JPH07169579A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To protect an element such as a switching transistor with an excellent follow up characteristic to overvoltage input such as a surge as well as to eliminate flickering of a discharge lamp at overvoltage input time. CONSTITUTION:A parallel circuit 81 of a resistance 79 and a switching element 80 is connected in series to a switching transistor 56, and an input voltage detecting circuit 59 is arranged to detect high voltage input to an inverter circuit 58. The switching element 80 is opened by an action of a switch control circuit 60 in response to high voltage detecting output from this detecting circuit 59, and a collector current of the switching transistor 56 is reduced by connecting the resistance 79 in series to the switching transistor 56. An element such as the switching transistor 56 is protected from overvoltage input by restraining an increase in voltage between an collector and an emittor of the switching transistor 56.

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 using an inverter circuit.

[0002]

2. Description of the Related Art A conventional discharge lamp lighting device using an inverter circuit is shown in FIG.

That is, a first varistor 2 which is a surge absorbing element is connected in parallel to an AC power source 1 and an input terminal of a full wave rectifying circuit 3 is connected. A second varistor 4 which is a surge absorbing element is connected in parallel to the output terminal of the full-wave rectifier circuit 3 and a smoothing capacitor 5 is connected in parallel to form a DC power supply.

Inverter circuits 6 are connected to both ends of the smoothing capacitor 5. This inverter circuit 6 is
A series circuit for performing valley filling smoothing of the capacitor 7, the inductor 8 and the diode 9 is connected in parallel to the smoothing capacitor 5, and the primary winding 10a of the inverter transformer 10 and the NPN type are connected in parallel to the series circuit. A series circuit with the switching transistor 11 is connected.

A resonance capacitor 12 is connected in parallel to the primary winding 10a, and the capacitor 12 and the primary winding 10a form a resonance circuit. Further, a diode 13 is connected with the polarity shown in the figure from the connection point between the inductor 8 and the diode 9 toward the collector of the switching transistor 11.

The base of the switching transistor 11 is connected to the positive electrode of the full-wave rectifier circuit 3 via a starting resistor 14. A series circuit of a diode 15 and a resistor 16 is connected between the base and the emitter.

Secondary winding 1 of the inverter transformer 10
The filament electrode 20a, 20b of the discharge lamp 20 is connected to 0b through a series circuit of the detection winding 17a of the current transformer 17 and the capacitor 18, and a parallel circuit of the resistor 19. Further, a capacitor 21 for preheating the filament is connected between the filament electrodes 20a and 20b.

A diode 22 having the illustrated polarity is connected in parallel to the control winding 17b of the current transformer 17.
Further, one end of the control winding 17b is connected to the base of the switching transistor 11, and the other end is connected to the negative electrode of the full-wave rectifier circuit 3 via a parallel circuit of a capacitor 23 and a diode 24.

A series circuit of a capacitor 25 and a field effect transistor 26 is connected to both ends of the capacitor 23.

On the other hand, a series circuit of a resistor 27 and a capacitor 29 is connected to both ends of the smoothing capacitor 5, and a zener diode 28 of the illustrated polarity is connected in parallel to both ends of the capacitor 29.

Further, a series circuit of a resistor 30, a PNP transistor 31, a resistor 32 and a resistor 33 is connected to both ends of the capacitor 29, and a capacitor 34 is connected in parallel to the resistor 33. The connection point between the resistor 32 and the resistor 33 is connected to the gate terminal of the field effect transistor 26.

The base of the transistor 31 has a resistor 3
It is connected to the negative electrode of the full-wave rectifier circuit 3 via 5 and to the collector of the switching transistor 11 via a series circuit of a resistor 36, a resistor 37 and a diode 38. Further, the connection point between the diode 38 and the resistor 37 is connected to the negative electrode of the full-wave rectification circuit 3 via a capacitor 39.

Here, the field effect transistor 26, the transistor 31, the capacitors 25, 34 and 39, the diode 38 and the resistors 30, 32, 33, 35, 36 and 37.
Forms a protection circuit 40 for protecting elements such as the switching transistor 11 from an overvoltage input such as a surge.

That is, when an overvoltage such as a surge is input, the collector-emitter voltage of the switching transistor 11 increases. Then, the voltage of the resistor 35 that divides the collector-emitter voltage, that is, the base potential of the transistor 31 increases, so that the collector current of the transistor 31 decreases. Accordingly, the voltage of the resistor 33, that is, the field effect transistor 2
Since the gate potential of 6 decreases, the base current of the switching transistor 11 decreases, the oscillation frequency increases, and the output voltage decreases. Thus, the collector-emitter voltage of the switching transistor 11 is lowered, and protection from overvoltage is achieved.

[0015]

However, in the discharge lamp lighting device having the conventional protection circuit 40, since the time constant circuit of the resistor 33 and the capacitor 34 is formed in the protection circuit 40, the overvoltage input is prevented. The followability was poor. Further, when the overvoltage is input, the field effect transistor 2
Although the capacitance of the capacitor connected to the base of the switching transistor 11 is switched by lowering the gate potential of 6, the discharge lamp 20 may go out and flicker during this switching.

