JPH0850994A - Lighting device for electric discharge lamp - Google Patents

Abstract

PURPOSE:To stably retain a lighting state even when power voltage is decreased down to below discharge voltage for an electric discharge lamp by increasing a preheating frequency on detecting a decrease in voltage and by activating thermionic emission from the electric discharge lamp. CONSTITUTION:A voltage decrease detecting circuit 31 is operated when DC output voltage VDC from an AC/DC inverting circuit 8 is decreased to around discharge voltage for an electric discharge lamp 9. A resistor R32 is connected in parallel with a resistor R26b on a preheating timer circuit 26 to decrease charging voltage for a capacitor C26. A transistor Tr26 on the circuit 26 is, therefore, lead to an off state to set collector voltage to VDC, resulting in sending operating instructions 26S to a preheating frequency switching circuit 24, and increasing the entire light-lighting frequency of a modulated light controlling circuit 20S to preheating frequency. Thus flickering due to a decrease in voltage or troubles due to lights-off are eliminated to stably retain lighting by switching an oscillating frequency to the preheating frequency through the preheating timer circuit on decreasing power voltage and by activating thermoelectron emission from an electric discharge lamp.

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 including an inverter circuit for lighting a discharge lamp at a high frequency, and in particular, a discharge lamp provided with means for preventing the discharge lamp from being turned off due to a decrease in power supply voltage. Regarding lighting device.

[0002]

2. Description of the Related Art FIG. 3 is a simplified connection diagram showing a conventional discharge lamp lighting device. A half-bridge inverter circuit 1 for converting an output DC voltage of an AC / DC conversion circuit 8 into a high frequency AC voltage V ₁ and outputting the converted high frequency AC voltage V 1 is shown. The switching elements 2 and 3 are composed of a pair of MOSFETs. In addition, a capacitor 6 is provided on the output side of the half bridge inverter circuit 1.
A pair of filaments of the discharge lamp 9 is connected via a (capacitance C ₀ ) and a reactor 4 (inductance L), and a capacitor 5 (capacitance C) is connected between the pair of filaments to form a discharge lamp circuit 7 as a load. Is configured.

Further, the half bridge inverter circuit 1
ON / OFF control of a pair of switching elements 2 and 3 alternately
Control the DC voltage to the high frequency AC voltage V₁Drive times to convert to
Path 10 is connected to the control terminals of switching elements 2 and 3.
Pulse transformer 12 to which a pair of secondary windings 12S is connected
And a driving I whose output side is connected to the primary winding 12P
And C11. Resistance R_13,Capacitor C_13,Oh
And constant voltage diode D ₁₃Receives a stabilized power supply voltage at
The driving IC 11 that operates in accordance with₁Oscillation
Dimmer 11A that determines the frequency, and oscillation frequency of the dimmer
Drive unit 11B that generates a drive voltage corresponding to the number
In the figure, the final stage of the drive unit 11B is alternately turned on and off.
Not composed of a pair of transistors,
Connected to the primary winding of the pulse transformer 12,
The midpoint of the line is connected to the regulated power supply. Also, the light control unit 11
A is a resistor R as an external circuit_{twenty one,}Variable resistance VR_{twenty one,}And
And capacitor C_{twenty one}The dimming control circuit 20 is configured to include
For example, the all-light lighting frequency ff, which is the reference, is determined.
It

When the discharge lamp 9 is turned on, the filament preheating, all-light lighting, and dimming lighting are generally controlled by changing the frequency, and the frequency is the resonance frequency of the discharge lamp circuit. _0, filament preheat frequency f _p, total light lighting frequency ff, dimming lighting frequency f _d
, The center frequency is f _p = 100 kHz _, f ₀ = 8 so that the condition f _p > f ₀ > f _d > ff is satisfied.
_{0~90kH Z, f d = 82kH Z} , ff = 56kH Z, is set to. The control of the oscillation frequency of the driving IC 11 is performed by a resistor R _21, which determines the total light lighting frequency ff as a reference frequency _.
This is performed by the frequency switching circuit 24 provided in parallel with the series circuit of the VR ₂₁ . In the case of the figure, the frequency switching circuit 24 is composed of a series circuit of a preheating frequency setting resistor R ₂₄ and a transistor switch T _r24 (preheating switch) _whose collector is connected in series to the preheating frequency setting resistor R ₂₄ (in addition to this, a dimming frequency not shown). A series circuit of setting resistance and changeover switch is provided).

