JPH0785982A - High frequency lighting circuit for high brightness discharge lamp - Google Patents

Abstract

PURPOSE:To prevent flickers caused by acoustic resonance and maintain the lamp power constant by varying the frequency of the lamp drive current according to the level of the ripple voltage in the voltage smoothed. CONSTITUTION:The rectified voltage is smoothed by a smoother circuit 30, where about 5% of the voltage after rectification becomes ripple voltage. In the case the ripple voltage is high, the frequency of the lamp drive current I becomes high, but decrease in the effective value of the current I is suppressed owing to steeper gradient of the waveform of the current I. In the case the ripple voltage is low, on the other hand, the frequency of the current I becomes low, but increase in the effective value of the current I is suppressed owing to milder gradient of the waveform of the current I. Accordingly change in the frequency of the current I does not lead to change in the effective value of the current I, and the light-quantity of the lamp remains unchanged despite changing frequency of the current I. Also coincedence of the frequency of the current I with the natural frequency of high brightness discharge lamp becomes unlikely to lead to prevention of flickers caused by acoustic resonance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency discharge circuit for a high-intensity discharge lamp, which prevents flickering due to an acoustic resonance phenomenon when a high-intensity discharge lamp such as a metal halide lamp is lit at high frequency.

[0002]

2. Description of the Related Art A natural frequency of a metal halide lamp is a frequency close to a frequency of a lamp driving current supplied to the metal halide lamp when the metal halide lamp is lit at a high frequency. When they match, an acoustic resonance phenomenon occurs, the light emission amount of the metal halide lamp changes, and for a person who is near the lit metal halide lamp,
I feel that the metal halide lamp is flickering.

On the other hand, the natural frequency of the metal halide lamp differs for each metal halide lamp, and the natural frequency changes during the operation of the metal halide lamp. Therefore, when the frequency of the lamp driving current is set to a certain fixed value, an acoustic resonance phenomenon occurs in one metal halide lamp and an acoustic resonance phenomenon does not occur in another metal halide lamp. Even in the case of a metal halide lamp in which an acoustic resonance phenomenon does not occur at the start of lighting, its natural frequency may change and a acoustic resonance phenomenon may start to occur after a predetermined time elapses from lighting.

Therefore, if the frequency of the lamp driving current is set to a fixed value at the stage of designing a high frequency lighting circuit for a metal halide lamp, flicker due to an acoustic resonance phenomenon will occur at any time.

[0005]

Therefore, conventionally, the frequency of the lamp driving current is constantly changed by about ± 10%,
The frequency of the lamp drive current is reduced to match the natural frequency of the metal halide lamp, thereby reducing the flicker.

FIG. 5 is a diagram showing an equivalent circuit of the above conventional example.

In the above conventional example, when the pulse generated by the pulse power supply 1 is applied to the inductor 1, a sawtooth-shaped lamp driving current I is generated and the lamp driving current I flows through the metal halide lamp La. The lamp drive current I is a high frequency current, and the lamp drive current I is represented by the following formula. I = (E / R) (1−e ^{− (R / L) · t} ) In the above equation, L is the inductance of the inductor 2, and R is the case where the metal halide lamp La is regarded as a resistance component. The resistance value, E is the voltage of the pulse power supply 1, t is the elapsed time from the rise of the pulse generated by the pulse power supply 1, and is the cycle of the lamp drive current I.

FIG. 6 is a diagram showing a state in which the lamp drive current I generated by the equivalent circuit shown in FIG. 5 changes when its cycle is changed.

In the equivalent circuit shown in FIG. 5, when the pulse voltage E is constant, by changing the width of this pulse, the cycle t of the lamp driving current I changes, that is, as shown in FIG. The peak value of the lamp drive current I is
It changes according to the cycle of the lamp drive current I. That is,
The maximum value of the cycle is t _max , and the minimum value of the cycle is t _min
Then, the lamp drive current I _changes between its maximum value I _max and its minimum value I _min . In other words, when the frequency of the lamp drive current I is changed, the lamp drive current I
Also changes. Therefore, in the above-mentioned conventional example, the light emission amount of the lamp La is not stable.

As described above, in the above-mentioned conventional example, when the frequency of the lamp driving current I is gradually changed in order to prevent the flicker due to the acoustic resonance phenomenon, the effective current of the lamp driving current I changes, so that light emission occurs. There is a problem that the amount changes slowly and the lamp power is not stable. In this case, for example, the lamp power fluctuates within a range of ± several W with respect to the rated power. Further, this problem occurs not only in the metal halide lamp but also in other high-intensity discharge lamps.

