JP2000133481A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the structure of a control circuit while reducing a D.C. component applied to a discharge lamp to prevent a cataphoresis phenomenon under low temperatures, and to restrain the fluctuation of load output with respect to an A.C. power voltage and the low frequency ripple of a high-frequency current. SOLUTION: This discharge lamp lighting device of a high-frequency charge type changes control parameters of switching elements Q1, Q2 of a half-bridge inverter circuit according to an instantaneous value of an A.C. power supply voltage. Switching frequency is controlled by using a control signal formed by adding, with appropriate detection gain, the high-voltage side potential of a rectifier DB to the low-voltage side potential thereof, and its duty factor is fixed at approximately 50%. The detection gain is adjusted to a value that reduces the ripple at a commercial power frequency of a high-frequency current fed to a load.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a discharge lamp lighting device, and more particularly to a discharge lamp lighting device having a high input power factor and an input current distortion improving function.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram of a conventional example. Hereinafter, the circuit configuration will be described. The AC power supply E is connected to an AC input terminal of the full-wave rectifier DB via a filter circuit F for removing high frequency. A small-capacity capacitor C1 is connected in parallel to the DC output terminal of the full-wave rectifier DB.
The high-voltage output terminal of the full-wave rectifier DB is connected to the high-voltage terminal of the power supply capacitor C5. The low voltage side terminal of the power supply capacitor C5 is connected to the ground, and is used as the reference potential of the inverter circuit 1. Low-voltage output terminal of full-wave rectifier DB and power supply capacitor C5
Is connected to a series circuit of diodes D1 and D2. A capacitor C2 is connected in parallel to both ends of the diode D2. A series circuit of the switching elements Q1 and Q2 of the inverter circuit 1 is connected to both ends of the power supply capacitor C5. The primary winding of the leakage transformer T2 is connected between the connection point of the switching elements Q1 and Q2 and the connection point of the diodes D1 and D2 via a coupling capacitor C4. The secondary winding of the leakage transformer T2 has a discharge lamp L
a is connected to the power supply side terminal. A resonance capacitor C6 is connected between the non-power-supply-side terminals of the discharge lamp La. The output voltage of the inverter circuit 1 is converted into a sinusoidal high-frequency current by the leakage inductance of the leakage transformer T2 and resonance of the capacitor C6 and supplied to the discharge lamp La. A circuit including diodes D3 and D4, an inductor L2, and a smoothing capacitor C3 is a switching element Q
2, the smoothing capacitor C3 is charged through the diode D3 and the inductor L2, and the diode D3 is charged while the output voltage of the rectifier DB is lower than the charged voltage of the capacitor C3.
4, the charging voltage of the smoothing capacitor C3 acts as the power supply circuit 2 of the inverter circuit 1, and this constitutes a step-down chopper circuit.

[0003] This circuit comprises switching elements Q1 and Q2.
And a half-bridge type inverter circuit 1 that turns on the discharge lamp La, which is a load, at a high frequency by alternately turning on and off the first diode D1 and the second diode D1.
And the parallel circuit of the diode D2 and the capacitor C2, the AC power supply E according to the ON / OFF of the switching elements Q1 and Q2 over almost the entire section of one cycle of the AC power supply E.
, The input current flows through the load circuit of the inverter circuit 1 to make the input current waveform substantially sinusoidal. Therefore, the input power factor is high and the input current waveform distortion can be improved. Becomes

The switching elements Q1 and Q2 are connected to an oscillation circuit 3
Is driven via the drive circuit 4 and is alternately turned ON / OFF at a predetermined frequency and a predetermined duty. The driving frequency of the switching elements Q1 and Q2 is controlled by the frequency control circuit 5 according to the low-voltage potential of the rectifier DB, and the driving duty of the switching elements Q1 and Q2 is duty-controlled according to the high-voltage potential of the rectifier DB. Controlled by the circuit 6.

FIG. 6 shows an operation waveform diagram of each part of the conventional example. FIG. 6A shows the AC power supply voltage E, and FIG.
FIG. 6C shows a voltage Vc5 across the capacitor C5 corresponding to the power supply applied to the inverter circuit 1, and FIG.
(D) shows the lamp current ILa supplied to the discharge lamp La.

The operation will be briefly described with reference to the operation waveforms of the respective parts shown in FIG. By setting the power supply voltage of the inverter circuit 1 having the input waveform distortion improving function to a partially smoothed power supply such as Vc5 shown in FIG. 6C, the lamp current waveform ILa becomes alternating current as shown in FIG. The absolute value increases near the peak of the power supply voltage E and near zero crossing, and therefore, the crest factor CF (= peak value / effective value) of the lamp current ILa is also improved.

In the above-described main circuit configuration, a power supply device capable of obtaining a stable optical output, such as a fluctuation width of a load output due to a fluctuation of an AC power supply voltage E and a reduction of a low-frequency ripple of a high-frequency current flowing through the load, is constituted. The oscillation circuit 3 includes a frequency control circuit 5 and a duty control circuit 6 for changing the operating frequency of the switching elements Q1 and Q2 in accordance with the low-voltage output voltage of the rectifier DB. The duty control circuit 6 controls the conduction period of the switching elements Q1 and Q2 according to the output voltage on the high voltage side of the rectifier DB. Such a configuration and detailed operation of the main circuit are described in Japanese Patent Laid-Open No. 7-279.
No. 514.

