JPH04294096A - Discharge lamp lighting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 for controlling the lighting of a discharge lamp such as a metal halide lamp.

0002

2. Description of the Related Art Conventionally, discharge lamps such as metal halide lamps are operated using a series inverter circuit as shown in FIG. 7, for example.

In FIG. 7, a switching transistor Q9 and a switching transistor Q10 are connected in series to both ends of a DC power supply 1, and a light is emitted at the gates of the switching transistors Q9 and Q10 and at the connection point a between the switching transistors Q9 and Q10. Each control signal is inputted from the control means 9. Further, a resonant circuit consisting of a choke coil 3 and capacitors 5 and C2 is connected to the connection point a via a coupling capacitor C4. Connection point b of capacitor 5 and C2
A lamp voltage detection means 6 is connected to the lamp voltage detection means 6, and the output signal of this lamp voltage detection means is input to the lighting control means 9.

[0004] In the above configuration, the operation when starting the lamp will be explained next. First, when a DC voltage is applied to switching transistors Q9 and Q10 by DC power supply 1, 5k is applied to the gates of switching transistors Q9 and Q10.
Drive signals of about Hz having mutually opposite phases are input, switching transistors Q9 and Q10 alternately turn on and off, and an alternating current voltage is generated at the connection point c between the coupling capacitor C4 and the choke coil 3. At this time, since the discharge lamp 7 is in the off state, the voltage value at both ends of the discharge lamp is approximately the above-mentioned AC voltage value. The voltage across the discharge lamp 7 is divided by the capacitors 5 and C2, converted into a DC voltage signal by the lamp voltage detection means 6, and inputted to the lighting control means 9. When the DC voltage signal level from the lamp voltage detection means 6 is equal to or higher than a certain predetermined value, the lighting control means 9 determines that the discharge lamp 7 is off, and generates a high voltage to start the discharge lamp 7. Change the oscillation frequency so that The oscillation frequency of the inverter depends on the output voltage of the sawtooth wave generation circuit in the lighting control means 9, and the choke coil 3, capacitor 5,
It is controlled to vary within a certain range that includes the resonant frequency of the resonant circuit consisting of C2. Therefore, switching transistors Q9 and Q10 alternately turn on and off, and coupling capacitor C4 and choke coil 3
An alternating current voltage of the above frequency is generated at the connection point c between the choke coil 3 and the capacitor 5, and a resonant current flows through the choke coil 3 and the capacitor 5, C2.
A high voltage of kV to 15kV is generated. After the discharge lamp 7 is started by this high voltage, it will be lit at a rated frequency of about 10 kHz.

[0005]

[Problem to be Solved by the Invention] However, when starting the discharge lamp 7 with the series inverter circuit having the above configuration,
Even if the discharge lamp 7 undergoes dielectric breakdown due to the high voltage generated by the first sawtooth wave voltage from the sawtooth wave generation circuit (the voltage across the discharge lamp 7 when the discharge lamp 7 undergoes dielectric breakdown is shown in Figure 8 (
(a)), as shown in FIG. 8(b), the decay time of the pulsed discharge lamp current flowing at this time is short, so
There was a problem in that the lighting could not be maintained and the startability was uncertain.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a discharge lamp lighting device that can reliably start a discharge lamp.

[0007]

[Means for Solving the Problems] In order to achieve this object, the discharge lamp lighting device of the present invention includes an inverter means that is driven by a DC power source to oscillate, and a first choke coil connected to the inverter means. and a capacitor in series, a series circuit including a discharge lamp and a second choke coil connected in parallel with the capacitor, and detecting at least one of a lamp voltage and a lamp current of the discharge lamp. The lamp includes a lamp characteristic detecting means, and a lighting control means for controlling lighting of the discharge lamp by varying the oscillation frequency or duty ratio of the inverter means based on the output signal of the lamp characteristic detecting means.

