JP2617459B2 - Discharge lamp lighting device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a discharge lamp lighting device for lighting a discharge lamp using an inverter circuit whose oscillation frequency is variable.

(Background Art) FIG. 5 is a circuit diagram showing a basic configuration of a discharge lamp lighting device using an inverter circuit. At both ends of the DC power supply E, a series circuit of switching elements Q ₁ and Q ₂ and capacitors C ₁ and C ₁ ′
Are connected in parallel. Diodes D ₁ and D ₂ are connected in anti-parallel to switching elements Q ₁ and Q ₂ , respectively. A load circuit is connected between a connection point between the switching elements Q ₁ and Q _{2 and} a connection point between the capacitors C ₁ and C ₁ ′. The load circuit, the capacitor C ₂ for preheating the non-power supply side is connected to the series circuit of the parallel connected discharge lamp l and the inductance L, the load circuit is generally designed to exhibit an inductive reactance I have. Discharge lamp l
The capacitor C ₂ and the inductance L connected to the non-power supply side of an LC resonant circuit, to generate a high voltage across the discharge lamp l by utilizing the resonance circuit, starting and sustaining a discharge lamp l It is what is being done.

2. Description of the Related Art Conventionally, when a discharge lamp is turned on, a method of applying a high voltage and then turning on the filament after sufficiently heating the bipolar filament has been widely used because the life of the discharge lamp is extended. In the conventional example, as shown in FIG. 6 (a), during the preheating time t ₁ is oscillating the inverter circuit lowered below the lighting voltage across the voltage Vc ₂ of the capacitor C ₂ at the frequency f ₁ Te sufficiently preheated filament of the lamp l release, after a preheating time t ₁ is to oscillate the inverter circuit at the frequency f _2, and higher than the operating voltage of the voltage across Vc ₂ of the capacitor C _2, the discharge lamp 1 is started.

Figure 6 (b) shows the current Ic ₂ flowing through the capacitor C _2, the (c) shows the current Il flowing through the discharge lamp l. FIG (d) shows a current waveform flowing through the switching element in the preheating time t _1, FIG. (E) is flowing through the switching element at the time t ₂ to the discharge lamp l is lit by applying a high voltage 4 shows a current waveform. FIG. 3F shows a current waveform flowing through the switching element after the discharge lamp 1 is turned on. FIG.
3 shows the relationship between the voltage Vc ₂ generated at both ends of the capacitor C ₂ and the oscillation frequency f.

As shown in FIG. 6 (a), and after elapse of the preheating time t _1, changing the frequency from f ₁ to f _2. In this case in order to generate a high voltage to the capacitor C _2, it is often lower than the natural vibration frequency f ₀ of the oscillation frequency f ₂ the inductance L and the capacitor C _2. In addition, in order to obtain a predetermined discharge lamp current at the time of lighting, f ₂ <f ₀ is almost always satisfied. In this case, during a period from switching the frequency to the discharge lamp l is lit, the shorter the time t ₂ the case, the leading phase current as shown in FIG. (E) flows through the switching element, the simultaneous ON state Surge current flows. Particularly when the power supply voltage E is low, the effective value of the current is large, the surge current is also large, and the ASO
There is a problem such as exceeding the area (safe operation area).

As another conventional example, a lighting method like a soft start as shown in FIG. 7 has also been proposed. The circuit configuration in this case is the same as the circuit in FIG. FIG. 7 (a)
The oscillation frequency f is indicative of the temporal change of gradually lowering the frequency over time, a control system for changing up to a frequency f ₂ which is obtained a predetermined current during lighting.
In this case, the temporal changes of the current Ic ₂ flowing through the capacitor C ₂ and the current Il flowing through the discharge lamp 1 are shown in FIG.
(D).

In this prior art example, as can be seen from the resonance characteristic curve shown in FIG. 7 (b), during the oscillation frequency f up to the frequency f ₂ is gradually lowered from the frequency f _1, always a resonance point f ₀ Therefore, the discharge lamp 1 is turned on by applying a sufficiently high voltage in a state where the current of the switching element is in the slow mode, and the discharge lamp 1 is operated in the fast mode as in the control method shown in FIG. It will not light up.

