JPH03246899A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To prevent an unstable discharge and an increase of stress to switching devices of an inverter at the start of the on-period by providing a duty ratio control means and a means controlling the feed power from the inverter when a discharge lamp is lighted. CONSTITUTION:When a dimming switch 8 is turned on, the action of a drive circuit 6 is stopped. The resistance value determining the output frequency of an oscillation control circuit 74 is reduced, the output frequency of an oscillating circuit 7 rises, the impedance of a coil 25 is increased, and the current of a discharge lamp 3 is decreased. The duty ratio for the preset dimming level can be increased, and the stop period of the power feed can be shortened. An unstable discharge and an increase of stress to switching devices 21, 22 of the inverter 2 at the start of the on-period for dimming by duty ratio control can be suppressed.

Description

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

[Prior art] A device that supplies high-frequency power from an inverter to a discharge lamp to light the discharge lamp, and controls the power supplied to the discharge lamp to dim the discharge lamp is known as -4
The one disclosed in Japanese Patent No. 4600 is known.

FIG. 8 is a circuit diagram of this conventional example, and FIG. 9 is an explanatory diagram of its operation. In FIG. 8, 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 unstable multivibrator 10 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 VB of the voltage dividing circuit including R is a DC voltage with a voltage change rate larger 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 1c2 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 applied to the inverter 2, and the inverter 2 oscillates as shown in the oscillation operation period T0° in FIG. 9, 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 high level (the output transistor of IC2 is turned off), and the inverter 2 is turned off as shown in the oscillation stop period T Off in FIG. oscillation stops.

In this way, the inverter 2 alternates between oscillating operation and stopping oscillation every oscillation period T of the unstable multivibrator 10.

The dimming of the discharge lamp can be performed 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
f becomes longer and 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 so that the fluctuation in the brightness of the discharge lamp 3 is reduced, and the fluctuation in the brightness of the discharge lamp 3 is suppressed.

[Invention or problem to be solved]

As explained above, in the conventional example shown in Fig. 8, 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, that is, 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.

An object of the present invention is to provide a discharge lamp lighting device that can solve these problems.

(Means for Solving the Problem) In order to achieve the above object, the present invention uses power control in combination with duty ratio control. Specifically, a discharge lamp lighting device is configured as follows (1). It is something.

(1) An inverter that supplies high-frequency power to a discharge lamp, a duty ratio control means that controls a duty ratio of power supply of the inverter, and a duty ratio control means that controls the power supplied from the inverter to the discharge lamp when the discharge lamp is lit. A discharge lamp lighting device comprising a power control means for controlling.

(Function) According to the configuration (1) above, when the dimming is deepened, the duty ratio of power supply to the discharge lamp decreases, and the power supplied during lighting also decreases.

(Example) This invention will be explained in detail based on an example below.
The figure is a circuit diagram of a "discharge lamp lighting device" which is a first embodiment of the present invention. 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 82 or more, 21, 22 is a switching device of the inverter, 23°, 24 is a diode, and 25 is a coil (ballast). , 26 and 27 are capacitors, 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 circuit that generates a signal to control the power supply period and the stop period at a predetermined ratio; a counter 51 that divides the frequency of the output signal of the oscillation circuit; and a counter 51 that generates a time for determining the stop period. It is composed of a time limit circuit 52 and the like. 7 is an oscillation circuit, 74 is an oscillation control circuit, and the oscillation frequency is determined by the capacitor 71, the resistor 72, and the resistor 73.

6 is a drive circuit for the switching devices 21.22, including flip-flop circuits 61.22. AND circuits 62, 63,
It consists of drivers 64 and 65. 8 is a dimmer switch, and 81.82 are each of the switches. 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 heater circuit that constitutes a series resonant circuit with the coil 25 at the start.

Moreover, FIG. 2 is an explanatory diagram of the operation of this embodiment, in which (a) shows the inverter output frequency f1 and the discharge lamp current A in the full light state,
, (b) is the dimming state, (c) is the output signal of the duty ratio control circuit 5, and T is the period of the duty ratio control circuit 5.

Next, the operation will be explained.

First, assume that each switch 81, 82 of the dimmer switch 8 is open. The oscillation control circuit 74 includes a capacitor 71 . A high frequency wave with a frequency f1 determined by the time constant of the resistor 72 is generated, this high frequency wave is converted into a rectangular wave by the flip-flop circuit 61, and is transmitted to the drivers 64.
65.

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 supply 1 is converted to high frequency power of frequency f1, and is then transmitted through the coil 25, which is a ballast. The light is supplied to the discharge lamp 3, and the discharge lamp 3 lights up in a full-light state. The current of the discharge lamp 3 is set to a predetermined value by a coil 25.

Next, when the dimmer switch 8 is turned on, each switch 8
1 and 82 close. When the switch 81 closes, the output of the oscillation circuit 7 or the counter 51 of the duty ratio control circuit 5
The timer circuit 52 starts operating at the falling point of the divided frequency wave, that is, the point a in FIG. The output of the flip-flop 61 becomes L level, and the output of the flip-flop 61 becomes the ant circuit 62.
．． 63, and the drive circuit 6 stops operating. Therefore, the output of inverter 2 is stopped and the duty ratio (TI/
T) decreases. At the same time, switch 82 closes, so
The resistance value that determines the output frequency of the oscillation control circuit 74 decreases, and therefore the output frequency of the oscillation circuit 7 increases, and the output frequency of the inverter 2 increases to f2 shown in (b). Therefore, the impedance of the coil 25 increases and the current of the discharge lamp 3 also decreases to A2. The voltage of the discharge lamp 3 is substantially constant regardless of current fluctuations, and as the power supplied to the discharge lamp 3 decreases, the amount of light decreases.

In this way, compared to the conventional example where the supplied power is constant and only the duty ratio is changed, the dimming can be made deeper by the amount of the decrease in the amount of light.

That is, according to this embodiment, the duty ratio at a predetermined dimming level can be made larger than in the case of the conventional example described above, and the period during which the power supply is stopped can be shortened. device 2
1.22 stress can be suppressed.

FIG. 3 is a circuit diagram of a control circuit of a "discharge lamp lighting device" which is a second embodiment of the present invention. Inverter 2. The circuit of the discharge lamp 3 is constructed in the same manner as the first embodiment shown in FIG. 1, and therefore is omitted here.

In this embodiment, the output frequency of the oscillation circuit is controlled by the variable resistor 7.
This embodiment differs from the first embodiment in that the duty ratio of the duty ratio control circuit 5 is made continuously variable by using a variable resistor 54.

With the configuration shown in FIG. 3, the relationship between the output frequency of the inverter 2 and the duty ratio becomes as shown in FIG. 5. That is, as the duty ratio decreases, the output frequency f increases as shown in FIG. 4. Therefore, the duty ratio control of power supply from the inverter 2 to the discharge lamp 3 and the control of the power supply from the inverter 2 to the discharge lamp 3 can be performed simultaneously and continuously, and dimming can be performed continuously.

In this embodiment, as in the first embodiment, the duty ratio at a predetermined dimming level is reduced as the output frequency of the inverter 2 increases, compared to the case where only the duty ratio is controlled as in the conventional example described above. Since the power supply stop period can be shortened, the switching device 2 of the inverter 2 at the beginning of the on period can be
It is possible to suppress the increase in stress to 1°22.

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, switching of dimming is not limited to the switch as in each embodiment, but may be performed using other methods.

Further, in each embodiment, the duty ratio control circuit generates a signal with a predetermined cycle T, but in this way, the cycle is constant and the power supply period T1 or stop period T2 to the discharge lamp is varied. In addition to changing the duty ratio,
Power supply period T1 and stop period T to the discharge lamp by changing the cycle
The duty ratio may be changed by changing the ratio of 2 to 2, and the configuration of the duty ratio control circuit is not limited to the combination of a counter and a timer circuit as shown in each embodiment.

Further, control of the power supply during lighting may be used together when the duty ratio is equal to or less than a predetermined value. That is,
The characteristic shown in FIG. 5 may be a polygonal line.

Furthermore, in each of the above embodiments, the power supply during lighting is controlled by changing the output frequency of the inverter. You can go change it.

6 and 7 show different circuit examples of an inverter to which the present invention can be applied, and since such an inverter has a single switching device 21, the configuration of the drive circuit 6 can also correspond to this. For example, the driver may be one. Moreover, it goes without saying that the load discharge lamp may have a configuration for multiple lamps instead of a single lamp.

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 power supply period T to the discharge lamp and the cycle T for turning the stop period T2 green are not particularly limited, but should be selected so that they are not perceived as flickering by the human eye.

Note that by using the configuration of the present invention, it is possible to reduce electrode deterioration at the time of starting a discharge lamp.

In that case, at the time of startup, and prior to the start of discharge, the output of the inverter is further reduced than in the state in which the dimming level is increased in the present invention. (This can be achieved by sharply varying the frequency, by making the duty ratio of the power supply very small, or by a combination of these.) In this way, the electrodes are first preheated, and then the full By increasing the inverter's output and starting the discharge, we were able to reduce electrode deterioration during startup.

〔Effect of the invention〕

As described above, according to the present invention, 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.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a first embodiment of the present invention, Fig. 2 is an explanatory diagram of the operation of the same embodiment, Fig. 3 is a circuit diagram of main parts of a second embodiment of the invention, Figs. Figure 5 is an explanatory diagram of the operation of the same embodiment.
6 and 7 are circuit diagrams of the inverter, FIG. 8 is a circuit diagram of a conventional example, and FIG. 9 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 circuit, 25 is a coil, and 74 is an oscillation control circuit. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[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, and a duty ratio control means that controls the power supplied from the inverter to the discharge lamp when the discharge lamp is lit. A discharge lamp lighting device characterized by comprising a power control means for controlling.