JPH0531279B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a fritsker-free discharge lamp lighting device, and more specifically, it is capable of stably lighting a discharge lamp and minimizes changes in power due to changes in discharge lamp voltage (referred to as tube voltage). The present invention relates to a lighting device that can be used as a lighting device. [Technical Background of the Invention and Problems thereof] Discharge lamp lighting devices are generally of the type that use commercial alternating current as an input source, incorporate a current limiting reactor into the device circuit, and perform stable lighting using the current limiting characteristics of the device circuit. There are many things. However, depending on the frequency of the commercial alternating current used, flicker may occur, causing an undesirable phenomenon when used as a light source for television, movie shooting, etc. In order to prevent such flicker, lighting devices that use square waves instead of commercial alternating current are widely used. For example, a block diagram of a conventionally known flicker-free discharge lamp lighting device may be used as a block diagram.
As shown in the figure. In Figure 1, 1 rectifies commercial AC to create smooth DC.
A rectifier circuit for obtaining 250V, 2 an auxiliary power supply circuit for operating the control system of the entire device, 3 a DC-DC converter for converting the 250V DC obtained by the rectifier circuit 1 into the required voltage, 4 a This DC−DC
Control circuit that controls converter 3, 5 is DC-DC
A rectangular wave inverter for obtaining a rectangular wave alternating current from the direct current obtained by the converter 3, 6 an oscillation/control circuit for the rectangular wave inverter 5, and 7 a high voltage pulse superimposition circuit for applying high voltage pulses to the discharge lamp 8 at startup. It is. In the case of this device, if the waveform of the lamp current flowing through the discharge lamp 8 is not approximated to a square wave shape, flicker will occur, so the impedance of the circuit from the output side of the square wave inverter 5 to the discharge lamp 8 must be low. Therefore, it is necessary to provide the DC-DC converter 3 with current-limiting characteristics necessary for stable lighting. That is, the DC-DC converter 3 has a current-limiting characteristic in which the output voltage drops as the output current increases, and specifically, it is a so-called switching regulator using a power transistor or the like. Or it is composed of a chopper circuit. When the discharge lamp 8 is turned on with this device, a no-load voltage of 250V is initially applied to the discharge lamp, but due to the operation of the high-voltage pulse superimposition circuit 7, a high-voltage pulse of approximately several tens of kV is applied. When discharge starts, the terminal voltage of the discharge lamp 8 rapidly drops to 20 to 30V, and a necessary current flows based on the current limiting characteristics of the device. As the discharge continues, the discharge lamp 8
As the temperature continues to rise, the discharge lamp terminal voltage increases and reaches its steady value. This stationary discharge lamp terminal voltage is called tube voltage, and in the case of metal halide lamps, it is usually 70 to 100V. However, this tube voltage is not the same for all lamps and varies even within the same type of lamp, and moreover, it changes during use and generally increases with time. The rated range of this tube voltage variation and range of change is the value specified by the lamp manufacturer, and is usually ±20% of the rated voltage.
It is about %. In the device shown in Figure 1, the DC-DC converter 3 is provided with current-limiting characteristics, and an example of the output current-limiting characteristics when the reference power source of the feedback control circuit is constant is as shown in Figure 2. . In Figure 2, the relationship between tube voltage (vertical axis: V) and current (horizontal axis: A) is shown in the second quadrant, and the relationship between tube voltage and output power (axis: W) is shown in the third quadrant. be. In the figure, P represents the rated voltage and rated current of the discharge lamp, and the tube voltage between Q and R represents the practical tube voltage. Q is the lower limit and R is the upper limit, and the voltage range is usually ± of the rated voltage.
