JP2001326091A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device enabled to restrain a current flowing in a filament of the discharge lamp at lighting even in the case that a discharging voltage is high while lighting. SOLUTION: For the discharge lamp lighting device, output of an inverter circuit 2 converting a direct current power source into high frequency by switching elements Q1, Q2, is supplied to a discharge lamp (fluorescent lamp) through the serial circuit of an inductance (ballast choke) L1 and a direct current blocking capacitor C1. A resonance capacitor C2 is connected to the primary side of the discharge lamp 3, and a starter capacitor C3 is connected to the secondary side of the discharge lamp 3. The inverter circuit makes 2 the discharge lamp 3 conducting to the state of lighting by reducing oscillation frequency in the order of preheating, starting, and lighting. When a resonance frequency of L1, C1, C2, C3 is defined as f 01, and a resonance frequency of L1, C1, C2 is defined as f 02, and oscillation frequency of the inverter circuit 2 during the discharge lamp 3 is lighting, is defined as f 1, the relations are; f 02>f 01>f 1 and 2×f 1×f 02<=4×f 1, here, 4 is an external excitation control means to drive and control the inverter circuit 2.

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.

[0002]

2. Description of the Related Art The output of an inverter circuit for converting a DC power supply to a high frequency by a switching element is represented by an inductance L.
1 and a DC cut capacitor C1 are supplied to the discharge lamp through a series circuit, and a starting capacitor C3 is connected to the secondary side of the discharge lamp.
A circuit is known in which the inverter circuit leads the discharge lamp to lighting by preheating, starting, lighting, and lowering the oscillation frequency.

[0003]

However, if the capacitance of the starting capacitor C3 is large, the current flowing through the filament of the discharge lamp during lighting becomes larger than a predetermined value, which causes a short life of the discharge lamp. Particularly, in the case of a discharge lamp which has recently been used and has a small tube diameter and a long discharge path, the discharge lamp voltage during operation is high, so that the capacitance of the starting capacitor C3 cannot be increased so much. Therefore, if the capacitance of the starting capacitor C3 is reduced, the inductance value of the inductance L1 must be increased due to the relationship of the resonance frequency including the inductance L1, and the circuit efficiency during lighting deteriorates. For these reasons, in the case of a discharge lamp having a high discharge lamp voltage during operation, a preheating method using only the starting capacitor C3 is not suitable, and a preheating method having a separate preheating transformer is employed. In this case, since a preheating transformer is separately required, the cost increases. In view of such problems to be solved, the present invention provides a discharge lamp lighting device capable of suppressing a current flowing through a filament of a discharge lamp during lighting even when a discharge lamp voltage during lighting is high. At the same time, it aims to solve the problems inherent therein.

[0004]

Means for solving the problems are as described in the claims.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described. However, this is merely an exemplary embodiment adopted based on the present invention, and the present invention will be described based on matters unique to the embodiment. Therefore, the technical scope of the present invention should be determined based on the matters stated in the claims and matters substantially equivalent to the matters.

In the illustrated embodiment, an output of an inverter circuit 2 for converting a DC power supply 1 to a high frequency by switching elements Q1 and Q2 is connected to an inductance (ballast choke) L.
1 and a DC cut capacitor C1 are supplied to a discharge lamp (fluorescent lamp) 3 through a series circuit, and a resonance capacitor C2 is provided on the primary side of the discharge lamp 3 and a starting capacitor C3 is provided on the secondary side of the discharge lamp 3 respectively. The inverter circuit 2 is connected in parallel, and the inverter circuit 2 guides the discharge lamp 3 to lighting by lowering the oscillating frequency in advance preheating, starting, lighting, and the L1, C1, C
2, the resonance frequency composed of C3 is f01, and the L1, C1,
Assuming that the resonance frequency of C2 is f02 and the oscillation frequency of the inverter circuit 2 when the discharge lamp 3 is turned on is f1, f02> f
01> f1, and 2 × f1 ≦ f02 ≦ 4 × f
1 is a discharge lamp lighting device, which is the relationship of 1. Reference numeral 4 denotes another excitation control means for driving and controlling the inverter circuit 2.

While the discharge lamp 3 is on, the filament 5
The current If flowing through 6 is given by If = 2πfC3 × V (C3: starting capacitor capacity, V: discharge lamp voltage, f: oscillation frequency of the inverter circuit 2).
Therefore, as the discharge lamp voltage increases, the filament current necessarily increases. Here, if the oscillation frequency of the inverter circuit 2 is reduced in order to reduce the filament current, it is not possible to reduce the size of the lighting device, which is an advantage of high-frequency lighting. Further, when the capacitance of the starting capacitor C3 is reduced, the inductance value of the inductance L1 must be increased in order to maintain the resonance frequency properly. In this case, in order to obtain a predetermined discharge lamp current, the voltage of the DC power supply 1 must be increased. As a result, circuit efficiency is deteriorated, and the cost is increased due to an increase in the size of parts and an increase in a heat sink. Become. Therefore, another capacitor, that is, a resonance capacitor C2, is added to the extent that the starting capacitor C3 is reduced.
Are connected in parallel to the primary side of the discharge lamp 3. By doing so, the current flowing through the filaments 5 and 6 during which the discharge lamp 3 is lit can be suppressed while maintaining the resonance frequency appropriately.

