JP2706530B2 - Discharge lamp lighting device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a discharge lamp lighting device using an inverter circuit.

[Prior Art] Conventionally, a discharge lamp lighting device of this type is shown in FIG. The DC power supply 4 is formed by connecting an AC input terminal of a full-wave rectifier diode bridge circuit 2 to an AC power supply 1 and connecting a Schottney circuit 3 to an output terminal of the bridge circuit 2.

The Schottney circuit 3 has the positive terminal of the output terminal of the bridge circuit 2 directly connected to the cathode of the diode 5 and the anode of the diode 7 and the cathode of the diode 8 via the capacitor 6. The negative terminal of the output terminal of the bridge circuit 2 is directly connected to the anode of the diode 8, and also connected to the cathode of the diode 7 and the anode of the diode 5 via a capacitor 9.

One self-excited inverter circuit 10 is connected to the DC power supply 4.

The inverter circuit 10 is provided with an NPN type switching transistor 11, and a collector of the transistor 11 is connected to a positive terminal of a DC power supply via a parallel circuit of a primary winding of an output transformer 12 and a resonance capacitor 13. The emitter is connected to the negative terminal of the DC power supply. The transistor
The base of 11 is connected to the positive terminal of the DC power supply 4 via the starting resistor 14 and to one end of the secondary winding of the current transformer 15 and the cathode of the diode 16. The other end of the secondary winding of the current transformer 15 is connected via a capacitor 17 to the emitter of the transistor 11. The anode of the diode 16 is connected to the emitter of the transistor 11 via a resistor 18.

One end of each filament electrode 19a, 19b of the discharge lamp 19 is connected to the output terminal of the inverter circuit 10, that is, the secondary winding of the output transformer 12 via the primary winding of the current transformer 15. A starting capacitor 20 is connected between the other ends of the filament electrodes 19a and 19b of the discharge lamp 19.

In this lighting device, when the DC power supply 4 is turned on, a base current is supplied to the base of the transistor 11 via the starting resistor 14, and the transistor 11 is turned on. As a result, current flows through the resonance capacitor 13 and the primary winding of the output transformer 12, and the discharge lamp 19 flows from the secondary winding of the output transformer 12.
Filament electrode 19a, starting capacitor 20, discharge lamp 19
A load current flows through the filament electrode 19b and the primary winding of the current transformer 15, and the filaments 19a and 19b are preheated.
When a load current flows, a voltage is induced in the secondary winding of the current transformer 15, and positively fed back to the base of the transistor 11, and the capacitor 17 is charged. Thus, the transistor 11 is kept on.

When the core of the current transformer 15 is magnetically saturated, the voltage induced in the secondary winding of the current transformer 15 decreases, and the base current flows in the reverse direction. Thus, transistor 11
Turns off rapidly. At this time, the magnetic saturation of the current transformer 15 depends on the charging current of the capacitor 17,
The larger the capacity of 17, the slower the magnetic saturation and the transistor
11 ON period becomes longer. That is, the ON period of the transistor 11 is determined by the capacitance of the capacitor 17.

Thereafter, the electric energy stored in the tank circuit formed by the primary winding of the output transformer 12 and the resonance capacitor 13 resonates, and a resonance current flows through the load circuit of the discharge lamp 19. Then, the load current flows through the current transformer 15 and the capacitor 17 to the series circuit of the resistor 18 and the diode 16 to keep the transistor 11 off.

Thereafter, a positive feedback current to the transistor 11 flows through the secondary winding of the current transformer 15 due to the resonance load current, and the transistor 11 is turned off.

By repeating the above operation, the transistor
11 switches at a high frequency of 30 KHz to 50 KHz, for example. At this time, since the capacity of the starting capacitor 20 is set to a value that causes LC resonance with the leakage inductance of the output transformer 12, a high-frequency resonance current flows through each electrode 19a, 19b of the discharge lamp 19, and at the same time, between the both ends of the starting capacitor 20. A high voltage is generated, and the discharge lamp 19 is turned on by the high voltage.

After the discharge lamp 19 is turned on, the impedance of the discharge lamp 19 is connected in parallel with the starting capacitor 20, and using this as a load, the inverter circuit 10 continues the oscillating operation and the discharge lamp 19
High-frequency current limited by the leakage inductor of the output transformer 12 flows through 19 to maintain lighting.

[Problem to be Solved by the Invention] In such a discharge lamp lighting device, the voltage waveform output from the DC power supply 4 with respect to the AC power supply waveform shown in FIG. As shown, the waveform includes a valley (section A) and a non-smoothed peak (section B) of a partially smoothed waveform, and this voltage waveform is supplied to the inverter circuit 10.

