JP2001237093A - Electric discharge lamp lighting equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a non-lighting because of incorrect-detection of a voltage in a shape of a peak impressed to an electric discharge light at the time of low-temperature starting. SOLUTION: In the equipment which makes electric discharge lamp turn on with a half bridge inverter circuit of a self-excitation type driven by a voltage smoothed to flat in a manner of filling up a valley of a rectification output of an alternate current power supply, a frequency variable means to gradually reduce frequency from the frequency f1 at the time of preheating to the frequency f3 at the time of stable lighting, through the frequency f2 at the time of starting is provided with by making a frequency of switching variable by restricting the drive signal of at least one of switching elements in a direction where ON time is shortened in the predetermined time after the power supply is turned on. And a protection means to restrict an output when a detected lamp voltage is higher than a predetermined value and also a means to switch a control of immediately after the starting time to almost the same control of the stable lighting time by instantly shifting a frequency from the frequency f2 at the time of starting to the frequency f3 at the time of stable lighting.

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 apparatus for lighting a discharge lamp at a high frequency with a commercial power supply as an input.

[0002]

2. Description of the Related Art FIG. 2 shows a circuit diagram of a conventional example. The main circuit configuration is the same as that of Japanese Patent Application No. 10-270418. Less than,
The circuit configuration will be described. The anode of the diode D6 and one end of the capacitor C4 are connected to the positive output terminal of the rectifier circuit DB (bridge circuit of the diodes D1 to D4) via the anode and the cathode of the diode D5. The other end of the capacitor C4 is a leakage transformer T2
And the respective primary windings of the drive transformer CT are connected to a connection point between the switching elements Q1 and Q2. A capacitor C6 is connected in parallel to both ends of the diode D6. Between the cathode of the diode D6 and the negative output terminal of the rectifier circuit DB, a series circuit of the switching elements Q1 and Q2 and a valley filling power supply circuit (smoothing capacitors C3, diodes D8, D9, and a capacitor C7) are connected in parallel. I have. Each of the switching elements Q1 and Q2 is composed of a MOSFET having a built-in parasitic anti-parallel diode.
Between the sources, the secondary windings n1 and n2 of the driving transformer CT
Are connected via resistors R3 and R4, respectively.
An anti-series circuit of zener diodes ZD1 and ZD2 for overvoltage prevention and an anti-series circuit of ZD3 and ZD4 are connected in parallel.

A discharge lamp La1 is connected to the secondary winding output of the leakage transformer T2, and a resonance capacitor C5 is connected in parallel between the non-power supply terminals of the filament of the discharge lamp La1. One end of the Emiless detection winding T22 provided on the secondary side of the leakage transformer T2 is connected to the ground line, and the other end is input to the Vla detection protection means 2 via the diode D10. The output of the Vla detection protection means 2 is connected to the gate of the switching element Q2 together with the output of the frequency variable means 1,
The ON time width of the switching element Q2 can be controlled. Resistance R1, capacitor C8, trigger diode Q
3, the resistor R2 and the diode D7 constitute a start-up circuit.

The operation of this conventional example will be described below. The inverter circuit is of a self-excited drive type, and outputs a signal generated on the secondary side of the drive transformer CT to the switching element Q1,
The switching element Q1 is supplied to the switching element Q2 to turn on and off the switching elements Q1 and Q2 alternately. Hereinafter, a series of operations will be described.

First, when the power is turned on, the starting circuit charges the capacitor C8 via the resistor R1, and when the voltage Vc8 of the capacitor C8 exceeds the trigger voltage of the trigger diode Q3, a drive signal is sent to the switching element Q2. Input and start oscillation. When the oscillation starts, the electric charge of the capacitor C8 is changed to the resistance R when the switching element Q2 is turned on.
2. Since the voltage is discharged via the diode D7, the voltage Vc8 of the capacitor C8 becomes lower than the trigger voltage of the trigger diode Q3, and no drive signal is input from the capacitor C8.

