JPH03246898A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To prevent a short life and difficulty in starting by providing a means feeding large power and small power in turn to a discharge lamp and a means changing the frequency of at least one of large power and small power and suppressing the current fluctuation of the discharge lamp when the voltage of a DC power source is changed. CONSTITUTION:When the voltage of a DC power source 1 rises by a certain value, the input voltage from voltage dividers 73, 74 to voltage control oscillators 71, 72 is increased, and output frequencies of the voltage control oscillators 71, 72 are increased respectively. Since the impedance of a coil 25 is increased by this frequency rise, the current increase of the discharge lamp 3 is suppressed regardless of the output voltage rise of the inverter 2 due to the voltage rise of the DC power source 1, the amplitude of the current of the discharge lamp 3 is kept at nearly the same value, the brightness of the discharge lamp 3 is not changed, and the depth of dimming is not changed. The fluctuation of the brightness of the discharge lamp 3 due to the voltage fluctuation of the DC power source 1 can be suppressed, and difficulty in starting and a short life of the discharge lamp 3 due to the voltage fluctuation can be prevented.

Description

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

(Related technology) Conventionally, as a device that supplies high-frequency power from an inverter to a discharge lamp to light the discharge lamp, and also controls the power supplied to the discharge lamp to dim the discharge lamp, there has been no practical application. Showa 6
The one disclosed in Japanese Patent No. 4-44600 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 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 Z1. 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 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
B, the output of voltage comparator IC2 becomes low level (the output transistor of IC2 is turned on), and each transistor Q1 . Q2. The base bias is added to the oscillation 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 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 vll.

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 of the inverter 2
. tr becomes longer, Ton/T (hereinafter referred to as duty ratio) becomes smaller, and the discharge lamp 3 becomes darker.

If the voltage of the DC power supply 1 fluctuates, the voltage fluctuation rate of the reference voltage VB will change to the voltage of the unstable multivibrator 10 ■8
, 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.

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 quite small. In other words, 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.

In order to solve this problem, the inventor of the present invention has separately proposed a discharge lamp lighting device that supplies a small amount of electric power even during the period when the electric power supply is suspended.

In this separately proposed discharge lamp lighting device, the inverter has a period of supplying high power and a period of supplying low power from the inverter to the discharge lamp. When the amount of light due to electric power is set to a negligible value, dimming equivalent to that achieved by duty ratio control in the conventional example can be obtained.

[Problem to be solved by the invention]

As described above, in the conventional example shown in FIG. 5, variations in the brightness of the discharge lamp due to voltage variations in the DC power supply are suppressed by changing the duty ratio of the inverter.

Therefore, by suppressing the brightness fluctuation of this discharge lamp,
A margin must be allowed for the duty ratio, which narrows the dimming range. In other words, if the duty ratio is set to 1 when the voltage of the DC power supply is at its lowest, resulting in a full-light state, then when the voltage is at the rated voltage and the full-light state is achieved, the duty ratio is (rated voltage -
is smaller than 1 by the amount corresponding to the minimum voltage), and
When the voltage of the DC power supply is the highest, the duty ratio is set to 0. 1
If the maximum dimming is performed at the rated voltage, the duty ratio will be larger than 0.1 by an amount corresponding to (maximum voltage - rated voltage), so for dimming However, there is a problem that a sufficient duty ratio cannot be obtained and the dimming range becomes narrow.

Further, according to the conventional example, although fluctuations in the brightness of the discharge lamp due to voltage fluctuations of the DC power source can be suppressed by changing the duty ratio, fluctuations in the voltage applied to the discharge lamp lighting circuit cannot be suppressed. The voltage increases, the discharge lamp current increases, and the evaporation of the electron emitting material in the electrodes increases, promoting blackening of the tube end and shortening the lifespan.Alternatively, the applied voltage decreases, making it difficult to start. There is a problem that early scattering of electron emitting material occurs, resulting in a short lifespan.