Accordingly, the lamp current waveform flowing from the inverter circuit 10 via the discharge lamp 19 becomes a waveform in which the lamp current extremely decreases in the section A as shown in FIG.

Further, when the AC power supply voltage fluctuates, the DC power supply voltage fluctuates, and as a result, the light output of the discharge lamp fluctuates.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a discharge lamp lighting device capable of improving the lamp luminous efficiency and making the light output substantially constant with respect to fluctuations in the power supply voltage.

Means for Solving the Problems The present invention provides a DC power supply that outputs a DC voltage by partially smoothing a valley of a pulsating voltage obtained by rectifying an AC voltage from an AC power supply, and a DC power supply connected to the DC power supply. An inverter circuit that converts a DC voltage input by the switching operation of the switching transistor into a high-frequency voltage, a discharge lamp that is lit by the high-frequency voltage from the inverter circuit, and a power supply path from the inverter circuit to the discharge lamp. A primary winding is inserted in series, a secondary winding is connected between the base and the emitter of the switching transistor via a capacitor, and a DC voltage from a DC power supply is detected. A voltage inverting amplifier circuit that inverts and amplifies the voltage and an output of the voltage inverting amplifier circuit. base,
A variable capacitance circuit is provided to control the capacitance of the circuit connected between the emitters to decrease, and to control the capacitance of the circuit connected between the base and the emitter of the switching transistor to increase when the DC voltage level decreases. In this variable capacitance circuit, an amplifying element is connected in parallel to a capacitor connected between the base and the emitter of the switching transistor via an auxiliary capacitor, and the amplifying element is operated in class A by the output of the voltage inverting amplifying circuit. is there.

Further, a light emitting diode of a photocoupler is provided at an output portion of the voltage inverting amplifier circuit, a phototransistor of the photocoupler is used as an amplifying element of the variable capacitance circuit, and the phototransistor is operated in class A.

[Operation] In the present invention having such a configuration, when the level of the voltage waveform output from the DC power supply becomes higher, the circuit connected between the base and the emitter of the switching transistor by the class A operation of the amplifying element of the variable capacitance circuit. Is controlled so as to reduce the capacitance, the ON period of the switching transistor is shortened, and the oscillation frequency of the inverter circuit is increased. Thus, the lamp current flowing through the discharge lamp is controlled to decrease. When the level of the voltage waveform output from the DC power supply becomes low, the class A operation of the amplifying element of the variable capacitance circuit causes
Since the capacitance of the circuit connected between the base and the emitter of the switching transistor is controlled to be large, the ON period of the switching transistor is lengthened, and the oscillation frequency of the inverter circuit is reduced. Thus, the lamp current flowing through the discharge lamp is controlled to increase.

In this way, the lamp current is controlled to decrease at the peaks of the voltage waveform of the DC power supply, and the lamp current is controlled to increase at the troughs, so that the lamp current becomes a current with little fluctuation.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, an AC power supply 21 is connected to an AC input terminal of a full-wave rectifier diode bridge circuit 22, and an output terminal of the bridge circuit 22 is connected to a Schottney circuit 23 to form a DC power supply 24. I have.

In the shotney circuit 23, the positive terminal of the output terminal of the bridge circuit 22 is directly connected to the cathode of the diode 25, and also connected to the anode of the diode 27 and the cathode of the diode 28 via the capacitor 26. Further, the negative terminal of the output terminal of the bridge circuit 22 is directly connected to the anode of the diode 28, and also connected to the cathode of the diode 27 and the anode of the diode 25 via a capacitor 29.

A single self-excited inverter circuit 30 is connected to the DC power supply 24.

The inverter circuit 30 is provided with an NPN type switching transistor 31, and the collector of the transistor 31 is connected to the positive terminal of the DC power supply 24 via a parallel circuit of a primary winding of an output transformer 32 and a resonance capacitor 33. The emitter is connected to the negative terminal of the DC power supply 24. The base of the transistor 31 is connected to a positive terminal of the DC power supply 24 via a starting resistor 34 and to one end of a secondary winding of a current transformer 35 and a cathode of a diode 36.

The other end of the secondary winding of the current transformer 35 is connected to the emitter of the transistor 31 via a capacitor 37.
A diode 38 is connected to the capacitor 37 in parallel. The diode 38 is oriented such that its anode is connected to the other end of the secondary winding of the current transformer 35.