The operation of the transistor switch T _r24 is performed by a preheat timer circuit 26 provided on the output side of the AC / DC converting circuit 8. The preheat timer circuit 26 has resistors R _26a, R
A capacitor C ₂₆ which is charged by the divided DC voltage with a resistor divider consisting of _26b, includes a transistor switch T _r26 which operates by receiving the base-side charging voltage of the capacitor C ₂₆ through a constant voltage diode D _26, Capacitor C ₂₆
The charging voltage rises to a voltage equivalent to the sum of the breakdown voltage of D ₂₆ and the base voltage of T _r26 , and the voltage corresponding to the output DC voltage of the AC / DC converter circuit 8 is frequency-switched for a certain period of time until T _r26 is turned on. Output to the circuit 24. Therefore, the transistor switch T _r24 of the frequency switching circuit 24 for a certain period of time is turned on, and the preheating frequency setting resistor R _{24 is} set.
Is connected in parallel to the series circuit of the resistors R _{21 and} VR ₂₁ , the oscillation frequency of the driving IC rises to the preheating frequency f _p with the above fixed time as the preheating period.

The operation of lighting the discharge lamp lighting device thus constructed is as follows.
Since the charging of the capacitor C ₂₆ of the preheat timer circuit 26 is started and the operation command 26 _S is output to the preheat frequency switching circuit 24 for a certain time until the transistor switch T _r26 is turned on, the transistor switch T _r24 (preheat switch ) Is turned on, and the preheating frequency setting resistor R
Connected in parallel with the series circuit of a resistor R _21, VR ₂₁ and _24. Therefore, the oscillation frequency of the light control section 11A of the drive IC 11 becomes the preheating frequency f _p , and the drive signal having the preheating frequency f _p is output from the driving section 11B. The pulse transformer 12 that receives this drive signal in the primary winding 12P operates in an alternating current manner, and an in-phase alternating current signal is generated in the secondary winding.
By applying two AC signals to the switching elements 2 and 3 so as to have mutually opposite phases, the switching elements 2 and 3 are alternately turned on and off, and the high-frequency AC voltage V ₁ of the preheating frequency f _p includes the discharge lamp 9. The residual heat of the filament is started by the high frequency AC voltage having the residual heat frequency f _p applied to the circuit 7. When the temperature of the filament rises, the thermoelectron emission of the discharge lamp 9 is activated and it becomes easier to light the lamp, so that the preheat period ends, the transistor switch T _r26 turns on, and the transistor switch T _r24 turns off. By switching the frequency of the AC voltage V _{1 to} the all-light lighting frequency ff, the impedance of the discharge lamp circuit is lowered and the discharge current (lamp current) easily flows, and then the all-light lighting frequency ff is maintained and stabilized. All light operation is maintained.

[0007]

In the conventional discharge lamp lighting device, while the discharge lamp has a substantially constant discharge voltage in the lighting state, its power source converts the AC voltage of the low voltage distribution line into a DC voltage. Since it is received from the AC-DC converter circuit, the DC voltage fluctuates as the distribution voltage fluctuates, and sometimes the DC voltage drops below the discharge voltage of the discharge lamp, causing flicker in the illuminance of the discharge lamp. In addition, a situation occurs in which the discharge lamp cannot be maintained in the lighting state and is turned off. Also, if the discharge lamp goes off due to a drop in the power supply voltage, it is necessary to perform the lighting operation again when the power supply voltage returns to the specified level. Since there is no means for doing so, there is a problem in that the light must be repeatedly turned on.

An object of the present invention is to provide a discharge lamp lighting device capable of stably maintaining the lighting state even when the power supply voltage drops below the discharge voltage of the discharge lamp.

[0009]

In order to solve the above-mentioned problems, according to the present invention, a half-bridge inverter circuit for converting an output DC voltage of an AC / DC converting circuit into a high-frequency AC voltage and supplying it to a discharge lamp circuit. , A drive circuit for alternately turning on and off a pair of switching elements of this half-bridge inverter circuit, and a dimming control for outputting to the drive circuit a frequency signal corresponding to an all-lighting frequency lower than the resonance frequency of the discharge lamp circuit. With a circuit,
A preheating timer circuit that detects the generation of the DC voltage and issues an operation command for a fixed time, and controls the oscillation frequency of the dimming control circuit to a preheating frequency that is higher than the resonance frequency of the discharge lamp circuit in response to the operation command. The preheat frequency switching circuit detects this when the DC voltage drops near the discharge voltage of the discharge lamp while the discharge lamp is lighting, and instructs the preheat frequency switching circuit to switch to the preheat frequency via the preheat timer circuit. It is assumed that the lighting stabilization means is composed of a voltage drop detection circuit that operates.

