _{1 to} D ₄ are connected in antiparallel to the switching elements Q _{1 to} Q ₄ , respectively. Switching elements Q ₁ and Q ₂ turn on at high frequency (several + kHz)
It is turned off, and switching elements Q ₃ and Q ₄ are switching elements.
It is turned on and off at a sufficiently low frequency (hundreds Hz) than Q _1, Q _2. As shown in FIGS. 5 (c) and 5 (d), the switching elements Q ₃ and Q ₄ are alternately turned on and off.
Figure (b), (c), the switching element Q ₂ is turned on and off during a period the switching element Q ₃ is turned on, FIG. 5 (a), (d), the switching The operation timing is set so that the switching element Q ₁ is turned on / off while the element Q ₄ is on. Therefore, when the switching element Q ₄ is on and the switching element Q ₁ is on, the DC power supply → the switching element Q ₁ → the current limiting inductance L → the discharge lamp 2 and the capacitor C ₁ → the switching element Q ₄ → the resistor R.
→ Switching element
When Q ₁ is turned off, due to the energy stored in the current limiting inductance L, the current limiting inductance L → discharge lamp 2 and capacitor C ₁ → switching element Q ₄ → resistor R → diode D ₃ → current limiting inductance L An electric current flows. On the other hand, when the switching element Q ₃ is on and the switching element Q ₂ is on, the DC power supply → the switching element Q ₂ → the discharge lamp 2 and the capacitor C ₁ → the current limiting inductance L → the switching element Q ₃ → the resistance R. → Current flows through the route called DC power supply,
When the switching element Q ₂ is turned off, the energy accumulated in the current limiting inductance L causes the current limiting inductance L → switching element Q ₃ → resistance R → diode D ₄
→ Discharge lamp 2 and capacitor C ₁ → Current flows through the path of inductance L for current limiting. By the above operation, the high frequency current I _L flows through the current limiting inductance L as shown in FIG. 5 (e). As shown in FIG. 5 (f), the capacitor C ₁ is set so as to pass the high frequency component I _C1 flowing in the current limiting inductance L, so that the lamp current 1 flowing in the discharge lamp 2 is As shown in (g),
A rectangular wave corresponding to the on-off cycle of the switching element Q _3, Q _4, becomes superimposed high frequency ripple component of the on-off cycle of the switching elements Q _1, Q _2. By the way, in the above circuit, a current corresponding to the lamp current is detected as the voltage across the resistor R, and the control circuit 3 is controlled so that the lamp current becomes constant according to the magnitude of the voltage across the resistor R.
The on-duty of switching elements Q ₁ and Q ₂ is feedback-controlled via. The control circuit 3 includes a lamp current detection circuit 11 and a high frequency generation circuit.
12, low frequency generation circuit 13, gate circuit 14, drive circuit 15
_{It is} composed of ₁ to 15 ₄ . The high frequency generation circuit 12 includes a sawtooth wave generation circuit 16, a pair of comparison circuits 17a and 17b, and an OR circuit 18 that outputs the logical sum of the outputs of both comparison circuits.
17b, when the output level of the sawtooth wave generation circuit 16 is lower than the reference voltage V _S , as shown in FIGS.
Output level becomes “H”. On the other hand, when the current I _L as shown in FIG. 6 (a) is flowing through the current limiting inductance L, the output of the lamp current detection circuit 11 is as shown by the broken line in FIG. 6 (b). When the output level of the lamp current detection circuit 11 is higher than the output level of the sawtooth wave generation circuit 16, the comparison circuit 17a sets the output level to "H" as shown in FIG. 6 (d). Therefore, the output of the OR circuit 18 is as shown in FIG. 6 (e). The low frequency generation circuit 13 includes a pulse generation circuit 19, a flip-flop circuit 20, a pair of NAND circuits 21a and 21b, etc., and a duty ratio of approximately 5 from each of the NAND circuits 21a and 21b.
The 0% pulse is output so that it turns on alternately. The gate circuit 14 is composed of a pair of NOR circuits 22a and 22b. Each of the NOR circuits 22a and 22b receives the output of the other when the output level of the low frequency generation circuit 13 is "H". An output obtained by inverting the output of the high frequency generation circuit 12 is obtained from the circuits 22a and 22b. Drive circuit 15 ₁ to 15 ₄ receives the output of the NOR circuit 22a, 22b of the output and the low frequency generation circuit 13 is to control the corresponding switching elements to Q ₁ to Q _4. As described above, in the control circuit 3, the high frequency generation circuit 12
By controlling the on-duty of, the lamp current is controlled so as to be kept substantially constant.

[Problems to be Solved by the Invention]

By the way, in such a discharge lamp lighting device, for example, if a discharge lamp 2 having a positive characteristic like a high pressure discharge lamp and having a lamp voltage rising as the life approaches, is used, the life of the discharge lamp 2 As the lamp voltage rises at the end, the current limiting inductance L
The current I _L flowing in
The period in which the output level of one of the 12 comparison circuits 17a is "H" is shortened. As a result, the control circuit 3 controls so that the ON period of the switching elements Q ₁ and Q ₂ is lengthened, the decrease of the lamp current is suppressed, and the lamp power is increased. That is, the lamp voltage and the lamp power have a relationship as shown by the solid line in FIG. Therefore, when the discharge lamp 2 reaches the end of its life and the lamp voltage exceeds the rating, an overload is caused, which shortens the life of the lamp or destroys the discharge lamp 2. In order to avoid such a problem, it is desirable to control so that the lamp power is sharply reduced when the lamp voltage exceeds the rating, as shown by the broken line in FIG. As a configuration for performing such control, a configuration as shown in FIG. 8 can be considered. That is, the lamp current detection circuit 11
The output of is averaged by the integrating circuit 23, and the average value _IX of the lamp current and the output of the sawtooth wave generating circuit 16 are compared by the comparing circuit 24, as shown in FIGS. 9 (a) and 9 (b). Further, the output level of the comparison circuit 24 is set to "H" during the period when the output level of the sawtooth wave generation circuit 16 is larger than the average value _{IX of the} lamp current. The output of the comparison circuit 24 thus obtained is logically ORed with the output of the high frequency generation circuit 12 by the OR circuit 25. Therefore, when the lamp voltage rises and the lamp current decreases, as described above, the period during which the output level of the high frequency generation circuit 12 becomes "H" becomes short, but conversely, the output level of the comparison circuit 24 becomes "H". The period during which the output level of the OR circuit 25 is "H" decreases with the lamp voltage in the region where the lamp voltage is relatively small, and increases when the lamp voltage exceeds a certain value. . That is, the switching elements Q ₁ , Q ₂
The ON period of is shortened. As a result, in a region where the lamp voltage is lower than the predetermined value, the lamp power increases with the rise of the lamp voltage, and in a region where the lamp voltage is higher than the predetermined value, the lamp power decreases as the lamp voltage increases. Of. However, in this configuration, in the region where the lamp voltage is equal to or higher than the set value, when the ON period of the switching elements Q ₁ and Q ₂ is reduced as the lamp current is reduced, the lamp current is further reduced by the feedback control. Rapidly decreases, the discharge of the discharge lamp 2 is likely to be unstable, and problems such as flicker and extinguishing occur. Further, as described above, the output of the sawtooth wave generation circuit 16 and the average value I _{X of the} lamp current are compared to each other, and the switching elements Q ₁ , Q ₂
When the on-duty of the switching elements Q ₃ and Q ₄ is controlled, the switching elements Q ₁ and Q ₂
The on-duty of is almost unchanged. On the other hand, when the switching frequency of the switching elements Q ₃ and Q ₄ is several hundreds Hz or less, the impedance of the discharge lamp 2 is high when the polarity is inverted and gradually becomes low. That is, while the impedance of the discharge lamp 2 changes during the half cycle of discharge, the on-duty of the switching elements Q ₁ and Q ₂ is almost constant, so the peak value of the lamp current changes and flicker occurs. The problem occurs. The present invention is intended to solve the above problem, in a region where the lamp voltage is lower than a predetermined value set to a rated voltage or higher, the lamp power is increased with an increase in the lamp voltage, and the lamp power is equal to or higher than the predetermined value. It is an object of the present invention to provide a discharge lamp lighting device in which flicker or extinguishing does not occur in a region having a predetermined value or more, while controlling the lamp power to decrease when the lamp voltage rises in the region.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides, in the configuration of claim 1, an inverter equipped with a switching element for intermittently converting an output of a DC power supply into an AC, and a discharge lamp having a positive characteristic that is turned on by the output of the inverter. In a discharge lamp lighting device equipped with a control circuit for controlling the on-duty of a switching element so that the lamp current to the lamp is almost constant, the average value of the lamp voltage is detected and the average value of the lamp voltage is increased. The lamp voltage detection circuit reduces the output level, the lamp current detection circuit that detects the instantaneous value of the lamp current and the output level changes according to the instantaneous value of the lamp current, and the output level of the ramp voltage detection circuit is the lamp current. Output that continuously reduces the on-duty of the switching element as the period during which it falls below the output level of the detection circuit increases A comparison circuit which is obtained with each other to comprise a.

[Action]

According to the above configuration, the average value of the lamp voltage is compared with the instantaneous value of the lamp current, and the output level of the lamp voltage detection circuit that decreases steplessly as the average value of the lamp voltage rises is The on-duty of the switching element of the inverter is reduced with the increase of the period when the output level becomes lower than the output level.Therefore, the feedback control is not performed only by the lamp current as in the conventional method, but the switching is performed by adding the average value of the lamp voltage. Since the on-duty of the element is controlled, by appropriately setting the relationship between the output level of the lamp current detection circuit and the output level of the lamp voltage detection circuit, the lamp voltage is kept slightly higher than the rated voltage. The rise of the lamp voltage (that is, the average value of the voltage does not affect the on-duty of the switching element) Controlled to lamp power increases with pump decrease in current), the lamp voltage is can be controlled to reduce the lamp power in accordance with the increase of the lamp voltage exceeds a predetermined value. That is, when a discharge lamp having a positive characteristic with respect to the lamp current is used, when the lamp voltage exceeds a predetermined value, the rise of the lamp voltage is suppressed, and the lamp life is shortened and the discharge lamp is prevented from being destroyed due to overload. It is. Moreover, while suppressing the rise of the lamp voltage, the on-duty of the switching element follows the change of the impedance with respect to the change of the instantaneous value of the lamp current, so that the impedance of the discharge lamp changes in a relatively short time. Also, the peak value of the lamp current can be kept almost constant, the rapid decrease of the lamp current at the end of the life of the discharge lamp, etc. can be prevented, the discharge can be stabilized, and the flicker and extinguishing can be prevented.
Even if the impedance of the discharge lamp changes in a relatively short time, the peak value of the lamp current can be kept almost constant, and the flicker and extinguishing unlike the conventional case do not occur.

Embodiment 1 The basic structure is the same as the conventional structure shown in FIG.
Since only part of the control circuit 3 is different, only the difference will be described. As shown in FIG. 1, a ramp voltage detection circuit 26, a comparison circuit 27, and an OR circuit 28 are added to the control circuit 3. Low frequency generation circuit 13, the gate circuit 14, the drive circuit 15 ₁ to 15 ₄ are the same as Figure 4 configuration. The lamp voltage detection circuit 26 is connected to the connection point between the discharge lamp 2 and the current limiting inductance L, and outputs the lamp voltage to the resistors R _{1 to} R ₃ and the capacitor.
Averaging is performed by an integrating circuit consisting of C ₂ and C ₃ . The average value of the lamp voltage is input to the differential amplifier circuit 29 via the diode D _5, etc., and the difference from the reference voltage set by the resistors R ₄ and R ₅ is obtained. Here, the output of the differential amplifier circuit 29 is set so as to decrease as the average value of the lamp voltage rises. As shown in FIG. 2 (b), the output of the lamp current detection circuit 11 is compared with the output level V _X of the lamp voltage detection circuit 26 by the comparison circuit 27, and the output of the lamp current detection circuit 11 is compared with the output level of the lamp voltage detection circuit 11. When the output level V _{x of} 26 is exceeded, the output level of the comparison circuit 27 becomes "H" as shown in FIG. 2 (c). That is, as the lamp voltage increases, the comparison circuit
The period in which the output level of 27 becomes "H" becomes longer.
The output of the comparison circuit 27 is logically ORed with the output of the high frequency generation circuit 12 by the OR circuit 28, and the output of the OR circuit 28 is input to the gate circuit 14. However, if the lamp voltage rises when the output of the high frequency generation circuit 12 is as shown in FIG. 2 (a), the comparison circuit
The period in which the output level of 27 is "H" is long, and as shown in FIG. 2 (d), the on period of the OR circuit 28 is longer than that in the case where only the high frequency generation circuit 12 is used. That is, the lamp power is reduced. put it here,
By selecting each constant value of the lamp voltage detection circuit 26, until the lamp voltage reaches a predetermined value which is slightly higher than the rated voltage, the lamp power is also increased with the increase of the lamp voltage, and the lamp voltage is the above-mentioned predetermined value. When it exceeds the value, the output level of the comparison circuit 27 becomes "H" so that the lamp power can be controlled to decrease with the increase of the lamp voltage. By the way, by comparing the output of the lamp voltage detection circuit 26 set to decrease with the increase of the average value of the lamp voltage and the instantaneous value of the lamp current, the switching elements Q ₁ and Q ₂ (see FIG. 4) are compared. Since the on-duty of the lamp is controlled, even if the impedance of the discharge lamp 2 changes, the peak value of the lamp current can be kept substantially constant by the feedback control based on the instantaneous value of the lamp current.
The flickering does not occur when the feedback control based on the average value of the lamp current is performed. Also,
Since the average value of the lamp voltage is detected and the ON period of the switching elements Q ₁ and Q ₂ is reduced with the rise of the lamp voltage, the discharge lamp 2 having a positive characteristic with respect to the lamp current is used. Even if it is present, the rise of the lamp voltage is suppressed and the discharge does not become unstable.

