JPH03246900A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To suppress an unstable discharge and an increase of stress to switching devices of an inverter at the start of the on-period by providing a selecting means selecting a duty ratio control means to perform a dimming action for a shallow dimming level and selecting a power control means to perform a dimming action for a deep dimming level. CONSTITUTION:When the voltage 8a of a reference voltage source 8 is lowered, the value of a variable resistor 72 is also decreased accordingly, the output frequency of an oscillating circuit 7 rises, the current amplitude of a discharge lamp 3 is decreased, and the dimming level is gradually made deep. When the dimming level becomes deep, a dimming means selected by a dimming means selecting circuit 9 is switched from a duty ratio control means 5 to a power control means in the middle, and the value of the variable resistor 72 is set not to generate a step in the brightness of the discharge lamp 3 at the time of this switching. An unstable discharge and an increase of stress to switching devices 21, 22 of an inverter 2 at the start of the on-period can be suppressed during dimming by duty ratio control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The invention of this application relates to dimming of a high-frequency lighting discharge lamp.

[Conventional technology]

Utility Model No. 64-4 is a device that supplies high-frequency power to a discharge lamp from an inverter to light the discharge lamp, and controls the power supplied to the discharge lamp to dim the discharge lamp.
The one disclosed in Japanese Patent No. 4600 is known.

FIG. 5 is a circuit diagram of this conventional example, and FIG. 6 is an explanatory diagram of its operation. In FIG. 5, 1 is a DC power supply, 2 is an inverter, 3 is a discharge lamp, 10 is an unstable multivibrator, and IC 2 is a voltage comparator.

The oscillation frequency of the unstable multivibrator 10 is set sufficiently lower than the oscillation frequency of the inverter 2 (however, the frequency is set to a level that does not cause flickering to the human eye). The voltage vA of the astable multivibrator IO is a triangular wave with a DC component, and is supplied to the inverting input terminal of the voltage comparator IC2. Constant voltage diode 21. variable resistance V
The voltage V8 of the voltage dividing circuit including R is a DC voltage with a voltage change rate greater than the voltage change rate of the DC power supply 1, and is supplied as a reference voltage to the non-inverting input terminal of the voltage comparator IC2. The reference voltage can be changed by operating the variable resistor VR. The output of the voltage comparator IC2 is supplied to the bases of the transistors Ql and Q2 of the inverter 2 as a base bias.

In the above configuration, the voltage vA, which is the triangular wave output having a DC component of the unstable multivibrator 10, is the reference voltage V
When the voltage becomes higher than B, the output of the voltage comparator IC2 becomes a low level (the output transistor of IC2 is turned on), and each transistor Ql, Q2 . A base bias is added to the oscillation operation period T shown in FIG. 0, the inverter 2 oscillates, and as a result, the discharge lamp 3 lights up.

When the voltage VA of the unstable multivibrator 10 becomes lower than the reference voltage VB, the output of the voltage comparator IC2 becomes a high level (the output transistor of IC2 is turned off), and as shown in the oscillation stop period T Otr in FIG. oscillation stops.

In this way, the inverter 2 alternates between oscillation operation and oscillation stop every cycle T of the oscillation transition of the unstable multivibrator 10.

The light of the discharge lamp can be controlled by changing the resistance value of the variable resistor VR and changing the reference voltage VB. For example, if the resistance value of the variable resistor VR is increased, the reference voltage VB becomes higher and the OFF period of the output transistor of the voltage comparator IC2, that is, the oscillation stop period T of the inverter 2. f
t becomes longer, To, /T (hereinafter referred to as duty ratio)
becomes smaller, and the discharge lamp 3 becomes darker.

When the voltage of the DC power supply 1 fluctuates, the voltage fluctuation rate of the reference voltage VB is equal to the voltage vA of the unstable multivibrator 10.
Therefore, the duty ratio of the inverter 2 changes to reduce the fluctuation in the brightness of the discharge lamp 3, and the fluctuation in the brightness of the discharge lamp 3 is suppressed.

It is also known to perform dimming by controlling the power while continuously supplying high-frequency power to the discharge lamp.

[Problem to be solved by the invention]

As explained above, in the conventional example shown in FIG. 5, dimming is performed by controlling the duty ratio of power supply to the discharge lamp, so in order to deepen the dimming, the duty ratio must be made considerably smaller, i.e. It is necessary to reduce the on-period ratio considerably. As a result, the period during which the power supply is suspended becomes longer, leading to problems such as unstable discharge and increased stress on the switching devices of the inverter (increase in instantaneous power) at the beginning of the on-period.