Further, even if this conventional power supply voltage compensation method is applied to the above-mentioned separately proposed discharge lamp lighting device, the same problem will occur.

The present invention was made to solve these problems, and an object of the present invention is to provide a discharge lamp lighting device with a modified duty ratio control that does not shorten its life or become difficult to start. It is something to do.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention controls the output frequency of an inverter according to the voltage of a DC power supply. Specifically, a discharge lamp lighting device is configured as shown in (1) below.

(1) An inverter that converts the power of a DC power supply into high-frequency power and supplies it to the discharge lamp, a means for alternately supplying high power and low power from the inverter to the discharge lamp, and a voltage of the DC power supply that fluctuates. and a means for suppressing current fluctuations of the discharge lamp by changing the frequency of at least one of the high power and low power according to the fluctuations.

(Function) According to the configuration (1) above, even if the voltage of the DC power source fluctuates, the current fluctuation of the discharge lamp is suppressed.

(Example) The present invention will be explained in detail below with reference to Examples.

FIG. 1 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 DC power supply 1 into high frequency power of 82 or higher, 21, 22 is a switching device for inverter 2, 23° and 24 are diodes, and 25 is a stabilizer. Coil, 26 is a filament circuit resonant capacitor that forms a series resonant circuit with the coil 25 during startup, 27
is a large capacitor that constitutes a part of the inverter 2. 3 is a discharge lamp, and 4 is a control circuit that controls power supply to the discharge lamp. 5 is a rectangular wave generation circuit, 6 is a drive circuit for the inverter 2, 7 is an oscillation circuit, and resistor voltage dividers 73 and 74
, voltage controlled oscillators 71 and 72, switches 75 and 76, and an inverter (not gate) 78. 8 is a dimmer switch.

The rectangular wave generation circuit 5 includes C-MOS inverters 53 and 54.
．． 59 is a protection resistor for suppressing the input amplitude, 56 is a capacitor that determines the oscillation frequency, and 51 and 52 are resistors that determine the oscillation frequency. 58° 57 is a diode for changing the charging/discharging time constant, and the value of the charging resistance of the capacitor 56 is the sum of the lower side of the variable resistor 51 and the resistor 52 due to the diode 58.
Due to the diode 57, the value of the discharge resistance of the capacitor 56 becomes the sum of the upper side of the variable resistor and the resistor 52. Therefore, for example, if the tap of the variable resistor 51 is moved above the midpoint, "charging resistance value>discharging resistance value", and the output of the square wave generating circuit 5 becomes "high level period>low level". period”. When the dimmer switch 8 is closed to the rectangular wave generation circuit 5 side, the switch 76 is closed at this high level, and the switch 75 is closed at this low level.

The voltage controlled oscillators 71 and 72 have an output frequency that changes in proportion to the input voltage from the resistive voltage divider 73 and 74, and 72 has a higher output frequency than 71.

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 voltage of the DC power supply 1 is the rated voltage, and (b) shows the current waveform of the discharge lamp 3 when the voltage of the DC power supply 1 fluctuates from the rated voltage. 3 is a diagram showing the current waveform of the electric lamp 3, and (c) is a diagram showing the output waveform of the rectangular wave generation circuit 5. FIG. Further, T is a period of high power, fl is its frequency, T2 is a period of small power, f2 is its frequency, and T is a control period.

Next, the operation will be explained.

First, it is assumed that the dimmer switch 8 is closed to the ground side. In the oscillation circuit 7, when the switch 75 is closed, the voltage controlled oscillator 71 outputs a high frequency wave having a frequency f. This high frequency wave is converted into a rectangular wave by a flip-flop 61 of the drive circuit 6, and is supplied to drivers 62 and 63.

The switching devices 21, 22 of the inverter 2 are turned on and off alternately by the output of the driver 62, 63, and the DC power of the DC power source 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 closed to the square wave generation circuit 5 side,
At the low level of the output of the same circuit 5, the switch 7 of the oscillation circuit 7
The switches 75 and 76 are alternately closed, and the outputs of the voltage controlled oscillators 71 and 72 are alternately output as the output of the oscillation circuit 7.

