JP2623872B2 - Discharge lamp lighting device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a discharge lamp lighting device provided with a high frequency generator.

[Conventional technology]

A conventional discharge lamp lighting device provided with a high frequency generator is disclosed, for example, in Japanese Patent Application Laid-Open No. Sho 64-6099.

FIG. 5 is a block circuit diagram showing a conventional example, and FIGS. 6 and 7 are waveform diagrams at the time of operation.

In FIG. 5, 1 is a DC external current of 24 [V], and 2 is a fluorescent tube. A is a boosting unit composed of a DC-DC converter that boosts the voltage to a voltage required to start lighting of the fluorescent tube, and B is a converting unit composed of an inverter circuit that converts DC to AC. In the booster A, 3 is a coil for generating a high voltage,
Is a switching transistor (hereinafter referred to as transistor 4) for interrupting the current flowing through the coil 3, 5 is a control circuit for the transistor 4, 6 is a rectifying diode, and 7 is a smoothing capacitor. Reference numeral 8 denotes a switch for instructing the control circuit 5 to perform an operation. The switch 8 is closed only when the fluorescent lamp is started, and the transistor 4 is turned on at a frequency of about 20 [kHz] according to a signal from the control circuit. Repeat OFF.

Next, in the conversion section B, T is a step-up transformer having a center tap provided on the primary winding, and the fluorescent tube 2 is connected to the secondary side of the step-up transformer T. 9 and 10 are switching transistors, and 11 is a control circuit for controlling the transistors 9 and 10. The hot side line 13 is connected to the center tap of the primary winding of the step-up transformer T, and both ends of the primary winding of the step-up transformer T are connected to transistors 9 and 10, respectively.
Connected to the collector. The emitters of the transistors 9 and 10 are connected to each other, and are connected to the cold line 14 via the current detecting resistor 12. Reference numerals 15 and 16 denote a capacitor and a resistor, respectively, and the capacitor 15 and the resistor 16 constitute a smoothing circuit. The control circuit 11 sends control signals as shown in FIGS. 6A and 6B to the transistors 9 and 10 so that the transistors 9 and 10 are turned on alternately. Also to the control circuit 11 and the voltage V _i obtained by the voltage of the ends of the resistor 12 and smoothing is applied as a feedback voltage, the control circuit 11 control signals a, b High become time in accordance with V _i is configured to automatically vary the T _2. In this case, the control signal a, the fundamental period T ₁ of the b duty ratio since it is fixed and the voltage V _i varies control signals a, b are changed. More specifically, when the specifications of the fluorescent tube 2 are determined at the time of design, an appropriate current to flow through the secondary winding of the step-up transformer T is determined. The control circuit 11 and its feedback loop owes role to determine the pulse width T ₂ to flow a current of appropriate value to the secondary side of the step-up transformer T.

By using the relationship between the value of the secondary current and the value of the primary current of the transformer, the measurement of the secondary current can be substituted by the measurement of the primary current. The average value of the voltage generated across the resistor 12 is substantially proportional to the current flowing through the primary side of the step-up transformer T. As a result, the current flowing through the fluorescent tube 2, that is, the current flowing through the secondary side of the step-up transformer T Can be determined by measuring the voltage across the resistor 12. Therefore, in the control circuit 11, a voltage value generated at both ends of the resistor 12 when an appropriate current flows through the fluorescent tube 2 is preset as a reference voltage, and the control circuit 11 determines that the measured voltage matches the reference voltage. It is configured to adjust the pulse width T ₂ of the constant control signal to.

