JPH097780A - Discharge lamp lighting circuit - Google Patents

Abstract

PURPOSE: To allow to use a smoothing capacitor C1 having a small capacity, and to allow to use a diode D3 and a full wave rectifier DB which cannot bear to a large current. CONSTITUTION: This is a discharge lamp lighting circuit which has a series circuit of the first switching element Q1 and the second switching element Q2 turned on and off alternatively being connected to both ends of a smoothing capacitor C1, and connecting a discharge lamp La between the connecting point of the DC output terminal of a full wave rectifier DB and a diode D3; and the connecting point of the first switching element Q1 and the second switching element Q2; through a capacitor C3. A capacitor C7 is connected in parallel to the smoothing capacitor C1 through the series circuit of a diode D5 and an inductor L2, while a diode 4 is connected to the capacitor C7 in order to charge through the capacitor 3.

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 for converting a direct current power source obtained by rectifying and smoothing an alternating current power source into a high frequency and supplying it to a discharge lamp.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional discharge lamp lighting circuit (for example, Japanese Patent Laid-Open No. 5-38161). As shown in FIG. 4, a transformer L3 and a capacitor C5 are provided at an AC input terminal of a full-wave rectifier DB. An AC power supply V _S is connected via a filter circuit made of C6. The smoothing capacitor C1 is connected to the DC output terminal of the full-wave rectifier DB via the diode D3.
Is connected. A series circuit of transistors Q1 and Q2 is connected to the smoothing capacitor C1. Each of the transistors Q1 and Q2 has a diode D1 and a diode D2, respectively.
Are connected in anti-parallel. One end of a capacitor C3 is connected to a connection point between the diode D3 and the full-wave rectifier DB, and one end of an inductor L1 is connected to a connection point between the transistors Q1 and Q2. The power supply side terminal of the filament of the discharge lamp La is connected between the other end of the capacitor C3 and the other end of the inductor L1. A capacitor C2 is connected in parallel between the non-power supply terminals of the filament of the discharge lamp La. Moreover, at both ends of the diode D3,
The capacitor C4 is connected in parallel.

The following circuit operation will be described. Transistor Q
1, Q2, diodes D1 and D2, inductor L1, capacitors C2 and C3 form an inverter, transistors Q1 and Q2 are alternately turned on and off at high speed, and the DC voltage of the smoothing capacitor C1 is converted into a high frequency to discharge the lamp. La is lit at high frequency. The condenser C2 is a discharge lamp L
It constitutes the preheating current conduction path of the filament of a,
It also serves as a resonance capacitor with the inductor L1. The capacitor C3 is a coupling capacitor for cutting a DC component.

When the transistor Q2 is turned on, a current flows from the capacitor C1 to the capacitor C4, the capacitor C3, the discharge lamp La, the capacitor C2, the inductor L1, and the transistor Q2, and then returns to the capacitor C1. Connected to the output terminal of the full-wave rectifier DB is a series circuit of a capacitor C3, a discharge lamp La and a capacitor C2, and an inductor L1.
In a partial section of ON / OFF of 2, the full-wave rectifier D is passed from the full-wave rectifier DB through the capacitor C3, the discharge lamp La, the capacitor C2, the inductor L1, and the transistor Q2.
A current will flow in the route returning to B.

Output terminal of full-wave rectifier DB and capacitor C
The capacitor C4 inserted between 1 and 1 will share the voltage difference between the current output voltage of the full-wave rectifier DB and the voltage V1 across the capacitor C1, and the absolute value of the input voltage Vin will be the voltage V1 across the capacitor C1. The input current Iin flows even at a lower temperature than the above. Therefore, the input power factor becomes high. Further, the input current waveform obtained by removing the high frequency component by the filter circuit including the capacitors C5 and C6 and the transformer L3 is
The waveform can be close to a sine wave with few harmonic components. Further, in this circuit, when the transistor Q is turned on, a current is caused to flow directly from the full-wave rectifier DB to the discharge lamp La, so that the overall efficiency of the circuit is high and the input current quiescent period is shortened. It was possible to reduce the harmonic components of, and it was a circuit system suitable for a relatively small and small capacity discharge lamp lighting circuit.

In FIG. 4, K2 is a control circuit for controlling the switching frequency of the transistors Q1 and Q2.

[0007]

However, conventionally, when the power switch SW1 is turned on, a large spike current flows from the power source, which causes a problem that a large current charging the capacitor C1 flows. Further, since only the transformer L3 limits the current, the capacitor C1 has a large capacitance (for example, 100 μF). Then, as the diode D3 and the full-wave rectifier DB, those capable of sufficiently withstanding a large current were required.

In view of the above problems, the present invention is such that the smoothing capacitor C1 has a small capacity, and the diode D3 and the full-wave rectifier DB do not have to withstand a large current.

[0009]

The technical means of the present invention for solving this technical problem is to provide a full-wave rectifier DB for full-wave rectifying the AC power supply V _S and a DC output terminal of the full-wave rectifier DB. The full-wave rectifier DB includes a smoothing capacitor C1 connected via a diode D3, and a series circuit of a first switching element Q1 and a second switching element Q2 connected to both ends of the smoothing capacitor C1 and turned on / off alternately.
Connection point between the DC output terminal of the diode and the diode D3, the first switching element Q1 and the second switching element Q
In the discharge lamp lighting circuit in which the discharge lamp La is connected via the capacitor C3 between the connection point and the connection point with the capacitor C3, the smoothing capacitor C1 is connected in parallel with the capacitor C7 via the series circuit of the diode D5 and the inductor L2. The diode D4 is connected to the capacitor C7 so as to be charged via the capacitor C3.