However, in this case, in order to gradually lower the frequency from a high frequency, a preheating current cannot be obtained in most of the preheating time (the time from when the power is turned on until the discharge lamp l is turned on). A problem arises with the life of the discharge lamp.

(Objects of the Invention) The present invention has been made in view of the above points, and an object of the present invention is to enable a sufficient preheating current to be obtained during a preheating time and to provide an inverter circuit at the time of starting. Another object of the present invention is to provide a discharge lamp lighting device in which a large stress is not applied to the switching element.

(Disclosure of the Invention) In the discharge lamp lighting device according to the present invention, in order to achieve the above object, a series resonance circuit including a resonance inductor and a resonance capacitor is provided in parallel with the resonance capacitor. Including a load circuit consisting of a connected discharge lamp,
In a discharge lamp lighting device for lighting a discharge lamp with an oscillation output of an inverter circuit having a variable oscillation frequency, after oscillating the inverter circuit at a predetermined frequency higher than the natural oscillation frequency of the load circuit for a predetermined time during preheating of the discharge lamp, With the passage of time, the oscillation frequency is higher than the natural oscillation frequency of the load circuit, and is smoothly changed to a lower direction in a range lower than the preheating frequency to start, and smoothly changes to a lighting frequency in a range in which the slow current flows. This is provided with a frequency control unit for performing the control.

FIG. 1A shows the relationship between the temporal change of the oscillation frequency f and the voltage Vc ₂ across the capacitor in the present invention. The circuit configuration in this case is the same as the circuit in FIG. Oscillation frequency f is, during the preheating time t ₁ is the frequency f ₁
In this state, the filament of the discharge lamp 1 is sufficiently preheated, so that the life of the discharge lamp is not impaired. Also, in this example, because of an resonance point f ₀ between the frequency f ₂ at the time of lighting the frequency f ₁ during preheating, the same as the slow mode of the current waveform flowing in the frequency f ₁ to the switching element The lamp is lit in the state of the current waveform, and the current in the phase advance mode stops flowing. FIG. 1 (b),
(C) in respectively the temporal variation of the current Il flowing in the current Ic ₂ and the discharge lamp l flowing through the capacitor C _2.

 Hereinafter, examples of the present invention will be described.

Embodiment 1 FIG. 2 is a circuit diagram of one embodiment of the present invention. In the present embodiment, portions having the same functions as those of the conventional circuit are denoted by the same reference numerals, and redundant description will be omitted. The load circuit, a discharge lamp l of the capacitor C ₂ for preheating the non-power side connected in parallel, an inductance L and a series circuit of a capacitor C ₁ is connected. The capacitance of the capacitor is C ₁ ≫C ₂
, And the natural vibration frequency of the load circuit is substantially determined by the inductance L and the capacitor C _2.

To both ends of the DC power supply E, a control unit power supply circuit composed of a series circuit of a resistor R ₁ and a capacitor C ₃ is connected. The voltage of the capacitor C ₃ is applied to the series circuit of the resistor R ₄ and the Zener diode ZD. The reference voltage generated across the Zener diode ZD is applied to the inverting input terminal of the comparator CP. The voltage of the capacitor C ₅ is applied to the non-inverting input terminal of the comparator CP. Capacitor C ₅ via the transistor Q _4, are charged at the charging voltage of the capacitor C _3. The transistor Q ₄ are, so as to form a current mirror circuit, the transistor Q ₃ is connected. Assuming that the current gain hfe of each of the transistors Q ₃ and Q ₄ is sufficiently large, the current flowing through the transistor Q ₄ becomes the same as the current flowing through the transistor Q ₃ . The transistor Q ₃ is connected to the resistors R ₂ and R
Through a series circuit of ₃ are connected to both ends of the capacitor C _3. Capacitor C ₄ and the transistor Q ₅ is connected in parallel to the resistor R _3. To the base of the transistor Q _5, the resistance R ₆
To the output of the timer circuit 3. The timer circuit 3 is used to set the preheat time, it is the DC power supply E is turned on, since the increase in the charging voltage of the capacitor C _3, and outputs a high level signal for a predetermined time. Accordingly, current flowing through the transistor Q ₃ are predetermined time after power-on is determined by the resistor R _2, then, with increasing charge voltage of the capacitor C _4, gradually decreases, and eventually the resistance R _2, R _The constant value is determined by the series resistance of ₃ . The frequency control unit 4 is configured by the CR circuit.

