JPH07240288A - Discharge lamp lighting circuit - Google Patents

Abstract

PURPOSE:To improve the power factor while securing the constancy of a smooth voltage, by connecting the first and the second diodes between a DC power source and a capacitor for smoothing, and between the DC power source and the second switching element side of a resonance capacitor respectively. CONSTITUTION:When a resonance inductor voltage VCO generated by the resonance of the resonance inductor L0 of an inverter circuit 5 and a resonance capacitor C0 is made equal to the power source voltage Vin, the second diode D4 is turned ON. As a result, a power factor improving current flows from the second switching element S3 to a capacitor C1 for smoothing through the resonance inductor L0, and a current with a high peak to the capacitor C1 can be suppressed. Consequently, a low distortion circuit which can maintain the smooth electrode constant as well as can improve the power factor in a simple structure is formed. And the voltage applied to the discharge lamp as a load 8 is made flat.

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 circuit using an inverter circuit.

[0002]

2. Description of the Related Art Conventionally, as a power supply section for a discharge lamp lighting circuit of this type, there is a capacitor input type as shown in FIG. 9 (a). That is, the full-wave rectifying circuit 2 is connected between the AC power supply 1, the full-wave rectification circuit 2 is connected to the smoothing capacitor C ₁ between the DC power source which is full-wave rectified, the both ends of the smoothing capacitor C ₁ The obtained smoothed voltage is provided as a power source for the following inverter circuit (not shown).

[0003]

In the case of such a capacitor input method, although the smoothness is good, the input current I _IN flowing from the commercial AC power source 1 side is different from the input voltage V _IN in the same figure (b). As shown in, the rest section is created,
Since the peak value also becomes large, the harmonic distortion of the input current I _IN becomes large.

There is a step-up chopper type as a means for improving the occurrence of such a pause section. According to this,
Although the input current distortion is improved, there is a drawback that the configuration becomes complicated.

[0005]

A smoothing capacitor is connected between full-wave rectified DC power supplies, and a series circuit of a first switching element and a resonant inductor is connected between both ends of the smoothing capacitor, and An inverter circuit using a smoothing capacitor as a power source is provided by connecting a series circuit of a second switching element and a resonance capacitor in parallel to one switching element, and the first and second switching elements are alternately turned on / off controlled. In a discharge lamp lighting circuit for lighting a discharge lamp at a high frequency, a first diode is connected between the DC power supply and the smoothing capacitor, and the DC power supply and the second switching element side of the resonance capacitor are connected. A second diode was connected between them.

[0006]

When the resonance inductor voltage generated by the resonance between the resonance inductor and the resonance capacitor in the inverter circuit becomes equal to the power supply voltage, the second diode is turned on. Therefore, the power factor is improved from the second switching element through the resonance inductor to the smoothing capacitor. Since a current flows, a high peak current for the smoothing capacitor can be suppressed. Therefore, the power factor can be improved with a simple structure, and the low distortion circuit can keep the smoothing voltage constant. Therefore, the voltage applied to the discharge lamp becomes almost flat.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIGS. First, the full-wave rectifier circuit 4 is connected to the alternating-current power supply 3, and a direct-current power supply that obtains a direct-current voltage that is the input voltage Vin is configured between the output terminals of the full-wave rectifier circuit 4. A smoothing capacitor C ₁ is connected between the output terminals of the full-wave rectifier circuit 4 via a first diode D ₁ . An inverter circuit 5 for the smoothing capacitor C ₁ and the power supply are connected to both ends of the smoothing capacitor C _1. This inverter circuit 5 is alternately controlled to be turned on and off first and second.
The switching elements S ₁ and S ₂ (specifically, transistors, etc.) and the first and second switching elements S
Anti-parallel diodes D ₂ and D ₃ connected to ₁ and S ₂ ,
LC with resonance inductor L ₀ and resonance capacitor C ₀
And a resonance circuit 6. Here, the resonance inductor L ₀ is connected in series to the first switching element S ₁ , and this series circuit is connected between both ends of the full-wave rectification circuit 4 and the first diode D ₁ . The resonance capacitor C ₀ is connected in series with the second switching element S ₂ , and this series circuit is connected in parallel between both ends of the first switching element S ₁ . Further, a second diode D ₄ for power factor improvement is connected between one end of the resonance capacitor C ₀ (on the side of the second switching element S ₂ ) and one of the output terminals of the full-wave rectification circuit 4. .

