JP2000058287A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device which has good efficiency of the lamp load even when the lamp is on in the low light flux dimmer condition and can preclude darkening of the end of the lamp or its being put off in the dimmer condition. SOLUTION: Piezo transformers A and B having different resonance frequency are connected parallel, and a high frequency power supply 1 for driving the transformers A and B is connected with their primary side terminals, while one end of a discharge lamp load 2 is connected with their secondary side terminals. When the lamp load 2 is full lighted, the drive frequency of the power supply 1 is controlled so that the transformers A and B are driven near the resonance frequency f1 of the transformer A, and when lighted in dimmer condition, the two transformers A and B are driven upon lowering the drive frequency by a dimmer control circuit 5 down to near the resonance frequency f2 of the transformer B. Even when the lamp load 2 is lighted in dimmer condition, a high efficiency at the same level as fully lighted can thereby be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device using a piezoelectric transformer.

[0002]

2. Description of the Related Art Conventionally, a discharge lamp lighting device using a piezoelectric transformer utilizes the dependence of the driving frequency on the boosting ratio of the piezoelectric transformer when controlling the output voltage (output current) to a desired value. Things have been suggested. For example, in a discharge lamp lighting device described in Japanese Patent Application Laid-Open No. 6-167694 shown in FIG. 6, the step-up ratio of a ceramic piezoelectric transformer 10 (hereinafter, referred to as a ceramic transformer) is determined as shown in FIG. Since the driving frequency of the astable multivibrator 17 is given to the ceramic transformer 10 and the driving frequency is swept from high to low to turn on the cold cathode tubes 12, the driving frequency of the ceramic transformer 10 is further reduced. The brightness of the cold cathode tube 12 is adjusted under the control.

[0003]

However, in this discharge lamp lighting device, the present inventors have found that the efficiency at the time of low luminous flux dimming lighting of about 10% when the total lighting time is 100% is low. It was clarified by actual measurement. FIG. 8 shows an output current Il in a piezoelectric transformer having a resonance frequency of 120 kHz.
9 is an actual measurement example of frequency characteristics of a (curve G in FIG. 8) and efficiency η (curve H in FIG. 8). As shown in the figure, when the discharge lamp load is fully lit, the frequency of the piezoelectric transformer is 120 k.
It is driven around Hz, and the output current is about 12 mA, and the efficiency is very good. At the time of low luminous flux dimming lighting of about 10%, the frequency is increased to about 134 kHz to make the output current about 1 mA, but the efficiency at that time drops sharply and is only about 20%. That is, the piezoelectric transformer has a property that the efficiency decreases when the difference between the driving frequency and the resonance frequency increases.

FIG. 9 shows the load resistance dependence of the efficiency of the piezoelectric transformer. The load resistance of the discharge lamp is about 50 kΩ when fully lit, but the resistance increases due to dimming, and becomes about 600 kΩ when dimming with a low luminous flux of about 10%. As is clear from the figure, the efficiency η when the discharge lamp is dimmed is lower than when the discharge lamp is fully lit.

As described above, the efficiency of the piezoelectric transformer depends on the driving frequency and the load resistance. Even if the efficiency is high when the discharge lamp is fully lit, a low luminous flux dimming of about 10% is achieved. At times, the efficiency is greatly reduced. One of the purposes of dimming is to save energy, and it goes without saying that it is a problem that the efficiency is extremely reduced during dimming operation.

In a conventional discharge lamp lighting device,
As shown in FIG. 10, the stray capacitance Cs parasitic on the discharge lamp La
The load current Ila becomes Ila-Ics at the end of the discharge lamp La due to the leakage current Ics flowing through the discharge lamp La. When the load current Ila becomes smaller due to dimming, the current at the end of the discharge lamp La becomes smaller, and the end of the discharge lamp La becomes smaller. Or the discharge lamp La is turned off.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems. The load of the discharge lamp is high even during low-luminance dimming operation, and the end of the discharge lamp becomes dark during dimming operation. It is an object of the present invention to provide a discharge lamp lighting device capable of preventing the light from being turned off.

[0008]

According to a first aspect of the present invention, a plurality of piezoelectric transformers connected in parallel to each other and having different resonance frequencies and a primary side of the plurality of piezoelectric transformers are provided to achieve the above object. In a discharge lamp lighting device having a high-frequency power supply connected to and driving a high-frequency voltage to each of the piezoelectric transformers, and a discharge lamp load connected to the secondary sides of the plurality of piezoelectric transformers, all of the discharge lamp loads are provided. At the time of lighting, each of the piezoelectric transformers is driven in a frequency region near a higher resonance frequency of the plurality of piezoelectric transformers, and at the time of dimming lighting, the lower one of the resonance frequencies of the plurality of piezoelectric transformers is resonant. By providing control means for controlling the high-frequency power supply so as to drive each piezoelectric transformer in a frequency region near the frequency, when dimming the discharge lamp load, a plurality of Even when driving each piezoelectric transformer in the frequency region near the lower resonance frequency of the transformer's resonance frequencies and lighting the discharge lamp load with low luminous flux, high efficiency equivalent to that at full lighting can be maintained. In addition, it is possible to prevent the end of the discharge lamp from being darkened or extinguished during dimming lighting.

According to a second aspect of the present invention, in order to achieve the above object, a plurality of piezoelectric transformers connected in parallel to each other and having different resonance frequencies, and connected to a primary side of the plurality of piezoelectric transformers, and each In a discharge lamp lighting device having a high-frequency power supply for driving a transformer by applying a high-frequency voltage and a discharge lamp load connected to the secondary side of a plurality of piezoelectric transformers, when the discharge lamp load is fully lit, Each of the piezoelectric transformers is driven in a frequency region near a higher resonance frequency among the resonance frequencies of the transformers, and at the time of dimming lighting, the resonance frequencies of the plurality of piezoelectric transformers are reduced from the frequency region near the resonance frequency at the time of full lighting. By adjusting the discharge lamp load by having a dimming control circuit that controls the high-frequency power supply so as to lower it to a frequency region near the lower resonance frequency. The driving frequency of the high-frequency power supply is controlled by the dimming control circuit from a frequency region near the resonance frequency at full lighting to a frequency region near the lower resonance frequency of the resonance frequencies of the plurality of piezoelectric transformers at dimming lighting. In the case where the discharge lamp load is low-luminous dimming lighting by lowering the discharge lamp load, the same high efficiency as in full lighting can be maintained, and the end of the discharge lamp becomes dark or disappears during dimming lighting. Can be prevented.

[0010]

FIG. 1 is a circuit block diagram of the present embodiment. In FIG. 1, two types of piezoelectric transformers A and B having different resonance frequencies are connected in parallel to each other, and their primary terminals are connected to the piezoelectric transformer A and the piezoelectric transformer B at high frequency voltages near their respective resonance frequencies. A high-frequency power supply 1 for driving by applying an electric current is connected, and one end of a discharge lamp load 2 is connected to a secondary terminal. Here, if the resonance frequency of the piezoelectric transformer A is f1 and the resonance frequency of the piezoelectric transformer B is f2, f1> f2
Have a relationship. Further, the piezoelectric transformer A has a step-up ratio which is an output characteristic when the discharge lamp load 2 is fully lit, and a piezoelectric transformer A that matches the load impedance when the discharge lamp load 2 is fully lit is used. Has a boost ratio which is an output characteristic at the time of dimming lighting of the discharge lamp load 2,
Those that match the load impedance at the time of dimming lighting of the discharge lamp load 2 are used.

The other end of the discharge lamp load 2 is connected to one end of a load current detection circuit 4, and the other end of the load current detection circuit 4 is connected to a high frequency power supply via a frequency control circuit 3 and a dimming control circuit 5. 1 connected. Load current detection circuit 4
Detects a load current Ila flowing through the discharge lamp load 2 and sends a voltage signal to the frequency control circuit 3 for controlling the frequency so that the value of the load current becomes a predetermined value (hereinafter, referred to as a detection set value). For example, there are two types of detection set values: a current value of the load current Ila when the discharge lamp load 2 is fully lit and a current value of the load current Ila when the discharge lamp load 2 is dimly lit. Then, the detection setting value is compared with the current value of the load current Ila, and a voltage signal is output to the frequency control circuit 3. The frequency control circuit 3 controls the driving frequency of the high frequency power supply 1 according to the voltage signal of the load current detection circuit 4. That is, the load current detection circuit 4 and the frequency control circuit 3
Thus, the driving frequency of the high-frequency power supply 1 is controlled so that the load current Ila flowing through the discharge lamp load 2 substantially matches the detection set value, and the discharge lamp La is lit in a stable state.

When the discharge lamp load 2 is dimmed and lit, the dimming control circuit 5 changes the detection set value of the load current detection circuit 4 to the detection set value at the time of dimmed lighting, and the frequency control circuit 3 controls the dimming. The driving frequency of the high frequency power supply 1 is changed from the vicinity of the resonance frequency f1 of the piezoelectric
In the vicinity of the resonance frequency f2. As a result, when the discharge lamp load 2 is dimmed and lit, the driving frequency of the high frequency power supply 1 is reduced from the vicinity of the resonance frequency f1 of the piezoelectric transformer A when the lamp is fully lit to a frequency region near the resonance frequency f2 of the piezoelectric transformer B. Since the current detection circuit 4 maintains the current value of the load current Ila at the detection set value at the time of dimming lighting, the dimming lighting of the discharge lamp load 2 is stably performed even at the time of dimming lighting.

