JPS60250599A - Device for firing flicker-free discharge lamp - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] Regarding the 611-year-old's car-free lamp lighting device, in detail, it is possible to stably light a discharge lamp, and the voltage of the discharge lamp, C,... The present invention relates to a lighting device that can minimize changes in power due to changes in tube voltage (referred to as tube voltage). .

[Technical background of the invention and its problems] Discharge lamps and lighting devices generally use commercial alternating current as an input source, and a current-limiting reactor is incorporated into the device circuit to achieve stable lighting using its current-limiting characteristics! However, depending on the frequency of the commercial alternating current that is used, it may cause distortion, which is an undesirable phenomenon when used as a pre-application for television, movie shooting, etc.

In order to prevent such flicker, lighting devices that use square waves instead of commercial alternating current have been widely adopted.

For example, a block diagram of a conventionally known power-free discharge lamp lighting device is shown in FIG. 1 as a block diagram.

In Figure 1, 1 is a rectifier circuit for rectifying commercial AC to obtain smoothed DC 250V, 2 is an auxiliary power supply circuit for operating the control system of the entire device, and 3 is the 250V DC obtained by rectifier circuit l. 4 is a control circuit for controlling this DC-DC converter 3, and 5 is a square wave inverter for obtaining a square wave alternating current from the direct current obtained by the DC-DC converter 3. , 6 is an oscillation/control circuit for the rectangular wave inverter 5, and 7 is a discharge lamp 8 at startup.
This is a high-voltage pulse superimposition circuit for applying high-voltage pulses to the In the case of this device, if the waveform of the lamp current flowing through the discharge lamp 8 is not approximated to a rectangular wave shape, flickering will occur, so the impedance of the circuit from the output side of the rectangular wave inverter 5 to the discharge lamp 8 is low. Therefore, it is necessary to provide the DC-D(,=j inverter 3 with current-limiting characteristics necessary for stable lighting. In other words, DC
- The DC converter 3 has a current-limiting characteristic in which the output voltage drops as the output current increases, and is specifically constructed of a so-called switching regulator or chopper circuit using power transistors, etc. ing.

With this device, when the discharge lamp 8 is turned on, a no-load voltage of about 250 V is applied to the discharge lamp at first, but due to the operation of the high-voltage pulse superimposition circuit 7, a high-voltage pulse of about several tens of kV is applied. When the discharge starts, the terminal voltage of the discharger 58 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 temperature of the discharge lamp 8 increases, and the discharge lamp terminal voltage increases accordingly 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 furthermore, it changes during use and generally increases with time.

In the device shown in FIG. 1, the DC-DC converter 3 is provided with current-limiting characteristics, and an example of the output current-limiting characteristics is shown in FIG. 2. In Figure 2, the I quadrant is the tube voltage (vertical axis:
In the figure, P is the rated voltage of the discharge lamp. and the rated current, and the tube voltage between Q and R represents the practical tube voltage. In Figure 2, when the PC'-PC converter 3 has current limiting characteristics as shown by the solid line a in the figure. , the discharge lamp 8 has a tube voltage-power characteristic as shown by the solid line i in the figure.Such a characteristic can be easily imparted by a switch or the like. However, in this case,
The electric power generated is proportional to the tube voltage, and the electric power increases with the tube voltage, causing a large difference in illumination of the discharge lamp. Moreover, the increase in tube voltage over time is also disadvantageous for the lifespan of the discharge lamp.

When the current-limiting characteristic is shown by a dotted line, 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 not only difficult to provide a current-limiting characteristic like a curved line, but also the discharge-like lighting power becomes unstable, and in the case of a first-class characteristic as shown by the dashed line The power increases slightly as the tube voltage increases, as indicated by the dot-dotted line C'. The lighting of the discharge lamp is also stable. However, it is difficult to provide such current limiting characteristics. □ Based on these facts, the overnight current limiting characteristics of DC-D and C lamps can be approximated by a straight line within the practical tube voltage range QNR, as shown in Figure 3. For example, it is possible to reduce the increase in output power due to an increase in tube voltage, but to date no lighting device based on such an idea has been proposed.

