JPH04196094A - Power control apparatus for ac discharge lamp - Google Patents

Abstract

PURPOSE:To guarantee lighting of an AC dicharge lamp and to eliminate flicker and degradation of lifetime of the AC discharge lamp by normally feedback controlling consumprion power od the AC discharge lamp to be constant with good response characteristics and reducing response characteristcs of a system for making the feedback control to a level lower tha that of the response characteristics after lighting in the case of lighting of the AC discharge lamp or the like. CONSTITUTION:A high voltage is applied to an AC discharge lamp 20 to light the AC discharge lamp, power consumed by the AC lamp 20 is detected by power detection circuit 24, 28 during lighting and after lighting, and power consumption of the AC discharge lamp 20 is feedback-controlled to be constant by stationary power control circuits 26, 30. In the case of lighting of the AC discharge lamp or the like, response characteristics of a system for making the feedback control is reduced to a level lower than that of the response chracteristics after lighting by a response characteristics switching circuit 43. Accordingly, the AC discharge lamp 20 can be surely lighted without any negative influence to the AC discharge lamp 20.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power control device for an AC discharge lamp that applies a high voltage during lighting of an AC discharge lamp and controls the power of the AC discharge lamp after lighting. (Prior art) In recent years, due to the high efficiency of electrical-to-optical conversion, overheating projectors and film photography have become popular. AC discharge lamps have been used as light sources for film photography lighting equipment and vehicle headlights. This type of AC discharge lamp includes metal halide lamps, etc. After lighting, the device that controls the AC discharge lamp adjusts the voltage and current so that the voltage between the electrodes or the power consumption of the AC discharge lamp remains constant. Also, when lighting, it is easy to cause dielectric breakdown between the electrodes and start a discharge (this is why it is common to flow a large current compared to the current after lighting. However, If an unlimited current flows during lighting, the elements that directly drive the AC discharge lamp may be destroyed or the electrodes of the AC discharge lamp may be excessively consumed. A configuration in which a current several times the current flows has been proposed. [Problem to be solved by the invention] However, in a power control device for an AC discharge lamp that performs power control during lighting, the maximum current during lighting is set to a steady current. There was a problem in that lighting could fail if the limit was set to several times the current.When high voltage is applied to cause dielectric breakdown and discharge current begins to flow, AC discharge lamps are still unstable. Therefore, the power control is responsive according to the voltage and current that fluctuate during lighting. However, if you simply reduce the responsiveness of the power control, the control characteristics of the power control during steady lighting will deteriorate, and the current flowing through the AC discharge lamp will not form a square wave. As a result, the discharge lamp may flicker,
This poses the problem of significantly shortening the life of the discharge lamp, and is not a practical solution. The present invention has been made to solve the above-mentioned problems and to reliably light an AC discharge lamp without adversely affecting the AC discharge lamp.The configuration of the present invention that achieves this object will be described below. [Means for Solving the Problems] The power control device for an AC discharge lamp of the present invention applies a high voltage when lighting an AC discharge lamp that emits light by applying an AC voltage,
A device that controls the power consumed by the AC discharge lamp after lighting, the device comprising: a power detection circuit that detects the power consumed by the AC discharge lamp; and a power detection circuit that detects the power consumed by the AC discharge lamp; A steady-state power control circuit that performs constant feedback control of power; and a responsiveness switching circuit that reduces the responsiveness of the system that performs feedback control during lighting of the AC discharge or the like compared to the responsiveness after lighting. This is the summary. [Function] The power control device for an AC discharge lamp of the present invention having the above configuration applies a high voltage to the AC discharge lamp to light the AC discharge lamp. Both during lighting and after lighting, the power control device for an AC discharge lamp of the present invention uses a power detection circuit to detect the power consumed by the AC discharge lamp, and uses a steady power control circuit to feedback control the power consumption of the AC discharge lamp to a constant level. are doing. Furthermore, during lighting such as AC discharge, the response switching circuit causes the responsiveness of the feedback control system to be lower than the responsiveness after lighting. As a result, the responsiveness of the feedback control is low at the time of lighting (the current necessary to start the discharge is sufficiently secured, but after the AC discharge lamp is lit due to continuous discharge, the AC discharge lamp Feedback control of power consumption is performed with good responsiveness. [Embodiment] In order to further clarify the configuration and operation of the present invention described above, a preferred embodiment of the power control device for an AC discharge lamp of the present invention will be described. will be explained below. Fig. 1 is a block diagram showing the configuration of a metal halide lamp control device 1 as an embodiment, and Fig. 2 is a perspective view showing the appearance of an overhead projector 3 in which this metal halide lamp control device 1 is incorporated. First, the configuration of the overhead projector 3 will be briefly explained.As shown in FIG. It is composed of a lens 7, an arm section 12 that supports a projection lens 9, and a reflecting mirror 10. A power switch 15 for turning the power on and off is provided on the front side of the main body 5. As shown in FIG. 1, the metal halide lamp control device 1 of the embodiment sequentially connects the rectifier 22 to the commercial AC power switch 15 side in order to light the metal halide lamp 20.