It is an object of the present invention to provide a high-frequency lighting circuit for a high-intensity discharge lamp, which can prevent flickering due to an acoustic resonance phenomenon and can keep the lamp power constant. .

[0012]

According to the present invention, a high-intensity discharge lamp for generating a lamp drive current for driving a high-intensity discharge lamp by rectifying and smoothing an AC power supply voltage and switching the smoothed voltage at a high frequency. The high-frequency lighting circuit for increasing the frequency of the lamp driving current when the ripple voltage of the smoothing voltage is high, while lowering the frequency of the lamp driving current when the ripple voltage of the smoothing voltage is low. is there.

[0013]

The present invention is a high-frequency lighting circuit for a high-intensity discharge lamp, which rectifies and smoothes an AC power supply voltage and switches the smoothed voltage at a high frequency to generate a lamp drive current for driving the high-intensity discharge lamp. When the ripple voltage of the smoothed voltage is high, the frequency of the lamp drive current is increased, while when the ripple voltage of the smoothed voltage is low, the frequency of the lamp drive current is decreased. Can be prevented, and the lamp power can be kept constant.

[0014]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In this embodiment, the rectifier circuit 20 is a bridge circuit for full-wave rectifying the voltage of the AC power source 10,
The smoothing circuit 30 is composed of a capacitor that smoothes the output voltage of the rectifier circuit 20.

The transformer T has a first primary coil W11.
And a second primary coil W12 and a secondary coil W2, and the secondary coil W2 supplies a lamp driving current to the metal halide lamp La. The lamp drive current is a current that drives the metal halide lamp La.

The transistor TR1 as the first switching means is a transistor connected to the smoothing circuit 30 via the first primary side coil W11, and the second
The transistor TR2 as the switching means of is a transistor connected to the smoothing circuit 30 via the second primary side coil W12.

The control signal generating means 40 is means for controlling the transistors TR1 and TR2 so as to control the frequency of the lamp driving current based on the ripple voltage of the voltage smoothed by the smoothing circuit 30. This control signal generating means 40 cuts a DC voltage of the smoothed voltage and passes only an AC component, a timing capacitor C _T , a timing resistor R _T , a switching regulator control IC.
42 and. The switching regulator control IC 42 has an input terminal 42a for connecting the timing capacitor C _T , an input terminal for connecting the timing resistor R _T , a Q output terminal, and a Q bar output terminal.
In addition, the switching regulator control IC 42
Is connected to the base of the transistor TR1 and its Q-bar output terminal is connected to the base of the transistor TR2.

The ripple voltage signal extracted by the capacitor 41 is supplied to the input terminal 42a, and the switching regulator control IC 42 outputs to the Q output terminal and the Q bar output terminal as the voltage received at the input terminal 42a is higher. The frequencies of the Q signal and the Q bar signal that are generated increase.

Further, a coil in series with the secondary coil TW2 of the transformer T and a capacitor in parallel with the lamp La constitute a resonance circuit, which generates a high voltage when the lamp La is started, La is brought into an arc state.

Next, the operation of the above embodiment will be described.

Although the smoothing circuit 30 smoothes the rectified voltage, about 5% of the rectified voltage becomes a ripple voltage. Only the ripple voltage is taken out by the capacitor 41, and the signal waveform at the point P1 on the output side of the capacitor 41 is shown in FIG. 1. At time t1, the maximum value of the ripple voltage occurs, and at time t2, the ripple voltage A voltage of the order of magnitude is generated, and at time t3, the minimum value of the ripple voltage is generated.

The ripple voltage signal taken out by the capacitor 41 is applied to the input terminal 42a of the switching regulator control IC 42, and the higher the voltage (ripple voltage) received at the input terminal 42a, the more the switching regulator control IC 42 becomes Q. The frequencies of the Q output signal and its inverted signal output to the output terminal and the Q bar output terminal become high.

FIG. 2 is a diagram for explaining how the frequency of the Q output signal and the inverted signal of the Q output signal changes when the ripple voltage changes in the above embodiment.

As shown in FIG. 2, when the ripple voltage is high (time t1) and when the ripple voltage is medium (time t).
2), in the order of low ripple voltage (time t3), Q
The frequency of the output signal and its inverted signal is low.