[0008]

[Operation] With the above configuration, when starting a discharge lamp,
It is possible to lengthen the decay time of the pulsed discharge lamp current that flows when the discharge lamp undergoes dielectric breakdown due to the high voltage generated in the resonant circuit.

[0009]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the basic configuration of a discharge lamp lighting device according to the present invention. In FIG. 1, an inverter circuit 2 is driven by a DC power supply 1 to oscillate a clock signal of a predetermined frequency. This inverter circuit includes a resonant circuit as a load circuit consisting of a series body of a first choke coil 3 and a capacitor 5, a second choke coil 4 connected in parallel with the capacitor 5, and a discharge lamp 7 consisting of a metal halide lamp or the like. It has a series body with. Furthermore, the load circuit includes a lamp voltage detection means 6 connected in series with the resonant circuit to detect the start-up of the discharge lamp 7 and thereafter control rated lighting, etc., and a lamp voltage detection means 6 for detecting the current flowing in the load circuit. A lamp current detection means 8 is provided. The output signals of the lamp voltage detection means 6 and the lamp current detection means 8 are input to the lighting control means 9, and the lighting control means 9 varies the oscillation frequency of the inverter circuit 2 or its duty ratio based on these signals, thereby controlling the discharge lamp. Controls the lighting operation of 7.

Next, the operation of the above configuration will be explained. Now, when the DC power supply 1 is turned on, the inverter circuit 2 first oscillates at a low frequency of about 5kHz, and this low frequency voltage is applied to the first choke coil 3 and the capacitor 5.
is applied to a resonant circuit consisting of A high frequency resonant voltage from the resonant circuit is superimposed on this low frequency voltage, and the lamp voltage detection means 6 detects this resonant voltage. The lighting control means 9 changes the oscillation frequency of the inverter circuit 2 to a high frequency based on the detected voltage, and causes the resonant circuit to generate a high resonant voltage in the capacitor 5 at a frequency within a predetermined range of, for example, around 100 kHz (see FIG. 2). a))
. This causes dielectric breakdown of the discharge lamp 7. Then, the charge accumulated in the capacitor 5 is discharged through the second choke coil 4 and the discharge lamp 7 while undergoing damped oscillation (FIG. 2(b)). At this time, since the inverter circuit 2 is operating at a frequency of about 100kHz,
If the decay time of the damped oscillating current flowing through the discharge lamp 7 is at least 10 μs or more with a period of 100 kHz, it is easy to prevent the inverter circuit 2 of the discharge lamp 7 from turning off when the lamp current polarity is reversed, and the lamp can be turned on at 100 kHz. It can be migrated quickly. After repeating such dielectric breakdown a certain number of times, the discharge lamp 7 is started by being supplied with current from the inverter circuit 2 via the first choke coil 3 during a period when the current is flowing while damping and oscillating. . That is, the second choke coil 4 operates to limit the current flowing through the discharge lamp 7 when the dielectric breakdown occurs, and to keep the lamp current flowing for a period of about several tens of microseconds. FIG. 3 shows the experimental results of the relationship between the inductance value of the second choke coil and the decay time τ of the lamp current shown in FIG. 2(b). From this, if the inductance value of the second choke coil 4 is 100 μH or more, the decay time τ is approximately 10 μs.
It is clear that the above results are achieved, and the probability of starting the lamp is also greatly improved. The decay time τ of the lamp current is determined by the inductance of the second choke coil 4 and the resistance component at the time of dielectric breakdown of the discharge lamp, and is expressed as τ=2L/R, where L is the inductance and R is the resistance component. The larger the inductance L is, the larger the decay time τ of the lamp current becomes.
The probability of starting the lamp increases. However, if the inductance value is too large, not only will the physical size and weight of the coil increase, but also a voltage component due to the current flowing through the second choke coil 4 will be included in the signal detected by the lamp voltage detection means 6. The ratio increases, causing the inconvenience of not being able to accurately detect the lamp voltage.
It is appropriate that the inductance L is 100 μH to 200 μH.

