JP2829876B2 - Discharge lamp lighting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a metal halide lamp or the like in which current is controlled by a step-down chopper circuit to which a direct current is input and a rectangular wave is lit by a full-bridge inverter. The present invention relates to improvement of a lighting device for a luminance discharge lamp.

[Conventional technology]

In recent years, high-intensity discharge lamps such as metal halide lamps have begun to spread, and lighting devices for such discharge lamps also include, as shown in FIG. 3, a phase-adjustment type ballast including a leakage transformer _Tr and a main capacitor C. From the method of lighting the lamp L using a copper-iron type ballast, as shown in FIG.
HI-based systems are being reduced in size and weight.

However, in a lighting device using such a high-frequency inverter, there is a problem that when a current in a certain frequency region is supplied, an acoustic resonance phenomenon occurs and an arc extinguishes and becomes unstable.

Conventionally, in order to remove instability due to the acoustic resonance phenomenon, for example, a rectangular wave lighting method as shown in FIG. 5 has been proposed. That is, in FIG. 5, 1 is a commercial power supply,
D ₁ is the rectifying element, C ₁ is a smoothing capacitor, 2 in step-down type chopper circuit, driving a switching transistor Q _1, the freewheeling diode D ₂ DC reactor L ₁ and a smoothing capacitor C ₂ of the switching transistor Q ₁ And a constant current feedback circuit 3 to be controlled. R ₁ is a current detecting element for inputting a detection output to the constant current feedback circuit 3, and 4 is a switching transistor Q ₂ , Q ₃ ,
Q is a full-bridge inverter consisting of _4, Q _5.

Then in the produced lighting device in this way, the commercial power supply 1 is rectified by the rectifier elements D _1, the DC output is inputted to the step-down type chopper circuit 2, the constant current control is performed,
The output of the chopper circuit 2 is a full bridge type inverter 4
Is input to Then, by the operation of the inverter 4, a rectangular wave alternating voltage is applied to the lamp 5, and rectangular wave lighting is performed. In this rectangular wave lighting, since a rectangular wave is applied, it is said that good lighting is performed with little flicker of the lamp.

However, in the above-described conventional discharge lamp lighting device, the constant current control is performed in the step-down type chopper circuit, so that only the current when the lamp is stable can flow at the start of the lamp. However, in general, when a discharge lamp is turned on, a current that is about 1.2 to 2.5 times that of a stable state is required when starting the lamp,
Therefore, when starting with a stable current, the starting time may be long, or the discharge may not be stable and the lamp may not start. Also, when the current is stable, constant current control is performed, so the change in lamp voltage directly changes the lamp power,
Therefore, there is a disadvantage that it is not possible to prevent variations in lamp voltage due to variations during manufacturing of the lamp and excessive input due to a rise in lamp voltage at the end of life.
Further, there is a problem that the lamp power greatly changes due to the fluctuation of the input voltage.

In order to solve the above problems in the conventional discharge lamp lighting device, the present inventor previously described in Japanese Patent Application No. 63-329439,
A discharge lamp lighting device as shown in FIG. 6 has been proposed. 6, the same components as those of the conventional example shown in FIG. 5 are denoted by the same reference numerals. Step-down chopper circuit 2, the switching transistor Q _1, the freewheeling diode D _2, a DC reactor L _1, a smoothing capacitor C _2,
Driving circuit 11 of the switching transistor Q _1, it is composed of a switching circuit 12 for sending a control signal to input the detection output of the current detection element R ₁ to the drive circuit 11. Reference numeral 13 denotes a flip-flop circuit for driving the switching transistors Q ₂ , Q ₃ , Q ₄ , and Q ₅ constituting the full-bridge inverter 4, and reference numeral 14 denotes a starting circuit connected to the output terminal of the inverter 4. Incidentally C ₃ are capacitors for bypassing the high voltage pulse generated from the starting circuit 14. Further, in this lighting device, a DC power supply circuit and a step-down chopper circuit 2 are provided.
An input voltage detection circuit 21 is provided between the, the detection output via a signal inverting circuit 22, the switching circuit 12 of the step-down chopper circuit 2 is input with a detection output of the current detection element R ₁ It is configured to:

FIG. 7 shows the input voltage detection circuit 21 and the signal inversion circuit 22.
And switching circuit 12 in step-down chopper circuit 2
3 is a diagram showing a detailed circuit configuration of FIG. In the switching circuit 12 in the step-down chopper circuit 2, 15 is an oscillator of triangular reference wave, resistor R ₄ and the capacitor C ₄ is the generator
The oscillation frequencies of 15 generated reference waves are determined. 16 is an operational amplifier, R ₅ is drift compensation resistor of the amplifier 16, R ₆ is the input resistor, the detection output of the current detecting element R ₁ through their resistance R _5, R ₆ is an operational amplifier 16 Is to be entered. A resistor is connected between the input and output terminals of the operational amplifier 16.
A feedback circuit is connected in which a series circuit of R ₇ , a resistor R ₈ and a Zener diode ZD, and a series circuit of a resistor R ₉ and a capacitor C ₅ for phase compensation are connected in parallel. Reference numeral 17 denotes a comparator for comparing and amplifying the reference voltage from the operational amplifier 16 and the triangular wave from the oscillator 15. The output of the comparator 17 is input to the drive circuit 11 of the chopper circuit 2.

