JP3865597B2 - AC voltage adjustment method and circuit for discharge lamp - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an AC voltage adjustment circuit that controls an AC voltage by controlling an AC waveform, and more particularly, to an adjustment circuit suitable for an operating power supply for a discharge lamp .
[0002]
[Prior art]
As shown in FIG. 1, the AC voltage adjusting circuit that has been conventionally used is a full-wave rectification in which four diodes for full-wave rectification of a sine-wave AC input of a commercial power supply 6 through a noise elimination capacitor 61 are bridge-connected. A modulation circuit 4 in which four power FETs 41 to 44 for pulse-width modulating the output of the full-wave rectifier circuit 5 are bridge-connected, a modulation pulse generation circuit 1 for generating a pulse with a variable duty ratio, and the modulation A drive circuit 2 for driving the modulation circuit 4 by the pulse output of the pulse generation circuit 1; a smoothing circuit 71 for smoothing and applying to the load 7 the output of the modulation circuit 4 whose envelope is substantially the same sine wave as the AC input; It has.
[0003]
The modulation pulse generation circuit 1 is an oscillation circuit that generates a pulse having a repetition frequency (for example, 20 kHz) higher than the AC frequency (50 Hz) of a commercial power supply. The repetition frequency of the output pulse is constant and the duty ratio is It is a conventionally well-known circuit that can change.
[0004]
As shown in FIG. 4, the drive circuit 2 is connected to the commercial power supply 6 via a series circuit composed of two rectifying diodes 25 and 26 and current limiting resistors 27 and 28, and the positive half of the AC input. A photocoupler 29 that conducts periodically and a photocoupler 30 that conducts in a negative half cycle, and NPN transistors 31 and 32 that repeat conduction and non-conduction by switching signals output from the phototransistors of these two photocouplers 29 and 30 And four photocouplers 21 whose output sides (phototransistors) are connected to the gate electrodes of the four power FETs 41 to 44 of the modulation circuit 4, respectively, driven by the output of the modulation pulse generation circuit 1. With ~ 24.
[0005]
The emitter electrode of the NPN transistor 35 is connected to the positive terminal of the DC power supply, and each emitter electrode of the NPN transistors 31 and 32 is connected to the negative terminal of the DC power supply.
[0006]
Among the four photocouplers 21 to 24, the photodiodes of the photocouplers 21 and 23 are connected in series, and are connected between the collector electrode of the PNP transistor 35 and the collector electrode of the NPN transistor 31 via the current limiting resistor 33. The photo diodes of the photocouplers 22 and 24 are connected in series, and are connected between the collector electrode of the PNP transistor 35 and the collector electrode of the NPN transistor 32 via a current limiting resistor 34.
[0007]
Next, the operation of the drive circuit shown in FIG. 4 will be described. In the positive half cycle of the AC input, the transistor 31 is turned on by the switching signal generated from the photocoupler 29. Conversely, in the negative cycle, the transistor 32 is turned on by the switching signal generated from the photocoupler 30.
[0008]
On the other hand, when the output level of the pulse generated by the modulation pulse generating circuit 1 is low, the NPN transistor 35 is turned on, and when the output level of the pulse generated by the modulation pulse generating circuit 1 is high, the PNP transistor 35 is cut off. The PNP transistor 35 is repeatedly turned on and off at a high repetition frequency (for example, 20 kHz) by the pulse output from the pulse signal generation circuit 1 so as to be in a state.
[0009]
Accordingly, in the positive half cycle of the AC input, the photocouplers 21 and 23 cause the pair of power FETs 41 and 43 of the modulation circuit 4 to repeatedly turn on and off at a high repetition frequency, and in the negative half cycle of the AC input, The pair of power FETs 42 and 44 is repeatedly turned on and off at a high repetition frequency by the couplers 22 and 24.
