JP2772175B2 - Discharge lamp lighting device - Google Patents

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 a high frequency inverter circuit.

[0002]

2. Description of the Related Art FIG. 3 shows a known discharge lamp lighting apparatus of this type. In this method, a smoothing capacitor 3 is connected to an AC power supply 1 via a full-wave rectifier diode bridge circuit 2, and a switching transistor 4, an inverter transformer 5, and a resonance capacitor 6 are connected to the smoothing capacitor 3.
Are connected. One end of each filament electrode of the discharge lamp 8 is connected to the output terminal of the inverter circuit 7, that is, the secondary winding of the inverter transformer 5, and a capacitor 9 is connected between the other ends of each filament electrode.

[0003]

In such a discharge lamp lighting device, distortion of the harmonic current waveform occurs during the period when the output from the diode bridge circuit 2 is higher than the charging voltage of the smoothing capacitor 3. Then, during this period, the smoothing capacitor 3 is charged. During this period, all the necessary charges must be charged to the smoothing capacitor 3 in a short time, and as shown in FIG. Therefore, the input current b has a spike-like waveform. Therefore, there is a problem that the amount of harmonics contained in the power supply increases and the power factor decreases.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a discharge lamp lighting device which can reduce a harmonic component and increase a power factor and has a simple structure.

[0005]

According to the present invention, a rectifying circuit connected to an AC power supply, a first switching element is connected between output terminals of the rectifying circuit via a choke coil, and further a diode is connected via a diode. Step-up chopper circuit having a smoothing capacitor connected thereto, a high-frequency inverter circuit having a second switching element connected to the smoothing capacitor, a discharge lamp connected to an output terminal of the inverter circuit, and a discharge lamp and an inverter A primary winding is inserted in series with an output terminal of the circuit, and a secondary winding is connected to a switching control unit of the first switching element, and the output terminal of the rectifier circuit is connected to a current transformer. A pulsating voltage detection circuit, and a second switching element of an inverter circuit that is turned on in response to the pulsating voltage detection output from the pulsating voltage detection circuit; The Yuti linear is provided with a control circuit for variably controlling.

[0006]

According to the present invention having such a configuration, the pulsating voltage output from the rectifying circuit is detected by the pulsating voltage detecting circuit.
The control circuit linearly variably controls the on-duty of the second switching element of the inverter circuit based on the detection output. Thus, the frequency of the current flowing to the output terminal side of the inverter circuit changes linearly in accordance with the pulsating voltage from the rectifier circuit.

[0007] The current flowing to the output terminal side of the inverter circuit is positively fed back to the first switching element of the step-up chopper circuit by the current transformer, whereby the oscillation frequency of the first switching element also changes linearly.

[0008] Since the oscillation frequency of the first switching element linearly changes in accordance with the pulsating voltage from the rectifier circuit, an input current having no phase difference with respect to the input voltage can flow.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, an input terminal of a diode bridge type full-wave rectifier circuit 12 is connected to an AC power supply 11. The boost chopper circuit 13 is connected between the output terminals of the full-wave rectifier circuit 12.

The boost chopper circuit 13 connects an NPN-type switching transistor 15 as a first switching element between output terminals of the full-wave rectifier circuit 12 via a first choke coil 14, and further includes a diode. A smoothing capacitor 17 is connected via the reference numeral 16.

A high-frequency inverter circuit 18 is connected to the smoothing capacitor 17. In the high frequency inverter circuit 18, a series circuit of a primary winding 19p of an inverter transformer 19 and a field effect transistor 20 as a second switching element is connected to the smoothing capacitor 17,
A resonance capacitor 21 is connected in parallel to the next winding 19p, and a diode 22 is connected between the drain and source of the field-effect transistor 20 with its cathode on the drain side. The field effect transistor 20
A control circuit 23 for switching the transistor 20 in a separately excited manner is connected between the gate and the source.

The discharge lamp 2 is connected to the output terminal of the inverter circuit 18, that is, to the secondary winding 19s of the inverter transformer 19 via the primary winding 24p of the current transformer 24.
5, one end of each filament electrode 25a, 25b is connected, and a capacitor 26 is connected between the other end of each filament electrode 25a, 25b. The secondary winding 24s of the current transformer 24 is connected between the base and the emitter of the switching transistor 15 via a resistor 27.

Between the output terminals of the full-wave rectifier circuit 12,
Also, a pulsating voltage detection circuit composed of a series circuit of resistors 28 and 29 is connected. The voltage generated between both ends of the resistor 29 is supplied to the control circuit 23 as a pulsating voltage detection output. The control circuit 23 linearly variably controls the on-duty of the field effect transistor 20 according to the pulsating voltage detection output.

In the embodiment having such a configuration, when the AC power supply 11 is turned on, a current flows from the output terminal of the full-wave rectifier circuit 12 to the smoothing capacitor 17 via the choke coil 14 and the diode 16, and the smoothing capacitor 17 Is charged.

In this state, when the field effect transistor 20 is turned on by a start signal from the control circuit 23, the output terminal of the full-wave rectifier circuit 12 passes through the choke coil 14, the diode 16, and the primary winding 19p of the inverter transformer 19. Electric current flows. At a certain stage, the primary winding 1 of the inverter transformer 19 is also supplied from the smoothing capacitor 17.
Current flows through 9p.