Input voltage detection circuit 21 includes a voltage dividing series resistors R _10, R ₁₁ connected in parallel to the DC power source circuit, dividing resistors R _10, R
A light emitting diode LED via a resistor R ₁₂ is the input side of the photocoupler 23 connected between the ₁₁ connection point and the negative line
It is composed of The signal inverting circuit 22 is a constant voltage source.
24 and the voltage source 24 to the resistor R _13, R ₁₄ is constituted by a phototransistor PT of the output side of the connected photocoupler 23 via a resistor R ₁₃ connected to the positive side of the constant voltage source 24 Are connected to input terminals a and b of the switching circuit 12, respectively. Then, the detection signal detected by the light emitting diode LED constituting the input side of the photocoupler 23 of the input voltage detection circuit 21 is received by the phototransistor PT of the signal inversion circuit 22 constituting the output side of the photocoupler 23, and the detection signal is received. The switching circuit 12 is configured to invert and supply a negative input to the operational amplifier 16 of the switching circuit 12.

Next, the operation of the previously proposed discharge lamp lighting device configured as described above will be described with respect to portions different from the conventional example shown in FIG. In first as in the conventional lighting device shown in FIG. 5, the commercial power supply 1 is rectified by the rectifier elements D _1, the DC output is performed is input current control to the step-down type chopper circuit 2, the chopper circuit 2 Are input to the full-bridge inverter 4. The lamp 5 is started and lit by the operation of the inverter 4 and the operation of the starting circuit 14. During lamp starting, the detection output V ₁ of the current detecting element R ₁ is large because the starting current is large. Thus output difference of the operational amplifier 16 of the switching circuit 12 to the detection output V ₁ is inputted is increased and thereby the Zener diode ZD conductive state of the feedback circuit. as a result,
The amplification factor α of the operational amplifier 16 is substantially expressed by the following equation (1).

The amplification factor alpha, since the resistor R ₈ of the feedback circuit including a Zener diode ZD and a resistor R ₇ is connected in parallel, the amplification factor represented by the following formula in the case of only the feedback resistor R ₇ (2) alpha ′.

As a result, as shown in FIG.
The output reference voltage B of 16 is the value at the time of the amplification rate α. Value at amplification rate α ' Lower. Output reference voltage of the operational amplifier 16 B ₁ or
B ₂ is also compared in FIG. 8 (b) to the comparator 17 and the triangular wave A of the oscillator 15 shown, comparing an output waveform shown in Figure 8 (b)
C ₁ or C ₂ is obtained. The comparison output C is input to the drive circuit 11 of the step-down chopper circuit 2 and the step-down chopper circuit 2
Of the switching transistor Q ₁ same drive pulse is driven and controlled is applied to the pulse width t ₁ or t ₂ shown in Figure 8 (b). The pulse width t ₁ when the amplification factor of the operational amplifier 16 is α
Since the pulse width is wider than the pulse width t ₂ when the amplification factor is α ′, a large starting current flows at the time of starting.

Starting up after the lamp voltage rises, and decrease the detection output V ₁ of the current detecting element R ₁ with it, the output reference voltage B of the operational amplifier 16 is descending, but before the predetermined reaching the rated lamp voltage After reaching the voltage of, the Zener diode ZD of the feedback circuit of the operational amplifier 16 is cut off,
The Zener voltage of the Zener diode ZD is set to the input / output potential difference of the operational amplifier 16 at that time.

As a result, when the predetermined lamp voltage is reached, the operational amplifier 16 thereafter becomes an amplifier having an amplification factor α ′, and during the time when the predetermined lamp voltage is reached, the amplification factor is increased in an analog manner due to the nonlinear characteristics of the Zener diode ZD. To increase.

Therefore, as shown in FIG. 9, the rainbow curve showing the relationship between the lamp voltage and the lamp power is obtained from the characteristic curve a in which the zener diode ZD indicated by the dotted line is in the conducting state, and the zener diode ZD indicated by the dashed line is in the off state. The characteristic curve b continuously changes due to the non-linear characteristic of the Zener diode ZD over the points P and Q, and becomes a characteristic shown by a solid line c. Has a function of making the power substantially constant, and prevents an overpower due to an increase in the lamp voltage.