It is about 20%. In Figure 2, DC-DC converter 3
When the discharge lamp 8 has a current-limiting characteristic as shown by a solid line a in the figure, the discharge lamp 8 has a tube voltage-power characteristic as shown by a solid line a' in the figure. Such characteristics can be easily provided using a switching regulator or the like. However, in this case, the power supplied to the discharge lamp is proportional to the tube voltage, and the power increases with the tube voltage, causing a large difference in illuminance of the discharge lamp. Furthermore, the increase in tube voltage over time is also detrimental to the lifespan of the discharge lamp. When the current-limiting characteristic is as shown by the dotted line b, that is, when the product of voltage and current is a constant hyperbola, the output power to the discharge lamp is determined by the tube voltage as shown by the dotted line b'. It is a constant value that is unrelated to
However, it is difficult to provide current-limiting characteristics like curve b. In the case of current-limiting characteristics as shown by the dashed-dotted line c, the output power is shown by the dashed-dotted line
As shown by c', it increases slightly as the tube voltage increases. The lighting of the discharge lamp is also stable. However, it is difficult to provide such current limiting characteristics. Further, in both cases b and c, the current becomes extremely small when the output voltage is high in the initial stage of lighting, and therefore the starting tends to become unstable. On the other hand, in a range where the output voltage is low, the current increases significantly and may exceed the specified maximum current of the bulb.
The inverter used in the circuit also needs to have a large current capacity. For this reason, as shown in Figure 3, the current-limiting characteristics of the DC-DC converter are approximated by a straight line in the practical tube voltage range Q to R, and in the high voltage region, the required current is passed. By limiting the current in the low voltage region, it is possible to reduce the increase in output power due to the increase in tube voltage, facilitate startup at the initial stage of lighting, and prevent excessive tube current and reduce the inverter capacity. However, no lighting device based on this idea has been proposed to date. In addition, the tube voltage range Q to R is ±25% of the rated voltage.
For example, when the rated voltage is 80V, Q
is in the range of 60V and R is in the range of 100V. [Object of the Invention] The present invention provides stable discharge within a practical tube voltage range, minimizes changes in output power due to tube voltage, provides good lighting effects, and facilitates initial startup. An object of the present invention is to provide a flicker-free discharge lamp lighting device that prevents excessive tube current and has an economical circuit configuration. [Summary of the Invention] The discharge lamp lighting device of the present invention includes a rectifier circuit, a DC-DC converter connected to the rectifier circuit and having current-limiting characteristics, and converts the output of the DC-DC converter into a rectangular wave alternating current. In a discharge lamp lighting device consisting of a rectangular wave inverter, a high voltage pulse superimposing circuit connected to the rectangular wave inverter, and a discharge lamp connected to the high voltage pulse superimposing circuit, a voltage proportional to the tube voltage is used as a variable, and a voltage proportional to the tube voltage is used as a variable. The generated functional voltage is used as the reference voltage of the feedback control circuit; in the vicinity of the rated voltage of the tube voltage, the tube voltage and the DC-DC
The output current is controlled with a current limiting characteristic approximating a straight line or a broken line so that the output of the discharge lamp, which is the product of the output current of the converter, is approximately constant; In a high voltage range, the output current is controlled to a constant value necessary to start lighting; in a low voltage range where the tube voltage is below the rated area, the current is limited; characterized by having a control circuit. This is a fritz-free discharge lamp lighting device. An example of the device of the present invention will be explained below based on the drawings. First, in FIG. 4, 11 is a rectifier circuit that uses commercial AC as an input source, and 33 is a DC that receives the DC obtained from the rectifier circuit 11 as an input source and has predetermined current-limiting characteristics.
- In the DC converter, the power transistor TR,
It consists of a high frequency transformer T, diodes D ₁ and D ₂ , a high frequency choke CH, and a capacitor C.