When the switching element Q2 is on (the switching element Q1 is off), the capacitors C7 to C6 → capacitor C4 → resonance load circuit (leakage transformer T2, lamp La1, capacitor C5) →
When a resonance current flows through the path from the drive transformer CT to the switching element Q2, and the sum of the voltage of the capacitor C6 and the output voltage of the rectifier circuit DB is balanced with the voltage of the capacitor C7, the diode D5 from the input side → the capacitor C4 → the resonance load circuit. (Leakage transformer T2, lamp La1, capacitor C5) → resonance current flows through the path of drive transformer CT → switching element Q2, and at the same time, input current flows.

When the switching element Q2 is off (the switching element Q1 is on), a regenerative current mode is set,
Regenerative current is supplied from leakage transformer T2 to drive transformer C
T → parasitic diode of switching element Q1 → capacitor C7 → rectifier circuit DB → diode D5 → capacitor C
It flows in the route of 4. At this time, the input current also flows.

When the switching element Q2 is turned off (the switching element Q1 is turned on) and the regenerative current stops flowing, the capacitor C6 is switched from the capacitor C6 to the switching element Q1.
A resonance current flows through a path from the drive transformer CT to the resonance load circuit (leakage transformer T2, lamp La1, capacitor C5), and when the switching element Q2 is turned on, the charge stored in the capacitor C6 is released, and the charge of the capacitor C6 becomes zero. Then, the resonance current flows from the capacitor C4 through the path of the diode D6 → the switching element Q1 → the drive transformer CT → the resonance load circuit (leakage transformer T2, lamp La1, capacitor C5).

When the switching element Q2 is on (the switching element Q1 is off), a regenerative current mode is set,
A regenerative current flows from the leakage transformer T2 through the path of the capacitor C4 → the diode D6 → the capacitor C7 → the parasitic diode of the switching element Q2 → the drive transformer CT.

[0010] By repeating these series of operations, high-frequency power is supplied to the load. At the same time, in a part of the operation mode, by flowing an input current proportional to the input voltage from the AC power supply Vs, the current can be waveform-shaped by the filter circuit F to obtain a sinusoidal input current. it can. Therefore, it is possible to improve the input power factor and the input current distortion.

In the valley filling power supply circuit, when the switching element Q2 is turned on, a current flows from the power supply through the path of the capacitor C3 → the diode D8 → the leakage transformer T2 → the driving transformer CT → the switching element Q2, so that the capacitor C3 is charged. And smoothed with a voltage lower than the peak value of the output of the rectifier circuit. Further, during a period in which the rectified output voltage is lower than the voltage of the capacitor C3, the capacitor C3
Power is supplied to the inverter circuit via the diode D9.

In this conventional example, a frequency variable means 1 for changing the oscillation frequency is provided in order to change the lamp La1 from starting to stable lighting. Further, as a means for protecting against circuit stress at the end of lamp life, the lamp voltage Vla
And Vla detection protection means 2 for intermittently oscillating the inverter when the detected value is equal to or more than a predetermined value. This Vl
The a detection protection means 2 stops the detection operation so that the protection operation is not erroneously performed by the application of the starting voltage until the AC power supply Vs is turned on and the lamp La1 is started.

[0013]

In the prior art, the lamp L
a1 is provided with a frequency variable means 1 for changing the oscillation frequency in order to make the lamp a stable lighting from the start.
After a1 starts after passing through the preheating state, the oscillation frequency of the inverter changes to the frequency at the time of rated lighting, but immediately after starting, the inverter operates at a higher frequency than at the time of rated lighting. Therefore, in particular, immediately after the start at the time of the low temperature start, as shown in FIG. 3, a peak voltage may be generated as the lamp voltage Vla during a period when the power supply voltage Vdc of the inverter is low. In FIG. 3, Vs is an AC voltage input from a commercial AC power supply, Vdc is an output voltage of a valley filling power supply circuit which is a power supply voltage of an inverter, and Vla is an envelope of a lamp voltage. As described above, when a peak voltage is generated in the lamp voltage Vla, the Vla detection protection means 2 sets the lamp voltage Vla.
Since the inverter performs the intermittent oscillating operation by detecting the rise of la, there is a problem that the lamp is turned off immediately after starting at a low temperature.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to prevent a voltage applied to both ends of a discharge lamp from being erroneously detected at a low temperature start, thereby preventing the discharge lamp from being turned off. It is to provide a discharge lamp lighting device capable of doing so.

