JP2002315347A - Method and circuit for regulating alternating-current voltage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alternating-current voltage regulating circuit which is capable of maintaining stable discharge, even if the output of a discharge lamp is adjusted. SOLUTION: The alternating-current voltage regulating method is for pulse- width modulating a sinusoidal alternating-current input from a commercial power supply by modulation pulses with a variable duty ratio of a frequency (e.g., 20 kHz) higher than the power supply frequency (e.g., 50 Hz). With respect to the voltage regulating method, in voltage ranges within the slice level (Ed) of sinusoidal alternating-current voltage, the duty ratio of modulation pulses (D) is kept constant, and in voltage ranges beyond the slice level (Ed), the duty ratio of the modulation pulses (D) is varied to deform the waveform (E) of the sine waves of alternating-current voltage to output, and alternating- current voltages (EH) to (EL) are thereby regulated. This alternating-current voltage regulating method is applied to an alternating-current power supply to a discharge lamp, and the slice level is set to the discharge starting voltage of the discharge lamp. Thus, stable operation is maintained, even if the output of the discharge lamp is adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC voltage adjusting circuit for controlling an AC voltage by controlling an AC waveform, and more particularly to an adjusting circuit suitable for an operation power supply of a discharge lamp or a magnetron.

[0002]

2. Description of the Related Art As shown in FIG. 1, a conventionally used AC voltage adjusting circuit is a bridge composed of four diodes for full-wave rectification of a sine wave AC input of a commercial power supply 6 through a noise removing capacitor 61. A full-wave rectifier circuit 5 connected thereto; a modulation circuit 4 in which four power FETs 41 to 44 for pulse width modulation of the output of the full-wave rectifier circuit 5 are connected in a bridge; 1
And a drive circuit 2 for driving the modulation circuit 4 by the pulse output of the modulation pulse generation circuit 1, and smoothing and applying the output of the modulation circuit 4 whose envelope is substantially the same sine wave as the AC input to the load 7. And a smoothing circuit 71.

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. , Which can change the duty ratio.

As shown in FIG. 4, a drive circuit 2 is connected to a commercial power supply 6 via a series circuit composed of two rectifying diodes 25 and 26 and current limiting resistors 27 and 28, and has an AC input. A photocoupler 29 conducting in a positive half cycle and a photocoupler 30 conducting in a negative half cycle, and an NPN transistor which repeats conduction / non-conduction by switching signals output from the phototransistors of these two photocouplers 29, 30 31, 32, a PNP transistor 35 driven by the output of the modulation pulse generation circuit 1, and four PFETs whose output sides (phototransistors) are connected to the gate electrodes of four power FETs 41 to 44 of the modulation circuit 4, respectively. Photocoupler 21
~ 24.

The emitter electrode of the NPN transistor 35 is
Connected to the positive terminal of DC power supply, NPN transistor 31,
Each of the 32 emitter electrodes is connected to the negative terminal of the DC power supply.

[0006] Of the four photocouplers 21 to 24, the photodiodes of the photocouplers 21 and 23 are connected in series, and a PNP transistor is connected via a current limiting resistor 33.
The photodiodes of the photocouplers 22, 24 are connected in series between the collector electrode of the NPN transistor 31 and the collector electrode of the NPN transistor 31.
It is connected between the collector electrode of the PNP transistor 35 and the collector electrode of the NPN transistor 32.

Next, the operation of the drive circuit shown in FIG. 4 will be described. In the positive half cycle of the AC input, the switching signal generated from the photocoupler 29 causes the transistor 31 to be conductive, and conversely, in the negative cycle, the switching signal generated from the photocoupler 30 causes the transistor 32 to be conductive.

On the other hand, when the output level of the pulse generated by the modulation pulse generation circuit 1 is low, the NPN transistor
During a period in which the PNP transistor 35 is turned on and the output level of the pulse generated by the modulation pulse generation circuit 1 is high, the PNP transistor 35 is repetitively operated by the pulse output from the pulse signal generation circuit 1 so that the PNP transistor 35 is turned off. ON / OFF is repeated at a frequency (for example, 20 kHz).

Therefore, in the positive half cycle of the AC input, the photocouplers 21 and 23 use the power FE of the modulation circuit 4 for power FE.
The pair of T41 and 43 repeats on / off at a high repetition frequency, and in the negative half cycle of the AC input, the photocoupler
22 and 24 cause the pair of power FETs 42 and 44 to be repeatedly turned on and off at a high repetition frequency.

The AC voltage output from the modulation circuit 4 is changed by changing the duty ratio of the pulse signal output from the modulation pulse generation circuit 1, as shown in the waveform diagram of FIG. 6. An output of a pulse-width-modulated waveform having the sine wave AC input from 6 as an envelope is obtained,
When this output is smoothed by the smoothing circuit 71, as shown in the waveform diagram of FIG. 5B, the output is adjusted to a sine wave AC output voltage (Eh) to (El) having a peak value proportional to the duty ratio of the pulse signal. can do.