The anode of the diode 36 is connected to the emitter of the transistor 31.

One end of each filament electrode 39a, 39b of the discharge lamp 39 is connected to the output terminal of the inverter circuit 30, that is, the secondary winding of the output transformer 32 via the primary winding of the current transformer 35. A starting capacitor 40 is connected between the other ends of the filament electrodes 39a and 39b of the discharge lamp 39.

A voltage inverting amplifier 41 is connected between the output terminals of the DC power supply 24.

The voltage inverting amplifier circuit 41 connects a capacitor 43 between output terminals of the DC power supply 24 via a resistor 42,
A voltage dividing circuit in which resistors 44 and 45 are connected in series is connected. A constant voltage diode 46 is connected to the capacitor 43 in parallel. The cathode of the constant voltage diode 46 is connected to the collector of an NPN transistor 48 via a resistor 47, and the connection point of the resistors 44 and 45 is connected to the base of the transistor 48. The emitter of the transistor 48 is connected via a resistor 49 to the negative terminal of the output terminal of the DC power supply 24.

Switching transistor 31 of the inverter circuit 30
A variable capacitance circuit 50 is connected in parallel with the capacitor 37 inserted in a circuit connected between the base and the emitter.

The variable capacitance circuit 50 connects an FET (field effect transistor) 52 in parallel with the capacitor 37 via an auxiliary capacitor 51, and connects the diode 52 to the FET 52 and the cathode to
Connected in parallel on the drain side of ET52.

The collector of the transistor 48 of the voltage inverting amplifier circuit 41 is connected to the gate of the FET 52 of the variable capacitance circuit 50. The two circuits 41 and 50 constitute a frequency conversion circuit.

 Next, the operation of the present embodiment will be described.

When the DC power supply 24 is turned on, the inverter circuit 30 starts an oscillating operation, applies a preheating current to each filament electrode 39a, 39b of the discharge lamp 39, and applies a high voltage between the electrodes to discharge the lamp.
Turn on 39. Thus, the discharge lamp 39 is turned on.

In this operation, the voltage waveform from the AC power supply 21
Given the waveform shown in FIG. 2A, the voltage waveform output from the DC power supply 24 is as shown in FIG. 2B.

As a result, a voltage waveform shown in FIG. 2C is generated at the connection point between the resistors 44 and 45 of the voltage inverting amplifier circuit 41. Since this voltage waveform is applied to the base of the transistor 48, the voltage waveform shown in FIG. 2D is generated at the collector of the transistor 48. This voltage waveform corresponds to FET5 of the variable capacitance circuit 50.
2 are supplied to the gate.

Here, the FET 52 performs a class A amplification operation, and the discharge time constant and the charge time constant of the capacitor 51 change depending on the magnitude of the voltage input to the gate. That is, a DC potential corresponding to the gate voltage of the FET is superimposed on the capacitor 51 in advance according to the magnitude of the gate voltage of the FET 52, and the capacitance of the capacitor 51 is apparently changed.

In section B where the voltage waveform of the DC power supply 24 is high, FE
Since the voltage input to the gate of T52 decreases as shown in FIG. 2D, the capacity of the circuit connected to the secondary winding of the current transformer 35 decreases. Thus, the ON period of the switching transistor 31 is shortened, and the oscillation frequency of the inverter circuit 30 increases. As a result, the lamp current flowing through the discharge lamp 39 is controlled to decrease in the section B as shown in FIG.

In the section A where the voltage waveform of the DC power supply 24 is low, the voltage inputted to the gate of the FET 52 becomes high as shown in FIG. 2 (d), so that it is connected to the secondary winding of the current transformer 35. Circuit capacity increases. As a result, the ON period of the switching transistor 31 becomes longer, and the inverter circuit 30
Oscillation frequency becomes lower. As a result, the lamp current flowing through the discharge lamp 39 is controlled to increase in the section A as shown in FIG.

In this way, the lamp current increases in the section A where the voltage waveform of the DC power supply 24 has a low level and decreases in the section B where the voltage has a high level. Therefore, the lamp current flowing through the discharge lamp 39 is as shown in FIG. As shown in (e), the current has a small increase and decrease, and the luminous efficiency of the discharge lamp can be improved.

When the voltage of the AC power supply 21 changes as shown by a dotted line in FIG. 2A, the output voltage of the DC power supply 24 also changes as shown by a dotted line in FIG. 2B. Accordingly, the voltage applied to the base of the transistor 48 also varies as shown by the dotted line in FIG. 2C, and the voltage applied to the gate of the FET 52 is changed as shown by the dotted line in FIG. fluctuate.

