JPH0529089A - Discharge lamp lighting device - Google Patents

Abstract

(57) [Abstract] [Purpose] A choke coil, which is a lamp current limiting element, is miniaturized to continuously control the lamp current in a wide range while avoiding the occurrence of an acoustic resonance phenomenon. [Structure] A high frequency inverter 12 is used as means for lighting a discharge lamp 15, and frequency control of the inverter and PW are performed.
Combined with M control, the lamp current is continuously controlled. [Effect] The choke coil that is a lamp current limiting element can be made smaller than the conventional series inverter,
In addition, a discharge lamp lighting device that realizes a fast rise of the luminous flux even when the frequency control range is narrowed, minimizes distortion of the lamp current while avoiding the occurrence of an acoustic resonance phenomenon, and can continuously control the lamp current in a wide range Can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device for starting a discharge lamp and controlling lighting.

[0002]

2. Description of the Related Art Conventionally, as a lighting system for suppressing the distortion of the lamp current and for controlling the discharge lamp while maintaining a constant lighting frequency, it has already been described on page 16 of the National Convention of the Lighting Society of 1987. The configuration applied to the self-excited half-bridge inverter, which is a PWM dimming method, is introduced.

In general, in a discharge lamp, particularly in a high-intensity discharge lamp such as a metal halide lamp, a change in light output causes a time delay due to thermal inertia with respect to a change in input. Also,
The lamp voltage is low immediately after startup, and a large starting current must be supplied to the lamp in order to rapidly raise the light output immediately after startup.

The PWM dimming method is a method of increasing the output of the inverter by maximizing the conduction period of the switch element immediately after starting when such a large starting current is supplied to the lamp.

[0005]

However, when the ratio of the lamp current at the time of supplying the maximum starting current and at the time of rated lighting (at the time of dimming) is several times or more, the conduction period of the switching element as in the prior art is reduced. There is a problem that it is not easy to supply a sufficient starting current only by the PWM control method for controlling.

[0006]

In order to solve the above-mentioned problems, a discharge lamp lighting device of the present invention includes a DC power source, a high frequency inverter driven by the DC power source and oscillating, and an output terminal of the high frequency inverter. A resonance circuit including a series circuit of a connected choke coil and a capacitor, a series circuit including a discharge lamp and a pulse transformer connected to a connection point of the choke coil and a capacitor, and a high voltage to the discharge lamp via the pulse transformer. A starting pulse generator connected to apply a voltage pulse, a detector for detecting characteristics relating to lamp characteristics, and an output signal of the detector to change the oscillation frequency and duty ratio of the high frequency inverter to change the discharge lamp. And a lighting control device for controlling the lighting.

[0007]

With the above configuration, by combining the frequency control of the high frequency inverter and the PWM control during the starting current supply period, a quick rise of the luminous flux is realized, and the distortion of the lamp current is minimized, so that the lamp current can be spread over a wide range. Control continuously.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A discharge lamp lighting device according to the present invention uses a DC power source as an input, and includes a capacitor, a choke coil, a discharge lamp,
And a series circuit composed of a pulse transformer and a high frequency inverter circuit using a discharge lamp and a capacitor connected in parallel to the pulse transformer as a load, control the oscillation frequency of the high frequency inverter and the conduction period of the main switching element that constitutes the inverter. Control (hereinafter duty control,
Or PWM control) is performed in combination to control the lamp current during lighting.

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a configuration diagram showing an embodiment in which the discharge lamp lighting device of the present invention is applied to a series inverter. In FIG. 1, 11 is a DC power supply, 12 is a high frequency inverter,
13 is a capacitor, 14 is a choke coil, 15 is a discharge lamp, 16 is a start pulse generator, 17 and 18 are capacitors, 19 is a detector, and 20 is a lighting controller.
The DC power supply 11 is a high frequency inverter 12, a capacitor 1
3, choke coil 14, and starting pulse generator 1
The discharge lamp 15 is connected via the secondary winding of the pulse transformer 21 that constitutes 6 to start and light the discharge lamp 15.