[0010]

The voltage V1 across the capacitor C1 is the input current Vi.
In a section in which the absolute value of n fluctuates and the absolute value of the input voltage Vin is high, the same operation as in the conventional discharge lamp lighting circuit shown in FIG. 4 is performed, and the capacitor C3, the discharge lamp La, and the capacitor While current flows through C2 and inductor L1,
A part of this current flows through the diode D4 to the capacitor C
Charge 7. Therefore, when the power switch SW1 is turned on, even if a large spike current flows from the power source, the large current for charging the capacitor C1 does not flow, and the capacity of the smoothing capacitor C1 can be small.

[0011]

The present invention will be described below with reference to the illustrated embodiments. FIG. 1 shows an embodiment of the present invention. In FIG. 1, the smoothing capacitor C1 is set to a small capacity (for example, 0.47).
μF) and a new large capacity (eg 10
0 μF) A capacitor C7 is provided. The diode D4 is connected between the capacitor C7 and the capacitor C3 so that the capacitor C7 is charged via the capacitor 3.

A diode D is connected to the smoothing capacitor C1.
Capacitor C7 through a series circuit of the inductor 5 and the inductor L2.
Are connected in parallel and the voltage across the capacitor C7 is lower than the voltage V1 across the capacitor C1.
The electric charge of 7 is discharged through the inductor L2 and the diode D5. In this case, only a high-frequency current flows through the capacitor C3, so a small capacity (for example, 0.4
7 μF), and the charging current to the capacitor C7 becomes small when the power switch SW1 is turned on. Since the capacity of the capacitor C1 is small and it is discharged immediately, the capacitor C1
The voltage V1 across both ends and the input voltage Vin have the waveforms as shown in FIG. 2 (a) in the case of the conventional circuit of FIG. 4, but are shown in FIG. 2 (b) in the case of the embodiment of the present invention of FIG. The voltage V1 across the capacitor C1 becomes the input current Vi.
In a section in which the absolute value of n fluctuates and the absolute value of the input voltage Vin is high, the same operation as in the conventional discharge lamp lighting circuit shown in FIG. 4 is performed, and the capacitor C3, the discharge lamp La, and the capacitor While current flows through C2 and inductor L1,
A part of this current flows through the diode D4 to the capacitor C
Charge 7.

Since the voltage generated in the capacitor C3 is 1/2 of the absolute value of the input voltage Vin, the charging voltage of the capacitor C7 is approximately 1/2 of the peak value of the input voltage Vin. When the electric charge of the capacitor C7 suddenly flows out, the input current may suddenly decrease, and the input current quiescent period may become long. However, the inductor L2 is used when the electric charge of the capacitor C7 is about to increase the voltage of the capacitor C1. The sudden flow is prevented, and the harmonic component in the input current Iin is prevented from increasing.

FIG. 4 shows another embodiment, which is a capacitor C4.
Is connected between the DC output terminals of the full-wave rectifier DB, and the capacitor C2 is connected to both ends of the discharge lamp La.
A diode D4 is connected between 7 and the capacitor C3 via an inductor L2. Also, the diode D1
And the diode D2 is omitted. In other respects, the configuration is the same as that of the above-described embodiment, and the same operational effect as that of the above-described embodiment is obtained.

In the above embodiment, the first switching element Q1 and the second switching element Q2 are composed of transistors. However, the first switching element Q1 and the second switching element Q2 are not limited to transistors, and thyristors and others. You may comprise by the switching element of.

[0016]

According to the present invention, the smoothing capacitor C1 has a small capacity, and the diode D3 and the full-wave rectifier DB do not have to withstand a large current.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram for explaining the same operation.

FIG. 3 is a circuit diagram showing another embodiment.

FIG. 4 is a circuit diagram showing a conventional example.

[Explanation of symbols]

AC power supply V _S DB full-wave rectifier D3 diode C1 capacitor Q1 first switching element Q2 second switching element C3 capacitor La discharge lamp D5 diode L2 inductor D4 diode

Claims (1)

[Claims] 1. A full-wave rectifier (DB) for full-wave rectifying an AC power supply (V _S ), and a smoothing capacitor (C1) connected to a DC output terminal of the full-wave rectifier (DB) through a diode (D3). And a first switching element (Q1) connected to both ends of the smoothing capacitor (C1) and alternately turned on and off.
And a series circuit of the second switching element (Q2), a connection point between the DC output terminal of the full-wave rectifier (DB) and the diode (D3), the first switching element (Q1) and the second switching element. In a discharge lamp lighting circuit in which a discharge lamp (La) is connected via a capacitor (C3) to a connection point with (Q2), a diode (D5) and an inductor (L2) are added to the smoothing capacitor (C1). ) Series circuit via a capacitor (C
7) are connected in parallel, and a diode (D4) is connected to the capacitor (C7) so as to be charged through the capacitor (C3), a discharge lamp lighting circuit.