Therefore, when the power supply voltage fluctuates in a direction to increase, the oscillation frequency of the inverter circuit 30 increases, and the lamp current is suppressed. Also, when the power supply voltage fluctuates in a direction to decrease, the oscillation frequency of the inverter circuit 30 decreases,
Increase lamp current.

Thus, even if the power supply voltage fluctuates, the lamp current can be stabilized, and the light output of the discharge lamp can be kept substantially constant.

Next, another embodiment of the present invention will be described with reference to the drawings.
The same parts as those in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 3 shows a load current feedback type dual-bridge half-bridge self-excited inverter circuit 60 as an inverter circuit.
You are using

The inverter circuit 60 is provided with a series circuit of a pair of NPN type switching transistors 61 and 62 and a series circuit of a pair of capacitors 63 and 64, and each series circuit is connected to the output terminal of the DC power supply 24. Diodes 65 and 66 are connected in parallel to the transistors 61 and 62, respectively.

The connection point of the transistors 61 and 62 is connected in series with the primary winding of the first current transformer 67, the primary winding of the second current transformer 68, and further through the inductance 69 of the discharge lamp 39. It is connected to one end of one filament electrode 39a.

The connection point between the capacitors 63 and 64 is connected to one end of the other filament electrode 39b of the discharge lamp 39.

The base of the other transistor 62 is connected to one end of a secondary winding of the first current transformer 67 and the cathode of a diode 70.

The other end of the secondary winding of the first current transformer 67 is connected via a capacitor 71 to the emitter of the transistor 62. A diode 72 is connected to the capacitor 71 in parallel. The diode 72 is oriented such that its anode is connected to the other end of the secondary winding of the first current transformer 67.

The anode of the diode 70 is connected to the emitter of the transistor 62.

The base of the one transistor 61 is connected to one end of the secondary winding of the second current transformer 68 and the cathode of the diode 73.

The other end of the secondary winding of the second current transformer 68 is connected to the emitter of the transistor 61 via a capacitor 74. A diode 75 is connected to the capacitor 74 in parallel. The diode 75 is oriented such that its anode is connected to the other end of the secondary winding of the second current transformer 68.

The anode of the diode 73 is connected to the emitter of the transistor 61.

A voltage inverting amplifier 81 is connected between the output terminals of the DC power supply 24.

The voltage inversion amplifying circuit 81 connects a capacitor 83 via a resistor 82 between output terminals of the DC power supply 24,
A voltage dividing circuit in which resistors 84 and 85 are connected in series is connected. A constant voltage diode 86 is connected to the capacitor 83 in parallel. The cathode of the constant voltage diode 86 is connected to the collector of an NPN transistor 88 via a resistor 87, and the NPN transistor 91 is connected in series with the light emitting diodes 89D and 90D of the first and second photocouplers 89 and 90. Connected to the collector. The connection point of the resistors 84 and 85 is connected to the base of the transistor 88. The collector of the transistor 88 is connected to the base of the transistor 91. The emitter of the transistor 88 is connected to the negative terminal of the output terminal of the DC power supply 24 via a resistor 92, and the emitter of the transistor 91 is connected to the negative terminal of the output terminal of the DC power supply 24 via a resistor 93. ing.

A first variable capacitance circuit is connected in parallel with the capacitor 71 inserted in a circuit connected between the base and the emitter of the other switching transistor 62 of the inverter circuit 60.
94 are connected.

The first variable capacitance circuit 94 connects the phototransistor 89T of the first photocoupler 89 in parallel to the capacitor 71 via an auxiliary capacitor 95, and connects the diode 96 to the phototransistor 89T and the phototransistor 89T to the cathode. Are connected in parallel on the collector side.

A second variable capacitance circuit is connected in parallel with the capacitor 74 interposed in a circuit connected between the base and the emitter of one switching transistor 61 of the inverter circuit 60.
97 is connected.

The second variable capacitance circuit 97 connects the phototransistor 90T of the second photocoupler 90 in parallel to the capacitor 74 via an auxiliary capacitor 98, and connects a diode 99 to the phototransistor 90T and a phototransistor 90T to the cathode. Are connected in parallel on the collector side.