Therefore, the present invention is to provide a discharge lamp lighting device capable of protecting elements such as a switching transistor and the like with good followability to an overvoltage input such as a surge and eliminating flicker of the discharge lamp at the time of overvoltage input. It is what

[0017]

DISCLOSURE OF THE INVENTION The present invention relates to a discharge lamp lighting device provided with an inverter circuit which is connected to a DC power source and operates a resonance circuit by a switching operation of a switching transistor to supply a high frequency voltage to a discharge lamp for lighting. , A parallel circuit of a resistor and a switching element connected in series to the switching transistor, an input voltage detection circuit that detects a high voltage input to the inverter circuit, and a high voltage detection output from this detection circuit. And a switch control circuit for opening the switching element.

[0018]

According to the present invention having such a configuration, when the input voltage to the inverter circuit is normal, the switching element is closed in the parallel circuit of the resistor and the switching element connected in series with the switching transistor. So the resistor is shorted. Here, when a high voltage input such as a surge is detected by the input voltage detection circuit, the switching element is opened by the switching control circuit. As a result, the resistor is connected in series to the switching transistor, the collector current of the switching transistor is reduced, oscillation is weakened, and the rise of the collector-emitter voltage of the switching transistor is suppressed.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

The discharge lamp lighting device shown in FIG.
A first varistor 52, which is a surge absorbing element, is connected in parallel with the input terminal 1, and an input terminal of a full-wave rectifier circuit 53 is connected. A second varistor 54, which is a surge absorbing element, is connected in parallel to the output terminal of the full-wave rectifier circuit 53, and a smoothing capacitor 55 is connected in parallel to form a DC power supply.

At both ends of the smoothing capacitor 55, an inverter circuit 58 for operating a resonance circuit by a switching operation of a switching transistor 56 to supply a high frequency voltage to a discharge lamp 57 to light it, and this inverter circuit 5
An input voltage detection circuit 59 that detects a high voltage input to the switch 8 and a switch control circuit 60 that opens a switching element described later in response to a high voltage detection output from the input voltage detection circuit 59 are connected in parallel. .

The inverter circuit 58 is connected in parallel with the smoothing capacitor 55 to a series circuit for performing valley filling smoothing of the capacitor 61, the inductor 62 and the diode 63, and an inverter transformer in parallel to the series circuit. A series circuit of 64 primary windings 64a and the NPN type switching transistor 56 is connected.

A resonance capacitor 65 is connected in parallel to the primary winding 64a, and the resonance circuit is formed by the capacitor 65 and the primary winding 64a. Further, a diode 66 is connected with the polarity shown in the drawing from the connection point of the inductor 62 and the diode 63 toward the collector of the switching transistor 56.

The base of the switching transistor 56 is connected to the full-wave rectifying circuit 53 via a resistor 67 for starting.
Is connected to the positive electrode of. A series circuit of a diode 68 and a resistor 69 is connected between the base and the emitter.

Secondary winding 6 of the inverter transformer 64
Filament electrodes 74a and 74b of the discharge lamp 57 are connected to 4b through a series circuit of a detection winding 70a of a current transformer 70 and a capacitor 72 and a parallel circuit of a resistor 73. Also, the filament electrodes 74a, 74b
A capacitor 75 for preheating the filament is connected between them.

A diode 76 having the illustrated polarity is connected in parallel to the control winding 70b of the current transformer 70.
Further, one end of the control winding 70b is connected to the base of the switching transistor 56, and the other end is connected to the negative electrode of the full-wave rectifier circuit 53 via a parallel circuit of a capacitor 77 and a diode 78. .

Further, the switching transistor 5
The emitter of 6 is connected to the negative electrode of the full-wave rectifier circuit 53 through a parallel circuit 81 of a resistor 79 and the field effect transistor 80 as a switching element described above.

On the other hand, the switch control circuit 60 has a resistor 82 and a resistor 83 in parallel with the smoothing capacitor 55.
Is connected in series, and an NPN transistor 84 is connected in parallel with the resistor 83. The connection point between the resistor 82 and the resistor 83 is connected to the gate terminal of the field effect transistor 80 which is the switching element.

Further, the input voltage detection circuit 59 has a resistor 85 and a resistor 86 in parallel with the smoothing capacitor 55.
And a series circuit with is connected. And the resistance 85
Zener diode 8 with the polarity shown in the drawing
It is connected to the base of the transistor 84 in the switch control circuit 60 via 7.

In the discharge lamp lighting device having such a configuration, when the power is turned on, the full-wave rectification circuit 53 performs full-wave rectification to apply a pulsating current to the smoothing capacitor 55.
Then, from this smoothing capacitor 55 to the inverter circuit 5
When a DC voltage is supplied to the transistor 8, in the inverter circuit 58, a base current flows to the base of the switching transistor 56 through the starting resistor 67, and the transistor 5 is supplied.
6 turns on. Then, the primary winding 64a of the inverter transformer 64 is passed through the switching transistor 56.
Current flows into the secondary winding 64b of the inverter transformer 64 to induce a voltage.