In the discharge lamp lighting device configured as described above, at the time of starting discharge and near the time of stable operation, the operation is performed as described above, and a stable start is performed. Next, the operation when the DC input voltage fluctuates will be described.
The detection signal detected by the input voltage detection circuit 21 is inverted by a signal inversion circuit 22 and a negative signal is input to the operational amplifier 16 of the switching circuit 12. On the other hand, in the lamp current detection element R _1, a current flows toward the point b from point a, point b when the reference point a becomes negative, with respect to the detection signal is also operational amplifier 16 by the current detection element R ₁ Input is negative. Therefore, the DC input voltage detection signal is superimposed on the lamp current detection signal, and when the DC input voltage increases, the input voltage to the operational amplifier 16 increases by the amount of the increase. As a result, the output voltage B of the operational amplifier 16 increases, the pulse width t of the comparison output waveform C decreases, and the current is reduced in the step-down chopper circuit 2. Conversely, when the DC input voltage drops, the reverse operation is performed and the chopper circuit 2 is controlled so that the current increases. Therefore, a constant power characteristic is achieved even in a wide range of fluctuations of the lamp voltage and the input voltage.

[Problems to be solved by the invention]

However, in the discharge lamp lighting device proposed above, a constant power characteristic is achieved even in a wide range of fluctuations of the lamp voltage and the input voltage, but the switching circuit 12 in the step-down chopper circuit 2 is not required. Since the Zener diode ZD is inserted in the feedback circuit of the operational amplifier 16 which constitutes the above, there is a problem that the switching circuit 12 lacks temperature stability. In other words, when the temperature of the Zener diode rises, the Zener voltage as low as about 2 V drops, so if such a Zener diode is inserted in the feedback circuit of the operational amplifier, the amplification of the operational amplifier will increase as the temperature rises. The rate is reduced, which causes the lamp power to be overpowered. Furthermore, there has been a problem that the temperature of the transistors in the peripheral circuit rises due to the overpower, and the temperature of the Zener diode further rises.

The present invention has been made to solve the above-described problem in the previously proposed discharge lamp lighting device, and has a temperature compensation function that can always supply constant lamp power even when the ambient temperature of the power supply rises. It is an object to provide a discharge lamp lighting device provided with the same.

[Means and actions for solving the problem]

In order to solve the above problems, the present invention provides a step-down chopper circuit which controls a current by inputting a direct current to an output of the step-down chopper circuit and inputs the output of the step-down chopper circuit to a full-bridge inverter. A discharge lamp lighting device for connecting and lighting the DC input voltage, a current detection element inserted between a free wheel diode and a smoothing capacitor at an output section of the step-down chopper circuit, and A switching circuit for controlling a pulse width of the step-down chopper circuit having a built-in operational amplifier for inputting a detection output of input voltage detection means and a detection output of the current detection element, wherein the operational amplifier has a first resistor and a Zener A feedback circuit comprising a series circuit of a diode and a parallel circuit of a second resistor; and a temperature compensating circuit connected to the input terminal. Response to changing the amplification factor of the operational amplifier into a DC input voltage and the lamp current while compensating for variations in the amplification factor of the operational amplifier based on, is to configured to control the pulse width of the chopper circuit.

With such a configuration, the temperature characteristic of the Zener diode inserted in the feedback circuit of the operational amplifier is compensated for by the temperature compensation circuit connected to the input terminal of the operational amplifier, and the temperature characteristic is compensated over a wide range of the ambient temperature. Thus, constant lamp power can be supplied at all times, and stable lighting operation can be performed.

〔Example〕

Hereinafter, embodiments will be described. FIG. 1 is a circuit diagram showing an embodiment of a discharge lamp lighting device according to the present invention.
The same components as those of the previously proposed discharge lamp lighting device shown in the drawings are denoted by the same reference numerals, and description thereof will be omitted.

In the present invention, the temperature compensation circuit 31 outputs, as well as the detection output of the current detection element R ₁ of the step-down type chopper circuit 2 of the signal inversion circuit 22 which detects the output is the input of the input voltage detection circuit 21
And input to the switching circuit 12 via the.

FIG. 2 shows the input voltage detection circuit 21, the signal inversion circuit 22,
FIG. 9 is a diagram showing a detailed circuit configuration of the switching circuit 12 and the temperature compensation circuit 31 in the step-down chopper circuit,
The same components as those of the previously proposed discharge lamp lighting device shown in the drawings are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, a negative temperature coefficient thermistor 32 is used as the temperature compensation circuit 31, and the thermistor 32 is connected between the input terminal b of the switching circuit 12 and the minus input terminal of the operational amplifier 16.
It is intended to be connected in series with the input resistor R _6.