The voltage across the capacitor C ₅ is No. 2 timers ICTM, 6
No. 7 terminal. This timer ICtm
Is a general-purpose timer IC (NEC µPD15555). As is well known, when the trigger terminal (terminal 2) falls below (1/3) Vcc, it is triggered and the output terminal (terminal 3 not shown) )
Becomes high level, and the discharge terminal (7th terminal) becomes high impedance. When the threshold terminal (terminal 6) becomes (2/3) Vcc, the output terminal (terminal 3) becomes low level, and the discharge terminal (terminal 7) also becomes low level. Therefore, the both ends of the capacitor C ₅ sawtooth wave voltage is generated.
This voltage is compared with the reference voltage by the comparator CP,
A rectangular wave oscillation output is obtained from the comparator CP.

The output of the comparator CP is divided by the D flip-flop FF. The output Q of the D flip-flop FF is NA
The ND gates G ₁ and G ₂ are respectively connected to one input. The output is connected to the data input D. The output of the aforementioned comparator CP is connected to the clock input C. Each time the clock input C rises from a low level to a high level, the output of the D flip-flop FF is inverted, and a square wave having a duty factor of 50% obtained by dividing the output of the comparator CP by half is output from the output Q. can get. On the other hand, the output of the comparator CP
It is connected to the other inputs of the NAND gates G ₁ and G ₂ via G ₃ and G ₄ and a resistor R ₅ . Outputs of the NAND gates G ₂ and G ₁ are input to driving circuits 1 and ₂ of the switching elements Q ₁ and Q ₂ , respectively. Therefore, the drive signals of the switching elements Q ₁ and Q ₂ alternate between a first period in which one is at a high level and the other is at a low level, and a second period in which one is at a low level and the other is at a high level. A signal is present, and between the first and second periods there is a third period during which both outputs are low. During this third period, the switching elements Q ₁ , Q ₂
Is a dead-off time for preventing both of them from being turned on, and may be a short time in consideration of the charge accumulation time of the switching element in the on-state. In the circuit of FIG. Has been determined by

With the above configuration, frequency control as shown in FIG. 1A can be performed. That is, when turning on the DC power source E, a certain time the transistor Q ₅ by the output of the timer circuit 3 is turned on. Accordingly, the oscillation frequency of the inverter circuit, becomes almost stated value by the value of capacitor C ₅ and the resistor R _2, the preheating is carried out at a frequency f _1. Then, when the timer time t ₁ of the timer circuit 3 has passed, the output goes low, the transistor Q ₅ is turned off. Therefore, the charging capacitor C ₄ is gradually its charging voltage reaches the divided voltage of the resistors R _2, R _3. At this time, the oscillation frequency of the inverter circuit from the frequency f ₁ during the above-mentioned preheating, resistors R _2, R
Gradually changing the frequency f ₂ determined by ₃ and the capacitor C _5. During the change of the frequency, the discharge lamp 1 is turned on.

Embodiment 2 FIG. 3 is a circuit diagram of another embodiment of the present invention. In this embodiment, a well-known push-pull circuit is used as an inverter circuit. Oscillation transformer OT for inverter circuit
Consists of a leakage transformer having an intermediate tap in the primary winding, and the switching elements Q ₁ and Q ₂ are turned on alternately, so that an alternating current flows through a load circuit connected to the secondary winding. As the load circuit, the same circuit as that used in the first embodiment is connected, but the leakage inductance of the oscillation transformer OT is used instead of the inductance L.

