JPH03171596A - Lighting apparatus for discharge lamp - Google Patents

Abstract

PURPOSE:To supply constant electric power for a lamp in a wide range of ambient temperature by changing amplification ratio of a computing amplifier having a temperature compensating circuit corresponding to d.c. input voltage and a lamp current and controlling the pulse width of a chopper circuit. CONSTITUTION:D.C. output of a commercial power source 1 rectified by a rectifier device D1 is put into a voltage-descending type chopper circuit 2 to adjust current and operates a full bridge-type inverter 4 to light a discharge lamp 5. Output of a signal reverse circuit 22 to which a detection output of an input voltage detection circuit 21 is sent and a detection output of a current detection device R1 of the chopper circuit 2 are put into a switching circuit 12 through a temperature compensating circuit 31. Under constant conditions, when temperature rises, impedance of a feedback circuit consisting of a Zener diode ZD of a computing amplifier 16 descends. At this time, impedance of a resistor R6 to be inserted into an input terminal of a computing amplifier 12 and a negative terhmistor 32 decreases to that the computing amplifier 16 maintains a constant amplification ratio and constant electric power is supplied.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention controls the current using a step-down chopper circuit that inputs direct current, and uses a full-bridge inverter to perform rectangular wave lighting. This invention relates to improvements in lighting devices for brightness discharge lamps.

[Conventional technology]

In recent years, high-intensity discharge lamps such as metal halide lamps have become popular, and the lighting devices for such discharge lamps also include a phase-advanced ballast consisting of a leakage transformer Tr and a main capacitor C, as shown in Figure 3. From the method of lighting the lamp L using a steel type ballast, to the method of lighting the lamp L using a high frequency inverter H. as shown in FIG. A system using I is becoming more compact and lightweight.

However, in a lighting device using such a high frequency inverter, there is a problem in that when a current in a certain frequency range is supplied, an acoustic resonance phenomenon occurs, causing the arc to disappear and becoming unstable.

Conventionally, in order to eliminate instability caused by such an acoustic resonance phenomenon, a rectangular wave lighting system as shown in FIG. 5, for example, has been proposed. In other words, in Fig. 5, 1 is the commercial power supply, D
, is a rectifying element, C1 is a smoothing capacitor, and 2 is a step-down chopper circuit that drives and controls the switching transistor Q, the freewheel diode D2, the DC reactor L, the smoothing capacitor C2, and the switching transistor Q. It is composed of a constant current feed circuit 3. R, is a current detection element that inputs a detection output to the constant current feedback circuit 3, and 4 is a switching transistor Q2. Q3. Q. ．． This is a full bridge type inverter consisting of Qs.

In the lighting device configured in this manner, commercial power #1 is rectified by the rectifying element D, and its direct output is input to the step-down chopper circuit 2, where constant current control is performed.
The output of the chopper circuit 2 is a full bridge inverter 4.
is input. 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 the lamp can be lit well with less flickering.

However, in the above-mentioned conventional discharge lamp lighting device, constant current control is performed in the step-down type chopper circuit.
Even when the lamp is started, only current can flow when the lamp is stable. However, in general, when lighting a discharge lamp, 1.2 to 2.5 times as much electricity is required when the lamp is pulsating as when it is stable, so starting with the current when it is stable may take a long time to start. , or the lamp may not start due to unstable discharge. In addition, constant current control is performed when stable, so changes in lamp voltage directly result in changes in lamp power.
Therefore, there is a drawback that it is impossible to prevent variations in lamp voltage due to variations in lamp manufacturing or excessive input due to an increase in lamp voltage at the end of the lamp's life.

Furthermore, there is another problem in that the lamp power changes greatly due to fluctuations in input voltage.

In order to solve the above problems in the conventional discharge lamp lighting device, the present inventor previously proposed a discharge lamp lighting device as shown in FIG. 6 in Japanese Patent Application No. 63-329439.

In FIG. 6, the same components as those in the conventional example shown in FIG. 5 are denoted by the same reference numerals. The step-down chopper circuit 2 inputs the switching transistor Q1, the freewheel diode D2, the DC reactor L, the smoothing capacitor Cz, the driving circuit 11 of the switching transistor Q1, and the detection output of the current detection element R1 to the driving circuit 11. Switching circuit I that sends control signals
It is composed of 2. l3 is a switching transistor Qz+Q that protects the full-bridge inverter 4.
．． ．． Q. ．． 14 is a pulsating circuit connected to the output of the inverter 4. Note that C3 is a capacitor for bypassing the high voltage pulse generated from the starting circuit 14. Furthermore, in this lighting device, an input voltage detection circuit 21 is provided between the DC voltage reducing circuit and the step-down chopper circuit 2, and its detection output is transmitted through the signal inversion circuit 22 to the switching of the step-down chopper circuit 2. The circuit 12 includes the current detection element R1.
is configured to be input together with the detection output of.