[0008] Here, the no-load resonance frequency f01 when the discharge lamp 3 is not in the spot is

(Equation 2) Also, the no-load resonance frequency f02 when the discharge lamp 3 comes off is

(Equation 3) In addition, the oscillation frequency f1 of the inverter circuit 2 when the discharge lamp 3 is turned on is set to have a relationship of f02>f01> f1.
That is, f1 is a frequency on the leading side with respect to f01,
By setting f1 to the phase-advancing frequency, the circuit efficiency when the discharge lamp 3 is turned on is improved. Note that the oscillation frequency of the inverter circuit 2 at the time of the preheating / starting is set higher than f01, and the operation is on the late side.

Here, assuming that the filaments 5, 6 are disconnected or the discharge lamp 3 is detached while the discharge lamp 3 is lit, the resonance frequency at this time is f02. Here, the oscillation frequency of the inverter circuit 2 is f1, which is also a frequency on the leading side with respect to f02.
1, Q2 is a leading phase current, that is, the switching element Q1,
It can easily be assumed that an excessive stress is applied by the forward current flowing when Q2 is turned on. However,
If 2 × f1 ≦ f02 ≦ 4 × f1, no forward current flows when the switching elements Q1 and Q2 are turned on,
Since no excessive stress is applied, there is no possibility that the switching elements Q1 and Q2 are broken.

On the other hand, the relationship between the oscillation frequency f1 when the discharge lamp 3 is turned on and the no-load resonance frequency f01 when the discharge lamp 3 is not lit is represented by a frequency fc expressed by the following equation.

(Equation 4) At a certain frequency, the effective value of the current flowing through the inductance L1 is constant regardless of the lighting state of the discharge lamp 3 such as rating and dimming (even when the discharge lamp equivalent resistance changes from 0 to ∞). Therefore, at this frequency, the current flowing through the inductance L1 can be stabilized, so that an excessive current can be prevented from flowing, and the size of the inductance L1 can be reduced. That is, the oscillation frequency f1 of the inverter circuit 2 when the discharge lamp 3 is turned on is preferably set at about fC. That is,

(Equation 5) Then, a very good effect can be obtained.

In addition, since C1 >> C2 + C3 in reality,
It is approximately given by fC ≒ (1 / 1.4142) × f01. That is,
Under the condition of C1 >> C2 + C3, if f1 = fC = 50 kHz, f01 = 70.71 kHz. And just f02 = 2 ×
f1, that is, the relationship between C2 and C3 that becomes 100 kHz is C3 = 2
× C2. From the above, how to select f1 for fC and C1
Depending on how to choose, the capacitance of C3 is the capacitance of C2
When the ratio is 1.6 times to 2.4 times, an extremely good effect can be obtained, and an inverter circuit capable of avoiding excessive stress even if the filament is disconnected or the discharge lamp is disconnected while the discharge lamp is on can be provided. It becomes. The present invention is a very effective means especially for a lamp with a small tube diameter of 20 mm or less because the tube voltage at the time of lighting the discharge lamp is high. Although a half-bridge inverter is shown in the embodiment, a similar effect can be obtained with a full-bridge inverter. The same effect can be obtained even when a transformer or a tapping choke is interposed in the load. In this case, the capacitance values of C2 and C3 may be set in consideration of the turns ratio N.

[Brief description of the drawings]

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

FIG. 2 is an equivalent circuit diagram when the discharge lamp (lamp) is out of order and when it comes off.

FIG. 3 is a resonance curve diagram showing the same operation.

[Explanation of symbols]

 Reference Signs List 1 DC power supply Q1, Q2 Switching element 2 Inverter circuit L1 Inductance (ballast choke) C1 DC cut capacitor 3 Discharge lamp (fluorescent lamp) C2 Resonant capacitor C3 Starting capacitor

Claims (3)

[Claims] An output of an inverter circuit for converting a DC power supply to a high frequency by a switching element has an inductance L.
1 and a DC cut capacitor C1 are supplied to the discharge lamp through a series circuit, and a resonance capacitor C is connected to the primary side of the discharge lamp.
2. A starting capacitor C3 is connected in parallel to the secondary side of the discharge lamp, and the inverter circuit leads the discharge lamp to lighting by lowering the oscillating frequency with advance preheating / starting / lighting. , C1, C2, C3, f01, the resonance frequency of L1, C1, C2 is f02, and the oscillation frequency of the inverter circuit when the discharge lamp is turned on is f01.
When it is set to 1, the relationship of f02>f01> f1 is satisfied, and
A discharge lamp lighting device having a relationship of 2 × f1 ≦ f02 ≦ 4 × f1. 2. An oscillation circuit according to claim 1, wherein the oscillation frequency f1 of the inverter circuit when the discharge lamp is turned on is Discharge lamp lighting device. 3. The discharge lamp lighting device according to claim 1, wherein the capacitance of C3 is 1.6 to 2.4 times the capacitance of C2.