JPH04294097A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To ensure the start of a metal halide lamp even with changing ambient temperature. CONSTITUTION:A series circuitry of a choke coil 3, a capacitor 5 consisting of polyester capacitor, and a lamp voltage sensing capacitor is connected with an inverter circuit 2 which oscillates when driven by a DC power supply 1. A lamp current sensing resistance is put in parallel connection with this series circuitry, and a discharge lamp 7 is put in parallel connection with a series circuitry consisting of the capacitor 5 and the lamp voltage sensing capacitor. The voltages generated at the respective two ends of the lamp voltage sensing capacitor and lamp current sensing resistance are fed to a lighting control means 9, and the inverter circuit 2 oscillating frequency or duty ratio is made variable in conformity to the output signal of this control means, and thus lighting of the discharge lamp 7 is controlled.

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 have been lit using a series inverter circuit as shown in FIG. 5, for example.

In FIG. 5, 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 turned on 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 5a and C2 is connected to the connection point a via a coupling capacitor C4. A lamp voltage detection means 6 is connected to the connection point b between the capacitors 5a and C2, and the output signal of this lamp voltage detection means is inputted 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 5a 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 and capacitor 5
a, C2 is controlled to vary within a certain range including the resonant frequency of the resonant circuit consisting of C2. Therefore, the switching transistors Q9 and Q10 alternately turn on and off, and an alternating current voltage of the above frequency is generated at the connection point c between the coupling capacitor C4 and the choke coil 3, and a resonant current flows through the choke coil 3 and the capacitors 5a and C2. flows, and a high voltage of 12 kV to 15 kV is generated at the connection point d between the choke coil 3 and the capacitor 5a. 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,
When the ambient temperature changes from -40℃ to 100℃,
As a countermeasure against high pressure, the area around the choke coil 3 is impregnated with silicone, so the gap between the choke coil 3 widens due to thermal expansion of silicone at high temperatures, causing the choke coil 3 to have negative temperature characteristics, as shown in FIG. , and a resonance capacitor 5 made of a polypropylene capacitor.
a and C2 also have negative temperature characteristics. As a result, at high temperatures, the inductance value of the choke coil 3 and the capacitor 5a
, C2 is negatively increased, and its resonant frequency becomes 20
It will be higher than at ℃. For this reason, the frequency range of the sawtooth wave generating circuit is exceeded, making it impossible to generate a voltage high enough to cause dielectric breakdown of the discharge lamp 7, resulting in a problem that starting performance is 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 even when the ambient temperature changes.

[0007]

[Means for Solving the Problem] 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 choke coil and a capacitor connected to the inverter means. a resonant circuit consisting of a series body, a discharge lamp connected in parallel with the capacitor, a lamp characteristic detection circuit for detecting at least one of a lamp voltage and a lamp current of this discharge lamp, and this lamp characteristic detection circuit. lighting control means for controlling lighting of the discharge lamp by varying the oscillation frequency or duty ratio of the inverter means according to the output signal of the resonant circuit, and the capacitor of the resonant circuit is made of a polyester capacitor.

[0008]

[Operation] With the above configuration, when starting a discharge lamp,
When the ambient temperature changes from -40℃ to 100℃,
Even if the choke coil has negative temperature characteristics, a polyester capacitor with positive temperature characteristics is used as the capacitor of the resonant circuit, so even if the inductance value of the choke coil increases negatively at high temperatures, the capacitance of the capacitor will decrease. Since the value has a positive characteristic, the resonance frequency hardly changes compared to the point at 20°C.

[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 an embodiment of 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 has, as a load circuit, a resonant circuit made up of a choke coil 3 and a capacitor 5 made of a polyester capacitor connected in series, and a discharge lamp 7 made of a metal halide lamp or the like connected to both ends of the capacitor 5. Since the choke coil 3 is impregnated with silicone around it as a countermeasure against high voltage, it is further connected in series to the resonance circuit in the load circuit to detect the start-up of the discharge lamp 7 and control the subsequent rated lighting, etc. A lamp voltage detection means 6 for detecting the current flowing through the load circuit and a lamp current detection means 8 for detecting the current flowing in the load circuit are provided. The output signals of the lamp voltage detection means 6 and the lamp current detection means 8 are inputted to the lighting control means 9.
controls the lighting operation of the discharge lamp 7 by varying the oscillation frequency of the inverter circuit 2 or its duty ratio based on these signals.

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 5 kHz, and this low frequency is applied as a voltage to the resonant circuit of the choke coil 3 and the capacitor 5. 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. Lighting control means 9
changes the oscillation frequency of the inverter circuit 2 to a higher frequency using the detected voltage, and uses the resonance circuit to increase the oscillation frequency, for example, 10
A high resonant voltage is generated in the capacitor 5 at a frequency within a predetermined range around 0 kHz. This causes dielectric breakdown of the discharge lamp 7. At this time, as shown in FIG. 4, even if the ambient temperature changes from -40°C to 100°C and the choke coil 3 has negative temperature characteristics, the temperature characteristics of the capacitor 5 are positive. The resonant frequency hardly changes. For this reason, a high voltage sufficient to cause dielectric breakdown of the discharge lamp 7 is generated within the frequency range of a sawtooth wave generation circuit, which will be described later. Further, the lamp voltage detection means 6 includes a capacitor 5
A sudden decrease in the current flowing through the discharge lamp 7 is detected by a voltage drop in the lamp voltage detection means 6, thereby detecting that the discharge lamp 7 has started. The lighting control means 9 controls the oscillation frequency of the inverter circuit 2 to a low frequency of about 10 kHz based on the voltage detected by the lamp voltage detection means 6, and shifts the discharge lamp 7 to rated lighting.

FIG. 2 shows a circuit diagram of a specific example of the inverter circuit 2 etc. in FIG. 1. In FIG. 2, the inverter circuit 2 has a series inverter configuration consisting of two switching transistors Q1 and Q2 that drive an external circuit 10 consisting of a choke coil 3, a capacitor 5, and a discharge lamp 7. Both ends of the primary winding of the drive transformer DT are grounded via drive transistors Q3 and Q4,
The lighting control means 9 is connected to the resistors R1 and R2 of the inverter circuit 2.
, clocks E1 and E2 whose phases are inverted to each other are inputted, and a driving voltage VD is applied to the midpoint of the primary winding of the driving transformer DT. Two secondary windings are provided on the secondary side of the drive transformer DT, and one end of each winding is connected to switching transistors Q1 and Q via resistors R6 and R7.
Connected to gate 2. Further, a series body consisting of switching transistors Q1 and Q2 and a resistor R8 is connected between the DC power supply voltage VDD and the ground, and a series body consisting of a coupling capacitor C1 and an external circuit 10 is connected to the connection point of the switching transistors Q1 and Q2. connected between ground. The capacitor C2 constitutes the lamp voltage detection means 6 in FIG. 1, and the resistor R8 constitutes the lamp current detection means 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. 3 shows a circuit diagram of a specific example of the lighting control means 9 in FIG. In FIG. 3, 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 lamp is turned on by the first cutoff circuit 15. First constant current circuit 16
The output terminal of the switching regulator control IC22
It is connected to a timing resistor terminal RT for setting the frequency of . Switching regulator control IC22
The switching regulator frequency is determined by the current flowing from the timing resistor terminal RT to the ground C3 and the capacitance of the capacitor connected to the timing capacitor terminal CT. Therefore, after starting the lamp, the oscillation frequency of the inverter circuit 2 is changed in accordance with the change in the output voltage of the lamp starting current control circuit 14, and the operation is performed so that the relationship between the lamp voltage and the lamp current is in a predetermined relationship.

The output voltage of the sawtooth wave generating circuit 17 and the 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 includes an operational amplifier OP2, resistors R20 and R21, and a transistor Q8. The bias current circuit 21 consists of a series resistor R22 and a resistor R23. The second constant current circuit 20 operates to flow a current corresponding to the output voltage added by the resistors R17 and R18 from the timing resistor terminal RT of the switching regulator control IC 22 to the 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 is set to 10 by the sawtooth voltage.
The voltage is varied within a certain predetermined range around 0 kHz, and controlled so that a high voltage for starting the lamp is output.

[0016]

[Effects of the Invention] As explained above, according to the present invention,
Even if the ambient temperature changes significantly, the resonant frequency can be kept almost constant, so the discharge lamp can be started reliably. Furthermore, since polyester capacitors are smaller than polypropylene capacitors, it is possible to downsize the lighting device.

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

FIG. 3 is a circuit diagram showing a specific example of lighting control means in the discharge lamp lighting device of the present invention.

[Figure 4] Temperature characteristic diagram of the resonance choke coil and capacitor used in the discharge lamp lighting device of the present invention

[Figure 5]
Block diagram showing the configuration of a series inverter circuit in a conventional discharge lamp lighting device

[Fig. 6] (a) Diagram of the output voltage waveform of the sawtooth wave generation circuit when starting the discharge lamp of the same lighting device (b) Diagram showing the high voltage waveform generated in the resonance capacitor (c) Output signal of the lamp voltage detection means Waveform diagram

[Figure 7] Temperature characteristics diagram of conventional resonance choke coil and capacitor

[Explanation of symbols]

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

Claims (1)

[Claims] 1. Inverter means driven by a DC power source to oscillate, a resonant circuit consisting of a series body of a choke coil and a capacitor connected to the inverter means, and a discharge lamp connected in parallel with the capacitor. A lamp characteristic detection circuit for detecting at least one of a lamp voltage and a lamp current of the discharge lamp, and an output signal of the lamp characteristic detection circuit to vary the oscillation frequency or duty ratio of the inverter means to detect the discharge lamp. A discharge lamp lighting device comprising a lighting control means for controlling lighting, wherein a capacitor of the resonant circuit is made of a polyester capacitor.