[0011]

When the discharge lamp is turned on, the discharge does not start unless a voltage equal to or higher than the discharge starting voltage (Ed) is applied. The discharge is not stopped unless the applied voltage is reduced to the discharge stop voltage (Es) or less.

For example, as shown in the waveform diagram of FIG.
When a high sine wave AC voltage (Eh) is applied to turn on the discharge lamp, discharge starts when the AC voltage rises to the discharge start voltage (Ed), and drops when the discharge voltage drops to the discharge stop voltage (Es). Since the light is turned off, the discharge period (t21) and the stop period (t22) are alternately repeated. Similarly, when the discharge lamp is lit by applying a low sine wave AC voltage (El), the discharge period (t11) and the stop period (t12) are alternately repeated.

As is apparent from the waveform diagram of FIG. 5B, when the sine wave AC voltage applied to the discharge lamp is adjusted using the conventional AC voltage adjustment circuit, the ratio between the discharge period and the stop period is reduced. Changes. That is, when the discharge lamp is turned on at a high AC voltage (Eh), the discharge period (t21) becomes longer and the stop period (t2
When the discharge lamp is turned on at a low AC voltage (El), the discharge period (t11) becomes short and the stop period (t12) becomes long (t21> t11, t22 <t12).

As described above, since the current flowing through the discharge lamp depends on the peak value of the AC voltage applied to the discharge lamp, when the AC voltage of the applied sine wave is changed for the purpose of adjusting the output of the discharge lamp. , The ratio between the discharge period and the stop period changes.

If the AC voltage of the applied sine wave is reduced in order to lower the output of the discharge lamp, the stop period becomes longer, the temperature of the discharge gas decreases, and the discharge restart voltage tends to increase. The start time is delayed, the stop period is lengthened, and the discharge becomes unstable.

Therefore, the present invention has been conceived in order to solve such a problem. Even if the output of the discharge lamp is adjusted, the ratio between the discharge period and the stop period can be stabilized without changing. It is an object of the present invention to provide an AC voltage adjustment circuit that can maintain discharge.

[0017]

According to the AC voltage adjusting method of the present invention, an AC input of a sine wave from a commercial power supply is pulse width-modulated by a modulation pulse having a variable duty ratio higher in frequency than the power supply frequency. A voltage adjustment method, wherein a duty ratio of the modulation pulse is kept constant in a voltage range within a slice level of the sine wave AC voltage, and a duty ratio of the modulation pulse is maintained in a voltage range exceeding the slice level. The AC voltage is adjusted by changing the ratio to deform the sine wave of the AC voltage.

The AC voltage adjusting method according to the present invention is suitable for an AC power supply for a discharge lamp. By setting the slice level to the discharge starting voltage of the discharge lamp, the output of the discharge lamp is always operated stably even when the output is adjusted. be able to.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment to which the AC voltage adjusting circuit of the present invention is applied. In addition,
FIG. 1 is the same as the AC voltage adjusting circuit described in the prior art, but the present invention has a feature in the modulation pulse generating circuit, and a detailed description of other components will be omitted because they are duplicated.

FIG. 3 (E) shows an AC voltage adjusting circuit according to the present invention.
As shown in the waveform diagram, as the AC voltage applied to the load, the rising waveform up to the discharge starting voltage (Ed) of the discharge lamp and the falling waveform below the discharge stop voltage (Es) remain unchanged. (Ed) and discharge stop voltage (Es) period T21
In addition, the duty ratio of the pulse signal to be pulse width modulated is changed to adjust the AC power applied to the discharge lamp.

Therefore, in order to generate a pulse having a variable duty ratio, a modulated pulse generating circuit 1 shown in FIG. 2 is used. The modulation pulse generating circuit 1 generates a pulse of a constant frequency (for example, 20 kHz), and sets a discharge starting voltage (Ed) of a discharge lamp to a slice level. Voltage (Fig. 3 (A))
The voltage exceeding the level value (Ed) that becomes the discharge starting voltage (Fig. 3
(B)) A slice circuit 12 for generating
An operational amplifier 13 to which the output of 12 and a reference voltage are applied,
A pulse width control circuit 14 for controlling the duty ratio of the pulse output from the oscillation circuit 11 by the output of the operational amplifier 13
It is composed of

The inverting input terminal of the operational amplifier 13 is connected to the output of the slice circuit 12 via an input resistor R2, and to the output terminal via a feedback resistor R1. A reference voltage Vs that determines a reference duty ratio is applied to a non-inverting input terminal of the operational amplifier 13 via a resistor R3.

Next, the operation of the modulated pulse generating circuit 1 will be described with reference to FIG.
A description will be given based on the waveform diagram of FIG.

In the slicing circuit 12, a voltage (FIG. 3 (B)) exceeding the slicing level discharge start voltage (Ed) is output from the signal rectified by the full-wave rectifying circuit (FIG. 3 (A)). I do. 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.

The amplification factor of the operational amplifier 13 is determined by the input resistance R
2 and the resistance value of the feedback resistor R1 (R1 / R2). By adjusting the ratio (R1 / R2) of the resistance values, the amplitude G of the signal output from the operational amplifier 13 is obtained. The pulse width control circuit 14 is controlled by the output signal of the operational amplifier 13.