The high frequency inverter 12 is composed of FETs 22 and 23 which are a pair of switching elements which perform 0N-0FF in mutually opposite phases, and a drive circuit 2 which drives them.
4 and 25, and the oscillation circuit 26, the DC power supply 11 as an input, a series circuit including a capacitor 13, a choke coil 14, a discharge lamp 15 and a pulse transformer 21, a discharge lamp 15 and a pulse transformer. Two
The capacitors 17 and 18 connected in parallel to 1 operate as loads.

The oscillating circuit 26 is controlled by the lighting control device 20, so that the oscillating frequency of the high-frequency inverter 12 is such that the capacitors 13, 1 constituting the LC series resonance circuit.
When the resonance frequency is controlled to be a resonance frequency determined by the capacitances of the capacitors 7 and 18 and the inductance of the choke coil 14 and the secondary winding of the pulse transformer 21, the capacitance of the capacitor 13 arranged in parallel with the discharge lamp 15 is controlled. A sine wave voltage (resonance voltage) is generated at both ends, and the lamp voltage also becomes a sine wave.

The inductance component of the choke coil 14 becomes an inductance that limits the lamp current when the discharge lamp 15 is turned on. Further, the capacitor 13 is charged with electric charge while the FET 22 is on and the FET 23 is off, and conversely, the FET 22 is off and the FET 2 is
3 has a function of maintaining the lighting of the discharge lamp 15 by discharging the electric charge during the ON period.

The capacitors 17 and 18 form a series resonance circuit with the capacitor 13 and the choke coil 14, and also circulate the high voltage pulse generated by the starting pulse generator 16 to protect the high frequency inverter 12. It also has a function.

Here, the starting pulse generator 16 includes a pulse transformer 21, a FET 27 which is a switching element,
A flyback that is generated at both ends of the primary winding of the pulse transformer 21 when the FET 27 connected in series with the primary winding of the pulse transformer 21 is turned on at high speed after being turned on. The voltage is boosted via the pulse transformer 21 and applied to the discharge lamp 15 as a high voltage pulse.

The operation of the discharge lamp lighting device having the above configuration will be described. When power is supplied to the lighting device, a start signal is first sent from the lighting control device 20 to the DC power supply 11, the DC power supply 11 operates, and the output voltage thereof is supplied to the high frequency inverter 12. At the same time, the oscillation circuit 26 that constitutes the high-frequency inverter 12 starts to oscillate, and the FETs 22, 2
The drive circuits 24 and 25 for driving 3 respectively operate, and the FETs 22 and 23 repeat 0N-0FF in mutually opposite phases.

In the series inverter of this embodiment, the FE
The output power is supplied from the DC power supply 11 to the load in the subsequent stage only when T22 is turned on, and the supplied power is maximum when the ON duty of the FET 22 is maximum (50%). It should be noted that the FETs 22 and 23 are controlled so that one of them is turned on except for a minimum mutual pause period for avoiding simultaneous ON.

When the high frequency inverter 12 is driven, until the discharge lamp 15 is lit, the load of the high frequency inverter 12 is the capacitor 13, the choke coil 14,
There is an LC series resonance circuit that forms a closed loop composed of the capacitors 17 and 18, and a resonance voltage is generated across the capacitors 17 and 18. This resonance voltage corresponds to the output open voltage of the high frequency inverter 12 supplied to the discharge lamp 15, and the higher the ON duty of the FET 22, the higher the resonance voltage.

From the lighting control device 20, an activation signal is further sent to the oscillation control circuit 28 which constitutes the activation pulse generator 16, and the oscillation control circuit 28 issues a gate signal to generate the F signal.
Turn ET27 on and off.

The FET 27 forms a closed loop with the DC power supply 11 via the primary winding of the pulse transformer 21. Therefore, the FET 27 is turned on and the OF is suddenly changed.
Then, at the moment when the FET 27 is turned off at high speed due to the inductance of the primary winding of the pulse transformer 21, a flyback voltage is generated across the primary winding of the pulse transformer 21. This voltage is further boosted by the pulse transformer 21, and a high voltage pulse is supplied to the discharge lamp 15 so as to establish conduction between the main electrodes of the discharge lamp 15.