Second Embodiment In the first embodiment, the lamp voltage is detected from the connection point between the discharge lamp 2 and the current limiting inductance L, but in the present embodiment, the current limiting inductance L is detected as shown in FIG. A transformer T that also serves as a transformer is provided, and the output voltage of the secondary winding of the transformer T is full-wave rectified by the rectifier 29, and then the capacitor is formed.
The average value of the lamp voltage is indirectly obtained by smoothing with C ₄ . In this configuration, when a substantially constant voltage is applied to the series circuit of the discharge lamp 2 and the primary winding of the transformer T on average, when the lamp voltage rises, the secondary winding of the transformer T Since the output voltage decreases,
The differential amplifier circuit becomes unnecessary. In each of the above embodiments, the inverter 1 having the configuration shown in FIG. 4 is illustrated, but a half-bridge type inverter is used, or a full-bridge type inverter is loaded in the subsequent stage of the chopper circuit for converting direct current into alternating current. The same effect can be obtained even with the configuration used as.

【The invention's effect】

As described above, the present invention compares the average value of the lamp voltage with the instantaneous value of the lamp current, and the output level of the lamp voltage detection circuit that decreases with the increase of the average value of the lamp voltage is the output of the lamp current detection circuit. Since the on-duty of the switching element of the inverter is reduced steplessly with an increase in the period of time below the level, feedback control is performed only with the lamp current as in the past, and switching is performed with the average value of the lamp voltage taken into consideration. By controlling the on-duty of the element, the relationship between the output level of the lamp current detection circuit and the output level of the lamp voltage detection circuit can be set appropriately until the lamp voltage reaches a predetermined value that is slightly higher than the rated voltage. The lamp voltage rises (that is, the run voltage is adjusted so that the average value of the voltage does not affect the on-duty of the switching element). Controlled to the lamp power increases with decreasing current), the lamp voltage can be controlled to reduce the lamp power in accordance with the increase of the lamp voltage exceeds a predetermined value. That is, when a discharge lamp having a positive characteristic with respect to the lamp current is used, when the lamp voltage exceeds a predetermined value, the rise of the lamp voltage is suppressed, and the lamp life is shortened and the discharge lamp is prevented from being destroyed due to overload. Has the effect of Moreover, while suppressing the rise of the lamp voltage, the on-duty of the switching element follows the change of the impedance with respect to the change of the instantaneous value of the lamp current, so that the impedance of the discharge lamp changes in a relatively short time. Also, the peak value of the lamp current can be kept substantially constant, the rapid decrease of the lamp current at the end of the life of the discharge lamp, etc. can be prevented, the discharge can be stabilized, and flicker and extinguishing can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram of essential parts showing a first embodiment of the present invention, FIG. 2 is an operation explanatory diagram of the same as above, FIG. 3 is a circuit diagram of essential parts showing a second embodiment of the present invention, and FIG. 4 is a conventional example. FIG. 5 to FIG. 7 are operation explanatory diagrams of the same as above, FIG. 8 is a main part circuit diagram showing another conventional example, and FIG. 9 is an operation explanatory diagram of the same. 1 ... Inverter, 2 ... Discharge lamp, 3 ... Control circuit, 11 ...
Lamp current detection circuit, 26 ... lamp voltage detection circuit, 30 ... comparator circuit, Q ₁ to Q ₄ ... switching elements.

Claims (1)

[Claims] 1. An inverter equipped with a switching element for intermittently converting the output of a DC power supply to convert it into an alternating current, and a switching element for switching so that the lamp current to a positive-characteristic discharge lamp lit by the output of the inverter is substantially constant. In a discharge lamp lighting device including a control circuit for controlling on-duty, the control circuit detects an average value of a lamp voltage and a lamp voltage detection circuit whose output level decreases as the average value of the lamp voltage rises. A lamp current detection circuit that detects the instantaneous value of the lamp current and the output level changes according to the instantaneous value of the lamp current, and the period during which the output level of the lamp voltage detection circuit falls below the output level of the lamp current detection circuit. And a comparison circuit that can obtain an output that continuously reduces the on-duty of the switching element as the The discharge lamp lighting device characterized by comprising.