The control unit of the inverter circuit uses a switching regulator IC (μPC494 manufactured by NEC). The oscillation frequency of the switching regulator for IC5 is a capacitance of the capacitor C ₇ connected to the fifth terminal, determined from the resistance value connected to the sixth terminal. The fourth terminal receives the potential obtained by dividing the reference voltage of the fourteenth terminal by the resistors R ₇ and R ₈ , thereby determining the dead-off time of the switching elements Q ₁ and Q ₂ . The Pin 13 has given high level signal through the resistor R ₁₀ in order to be used for 2 stone. The resistors R ₁₁ and R ₁₂ are used as collector resistors of an open-collector transistor inside the switching regulator IC 5.

The configuration and operation of the frequency control unit 4 used in the present embodiment are the same as those in the first embodiment, and a duplicate description will be omitted.

Embodiment 3 FIG. 4 is a circuit diagram of still another embodiment of the present invention.
This embodiment is an inverter circuit 1 transistor type, are used MOSFET for power as the switching element Q _1. The switching element Q ₁ and the capacitor C ₀ is connected in parallel, through the switching element Q _1, 1 winding of the oscillating transformer OT consisting leakage transformer is connected to a DC power source E. The same load circuit as in the second embodiment is connected to the secondary winding of the oscillation transformer OT. In this case, the reverse current of the switching element Q ₁ is, flows through the MOSFET parasitic diode.

A series circuit of the resistor R ₁ and the capacitor C ₃ is connected to both ends of the DC power supply E, and supplies a power supply voltage Vcc to a drive circuit and a control circuit of the switching element Q ₁ . First, an explanation will be made for a driving circuit of the switching element Q _1. Capacitor
The C _3, the transistor Q ₆ through the resistor R ₁₃ is connected. The collector of the transistor Q _6, the transistor Q _7, Q
Connected to ₈ bases. The emitters of the transistors Q ₇ and Q ₈ are connected through a resistor R ₁₄ , and the transistors Q ₇ and Q ₈
The collectors are connected to both ends of the capacitor C _3, respectively. When the transistor Q ₆ is turned on, since the collector potential drops, the transistor Q ₇ is turned off, a state where the transistor Q ₈ can be turned on, the gate of the switching element Q ₁ is, resistors R _15, via the transistor Q _8, Pulled down to ground level. When the transistor Q ₆ is turned off, because the collector potential rises, transistor Q ₈
But off, the transistor Q ₇ is turned on, the resistor R _14, R _15, R
₁₆ the charging voltage of the capacitor C ₃ is applied to the series circuit of the switching element Q by a divided voltage generated across the resistor R ₁₆
The gate potential of ₁ rises. Thereby, in which the gate of the switching element Q ₁ is are voltage driven.

Next, a description will be given of the control circuit of the switching element Q _1. tm ₁ and tm ₂ are general-purpose timer ICs (μPD15555 manufactured by NEC). Resistors R ₁₇ and R constituting the time constant circuit of timer ICtm _1
18, the power supply voltage Vcc is applied to the series circuit of the capacitor C _8. Connection point of the resistors R ₁₇ and R ₁₈ are connected to the discharge terminal of the timer ICTM ₁ (7 Pin), the resistor R ₁₈ and capacitor C ₈
The connection point is connected to a timer ICTM ₁ threshold terminal (6 Pin) and a trigger terminal (pin 2). Thus, the timer ICTM ₁ operates as an astable multivibrator. The oscillation frequency is determined by the time constants of the resistors R ₁₇ and R ₁₈ and the capacitor C ₈ and the voltage of the control terminal (the fifth terminal). Timer ICTM ₁ output terminal (third terminal) is connected to a timer ICTM ₂ trigger terminal (pin 2).

The power supply voltage Vcc is applied to a series circuit of the resistor R ₁₉ and the capacitor C ₁₀ constituting the time constant circuit of the timer ICtm ₂ . Connection point of the resistors R ₁₉ and capacitor C ₁₀ Timer ICTM ₂
Are connected to the discharge terminal (No. 7 terminal) and the threshold terminal (No. 6 terminal). Control terminal of timer ICtm ₂ (5
Ban terminal) is grounded via a capacitor C _9. Thus, the timer ICTM ₂ operates as a monostable multivibrator. Timer ICTM ₂ output terminal (third terminal) is connected to the base of the transistor Q ₆ in the drive circuit of the switching elements to Q ₁ described above.