The Q output signal is the transistor TR1.
Is supplied to the base of the transistor TR2 and the inverted signal of the Q output signal is supplied to the base of the transistor TR2, and the inverted signal of the Q output signal becomes "H" alternately.
R2 turns on alternately.

When the transistor TR1 is turned on, the voltage of the smoothing circuit 30 is applied to both ends of the first primary coil W11, and the boosted voltage is generated in the secondary coil W2, and the lamp drive current shown in FIG. Among them, a monotonically increasing current flows through the lamp La and the lamp is lit. On the other hand, the transistor TR2
Is turned on, the voltage of the smoothing circuit 30 is applied to both ends of the second primary side coil W12, and the voltage boosted in the secondary side coil W2 (generated in the secondary side coil W2 when the transistor TR1 is turned on). Voltage of the opposite polarity to the voltage) is generated,
Among the lamp drive currents shown in FIG. 3, a monotonically decreasing current flows through the lamp La, and the lamp La lights up. At this time, the energy remaining in the first primary side coil W11 passes through the diode D1 and passes through the second primary side coil W12.
Flow to. Even when the transistor TR1 is turned on, the energy remaining in the second primary side coil W12 flows into the first primary side coil W11 via the diode D2 as in the above. After that, the transistors TR1 and TR2 are alternately turned on and the operation is repeated.

FIG. 3 is a diagram showing the waveform of the lamp drive current when the ripple voltage changes in the above embodiment.

As shown in FIG. 3, when the ripple voltage is high as at time t1, the frequency becomes high as shown by the dashed-dotted line current waveform (for example, 24 KHz), and the slope of the current waveform is steepest. . When the ripple voltage is in the middle level as at time t2, the frequency is in the middle level (for example, 22 KH as shown by the current waveform in the solid line).
z) Moreover, the slope of the current waveform is also moderate. When the ripple voltage is low as at time t3, the frequency becomes low as shown by the two-dot chain line current waveform (for example, 20K).
Moreover, the slope of the current waveform becomes the gentlest.

The slope of the lamp drive current waveform shown in FIG.
It is determined by the value of the voltage applied to the first and second primary side coils W11 and W12. The higher the voltage, the steeper the slope of the lamp drive current waveform. The voltage applied to the first and second primary coils W11 and W12 is the voltage of the smoothing circuit 30, and this smoothing voltage contains ripples. The higher the smoothing voltage, the more the slope of the lamp drive current waveform. Becomes steep.

In the above embodiment, when the ripple voltage is high, the frequency of the lamp driving current becomes high, but the steep slope of the lamp driving current waveform suppresses the reduction of the effective value of the lamp driving current. On the other hand, when the ripple voltage is low, the frequency of the lamp drive current is low, but the increase in the effective value of the lamp drive current is suppressed due to the gentle slope of the lamp drive current waveform. Therefore, in the above embodiment, even if the frequency of the lamp drive current changes, the effective value of the lamp drive current does not change, and the light amount of the lamp La changes even if the frequency of the lamp drive current changes. do not do. Also, since the frequency of the lamp drive current is constantly changed according to the height of the ripple voltage, the frequency of the lamp drive current is less likely to match the natural frequency of the high-intensity discharge lamp, resulting in acoustic resonance. Flicker due to a phenomenon can be prevented.

Metal halide lamp La in the steady state
Can be regarded as a resistance R, the tube voltage V _La is constant, and the effective value of the lamp driving current is constant as described above, so that the tube power P _L is maintained constant, and therefore, in the above embodiment, , It is possible to stabilize the effective value of the tube power.

FIG. 4 is a diagram showing the time relationship between the smoothing voltage, the ripple voltage and the lamp driving current in the above embodiment. 4 (2) and 4 (3),
The time axis is common.

In the above embodiment, as the rectifying circuit 20, a circuit adopting a rectifying method other than full-wave rectifying such as half-wave rectifying may be used, and instead of the metal halide lamp La, another high-intensity discharge lamp is used. May be used. Further, instead of the switching regulator control IC 42, a microcomputer may be used to process the above operation by software.

Further, in the above embodiment, the frequency of the lamp drive current is set to 22 when the ripple voltage is medium.
The frequency is set to KHz and ± 2 KHz of 22 KHz is set to the frequency variation range of the lamp drive current, but the center frequency and the frequency variation range may be set to values other than the above.

Further, in the above embodiment, the transformer T may be removed, and instead of this, a circuit for generating positive and negative pulses may be provided.