The second choke coil 4 is connected to the discharge lamp 7.
In order to prevent saturation of the inductance due to large current when the choke coil 4 undergoes dielectric breakdown, and to insulate the high voltage generated across the choke coil 4 at this time, the core 4 is
a has a rod-like shape.

When current flows through the discharge lamp 7, the voltage across the discharge lamp 7 decreases. At this time, the lamp voltage detecting means 6 detects that the discharge lamp 7 has started by detecting the sudden decrease in the current flowing through the capacitor 5 from the voltage drop in the lamp voltage detecting means 6. The lighting control means 9 controls the oscillation frequency of the inverter circuit 2 to a low frequency of around 10 kHz based on the voltage detected by the lamp voltage detection means 6, and shifts the discharge lamp 7 to rated lighting.

FIG. 5 shows a specific circuit diagram of the inverter circuit 2 etc. in FIG. 1. In FIG. 5, the inverter circuit 2 includes two switching transistors Q that drive an external circuit 10 consisting of a first choke coil 3, a capacitor 5, a second choke coil 4, and a discharge lamp 7.
It has a series inverter configuration consisting of Q1 and Q2. Both ends of the primary winding of the drive transformer DT are grounded via drive transistors Q3 and Q4, and clocks E1 and E2 whose phases are inverted from each other are input from the lighting control means 9 to the resistors R1 and R2 of the inverter circuit 2. , a drive voltage VD is applied to the midpoint of the primary winding of the drive transformer DT. Two secondary windings are provided on the secondary side of the drive transformer DT, and one end of each is connected to the gates of switching transistors Q1 and Q2 via resistors R6 and R7. Further, a series body of switching transistors Q1 and Q2 and a resistor R8 is connected between the DC power supply voltage VDD and the ground, and a coupling capacitor C1 and an external circuit 10 are connected to the connection point between the switching transistors Q1 and Q2. Series bodies are connected. The capacitor C2 constitutes the lamp voltage detection means 6 in FIG.
Since the choke coil 4 is sufficiently smaller than the first choke coil 3 by 1/10 or less, the voltage generated across the capacitor C2 is detected as a lamp voltage. The resistor R8 constitutes the lamp current detection means 8 in FIG. 1, and the voltage generated across the resistor R8 is detected as the lamp current. The output voltage signals of these lamp voltage detection means and lamp current detection means are input to the lighting control means 9.

FIG. 6 shows a specific circuit diagram of the lighting control means 9 in FIG. In FIG. 6, a DC voltage detection circuit 11 whose input terminal is connected to the lamp voltage detection terminal VL of the lamp voltage detection means 6 outputs a DC voltage corresponding to the lamp voltage. The lamp lighting detection circuit 12, which determines whether the discharge lamp 7 is lit, is composed of resistors R9, R10, R11 and a comparator COMP1, and when the output voltage of the DC voltage detection circuit 11 exceeds a certain value, a high level signal (lamp non-lighting state) is generated. ), and when it is smaller than a certain value, a low level signal (lamp lighting state) is output. The input terminal is the lamp current detection terminal I of the lamp current detection means 8.
The DC current detection circuit 13 connected to L outputs a DC voltage corresponding to the lamp current. The lamp starting current control circuit 14 calculates the output voltage of the DC voltage detection circuit 11 and the output voltage of the DC current detection circuit 13, and outputs the calculation result. The first cutoff circuit 15 includes a resistor R12 and a transistor Q5, and includes a lamp lighting detection circuit 1.
Only when the output of No. 2 is at a low level, that is, when the lamp is in the lighting state, the output of the lamp starting current control circuit 14 is output to the next stage circuit. A first constant current circuit 1 for flowing a current corresponding to the output voltage of the lamp starting current control circuit 14
6 is composed of an operational amplifier OP1, resistors R13 and R14, and a transistor Q7. This first constant current circuit operates effectively only when the discharge lamp 7 is turned on by the first cutoff circuit 15. The output terminal of the first constant current circuit 16 is connected to the switching regulator control I
Timing resistor terminal R for setting the frequency of C22
Connected to T. Switching regulator control I
The oscillation frequency of C22 is determined by the current flowing from the timing resistor terminal RT to ground and the capacitance of the capacitor C3 connected to the timing capacitor terminal CT. Therefore, after starting the lamp, the inverter circuit 2
The lamp operates by changing the oscillation frequency of the lamp so that the lamp voltage and lamp current have a predetermined relationship.