Next, the operation of the discharge lamp lighting device will be described with reference to FIG.
This will be described in more detail with reference to FIGS.

First, when the discharge lamp load 2 is fully lit,
The piezoelectric transformer A and the piezoelectric transformer B are driven near the resonance frequency f1 by controlling the drive frequency of the high-frequency power supply 1. When both piezoelectric transformers A and B are driven in this frequency range,
Since the resonance frequency f2 of the piezoelectric transformer B is lower than the resonance frequency f1 of the piezoelectric transformer A, only the piezoelectric transformer A resonates at the resonance frequency f1 and outputs the output current Ila and the output voltage V1 to the secondary side.

Next, when the discharge lamp load 2 is dimmed and lit, the above-mentioned dimming control circuit 5 changes the load current detection setting value of the load current detection circuit 4 to the current value at the time of dimmed lighting. At the same time, the driving frequency of the high frequency power supply 1 controlled by the frequency control circuit 3 is changed from the vicinity of the resonance frequency f1 of the piezoelectric transformer A to the resonance frequency f2 of the piezoelectric transformer B.
Lower to near. At the resonance frequency f2, only the piezoelectric transformer B resonates and outputs an output current Ila to the secondary side,
Dimming lighting of the discharge lamp load 2 is performed.

That is, when the discharge lamp load 2 is fully lit, as shown in FIG. 2, the high frequency power supply 1 is driven in a frequency region near the resonance frequency f1 (120 kHz) of the piezoelectric transformer A, and only the piezoelectric transformer A resonates. As a result, an output current of about 12 mA required at the time of full lighting of the discharge lamp load 2 (curve A in FIG. 2) can be output with high efficiency (curve B in FIG. 2),
When the discharge lamp load 2 is dimmed and lit, as shown in FIG. 3, the dimming control circuit 5 changes the driving frequency of the high frequency power supply 1 via the frequency control circuit 3 to the resonance frequency f2 ( 40 kHz), the piezoelectric transformer B alone resonates at the resonance frequency f2, and an output current of about 2 mA (curve C in FIG. 3) required for dimming lighting is fully turned on for the discharge lamp load 2. It is possible to stably output with high efficiency (curve d in FIG. 3) which is not different from the time.

When the discharge lamp load 2 is lit and lit, the driving frequency of the high frequency power supply 1 is changed to the resonance frequency f of the piezoelectric transformer A.
The resonance frequency f of the piezoelectric transformer B from the frequency region near 1
When the discharge lamp load 2 is lowered to a frequency region near 2, the efficiency of the discharge lamp load 2 with respect to the load resistance shifts to the high resistance side. That is, as shown in FIG.
When the discharge lamp load 2 is fully lit in a frequency region near 1, the efficiency becomes a peak when the load resistance value is R 1, and the load resistance value rises to R 2 when the dimming light is turned on to become R 2, and the discharge lamp load 2 Efficiency decreases. On the other hand, in the present embodiment, since the driving frequency of the high-frequency power supply 1 is reduced to the resonance frequency f2 of the piezoelectric transformer B at the time of dimming lighting, the efficiency with respect to the load resistance (curve E in FIG. The efficiency shifts to a peak at the load resistance value R2. Thereby, even if the resistance value of the load resistance increases during the dimming lighting of the discharge lamp load 2, the discharge lamp load 2
Can be maintained as high as at the time of full lighting.

In the discharge lamp lighting device according to the present embodiment, when the discharge lamp load 2 is dimly lit, the piezoelectric transformer B is driven in a frequency region near a resonance frequency f2 lower than the resonance frequency f1 in full lighting. In FIG. 1, the driving frequency of the high-frequency power supply 1 is greatly reduced as compared with the case of full lighting.
0, the leakage current Ics can be reduced (Ics = ωC
ω of sVo ′ becomes smaller), and the end of the discharge lamp La can be prevented from being darkened or extinguished even during dimming lighting.

In this embodiment, the resonance frequencies f1 and f2 of the piezoelectric transformers A and B are set to 120 kHz and 40 kHz, respectively. However, the resonance frequencies of the piezoelectric transformers A and B are not limited to these values. Absent.