In the above embodiment, the AC power supply voltage is rectified and smoothed, and the smoothed voltage is switched at a high frequency to generate a lamp drive current for driving the high-intensity discharge lamp, and the ripple voltage of the smoothed voltage is high. At the same time, the frequency of the lamp drive current is increased, while the frequency of the lamp drive current is decreased when the ripple voltage of the smoothed voltage is low, but basically the same operation as in the above embodiment is performed. However, a circuit having no relation with the ripple voltage may be configured.

That is, the DC voltage control means VC for freely changing the DC voltage by about 5% and supplying a current to the high-intensity discharge lamp is prepared, and the frequency of the lamp drive current can be constantly changed. When FC is prepared, when the voltage output by the DC voltage control means VC becomes high, the frequency control means FC increases the frequency of the lamp drive current and when the voltage output by the DC voltage control means VC becomes low. The frequency control means FC may lower the frequency of the lamp drive current.

That is, in the high-frequency lighting circuit of the high-intensity discharge lamp that supplies the lamp drive current to the high-intensity discharge lamp while changing its frequency, the effective value of the lamp drive current is calculated regardless of the change in the frequency of the lamp drive current. It suffices if it has a means for keeping it constant.

[0040]

According to the present invention, the frequency of the lamp drive current constantly changes due to the constant change of the ripple voltage, so that the frequency of the lamp drive current matches the natural frequency of the high-intensity discharge lamp. As a result, flicker due to an acoustic resonance phenomenon can be prevented, the lamp power can be kept constant, and a gradual change in the light emission amount can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating a state in which the frequency of a Q output signal and its inverted signal changes when the ripple voltage changes in the above embodiment.

FIG. 3 is a diagram showing a waveform of a lamp drive current when the ripple voltage changes in the above embodiment.

FIG. 4 is a diagram showing a time relationship between a smoothed voltage, a ripple voltage, and a lamp driving current in the above embodiment.

FIG. 5 is a diagram showing an equivalent circuit of a conventional example.

6 is a diagram showing a state in which a lamp drive current I generated by the equivalent circuit shown in FIG. 5 changes when its cycle is changed.

[Explanation of symbols]

10 ... AC power supply, 20 ... Rectifier circuit, 30 ... Smoothing circuit, T ... Transformer, W11 ... First primary coil, W12 ... Second primary coil, W2 ... Secondary coil, La ... High brightness Metal halide lamp as discharge lamp, TR1 ... Transistor as first switching means, TR2 ... Transistor as second switching means, 40 ... Control signal generating means, 41 ... Capacitor, 42 ... Switching regulator control IC, I ... Lamp Drive current.

Claims (4)

[Claims] 1. A high-frequency lighting circuit for a high-intensity discharge lamp, which supplies a lamp-driving current to a high-intensity discharge lamp while changing the frequency of the lamp-driving current. A high-frequency lighting circuit for a high-intensity discharge lamp, characterized in that it has means for keeping the value constant. 2. A high-frequency lighting circuit for a high-intensity discharge lamp, which rectifies and smoothes an AC power supply voltage and switches the smoothed voltage at a high frequency to generate a lamp drive current for driving the high-intensity discharge lamp, Control signal generating means for increasing the frequency of the lamp driving current when the ripple voltage of the smoothing voltage is high, and lowering the frequency of the lamp driving current when the ripple voltage of the smoothing voltage is low. High-frequency lighting circuit for high-intensity discharge lamps. 3. A rectifier circuit for rectifying an AC power supply voltage; a smoothing circuit for smoothing this rectified voltage; a first primary side coil, a second primary side coil, and a high-intensity discharge lamp. A transformer provided with a secondary coil for supplying a lamp driving current to the high-intensity discharge lamp; a first switching means connected to the smoothing circuit via the first primary coil; Second switching means connected to the smoothing circuit via the second primary side coil and performing an operation opposite to that of the first switching means; and when the ripple voltage of the smoothed voltage is high. Controlling the first switching means and the second switching means so as to increase the frequency of the lamp drive current, while the ripple drive voltage of the lamp drive current is reduced when the ripple voltage of the smoothed voltage is low. Frequency A high-frequency discharge circuit for a high-intensity discharge lamp, comprising: control signal generating means for controlling the first switching means and the second switching means so as to lower the voltage. 4. The high-frequency lighting circuit for a high-intensity discharge lamp according to claim 3, wherein the control signal generating means detects a ripple voltage of the smoothed voltage with a capacitor.