JPH03167789A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To prevent occurrence of flicker and going out by detecting the mean value of lamp voltage, and by increasing or decreasing on-duty following rising of the lamp voltage in a range where the obtained mean value of the lamp voltage is either lower or higher than the specific value, which is set over the rated voltage of the discharge lamp. CONSTITUTION:A comparator circuit 27 compares a momentary value of lamp current with the output of a lamp voltage detecting circuit 26, which is so set as decreasing with rise of the mean value of the lamp voltage, and the result is used for controlling the on-duty of a switching element. That is, control is so made that the lamp power is increased with rise of the lamp voltage in a range where the lamp voltage is lower than a specific value, which is set over the rated voltage, while the lamp power is decreased with rise of the lamp voltage in a range where the lamp voltage is over the specific value. This prevents the discharge from becoming unstable in the range where the lamp voltage is over the specific value, and also prevents flickering.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a discharge lamp lighting device that lights a discharge lamp using an inverter equipped with a switching element that intermittents the output of a DC power source and converts it into AC.

[Conventional technology]

As this type of discharge lamp lighting device, for example, a circuit ellipse as shown in FIG. 4 is known. That is, AC power R
The AC is full-wave rectified by a rectifier DB, and the output of the rectifier DB is smoothed by a smoothing capacitor C to obtain a DC power supply voltage V. The output of this DC power source is intermittently converted into alternating current by an inverter 1 equipped with a switching element, and the discharge lamp is lit by the output voltage of the inverter 1. The inverter 1 is configured to intermittent the DC power supply voltage V0 using four switching elements Q1 to Q4, and supply power to the discharge lamp 2 via the current limiting inductance L. Further, a high frequency bypass capacitor C1 is connected in parallel to the discharge lamp 2. That is, two of the four switching elements Q to Q, (Q, and Q, and Q2 and Q.) are connected in series, and each series circuit is connected between both ends of the DC power supply. , and the switching element Q. of each series circuit. ．． Q. ,Q2,Q. A series circuit of the current-limiting inductance L and the discharge lamp 2 is connected between the connection points. Furthermore, diodes D1 to D are connected in antiparallel to each of the switching elements Q1 to Q, respectively. Switching element Q. , Q2 are turned on and off at a high frequency of several tens of kHz, and the switching elements Q, . Q. is the switching element Q. ．． Frequency sufficiently lower than Q2 (several hundred H
z) is turned on and off. Figure 5(c). As shown in (d), switching elements Q, . Q. are turned on and off alternately, as shown in Figure 5(b). As shown in FIG. 5(c), the switching element Q2 is turned on and off during the period when the switching element Q3 is on, and as shown in FIG. 5(a).
As shown in (d), the operation timing is set so that the switching element Q is turned on and off during the period when the switching element Q4 is on. Therefore, switching element Q. When is on, switching element Q1 is on, DC power →
Switching element Q1 - current limiting inductance L → discharge lamp 2 and capacitor C, - switching element Q,
Current flows through the path of one resistor R and one DC power supply, and...
When the notching element Q1 is turned off, the energy transferred to the current limiting inductance causes a current to flow through the path of current limiting inductance L → discharge lamp 2 and capacitor CI - switching element Q4 → resistor R → diode D, → current limiting inductance L. flows. on the other hand,
When the switching element Q3 is on, and the switching element Q2 is on, the DC power source - the switching element Q2 - the discharge lamp 2 and the capacitor C1 -> the current limiter/ductor L - the switching element Q, - the resistor R ->
Current flows through the path called the DC power supply, and the switching element Q
2 is turned off, the energy stored in the current limiting inductance causes the current limiting inductance L - switching element Q1 - resistor R - diode D. - A current flows through the path of the discharge lamp 2 and the single-lens inductance L of the capacitor C1. As a result of the above-described operation, a high frequency current {circle around (2)} flows through the current limiting inductance, as shown in FIG. 5(e). As shown in No. 5D(f), the capacitor C is a high-frequency component (■) flowing through the current-limiting inductance. 1, the lamp current 11 flowing through the discharge lamp 2 becomes a rectangular wave corresponding to the on/off period of the switching elements Q, , Q, as shown in Fig. 5 (g>). ,, it is a superimposition of the high frequency real components of switching on/off m + m of switch switching element Q.. The control circuit 3
The on-duty of the switching elements Q, . The control circuit 3 includes a lamp current detection circuit 1l, a high frequency generation circuit 12, a low frequency generation circuit 13, a gate circuit 14, and drive circuits 151 to 154. The high frequency generation circuit 12 includes a sawtooth wave generation circuit 16 and a pair of comparison circuits 17.
a, 17b, and the OR circuit 18 which outputs the logical sum of the outputs of both comparison circuits, the comparison circuit 17b is
As shown in c), when the output level of the sawtooth wave generation circuit 16 is lower than the reference voltage V3, the output level is "H".
become. On the other hand, the 6th [m
When a current T Ll as shown in (a) is flowing, the output of the lamp current detection circuit 1↓ (2) becomes as shown by the broken line in Fig. 6 (b). When the output level of the detection circuit 11 is higher than the output level of the sawtooth wave generation circuit 16, the output level is set to "H" as shown in FIG. 6(e).The low frequency generation circuit 13 includes a pulse generation circuit 19, a flip-flop circuit 20, and a pair of Nantes circuits 21a.2l.
The NAND circuits 2 1 a and 2 lb each output pulses having a duty ratio of approximately 50% so as to be alternately turned on. The gate circuit l4 includes a pair of NOR circuits 22a. 22b, and each NOR circuit 22a, 22b is a low frequency generating circuit 13.
When the output level of one of the NOR circuits 22a. is "H", the output of the other is input. An output obtained by inverting the output of the high-frequency generating circuit 12 is obtained from the high-frequency generating circuit 22b. Drive circuits 15+ to 15 are NOR circuits 22a22b
The corresponding switching elements Q1 to Q are controlled in response to the output of the low frequency generating circuit 13 and the output of the low frequency generating circuit 13. As described above, in the control circuit 3, the high frequency generation circuit 1
By controlling the on-duty in step 2, the lamp current is controlled to be kept approximately constant.

[Problem to be solved by the invention]

By the way, in such a discharge lamp lighting device, if a discharge lamp 2 having positive characteristics such as a high-pressure discharge lamp and in which the lamp voltage increases as the life approaches, the life of the discharge lamp 2 As the lamp voltage increases in the final stage, the current-limiting inductance L
The slope of the current IL flowing through the current IL becomes steeper, and the period during which the output level of one comparison circuit 17a of the high frequency generation circuit 12 is at "H" becomes shorter. As a result, the control circuit 3 lengthens the on period of the switching elements Q, , Q2, suppresses a decrease in lamp current, and increases lamp power. That is, the lamp voltage and 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 rated value, problems such as overloading may occur, shortening the lamp life or destroying the discharge lamp 2. In order to avoid such problems, it is desirable to perform control such that when the lamp voltage exceeds the rated value, the lamp power is rapidly reduced, as shown by the broken line in FIG. As a configuration for performing the second type of control, a horizontal configuration as shown in FIG. 8 can be considered. That is, lamp current detection circuit 1
1 is averaged by an integrating circuit 23, and the average value of the lamp current (3) and the output of the sawtooth wave generating circuit 16 are compared by a comparing circuit 24, as shown in FIG. 9 (aHb). The output level of the comparator circuit 24 is set to ``H'' during the period when the output level of the sawtooth wave generating circuit 16 is greater than the average value Iu of the lamp current. The output is logically summed with the output of the high frequency generation circuit 12 by the OR circuit 25. Therefore, when the lamp voltage increases and the lamp current decreases, the output level of the high frequency generation concave path 12 changes as described above. { '' becomes shorter, but conversely, the period when the output level of the comparator circuit 24 is "H" becomes longer, so during the period when the output level of the OR circuit 25 is "H", the lamp voltage In the region where the target is small, it decreases with the lamp voltage, and increases when the lamp voltage exceeds a certain value. That is, the switching element Q. , Q2's on period becomes shorter. As a result, in the region where the lamp voltage is lower than a predetermined value, the lamp power increases as the lamp voltage increases, and in the region where the lamp voltage exceeds the predetermined value, the lamp power decreases as the lamp voltage increases. It becomes. However, in this configuration, in a region where the lamp voltage is above the set value, when the ON period of the switching elements Q, Q2 decreases as the lamp radiation decreases, the lamp current further decreases due to feedback control. The lamp current decreases rapidly, and the discharge of the discharge lamp 2 tends to become unstable, causing problems such as flickering and turning off. Furthermore, as described above, the output of the sawtooth wave generating circuit 16 is compared with the average value IX of the lamp current, and the switching element Q
．． ．． When controlling the on-duty of switching elements Q, . Q. During the on period of switching element Q. , the on-duty of Q2 hardly changes. On the other hand, the switching element Q. When the switching frequency of Q4 is several hundred Hz or less, the impedance of the discharge lamp 2 is high when the polarity is reversed and gradually becomes low. That is, while the impedance of the discharge lamp 2 changes during a half cycle of discharge, the impedance of the switching element Q. , Q2 are substantially constant, the peak value of the lamp current changes, causing a problem of flickering. The present invention aims to solve the above-mentioned problem, and in a region where the lamp voltage is lower than a predetermined value set above the rated voltage, the lamp power is increased as the lamp voltage increases. It is an object of the present invention to provide a discharge lamp lighting device that does not cause flickering or turning off in the region above the predetermined value, while controlling the lamp power to decrease as the lamp voltage increases in the region.

[Means to solve the problem]

In order to achieve the above object, the present invention has an inverter equipped with a switching element that intermittents the output of a direct 7fL power source and changes it to alternating current, and a positive characteristic discharge that is lit by the output of the inverter. In a discharge lamp lighting device equipped with a control circuit that controls the on-duty of a switching element so that the lamp current to the lamp is approximately constant, the average value of the lamp voltage is detected, and the average value of the lamp voltage is In a region lower than a predetermined value set above the rated voltage, the on-duty increases as the lamp voltage increases, and in a region where the average value of the lamp voltage is above the predetermined value, the average value of the lamp voltage increases. Accordingly, the control circuit is designed to reduce the on-duty. Further, in the configuration of claim 2, the control circuit includes a lamp voltage detection circuit that detects the average value of the lamp voltage and reduces the output level as the average value of the lamp voltage increases, and a lamp voltage detection circuit that detects the instantaneous value of the lamp current. The lamp current detection circuit is provided with a lamp current detection circuit that detects the lamp voltage, and a comparison circuit that obtains an output that reduces the on-duty of the switching element as the period in which the output level of the lamp voltage detection circuit exceeds the output level of the lamp current detection circuit increases. be.

[Effect]

According to the structure of claim 1, since the lamp voltage is detected and the on-demand switching element is controlled by detecting the lamp voltage, instead of performing feedback control using only the lamp current as in the past, the lamp voltage is The lamp power can be controlled to increase as the lamp voltage increases in a region lower than a predetermined value set above the rated voltage, and to decrease the lamp power when the lamp voltage increases in a region above the predetermined value. Not only is this possible, but the discharge does not become unstable in the range above the predetermined value, and flickering can be prevented. In addition, in the configuration of claim 2, since the on-duty of the switching element is determined by comparing the average value of the lamp voltage and the instantaneous value of the lamp discharge, the on-duty of the switching element is determined. Even if the impedance changes, the peak value of the lamp current can be kept almost constant, and there is no flickering or turning off like in conventional lamps.

[Embodiment 1] The basic configuration is the same as the conventional configuration shown in FIG.
Since only a part of the control circuit 3 is different, only the differences will be explained. As shown in FIG. 1, a lamp voltage detection circuit 26, a comparison circuit 27, and an OR circuit 28 are added to the control circuit 3. The low frequency generation circuit 13, gate circuit 14, and drive circuits 15, . . . , are the same as those in FIG. 4. The lamp voltage detection circuit 26 is connected to the connection point between the discharge lamp 2 and the current-limiting inductance L, and detects the lamp voltage through the resistors R1 to R and the capacitor C2. Averaging is performed by an integrating circuit consisting of C3. The average value of the lamp voltage is input to two differential amplifier circuits via a diode D, etc., and is input to two differential amplifier circuits via a diode D, etc., and is input to two differential amplifier circuits via a diode D, etc. The difference from the reference voltage set by is obtained. Here, the outputs of the two differential amplifier circuits are set so that they decrease as the average value of the lamp voltage increases. As shown in FIG. 2(b), the output of the lamp current detection circuit 11 is sent to the lamp voltage detection circuit 26 by the comparison circuit 27.
is compared with the output level VX of the lamp current detection circuit 1l.
When the output of the comparison circuit 27 exceeds the output level VX of the lamp voltage detection circuit 26, the output level of the comparison circuit 27 becomes "H" as shown in FIG. 2(e). That is, as the lamp voltage increases, the period during which the output level of the comparator circuit 27 is "H" becomes longer. The output of the comparison circuit 27 is ORed with the output of the high frequency generation circuit 12 by an OR circuit 28, and the output of the OR circuit 28 is input to the gate circuit 14. However, the output of the high frequency generation circuit 12 is as shown in FIG. 2(a).
If the lamp voltage increases when Also, the ON period of the OR circuit 28 becomes longer. That is, the lamp power is reduced. Here, by selecting each constant value of the lamp voltage detection circuit 26, the lamp power is increased as the lamp voltage increases until the lamp voltage reaches a predetermined value slightly higher than the rated voltage. When the voltage exceeds the predetermined value, the output level of the comparator circuit 27 becomes "H", so that the lamp power can be controlled to decrease as the lamp voltage increases. By the way, the instantaneous value of the lamp current is compared with the output of the lamp voltage detection circuit 26, which is set to decrease as the average value of the lamp voltage increases, and the output of the switching element Q. ,Q
．． Since the on-duty of the lamp (see Figure 4) is controlled, even if the impedance of the discharge lamp 2 changes, the peak value of the lamp current is kept almost constant through feedback control based on the instantaneous value of the lamp current. This eliminates the flickering that occurs when feedback control is performed using the average value of the lamp current. Also, the average value of the lamp voltage is detected, and the switching element Q. ．． Since the on-period of Q is reduced, even when a discharge lamp 2 having positive characteristics with respect to lamp current is used, the increase in lamp voltage is suppressed and the discharge does not become unstable.