The resonance inductor L ₀ forming the output portion of the inverter circuit 5 is 1 of the inverter transformer 7.
It also serves as a secondary winding, and a load 8 which is a discharge lamp is connected through the secondary winding L ₁ .

In such a structure, the operation will be described with reference to the voltage waveform and the current waveform shown in FIG. In the illustrated example, the full-wave rectified input voltage Vin is Vin = 100V (100 in the full-wave rectified half-wave waveform as shown in FIG. 7).
V _S1 is a voltage across the first switching element S ₁ , V _C0 is a voltage across the resonant capacitor C ₀ , and I _S1 is a first switching element S. Let I _S2 be the current flowing through ₁ , I _S2 be the current flowing through the second switching element S ₂ , and I _D4 be the current flowing through the second diode D ₄ .

[0010] First, power is turned on and charges the smoothing capacitor C ₁ through the diode D ₁ is stored, the diode D ₁ in a section in which the voltage across V _C1 is V _C1> Vin
Turns off. On the other hand, in the inverter circuit 5, when the first switching element S ₁ is turned on (the current I _S1 flows), a current flows in the resonance inductor L ₀ to store energy, and when the first switching element S ₁ is turned off, the antiparallel connection is performed. A current flows through the resonance capacitor C ₀ through the diode D ₃ . As a result, the LC resonance state is substantially achieved,
Due to the resonance between the resonance inductor L ₀ and the resonance capacitor C ₀ , the voltage V _L0 of the resonance inductor L ₀ rises and then falls. In parallel with this, the first and second switching elements S
_{Since 1} and S ₂ are alternately turned on and off repeatedly, when the voltage V _C0 across the capacitor eventually becomes V _C0 ≉Vin, the second diode D ₄ turns on as shown in FIG. _{Becomes the} rate improvement current I _D4, and the second switching element S ₂ →
The current flows through the path from the resonance inductor L _{0 to the} smoothing capacitor C ₁ . That is, a current flows directly from the DC power source side to the smoothing capacitor C ₁ , and the shaded portion in FIG. 2 contributes to the power factor improvement. This power factor correction current I _D4
Therefore, V _C1 > Vin. Second switching element S
_{When 2} is turned off, the resonance inductor L ₀ is regenerated by the anti-parallel diode D ₂ , and the first switching element S ₁ is turned on again, so that the smoothing capacitor C ₁ →
A current flows through the path of the resonance inductor L ₀ → the first switching element S ₁ . Hereinafter, the same operation is repeated.

Therefore, the voltage and current waveforms of the input portion in this embodiment are shown in the output portion of the full-wave rectifying circuit 4 for the AC voltage E of the sinusoidal AC power source 3 as shown in FIG. The input current Iin to be supplied is as shown in the figure, and the power factor improving current continues to flow from the power source side even in the low phase portion of the AC voltage E so that no pause section is generated. As a result, in controlling the operation of the inverter circuit 5, it is possible to easily control the on-duty and frequency of the _first and second switching elements S ₁ and S ₂ . After all, since the smoothing voltage obtained in the smoothing capacitor C ₁ is also made constant while improving the power factor, the output (output voltage) applied to the load 8 through the inverter circuit 5 which operates using the smoothing capacitor C ₁ as a power source. The expanded waveform of the rectified half-wave with respect to V _L and the output current I _L is almost flat as shown in FIG.

Considering the operation of this embodiment, since the first and second switching elements S ₁ and S ₂ are alternately turned on and off and the resonance current I _L0 is used with a delay, no switching loss occurs. Will also be. Further, since the voltage applied to the second switching element S ₂ is the input voltage Vin = 100V, an element having a lower breakdown voltage than the first switching element S ₁ side can be used.