FIG. 7 shows the input voltage detection circuit 21 and the signal inversion circuit 2.
2 is a diagram showing a detailed circuit configuration of the switching circuit 12 in the step-down chopper circuit 2 and the step-down chopper circuit 2. FIG.

In the switching circuit 12 in the step-down chopper circuit 2, 15 is an oscillator of a triangular reference wave, and a resistor R4 and a capacitor C4 determine the oscillation frequency of the reference wave generated by the oscillator 15. 16 is an operational amplifier, R5 is a drift compensation resistor of the amplifier 16, R6 is an input resistor, and these resistors R, . The detection output of the current detection element R1 is input to the operational amplifier 16 via Rb. A resistor R7 is connected between the input and output terminals of the operational amplifier 16.
, resistance R, and? A feedback circuit is connected in parallel with a series circuit of an energy diode ZD, a series circuit of a resistor R for phase compensation, and a capacitor C. A comparator 17 compares and amplifies the reference voltage from the operational amplifier 16 and the triangular wave from the oscillator 15, and the output of the comparator 17 is input to the drive circuit 11 of the chopper circuit 2.

The input voltage detection circuit 21 includes a series-connected voltage dividing resistor R, which is connected in parallel to a DC power supply circuit. +RI+, and a light emitting diode LED which is connected to the input side of a photocoupler 23 via resistors R and ■ between the connection point of the voltage dividing resistor R lo+ R I + and the negative line. Further, the signal inverting circuit 22 connects a constant voltage source 24 and the voltage jg. 2
4 and a phototransistor PT, which is the output side of the photocoupler 23, connected to the resistor R13+R14 via the resistor R13+R14, and a resistor R13 connected to the positive side of the constant voltage source 24.
Both ends of l3 are connected to the input terminal a of the switching circuit 12.
, b, 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 sent to the photocoupler 23.
The phototransistor PT of the signal inversion circuit 22 receives the output side of the detection signal 3, inverts the detection signal, and supplies the 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 explained with respect to the differences from the conventional example shown in FIG. 5. First, similar to the conventional lighting device shown in FIG. 5, the commercial power supply l is rectified by a rectifying element D, and its DC output is input to a step-down Chonopa circuit 2 to perform current control.
The output of the chopper circuit 2 is connected to a full bridge inverter 4.
is input. Then, the lamp 5 is started and lit by the operation of the inverter 4 and the starting circuit 14. During lamp pulsation, the starting current is large, so the detection output (1) of the current detection element R becomes large. Therefore, the difference between the input and output of the operational amplifier 16 of the switching circuit 12 to which this detection output (2) is input becomes large, and the Zener diode ZD of the feedback circuit becomes conductive.

As a result, the amplification factor α of this operational amplifier 16 is approximately expressed by the following formula (
1).

R7+R8 This amplification factor α is determined by the resistance R. of the feedback circuit including the Zener diode ZD. and resistor R7 are connected in parallel, so the following equation (2
) can be kept lower than the amplification factor α'.

R6 As a result, as shown in FIG. 8(a), the operational amplifier 1
The output reference voltage B of R6 is lower than the value Bz (1 V, .multidot.) when the amplification factor is α and the value B when the width factor is α'. The output reference voltage B or B2 of the operational amplifier 16 is compared with the angular wave A of the oscillator 15 shown in FIG. ▼The small and medium comparison output C is the drive circuit 1 of the step-down chopper circuit 2.
1 and the switching transistor Q.1 of the step-down chopper circuit 2. A drive pulse having the same pulse width t1 or L2 as shown in FIG. 8(b) is applied to perform drive control.

Since the pulse width 1 when the amplification factor of the operational amplifier 16 is α is wider than the pulse width L2 when the amplification factor is α', a large starting current is caused to flow during pulsation.

After the lamp starts, the lamp voltage increases, and the detection output (1) of the current detection element R decreases accordingly, and the output reference voltage B of the operational amplifier 16 decreases, but the voltage decreases to a predetermined value before reaching the rated lamp voltage. After reaching the voltage, the Zener voltage of the Zener diode ZD is set to the current output potential difference of the operational amplifier 16 so that the Zener diode ZD of the feed path circuit of the operational amplifier 16 is cut off.

As a result, when the predetermined lamp voltage is reached, the operational amplifier 16 becomes an amplifier with an amplification factor α', and while the predetermined lamp voltage is reached, ▼Topf 4-The amplification rate of each word increases.