Further, in the conventional example in which dimming is performed by controlling continuously supplied power, there is a problem in that when the dimming is deep, the discharge becomes unstable and bright and dark moving stripes occur in the length direction of the tube.

The invention of this application was made in view of these problems, and provides: ■ a discharge lamp lighting device that does not cause unstable discharge or increase stress on the switching device of the inverter at the beginning of the on period, and ■ generates moving stripes of light and dark. It is an object of the present invention to provide a discharge lamp lighting device that is free from the above.

[Means to solve the problem]

In order to achieve the above-mentioned object, the invention of No. 1]4 comprises a discharge lamp lighting device as shown in (1) and (2) below.

(1) An inverter that supplies high-frequency power to a discharge lamp, a duty ratio control means that controls the duty ratio of power supply of the inverter, a power control means that controls the power supply of the inverter, and A discharge lamp lighting device comprising a selection means for selecting a duty ratio control means to perform a dimming operation, and selecting the power control means for performing a dimming operation when the dimming level is high.

(2) an inverter that supplies high-frequency power to the discharge lamp; a duty ratio control means that controls the duty ratio of the power supply of the inverter; and a power control means that controls the power supply of the inverter; A discharge lamp lighting device comprising a selection means for selecting a power control means to perform a dimming operation, and selecting the duty ratio control means for performing a dimming operation when the dimming level is deep.

[Effect]

With the configuration (1) above, when the dimming level is shallow, the dimming is performed by Tutee ratio control, and when the dimming level is deep, the dimming is performed by the power control means.

Further, according to the configuration (2) above, when the dimming level is shallow, the power control means performs the dimming, and when the dimming level is deep, the dimming is performed by duty ratio control.

〔Example〕

The invention of this application will be explained in detail below based on examples. FIG. 1 is a block diagram of a discharge lamp lighting device which is an embodiment of the invention of this application. In the figure, 1 is a DC power supply, 2 is an inverter that converts the power of the DC power supply 1 into high frequency power of 20 KH2 or more, 21.22 is a switching device of the inverter, 23.24 is a diode, 2
5 is a coil (ballast), 26.27 is a capacitor, and 3 is a discharge lamp. 4 is a control circuit that controls power supply to the discharge lamp.

5 is a duty ratio control means that generates a triangular wave generating circuit 51, a voltage comparator circuit 52, and a reference voltage source 8 that instructs the degree of dimming. The voltage comparison circuit 52 compares the voltage 8a of the reference voltage source 8 with the triangular wave generation circuit 5.
When the voltage is higher than the voltage 51a of 1, a high level signal is output, and when it is lower, a low level signal is output.

7 is an oscillation circuit that increases the oscillation frequency as the value of the resistor decreases, and resistor 71. The variable resistor 72 has an external resistor. The variable resistor 72 is connected to the reference voltage source 8, and its resistance value decreases as the voltage 8a of the reference voltage source 8 decreases.

6 is a drive circuit for the switching device 2122 of the inverter 2, and includes a flip-flop circuit 61. It is composed of ant circuits 62 and 63 and driver 64 and 65.

Reference numeral 9 denotes a dimming means selection circuit, which is comprised of a resistive voltage divider 93 consisting of resistors 91 and 92 connected to a suitable DC voltage source, a voltage comparison circuit 94, an OR circuit 95, a relay 96 and its contact 97.

The relay 96 closes the contact 97 when the input is at a high level, and the voltage comparator circuit 94 is configured so that the voltage 8a of the reference voltage source 8 is equal to the divided voltage 93 of the resistor voltage divider 93.
It is configured to output a low level signal when it is higher than a, and output a high level signal when it is lower than a. The resistive voltage divider 93 is set so that the divided voltage 93a becomes lower than the voltage 8a until the brightness reaches a predetermined dimming level from the full light state.

Oscillation circuit 7. Variable resistance 72. The coil 25 constitutes power control means that controls the power supplied to the inverter 2.

Note that the capacitor 27 is a large-capacity capacitor that constitutes a part of the inverter 2, and the capacitor 26 is a resonant capacitor of a filament circuit that constitutes a series resonant circuit with the coil 25 at the time of starting.