[0020]

According to the first aspect of the present invention, a plurality of piezoelectric transformers connected in parallel to each other and having different resonance frequencies are connected to the primary side of the plurality of piezoelectric transformers, and a high-frequency voltage is applied to each of the piezoelectric transformers. And a discharge lamp load connected to the secondary side of the plurality of piezoelectric transformers, the discharge frequency of the plurality of piezoelectric transformers when the discharge lamp load is fully lit. And driving each piezoelectric transformer in a frequency region near a higher resonance frequency, and at the time of dimming lighting, driving each piezoelectric transformer in a frequency region near a lower resonance frequency among the resonance frequencies of the plurality of piezoelectric transformers. The control means for controlling the high frequency power supply as described above allows the lower one of the resonance frequencies of the plurality of piezoelectric transformers to be shared when dimming the discharge lamp load. Even when driving each piezoelectric transformer in the frequency range near the frequency and lighting the discharge lamp load with low flux dimming, the same high efficiency as at full lighting can be maintained and the end of the discharge lamp at dimming lighting There is an effect that darkening or disappearing can be prevented.

According to a second aspect of the present invention, a plurality of piezoelectric transformers which are connected in parallel to each other and have different resonance frequencies are connected to a primary side of the plurality of piezoelectric transformers, and a high frequency voltage is applied to each of the piezoelectric transformers. In a discharge lamp lighting device having a high-frequency power supply to be driven and a discharge lamp load connected to the secondary side of a plurality of piezoelectric transformers, when the discharge lamp load is fully lit, the resonance frequency of the plurality of piezoelectric transformers is higher. Each of the piezoelectric transformers is driven in a frequency region near one of the resonance frequencies, and at the time of dimming lighting, from the frequency region near the resonance frequency at the time of full lighting to the lower resonance frequency of the resonance frequencies of the plurality of piezoelectric transformers. By having a dimming control circuit that controls the high-frequency power supply to lower the frequency range to The driving frequency of the high-frequency power supply is lowered from the frequency region near the resonance frequency when the lamp is fully lit to the frequency region near the lower resonance frequency of the plurality of piezoelectric transformers when the dimming lamp is lit. It is possible to maintain the same high efficiency as in full lighting even when performing low-luminance dimming lighting, and to prevent the end of the discharge lamp from being darkened or extinguished during dimming lighting. effective.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram according to a first embodiment.

FIG. 2 is a diagram showing frequency characteristics of output current and efficiency of the piezoelectric transformer A according to the first embodiment.

FIG. 3 is a diagram showing frequency characteristics of output current and efficiency of the piezoelectric transformer B according to the first embodiment.

FIG. 4 is a diagram showing the resistance dependence of the efficiency of the piezoelectric transformer A according to the first embodiment.

FIG. 5 is a diagram showing the resistance dependence of the efficiency of the piezoelectric transformer B according to the first embodiment.

FIG. 6 is a circuit block diagram showing a conventional discharge lamp lighting device.

FIG. 7 is a diagram showing a frequency characteristic of a step-up ratio of the piezoelectric transformer according to the first embodiment.

FIG. 8 is a diagram showing output current and efficiency frequency characteristics of the piezoelectric transformer.

FIG. 9 is a diagram showing the resistance dependence of the efficiency of the piezoelectric transformer of the above.

FIG. 10 is a diagram showing a leakage current flowing through a floating capacitance of the discharge lamp of the above.

[Description of Signs] A Piezoelectric transformer B Piezoelectric transformer 1 High-frequency power supply 2 Discharge lamp load 3 Frequency control circuit 4 Load current detection circuit 5 Dimming control circuit

Claims (2)

[Claims] 1. A plurality of piezoelectric transformers connected in parallel to each other and having different resonance frequencies, and a high-frequency power supply connected to a primary side of the plurality of piezoelectric transformers and applying and driving a high-frequency voltage to each piezoelectric transformer. And a discharge lamp load connected to the secondary side of the plurality of piezoelectric transformers, when the discharge lamp load is fully lit, the vicinity of the higher one of the resonance frequencies of the plurality of piezoelectric transformers And driving the piezoelectric transformers in a frequency region of the plurality of piezoelectric transformers at the time of dimming lighting so as to drive each piezoelectric transformer in a frequency region near a lower resonance frequency among the resonance frequencies of the plurality of piezoelectric transformers. A discharge lamp lighting device comprising control means. 2. A plurality of piezoelectric transformers connected in parallel to each other and having different resonance frequencies, and a high-frequency power supply connected to a primary side of the plurality of piezoelectric transformers and applying a high-frequency voltage to each of the piezoelectric transformers to drive them. And a discharge lamp load connected to the secondary side of the plurality of piezoelectric transformers, when the discharge lamp load is fully lit, the vicinity of the higher one of the resonance frequencies of the plurality of piezoelectric transformers While driving each of the piezoelectric transformers in the frequency range of the dimming, the frequency range near the resonance frequency at the time of full lighting during the dimming lighting is reduced to a frequency range near the lower resonance frequency of the resonance frequencies of the plurality of piezoelectric transformers. A discharge lamp lighting device comprising a dimming control circuit for controlling a high-frequency power supply so as to control the power supply.