The pulse width control circuit 14 converts a pulse signal input from the oscillation circuit 11 into a signal whose pulse width is changed in accordance with the voltage of the signal (FIG. 3C) input from the operational amplifier 13 (FIG. 3C). (D)) is output. Therefore, the slice circuit
While the output level of 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 when the output level of the slice circuit 12 is high, the operational amplifier The output level of the pulse 13 decreases, and the duty ratio of the pulse decreases corresponding to the output level.

As described above, the AC voltage in the period (T21) during which the discharge starting voltage (Ed) of the discharge lamp is exceeded is pulse-width-modulated by the pulse whose duty ratio has been adjusted. It can be converted to an AC voltage having a peak value indicated by EH) to (EL).

As is clear from (EH) to (EL) of the waveform diagram E in FIG. 3, during the period T22 in which the duty ratio of the pulse signal in the AC voltage is constant (below the discharge starting voltage (Ed) of the discharge lamp). Since there is no change in the waveform of the sine wave and the duty ratio decreases in the period T22 which is equal to or higher than the discharge start voltage (Ed), the peak value of the AC voltage can be adjusted to be low. This duty ratio, that is, the peak value (EH) to (EL) of the AC voltage,
Since it is determined by the amplification factor of the operational amplifier 13 (the ratio (R1 / R2) between the resistance value of the input resistor and the resistance value of the feedback resistor), the gain can be arbitrarily set by adjusting the amplification factor.

When the discharge lamp is turned on by the AC voltage whose peak value has been adjusted, the discharge period T21 and the stop period T22
Therefore, the output of the discharge lamp can be adjusted while maintaining stable discharge.

In the embodiment described above, the output of the rectifier circuit 5 is guided to the modulation pulse generating circuit 1, the discharge starting voltage (Ed) of the discharge lamp is set to the slice level, and sliced by the slice circuit 12. Since the modulation pulse is generated, the voltage waveform on the output side of the pulse width modulation circuit 12 via the smoothing circuit 71 has a deviation from the ideal value. If this deviation cannot be tolerated, the slice level may be corrected in advance.

The configuration and operation of the embodiment of the AC voltage adjusting circuit according to 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 in any way. The AC voltage adjusting circuit according to the present invention can be applied to an AC power supply other than a discharge lamp. In the embodiment described above, the power FET is added to the modulation circuit.
However, the same operation can be performed by using an insulated gate bipolar transistor (IGBT).

[0033]

As is clear from the description based on the above embodiment, 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 sine wave AC voltage. At the slice level (Ed)
In the voltage range that exceeds, the pulse width is modulated by the modulation pulse having the duty ratio of the modulation pulse changed, and the sine wave of the output AC voltage is transformed to change the AC voltage (EH) to (EH).
Since L) is adjusted, it is possible to adjust the output of the discharge lamp while maintaining stable discharge by applying 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 according to the present invention is applied;

FIG. 2 is a block diagram showing a modulation pulse generation circuit that generates a pulse having a variable duty ratio used in the AC voltage adjustment circuit shown in FIG. 1;

FIG. 3 is a waveform diagram showing voltage waveforms at various parts of the AC voltage adjusting circuit shown in FIG.

FIG. 4 is a circuit diagram showing a driving circuit used in the AC voltage adjusting circuit shown in FIG. 1;

FIG. 5 is a waveform diagram used to explain the operation of the conventional AC voltage adjustment 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 (4)

[Claims] An AC voltage adjustment method for pulse width modulating a sine wave AC input from a commercial power supply with a modulation pulse having a variable duty ratio higher in frequency than the power supply frequency. The duty ratio of the modulation pulse is kept constant in the voltage range within the voltage slice level, and the sine wave of the AC voltage is transformed by changing the duty ratio of the modulation pulse in the voltage range exceeding the slice level. An AC voltage adjustment method characterized in that the AC voltage is adjusted by causing the AC voltage to be adjusted. 2. The AC voltage adjusting method according to claim 1, wherein the load to which the adjusted AC voltage is applied is a discharge lamp, and the slice level is a discharge starting voltage of the discharge lamp. . 3. An AC voltage adjustment system for performing pulse width modulation of a sine wave AC input from a commercial power supply with a modulation pulse having a variable duty ratio higher in frequency than the power supply frequency. A slice circuit for obtaining a voltage exceeding the voltage slice level, a modulation pulse generation circuit for controlling a duty ratio of a modulation pulse to be output based on an output of the slice circuit, and an AC voltage of the sine wave by the modulation pulse A modulation circuit for performing pulse width modulation of the modulation pulse, and keeping a duty ratio of the modulation pulse constant in a voltage range within the slice level, and a duty ratio of the modulation pulse in a voltage range exceeding the slice level. And an AC voltage adjusting circuit for adjusting the AC voltage by changing a sine wave of the AC voltage by changing the AC voltage. 4. The AC voltage adjusting circuit according to claim 3, wherein the load to which the adjusted AC voltage is applied is a discharge lamp, and the slice level is a discharge starting voltage of the discharge lamp. .