[0010]
The AC voltage output from the modulation circuit 4 changes the duty ratio of the pulse signal output from the modulation pulse generation circuit 1 to change the duty ratio from the commercial power supply 6 as shown in the waveform diagram of FIG. An output of a pulse width modulated waveform having a sinusoidal AC input as an envelope is obtained. When this output is smoothed by the smoothing circuit 71, the duty ratio of the pulse signal is obtained as shown in the waveform diagram of FIG. Can be adjusted to sinusoidal AC output voltages (Eh) to (El) having a peak value proportional to.
[0011]
[Problems to be solved by the invention]
When the discharge lamp is lit, the discharge is not started unless a voltage higher than the discharge start voltage (Ed) is applied.When the discharge lamp is stopped during discharge, the applied voltage is set to the discharge stop voltage (Es). The discharge is not stopped unless it is lowered to the following.
[0012]
For example, as shown in the waveform diagram of FIG. 5 (B), when a high sine wave AC voltage (Eh) is applied to light the discharge lamp, the discharge occurs when the AC voltage rises to the discharge start voltage (Ed). Is started and the light is extinguished when the voltage drops to the discharge stop voltage (Es), so that the discharge period (t21) and the stop period (t22) are alternately repeated. Similarly, when a low sine wave AC voltage (El) is applied to light the discharge lamp, the discharge period (t11) and the stop period (t12) are alternately repeated.
[0013]
As is apparent from the waveform diagram of FIG. 5B, the ratio of the discharge period to the stop period changes when the AC voltage of the sine wave applied to the discharge lamp is adjusted using the conventional AC voltage adjustment circuit. . In other words, when the discharge lamp is lit with a high AC voltage (Eh), the discharge period (t21) is lengthened and the stop period (t22) is shortened.When the discharge lamp is lit with a low AC voltage (El), The discharge period (t11) becomes shorter and the stop period (t12) becomes longer (t21> t11, t22 <t12).
[0014]
Thus, since the current flowing through the discharge lamp depends on the peak value of the AC voltage applied to the discharge lamp, if the AC voltage of the applied sine wave is changed for the purpose of adjusting the output of the discharge lamp, the discharge period And the ratio of the suspension period changes.
[0015]
If the AC voltage of the sine wave to be applied is lowered in order to reduce the output of the discharge lamp, the stop period becomes longer, the temperature of the discharge gas decreases, the discharge resumption voltage tends to increase, and the discharge start timing is further increased. The stop period becomes longer with a delay, and the discharge becomes unstable.
[0016]
Therefore, the present invention has been conceived to solve such problems, and even when the output of the discharge lamp is adjusted, stable discharge is maintained without changing the ratio of the discharge period to the stop period. It is an object of the present invention to provide an AC voltage regulating circuit that can be used.
[0017]
[Means for Solving the Problems]
The AC voltage adjustment method of the present invention is an AC voltage adjustment method in which a sine AC voltage from a commercial power supply is pulse-width modulated by a modulation pulse having a variable duty ratio having a frequency higher than the power supply frequency and applied to the discharge lamp. Wherein the modulation pulse duty ratio is kept constant in a voltage range in which the AC voltage of the sine wave is equal to or lower than the discharge start voltage of the discharge lamp , and the modulation is performed in a voltage range exceeding the discharge start voltage of the discharge lamp. The AC voltage is adjusted by changing the duty ratio of the pulse to deform the sine wave of the AC voltage.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0020]
FIG. 1 is a block diagram showing a configuration of an embodiment to which an AC voltage adjusting circuit of the present invention is applied. Although FIG. 1 is the same as the AC voltage adjusting circuit described in the prior art, the present invention has a feature in the modulation pulse generating circuit, and therefore, detailed description regarding other components is omitted because it is redundant. To do.
[0021]
As shown in the waveform diagram of FIG. 3 (E), the AC voltage adjusting circuit of the present invention has a rising waveform up to the discharge start voltage (Ed) of the discharge lamp and a discharge stop voltage (Es) as the AC voltage applied to the load. ) The following falling waveform is not changed, and during the period T21 between the discharge start voltage (Ed) and the discharge stop voltage (Es), the duty ratio of the pulse signal to be subjected to pulse width modulation is changed, and the alternating current applied to the discharge lamp The power is adjusted.