In the lighting device configured as described above, similarly to the previously proposed lighting device shown in FIGS. 6 and 7, when the discharge lamp is started, the gain of the operational amplifier is suppressed to increase the pulse width. Control and supply a sufficient current to start the motor to ensure stable starting, and to supply a suitable power so as not to be overpowered with the rise of the lamp voltage by increasing the operation amplification factor near the stable time. And the power can be made substantially constant with respect to the fluctuation of the input voltage.

Further, in the present invention, when the ambient temperature rises in the steady state, the Zener voltage of the Zener diode ZD of the feedback circuit of the operational amplifier 16 decreases, and the resistance increases.
Since the impedance of the feedback circuit including R ₇ , R ₈ and the Zener diode ZD decreases, the amplification factor of the operational amplifier 16 decreases and the power tends to be overpowered. At this time, since the impedance of the resistor R ₆ and a negative temperature coefficient thermistor 32 which is inserted into the negative input terminal of the operational amplifier 16 to decrease the ambient temperature rises, resulting in the ratio of the input impedance and the feedback impedance is constant, the ambient temperature Even if the temperature rises, the operational amplifier 16 can maintain a constant amplification factor, and therefore, in a steady state, can maintain a constant power even when the ambient temperature changes.

In the above embodiment, the temperature compensation circuit is constituted by a negative characteristic thermistor connected in series to the minus input terminal of the operational amplifier. However, any circuit that performs similar temperature compensation can be used.

〔The invention's effect〕

As described above with reference to the embodiments, according to the present invention, a series circuit of a resistor and a zener diode is added to a feedback circuit of an operational amplifier constituting a switching circuit for controlling a pulse width of a step-down chopper circuit. With a simple configuration, the input voltage detection signal and the current detection signal are input to the operational amplifier via the temperature compensation circuit via the temperature compensation circuit.When the discharge lamp is started, the amplification factor of the operational amplifier is controlled to increase the pulse width. In this case, it is possible to supply a sufficient electric power so that a sufficient current is supplied to perform a stable starting, and in the vicinity of a stable time, the operational amplification factor is increased so that the electric power is not overpowered with the rise of the lamp voltage. The lamp power can be made substantially constant with respect to a change in the input voltage and a change in the ambient temperature. Therefore, it is possible to provide a discharge lamp lighting device capable of significantly improving the life of the lamp.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a discharge lamp lighting device according to the present invention, and FIG. 2 is a diagram showing a switching circuit, an input voltage detection circuit, a signal inversion circuit, and a temperature compensation circuit of the step-down chopper circuit. FIG. 3 shows a specific circuit configuration, and FIG.
Diagram showing a discharge lamp lighting device using a conventional copper-iron ballast,
FIG. 4 is a diagram showing a conventional discharge lamp lighting device using a high frequency inverter, FIG. 5 is a diagram showing a circuit configuration example of a conventional low frequency rectangular wave lighting discharge lamp lighting device, and FIG. FIG. 7 is a circuit configuration diagram showing the previously proposed discharge lamp lighting device, FIG. 7 is a specific circuit configuration diagram of the switching circuit, the input voltage detection circuit and the signal inversion circuit, and FIGS. FIG. 9 is a signal waveform diagram for explaining the operation, and FIG. 9 is a diagram showing the relationship between the lamp voltage and the lamp power. In the figure, 2 is a step-down chopper circuit, 4 is a full bridge inverter, 5 is a discharge lamp, 11 is a driving circuit, 12 is a switching circuit, 14 is a starting circuit, 15 is an oscillator, 16 is an operational amplifier, and 17 is a comparator. , 21 is an input voltage detecting circuit, 22 is a signal inverting circuit, 23 is a photocoupler, 31 is a temperature compensation circuit, and 32 is a negative thermistor.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-177298 (JP, A) JP-A-62-252096 (JP, A) JP-A-63-301493 (JP, A) JP-A-62-1 150693 (JP, A) Japanese Utility Model Hei 2-65899 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H05B 41/24-41/29

Claims (1)

(57) [Claims] 1. A step-down chopper circuit for inputting a direct current to perform current control, an output of the step-down chopper circuit to a full-bridge inverter, and connecting a discharge lamp to an output terminal of the inverter to emit light. In the lamp lighting device, a means for detecting the DC input voltage, a current detection element inserted between a free wheel diode and a smoothing capacitor at an output part of the step-down chopper circuit, and a detection output of the DC input voltage detection means And a switching circuit for controlling a pulse width of the step-down chopper circuit having a built-in operational amplifier for inputting a detection output of the current detecting element, wherein the operational amplifier comprises a series circuit of a first resistor and a Zener diode, and a second circuit.
It has a feedback circuit consisting of a parallel circuit of resistors and a temperature compensation circuit connected to the input end, and performs calculations in response to DC input voltage and lamp current while compensating for fluctuations in the amplification factor of the operational amplifier due to changes in ambient temperature. Change the amplification factor of the amplifier,
A discharge lamp lighting device characterized in that a pulse width of a chopper circuit is controlled.