[0015]

According to the discharge lamp lighting device of the present invention, in order to solve the above problems, as shown in FIG. 2, a rectifier circuit DB connected to an AC power supply Vs and a rectifier circuit DB A smoothing capacitor C3 arranged on the output side of the DB and charged with a DC voltage, and a switching element Q1, which is turned on and off alternately so as to convert the DC voltage into a high-frequency voltage.
A series circuit of Q2, a load circuit including a discharge lamp load La1 and an LC resonance circuit (capacitor C5, leakage transformer T2) and supplied with a high-frequency current by switching;
A means (drive transformer CT) for self-excitingly driving the switching elements Q1 and Q2, and a predetermined time after the power is turned on, by limiting a driving signal of at least one of the switching elements Q2 in a direction in which the on-time is shortened, so that the switching frequency And a frequency varying means 1 for gradually decreasing the frequency from the frequency f1 at the time of preheating to the frequency f3 at the time of stable lighting through the frequency f2 at the time of starting, and when the lamp voltage Vla is detected and is higher than a predetermined value. And a protection means 2 for limiting the output, and the DC voltage Vdc applied to the series circuit of the switching elements Q1 and Q2 is lower near the zero cross of the AC power supply Vs than near the peak as shown in FIG. In a discharge lamp lighting device, as shown in FIG.
Immediately after starting, means for switching to control that is substantially the same as control during stable lighting is provided.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 is a diagram illustrating the operation of Embodiment 1 of the present invention. The circuit configuration of the present embodiment is the same as the conventional example shown in FIG. In the circuit of FIG. 2, the frequency is changed by the frequency variable means 1 in order to make the lamp light from a start to a stable lighting. Further, as protection means against circuit stress at the end of lamp life, there is provided Vla detection protection means 2 for detecting the lamp voltage and operating the inverter intermittently when the voltage is equal to or higher than a predetermined value.

The operation of the circuit will be described with reference to FIG.
The dotted line in FIG. 1 indicates the resonance characteristics of the output voltage before the lamp is turned on, and the solid line indicates the resonance characteristics of the output voltage when the lamp is turned on. Since it is necessary to preheat the lamp after the power is turned on by the frequency variable means 1, the oscillation frequency of the inverter is set to an operating point (frequency f1) higher than that during stable lighting. After preheating the lamp filament,
The frequency is changed from f1 to f2 to make the lamp start lighting.
→ Continuously shifting to f3. In the meantime, the output voltage shifts from the operating point a → b → c → d shown in FIG. Preheated at operating point a, the lamp starts at operating point b,
The lamp is turned on at the operating point c, and the lamp is stably turned on at the operating point d. Here, since the frequency is continuously changed, at the time of lighting at the frequency of f2, the frequency is higher than f3 which is the frequency at the time of stable lighting.
Then, the lamp voltage is different from the rated lighting. Conventional examples are
The protection circuit is stopped between f1 and f3, and f1 to f3
In contrast, in the present embodiment, the frequency is changed instantaneously from f2 to f3, while the frequency is continuously changed during the period 3. Therefore, the frequency may be higher immediately after starting than in the stable lighting. Thus, the period during which the lamp voltage becomes high is also eliminated, and malfunctions can be prevented when the lamp is unstable immediately after starting.

In this embodiment, the means for switching the frequency immediately after the lamp is turned on is shown. However, it is needless to say that the same effect can be obtained by switching the duty of the switching element to achieve stable lighting.

(Embodiment 2) FIG. 4 is a circuit diagram of a control circuit section according to Embodiment 2 of the present invention. The configuration of the main circuit is the same as that of FIG. 2; terminal G in the figure is the ground line of the main circuit (the negative output terminal of the rectifier circuit DB); terminal g is the gate of the switching element Q2; Each is connected to a cathode. In this embodiment, a preheating circuit 3 and a starting voltage clamp circuit 4 are provided as the frequency variable means 1 in FIG. 2, and an Emiless detection circuit 5, a latch circuit 6, an intermittent oscillation circuit as the Vla detection protection means 2 in FIG. 7 is provided. Further, a frequency switching circuit 8 is provided for instantaneously switching the frequency f2 → f3 in FIG.