Next, the operation will be described. First, when power is applied to each part,
The control circuit 11 starts operating first, while the control circuit 5 turns off the transistor 4 and enters a standby state. To start lighting, the switch 8 is closed. When the switch 8 is closed, the forcing circuit 5 starts operating, and the transistor 4 repeats ON and OFF at a high frequency. Then, a high voltage is generated in the coil 3 and a very high DC voltage is generated at the point D.
When the voltage at the point D rises in this manner, the average value of the voltage generated across the resistor 12 also increases, and for example, the output signal a of the control circuit 11 has a waveform as shown in FIG. And the pulse width T ₂ becomes very small. V _EG
Is a voltage between the terminals EG of the step-up transformer T, and the peak value is high at the time of starting. IE is a step-up transformer T
Of the current flowing between the terminals EG of FIG. When a pulse current having a small pulse width and a high peak value flows through the primary side of the step-up transformer T in this way, the secondary side of the step-up transformer T has a very high voltage as shown in FIG. A pulse-like voltage V _IJ indicating a peak value is generated, applied to the fluorescent tube, and discharge starts in the fluorescent tube.

The switch 8 is opened after a lapse of a predetermined time, and the control circuit 5 returns to the standby state. At this time, the transistor 4 remains OFF. Then, at point D, the voltage of the power supply, that is, 24 [V]
Will appear as it is. Since the voltage at point D to change from a very high voltage to 24 [V], a current flowing through the primary side of the step-up transformer T drops accordingly, also decreases the feedback voltage or voltage V _i input to the control circuit 11. The control circuit 11 as described above is set with the reference value of the voltage V _i, the control circuit 11 as the control signal a, the voltage V _i by changing the pulse width T ₂ of the b becomes the reference value Control. Then, an alternating current having a good waveform with low wave efficiency flows through the fluorescent tube 2. However, the wave efficiency means the ratio of the maximum value to the execution value of the AC waveform.

[Problems to be solved by the invention]

However, in the conventional example described above, at the end of the life of the discharge lamp or the like, the lighting state becomes unstable, and an abnormal state occurs such as repeated short-time intermittent operation, and the terminal voltage increases. And
Since there is no suppression of the peak value of the output voltage of the converter inverter circuit, the abnormal operation state of the inverter circuit is likely to continue, and there is a danger of shortening the service life and burning.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and can protect an inverter circuit without immediately turning off the light in an abnormal state such as the end of life of a discharge lamp. It is an object of the present invention to provide a discharge lamp lighting device that can be used.

[Means for solving the problem]

Therefore, the discharge lamp lighting device according to the present invention is a DC power supply circuit for inputting AC and converting it to DC, and a DC-DC for inputting DC output from the DC power supply circuit and outputting voltage-variable DC power. A converter, an inverter circuit that inputs a DC output from the DC-DC converter and outputs high-frequency power, a control circuit that generates a signal for driving a switching element of the DC-DC converter, and a high-frequency signal from the inverter circuit. A discharge lamp lighting device comprising: a detection unit that detects an abnormal state of the discharge lamp that is turned on by the output.
When the detecting means detects an abnormal state of the discharge lamp, the control circuit generates a signal to reduce the output voltage of the DC-DC converter, the DC-DC converter reduces the output voltage and the inverter Driving the circuit with low power,
An object of the present invention is to achieve the object by a configuration characterized in that a voltage rise of high-frequency power for lighting the discharge lamp is suppressed.

[Action]

With the above configuration, the DC power supply circuit inputs AC, converts it to DC, and supplies DC to the DC-DC converter.The DC-DC converter connected to the DC power supply circuit switches the switching element by a signal from the control circuit. The inverter circuit is driven to output variable-voltage DC power, and the inverter circuit inputs the DC power from the DC-DC converter and supplies high-frequency power to the discharge lamp to light it.

When the detecting means detects an abnormal state of the discharge lamp, the control circuit generates a signal to decrease the output voltage of the DC-DC converter. Then, the DC-DC converter lowers the output voltage to drive the inverter circuit with low power, and suppresses the voltage rise of the high-frequency power for lighting the discharge lamp. And
Instead of turning off the light immediately, the lighting is continued while preventing the inverter circuit from being damaged.