In FIG. 5, the input voltage Vin is 50 V, which is half the input voltage Vin.
2 is an enlarged waveform diagram showing the state of the transient voltage and current of the inverter operation in FIG. 6 corresponding to FIG. 2, and FIG. 6 is the transient voltage of the inverter operation when the input voltage Vin is 0V,
FIG. 7 is an enlarged waveform diagram showing a state of current corresponding to FIG. 2 (for Vin = 50V, 0V, refer to FIG. 7).

FIG. 8 shows a modification in which a resonance capacitor C ₀₁ is provided in parallel with the first switching element S _{1 in} addition to the resonance capacitor C ₀ . According to such a configuration, alternately relates first and second switching elements S _1, S _2, which is on-off controlled, it shall have the dead time first and second switching elements S _1, S ₂ is turned off together Since partial resonance occurs, switching noise is reduced.

[0015]

According to the present invention, a smoothing capacitor is connected between full-wave rectified DC power supplies, and a series circuit of a first switching element and a resonant inductor is connected between both ends of this smoothing capacitor. An inverter circuit in which a series circuit of a second switching element and a resonant capacitor is connected in parallel to the first switching element and the smoothing capacitor is used as a power source is provided, and the first and second switching elements are alternately turned on / off controlled. In a discharge lamp lighting circuit for lighting the discharge lamp at a high frequency, a first diode is connected between the DC power source and the smoothing capacitor,
Since the second diode is connected between the DC power source and the second switching element side of the resonance capacitor, when the resonance inductor voltage generated by the resonance between the resonance inductor and the resonance capacitor in the inverter circuit becomes equal to the power supply voltage, Since the 2 diodes are turned on, a power factor improving current flows from the second switching element to the smoothing capacitor through the resonance inductor, so that a high peak current for the smoothing capacitor can be suppressed. Therefore, the power factor is improved with a simple configuration. In addition, it is possible to provide a low-distortion circuit that can keep the smoothing voltage constant and to make the high-frequency voltage applied to the discharge lamp that is a load almost flat, and the voltage applied to the second switching element is a DC power supply. An element having a low withstand voltage can be used because it becomes a considerable voltage.

[Brief description of drawings]

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

FIG. 2 is an enlarged waveform diagram showing a transient voltage and current at Vin = 100V.

FIG. 3 is an enlarged waveform diagram showing a transient state of an AC voltage E and an input current Iin.

FIG. 4 is an enlarged waveform diagram showing a transient state of output voltage and current with respect to a load.

FIG. 5 is an enlarged waveform diagram showing a transient voltage and current at Vin = 50V.

FIG. 6 is an enlarged waveform diagram showing a transient voltage and current at Vin = 0V.

FIG. 7 is a waveform diagram of a full-wave rectified voltage showing each point of Vin.

FIG. 8 is a circuit diagram showing a modified example.

9A and 9B show a conventional example, FIG. 9A is a circuit diagram, and FIG. 9B is a waveform diagram showing its input current.

[Explanation of symbols]

4 DC power supply 5 Inverter circuit 8 Discharge lamp C ₀ Resonance capacitor C ₁ Smoothing capacitor D ₁ First diode D ₄ Second diode L ₀ Resonant inductor S ₁ , S ₂ Switching element

Claims (1)

[Claims] 1. A smoothing capacitor is connected between direct-current power sources that have undergone full-wave rectification, and a first capacitor is provided between both ends of this smoothing capacitor.
An inverter circuit is provided in which a series circuit of a switching element and a resonance inductor is connected and a series circuit of a second switching element and a resonance capacitor is connected in parallel to the first switching element to use the smoothing capacitor as a power source. In a discharge lamp lighting circuit configured to alternately turn on and off the first and second switching elements to light a discharge lamp at a high frequency, a first diode is connected between the DC power source and the smoothing capacitor, A discharge lamp lighting circuit, wherein a second diode is connected between a DC power supply and the second switching element side of the resonance capacitor.