Output voltage of sawtooth wave generating circuit 17 and resistor R1
5, the output voltage of the bias circuit 18 consisting of R16 is:
The results are added by resistors R17 and R18 and output to the second cutoff circuit 19. The second cutoff circuit 19 includes a resistor R19
and a transistor Q6, and outputs the output summed by resistors R17 and R18 to the next stage circuit only when the output of the lamp lighting detection circuit 12 is at a high level, that is, when the lamp is not lit. The second constant current circuit 20 is composed of an operational amplifier OP2, resistors R20, R21, and a transistor Q8, and includes resistors R17, R18.
The current corresponding to the output voltage added by is connected to the timing resistor terminal R of the switching regulator control IC22.
It operates to flow from T to ground. Therefore, when the lamp is not lit, that is, when the lamp is started, the oscillation frequency of the switching regulator control IC 22 changes within a predetermined range of around 100kHz by the sawtooth wave voltage, and is controlled to output a high voltage for starting the lamp. .

[0017]

[Effects of the Invention] As explained above, according to the present invention,
The decay time of the current that flows when the lamp breaks down can be lengthened, so it can quickly switch to the lighting state.
The discharge lamp can be reliably started.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of a discharge lamp lighting device of the present invention.

[Fig. 2] (a) Lamp voltage waveform diagram at the time of discharge lamp dielectric breakdown in the discharge lamp lighting device of the present invention; (b) Similarly lamp current waveform diagram.

FIG. 3 is a diagram showing the relationship between the inductance of the second choke coil and the decay time of the lamp current at the time of dielectric breakdown in the discharge lamp lighting device of the present invention.

FIG. 4 is a perspective view showing an example of a choke coil used in the discharge lamp lighting device of the present invention.

FIG. 5 is a circuit diagram showing a specific example of an inverter circuit in the discharge lamp lighting device of the present invention.

FIG. 6 is a circuit diagram showing a specific example of lighting control means in the discharge lamp lighting device of the present invention.

[Figure 7] Block diagram showing the configuration of a series inverter circuit in a conventional discharge lamp lighting device

[Figure 8] (a) Lamp voltage waveform diagram at the time of discharge lamp dielectric breakdown in a conventional discharge lamp lighting device (b) Similarly lamp current waveform diagram

[Explanation of symbols]

1 DC power supply 2 Inverter circuit 3 First choke coil 4 Second choke coil 5 Capacitor 6 Lamp voltage detection means 7 Discharge lamp 8 Lamp current detection means 9. Lighting control means

Claims (3)

[Claims] Claims: 1. A resonant circuit consisting of an inverter means driven by a DC power source to oscillate, a first choke coil connected to the inverter means, and a capacitor connected in series; 2, a series body of a choke coil and a discharge lamp, lamp characteristic detection means for detecting at least one of the lamp voltage and lamp current of the discharge lamp, and an oscillation frequency of the inverter means based on an output signal of the lamp characteristic detection means. Alternatively, a discharge lamp lighting device comprising lighting control means for controlling lighting of the discharge lamp by varying a duty ratio. 2. The discharge lamp lighting device according to claim 1, wherein the second choke coil has an inductance of 100 μH or more. 3. The discharge lamp lighting device according to claim 1, wherein the core of the second choke coil is rod-shaped.