Therefore, as shown in FIG. 9, the rain poker curve showing the relationship between the lamp voltage and the lamp power is as follows: from the characteristic curve a when the Zener diode ZD shown by the dotted line is in the conductive state, to the characteristic curve a when the Zener diode ZD shown by the dashed line is in the off state. There is a continuous transition to the characteristic curve b at points P and Q due to the nonlinear characteristics of the Zener diode ZD, and the solid line C
It has the characteristics shown in , and has the function of keeping the lamp power almost constant even when the lamp voltage fluctuates within a certain range around the rated value, and prevents overpowering due to a rise in lamp voltage.

In the discharge lamp lighting device configured in this way, when the discharge is started and when it is stable, it operates as described above.
While stably starting the lamp, it also prevents excessive input due to a rise in lamp voltage and supplies appropriate power.Next, the operation when the DC input voltage fluctuates will be explained. The detection signal detected by the input voltage detection circuit 21 is inverted by a signal inversion circuit 22 and inputted to the operational amplifier 16 of the switching circuit 12 as a negative signal. On the other hand, in lamp current detection element R, current flows from point a to point b, so if point a is used as a reference, point b becomes negative, and the detection signal from current detection element R is also applied to operational amplifier 16. is a negative input. 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 negatively by the upper bound thereof.

As a result, the output voltage B of the operational amplifier l6 increases, the pulse width t of the comparison output waveform C decreases, and the current in the step-down chopper circuit 2 is controlled to decrease. 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, constant power characteristics are achieved even over wide variations in lamp voltage and input voltage.

[Problem to be Solved by the Invention] However, in the above-mentioned discharge lamp lighting device proposed earlier, constant power characteristics are achieved even over a wide range of fluctuations in lamp voltage and input voltage. , since a Zener diode ZD is inserted in the feed Hanok circuit of the operational amplifier 16 that constitutes the switching circuit 12 in the step-down chopper circuit 2, the switching circuit l
2 has a problem in that it lacks thermal stability. In other words, when the temperature of a Zener diode rises by 2, the Zener voltage, which is as low as 2 cm, decreases, so if such a Zener diode is inserted into the feedback circuit of an operational amplifier, the operation will decrease as the temperature rises. The amplification factor of the amplifier decreases, resulting in overpowering the lamp power. Furthermore, overpowering caused the temperature of the transistors in the peripheral circuits to rise, which caused the temperature of the Zener diode to rise further, and this vicious cycle was repeated, eventually leading to thermal runaway.

The present invention was made to solve the above-mentioned problems in the previously proposed discharge lamp lighting device.
The object of the present invention is to provide a discharge lamp lighting device that can be used during the day.

[Means and effects for solving the problem] In order to solve the above problems, the present invention inputs direct current to a step-down chopper circuit, controls the current, and converts the output of the step-down chopper circuit into a full-bridge inverter. A discharge lamp lighting device that connects a discharge lamp to the output end of the inverter and lights the discharge lamp includes means for detecting the DC input voltage, and a freewheel diode and a smoothing capacitor at the output part of the step-down chopper circuit. a current detection element inserted between the two, and a switching circuit that controls the pulse width of the step-down chopper circuit that includes a built-in operational amplifier that inputs the detection output of the DC human horn voltage detection means and the detection output of the current detection element. Prepare,
The operational amplifier has a feedback circuit consisting of a series circuit of a first resistor and a Zener diode, and a parallel circuit of a second resistor, and a temperature compensation circuit connected to the input terminal, and the amplification factor of the operational amplifier is adjusted based on changes in ambient temperature. In response to the DC input voltage and lamp current while compensating for fluctuations in the
Mihahe, I am in the middle of the day, and I am taking precautions to control the width of the fire.

With this configuration, the temperature compensation circuit connected to the input terminal of the operational amplifier compensates for the temperature characteristics of the Zener diode inserted in the feedback circuit of the operational amplifier, and the temperature characteristics of the Zener diode inserted in the feedback circuit of the operational amplifier are compensated for over a wide range of ambient temperatures. This enables constant lamp power to be supplied at all times, enabling stable lighting operation.

〔Example〕

Examples will be described below. FIG. 1 is a circuit diagram showing an embodiment of a discharge lamp lighting device according to the present invention, and the same components as those of the previously proposed discharge lamp lighting device shown in FIG. 6 are given the same reference numerals. Therefore, the explanation thereof will be omitted.

In the present invention, the output of the signal inverting circuit 22 into which the detection output of the input voltage detection circuit 21 is inputted, as well as the detection output of the current detection element R of the step-down chopper circuit 2, is transferred to the switching circuit 12 through the temperature compensation circuit 3l. is configured to input.

FIG. 2 shows the input voltage detection circuit 21 and the signal inversion circuit 2.
2. Switching circuit l2 in step-down chopper circuit
and a diagram showing the detailed circuit structure of the temperature compensation circuit 31, in which the same structures or members as those of the previously proposed discharge lamp lighting device shown in FIG. do.