First, the configuration of the preheating circuit 3 will be described. A resistor R5, a diode D11, capacitors C10 and C11 are provided between the gate and the source of the switching element Q2.
Are connected in series. A diode D12 is connected in parallel in the reverse direction to the series circuit of the diode D11 and the capacitor C10, and a diode D13 is connected in parallel to both ends of the capacitor C11 in a direction opposite to the charging direction of the capacitor C11. The voltage of the capacitor C11 is
The voltage is applied between the base and the emitter of the transistor Q4 via the resistor R6. The gate of the switching element Q2
A series circuit of a diode D14 and a transistor Q4 is connected in parallel between the sources.

Hereinafter, the operation of the preheating circuit 3 connected to the gate circuit of the switching element Q2 will be described. When the inverter starts oscillating, the gate voltage of the switching element Q2 is changed from the resistance R5 to the diode D11 to the capacitor C
10 → integrated along the path of the capacitor C11, and the transistor Q4 is turned on after a predetermined time determined by the time constant of the resistor R5 and the capacitor C11.
The second gate signal is extracted. Here, when the switching element Q2 is off (the switching element Q1 is on), the electric charge of the capacitor C11 is stored in the drive transformer CT.
Capacitor C11 and diode D
12, the resistor R5, the resistor R4, the secondary winding n2 of the driving transformer CT, and a discharge through the ground line. When the voltage of the capacitor C11 becomes 0, the diode D13 turns on, so that the voltage of the capacitor C11 is maintained at 0.
Therefore, the capacitor C11 is connected to the switching element Q2
When the voltage of the capacitor C11 reaches a predetermined voltage again from the time when the gate drive signal is generated, the transistor Q4 is turned on to forcibly extract the gate drive signal of the switching element Q2. Thereby, while the switching element Q2 is self-excited,
This is a so-called self-excited / non-excited system in which the ON time is limited by the time constant circuit of the resistor R5 and the capacitor C11.

As time elapses after the power is turned on, electric charge is gradually stored in the capacitor C10, and the DC voltage is maintained. Therefore, the charging speed of the capacitor C11 is gradually reduced. Will not work. In other words, when the capacitor C10 is charged until it becomes substantially equal to the peak value of the gate voltage, no current flows through the time constant circuit of the resistor R5 and the capacitor C11, so that the gate signal of the switching element Q2 is not extracted. As the capacitor C10 is charged, the on-duty of the switching element Q2 approaches the on-duty at startup. With the change (sweep) of the on-duty of the switching element Q2, the operating frequency changes in the direction of decreasing, the voltage across the lamp increases, and the lamp starts up soon. Thus, after the power is turned on,
Until a predetermined voltage is stored in the capacitor C10,
The preheating start control of the load is performed by a sweep method in which the ON width of the switching element Q2 gradually widens.

Next, the configuration and operation of the starting voltage clamp circuit 4 will be described. Timer condenser C for preheating sweep
10, a discharge resistor R8 and a transistor Q5 are connected to both ends, a secondary winding T22 is provided in a leakage transformer T2 as a resonance inductance, and the high-frequency output voltage is detected by a diode D10 and resistors R10 and R11. When the detection voltage at both ends exceeds a predetermined value, the Zener diode ZD5 turns on and the transistor Q5
Turn on. Then, since the voltage of the capacitor C10 is maintained so as not to exceed a predetermined value, the switching element Q2
Is turned on, the time until the transistor Q4 turns on is substantially constant. That is, since the on-duty of the switching element Q2 is kept substantially constant and the preheating sweep is fixed, the oscillation voltage applied to both ends of the lamp (hereinafter, referred to as the “oscillation voltage”).
(Referred to as a starting voltage) does not exceed a predetermined value.