The output frequency of the voltage controlled oscillator 72 is f2, and as a result,
The oscillation circuit 7 outputs high frequencies of frequencies f and f2. Therefore, the inverter 2 supplies high-frequency power at frequencies f1 and f2 to the discharge lamp 3, but when f, < f, the frequency f
2, the impedance of the coil 25 becomes large, so that a current having the waveform shown in FIG. 2(a) flows through the discharge lamp 3 and dimming is performed. The depth of dimming can be changed by operating the variable resistor 51 of the rectangular wave generating circuit 5 and changing the T + /T ratio.

Suppose here that the voltage of the DC power supply 1 increases by a certain value for some reason. Then, the input terminals from the voltage dividers 73 and 74 to the voltage controlled oscillators 71 and 72 become larger, and the output frequencies of the voltage controlled oscillators 71 and 72 become f1→f, , f, respectively.
It increases from 2 to f2a. Due to this frequency increase, coil 2
5 increases, so regardless of the increase in the output voltage of the inverter 2 due to the increase in the voltage of the DC power supply 1,
The increase in the current of the discharge lamp 3 is suppressed, and the amplitude of the current of the discharge lamp 3 becomes approximately the same value A, as shown in FIGS. 2(a) and 2(b).
, A2, the brightness of the discharge lamp 3 does not change, and the depth of dimming does not change. The suppressing characteristic of fluctuations in the discharge lamp current with respect to fluctuations in the power supply voltage can be changed as appropriate by the input voltage-output frequency characteristics of the voltage controlled oscillators 71 and 72.

In addition, in the embodiment, the output frequency of both high power and low power is controlled according to the power supply voltage, but the present invention is not limited to this, and only one of the output frequencies can be controlled. You can.

Further, in the embodiment, a lighting circuit using the coil 25 as a ballast is employed, but 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 using capacitors. In this case, the characteristics of the voltage controlled oscillator may be such that the output frequency is inversely proportional to the input voltage.

Further, the configuration of the control circuit is not limited to the configuration of the embodiment, and, for example, the switching of dimming is not limited to the switch as in the embodiment, but may be performed using other methods.

In addition, in the embodiment, the rectangular wave generation circuit generates a signal with a predetermined period T, but the period is constant in this way and the period T for supplying large power to the discharge lamp or the period T2 for supplying small power to the discharge lamp is changed. In addition to changing the period T, the ratio between the high power supply period T1 and the low power supply period T2 to the discharge lamp may be changed by changing the cycle T. - Not limited to CR oscillation circuits using MOS inverters.

6 and 7 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 sufficient to use only one driver. In addition, the load discharge lamp is -
Of course, it is possible to use not only a light but also a structure for multiple 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.

(Effects of the Invention) As explained above, according to the present invention, fluctuations in the brightness of the discharge lamp due to voltage fluctuations of the DC power supply can be suppressed, and difficulty in starting the discharge lamp and short lifespan due to the voltage fluctuations can be prevented. can do.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is an explanatory diagram of the operation of the same embodiment, Figs. 3 and 4 are circuit diagrams of the inverter, Fig. 5 is a circuit diagram of a conventional example, and Fig. 6 The figure 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 square wave generation circuit, 7 is an oscillation circuit, 8 is a dimmer switch, 25 is a coil, 71.72 is a voltage controlled oscillator, and 73.74 is a resistor voltage divider. be. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) An inverter that converts the power of a DC power supply into high-frequency power and supplies it to the discharge lamp, a means for alternately supplying high power and low power from the inverter to the discharge lamp, and a voltage of the DC power supply that fluctuates. A discharge lamp lighting device characterized by comprising means for suppressing current fluctuations of the discharge lamp by changing the frequency of at least one of the high power and low power according to the fluctuations.