〔Example〕

FIG. 1 is a block circuit diagram showing a first embodiment of the discharge lamp lighting device according to the present invention. Parts that are the same as or correspond to those of the conventional example shown in FIG. 17 is an external AC power supply, 18 is a diode bridge for rectifying the AC voltage from the AC power supply, and 19 is a smoothing capacitor, which constitutes a DC power supply circuit K together with the diode bridge 18. M is a DC-DC converter that generates a variable DC voltage to be output to the inverter circuit, and includes a coil 3, a switching element 4 of a chopper circuit, a rectifying diode 6, and a smoothing capacitor 7. N is an inverter circuit that generates high-frequency power, and generates high-frequency power by turning on / off two switching elements 9 and 10 alternately by an inverter driving circuit 28. 20
Is a condenser, 21 is a current limiting element coil, 2 is a discharge lamp, 22
Is a capacitor connected in parallel to the discharge lamp. P
Is an abnormality detection circuit which constitutes a detecting means for detecting an abnormal state of the discharge lamp 2, which divides the voltage of the discharge lamp by the resistors 23 and 24 and outputs the voltage through the waveform shaping circuit 25.

Q is a control circuit for driving the switching element 4 of the DC-DC converter M, and includes a latch circuit 26 such as a flip-flop and an oscillator 27. Then, a signal is generated by the signal from the abnormality detection circuit P so as to lower the output voltage of the DC-DC converter M.

The operation of the apparatus of this embodiment configured as described above will be described.

FIG. 2 is an operation waveform diagram for explaining the first embodiment shown in FIG. First, a description will be given of normal lighting. The control circuit Q is connected to the chopper circuit switching element 4 of the DC-DC converter M.
Then, the control signal shown in FIG. 2A is added. When the switching element 4 is turned on, a DC voltage flows across the capacitor 7 as is well known. This DC voltage is used as an input voltage of the inverter circuit N, and a control signal as shown in FIGS.
When this is applied, high-frequency power is generated, and the discharge lamp 2 is turned on.
At this time, the voltage waveform at both ends of the discharge lamp 2 becomes a sinusoidal waveform as shown in the left half of FIG. (E) is DC-
4 shows a chopper circuit output of the DC converter M.

Next, a description will be given of abnormal lighting. When the voltage at both ends of the discharge lamp 2 becomes abnormally high due to the abnormality of the discharge lamp 2 or the inverter circuit N (see the right half of FIG. 2D), the high voltage is applied to the resistances 23 and 24 of the detecting means P. And is input to the waveform shaping circuit 25. The waveform shaping circuit 25 shapes the input sinusoidal waveform and outputs it to the control circuit Q as a rectangular wave (second
FIG. (F)). The latch circuit 26 stores a predetermined reference voltage in advance, and when the input signal is higher than the reference voltage, the
27, the control circuit Q works to increase the ON / OFF cycle of the switching element 4 and reduce the output voltage of the chopper circuit of the DC-DC converter M as shown in FIG. h)), the output voltage of the DC-DC converter M is reduced. As a result, even when the discharge lamp 2 is abnormal, the voltage across the discharge lamp 2 becomes lower than a certain value as shown in FIG. 2 (i). Then, an abnormal rise in current is also suppressed. The control circuit Q may be any circuit that performs V / F conversion that generates a frequency corresponding to the input signal voltage, for example.

(Second Embodiment) FIG. 3 is a block diagram showing a second embodiment of the discharge lamp lighting device according to the present invention. Portions that are the same as or correspond to those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted. 29,3
Numerals 0 and 31 constitute a voltage dividing circuit with resistors for detecting the output of the DC-DC converter M. The switch 32 opens the contact by a signal from the abnormality detection circuit P so that the voltage at the junction of the voltage dividing resistors 29 and 30, that is, the detection voltage in the abnormal state is increased.

Next, the operation will be described. FIG. 4 is an operation waveform diagram for explaining the second embodiment shown in FIG.

First, a description will be given of normal lighting. A control signal shown in FIG. 4 (a) is applied from the control circuit Q to the switching element 4. When the switching element 4 is turned on, a DC voltage appears across the capacitor 7 as is well known. When this DC voltage is used as the input voltage of the inverter circuit N and applied to the switching elements 9 and 10 from the control signal and the drive circuit 28 as shown in FIGS. 4B and 4C, high-frequency power is generated and the discharge lamp 2 is turned on. . At this time, the voltage waveform at both ends of the discharge lamp 2 is shown in FIG.
As shown in FIG. (E) shows the output of the chopper circuit of the DC-DC converter M.