When the AC power supply Vs is turned on and the starting circuit starts oscillating, the preheating circuit 3 starts preheating sweep, and the starting voltage clamp circuit 4 applies a predetermined starting voltage to the load. Here, the period from the start of oscillation to the end of the preheating sweep is referred to as a preheating mode, and the period in which the starting voltage is clamped is referred to as a starting mode.

Next, the Emiless detection circuit 5 will be described. One end of the secondary winding T22 provided in the leakage transformer T2 is connected to the ground line, and the other end is connected to the anode terminal of the diode D10. A series circuit of resistors R12 and R13 is connected between the cathode terminal of the diode D10 and the ground line.
A resistor C is connected to a resistor R13 via a diode D17.
13 and the resistor R14 are connected in parallel. Capacitor C
A DC voltage proportional to a voltage applied to both ends of the lamp La1 is obtained at both ends of the lamp 13.

Next, the latch circuit 6 will be described. A series circuit of a transistor Q6 and a resistor R17 is connected to both ends of the capacitor C13 of the Emiless detection circuit 5 via a diode D18 and a resistor R15. In this circuit, a capacitor C17 is connected in parallel, and a series circuit of a resistor R16 and a transistor Q7 is connected in parallel. The resistors R16 and R17 are connected to the transistors Q6 and Q7, respectively.
, And capacitors C16 and C15 are connected in parallel, respectively. The capacitor C14 is connected in parallel with the capacitor C15. The capacitor C15 is connected in parallel to the capacitor C13 via the Zener diode ZD6. Resistance R1
5, a diode D19 is connected in parallel in the illustrated direction.

Next, the operation of the Emiless detection circuit 5 will be described. A voltage proportional to the voltage across the lamp La1 is detected by a detection winding T22 connected to the secondary side of the leakage transformer T2. This voltage is applied to the diode D10
The voltage is converted into a DC voltage by performing voltage division and smoothing by the resistors R12 and R13 and the capacitor C13, and the Emiless state is detected. When the lamp La1 enters the emiless state, the potential of the capacitor C13 rises, and when the voltage exceeds the voltage of the Zener diode ZD6, the transistor C7 is turned on from the capacitor C13 via the Zener diode ZD6. Then, a current flows from the capacitor C13 through the diode D18 → the resistor R15 → between the emitter and the base of the transistor Q6 → between the collector and the emitter of the transistor Q7, and at the same time, the capacitor C13 →
A current flows through a path between the diode D18, the resistor R15, the emitter-collector of the transistor Q6, and the base-emitter of the transistor Q7. Therefore, the latch circuit 6
Transistors Q6 and Q7 are both turned on,
Since the charge of the capacitor C10 of the preheating circuit 3 is extracted through the resistor R9 and the diodes D15 and D13, and the gate drive signal of the switching element Q2 is extracted through the diode D16 of the intermittent oscillation circuit 7, the oscillation of the inverter circuit is stopped. Then, when the electric charge of the capacitor C13 gradually decreases, the driving power supply for the transistors Q6 and Q7 disappears, and when the transistors Q6 and Q7 are turned off, the switching element Q2 is turned on again by the starting circuit and oscillation starts. That is, when the load is in the Emiless state, the intermittent oscillation control is performed. Usually, the lamp is turned on before the voltage Vc13 of the capacitor C13 of the Emiless detection circuit 5 reaches a predetermined voltage, so that the intermittent oscillation operation does not occur.

The feature of this embodiment is that a frequency switching circuit 8 composed of a Zener diode ZDa, a resistor Ra, and a transistor Qa is added. The operation of the present embodiment will be described with reference to FIG. In the circuit of FIG. 4, after the power is turned on (in FIG. 5, the frequency decreases from f1), the capacitor C10 of the preheating circuit 3 is charged. When the output voltage reaches a constant voltage, the capacitor C10 is kept at a constant voltage by the starting clamp circuit 4 (the frequency is kept constant at f2 during the clamp period in FIG. 5). Since the voltage drops and is no longer clamped, the capacitor C10 is further charged. now,
When the voltage of the Zener diode ZDa is set to a point higher than the potential of the point A in the clamp period, the Zener diode ZDa turns on immediately after the lamp is turned on. When the Zener diode ZDa turns on, the transistor Qa turns on and the transistor Q4 turns off.
No other control is performed on T, and the frequency immediately becomes the frequency f3 at the time of rated lighting.