In this embodiment, a negative characteristic thermistor 32 is used as the temperature compensation circuit 31, and the thermistor 32 is connected in series with an input resistor R between the input terminal b of the switching circuit l2 and the negative input terminal of the operational amplifier 16. It is something that connects.

In the lighting device constructed in this way, as in the previously proposed lighting device shown in FIGS. 6 and 7, the amplification factor of the operational amplifier is suppressed to increase the pulse width when the discharge lamp pulsates. The lamp is controlled to flow enough current for stable starting, and when the lamp is stable, the operational amplification factor is increased to prevent overpowering as the lamp voltage increases. The power can be supplied and the power can be made to be approximately constant with respect to fluctuations in the input voltage.

Furthermore, in the present invention, in a steady state, when the ambient temperature rises, the Zener voltage of the Zener diode ZD of the feed hack circuit of the operational amplifier 16 decreases, and the impedance of the feedback circuit including the resistors R7, Rl1, and the Zener diode ZD decreases. , the amplification factor of the operational amplifier 16 decreases, leading to overpower. At this time, the impedance of the resistor R6 inserted into the negative input terminal of the operational amplifier 16 and the negative characteristic thermistor 32 decreases as the ambient temperature rises, and as a result, the ratio of input impedance to feedback impedance becomes constant, and the ambient temperature increases. However, the operational amplifier 16 can maintain a constant amplification factor, and therefore, in a steady state, it can maintain constant power even if the ambient temperature changes.

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

f b Rl'I/Tl6hA-) As described above based on the embodiments, according to the present invention, the feed bank of the operational amplifier that controls the switching circuit that controls the pulse width of the step-down chopper circuit. to the circuit,
This is done simply by adding a series circuit of a resistor and a Zener diode, and inputting the input voltage detection signal together with the current detection signal to the operational amplifier via a temperature compensation circuit.
When starting the discharge lamp, the amplification factor of the operational amplifier is suppressed and the pulse width is controlled to be large, allowing sufficient current to flow for starting and stable starting, and when the lamp is stable, the operational amplification factor is increased to increase the lamp voltage. Appropriate power can be supplied so that overpower does not occur as the voltage increases, and the lamp power can be kept approximately constant despite fluctuations in input voltage and changes in ambient temperature. Therefore, it is possible to provide a discharge lamp lighting device that can significantly improve the lamp life.

[Brief explanation of the drawing]

FIG. 1 shows an example of a discharge lamp lighting device according to the present invention. ! Figure 2 shows the specific circuit configuration of the switching circuit, input voltage detection circuit, signal inversion circuit, and temperature compensation circuit of the step-down chopper circuit, and Figure 3 shows the conventional copper-iron type. FIG. 4 is a diagram showing a discharge lamp lighting device using a ballast, FIG. 4 is a diagram showing a discharge lamp lighting device using a conventional high-frequency inverter, and FIG. 5 is a diagram showing a conventional discharge lamp lighting device using low-frequency rectangular wave lighting. Figure 6 is a circuit configuration diagram showing the previously proposed discharge lamp lighting device, and Figure 7 is a diagram showing an example of the circuit configuration.
The specific circuit configuration diagrams of the switching circuit, input voltage detection circuit and signal inversion circuit, FIG.
FIG. 9, a signal waveform diagram for explaining the operation, 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 drive circuit, 12 is a switching circuit, 14 is a pulse circuit, 15 is an oscillator, 1
6 is an operational amplifier, 17 is a comparator, 21 is an input voltage detection circuit, 22 is a signal inversion circuit, 23 is a photocoupler, 31 is a temperature compensation circuit, and 32 is a negative characteristic thermistor. + + Figure 8 B, 'C2 Figure 9 - Lamp voltage

Claims (1)

[Claims] 1. A discharge lamp lighting device that inputs direct current to a step-down chopper circuit to control the current, inputs the output of the step-down chopper circuit to a full-bridge inverter, and connects a discharge lamp to the output end of the inverter to light it. , a means for detecting the DC input voltage, a current detection element inserted between the freewheel diode and the smoothing capacitor of the output part of the step-down chopper circuit, and a detection output of the DC input voltage detection means and the current. a switching circuit that controls the pulse width of the step-down chopper circuit that includes a built-in operational amplifier that inputs the detection output of the detection element;
It has a feedback circuit consisting of a series circuit of a resistor, a Zener diode, and a parallel circuit of a second resistor, and a temperature compensation circuit connected to the input terminal. A discharge lamp lighting device characterized by being configured to change the amplification factor of an operational amplifier in response to a DC input voltage and lamp current to control the pulse width of a chopper circuit.