[0008]

However, in the above conventional example, the on-duty of the drive signal of the inverter circuit always changes, that is, the switching elements Q1 and Q2
Is imbalanced, a DC component is applied to the high-frequency voltage supplied to the load. In a discharge lamp load, the diffusivity in the lamp tube of charged gas molecules for emitting ultraviolet rays by colliding with the electrons decreases at low temperatures, and direct current components are applied, causing electrons to enter the lamp tube. A phenomenon (hereinafter, referred to as "cataphoresis phenomenon") occurs in which charged gas molecules are gradually attracted to one of the filaments on both sides to discharge, leading to a decrease in lamp illuminance. As a countermeasure against this problem, the on-duty of the switching element is set to 50
%, Which removes the DC component of the high-frequency voltage.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to solve the above-mentioned problems and to simplify the configuration of a control circuit. It is another object of the present invention to obtain an effect of suppressing a fluctuation width of a load output with respect to an AC power supply voltage and an effect of suppressing a low-frequency ripple of a high-frequency current, which are equivalent to those of the related art.

[0010]

According to the present invention, in order to solve the above-mentioned problems, as shown in FIG.
Rectifier DB, a power supply circuit 2 that converts an output voltage of the rectifier DB into a DC voltage Vc5 and outputs the DC voltage Vc5 to a smoothing capacitor C5, and two switching elements Q1 and Q2 that convert the DC voltage Vc5 into a high-frequency voltage. A power supply circuit 2 is a step-down chopper circuit including at least one switching element Q2. The half-bridge inverter circuit 1 includes at least one switching element Q2. A first diode D1 and a resonance circuit serving as a load are connected between a high voltage side terminal of the smoothing capacitor C5 and a connection point between the two switching elements Q1 and Q2 and a low voltage side output terminal of the rectifier DB. And a connection point between the first diode D1 and a resonance circuit including the load circuit; The second diode D2 and the first capacitor C between the low pressure side of the series circuit of elements Q1, Q2
Two parallel circuits are connected, the AC power supply voltage and the input current from the AC power supply have substantially similar waveforms, and the high-frequency current waveform supplied to the load has the peak near the peak value of the AC power supply voltage. The absolute value of the high-frequency current increases as the value approaches the zero-crossing, and a waveform containing a low-frequency ripple in which the absolute value of the high-frequency current increases as the value approaches the zero-crossing near the zero crossing of the AC power supply voltage. The on-duty of the signal for driving the two switching elements Q1 and Q2 is about 50% in the entire cycle of the AC power supply E, and the high-side output of the rectifier DB is based on the low-side of the inverter circuit 1. A first detection value that detects the potential of the terminal, and a second detection value that detects the potential of the low-voltage output terminal of the rectifier DB. And a means for generating a control signal by adding the following. When the absolute value of the control signal increases, the frequency for driving the two switching elements Q1 and Q2 is increased, and the absolute value of the high-frequency current is controlled in a decreasing direction. The frequency control circuit 5 is provided.

[0011]

(Embodiment 1) FIG. 1 shows a first embodiment of the present invention. FIG. 2 shows operation waveforms in the present embodiment. The difference between the conventional example shown in FIG. 5 and the first embodiment shown in FIG. 1 is that the voltage Vc5 (see FIG. 2C) of the capacitor C5 supplied to the inverter circuit 1 and the voltage on the low voltage side of the rectifier DB are different. Vf (see FIG. 2 (e)) is converted into a detection signal with the same detection gain, and these are added to generate a control signal. This control signal is a lamp current waveform ILa of FIG. 2 (d). Is a DC voltage having a waveform substantially similar to the low-frequency ripple. This control signal (see FIG. 2 (f)) is input to the frequency control circuit 5 of the oscillation circuit 3, and when the absolute value of the control signal increases, the oscillation frequency is increased, and when the absolute value of the control signal decreases, Lower the oscillation frequency. The drive circuit 4 generates a drive signal having an on-duty of about 50% based on the oscillation frequency of the frequency control circuit 5, and drives the switching elements Q1 and Q2. Thus, by controlling the frequency so as to suppress the output near the peak value and near the zero cross of the AC power supply E, the lamp current I
The variation of the absolute value of La is suppressed.

When the voltage Vc5 of the capacitor C5 applied to the inverter circuit 1 rises due to fluctuations in the power supply voltage or fluctuations in the load characteristics and a light load, the driving frequency increases in response to the rise. And the output is suppressed. When the voltage Vc5 of the capacitor C5 decreases, the driving frequency decreases and the output increases. As a result, the high-frequency voltage applied to the lamp La has no DC voltage component, and the cataphoresis phenomenon at low temperatures is unlikely to occur, and the control circuit has a simplified and low-cost circuit configuration. Further, the lamp output fluctuation is suppressed by the fluctuation of the power supply voltage E, and the crest factor CF of the lamp current waveform.
Can achieve the same effect as the conventional example.

