JP2004207063A - Discharge lamp lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the whole of a discharge lamp lighting device to be produced with ease at low cost by forming a comparator circuit from simple circuits using versatile components so as to discriminate both emission-less conditions on one side and on both sides of the discharge lamp. <P>SOLUTION: The discharge lamp lighting device comprises an inverter circuit 2 for converting a supply voltage from a DC power supply 1 into a high frequency voltage, where a discharge lamp La is lit by an output from the inverter circuit 2. A first comparison voltage corresponding to the sum of a negative voltage of the discharge lamp La and a positive voltage of the discharge lamp La and a second comparison voltage corresponding to the voltage across the discharge lamp La are input to a comparator circuit 5. The comparator circuit 5 discriminates the emission-less condition of the discharge lamp La by detecting that either the first comparison voltage or the second voltage exceeds a predetermined upper threshold. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a discharge lamp lighting device in which a discharge lamp is turned on at a high frequency by an output of an inverter circuit.
[0002]
[Prior art]
Conventionally, as a discharge lamp lighting device for lighting a discharge lamp, there is a device that includes an inverter circuit that converts a power supply voltage of a DC power supply into a high-frequency voltage, and the discharge lamp is turned on at a high frequency by an output of the inverter circuit. .
By the way, at the end of life of a discharge lamp, a phenomenon called Emiless occurs. Emiless means the loss of the electron-emitting substance applied to the filament.There are two types of Emiless, one of which is Emiless, and the other is Emiless, where both filaments are Emiless. Tend to be.
[0003]
For this reason, a conventional discharge lamp lighting device of this type includes a voltage detection circuit for detecting both ends of the discharge lamp, a positive voltage detection circuit for detecting a positive voltage of the discharge lamp, and a detection circuit for detecting a negative voltage of the discharge lamp. A negative voltage detection circuit is provided, which determines that both ends are Emiless when the voltage detected by the voltage detection circuit is equal to or higher than a predetermined value, and detects the positive voltage of the discharge lamp detected by the positive voltage detection circuit and the negative voltage detection circuit. Compared with the negative voltage of the discharge lamp, and when there is a difference equal to or more than a predetermined value between the two, it is determined to be one side Emiless, the output of the inverter circuit is reduced, or the oscillation of the inverter circuit is stopped, There is a discharge lamp in which the stress of parts of the discharge lamp lighting device is increased and the heat generation is prevented both at the time of one side of the discharge lamp and at the time of both sides of the discharge lamp (for example, Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-170695 [Patent Document 2]
JP-A-4-39895 [0005]
[Problems to be solved by the invention]
However, even if the positive voltage of the discharge lamp and the negative voltage of the discharge lamp are incorporated into one comparison circuit to determine the one-sided emission, there is generally no electronic component that operates at the negative voltage. It becomes difficult to compare the negative voltage with the negative voltage in the comparison circuit, and the circuit configuration of the comparison circuit becomes very complicated. Therefore, it is difficult to manufacture the entire discharge lamp lighting device and the manufacturing cost increases. There was a problem.
In view of the above problems, the present invention configures a comparison circuit with a simple circuit using general-purpose components so that both the one-sided Emiless and the two-sided Emiless of the discharge lamp can be determined, and the entire discharge lamp lighting device can be easily manufactured. It can be manufactured at low cost.
[0006]
[Means for Solving the Problems]
The technical means of the present invention for solving this technical problem includes an inverter circuit 2 for converting a power supply voltage of a DC power supply 1 to a high-frequency voltage, and the discharge lamp La is lit at a high frequency by an output of the inverter circuit 2. In the discharge lamp lighting device,
A first comparison voltage corresponding to the sum of the negative voltage of the discharge lamp La and the positive voltage of the discharge lamp La, and a second comparison voltage corresponding to a voltage across the discharge lamp La are input to one comparison circuit 5, The point is that the comparator circuit 5 detects that one of the first comparison voltage and the second comparison voltage exceeds a predetermined upper threshold value and determines the emission of the discharge lamp La.
[0007]
Further, another technical means of the present invention is provided with another comparison circuit 6 for comparing the first comparison voltage with a lower threshold value, and the first comparison voltage is lower than the lower threshold value by the comparison circuit 6. That is, the fact that the emission of the discharge lamp La is determined.
Another technical means of the present invention is that a stop means for stopping the oscillation of the inverter circuit 2 when the emission of the discharge lamp La is determined is provided.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a DC power supply, which is composed of, for example, an AC power supply, a rectifying / smoothing circuit, and a step-up chopper circuit.
Reference numeral 2 denotes an automatic separately-excited inverter circuit, which includes a pair of switch elements Q1 and Q2 formed of an insulated gate field effect transistor (MOSFET), a choke L1, and a DC cut capacitor C1, and a pair of switch elements Q1 , Q2 are connected in series with each other and connected between output terminals of the DC power supply 1, and a choke L1, a DC cut capacitor C1, and a discharge lamp La are connected from the middle point of the switch elements Q1 and Q2 so as to form a half bridge circuit. The choke L1, the capacitor C1, the discharge lamp La, and the capacitor C2 connected in parallel to the discharge lamp La form a series resonance circuit.
[0009]
Reference numeral 3 denotes a positive / negative voltage detection circuit for detecting a positive voltage and a negative voltage of the discharge lamp La, which includes resistors R3, R4, diodes D1, D2, and capacitors C3, C4, and detects a positive voltage of the discharge lamp La at a point A. (The potential at point A is a potential corresponding to the positive voltage of the discharge lamp La), and a negative voltage of the discharge lamp La is detected at point B (the potential at point B is a potential corresponding to the negative voltage of the discharge lamp La). is there).
The point A and the point B are connected to each other at a point C via a resistor R5 and a resistor R6. At the point C, a first comparison voltage corresponding to the sum of the positive voltage of the discharge lamp La and the negative voltage of the discharge lamp La. Is to be taken out.
[0010]
That is, the positive voltage (positive peak voltage) applied to the resonance capacitor C2 (or the discharge lamp La) is set to + Vop, and the negative voltage (negative peak voltage) applied to the resonance capacitor C2 (or the discharge lamp La) is set to + Vop. , −Vop, the potential at point A is + Vop × r2 / (r1 + r2), the potential at point B is −Vop × r2 / (r1 + r2), and the potential at point A and the potential at point B are at point C. A voltage obtained by adding the potential (first comparison voltage) is extracted. Here, r1 is the resistance value of the resistor R1, and r2 is the resistance value of the resistor R2.
[0011]
Therefore, the point C at which the point A and the point B are connected becomes 0 V when the discharge lamp La is normally lit. By connecting the point C to the control power supply Vcc via the resistor R7, the point C can have an arbitrary potential. This arbitrary potential varies depending on the values of + Vop and -Vop.
For example, when + Vop = | -Vop |, the potential at the point C is equal to the above-mentioned arbitrary potential, and when + Vop> | -Vop |, the potential at the point C is higher than the above-mentioned arbitrary potential, and + Vop When <│-Vop│, the potential at the point C is lower than the above-mentioned arbitrary potential.
[0012]
Reference numeral 4 denotes a voltage detection circuit for detecting the voltage between both ends of the discharge lamp La. The circuit includes a secondary winding L2 provided in the choke L1, a diode D7, resistors R13 and R14, and a capacitor C8. Detect the voltage at both ends. That is, in the operating state of the lighting device, a voltage proportional to the resonance voltage (the voltage between both ends of the discharge lamp La) is generated in the choke L1, and the voltage is divided by the resistors R13 and R14 to reach the point D at the discharge lamp. A second comparison voltage corresponding to (proportional to) the voltage across La is extracted.
Reference numeral 5 denotes a first comparison circuit. The first comparison voltage at the point C is inputted to the + input terminal of the first comparison circuit 5 via the diode D3, and the second comparison voltage at the point D is inputted via the diode D8. A predetermined upper threshold (upper limit REF) obtained by dividing the voltage of the control power supply Vcc by the resistor R8 and the resistors R9 and R10 is input to the negative input terminal of the first comparison circuit 5. Thus, the first comparison circuit 5 generates a first comparison voltage corresponding to the sum of the positive voltage of the discharge lamp La and a negative voltage of the discharge lamp La, and a second comparison voltage corresponding to the voltage across the discharge lamp La. Is detected to exceed one of the predetermined upper thresholds, and is determined to be Emiless on both sides or Emiless on one side of the discharge lamp La, and to output an "H" signal (Emiless determination signal S1). .