[0022]
Therefore, in order to generate a pulse with a variable duty ratio, the modulation pulse generation circuit 1 shown in FIG. 2 is used. The modulation pulse generation circuit 1 is full-wave rectified by a full-wave rectification circuit 5 with an oscillation circuit 11 that generates a pulse of a constant frequency (for example, 20 kHz) and a discharge start voltage (Ed) of a discharge lamp at a slice level. Slice circuit 12 that generates a voltage (FIG. 3B) that exceeds the level value (Ed) that becomes the discharge start voltage, and the output and reference voltage of this slice circuit 12 Is applied, and a pulse width control circuit 14 that controls the duty ratio of the pulse output from the oscillation circuit 11 by the output of the operational amplifier 13.
[0023]
The inverting input terminal of the operational amplifier 13 is connected to the output of the slicing circuit 12 through the input resistor R2, and is connected to the output terminal through the feedback resistor R1. A reference voltage Vs that determines a reference duty ratio is applied to the non-inverting input terminal of the operational amplifier 13 via a resistor R3.
[0024]
Next, the operation of the modulation pulse generating circuit 1 will be described based on the waveform diagram of FIG.
[0025]
The slice circuit 12 outputs a voltage (FIG. 3 (B)) that exceeds the discharge start voltage (Ed) at the slice level from the signal rectified by the full-wave rectifier circuit (FIG. 3 (A)). The output of the slice circuit 12 is compared with the reference voltage Vs in the operational amplifier 13, and the operational amplifier 13 outputs an inverted signal (FIG. 3C) proportional to the difference voltage.
[0026]
Since the amplification factor of the operational amplifier 13 is determined by the ratio (R1 / R2) of the resistance value of the input resistor R2 and the resistance value of the feedback resistor R1, by adjusting the ratio (R1 / R2) of this resistance value, The amplitude G of the signal output from the operational amplifier 13 can be changed, and the pulse width control circuit 14 is controlled by the output signal of the operational amplifier 13.
[0027]
The pulse width control circuit 14 changes the pulse width of the pulse signal input from the oscillation circuit 11 in accordance with the voltage of the signal input from the operational amplifier 13 (FIG. 3C) (FIG. 3D). ) Is output. Therefore, during a period when the output level of the slice circuit 12 is low, the output level of the operational amplifier 13 is high and the duty ratio of the pulse output from the pulse width control circuit 14 is constant and large, but the output level of the slice circuit 12 is high. As a result, the output level of the operational amplifier 13 decreases, and the duty ratio of the pulse decreases corresponding to the output level.
[0028]
As described above, the pulse voltage of the AC voltage in the period (T21) in which the discharge start voltage (Ed) of the discharge lamp is exceeded is modulated by the pulse whose duty ratio is adjusted, so that the waveform diagram E in FIG. It can be converted into a peak value AC voltage indicated by (EL).
[0029]
As is clear from (EH) to (EL) in the waveform diagram E of FIG. 3, the sine is obtained during the period T22 (below the discharge start voltage (Ed) of the discharge lamp) in which the duty ratio of the pulse signal of the AC voltage is constant. There is no change in the waveform of the wave, and the duty ratio becomes smaller in the period T21 that is equal to or higher than the discharge start voltage (Ed), so that the peak value of the AC voltage can be adjusted low. This duty ratio, that is, the peak value (EH) to (EL) of the AC voltage is determined by the amplification factor of the operational amplifier 13 (ratio of the resistance value of the input resistor to the resistance value of the feedback resistor (R1 / R2)). Therefore, it can be arbitrarily set by adjusting the amplification factor.
[0030]
When turning on the discharge lamp by such peak value AC voltage adjusted, since the ratio of the discharging period T21 and the stop period T22 is not changed, adjusts the output of the discharge lamp while maintaining a stable discharge be able to.