(Embodiment 2) FIG. 3 shows a configuration diagram of a second embodiment of the present invention. The circuit of FIG. 3 is different from the first embodiment in that the voltage Vc5 of the capacitor C5 supplied to the inverter circuit 1 (see FIG. 2C) and the voltage Vf on the low voltage side of the rectifier DB (FIG. )) So as to minimize the variation of the lamp current in the vicinity of the peak value of the AC power supply E and in the vicinity of the zero crossing.
The configuration is such that they are detected by A2 and these are added, and the other configuration is the same as that of the first embodiment. Further, the relationship between the detection gains A1 and A2 is expressed as A1> A2.
By doing so, the variation in the absolute value of the lamp current can be further suppressed.

(Embodiment 3) FIG. 4 shows a configuration diagram of a third embodiment of the present invention. The circuit shown in FIG. 4 has the voltage Vc5 supplied to the inverter circuit 1 as in the second embodiment.
(See FIG. 2C) and the voltage Vf on the low voltage side of the rectifier DB.
(See FIG. 2 (e)).
The signal is converted into a detection signal in A2 and added. At this time, the frequency for driving the switching elements Q1 and Q2 is set higher by further applying a DC voltage Vk having a certain amplitude. Is the same as that of the first embodiment. Thus, by always setting the drive frequency higher than the leakage inductance of the leakage transformer T2 and the resonance frequency of the resonance circuit including the capacitors C6 and C2, the delay operation of the inverter circuit 1 can be guaranteed. The DC voltage Vk may be a signal obtained by smoothing the absolute value of the detected value of the high-frequency voltage or the high-frequency current on the secondary side of the leakage transformer T2, whereby the stress at the time of an abnormal load can be suppressed. . In addition, lamp preheating mode, starting mode,
A signal for switching the lighting mode may be used.

[0015]

According to the first to fourth aspects of the present invention, the switching frequency is controlled using a control signal obtained by adding the high voltage side potential and the low voltage side potential of the rectifier with an appropriate detection gain. Is fixed at about 50%,
Provided is a discharge lamp lighting device that suppresses cataphoresis in a low-temperature discharge lamp with a simple control circuit configuration, and achieves the same power supply voltage fluctuation compensation characteristics and crest factor suppression effect as the conventional example. Can be.

[Brief description of the drawings]

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

FIG. 2 is an operation waveform diagram according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing a conventional example.

FIG. 6 is an operation waveform diagram in the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inverter circuit 2 Power supply circuit 3 Oscillation circuit 4 Drive circuit 5 Frequency control circuit Q1 Switching element Q2 Switching element E AC power supply DB Rectifier La Discharge lamp

Claims (4)

[Claims] 1. A rectifier for rectifying an AC power supply, a power supply circuit for converting an output voltage of the rectifier to a DC voltage and outputting the DC voltage to a smoothing capacitor, and two switching elements for converting the DC voltage to a high-frequency voltage. A half-bridge inverter circuit connected in series, wherein the power supply circuit is a step-down chopper circuit including at least one switching element, and includes a high-voltage output terminal of the rectifier and a high-voltage output terminal of the smoothing capacitor. A series circuit of a first diode and a resonant circuit as a load is connected between a connection point of the two switching elements and a low-voltage output terminal of the rectifier; A second diode and a first diode between a connection point between the first switching element and a resonance circuit including the load circuit, and a low voltage side of a series circuit of the two switching elements. A parallel circuit of capacitors is connected, the AC power supply voltage and the input current from the AC power supply have substantially similar waveforms, and the high-frequency current waveform supplied to the load has a waveform near the peak value of the AC power supply voltage. As the absolute value of the high-frequency current increases as approaching the peak value, and near the zero cross of the AC power supply voltage, the waveform includes a low-frequency ripple in which the absolute value of the high-frequency current increases as approaching the zero cross. The on-duty of the signal for driving the two switching elements of the circuit is approximately 50% in all periods of the AC power supply, and the potential of the output terminal on the high voltage side of the rectifier is detected with reference to the low voltage side of the inverter circuit. The first detection value is added to a second detection value that detects the potential of the low-voltage output terminal of the rectifier. A means for generating a control signal; and a frequency control circuit for increasing the frequency for driving the two switching elements and controlling the absolute value of the high-frequency current in a decreasing direction when the absolute value of the control signal increases. Discharge lamp lighting device characterized by the above-mentioned. 2. A means for adding a first detection value and a second detection value to generate a control signal, the means for adjusting a detection magnification of each of the first and second detection values to a different value. The discharge lamp lighting device according to claim 1, wherein the detection magnification is adjusted so as to reduce low-frequency ripple included in the high-frequency current. 3. A means for adding the first detection value and the second detection value to generate a control signal, wherein the control signal is generated by adding a constant DC voltage to the first and second detection values. The discharge lamp lighting device according to claim 1, wherein a frequency for driving the two switching elements of the circuit is set in a frequency range in which a slow current flows. 4. The discharge lamp lighting device according to claim 2, wherein a detection magnification of the second detection value is smaller than a detection magnification of the first detection value.