[0013]
Reference numeral 6 denotes a second comparison circuit. A predetermined lower threshold (lower limit REF) obtained by dividing the voltage of the control power supply Vcc by the resistors R8, R9 and the resistor R10 is input to the + input terminal of the second comparison circuit 6, The first comparison voltage at point C is input to the − input terminal of the second comparison circuit 6. Accordingly, the second comparison circuit 6 compares the first comparison voltage with a predetermined lower threshold, detects that the first comparison voltage has become lower than the lower threshold, determines one-side Emiless of the discharge lamp La, It is configured to output an “H” signal (Emiless discrimination signal S2).
[0014]
Reference numeral 7 denotes a driver IC which receives a voltage from the control power supply Vcc, outputs drive signals a and b for alternately turning on and off the switching elements Q1 and Q2 of the inverter circuit 2, and receives a voltage from the control power supply Vcc. When the output is lost, the output of the drive signals a and b is stopped, and the oscillation of the inverter circuit 3 is stopped.
Reference numeral 8 denotes a latch circuit for maintaining the oscillation stop state of the inverter circuit 2. The latch circuit 8 includes switch elements Q3 and Q4, a Zener diode ZD1, resistors R16 and R17, and capacitors C5 and C6. Are connected in parallel.
[0015]
Reference numeral 9 denotes an OR circuit constituted by diodes D4 and D5. If one of the first comparison circuit 5 and the second comparison circuit 6 outputs an "H" (high voltage) signal, the "H" signal is valid. As a result, an "H" signal (Emiless discrimination signal S1 or Emiless discrimination signal S2) is output to the latch circuit 8.
Next, the operation will be described. The switching elements Q1 and Q2 are connected in series to the DC power supply 1, and these are turned on and off alternately by driving of the driver IC7. By alternately turning on and off the switch elements Q1 and Q2, the discharge lamp La can be turned on at a high frequency.
[0016]
Here, when the discharge lamp La is normal, assuming that the voltage at the point A is VA and the voltage at the point B is VB, VA = | VB |, and the potential VC at the point C is expressed as “the first comparison circuit 5”. , The relationship of “upper threshold value of first comparator circuit 5> VD” holds, and the relationship of upper limit threshold value of VC> lower threshold value of second comparator circuit 6 holds. 5 and the output of the second comparison circuit 6 are both "L" (low voltage) signals. Therefore, when the discharge lamp La is normally lit, the latch circuit 8 inputs the "L" signal from the OR circuit 9, the switching elements Q4 and Q3 of the latch circuit 8 are turned off, and the voltage of the control power supply Vcc is supplied to the driver IC 7. To input, the driver IC 7 outputs the drive signals a and b to the pair of switch elements Q1 and Q2 to turn on and off the switch elements Q1 and Q2 alternately, and the oscillation of the inverter circuit 2 is continued.
[0017]
When the discharge lamp La becomes one-sided and the positive voltage of the discharge lamp La increases (VA> | VB |), the voltage VC at the point C increases from the normal state, and “VC> the first comparison circuit 5 In this case, the output of the first comparison circuit 5 becomes an “H” (high voltage) signal. As a result, the latch circuit 8 receives the “H” signal from the OR circuit 9 and switches the latch circuit 8. The elements Q4 and Q3 are turned on, and the control power supply Vcc is short-circuited, so that no voltage is input from the control power supply Vcc to the driver IC. Therefore, the driver IC 7 outputs the drive signals a and b to the switch elements Q1 and Q2. Is stopped, and the switching elements Q1 and Q2 are kept in the off state to stop the oscillation of the inverter circuit 2.
[0018]
When the discharge lamp La becomes one-sided Emiless in the reverse direction, "VC <lower threshold value of the second comparison circuit 6" is similarly satisfied, and the second comparison circuit 6 outputs an "H" (high voltage) signal. The oscillation of the inverter circuit 2 is stopped.
When the discharge lamp La becomes Emiless on both sides, the voltage VD at the point D rises and becomes “VD> the upper threshold value of the first comparison circuit 5”, and the output of the first comparison circuit 5 is an “H” (high voltage) signal. And the oscillation of the inverter circuit 2 is stopped.
Therefore, the stop means for stopping the oscillation of the inverter circuit 5 when the first comparison circuit 5 or the second comparison circuit 6 determines the emission of the discharge lamp La is constituted by the OR circuit 9, the latch circuit 8, the driver IC 7, and the like. When the discharge lamp La becomes Emiless on both sides or Emiless on one side, oscillation of the inverter circuit 5 is automatically stopped to prevent an increase in component stress and heat generation of the discharge lamp lighting device.