When the main electrodes of the discharge lamp 15 are electrically connected, that is, when the discharge lamp 15 is activated, a lamp current flows to the detection resistor 29, and a potential difference is generated across the detection resistor 29 whose one side is grounded. The detection device 19 detects this, and the lighting control device 20 to which the detection signal is sent determines that the discharge lamp 15 is turned on, and sends a signal to the oscillation control circuit 28 constituting the starting pulse generation device 16 to start up. Stop pulse generation. The impedance of the detection resistor 29 is extremely small and does not affect the lighting state of the discharge lamp 15.

When the discharge lamp 15 is activated, the lamp voltage drops sharply. After that, as the gas pressure in the arc tube of the lamp rises, the lamp voltage gradually increases to reach the rated lighting. In the present embodiment, the detection device 19 has a voltage corresponding to the lamp voltage, that is, the secondary winding of the pulse transformer 21, the discharge lamp 15, and the detection resistor 29. The voltage generated at both ends of 18 is divided by a capacitor, that is, the voltage at the connection point between the capacitors 17 and 18 is detected, and a detection signal is sent to the lighting control device 20.

The lighting control device 20 sends a control signal to the oscillating circuit 26 which constitutes the high frequency inverter 12 in response to the detection signal to turn on the duty of the FETs 22 and 23.
And the oscillation frequency is changed to control the lighting of the discharge lamp 15.

In this embodiment, when the discharge lamp 15 is started, an arc spot is formed at the tip of the electrodes after the main electrodes are electrically connected to each other, and the glow discharge is transferred to the arc discharge to form a discharge arc. The lighting control device 20 controls the O of the FET 22 so that sufficient energy can be supplied for the process performed, that is, the process until the initial lighting is completed.
A control signal is sent to the oscillation circuit 26 to increase the N duty, and the output voltage of the high-frequency inverter 12 is made higher than that at the rated lighting.

When the lighting control device 20 detects the start-up of the discharge lamp 15, the lighting control device 20 maximizes the output voltage of the high-frequency inverter 12 in order to supply the starting current to the discharge lamp 15. That is, the ON duty of the FET 22 is expanded to the maximum value of 50%.

As a result, it is possible to supply a larger starting current to the discharge lamp 15 than during rated lighting, while maintaining a constant lighting frequency, that is, a resonance frequency. However, the lighting frequency at this time is a resonance frequency determined by the parallel load circuit connected to the high frequency inverter 12, including the inductance component of the secondary winding of the pulse transformer 21 connected in series to the discharge lamp 15. Shall match. Therefore, during this period, the lamp current waveform changes while maintaining a substantially sine wave.

However, the lamp current control in a wide range, especially when the ratio of the lamp current at the time of supplying the maximum starting current to the rated lighting is required to be several times or more, the control is performed only by changing the ON duty of the FET 22. Is extremely difficult to achieve.

Therefore, in the present embodiment, when the maximum starting current is supplied, the ON frequency control of the FET 22 and the oscillation frequency control of the high frequency inverter 12 are combined. That is, by lowering the oscillation frequency of the high frequency inverter 12, the impedance of the choke coil 14 that is the lamp current limiting element and the secondary winding of the pulse transformer 21 is reduced, and a large starting current is supplied to the discharge lamp 15. It is possible. In the present embodiment, the oscillating frequency of the high frequency inverter 12 is about 10 [kHz] at the time of rated lighting, while the oscillating frequency is about 4.2 [kHz when supplying the maximum starting current immediately after the start.
z] and the lamp current is supplied to the discharge lamp 15 about eight times as much as the rated lamp current.