FIG. 2 is an explanatory diagram of the operation of this embodiment, in which (a) shows the current waveform of the discharge lamp 3 when the tute ratio control means 5 is selected and the dimming operation is performed, and (b) shows the current waveform of the discharge lamp 3. The input voltage waveform of the voltage comparison circuit 52 is shown, and (c) shows the current waveform of the discharge lamp 3 when the power control means is selected and the dimming operation is performed.

Next, the operation will be explained with reference to FIG. Now, the voltage 8a of the reference voltage source 8, which indicates the degree of dimming, is changed from the maximum value to the minimum value, thereby changing the degree of dimming from a shallow state to a deep state.

Voltage 8a of reference voltage source 8 or voltage 5 of triangular wave generation circuit 51
When the value is larger than the peak value of 1a, the intersection point a I + a 2 shown in FIG.
The output of No. 5 is always at a high level. Note that the voltage comparator circuit 94 outputs a low level signal according to the settings described above.

On the other hand, the oscillation circuit 7 has a frequency f determined by the resistance value of the resistor 71.
1, this high frequency is converted into a rectangular wave by the flip-flop circuit 61, and the AND circuits 62 and 63 are closed by the high level signal from the OR circuit 95.
are supplied to driver 64,65 via.

The switching devices 21, 22 of the inverter 2 are turned on and off alternately by the output of the driver 64, 65, and the DC power of the DC power source 1 is converted to high frequency power with a frequency f, and is transmitted through the coil 25, which is a stabilizer. The light is supplied to the discharge lamp 3, and the discharge lamp 3 is lit in a full-light state. The current of the discharge lamp 3 is set to a predetermined value by a coil 25.

The voltage 8a of the reference voltage source 8 is connected to the intersection a shown in FIG.
When the voltage is lowered slightly to the extent that I*a2..., the voltage comparator circuit 52 detects that the voltage 8a is
When the voltage is higher than the voltage 51a of 1, it outputs a high level signal,
When it is low, it outputs a low level signal.

That is, as shown in FIGS. 2(a) and 2(b), the signal is at a high level for a period of T1 and is at a low level for a period of T2. During the TI period, as described above, high frequency power of frequency f is supplied from the inverter 2 to the discharge lamp 3. Voltage comparison circuit 94
The person is still issuing low level No. 43, so
During period T2 when the output of the voltage comparison circuit 52 is at a low level, the OR circuit 95 outputs a low level, the output of the flip-flop 61 is blocked by the AND circuits 62 and 63, and the inverter 2 stops operating.

Therefore, the inverter 2 repeats the intermittent operation of the cycle T in which it operates for a period T1 and stops operating for a period T2, and the current waveform of the discharge lamp 3 is intermittent as shown in FIG. It will be done.

The degree of dimming can be changed by operating the reference voltage source 8 to change its voltage 8a and by changing the duty ratios T and /T.

When the voltage 8a of the reference voltage source 8 is further lowered to exceed a predetermined dimming degree, the voltage 8a becomes lower than the divided voltage 93a of the resistive voltage divider 93, and the output of the voltage comparison circuit 94 is inverted and becomes a high level. This high level signal causes OR circuit 9
5 becomes high level regardless of the output level of voltage comparison circuit 52, AND circuits 62 and 63 close, and relay 96 operates to close its contact 97.

Therefore, the external variable resistor 72 is connected in parallel to the resistor 71, the output frequency of the oscillation circuit 7 increases from f to T2, and the inverter 2 continuously operates at the output frequency f2. Further, since the output frequency of the inverter 2 increases from fl to T2, the impedance of the coil 25 increases, and the amplitude of the current of the discharge lamp 3 decreases to A2.

In this way, the dimming means selected by the dimming means selection circuit 9 is switched from the duty ratio control means to the power control means.

At the time of this switching, the value of the variable resistor 72 is determined so that there is no difference in the brightness of the discharge lamp 3.

Furthermore, when the voltage 8a of the reference voltage source 8 is lowered, the value of the variable resistor 72 is also reduced, and the oscillation circuit 7
The output frequency increases from T2, the current amplitude of the discharge lamp 3 also decreases from A2, and the degree of dimming gradually becomes deeper.

Dimming is performed as described above, but in this embodiment, when the degree of dimming becomes deep, the dimming means is switched from the duty ratio control means 5 to the power control means midway through, and the current stop period of the discharge lamp is T.
2 is eliminated, it is possible to prevent unstable discharge and increase in stress on the switching devices of the inverter at the beginning of the on-period due to interruption of power supply.

Contrary to the above embodiment, when the dimming level is low, the power control means is selected to perform the dimming, and when a predetermined dimming level is reached, the power control means is switched to dimming by the duty ratio control means, and the tuteity ratio is further reduced. An example of a "discharge lamp lighting device" that deepens the dimming level by adjusting the brightness is also conceivable.

That is, in FIG. 1, the voltage division ratio of the resistor voltage divider 93 is selected so that the output of the voltage comparison circuit 94 becomes a high level from the full light state to a predetermined dimming level, and becomes a low level when the dimming level is further increased. Bye.

According to this embodiment, when the dimming level is deep, the duty ratio control means performs the dimming, so the amplitude of the discharge lamp current becomes considerably larger than the amplitude when the same dimming level is achieved by the power control means. , the occurrence of bright and dark moving stripes can be prevented.

Although each of the above embodiments employs a lighting circuit using the coil 25 as a ballast, the present invention is not limited to this. For example, as in the conventional example shown in FIG. It can also be implemented for lighting circuits that use capacitors as ballasts. In this case, in order to reduce the power supplied to the discharge lamp, the output frequency of the inverter may be lowered.

Further, the configuration of the control circuit is not limited to the configuration of each embodiment, and for example, the dimming means selection circuit is not limited to the configuration of each embodiment, but may be of another method.

Further, in each embodiment, the duty ratio control means generates a signal with a predetermined cycle T, but the cycle is kept constant in this way, and the power supply period T to the discharge lamp or the stop period T2 is changed. In addition to changing the duty ratio by changing the cycle, the duty ratio may be changed by changing the ratio between the power supply period TI to the discharge lamp and the stop period T2. The present invention is not limited to the combination of a triangular wave generation circuit and a voltage comparison circuit as shown in the embodiment.

In addition, in each of the above embodiments, the power supply is controlled by changing the output frequency of the inverter, but the invention is not limited to this, for example, by changing the impedance of the ballast while keeping the output frequency of the inverter constant. You can go.

3 and 4 show different circuit examples of an inverter to which the present invention can be applied, and since such an inverter has only one switching device 21, the configuration of the drive circuit 6 can also correspond to this. For example, it is enough to make three pieces into one piece. In addition, the load discharge lamp is -
Of course, it is also possible to use a structure for multiple lights instead of single lights.

The structure of the DC power source 1 may be a DC power source obtained by rectifying an AC power source, or the like, in addition to a DC power source such as a battery.

The period T for repeating the power supply period T to the discharge lamp and the stop period T2 is not particularly limited, but should be selected so that it is not perceived as flickering by the human eye.

〔Effect of the invention〕

As explained above, according to the invention of claim 1 of this application, it is possible to suppress the instability of discharge and the increase in stress on the switching devices of the inverter at the beginning of the on period during dimming by duty ratio control. According to the second aspect of the invention, it is possible to prevent the occurrence of bright and dark moving stripes when continuously controlling the power supply.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment of the invention of this application, Fig. 2 is an explanatory diagram of the operation of the same embodiment, Figs. 3 and 4 are diagrams showing an example of an inverter circuit, and Fig. 5 is a conventional example. The circuit diagram of FIG. 6 is an explanatory diagram of the operation of the conventional example. In the figure, 2 is an inverter, 3 is a discharge lamp, 5 is a duty ratio control means, 7 is an oscillation circuit, 8 is a reference voltage source 9 is a dimming means selection circuit, 25 is a coil, and 72 is a variable resistor. In addition, in the figures, the same symbols indicate the same or equivalent parts.

Claims (2)

[Claims] (1) an inverter that supplies high-frequency power to a discharge lamp; a duty ratio control means that controls the duty ratio of the power supply of the inverter; a power control means that controls the power supply of the inverter; A discharge lamp lighting device comprising a selection means for selecting a duty ratio control means to perform a dimming operation and selecting the power control means for performing a dimming operation when the degree of dimming is deep. (2) an inverter that supplies high-frequency power to the discharge lamp; a duty ratio control means that controls the duty ratio of the power supply of the inverter; and a power control means that controls the power supply of the inverter; 1. A discharge lamp lighting device comprising a selection means for selecting a power control means to perform a dimming operation, and selecting the duty ratio control means for performing a dimming operation when the degree of dimming is deep.