When the field effect transistor 20 is turned off, the electromagnetic energy stored in the inverter transformer 19 is released to the resonance capacitor 21 during the on period. At this time, the primary winding 19 of the inverter transformer 19
p and the resonance capacitor 21 are in a resonance state, and a resonance current flows.

The above operation is repeated by turning on and off the field effect transistor 20, and high frequency power is supplied to the discharge lamp 25 from the secondary winding 19s of the inverter transformer 19. The secondary winding 19 of the inverter transformer 19
A resonance current flows through the filament electrodes 25a and 25b of the discharge lamp 25 by the resonance operation of the capacitor s and the capacitor 26, and the filament electrodes 25a and 25b are preheated. At the same time, a high voltage is applied between the filament electrodes 25a and 25b of the discharge lamp 25, and the discharge lamp 25 is turned on at a high frequency.

On the other hand, in the step-up chopper circuit 13, the switching transistor 15 is switched by a positive feedback current from the secondary winding 24s of the current transformer 24. Then, the switching operation of the switching transistor 15 causes the boost chopper circuit 13 to operate.
Works.

Now, the secondary winding 1 of the inverter transformer 19
When a current flows from 9s to the primary winding 24p of the current transformer 24, this current is positively fed back through the secondary winding 24s, and the switching transistor 15 is turned on. Thereby, the choke coil 1 is connected to the output terminal of the full-wave rectifier circuit 12.
A current flows through the switching transistor 15 through the switching transistor 4. At this time, electromagnetic energy is stored in the choke coil 14.

Thereafter, when the current flowing through the secondary winding 19s of the inverter transformer 19 reverses, the switching transistor 15 is reverse-biased and rapidly turns off. At this time, the electromagnetic energy stored during the ON period is released from the choke coil 14 to the smoothing capacitor 17 via the diode 16. As a result, the smoothing capacitor 17 charged with the power supply voltage is boosted by superimposing the electromagnetic energy.

The oscillation frequency of the switching transistor 15 is determined by the frequency of the positive feedback current from the current transformer 24, that is, the frequency of the resonance current flowing through the secondary winding of the inverter transformer 19.

The control circuit 23 responds to a pulsating voltage detection output generated from both ends of the resistor 29 by using the field effect transistor 20.
Of the inverter circuit 18 is controlled variably. That is, the control circuit 23 shortens the on-duty of the field effect transistor 20 when the pulsating voltage detection level is high, and sets the field effect transistor 2 when the pulsating voltage detection level is low.
The on duty of 0 is lengthened. Thus, a current along the pulsating voltage can be passed through the discharge lamp 25.

By the above operation, as shown in FIG. 2, the input current b having no phase difference with respect to the input voltage a can be flown, the harmonic component can be reduced, and the power factor can be increased. . Moreover, the switching transistor 15 of the boost chopper circuit 13 is connected to the inverter transformer 1
9 between the secondary winding 19 s and the discharge lamp 25.
Since the switching operation is performed by the positive feedback current from the secondary winding 24s of the current transformer 24 interposed with p, no special control circuit for switching control is required, and the configuration of the boost chopper circuit is simple. Becomes

[0025]

As described in detail above, according to the present invention, the harmonic component can be reduced and the power factor can be increased, and the switching element of the boost chopper circuit is connected to the output terminal of the inverter circuit. Since the switching operation is performed by the positive feedback current from the secondary winding of the current transformer with the primary winding inserted between the lamp and the lamp, no special control circuit for switching control is required, and the voltage is boosted. It is possible to provide a discharge lamp lighting device in which the configuration of the chopper circuit is simplified.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an input voltage waveform and an input current waveform in the embodiment.

FIG. 3 is a circuit diagram showing a conventional example.

FIG. 4 is a diagram showing an input voltage waveform and an input current waveform in the conventional example.

[Explanation of symbols]

11 ... AC power supply, 12 ... Full-wave rectifier circuit, 13 ... Boost chopper circuit, 14 ... Choke coil, 15 ... Switching transistor (first switching element), 16 ... Diode, 17 ... Smoothing capacitor, 18 ... High frequency inverter circuit, 20: field effect transistor (second switching element), 23: control circuit, 24: current transformer, 25: discharge lamp, 28, 29: resistor.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05B 41/24-41/29 H02M 7/42-7/98 H02M 1/12

Claims (1)

(57) [Claims] 1. A rectifier circuit connected to an AC power supply, a first switching element is connected between output terminals of the rectifier circuit via a choke coil, and a smoothing capacitor is further connected via a diode. A boost chopper circuit, a high-frequency inverter circuit having a second switching element connected to the smoothing capacitor, a discharge lamp connected to an output terminal of the inverter circuit, and an output terminal of the discharge lamp and the output terminal of the inverter circuit. A current transformer having a primary winding interposed in series and a secondary winding connected to a switching control unit of the first switching element, and a pulsating voltage detection connected between output terminals of the rectifier circuit. A pulsating voltage detection output from the pulsating voltage detection circuit. A discharge lamp lighting device comprising a control circuit for variably controlling the tee.