Therefore, as shown in FIG. 5, when the potential at the point A exceeds the threshold value of the Zener diode ZDa,
The lamp current Ila increases to the rated current, and the lamp voltage Vl
Since a decreases, there is no unstable lighting when the lamp voltage is high immediately after starting as shown in the conventional example (see FIG. 3), and no erroneous detection occurs.

(Embodiment 3) FIG. 6 is a circuit diagram of a control circuit section according to Embodiment 3 of the present invention. The circuit configuration other than the frequency switching circuit 8 is almost the same as that of the second embodiment, and the description of the circuit operation is omitted. This embodiment is different from the second embodiment in that resistors Ra, Rb, Rc, Rd, transistor Q
The point is that a frequency switching circuit 8 composed of a and Qb is used.

The operation of this embodiment will be described with reference to FIG. In the circuit shown in FIG. 6, when the lamp is under a light load such as preheating or starting after the power is turned on, the output power is smaller than the input power. Therefore, the voltage between both ends of the capacitor C7 (Vdc in FIG. Increase. Therefore, when the power is turned on, the voltage Vdc across the capacitor C7, which is the power source of the inverter, instantaneously increases. Thereafter, the frequency decreases, the output voltage reaches the starting voltage, and when the lamp is turned on, the voltage Vdc across the capacitor C7, which is the power supply of the inverter, gradually decreases. In the present embodiment, the voltage Vdc across the capacitor C7, which is the power source of the inverter,
While the potential at point B, which is obtained by dividing the resistance of the transistor Q is equal to or higher than the threshold value of the transistor Qa, the transistor Qa is turned on and the transistor Qb is turned off. By turning on the transistor Qb and turning off the transistor Q4, the switching element Q2 is not separately controlled, and the frequency becomes the frequency f3 at the time of rated lighting. Therefore, as shown in FIG. 7, when the potential at the point B falls below the threshold value of the transistor Qa, the lamp current Ila increases to the rated current and the lamp voltage Vla decreases. Immediately after the lamp voltage is high, there is no unstable lighting, and no erroneous detection occurs.

(Embodiment 4) FIG. 8 is a circuit diagram of a control circuit section according to Embodiment 4 of the present invention. Since the circuit configuration other than the frequency switching circuit 8 is almost the same as that of the second embodiment, the description of the circuit operation is omitted. This embodiment is different from the second embodiment in that resistors Ra, Rb, Rc, Rd, Re, a transistor Qa,
The point is that a frequency switching circuit 8 including Qb, diode Da, and capacitor Ca is used. The resistor Re is inserted in series between the source terminal of the switching element Q2 of the inverter and the ground line G to detect a resonance current.

The operation of this embodiment will be described with reference to FIG. In the circuit shown in FIG. 8, when the lamp is under a light load such as preheating or starting after the power is turned on, the output power is smaller than the input power, so that the resonance current of the inverter increases. Therefore, when the power is turned on, the voltage across the resistor Re detecting the resonance current instantaneously increases. Thereafter, the frequency decreases, the output voltage reaches the starting voltage, and when the lamp is turned on, the voltage across the resistor Re gradually decreases.

In this embodiment, while the voltage at the point C obtained by dividing the voltage between both ends of the resistor Re for detecting the resonance current is equal to or higher than the threshold value of the transistor Qa, the transistor Qa
Is turned on and the transistor Qb is turned off, but when the potential at the point C falls below the threshold value of the transistor Qa, the transistor Qb is turned on and the transistor Q4 is turned off, thereby controlling the switching element Q2. And the frequency becomes the frequency f3 at the time of rated lighting.
Therefore, as shown in FIG. 9, when the potential at the point C falls below the threshold value of the transistor Qa, the lamp current Ila increases to the rated current and the lamp voltage Vla decreases. Immediately after the lamp voltage is high, there is no unstable lighting, and no erroneous detection occurs.