[0019]
The first comparison voltage at the point C input to the first comparison circuit 5 and the second comparison circuit 6 is a voltage corresponding to the sum of the positive voltage of the discharge lamp La and the negative voltage of the discharge lamp La. By applying a constant potential to the voltage, the first comparison voltage has a positive value, and fluctuates within the positive voltage value even when the discharge lamp La is on one side of the emission. Further, the second comparison voltage and the upper threshold value input to the first comparison circuit 5 are within a positive voltage, and the lower threshold value input to the second comparison circuit 6 is also within a positive voltage. . Therefore, the first comparison circuit 5 and the second comparison circuit 6 can all perform processing within a positive voltage value, and the first comparison circuit 5 and the second comparison circuit 6 can be processed by a simple circuit using general-purpose components. , It is possible to determine both the one-sided and the two-sided emission of the discharge lamp La, and the entire discharge lamp lighting device can be manufactured easily and inexpensively.
[0020]
FIG. 2 shows another embodiment, in which a voltage detection circuit 4 for detecting the voltage between both ends of the discharge lamp La includes resistors R21 and R22 connected to both ends of the discharge lamp La, and a capacitor C11 connected in parallel to the resistor R22. Then, at point D, the voltage across the discharge lamp La is detected. That is, in the operating state of the lighting device, a voltage proportional to the resonance voltage (the voltage across the discharge lamp La) is generated in the resonance capacitor C2, and the voltage is divided by the resistors R21 and R22 and released to the point D. A second comparison voltage corresponding to (proportional to) the voltage between both ends of the lamp La is taken out.
[0021]
In other respects, the configuration is the same as that of the above-described embodiment. As in the case of the above-described embodiment, when the discharge lamp La is normal, the switch elements Q1 and Q2 are alternately turned on and off, and When the oscillation of the circuit 2 is continued and the discharge lamp La becomes one-sided Emiless and the positive voltage of the discharge lamp La increases (VA> | VB |), the switching elements Q1 and Q2 are kept in the off state, and the inverter circuit 2 When the discharge lamp La becomes one side Emiless in the reverse direction, the oscillation of the inverter circuit 2 is similarly stopped. When the discharge lamp La becomes Emiless on both sides, the oscillation of the inverter circuit 2 is also stopped. To stop. Further, as in the case of the above embodiment, the first comparison circuit 5 and the second comparison circuit 6 are constituted by simple circuits using general-purpose components, and both the one-side Emiless and the both-side Emiless of the discharge lamp La are determined. Therefore, the entire discharge lamp lighting device can be manufactured easily and inexpensively.
[0022]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, a comparison circuit is comprised with a simple circuit using general-purpose components, so that it is possible to determine both the one-sided and the two-sided emission of the discharge lamp, and the entire discharge lamp lighting device is easy to manufacture and inexpensive. Can be manufactured.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a discharge lamp lighting device according to an embodiment of the present invention.
FIG. 2 is a circuit diagram of a discharge lamp lighting device according to another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 DC power supply 2 Inverter circuit 3 Positive / negative voltage detection circuit 4 Both-ends voltage detection circuit 5 First comparison circuit 6 Second comparison circuit La Discharge lamp

Claims (3)

A discharge lamp lighting device comprising an inverter circuit (2) for converting a power supply voltage of a DC power supply (1) into a high-frequency voltage, wherein the discharge lamp (La) is turned on at a high frequency by an output of the inverter circuit (2).
The first comparison voltage corresponding to the sum of the negative voltage of the discharge lamp (La) and the positive voltage of the discharge lamp (La) and the second comparison voltage corresponding to the voltage across the discharge lamp (La) form one comparison. The comparison circuit (5) detects that one of the first comparison voltage and the second comparison voltage has exceeded a predetermined upper threshold value, and detects the voltage of the discharge lamp (La). A discharge lamp lighting device characterized in that Emiless is determined. Another comparison circuit (6) for comparing the first comparison voltage with a lower threshold is provided. The comparison circuit (6) detects that the first comparison voltage has become lower than the lower threshold, and discharges the discharge lamp. 2. The discharge lamp lighting device according to claim 1, wherein Emiless of (La) is determined. 2. The discharge lamp lighting device according to claim 1, further comprising a stop unit configured to stop the oscillation of the inverter circuit when the emission of the discharge lamp is determined. 3.

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