．． Current detection section 24. Main switching circuit 26. Voltage detection section 28. Inverter section 30. A high voltage starter section 32 is provided. In addition, the main switching circuit 26. In order to control and drive the inverter section 30, a pulse width modulation circuit (PWM) 35
．． Amplification section 372 Lighting detection section 39° Inverter control section 41
．． Monostable multivibrator43. AND gates 45 and the like are also provided. The rectifier 22 rectifies and smoothes the commercial alternating current, and after converting it to direct current, the main switching circuit 2
6, the on-time duty is controlled to control the power consumption of the metal halide lamp 20. The main switching circuit 26 is a circuit that chops the direct current to vary its on/off duty and controls the power consumption of the metal halide lamp 20. In order to control the power in the main switching circuit 26,
Current and voltage are detected by the current detection section 24 and the voltage detection section 28, and the rain detection signal is multiplied by the multiplication section 47 to obtain a signal corresponding to the power consumption, which is input to the amplification section 37. The amplifier section 37 is composed of an operational amplifier OPI, a feedback resistor R1 that determines the degree of amplification, a capacitor C1 that is connected in parallel to the feedback resistor R1 and determines the integral constant, and a contact X1 that turns on and off the connection of the capacitor C1. ing. The control signal after being amplified by the operational amplifier OPI causes PWM3
5, and the PWM 35 determines the duty in the main switching circuit 26. Note that the current detection unit 24 can also be configured to insert a detection resistor into the power supply line and measure the voltage across it, but since there is a voltage drop due to the resistor, it may have a secondary winding. It is desirable to insert a transformer and detect the voltage on the secondary side of the transformer. The inverter section 30 has an H-bridge type circuit configuration, and when the metal halide lamp 20 is driven steadily, turns on and off the four switching elements constituting the H-bridge alternately. 5
The direction of the current flowing through the metal halide lamp 20 is reversed at 00[Hzl. As a result, metal halide lamp 2
0 will continue to be lit by the AC power supply. Each switching element of the inverter section 30 is directly driven by an input control section 41. The main switching circuit 26 described above. Inverter section 3
0 and the circuit that controls them, when the metal halide lamp 20 is driven steadily after the metal halide lamp 20 is turned on, the multiplication value of current and voltage, that is, the power consumption of the metal halide lamp 20 is small ( Then, the duty is increased to increase the amount of electric power, and when the power consumption decreases, the duty is increased, and as a result, feedback control is performed with good responsiveness to keep the amount of electric power of the metal halide lamp 20 that is lit on AC constant. On the other hand, when the metal halide lamp 20 is turned on, the following control is performed based on the control signal from the monostable multivibrator 43. When the power switch 15 is turned on, the monostable multivibrator 43 operates as shown in FIG. As shown in the figure, a high level signal is output for a predetermined period of time (approximately 2 seconds in this embodiment). This signal is output to an AND gate 45 and an amplifying section 37. The signal is ANDed with the output of the lighting detection section 39 (a signal at a high level until lighting is detected), and the output signal drives the high voltage starter section 32. During the high level, therefore, during lighting and until the metal halide lamp 20 lights up, the inverter section 30 is connected between the electrodes of the metal halide lamp 20.