(Embodiment 5) FIG. 10 is a circuit diagram of a control circuit section according to Embodiment 5 of the present invention. Since the circuit configuration other than the frequency switching circuit 8 is almost the same as that of the second embodiment, the description of the circuit operation is omitted. This embodiment is different from the second embodiment in that resistors Ra, Rb, Rc, Rd, transistors Qa, Qb,
The point is that the frequency switching circuit 8 including the auxiliary winding T23 of the leakage transformer T2, the capacitor Ca, and the diode Da is used. Auxiliary winding T of leakage transformer T2
Reference numeral 23 denotes a winding added to the leakage transformer T2 constituting the load circuit of the main circuit.
2 is detected on the primary side.

The operation of this embodiment will be described with reference to FIG. In the circuit of FIG. 10, when the lamp is under a light load such as preheating or starting after the power is turned on, the output power is smaller than the input power, so that the power supply voltage and the resonance current of the inverter increase. Therefore, when the power is turned on, the voltage across the primary side of the leakage transformer T2 instantaneously increases. Thereafter, when the frequency decreases, the output voltage reaches the starting voltage, and the lamp is turned on, the voltage across the primary side of the leakage transformer T2 gradually decreases. In the present embodiment, while the voltage at point D obtained by dividing the voltage across the auxiliary winding T23, which detects the voltage across the primary side of the leakage transformer T2, is equal to or higher than the threshold value of the transistor Qa, the transistor Q2 is turned on.
a is turned on and the transistor Qb is turned off, but when the potential at the point D falls below the threshold value of the transistor Qa, the transistor Qb is turned on and the transistor Q4 is turned off to control the switching element Q2. And the frequency becomes the frequency f3 at the time of rated lighting. Therefore, as shown in FIG. 11, when the potential at the point D falls below the threshold value of the transistor Qa, the lamp current Ila
Since the lamp current increases to the rated current and the lamp voltage Vla decreases, there is no unstable lighting when the lamp voltage is high immediately after starting as described in the conventional example, and no erroneous detection occurs.

(Embodiment 6) FIG. 12 is a circuit diagram of a control circuit section according to Embodiment 6 of the present invention. Since the circuit configuration other than the frequency switching circuit 8 is almost the same as that of the second embodiment, the description of the circuit operation is omitted. This embodiment is different from the second embodiment in that resistors Ra, Rb, Rc, Rd, transistors Qa, Qb,
The point is that a frequency switching circuit 8 composed of Qc and a capacitor Ca is used. In the figure, a terminal P is connected to a positive output terminal of the rectifier circuit DB of FIG.

The circuit shown in FIG. 12 includes a capacitor Ca and a resistor R
In order to lower the base potential of the transistor Qa when the lamp is turned on and the lamp voltage is slightly reduced by the differentiating circuit constituted by d, the transistor Qa is kept turned on after the power is turned on, the lamp is turned on, and the lamp voltage is turned on. Is slightly reduced, the transistor Qa turns off. At this time, since the transistor Q4 is turned off by the latch circuit including the transistors Qb and Qc and the resistors Rb and Rc, the switching element Q2 is no longer controlled and the frequency becomes the frequency at the time of rated lighting. Therefore, instantly,
Since the lamp voltage Vla decreases, there is no unstable lighting when the lamp voltage is high immediately after starting as shown in the conventional example, and no erroneous detection occurs.

[0039]

According to the present invention, a rectifier circuit connected to an AC power supply, a smoothing capacitor disposed on the output side of the rectifier circuit and charged with a DC voltage, and a DC voltage converted to a high-frequency voltage are provided. A series circuit of switching elements that are alternately turned on and off, a load circuit that includes a discharge lamp load and an LC resonance circuit and that is supplied with a high-frequency current by switching, a means for self-exciting the switching elements, and a predetermined circuit after power-on. The switching time is variable by limiting the drive signal of at least one of the switching elements in a direction in which the on-time is reduced, and the frequency gradually increases from the frequency at the time of preheating to the frequency at the time of stable lighting through the frequency at the time of starting. And a protection means for detecting the lamp voltage and limiting the output when it is higher than a predetermined value, wherein the switch Lamp device in which the DC voltage applied to the series circuit of the switching elements is lower than near the peak of the AC power supply near the zero crossing, is provided with means for switching to control that is substantially the same as control during stable lighting immediately after starting. Therefore, there is no longer a period in which the lamp voltage is higher than that during stable lighting immediately after the start, and an effect of preventing a malfunction when the lamp is unstable immediately after the start of the lamp can be prevented.