The voltage drop detection circuit includes a voltage divider that divides a DC voltage, a first transistor switch that is turned off when the divided DC voltage falls below a threshold of the base voltage, and a base of the collector. The second transistor which is connected and turns on when the first transistor switch is turned off
And the collector of the second transistor switch is connected to the preheat timer circuit via a resistor.

The preheat timer circuit has a voltage divider for dividing a DC voltage, a capacitor charged by the divided DC voltage, a base connected to an intermediate point of the voltage divider via a constant voltage diode, and a collector resistor. With a transistor switch that receives a DC voltage between the collector and emitter,
The collector may be connected to a preheating frequency switching circuit and the intermediate point may be connected to a voltage drop detection circuit.

The preheating frequency switching circuit is provided with a series circuit of a transistor switch which is turned on by an operation command from the preheating timer circuit and a frequency setting resistor connected to the collector side of the transistor switch. It is preferable that the all-lighting frequency setting resistor is connected in parallel.

[0013]

In the first aspect of the invention, when the DC voltage drops near the discharge voltage of the discharge lamp while the discharge lamp is lit, the voltage drop detection circuit detects this, and the preheat frequency switching circuit sends the preheat frequency to the preheat frequency via the preheat timer circuit. Since the lighting stabilization means is configured to instruct the switching of the discharge lamp, the detection level of the voltage drop of the voltage drop detection circuit is set to a voltage slightly higher than the discharge voltage of the discharge lamp to prevent the discharge lamp from being turned off. Since the frequency of the high frequency AC voltage output from the half bridge inverter can be switched to a preheating frequency higher than the full lighting frequency to activate thermionic emission of the discharge lamp, if the high frequency AC voltage subsequently drops below the discharge voltage of the discharge lamp. Also maintains the lighting state of the discharge lamp, and the voltage drop detection circuit detects that the power supply voltage has recovered to the specified level and automatically switches to the all-optical lighting frequency. Since the ability to maintain the lighting state of the discharge lamp stably obtained.

Further, specifically, by configuring the voltage drop detection circuit as invention 2, the preheat timer circuit as invention 3, and the preheat frequency switching circuit as invention 4, it is originally provided for the lighting operation of the discharge lamp. The preheating timer circuit and the preheating frequency switching circuit are temporarily driven by the voltage drop detection circuit that detects a voltage drop, and the function of switching the full lighting frequency to a higher preheating frequency and stabilizing the lighting state can be obtained.

[0015]

EXAMPLES The present invention will be described below based on examples.
FIG. 1 is a schematic diagram showing a discharge lamp lighting device according to the present invention in a simplified manner, and FIG. 2 is a connection diagram showing a discharge lamp lighting device according to an embodiment of the present invention. Since the member has the same function as that of the conventional example, the description thereof will be omitted. In FIG. 1, a half-bridge inverter circuit 1 for converting the output DC voltage V _DC of the AC-DC converter circuit 8 into a high-frequency AC voltage V _AC and supplying it to the discharge lamp circuit 7, and a pair of switching elements 2 of this half-bridge inverter circuit.
The driving circuit 10 for alternately controlling ON and OFF of 3 and 3, and the all-light lighting frequency f lower than the resonance frequency f ₀ of the discharge lamp circuit 7.
In the discharge lamp lighting device provided with the dimming control circuit 20 which outputs the frequency signal corresponding to f to the drive circuit 10, the preheating for detecting the generation of the DC voltage V _DC and issuing the operation command 26 _S for a certain period of time. The oscillation frequency of the timer circuit 26 and the dimming control circuit 20 for a certain period of time in response to the operation command is set to the discharge lamp circuit 7
Preheating frequency switching circuit 24 for switching and controlling to a preheating frequency f _p higher than the resonance frequency f _{0 of the} above, and when the DC voltage V _DC drops near the discharge voltage of the discharge lamp while the discharge lamp 9 is lighting, this is detected and preheating is performed. The lighting stabilization means 30 is provided with a voltage drop detection circuit 31 for instructing the preheating frequency switching circuit 24 to switch to the preheating frequency f _p via the timer circuit 26.

As shown in FIG. 2, the voltage drop detecting circuit 31 divides the DC voltage V _DC by resistors R _{30a and} R _30b , and the divided DC voltage drops below the threshold of the base voltage. A second transistor switch T _r31 which is turned off at this time and a second transistor switch T ₃₂ which is turned on when the first transistor switch is turned off by connecting the base to the collector of the second transistor switch T _r31 ; It is configured to connect the collector of the transistor switch to the preheat timer circuit 26 via a resistor R ₃₂ . Further, the preheating timer circuit 26 and the preheating frequency switching circuit 24 use the conventional preheating timer circuit 26 and the preheating frequency switching circuit 24 which are provided for preheating the filament of the discharge lamp 9 during the lighting operation of the discharge lamp lighting device. And a resistor R ₃₂ of the voltage drop detection circuit 31.
Is connected to the intermediate connection point of the resistance voltage dividers R _{26a and} R _26b of the preheating timer circuit 26, thereby forming the lighting stabilizing means 30.