[0031]
In the embodiment described above, the output of the rectifier circuit 5 is guided to the modulation pulse generation circuit 1, the discharge start voltage (Ed) of the discharge lamp is set to the slice level, and the slice circuit 12 slices the modulation pulse. Therefore, the voltage waveform on the output side of the pulse width modulation circuit 12 that has passed through the smoothing circuit 71 produces a deviation from the ideal value. If this deviation cannot be allowed, the slice level may be corrected in advance.
[0032]
The configuration and operation of the embodiment of the AC voltage adjusting circuit of the present invention have been described above. However, this embodiment is merely an example of the present invention and does not limit the present invention. The AC voltage adjusting circuit of the present invention can be applied to AC power supplies other than discharge lamps. In the embodiment described above, the power FET is used for the modulation circuit, but the same operation can be performed even if an insulated gate bipolar transistor (IGBT) is used.
[0033]
【The invention's effect】
As is apparent from the description based on the above embodiments, according to the present invention, the duty ratio of the modulation pulse is kept constant in the voltage range within the slice level (Ed) of the AC voltage of the sine wave, In the voltage range exceeding the level (Ed), the pulse width is modulated by the modulation pulse with the duty ratio of the modulation pulse changed, and the AC voltage (EH) to (EL) is adjusted by deforming the sine wave of the output AC voltage. Therefore, the output of the discharge lamp can be adjusted while maintaining a stable discharge by applying it to the AC power supply of the discharge lamp.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment to which an AC voltage adjusting circuit of the present invention is applied;
2 is a block diagram showing a modulation pulse generating circuit that generates a variable duty ratio pulse used in the AC voltage adjusting circuit shown in FIG. 1;
FIG. 3 is a waveform diagram showing voltage waveforms at various parts of the AC voltage regulator circuit shown in FIG.
4 is a circuit diagram showing a drive circuit used in the AC voltage adjusting circuit shown in FIG.
FIG. 5 is a waveform diagram used for explaining the operation of a conventional AC voltage adjusting circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Modulation pulse generation circuit 2 Drive circuit 4 Modulation circuit 5 Rectifier circuit 6 AC power supply 7 Load
12 slice circuit
41 ~ 44 Power FET
21-24 Photocoupler
29, 30 Photocoupler

Claims (2)

An AC voltage adjustment method for applying a sinusoidal AC voltage from a commercial power supply to a discharge lamp by applying a pulse width modulation with a modulation pulse having a variable duty ratio having a frequency higher than the power supply frequency,
In the voltage range where the AC voltage of the sine wave is equal to or lower than the discharge start voltage of the discharge lamp, the duty ratio of the modulation pulse is kept constant, and in the voltage range exceeding the discharge start voltage of the discharge lamp, the duty ratio of the modulation pulse The AC voltage adjustment method for a discharge lamp is characterized in that the AC voltage is adjusted by changing the sine wave of the AC voltage by changing. An AC voltage adjusting circuit for applying a pulse width to a sinusoidal AC voltage from a commercial power supply by a modulation pulse having a variable duty ratio having a frequency higher than that of the power supply frequency, and applying the pulse width to the discharge lamp ,
A slice circuit for obtaining a voltage in which the AC voltage of the sine wave exceeds a discharge start voltage of the discharge lamp; a modulation pulse generating circuit for controlling a duty ratio of a modulation pulse output based on an output of the slice circuit; and the modulation A modulation circuit for pulse-width modulating the sine AC voltage by a pulse, and maintaining a constant duty ratio of the modulation pulse in a voltage range equal to or lower than a discharge start voltage of the discharge lamp, and starting discharge of the discharge lamp An AC voltage adjusting circuit for a discharge lamp, wherein the AC voltage is adjusted by changing a duty ratio of the modulation pulse to deform a sine wave of the AC voltage in a voltage range exceeding the voltage.

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