[Object of the Invention] The present invention provides a flicker-type discharge lamp lighting device that performs stable discharge within a practical tube voltage range and minimizes changes in output power due to tube voltage to provide good lighting effects. With the goal.

[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 a rectangular current characteristic, and a rectangular waveform for the output of the DC-DC converter. In a discharge lamp lighting device comprising a rectangular wave inverter for converting into alternating current, a high voltage pulse superimposing circuit connected to the rectangular wave inverter, and a discharge lamp connected to the high voltage pulse superimposing circuit, the current limiting characteristic is determined by the DC-DC converter. It is characterized in that it is applied from a current-limiting characteristic control circuit which detects a voltage proportional to the output current detection shunt and the tube voltage and controls the feedback control circuit by means of a group of operational amplifiers.

An example of the device of the present invention will be explained below based on the drawings. First, in No. 4-, 11 is a rectifier circuit that uses a commercial AC as an input source, 33 is a DC-DC converter that receives the DC obtained from the rectifier circuit 11 and has predetermined current-limiting characteristics, and the power transistor TR1 is a high-frequency transformer. device T, diode DI
55 is a rectangular wave inverter for converting the output of the DC-DC converter 33 into a rectangular wave, and power transistors Q+, Q2, Q3, Q4. 55a is an inverter control circuit for driving and controlling this inverter 55.A DC-DC circuit is connected between the DC-DC converter 33 and the square wave inverter 55.
A converter output current detection shunt resistor SH is inserted. 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.

44 is a drive circuit 44a that is driven by the auxiliary power supply 22 and turns on and off the power transistor TH;
A feedback control circuit 44b that transmits a drive signal to the tube voltage, and operational amplifiers OPH and O that detect and calculate a voltage proportional to the tube voltage.
This is a DC-DC converter control circuit that includes P2, OP3', and OPa 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 fixed period (for example, 30 seconds) of the power transistor TH, and the output voltage changes depending on its 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, 100H2 by a rectangular wave inverter 55, and is supplied to the discharge group.

At this time, the DC-DC converter 33 is controlled as follows to provide a predetermined current limiting characteristic.

, First, the drive circuit 44a of the control circuit 44
The power transistor TR of the converter 33 is driven,
Enter on-off operation. The power transistor TR is connected to the subsequent feedback control circuit 4. ．． 4 Amplification contained within b $4
As the output of 40 becomes higher, the on-time becomes shorter.

In the feedback control port, path 44b, the input side + terminal of the amplifier 44c is connected to the ground side (negative pole) of the auxiliary power supply 22, and one terminal is connected to the resistor R1, which is connected to the detection shunt resistor SH, and an operational amplifier described below. The resistor R2 is connected to each connection point of the resistor R2. Therefore, one terminal of amplifier -44c is connected to operational amplifier 0. The output voltage of Pa is the sum of eM and the voltage drop due to the DC-DC converter output current detection shunt resistor SH.

The potential is divided by resistors R1 and R2.

Therefore, for example, when eII is a constant value.

The DC-DC converter 33 functions as a constant current, current power source by negative feedback so that the voltage drop across the detection shunt resistor SH is constant. And the output current is defined by ewK, and if emM is high, the current also increases? Narima f, e
If @ is constant, it indicates a constant value.

On the other hand, OPI, OF2, OF3. OPa is an operational amplifier, OF is an inverting amplifier, OF2 is an inverting amplifier,
OF3 and OF4 operate as voltage followers.

The input side + terminal of operational amplifier OPI is connected to resistor R9 and Zener diode Dz via resistor R6. Therefore, the voltage at the child terminal is connected to resistor R9 and Zener diode D.
It is kept at a constant potential generated by z. One input terminal of OF is connected to DC.

- A potential obtained by dividing the output voltage of the DC converter 33 by resistors R7 and R8 is applied through resistor R5.

Moreover, negative feedback is provided from the output through the resistor R4. Therefore, the output of the operational amplifier OF falls linearly as the tube voltage increases. The output of OPI is input to operational amplifier OP4 via resistor R3.

The relationship between the tube voltage and the voltage eII at this time changes as shown by straight line A in FIG.