A spike-like high voltage (
several kilovolts). The metal halide lamp 20 causes dielectric breakdown due to the spike-like high voltage and eventually lights up. When the metal halide lamp 20 is turned on, the inter-electrode voltage of the metal halide lamp 20 increases to about 90 volts, so the lighting detection section 39 can easily detect this. metal halide lamp 20
After lighting, the application of high voltage by the high voltage starter section 32 is stopped. On the other hand, while the output signal from the monostable multivibrator 43 is at a high level, the contact X1 of the amplifier section 37 is closed. Therefore, during this period, the feedback resistor R1 of the operational amplifier OP1
A capacitor CI, which is a capacitance component, is connected in parallel to act as an integral element, and the overall responsiveness of the amplifier section 37 is reduced. Immediately after the metal halide lamp 20 is turned on, the operation of the metal halide lamp 20 is unstable and the voltage between its electrodes fluctuates, but in this embodiment, the power consumption immediately after the metal halide lamp 2o is turned on = 10- Since the control is performed with low responsiveness, the current will not be reduced too much until the metal halide lamp 20 is reliably lit. What's more, once the predetermined time when lighting has passed, it has high responsiveness.
Since the power consumption of the metal halide lamp 20 is controlled,
Not only is the power consumption of the metal halide lamp 2o constant and its light intensity stable, but there is no power fluctuation within a half wave of AC lighting (see symbol a in Figure 3), and the current flowing through the metal halide lamp 20 is completely rectangular. Since the metal halide lamp 20 becomes a wave, the life span of the metal halide lamp 20 can be extended. In addition, in the metal halide lamp control device 1 of this embodiment, after the output signal of the monostable multi-bi break 43 is inverted to low level, the peak current is gradually reduced to reduce the lamp current during lighting to the feedback control current. Therefore, fluctuations in the amount of light from the metal halide lamp 20 do not become a concern. Further, since the voltage is not suddenly increased to the feedback control voltage, the metal halide lamp 20 that has been lit for a while will not be turned off. Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments. For example, the present invention may be applied to a configuration applied to power control of a metal halide lamp used as a light source of a projection television, or a lighting lamp of a vehicle. The present invention can be implemented in various ways without departing from the gist of the present invention, such as a configuration applied to power control of metal halide lamps used for lighting buildings, etc., or a configuration in which the responsiveness of power control gradually decreases after lighting. Of course. [Effects of the Invention] As described in detail above, the power control device for an AC discharge lamp of the present invention normally performs feedback control of the power consumption of an AC discharge lamp to a constant level with good responsiveness, and when lighting an AC discharge lamp, feedback control is performed. The responsiveness of the control system is lower than the responsiveness after lighting. Therefore, according to the power control device for an AC discharge lamp of the present invention,
This provides an excellent effect in that the AC discharge lamp can be lit reliably, and the problems of flickering and shortened life of the AC discharge lamp do not occur.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the configuration of a metal halide lamp control device 1 as an embodiment of the present invention, Fig. 2 is a perspective view of an overhead projector 3 incorporating this device 1, and Fig. 3 shows the control state. This is a timing chart shown. ■... Metal halide lamp control device 3... Overhead projector 15... Power switch 20... Metal halide lamp 22... Rectifier section 24... Current detection section 26
... Main switching circuit 28 ... Voltage detection section 30 ... Inverter section 3
2...High pressure starter part 35...PWM37...
Amplification section 39... Lighting detection section 41... Inverter control section 43... Monostable multi-bi break

Claims (1)

[Scope of Claims] 1. A device for applying a high voltage when lighting an AC discharge lamp that emits light by applying an AC voltage, and controlling power consumed by the AC discharge lamp after lighting, wherein the AC discharge lamp is a power detection circuit that detects power consumption; a steady-state power control circuit that performs feedback control to keep the power consumption of the AC discharge lamp constant based on the detected power; and when lighting the AC discharge lamp, performs the feedback control. A power control device for an AC discharge lamp, comprising a responsiveness switching circuit that lowers the responsiveness of a system that performs this than the responsiveness after lighting.