[Brief description of the drawings]

FIG. 1 is an operation explanatory diagram of Embodiment 1 of the present invention.

FIG. 2 is a circuit diagram of a conventional discharge lamp lighting device.

FIG. 3 is an operation waveform diagram for explaining a problem of the conventional discharge lamp lighting device.

FIG. 4 is a circuit diagram according to a second embodiment of the present invention.

FIG. 5 is an operation explanatory diagram of Embodiment 2 of the present invention.

FIG. 6 is a circuit diagram according to a third embodiment of the present invention.

FIG. 7 is an operation explanatory view of Embodiment 3 of the present invention.

FIG. 8 is a circuit diagram according to a fourth embodiment of the present invention.

FIG. 9 is an operation explanatory view of Embodiment 4 of the present invention.

FIG. 10 is a circuit diagram according to a fifth embodiment of the present invention.

FIG. 11 is an operation explanatory view of Embodiment 5 of the present invention.

FIG. 12 is a circuit diagram according to a sixth embodiment of the present invention.

[Explanation of symbols]

 f1 Preheating frequency f2 Starting frequency f3 Stable lighting frequency

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiya Kamsha 1048 Kazuma Kadoma, Kadoma City, Osaka, Japan Matsushita Electric Works, Ltd. Inventor Shigeru Well 1048 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term (reference) 3K072 AC03 BA01 BB01 CA16 DB09 DC06 EA06 EB01 EB05 EB09 GB11 HA06

Claims (8)

[Claims] 1. A rectifier circuit connected to an AC power supply, a smoothing capacitor disposed on an output side of the rectifier circuit and charged with a DC voltage, and turned on and off alternately so as to convert the DC voltage into a high-frequency voltage. A series circuit of switching elements, a load circuit including a discharge lamp load and an LC resonance circuit and supplied with high-frequency current by switching, a means for self-excitingly driving the switching elements, and a predetermined time after power-on for at least one of the switching. The switching frequency is made variable by restricting the drive signal of the element in the direction that shortens the on-time, and the frequency is gradually reduced from the frequency at preheating to the frequency at stable lighting through the frequency at start-up. Variable means, and protection means for detecting the lamp voltage and limiting the output when the voltage is higher than a predetermined value, wherein a series circuit of the switching elements is provided. In a discharge lamp lighting device in which the DC voltage applied to the discharge lamp is lower than near the peak near the zero crossing of the AC power supply, means for switching to control that is substantially the same as control during stable lighting immediately after starting is provided. Discharge lamp lighting device. 2. The discharge lamp lighting device according to claim 1, further comprising means for switching the switching frequency immediately after the start to make the control substantially the same as the control at the time of stable lighting. 3. The discharge lamp lighting device according to claim 1, further comprising means for switching the duty of the switching element immediately after starting to make the control substantially the same as the control during stable lighting. 4. The method according to claim 1, wherein
A discharge lamp lighting device, comprising means for detecting a power supply voltage of an inverter as means for detecting lighting immediately after starting. 5. The method according to claim 1, wherein
A discharge lamp lighting device comprising: means for detecting a voltage between both ends of a switching element as means for detecting lighting immediately after starting. 6. The method according to claim 1, wherein
A discharge lamp lighting device comprising means for detecting resonance current of an inverter as means for detecting lighting immediately after starting. 7. The method according to claim 1, wherein
A discharge lamp lighting device comprising, as means for detecting lighting immediately after starting, means for detecting a change in lamp voltage connected to a load. 8. The method according to claim 1, wherein
A discharge lamp lighting device comprising, as means for detecting lighting immediately after starting, means for detecting a voltage of a timer capacitor of a control means for shifting from a frequency at the time of starting to a frequency at a time of stable lighting.