Discharge lamp according to the embodiment having the above-described structure
In the lighting device, the output DC voltage V of the AC / DC converter circuit_DCBut
Voltage drop detection when the discharge voltage of the discharge lamp 9 is sufficiently higher
First transistor switch T of circuit 31_r31Is on
State, the second transistor switch T_r32Is off
Therefore, the voltage drop detection circuit 31 affects the preheat timer circuit 26.
Doesn't sound. Therefore, turning on the AC / DC conversion circuit 8 will
The thermal timer circuit 26 has a DC voltage V_DCTo detect resistance R
_26a, R_26bThe voltage divided by₂₆Applied to
Capacitor C to start charging.₂₆Charging voltage is D
₂₆Breakdown voltage and T _r26Voltage equivalent to the sum of the base voltages of
Rise to T_r26AC / DC conversion for a certain period of time before turning on
Frequency switching of the voltage corresponding to the output DC voltage of the circuit 8
It will be output to the circuit 24.
Preheat switch T of the wave number switching circuit 24_r24Is on
And the preheating frequency setting resistor R_{twenty four}The total light lighting frequency ff
Resistance R that determines_{twenty one,}VR_{twenty one}Parallel to the series circuit of
Connecting. As a result, the oscillation frequency of the dimming control circuit 20 is
Preheating frequency f_pAnd the preheating of the filament of the discharge lamp 9
Is started.

On the other hand, a direct current is applied during lighting at the all-light lighting frequency ff.
Voltage V_DCWhen the voltage drops to near the discharge voltage of the discharge lamp 9,
This voltage drop is determined by the first transition of the voltage drop detection circuit 31.
Star switch T_r31Is the base threshold (V_f) With
It is detected by comparison and changes to the off state.
Second transistor switch T_r32Turns on
Therefore, the voltage dividing resistor R of the preheat timer circuit 26_26bParallel to
Resistance R₃₂Is connected to capacitor C₂₆Charge voltage is low
Down. Therefore, the capacitor C₂₆Charging voltage is D₂₆Descending
Breakdown voltage and T_r26Below the voltage equivalent to the sum of the base voltages of
Resistance R ₃₂If you set the resistance value of
V_DCDuring the period when the voltage drops below the discharge voltage of the discharge lamp 9
_r26Will remain in the off state.
T like Koke_r26The collector voltage of the DC voltage V_DCOn
Ascend, operation command 26_STo the preheating frequency switching circuit 24
To output. Further, the preheating frequency switching circuit 24
Is the operation command 26_SPreheat switch T_r24
Turns on and the preheating frequency setting resistor R_{twenty four}All lights around
Resistance R that determines the wave number ff_{twenty one}And variable resistor VR_{twenty four}Series of
Since it is connected in parallel to the path, the dimming control circuit 20
Vibration frequency is preheating frequency f_pRise to. In addition, voltage drop
First transistor switch T of detection circuit 31_r31But
Set the voltage to be slightly higher than the discharge voltage of the discharge lamp
If this is done, the discharge lamp will turn off due to the drop in DC voltage.
Since it can be controlled to switch to the preheating frequency before, half block
All points of the output high frequency AC voltage of the ridge inverter
Switching to a preheating frequency higher than the lamp frequency,
The high frequency AC voltage is activated by the discharge of the discharge lamp.
Maintains the lighting state of the discharge lamp even when the voltage drops below the electrical voltage
Discharge lamp due to the drop in power supply voltage
You can keep the lighting state stable by eliminating the lights off and flicker
The advantages that can be obtained are obtained. It also reduces the power supply voltage
Detection circuit detects and switches to all-optical mortgage frequency ff
Convenience to eliminate re-lighting operation as it is controlled automatically
Is obtained. Furthermore, the lighting stabilizing means 30 can be operated for lighting.
Required preheat timer circuit 26 and preheat frequency switching
The voltage drop detection circuit 31 is added to the circuit 24.
This stabilizes the lighting state by adding a simple circuit.
The advantage that can be obtained is obtained.