55 is a rectangular wave inverter for converting the output of the DC-DC converter 33 into a rectangular wave, and is composed of power transistors Q ₁ , Q ₂ , Q ₃ , and Q ₄ . 55a
is an inverter control circuit for driving and controlling this inverter 55. DC-DC converter 3
A DC-DC converter output current detection shunt resistor SH is inserted between the DC-DC converter output current detection shunt resistor SH and the rectangular wave inverter 55. 77 is a high-voltage pulse superimposing circuit that superimposes a high-voltage pulse on the output of the inverter 55 to start lighting the discharge lamp. The control circuit 44 is driven by the auxiliary power supply 22, and includes a drive circuit 44a that turns on and off the power transistor TR, a feedback control circuit 44b that sends a drive signal to the drive circuit 44a, and a function voltage based on a voltage proportional to the tube voltage. Operational amplifier that generates calculations
This is a DC-DC converter control circuit that includes _OP1 , _OP2 , _OP3 , and _OP4 and controls the current-limiting characteristics of the DC-DC converter 33. In this device, the DC-DC converter 33
is in an on state for an appropriate period of time during a certain period (for example, 30 μsec) of the power transistor TR, and the output voltage changes depending on the on-off duty. That is, the shorter the on-state time, the lower the output voltage. The output of the DC-DC converter 33 is converted into a rectangular wave of, for example, 100 Hz by a rectangular wave inverter 55 and supplied to the discharge lamp. At this time, the DC-DC converter 33 is controlled as follows to provide a predetermined current limiting characteristic. First, in the drive circuit 44a of the control circuit 44, the DC-
The power transistor TR of the DC converter 33 is driven and enters an on-off operation. The power transistor TR operates such that its on time becomes shorter as the output of the amplifier 44c included in the subsequent feedback control circuit 44b becomes higher. In the feedback control circuit 44b, the input side + terminal of the amplifier 44c is connected to the ground side (negative pole) of the auxiliary power supply 22, and the - terminal is connected to a resistor _R1 connected to the detection shunt resistor SH and a resistor connected to an operational amplifier described later. Connected to each connection point of R ₂ . Therefore, one terminal of the amplifier 44c is the sum of the output function voltage: e _s (+ side) of the operational amplifier OP ₄ and the voltage drop (- side) due to the DC-DC converter output current detection shunt resistor SH (that is, Substantially the difference between the two) is
The potential is divided by resistors _R1 and _R2 . Therefore, for example, when e _s is a constant value, DC
The -DC converter 33 is negatively fed back so that the voltage drop across the detection shunt resistor SH is constant, and functions as a constant current power source. The output current is defined by e _s , and if e _s is high, the current increases, and if e _s is constant, it shows a constant value. On the other hand, OP ₁ , OP ₂ , OP ₃ , OP ₄ are all operational amplifiers, OP ₁ is an inverting amplifier, OP ₂ , OP ₃ ,
OP ₄ operates as a voltage follower. The input side + terminal of operational amplifier OP ₁ is connected via resistor R ₆ to resistor R ₉ and Zener diode Dz.
Therefore, the voltage at the + terminal is kept at a constant potential generated by resistor _R9 and Zener diode Dz. A potential obtained by dividing the output voltage of the DC-DC converter 33 by resistors _R7 and _R8 is applied to the input side terminal of _OP1 through resistor _R5 , and negative feedback is provided from the output through resistor _R4. There is. Therefore, the output of operational amplifier _OP1 drops linearly as the tube voltage increases. The output of this OP ₁ is input to an operational amplifier OP ₄ via a resistor R ₃ . The relationship between the tube voltage and the voltage e _s at this time changes as shown by straight line A in FIG. A resistor R ₁₀ is connected to the input side + terminal of the operational amplifier OP ₂ .
and the potential divided by _R11 is input. Therefore, its output is equal to the input potential. therefore,
When the output of OP ₁ decreases and becomes as shown by the dotted line A' in Figure 5, the input to the operator OP ₄ is clamped equally to the output of the operator OP ₂ , as shown by the solid line B in Figure 5. Become. Similarly, the output of the arithmetic unit OP ₃ is connected to the resistor R ₁₂ and
Since it is equal to the potential divided by R ₁₃ , the arithmetic unit OP ₁
When the output of is high as indicated by the dotted line A'', the arithmetic unit
The input to OP ₄ is clamped to the output of arithmetic unit OP ₃ , resulting in a straight line C in FIG. Since the arithmetic unit _OP4 is a voltage follower, its output _es shows the same output as shown by the broken line BAC in FIG. In this way, if the output e _s of the arithmetic unit OP ₄ takes the form shown in FIG. 5 as the tube voltage changes, then the current limiting characteristic of the DC-DC converter 33 will behave as shown in FIG. 3. It becomes like that. Furthermore, if variable resistors are used for the feedback resistors R ₄ and R ₂ in the control circuit 44 and their values are changed,
The gradient of straight line A in FIG. 5 can be adjusted as desired. Therefore, it is extremely easy to stabilize the lighting of the discharge lamp and to minimize changes in power due to changes in tube voltage. Furthermore, if the output of arithmetic unit OP ₄ , that is, the functional voltage, is divided and used with a potentiometer, DC-DC can be obtained.