After the maximum starting current is supplied to the discharge lamp 15,
In accordance with the voltage generated at the connection point between the capacitors 17 and 18 detected by the detection device 19, the high frequency inverter 12 is gradually added.
Of the oscillation circuit 2 from the lighting control device 20 in order to increase the oscillation frequency of the
A control signal is sent to 6. As a result, the oscillating frequency of the high frequency inverter 12 gradually rises, and eventually reaches the oscillating frequency at the rated lighting of about 10 [kHz]. In this embodiment, the lamp current of about 0.9 [A] can still be supplied at this point.

In the present embodiment, the lamp current at the rated lighting is about 0.4 [A]. Therefore, in order to perform the rated lighting of the discharge lamp 15, it is necessary to further limit the lamp current thereafter. Therefore, in the present embodiment, the oscillation frequency of the high frequency inverter 12 is fixed to about 10 [kHz] and the ON duty of the FET 22 is gradually narrowed, so that the lamp current reaches about 0.4 [A] at the rated lighting. Restrict.

FIG. 2 shows the above lamp current control method. In FIG. 2, a portion surrounded by a dotted line is an equivalent circuit of a main part. It should be noted that the FETs 22 and 23 are turned on in opposite phases.
Since it is turned off, the FET 22 is turned on during the starting current supply period.
Widening the duty is equivalent to narrowing the ON duty of the FET 23. Further, the lamp current is continuously controlled in all the periods in the series of controls.

According to the lamp current control system of the present invention, the lamp current is limited by performing the duty control of the switching element forming the high frequency inverter 12 in the rated lighting state of the lamp, so that the normal series is performed. A choke coil 1 which is a lamp current limiting element, as compared with the case where the lamp current is controlled by the inverter method.
It is possible to reduce the inductance that 4 has. Therefore, miniaturization of the choke coil 14 can be realized.

Since the duty control of the switching elements is combined, a sufficiently large starting current can be supplied to the lamp even if the frequency control range is narrowed.

Further, as in claim 2, at the end of the starting current supply period, that is, near the rated lighting region, the oscillation frequency of the high frequency inverter 12 is fixed at about 10 [kHz].
By performing the lamp current control only by controlling the duty of the switching element, it is possible to avoid the occurrence of the acoustic resonance phenomenon near the rated lighting region. This is because, according to this control method, the lamp current waveform becomes a sine wave having almost no distortion in the vicinity of the rated lighting region and does not include a harmonic component. This also means that if there is a variation in the lamp characteristics of the lighting target, the lighting frequency does not change during the delicate lamp current adjustment in the vicinity of the rated lighting region, and the occurrence of acoustic resonance can be avoided. Is especially effective at.

In the present embodiment, the lamp current is controlled by detecting the voltage generated at the connection point of the capacitors 17 and 18 which is the voltage corresponding to the lamp voltage, but the voltage detection point is the capacitors 17 and 18. It doesn't matter at both ends. Also,
In the present embodiment, the lamp current was controlled by detecting the voltage corresponding to the lamp voltage, but the lamp current may be detected in addition to this, and other characteristics relating to the lamp characteristics such as the elapsed time after the lamp is turned off. It is possible to control the lamp current by means of. Further, in the present embodiment, the lamp current flowing through the detection resistor 29 is detected as a means for detecting activation / lighting of the discharge lamp 15. Others may be used as long as they are related to the lamp characteristics that can confirm the lighting. Further, although the series inverter is applied as the high frequency inverter in this embodiment, any other inverter such as a half bridge inverter can be used as long as it can fulfill the same function. Further, although the FET is used as the switching element in this embodiment, a bipolar transistor or the like may be used.

Next, control methods of different embodiments will be described. The configuration diagram of the discharge lamp lighting device according to the present embodiment is common to FIG. The difference of the present embodiment from the former is the lamp current control method, which is characterized by the method of detecting the voltage corresponding to the lamp voltage. As in this embodiment, the pulse transformer 21 for supplying the starting voltage to the discharge lamp 15 is
When connected in series to the discharge lamp 15 and connected in parallel with the capacitors 17 and 18 that maintain the resonance of the lighting circuit, the lamp voltage monotonically increases in the starting current supply period after the discharge lamp 15 is lit. The detection voltage at the connection point between the capacitors 17 and 18, which is the voltage corresponding to the lamp voltage, does not monotonically increase.