In this embodiment, when the voltage level of DC power supply 24 increases, transistor 88 in voltage inverting amplifier circuit 81
Of the transistor 91 becomes deep, and the base voltage of the transistor 91 becomes small. As a result, the current flowing through the light emitting diodes 89D and 90D of the photocouplers 89 and 90 decreases, and the internal resistance of the phototransistors 89T and 90T increases. Thus, the capacitance of the circuit between the base and the emitter of the switching transistors 62 and 61 is reduced by the first and second variable capacitance circuits 94 and 97, and the oscillation frequency of the inverter circuit 60 is increased. Therefore, the lamp current is controlled to decrease.

Also, when the voltage level of the DC power supply 24 decreases, the base bias of the transistor 88 in the voltage inverting amplifier circuit 81 decreases, and the base voltage of the transistor 91 increases. As a result, the current flowing through the light emitting diodes 89D and 90D of the photocouplers 89 and 90 increases, and the internal resistance of the phototransistors 89T and 90T decreases. Thus, the first and second variable capacitance circuits
94,97, base of switching transistors 62,61,
The capacity of the circuit between the emitters increases, and the oscillation frequency of the inverter circuit 60 decreases. Therefore, the lamp current is controlled to increase.

As described above, in this embodiment, the same effects as those of the above embodiment can be obtained.

In the above-described embodiment, the DC power supply using the Schottney circuit has been described.However, the present invention is not limited to this. For example, as shown in FIG. A high-frequency power feedback DC power supply is used in which a series circuit of a diode 101 and a diode 102 is connected, and a connection point between the inductor 101 and the cathode of the diode 102 is connected in series to the collector of the switching transistor 31 of the inverter circuit through the diodes 103 and 104. Alternatively, a completely smooth DC power source having a low power factor may be used.

[Effects of the Invention] As described in detail above, according to the present invention, the oscillation frequency of the inverter circuit increases when the level of the power supply voltage waveform increases, and the oscillation frequency of the inverter circuit decreases when the level of the power supply voltage waveform decreases. By doing so, it is possible to provide a discharge lamp lighting device capable of improving the lamp luminous efficiency and making the light output substantially constant with respect to fluctuations in the power supply voltage.

[Brief description of the drawings]

FIGS. 1 and 2 show an embodiment of the present invention. FIG. 1 is a circuit diagram, FIG. 2 is a voltage and current waveform diagram of each part, FIG.
FIG. 4 is a circuit diagram showing another embodiment of the present invention, FIG. 4 is a circuit diagram showing another embodiment of a DC power supply, FIGS. 5 and 6 show a conventional example, and FIG. FIG. 6 and FIG. 6 are voltage and current waveform diagrams of each part. 24: DC power supply, 30: Inverter circuit, 31: Switching transistor, 35: Current transformer, 39: Discharge lamp, 41: Voltage inverting amplifier circuit, 50: Variable capacity circuit

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-186790 (JP, A) JP-A-63-96897 (JP, A) JP-A-63-292599 (JP, A) JP-A-2- 288195 (JP, A) JP-A-1-274389 (JP, A) JP-A-1-160367 (JP, A) JP-A-56-48095 (JP, A)

Claims (2)

(57) [Claims] 1. A DC power supply for outputting a DC voltage by partially smoothing a valley of a pulsating voltage obtained by rectifying an AC voltage from an AC power supply, and a DC power supply connected to the DC power supply and performing a switching operation of a switching transistor. An inverter circuit that converts an input DC voltage into a high-frequency voltage, a discharge lamp that is lit by the high-frequency voltage from the inverter circuit, and a primary winding in series in a power supply path from the inverter circuit to the discharge lamp. A current transformer having a secondary winding connected between the base and the emitter of the switching transistor via a capacitor, and a voltage for detecting a DC voltage from the DC power supply and inverting and amplifying the DC voltage. In response to the output of the inverting amplifier circuit and the output of the voltage inverting amplifier circuit, when the level of the DC voltage rises, The variable capacitor circuit controls the capacitance of a circuit connected between the switching transistors in a direction in which the capacitance is reduced, and controls the capacitance of a circuit connected between the base and the emitter of the switching transistor in a direction in which the capacitance is increased when the level of the DC voltage is reduced. The variable capacitance circuit is configured by connecting an amplifying element in parallel with a capacitor connected between the base and the emitter of the switching transistor via an auxiliary capacitor, and classifying the amplifying element by an output of a voltage inverting amplifying circuit. A discharge lamp lighting device characterized by being operated. 2. The method according to claim 1, wherein a light emitting diode of a photocoupler is provided at an output portion of the voltage inverting amplifier circuit, a phototransistor of the photocoupler is used as an amplifying element of the variable capacitance circuit, and the phototransistor is operated in class A. The discharge lamp lighting device according to claim 1, wherein: