JPH118084A - Discharge lamp lighting device - Google Patents

Abstract

[PROBLEMS] To provide a discharge lamp lighting device capable of maintaining a constant no-load voltage at startup even when the length of a lamp wire changes. SOLUTION: A DC power supply unit 1, series connected transistors 2 and 3, a series resonance circuit composed of a choke coil 4 and a capacitor 5 connected in parallel to the transistor 3, a power supply capacitor 6, and 1 A transformer 7 having a secondary winding connected thereto, and a frequency modulation control circuit 8 having a resistor 9 and a capacitor 10 and alternately turning on and off the transistors 2 and 3 are provided. In a discharge lamp lighting device to which a discharge lamp is connected, a third winding is provided in a transformer, the output of the winding is rectified and smoothed by a diode 11 and a capacitor 12, and applied to a trimmer resistor 13, and the output of the trimmer resistor is output. Is connected to the base of a transistor 16 via a resistor 14 and a constant voltage diode 15, the collector of the transistor is connected to the capacitor 10 of the frequency modulation control circuit, and the emitter is connected to the power supply via a resistor 17. Continue to configure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a discharge lamp lighting device for lighting a low-pressure discharge lamp such as a germicidal lamp using a half-bridge type inverter, and more particularly to a constant no-load voltage regardless of a change in lamp wire length. The present invention relates to a discharge lamp lighting device that can be held in a discharge lamp.

[0002]

2. Description of the Related Art In recent years, as a lighting device for a low-pressure discharge lamp such as a germicidal lamp that radiates ultraviolet rays, a lightened discharge lamp lighting device using a half-bridge type inverter as shown in FIG. . The discharge lamp lighting device shown in FIG.
The lighting device A includes a lighting device A of a half-bridge type inverter, a discharge lamp C such as a germicidal lamp, and a lamp line B connecting the lighting device A and the discharge lamp C. The lighting device A rectifies a DC power supply or a commercial AC voltage. A DC power supply unit 1 such as a DC power obtained by smoothing, two switching transistors 2 and 3 connected in series connected in parallel to the DC power supply unit 1, and a common connection of the switching transistors 2 and 3 connected in series A series resonance circuit composed of a choke coil 4 and a capacitor 5 and a capacitor 6 serving as a power supply connected between the point and the negative power supply terminal, that is, in parallel with one switching transistor 3.
And a transformer 7 having a primary winding 7a connected in parallel with the capacitor 5 and an oscillation frequency set by a time constant circuit including an externally connected resistor 9 and a capacitor 10, and the switching transistor 2, 3 and a frequency modulation control circuit 8 for alternately turning on / off. A discharge lamp C is connected to a secondary winding 7b of the transformer 7 via a lamp wire B.

[0003] Next, the operation of the discharge lamp lighting device thus configured will be described. Frequency modulation control circuit 8
When the switching transistor 2 is turned on, a current flows from the DC power supply unit 1 in the order of the switching transistor 2 → the choke coil 4 → the capacitor 5 → the capacitor 6;
Is charged. Next, when the transistor 2 is turned off and the transistor 3 is turned on, the capacitor 6 becomes a power source, and a current flows from the capacitor 6 in the order of the capacitor 5 → the choke coil 4 → the transistor 3. Such operations are performed alternately, whereby the choke coil 4 and the capacitor 5 cause series resonance, and a high-frequency resonance voltage is generated between the terminals of the capacitor 5. Since the primary winding 7a of the transformer 7 is connected in parallel to the capacitor 5, the transformer 7
In the secondary winding 7b, a no-load secondary voltage boosted at a turn ratio (n2 / n1) is generated.

Since the series resonance state of the choke coil 4 and the capacitor 5 changes according to the switching frequency of the switching transistors 2 and 3, the no-load secondary voltage on the secondary winding 7b side of the transformer 7 due to the resonance voltage of the capacitor 5 is , As shown by the curve in FIG. In FIG. 5, the secondary voltage required for the discharge lamp C to start discharging is V
_{If 0} , the switching transistors 2 and 3 at this time
Becomes f ₀ . The voltage required in the secondary winding 7b of the transformer 7 in order to reliably start the discharge lamp, for example a V _1. The switching frequency of the switching transistors 2 and 3 for generating the voltages V ₁ required for starting the discharge lamp reliably becomes higher f ₁ than f _0.

[0005] By applying a no-load secondary voltage sufficient to start the discharge of the discharge lamp to the discharge lamp C, the discharge lamp C starts to discharge and the current limited by the choke coil 4 is applied. Light. Thereby, the choke coil 4
Since the series resonance condition by the capacitor and the capacitor 5 breaks down, the voltage generated in the secondary winding 7b of the transformer 7 becomes the lamp voltage of the discharge lamp and maintains the discharge of the discharge lamp.

[0006]

When the germicidal lamp is lit in the conventional discharge lamp lighting device, the lighting device and the germicidal lamp are often separately provided, and the length of the lamp wire B in FIG. Varies depending on the installation location and is not constant. Therefore, for example, when a discharge lamp is connected to a lighting device using a lamp line having a length including the capacitor b1 between the lamp lines, the lamp line capacity b1 is
And a capacitance value corresponding to the turn ratio is added to the capacitance value of the capacitor 5. As a result, the condition of resonance with the choke coil 4 is broken, and the no-load secondary voltage generated in the secondary winding 7a of the transformer 7 is a proceeds to point b from point a high voltage V ₂ than V ₁ is made to occur. When the lamp line length is further increased, the no-load secondary voltage of the transformer 7 is further increased due to the inter-lamp line capacitance b2 in FIG. 4, and the points b to c (V ₃ ) in FIG.
Will move to As described above, when the lamp wire length increases and the line capacitance increases, the no-load secondary voltage of the discharge lamp lighting device approaches the resonance point as shown in FIG. I will. When the no-load secondary voltage increases near the resonance point, a fast-phase current flows through the switching transistors 2 and 3 to increase switching loss. Transformer dielectric breakdown may occur.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems in the conventional discharge lamp lighting device, and even if the length of the lamp line connecting the lighting device and the discharge lamp changes, the discharge lamp is started. It is an object of the present invention to provide a discharge lamp lighting device capable of keeping a no-load secondary voltage generated at the time constant and preventing a switching transistor and a transformer from being destroyed.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a DC power supply unit, two series-connected switching elements connected in parallel to the DC power supply unit, A series resonance circuit including a choke coil and a capacitor connected between a common connection point of the series-connected switching elements and the other end of one of the switching elements; and a frequency modulation control circuit for alternately controlling the opening and closing of the two switching elements. A discharge lamp lighting device for connecting a discharge lamp via a lamp wire to a secondary side of a transformer connected in parallel to a capacitor of a series resonance circuit of the inverter, and lighting the discharge lamp. Means for detecting a no-load voltage generated in the transformer at the time of starting before the lamp starts discharging; and detecting the run-time voltage based on a detection signal of the detecting means. Wherein regardless of the length of the line as no-load voltage is constant, but to provide a means for controlling the switching frequency of the switching element by the frequency modulation control circuit.

With this configuration, when the no-load voltage of the transformer at the time of starting the discharge lamp is to be increased due to a change in the length of the lamp line of the discharge lamp connected to the secondary side of the transformer, The switching frequency of the frequency modulation control circuit is controlled by the detection signal of the no-load voltage detecting means so that the no-load voltage of the transformer is kept constant. Is effectively prevented.

[0010]

Next, an embodiment will be described. FIG. 1 is a circuit configuration diagram showing an embodiment of a discharge lamp lighting device according to the present invention. The same or corresponding members as those of the conventional device shown in FIG. Omitted. The difference between the discharge lamp lighting device according to the present invention and the conventional discharge lamp lighting device is as follows. That is, the third winding 7c is provided in the transformer 7, and the output voltage is
Rectifier / smoothing by 11 and capacitor 12, trimmer resistor
13 is applied to both ends. The output terminal of the trimmer resistor 13 has a resistor 14 and a constant voltage diode (Zener diode) 15.
And the collector of the transistor 16 is connected to the external connection capacitor 10 of the frequency modulation control circuit 8, and the emitter of the transistor 16 is connected to the negative side of the DC power supply 1 via the resistor 17. It is a connected point.

Next, the operation of the embodiment configured as described above will be described. When a discharge lamp such as a germicidal lamp is started, an unloaded secondary voltage is applied to the secondary side of the transformer 7 by the operation of the frequency modulation control circuit 8, the switching transistors 2 and 3, and the series resonance circuit including the choke coil 4 and the capacitor 5. This is the same as in the conventional example shown in FIG. At this time, in a state where the capacitance b1 is added by the lamp wire, the resonance frequency shifts to a lower one, and a higher voltage is applied to the third winding 7c of the transformer 7 than before the capacitance b1 due to the lamp wire length is added. Occurs. When such a high voltage is generated, the voltage is rectified and smoothed by the diode 11 and the capacitor 12, divided by the trimmer resistor 13, and the voltage applied through the resistor 16 is applied to the constant voltage diode.
It is assumed that the values of the trimmer resistors 13 and 14 are adjusted in advance so that 15 turns on and the constant voltage diode does not turn on depending on the voltage when the capacitance b1 is not added by the lamp line. Thus, when a high voltage is generated due to the addition of the capacitor b1 by the lamp line, the constant voltage diode 15 is turned on, and a voltage corresponding to the voltage generated by the third winding 7c is applied to the base of the transistor 16 so that the base is applied. A current flows, so that a combined resistor between the collector and the emitter of the transistor 16 and the resistor 17 is inserted in parallel with the capacitor 10 externally connected to the frequency modulation control circuit 8.