Next, a description will be given of abnormal lighting. When the voltage at both ends of the discharge lamp 2 becomes abnormally high due to the abnormality of the discharge lamp 2 or the inverter circuit N (see the right half of FIG. 4D), the high voltage is detected by the resistors 23 and 24 of the detecting means P. And input to the waveform shaping circuit 25. The waveform shaping circuit 25 shapes the sinusoidal waveform and outputs it as a rectangular wave, and the switch 32 is in an open state.
When the switch 32 is released, the output voltage of the DC-DC converter M is detected high by the voltage dividing circuit of the resistors 29 and 30, and is input to the control circuit Q. The control circuit Q is composed of a switching regulator control IC and stores a predetermined reference voltage in advance. When the input signal is higher than the reference voltage, the conduction time of the switching element 4 is shortened as shown in FIG. , Works to lower the output of the chopper circuit of the DC-DC converter M (see FIG. 4 (h)). As a result, the discharge lamp 2
4 (i), the voltage at both ends of the discharge lamp 2 becomes lower than a certain value, and the abnormal rise of the current is also limited.

Although not shown in the above description, the DC-DC converter M and the inverter circuit N are not limited to those shown in the present embodiment, but may be other DC-DC converters or inverter circuits. Further, the abnormality detection circuit P is not limited to the one shown in the above embodiment, but may be another one.

〔The invention's effect〕

As described above, according to the present invention, when the detecting means detects the abnormal state of the discharge lamp, the control circuit sets the DC
-Generate a signal to reduce the output voltage of the DC converter. The DC-DC converter lowers the output voltage to drive the inverter circuit with low power, suppresses the voltage rise of the high-frequency power for lighting the discharge lamp, limits the current flowing through the discharge lamp, and protects the inverter circuit. Prevent measurement damage.

That is, at the end of life of the discharge lamp or the like, the lighting state becomes an unstable abnormal state, and the terminal voltage increases. Then, an abnormal operation state due to an increase in the output voltage of the inverter circuit continues, and there is a risk of shortening the service life and causing a situation such as burning.

The present invention provides a discharge lamp lighting device capable of continuing to light while protecting the inverter circuit without immediately turning off the light in an abnormal state such as the end of life of the discharge lamp as described above. can do.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of a first embodiment of a discharge lamp lighting device according to the present invention, FIG. 2 is an operation waveform diagram illustrating the first embodiment, and FIG. 3 is a block diagram of a second embodiment of the present invention. FIG. 4 is a circuit diagram, FIG. 4 is an operation waveform diagram for explaining the second embodiment, FIG. 5 is a block circuit diagram of the conventional example, and FIGS. 6 and 7 are waveform diagrams at the time of operation of the conventional example. K is a DC power supply circuit, M is a DC-DC converter, N is an inverter circuit, P is a detection means, Q is a control circuit, 1 is an external DC power supply, 2 is a discharge lamp, 3,21 is a coil, 4,9,10 Is a switching element, 6 is a rectifying diode, 7 and 19 are smoothing capacitors, 18 is a diode bridge, 25 is a waveform shaping circuit, and 28 is an inverter driving circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A DC power supply circuit for inputting AC and converting it to DC, a DC-DC converter receiving a DC output from the DC power supply and outputting a variable voltage DC power,
An inverter circuit that inputs a DC output from the converter and outputs high-frequency power; a control circuit that generates a signal for driving a switching element of the DC-DC converter; and a discharge circuit that is lit by the high-frequency output from the inverter circuit. A discharge lamp lighting device comprising: a detection unit that detects an abnormal state of an electric lamp, wherein the control circuit reduces an output voltage of the DC-DC converter when the detection unit detects an abnormal state of the discharge lamp. Signal to generate the DC-
A discharge lamp lighting device, wherein a DC converter lowers an output voltage to drive the inverter circuit with low power and suppress a voltage rise of high-frequency power for lighting the discharge lamp.