The configuration of the frequency control unit 4 is substantially the same as that of the first embodiment. After power since a certain time output of the timer circuit 3 is the transistor Q ₅ at high levels is on, the divided voltage of the parallel circuit of the resistor R _0, R ₃ and the resistor R ₂ is input to the operational amplifier OP , Low impedance by the operational amplifier OP, control terminal of timer ICtm ₁ (5th terminal)
It is input to the oscillation frequency f ₁ during preheating is determined. Monostable multivibrator consisting timer ICTM ₂ is used to determine the OFF period of the switching element Q _1.

Then after the elapse of timer time t ₁ of the timer circuit 3, the transistor Q ₅ is turned off, the capacitor C ₄ is charged through the resistor R _0, the input voltage to the operational amplifier OP, than that in the preheating gradually increases, the oscillation frequency of the timer ICTM ₁ is gradually lowered thereby. This change, the oscillation frequency f ₂ at the time of lighting the oscillation frequency f ₁ during preheating
The transition is smooth.

(Effect of the Invention) As described above, the present invention includes a series resonance circuit including a resonance inductor and a resonance capacitor, and a load circuit including a discharge lamp connected in parallel with the resonance capacitor. In a discharge lamp lighting device using a variable frequency inverter circuit, when the discharge lamp is preheated, the inverter circuit oscillates for a fixed time at a predetermined frequency higher than the natural oscillation frequency of the load circuit, and thereafter, the oscillation frequency is increased with time. Since the starting is performed by changing the load circuit in a direction higher than the natural oscillation frequency of the load circuit and lower than the preheating frequency, and smoothly changing to a lighting frequency in a range in which the slow current flows, during the preheating time. Can obtain a sufficient preheating current, and therefore does not impair the life of the discharge lamp.
Since the frequency changes gradually, the switching element of the inverter circuit is not subjected to excessive stress due to a sudden change in the frequency unlike the conventional example, and the discharge lamp can be started smoothly. .

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the operation of the present invention, FIG. 2 is a circuit diagram of one embodiment of the present invention, FIG. 3 is a circuit diagram of another embodiment of the present invention, and FIG. FIG. 5 is a circuit diagram of a conventional example, FIG. 6 is an operation explanatory diagram of the above example, and FIG. 7 is an operation explanatory diagram of another conventional example. E is a DC power supply, Q ₁ and Q ₂ are switching elements, 1 is a discharge lamp, 3 is a timer circuit, and 4 is a frequency control unit.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hiroyasu Takeuchi 1048 Kadoma Kadoma Matsushita Electric Works Co., Ltd. (72) Inventor Kazuyuki Matsukawa 1048 Kadoma City Kazuma Kadomo Matsushita Electric Works Co., Ltd. (72) Inventor Ataka 1048 Kamon Kadoma City Oaza Kadoma Matsushita Electric Works, Ltd. (56) References JP-A-59-16300 (JP, A) JP-A-62-241295 (JP, A) JP-A-61-296696 (JP, A) Shokai Sho 59-126497 (JP, U)

Claims (1)

(57) [Claims] An oscillation circuit for an inverter circuit having a variable oscillating frequency includes a series resonance circuit including a resonance inductor and a resonance capacitor, and a load circuit including a discharge lamp connected in parallel with the resonance capacitor. In a discharge lamp lighting device for lighting a discharge lamp with an output, after oscillating an inverter circuit at a predetermined frequency higher than a natural oscillation frequency of the load circuit for a predetermined time during preheating of the discharge lamp, the oscillation frequency is increased with time. A frequency control unit is provided that starts by changing the load circuit in a direction higher than the natural oscillation frequency of the load circuit and lower than the preheating frequency in a smoothly lower direction, and smoothly changes to a lighting frequency in a range in which the slow current flows. Discharge lamp lighting device characterized by the above-mentioned.