As a result, the switching frequency of the frequency modulation control circuit 8 set by the time constant circuit composed of the resistor 9 and the capacitor 10 decreases, the secondary voltage of the transformer 7 without load decreases, and the third winding When the generated voltage of the capacitor 7c also decreases to a voltage at which the capacitance b1 due to the lamp line is not added, the constant voltage diode 15 is turned off, and thus the switching frequency at which the same no-load secondary voltage as in the state where the capacitance b1 is not added is generated. Balance at the point where is lower. In FIG. 2, the no-load secondary voltage indicated by the point a in the state where the capacitor b1 is not added changes the characteristic curve from the solid line to the dotted line due to the addition of the capacitor b1, but the switching frequency is f ₁ It is reduced to more f _2, whereby the no-load secondary voltage that occurs shifts to point b at the same level.

When the length of the lamp wire is further increased and the capacity b2 is added, the no-load secondary voltage tends to be further increased. The increased voltage is detected, and a voltage corresponding to the output voltage of the third winding 7c is applied to the base of the transistor 16 via the turned-on constant voltage diode 15, thereby reducing the combined resistance further reduced. 2 is connected in parallel to the external connection capacitor 10 of the modulation control circuit 8, so that the switching frequency of the frequency modulation control circuit 8 is further reduced, and the no-load secondary voltage has the same level of the characteristic curve shown by the dashed line in FIG. The point shifts to the point c to be balanced.

In this way, the no-load secondary voltage is kept constant irrespective of the length of the lamp wire, but when the discharge lamp starts discharging due to the no-load secondary voltage, the choke coil 4 restricts the discharge. And the series resonance condition of the choke coil 4 and the capacitor 5 breaks down.
The voltage generated in the secondary winding 7b of the transformer 7 decreases to become the lamp voltage of the discharge lamp. Therefore, the voltage generated in the third winding also decreases, and the constant voltage diode turns off. Is disconnected from the externally connected capacitor 10 of the frequency modulation control circuit 8, and the discharge of the discharge lamp is maintained as in the conventional discharge lamp lighting device.

As described above, the resonance condition at the time of no load in the discharge lamp lighting device according to the present embodiment is such that the resonance frequency shifts to a lower value as the lamp wire becomes longer. Since it is controlled to be low, the no-load voltage generated in the secondary winding of the transformer is kept constant as shown in FIG. 3, and therefore, the switching loss of the switching transistors 2 and 3 increases and the breakdown of the transformer occurs. Can be prevented.

[0016]

As described above with reference to the embodiment, according to the present invention, even when the length of the lamp line connecting the lighting device and the discharge lamp changes, the no-load secondary voltage due to the increase in capacity is obtained. Thus, it is possible to reliably start the discharge lamp and ensure the reliability of the discharge lamp lighting device.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a discharge lamp lighting device according to the present invention.

FIG. 2 is a graph showing a relationship between a change in switching frequency and a no-load secondary voltage in the embodiment shown in FIG. 1;

FIG. 3 is a graph showing a relationship between a lamp line capacity and a no-load secondary voltage in the embodiment shown in FIG. 1;

FIG. 4 is a circuit configuration diagram showing a conventional discharge lamp lighting device.

FIG. 5 is a graph showing the relationship between the switching frequency and the no-load secondary voltage in the conventional example shown in FIG.

6 is a graph showing a change in a no-load secondary voltage when a lamp line length changes in the conventional example shown in FIG. 4;

FIG. 7 is a graph showing a relationship between a change in lamp line capacitance and a no-load secondary voltage in the conventional example shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply part 2, 3 Switching transistor 4 Choke coil 5, 6 Capacitor 7 Transformer 8 Frequency modulation control circuit 9 External connection resistance 10 External connection capacitor 11 Diode 12 Capacitor 13 Trimmer resistance 14 Resistance 15 Constant voltage diode 16 Transistor 17 Resistance A half Bridge type inverter type lighting device B Lamp wire C Discharge lamp

Claims (1)

[Claims] 1. A direct-current power supply, two series-connected switching elements connected in parallel to the direct-current power supply, a common connection point between the two series-connected switching elements and one of the other switching elements. A half-bridge type inverter comprising a series resonance circuit composed of a choke coil and a capacitor connected between the two ends and a frequency modulation control circuit for alternately controlling the opening and closing of the two switching elements. A discharge lamp connected to a secondary side of a transformer connected in parallel to a capacitor through a lamp line to light the discharge lamp, the discharge lamp being generated in the transformer at the time of starting before the discharge lamp starts discharging. Means for detecting a no-load voltage, based on a detection signal of the detecting means, so that the no-load voltage is constant irrespective of the length of the lamp line, Means for controlling a switching frequency of a switching element by the frequency modulation control circuit.