Since the output of the converter 33 changes while maintaining the current-limiting characteristics shown in FIG. 3, it is also possible to control the illuminance of the discharge lamp. Also, if we use multiple operational amplifiers with different output slopes instead of operational amplifier OP ₁ , and use the logical sum of their outputs as the output, the solid line A in Figure 5 becomes a broken line, which is ideal. It can be approximated by a hyperbola with . For example, tube voltage 80V, tube current 2.5A, output power
When lighting a 200W discharge lamp, using the device of the present invention,
When the tube voltage, tube current, and output power were actually measured, the results shown in the table below were obtained.

[Table] As shown above, in the device of the present invention, the tube voltage is
Even if there was a ±25% change in the rated voltage of 80V from 60V to 100V, the output power to the discharge lamp only changed by 6%. [Effects of the Invention] As is clear from the above explanation, the device of the present invention shows a small change in output power even if the tube voltage changes within the practical tube voltage range, and immediately after the start of discharge at the lighting cut-off time. When the value of the tube voltage is low, the current drops to the current limit, so the current capacity of the square wave inverter 55 may be small, and when the value of the tube voltage at the initial stage of lighting is high, the required current is controlled to flow at a constant value. It is easy to start the discharge because
In addition, the output capacity of the DC-DC converter 33 may be small, and the functional voltage generating circuit that controls the current-limiting characteristics is composed of operational amplifiers OP ₁ , OP ₂ , OP ₃ , and OP ₄ .
Since 44b is also one integrated circuit, they are both easy to obtain and easy to configure.
Different types of lamps require different functional voltages due to differences in their characteristics, but the setting is easy, and for the same type of lamps, different functional voltages are required due to differences in their characteristics.
If R ₂ is made into a variable resistor, it can be easily adjusted, which has great industrial value.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional flicker-free discharge lamp lighting device. Figure 2 is a diagram showing an example of current limiting characteristics that should be given to a DC-DC converter.
FIG. 3 is a diagram showing an example of current-limiting characteristics imparted to a DC-DC converter by the device of the present invention. FIG. 4 is a circuit diagram showing one embodiment of the device of the present invention, and FIG. 5 is a diagram showing the relationship between voltage e _s and tube voltage in the device shown in FIG. 4. 1, 11... Rectifier circuit, 2, 22... Auxiliary power supply, 3, 33,... DC-DC converter, 4, 4
4... Current-limiting characteristic control circuit, 44a... Drive circuit,
44b...feedback control circuit, 44c...amplifier,
SH...DC-DC converter output current detection shunt resistor, 5, 55...Square wave inverter, 55a
... Inverter drive circuit, 6 ... Inverter oscillation/control circuit, 7, 77 ... Discharge lamp, R ₁ to R ₁₃ ...
...Resistance, Dz...Zener diode, OP ₁ ,
OP ₂ , OP ₃ , OP ₄ ... operational amplifier.

Claims (1)

[Claims] 1. A rectifier circuit, a DC-DC converter connected to the rectifier circuit and having current-limiting characteristics through feedback control,
A radiation source consisting of a square wave inverter that converts the output of the DC-DC converter into a square wave alternating current, a high voltage pulse weight circuit connected to the square wave inverter, and a member for connecting a discharge lamp to the high voltage pulse weight circuit. In a lamp lighting device: Using a voltage proportional to the tube voltage as a variable, a functional voltage generated by a group of operational amplifiers is used as the reference voltage of the feedback control circuit; In the vicinity of the rated voltage of the tube voltage, the tube voltage and the DC - The output current is controlled with a current limiting characteristic approximating a straight line or a broken line so that the output of the discharge lamp, which is the product of the output current of the DC converter, is approximately constant; the tube voltage is in the vicinity of the rated range. In the above high voltage range, the output current is controlled to the constant value required to start lighting by clamping the function voltage to a relatively low predetermined constant value. 1. A flicker-free discharge lamp lighting device, characterized in that it has a control circuit: in a voltage range, the current is limited by clamping the functional voltage to a predetermined relatively high constant value;