[0019]

As described above, according to the present invention, when the DC voltage drops near the discharge voltage of the discharge lamp while the discharge lamp is lit, this is detected by the voltage drop detection circuit, and the preheat frequency is supplied via the preheat timer circuit. The switching circuit is provided with lighting stabilizing means for instructing switching to the preheating frequency. As a result, before the discharge lamp goes out due to the voltage drop, it is possible to switch to a preheating frequency higher than the full lighting frequency, activate thermionic emission of the discharge lamp, and maintain the lighting state of the discharge lamp. Even if the AC voltage drops below the discharge voltage of the discharge lamp, the lighting state of the discharge lamp can be maintained in a stable manner. It is possible to provide a discharge lamp lighting device having a function of eliminating the above disadvantages and maintaining a stable lighting state.

Further, since the illuminance of the discharge lamp is automatically restored when the power supply voltage is restored to a steady state, it is possible to eliminate the trouble of re-doing the lighting operation, and it is necessary for the preheating operation of the filament of the conventional discharge lamp. By using a preheat timer circuit and a preheat frequency switching circuit, and simply changing the circuit to add a voltage drop detection circuit, the lighting stabilizing means can be configured. Therefore, a simple and stable lighting state can be achieved. There is an advantage that the obtained discharge lamp lighting device can be economically advantageously provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a simplified discharge lamp lighting device according to the present invention.

FIG. 2 is a connection diagram showing a discharge lamp lighting device according to an embodiment of the present invention.

FIG. 3 is a connection diagram showing a simplified conventional discharge lamp lighting device.

[Explanation of symbols]

1 Half Bridge Inverter Circuit 2 Switching Element 3 Switching Element 4 Reactor 5 Capacitor 7 Discharge Lamp Circuit 8 AC / DC Converter Circuit 9 Discharge Lamp 10 Driving Circuit 11 Driving IC 12 Pulse Transformer 20 Dimming Control Circuit 24 Frequency Switching Circuit 26 Preheating Timer Circuit 30 lighting stabilizing means 31 voltage detection circuit V _DC DC voltage (power source voltage) V _AC high-frequency alternating voltage f _p preheat frequency f ₀ the resonance frequency of the discharge lamp circuit (no lighting) ff full lighting frequency T _r24 preheating switch R ₂₄ preheat frequency Setting resistor T _r31 1st transistor switch T _r32 2nd transistor switch

Claims (4)

[Claims] 1. A half-bridge inverter circuit for converting an output DC voltage of an AC-DC converter circuit into a high-frequency AC voltage and supplying it to a discharge lamp circuit, and a drive circuit for alternately controlling ON / OFF of a pair of switching elements of the half-bridge inverter circuit. And a dimming control circuit that outputs a frequency signal corresponding to an all-lighting frequency lower than the resonance frequency of the discharge lamp circuit to a drive circuit, and detects the generation of the DC voltage for a certain period of time. A preheat timer circuit that issues an operation command, a preheat frequency switching circuit that controls the oscillation frequency of the dimming control circuit to a preheat frequency that is higher than the resonance frequency of the discharge lamp circuit in response to the operation command, and the discharge lamp is lighting. When the DC voltage drops near the discharge voltage of the discharge lamp, it is detected and the preheat frequency is switched off via the preheat timer circuit. The discharge lamp lighting apparatus characterized in that it comprises a lighting stabilizing means consisting of a voltage drop detecting circuit for instructing switching to the preheat frequency to the modified circuit. 2. A voltage divider for dividing a DC voltage by a voltage drop detecting circuit, a first transistor switch which is turned off when the divided DC voltage drops below a threshold of a base voltage, and its collector. A second transistor which is turned on when the base is connected and the first transistor switch is in an off state
2. The discharge lamp lighting device according to claim 1, further comprising a transistor switch of claim 2, wherein the collector of the second transistor switch is connected to a preheat timer circuit via a resistor. 3. A preheating timer circuit divides a DC voltage, a voltage divider, a capacitor charged by the divided DC voltage, a base connected to an intermediate point of the voltage divider via a constant voltage diode, and a collector resistance. And a transistor switch that receives a DC voltage between the collector and the emitter via
The discharge lamp lighting device according to claim 1 or 2, wherein the collector is connected to a preheating frequency switching circuit and the intermediate point is connected to a voltage drop detecting circuit. 4. A preheating frequency switching circuit is provided with a series circuit of a transistor switch that is turned on by an operation command from the preheating timer circuit and a frequency setting resistor connected to the collector side of the transistor switch, and the series circuit is dimming control. The discharge lamp lighting device according to claim 1 or 3, wherein the discharge lamp lighting device is connected in parallel to the all-light lighting frequency setting resistor of the circuit.