The potential divided by the resistors R7 and R1 is input to the input side + terminal of the operational amplifier OP2. Therefore, its output is equal to the input potential.Therefore, when the output of OPI decreases and becomes as indicated by the dotted line X in FIG.
The input to is clamped equally to the output of OF2 of the arithmetic unit, as shown by the solid line B in FIG. Similarly, arithmetic unit OP3
Since the output of is equal to the potential divided by the resistors Rlff1 and RIs, when the output of the arithmetic unit OF becomes high as shown by the dotted line, the input to the arithmetic unit OP4 is clamped to the output of the arithmetic unit OP3, and the It will look like straight line C in Figure 5.

Since the arithmetic unit OP4 is a voltage follower, its output es shows the same output as shown by the broken line DAC in FIG.

In this way, if the output e11 of the arithmetic unit OP a takes the form shown in FIG. 5 as the tube voltage changes, the lever, DC
, the current limiting physical properties of the DC converter 33 are as shown in FIG.

Furthermore, if a variable resistor is used as the feedback resistor R4 in the control circuit 44 and its value is changed, the slope of the straight line A in FIG. 5 can be adjusted to an arbitrary value tIRlti. Therefore, it is possible to stabilize the lighting of the discharge lamp and to make adjustments to minimize changes in power due to changes in tube voltage.

Furthermore, if the output of the arithmetic unit OP4 is divided by a potentiometer and used, the output of the DC-DC converter 33 changes while maintaining the current-limiting characteristics shown in Fig. 3, so the illuminance of the discharge lamp can be adjusted. It is also possible to emit light.

Furthermore, if a plurality of operational amplifiers with different output slopes are used instead of the operational amplifier OF, and the logical sum of the outputs is used as the output, the solid line A in Fig. 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 20
When lighting a 0W discharge lamp, the tube voltage, tube current, and output power were actually measured using the device of the present invention, and the results shown in the table below were obtained.

In this way, with the device of the present invention, even if the tube voltage increases by 100% from 60v to 120v.

“The output power to the discharge lamp changed by only 28%.

[Effects of the Invention] As is clear from the above explanation, the device of the present invention has the following advantages: ■ Even if the tube voltage changes within the practical tube voltage range, the change in output power is small, and the increase in tube voltage is The output power increases as the tube voltage increases, so the discharge is stabilized. ■When the tube voltage value is low, the current drops to the current limit, so the current capacity of the rectangular inverter 55 may be small. ■When the tube voltage value is high. In some cases, the current can be controlled to the necessary minimum, making it easy to start the discharge, and the DC-DC converter 33
The output capacitance of the circuit may be small. ■The circuit port for controlling the current-limiting characteristic is an operational amplifier OP s , OF 2 .

0P3. OPI is a 111 integrated circuit and also a 44b
Both are easily available and can be easily constructed as a single integrated circuit, and have great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a sub-i flasher-free discharge lamp lighting device. Fig. 2 is a diagram showing an example of the current-limiting characteristic to be imparted to the DC-DC converter, and Fig. 3 is a diagram showing an example of the current-limiting characteristic to be imparted to the 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,
FIG. 5 shows the relationship between the voltage e and the tube voltage in the device shown in FIG. 1.11 - Rectifier circuit 2.22 - Auxiliary power supply 3.33 - DC-DC converter 4.44 - Current-limiting characteristic control circuit 44a - Drive circuit 44b - Feedback control circuit 44c - Amplifier 5H - 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 R1"" R13 - Resistor Dz - Zener diode OF+, OP2', OF2.0Pa - Operational amplifier No. Figure 1

Claims (1)

[Claims] A rectifier circuit, and a D having current-limiting characteristics connected to the rectifier circuit.
a C-DC converter, a rectangular wave inverter that converts the output of the DC-DC converter into a rectangular wave alternating current;
In a discharge lamp lighting device comprising a high-voltage pulse superimposition circuit connected to a wave inverter and a discharge lamp connected to the high-voltage pulse superimposition circuit, 1. The current limiting characteristics are: DC-DC converter, detection of output voltage, A flicker-type discharge lamp lighting device characterized in that a voltage proportional to the shunt and tube voltage is applied from a current-limiting characteristic control circuit that controls the feedback control section by means of a group of operational amplifiers that detect and operate.