That is, as shown in FIG. 3, the discharge lamp 1
After turning on 5, the ON duty of the FET 22 is maximized, the oscillation frequency of the high-frequency inverter 12 is lowered to supply the maximum starting current, and the detected voltage shows the maximum value during the lamp lighting period. After that, in the period in which the lamp current is gradually limited, the detection voltage gradually decreases as the lamp current decreases. However, when the lamp current is further reduced, the detected voltage starts increasing at a certain inflection point. Therefore, if the lamp current is set to be controlled according to the detection voltage, there may be a plurality of lamp currents to be set for a certain detection voltage, which is inconvenient. Note that this effect is more remarkable as the secondary winding of the pulse transformer 21 has a larger inductance. The dotted line frame in FIG. 3 is an equivalent circuit of the main part.

Therefore, in the present embodiment, when there are a plurality of lamp currents to be set for a certain detection voltage, when the voltage at the connection point of the capacitors 17 and 18 is detected, it is compared with the detection voltage before and after the detection time. Then, it is determined whether the lamp being lit is at the beginning or the end of the lamp current control period, and the lamp current to be set is determined accordingly.

That is, when the detected voltage is in the process of decreasing, it is determined that it is in the beginning of the lamp current control period, and the lamp current to be set is set to the higher set value, that is, A. If it is in the process of increasing, it is determined that it is at the end of the lamp current control period, and the lamp current to be set is set to the lower set value, that is, B.

In this way, by determining the detected voltage and whether the detected voltage is in the increasing process or the decreasing process, the lamp current to be set is uniquely determined in all the lighting periods. It becomes possible to control the lamp current continuously.

[0040]

With the above structure, during the starting current supply period,
By combining frequency control and PWM control,
A current limiting element with a small inductance is used to achieve a fast rise of the luminous flux even in a narrow frequency control range, minimizing the distortion of the lamp current while avoiding the occurrence of acoustic resonance phenomenon, and continuously maintaining the lamp current in a wide range. A controllable discharge lamp lighting device can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a discharge lamp lighting device according to an embodiment of the present invention.

FIG. 2 is a lamp current voltage control diagram in the device.

FIG. 3 is a lamp current voltage control diagram in the device.

[Explanation of symbols]

11 power supply 12 high frequency inverter 13 capacitors 14 choke coil 15 discharge lamp 16 Starting pulse generator 17 Capacitor 18 capacitors 19 Detector 20 Lighting control device 21 pulse transformer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masataka Ozawa             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Kazutaka Koyama             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd.

Claims (4)

[Claims] 1. A direct current power supply, a high frequency inverter driven by the direct current power supply to oscillate, a resonance circuit comprising a series circuit of a choke coil and a capacitor connected to an output end of the high frequency inverter, the choke coil and a capacitor. A series circuit consisting of a discharge lamp and a pulse transformer connected to the connection point of, a start pulse generator connected so as to apply a high voltage pulse to the discharge lamp via the pulse transformer, and characteristics relating to lamp characteristics. A discharge lamp lighting device comprising: a detection device for detecting; and a lighting control device for controlling lighting of the discharge lamp by changing an oscillation frequency and a duty ratio of the high frequency inverter according to an output signal of the detection device. 2. The discharge lamp lighting device according to claim 1, wherein the oscillation frequency of the high frequency inverter is changed during the starting current supply period, and the duty ratio of the high frequency inverter is changed near the rated lighting region to control the lighting of the discharge lamp. . 3. The detection device detects a voltage corresponding to a lamp voltage during lighting, and changes an oscillation frequency and a duty ratio of a high frequency inverter according to an output signal of the detection device to control lighting of a discharge lamp. The discharge lamp lighting device described. 4. The lighting of a discharge lamp is controlled by determining whether the voltage corresponding to the detected lamp voltage is in the process of increasing or decreasing, and changing the oscillation frequency and the duty ratio of the high frequency inverter by this determination signal. The discharge lamp lighting device according to claim 3.