[Example 2] In Example 1, the lamp voltage was detected from the connection point between the discharge lamp 2 and the current-limiting inductance L, but in this example, the current-limiting inductance L was detected as shown in FIG. Transformer Tf that doubles as a Tf! : is provided, and after the output voltage of the secondary winding of this transformer T is full-wave rectified by a rectifier 29, it is smoothed by a capacitor C to obtain an average value of the lamp voltage. This is because when the lamp voltage increases, the output voltage of the secondary winding of the transformer T decreases.
A differential amplifier circuit becomes unnecessary. In addition, each of the above-mentioned fruits 'Il! In this example, the configuration shown in Figure 4 was used as the inverter 1, but a configuration using a half-brin' type inverter or a full-bridge type inverter as a load at the downstream stage of a chopper circuit that converts DC to AC is also possible. You can also get the same effect.

【Effect of the invention】

As described above, the configuration of claim 1 includes an inverter equipped with a switching element that intermittents the output of a DC power source and changes it to AC, and a lamp current flowing to a discharge lamp with a positive characteristic that is lit by the output of the inverter. In a discharge lamp lighting device equipped with a control circuit that controls the on-duty of a switching element so that it is almost constant, the average value of the lamp voltage is detected, and the average value of the lamp voltage is equal to or higher than the rated voltage of the discharge lamp. In the region where the lamp voltage is lower than the predetermined value, the on-duty increases as the lamp voltage increases, and in the region where the average value of the lamp voltage is equal to or higher than the predetermined value, the on-duty increases as the average value of the lamp voltage increases. The control circuit is configured to reduce the duty, and instead of feedback control based only on the lamp current like a slave flux, it detects the lamp voltage and switches!
Since the on-duty of the switching element is controlled, if the lamp voltage is stubbornly lower than a predetermined value set above the rated voltage, the lamp power is increased as the lamp voltage increases, and the lamp power is increased to the above-mentioned predetermined value. In the above range, it is possible to control the lamp power to decrease as the lamp voltage increases, and even in the range above the predetermined value, the discharge will not become unstable and flickering can be prevented. There are advantages. In addition, the control circuit includes a lamp voltage detection circuit that detects the average value of the lamp voltage and reduces the output level as the average value of the lamp voltage increases, and an instantaneous value of the lamp current. a lamp current detection circuit that detects the current, and a comparison circuit that obtains an output that reduces the on-duty of the switching element as the period in which the output level of the lamp voltage detection circuit exceeds the output level of the lamp current detection circuit increases. Since the on-denity of the switching element is determined by comparing the average value of the lamp voltage and the instantaneous value of the lamp current, the discharge occurs within a relatively short period of time, such as a half cycle of discharge. Even if the impedance of the lamp changes, the peak value of the lamp current can be kept almost constant, and the effect is that there is no flickering or turning off like in the conventional case.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a main part showing a first embodiment of the present invention, Fig. 2 is an explanatory diagram of the same operation as above, Fig. 3 is a circuit diagram of a main part showing a second embodiment of the invention, and Fig. 4 is a conventional example 5 to 7 are diagrams illustrating the operation of the same as above, FIG. 8 is a circuit diagram of a main part showing another conventional example, and FIG. 9 is a diagram illustrating the operation of the same. l...Inverter, 2...Discharge lamp, 3...Control circuit, 11...Lamp current detection circuit, 26...Lamp voltage detection circuit, 30...Comparison circuit, Q, ~Q,...・
・Switching element.

Claims (2)

[Claims] (1) An inverter equipped with a switching element that intermittents the output of a DC power source and changes it to AC, and an on-duty control of the switching element so that the lamp current to the positive characteristic discharge lamp that is lit by the inverter output is approximately constant. In the discharge lamp lighting device, the control circuit detects the average value of the lamp voltage, and the average value of the lamp voltage is lower than a predetermined value set to be equal to or higher than the rated voltage of the discharge lamp. The on-duty is increased as the lamp voltage increases in a low region, and the on-duty is decreased as the average lamp voltage increases in a region where the average value of the lamp voltage is equal to or higher than the predetermined value. discharge lamp lighting device. (2) The control circuit includes a lamp voltage detection circuit that detects the average value of the lamp voltage and whose output level decreases as the average value of the lamp voltage increases, and a lamp current detection circuit that detects the instantaneous value of the lamp current. , a comparison circuit that can obtain an output that reduces the on-duty of the switching element as the period in which the output level of the lamp voltage detection circuit exceeds the output level of the lamp current detection circuit increases. Item 1. The discharge lamp lighting device according to item 1.