As a result, the inverter transformer 64 2
A current flows through the secondary winding circuit of the detection winding 70a of the current transformer 71, the capacitor 72, the filament electrodes 74a and 74b of the discharge lamp 57, and the filament preheating capacitor 75 that are connected to the secondary winding 64b. A voltage is induced in the control winding 70b of the transformer 70 and is positively fed back to the base of the switching transistor 56.

After that, when the core of the current transformer 70 is magnetically saturated, the induced voltage in the control winding 70b is lowered and the base current is inverted. As a result, the electric charge of the base capacitance of the switching transistor 56 is extracted, and the switching transistor 56 is rapidly turned off.

After that, electric energy resonates by the resonance circuit of the primary winding 64a of the inverter transformer 64 and the resonance capacitor 65, and the resonance current flows through the secondary side circuit of the inverter transformer 64. Then, the control winding 70b of the current transformer 70 is again driven by this resonance current.
Then, the positive feedback current to the switching transistor 56 starts to flow, and the switching transistor 56 is turned on again.

In this way, the switching transistor 56 performs a switching operation at high frequency, and the inverter circuit 58 continues to oscillate. At this time, a high-frequency resonance current flows as a preheating current in each filament electrode 74a, 74b of the discharge lamp 57, and a high voltage is generated at both ends of the capacitor 75. By applying this high voltage, the discharge lamp 57 is started and lit.

At this time, the potential at the connection point between the resistors 85 and 86 in the input voltage detection circuit 59 is set lower than the Zener voltage of the Zener diode 87. Therefore, the Zener diode 87 is off, and the transistor 84 in the switch control circuit 60 is also off. As a result, the voltage divided by the resistors 82 and 83 in the switch control circuit 60 is applied between the gate and the source of the field effect transistor 80 in the parallel circuit 81, so that the field effect transistor 80 turns on.
The resistor 79 in the parallel circuit 81 is short-circuited.

In this normal lighting state, when an overvoltage such as a surge is applied from the outside, the full-wave rectification circuit 53.
The output terminal voltage of increases. Then, the potential at the connection point between the resistors 85 and 86 rises and the Zener diode 87 is turned on. As a result, the transistor 84 turns on, the gate-source voltage of the field effect transistor 80 becomes zero, and the field effect transistor 80 turns off.

As a result, the resistor 79 is connected between the emitter of the switching transistor 56 and the negative electrode of the full-wave rectification circuit 53, so that the collector current of the switching transistor 56 decreases. When the collector current decreases, the resonance between the resonance capacitor 65 and the primary winding 64a of the inverter transformer 64 weakens, and the collector-emitter voltage of the switching transistor 56 decreases.

Therefore, for an overvoltage input such as a surge,
The rise in voltage between the collector and the emitter of the switching transistor 56 can be suppressed to a low level, and damage to the switching transistor 56 can be prevented.

In this way, when the input voltage detection circuit 59 detects an overvoltage input such as a surge, the switch control circuit 60.
Acts to turn off the field effect transistor 80, which is a switching element, and connect the resistor 79 to the emitter of the switching transistor to reduce the collector current.
Since the voltage rise between the emitters is suppressed, the element protection function has excellent followability with respect to an overvoltage input.

Further, since the capacitor capacity connected to the base of the switching transistor 56 is not switched in response to the overvoltage input, the discharge lamp 57 is not turned off and flicker can be prevented.

In the above embodiment, the field effect transistor 80 is used as the switching element forming the parallel circuit 81.
However, the present invention is not limited to this, and it is also possible to use a triac or a photocoupler.

[0042]

As described above in detail, according to the present invention, a parallel circuit of a resistor and a switching element is connected in series to a switching transistor, and an input voltage detection for detecting a high voltage input to an inverter circuit is performed. A circuit is provided, and in response to a high voltage detection output from this detection circuit, the switching element is opened and a resistor is connected in series to the switching transistor to reduce the collector current of the switching transistor.・ Since the rise of the voltage between the emitters is suppressed, the elements such as the switching transistor are protected from the overvoltage input, so that the elements can be protected with good followability against the overvoltage input such as surge and the discharge at the time of the overvoltage input. Providing a discharge lamp lighting device that can eliminate the flickering of electric lights It can be.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a conventional example.

[Explanation of symbols]

 56 ... Switching transistor 57 ... Discharge lamp 58 ... Inverter circuit 59 ... Input voltage detection circuit 60 ... Switch control circuit 79 ... Resistor 80 ... Field effect transistor (switching element) 81 ... Parallel circuit

Claims (1)

[Claims] 1. A discharge lamp lighting device comprising an inverter circuit which is connected to a DC power supply and operates a resonance circuit by a switching operation of a switching transistor to supply a high frequency voltage to a discharge lamp to light the discharge lamp. A parallel circuit of a resistor and a switching element connected in series, an input voltage detection circuit for detecting a high voltage input to the inverter circuit, and the switching element opened in response to a high voltage detection output from the detection circuit. A discharge lamp lighting device, comprising: