JP2881764B2 - Multi-discharge lamp batch lighting circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a multi-discharge lamp collective lighting circuit.

2. Description of the Related Art In general, in a discharge lamp lighting circuit of this type, a commercial AC power supply is converted into a high frequency through an invar circuit, and the high frequency power supply is used for lighting. More specifically, two switching elements are connected between the rectified and smoothed output terminals of the AC power supply, and a current-limiting inductor is connected between the connection midpoint of these switching elements and the filament of the discharge lamp. A capacitor is connected between both ends of the discharge lamp via a filament to form an LC series resonance circuit. With such a current limiting inductor and capacitor
The LC series resonance circuit becomes a ballast circuit that functions as a lamp circuit, and is used for starting and lighting the discharge lamp.

A discharge lamp pair including such a high-frequency power supply-ballast circuit having an inverter circuit configuration is a basic unit as a discharge lamp lighting circuit. Are desirably configured to be turned on collectively. That is, a plurality of discharge lamps are connected in parallel to the load side power supply line of the high frequency power supply.

In any case, before the discharge lamp is started, a high lamp starting voltage is generated as a lamp secondary voltage by LC resonance of the ballast circuit. If the voltage at this time is low, the discharge lamp does not start lighting.

Problems to be Solved by the Invention However, it is impossible to keep all lamp circuit elements in a state where there is no variation. Due to this variation, a variation also occurs in the no-load secondary voltage between the lamp circuits. . As a result, the voltage at the time of starting the lamp causes a large variation due to the variation of the lamp circuit elements (current-limiting inductor L and capacitor C), and a discharge lamp which does not start because the lamp starting voltage is too low often occurs.

To prevent this, anticipate the variation of the secondary voltage,
It is considered that the target secondary voltage may be set so that the lower limit value of the secondary voltage may satisfy the lamp starting voltage even if the secondary voltage varies. However, this requires circuit elements,
In particular, since the inductor has to be made large so as not to be saturated even by a secondary voltage set higher, there is a problem that the whole device becomes expensive, large, and heavy. In addition, the size of the high-frequency power supply also increases, causing the same problem.

Means for Solving the Problems To achieve the above object, the present invention provides a high-frequency power supply having a variable output frequency; a plurality of discharge lamps connected in parallel between load-side power lines of the high-frequency power supply; A ballast circuit for starting lighting which is provided corresponding to the discharge lamps of the above and forms an LC resonance circuit; a voltage detection circuit for detecting a voltage between both ends of each discharge lamp; and a voltage between both ends detected by these voltage detection circuits An OR circuit for selecting a maximum value among the voltages; and a control circuit for controlling the output frequency of the high-frequency power supply so that the maximum voltage output from the OR circuit is equal to or higher than the lamp starting voltage. It is characterized by the following.

Operation Before starting, a high voltage is generated at both ends of each discharge lamp due to LC resonance of each ballast circuit. However, when the voltage becomes lower than the starting voltage due to variation in elements, the starting lamp may not be turned on. At this time, the voltage between both ends of each discharge lamp is detected by the voltage detection circuit, and the maximum value is selected by the OR circuit.
Then, the control circuit controls the operation of the high frequency power supply so that the maximum voltage between both ends becomes a constant value satisfying the stamp starting voltage. As a result, the discharge lamp is turned on and the voltage between both ends is reduced. Therefore, the same operation is repeated for the remaining unlit discharge lamps, a sufficient secondary voltage is supplied, and all of the discharge lamps are started and lit. After all the discharge lamps have been started and lit, the high frequency voltage for starting is unnecessary, as is well known, but is reduced to the voltage for lighting. This can be done by using timer means as is well known,
By using a means for detecting that all the discharge lamps have been turned on, the configuration can be made appropriately.

Embodiment An embodiment of the present invention will be described with reference to the drawings. First,
A high frequency power supply 1 is provided. In this example, the high-frequency power supply 1 is of a separately-excited type having an inverter configuration as described later, but is not limited thereto and may have any configuration. Load-side current lines 2a, 2b by this high-frequency power supply 1
Is configured such that a plurality of, for example, three discharge lamps 3a, 3b, 3c can be connected in parallel. Here, each discharge lamp 3a, 3
Ballast circuits a, 4b, 4c for starting lighting are connected to b, 3c. For example, to explain the ballast circuit 4a, the current limiting inductor La connected between the power supply line 2a and the filament 3a _{1 of} the discharge lamp 3a, and the current limiting inductor La connected between the filaments 3a ₁ and 3a ₂ for the discharge lamp 3a. On the other hand, it consists of an LC series resonance circuit with a capacitor Ca in series. The same applies to the other ballast circuits 4b and 4c, each of which comprises an LC series resonance circuit including current-limiting inductors Lb and Lc and capacitors Cb and Cc. These ballast circuits 4a, 4b, 4c are connected in parallel between the power supply lines 2a, 2b.

Further, each of the discharge lamps 3a, 3b, 3c is connected to a voltage detection circuit 5a, 5b, 5c for detecting a voltage between both ends (including a voltage proportional to the both ends voltage). Outputs (detection voltage) from these voltage detection circuits 5a, 5b, 5c are input to an OR circuit 6. The OR circuit 6 selects the maximum value among the detected voltages obtained from the voltage detection circuits 5a, 5b, 5c and outputs the selected value to the control circuit 7. The control circuit 7 is connected to the high-frequency power supply 1 and controls the output frequency of the high-frequency power supply 1 such that the maximum voltage between the terminals detected and detected is equal to or higher than the lamp starting voltage. For example,
When starting in a frequency range higher than the resonance point of the LC resonance circuit, if the maximum voltage between both ends is lower than the starting voltage of the lamp, control is performed so that the output voltage of the high-frequency power supply 1 decreases. When the lamp is started in a frequency region lower than the resonance point of the LC resonance circuit, if the maximum voltage between both ends is lower than the starting voltage of the lamp, the output voltage of the high-frequency power supply 1 is controlled to be higher. In what frequency range the operation is performed, it can be set sufficiently even in consideration of the variation of the circuit elements.

In such a configuration, a high voltage is generated across the discharge lamp 3 due to LC series resonance of the ballast circuit 4 before the discharge lamp 3 is turned on. However, the individual discharge lamps 3a, 3b, 3c
In consideration of the above, due to the variation of the elements L and C of the ballast circuits 4a, 4b and 4c provided as the respective lamp circuits, the voltage between both ends of the discharge lamps 3a, 3b and 3c causes a large variation, so that the lamp cannot be turned on. May be low.

In this regard, in this embodiment, each of the discharge lamps 3a, 3b, 3c
Are detected by the voltage detection circuits 5a, 5b, and 5c, and the one with the highest voltage is selected by the OR circuit 6. The control circuit 7 receives the highest voltage across the lamp from the OR circuit 6, and controls the operation of the high-frequency power supply 1 so that this voltage becomes the discharge lamp starting voltage. This allows
The discharge lamp 3 exhibiting the highest voltage across the lamp (for example, the discharge lamp 3a) is turned on, and the start-up lighting lowers the voltage across the lamp of the discharge lamp 3a. As a result, the voltage between both ends of the discharge lamp 3a does not become the maximum value, and the OR circuit 6 outputs the last-lit discharge lamp 3 obtained from the voltage detection circuits 5b and 5c.
Select the maximum value of the voltage across b or 3c. The control circuit 7 receives the new terminal voltage from the OR circuit 6, and controls the operation of the high-frequency power supply 1 by the control circuit 7 so that the terminal voltage becomes the starting lighting voltage. As a result, the discharge lamp 3 having a high voltage across the lamp, for example, the discharge lamp 3b is started and turned on, and the voltage across the discharge lamp 3b is reduced.
Therefore, the OR circuit 6 and the control circuit 7 are the remaining end-on discharge lamps.
A similar voltage control operation is performed on the discharge lamp 3c, and finally the discharge lamp 3c is also started, and all the discharge lamps 3a, 3b, 3c are turned on.

As described above, according to the present embodiment, even when the secondary voltages of the individual circuits generated due to the variations of the elements L and C vary, the starting lighting can be reliably performed. For this reason, the target secondary voltage does not need to be set to a high voltage in consideration of circuit variation, and it is not necessary to increase the size of the current-limiting inductor L or the high-frequency power supply 1, and it is possible to reduce the size. Also, the element
Since variations in L and C are allowed, it is easy to manufacture. In addition, since the lamp circuit can be separated from the high-frequency power supply 1, the circuit design can be simplified. Further, the individual lamp circuits can have different values, and a lighting circuit for lighting various types of lamps with one power supply can be configured.

Incidentally, this embodiment is specifically configured as shown in FIG. 2, for example. First, the high-frequency power supply 1 is composed of an inverter circuit 8 mainly composed of _two switching transistors Q ₁ and Q ₂ connected in series (for example, a field effect transistor MOS FET is used). In this inverter circuit, switching transistors Q ₁ and Q ₂ are connected in series between rectified and smoothed output terminals after passing through a full-wave rectifier circuit 10 to a commercial AC power supply 9. One power supply line 2a is drawn out from the connection midpoint of the switching transistors Q ₁ and Q ₂ , and the current limiting inductors La, Lb and Lc are connected to each other. Then, high frequency power according to a switching-operation of when to quenching transistors Q _1, Q ₂ is the power supply line 2a, is supplied to 2b.

On the other hand, the voltage detection circuit 5a includes voltage dividing resistors Ra ₁ and Ra ₂ connected to the discharge lamp 3a, and a transistor Qa connected to the connection midpoint. Similarly, the other voltage detection circuits 5b and 5c
Combination of voltage dividing resistors Rb ₁ and Rb ₂ and transistor Qb, voltage dividing resistor R
It is composed of a combination of c ₁ , Rc ₂ and a transistor Qc. The OR circuit 6 includes diodes Da, Db, and Dc connected to the respective emitters of the transistors Qa, Qb, and Qc. As a result, a high voltage is generated in the voltage dividing resistor corresponding to the one having the highest voltage among the discharge lamps 3a, 3b, and 3c. You. These diodes Da, Db,
On the output side of Dc, a capacitor C ₁ , resistors R ₁ and R ₂ , a variable resistor VR
The voltage circuit 11 is connected to output a voltage proportional to the voltage across the discharge lamp corresponding to the turned-on transistor Q (any of Qa, Qb, and Qc).

The control circuit 7 includes, for example, an IC circuit 12 and a current transformer 13.
And the like. Current transformer 13 are those whose operation is controlled by a transistor (not shown) in the IC circuit 12, when to quenching transistors Q _1, Q ₂ current windings 13a for driving for, 13b are provided respectively. The IC circuit 12 includes a not-shown comparator, comparator, oscillator, and the like, and is obtained through a diode D (any of Da, Db, or Dc) corresponding to the turned-on transistor Q (any of Qa, Qb, or Qc). The operating frequency of the switching transistors Q ₁ and Q ₂ is controlled in accordance with the voltage value from the voltage circuit 11, that is, the maximum voltage across the lamp at that time. As a result, the voltage across the selected lamp is controlled so as to satisfy the lamp starting voltage.

Advantageous Effects of the Invention As described above, the present invention provides a high-frequency power supply having a variable output frequency; a plurality of discharge lamps connected in parallel between load-side power supply lines of the high-frequency power supply; A ballast circuit for starting and lighting which forms an LC resonance circuit; a voltage detection circuit for detecting the voltage between both ends of each discharge lamp; and selecting a maximum value among the voltage between both ends detected by these voltage detection circuits. An OR circuit; and a control circuit that controls the output frequency of the high-frequency power supply so that the maximum voltage output from the OR circuit is equal to or higher than the lamp starting voltage. Even if there is a variation in the no-load secondary voltage due to the variation, all the discharge lamps can be reliably started and lit, so that the target secondary voltage satisfies the starting voltage at the lower limit of the variation. Since there is no need to set a large value, there is no need to use a large current-limiting inductor or a high-frequency power supply, and the power supply side and the lamp circuit side can be designed separately, so that circuit design can be simplified.

[Brief description of the drawings]

The drawings show an embodiment of the present invention, FIG. 1 is a block circuit diagram, and FIG. 2 is a circuit diagram showing a specific example. 1 ... high frequency power supply, 2a, 2b ... load side power supply line, 3a, 3
b, 3c …… Discharge lamp, 4a, 4b, 4c …… Ballast circuit, 5a, 5b, 5c
…… Voltage detection circuit, 6 …… OR circuit, 7 …… Control circuit

Continuation of front page (56) References JP-A-63-160194 (JP, A) JP-A-63-160195 (JP, A) JP-A-63-160196 (JP, A) JP-A-52-93181 (JP, A) , A) Fully open 1986-651464 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05B 41/24

Claims (1)

(57) [Claims] A high-frequency power supply having a variable output frequency; a plurality of discharge lamps connected in parallel between load-side power supply lines of the high-frequency power supply; and an LC resonance circuit provided for each discharge lamp. A ballast circuit for starting lighting to be formed; a voltage detection circuit for detecting the voltage between both ends of each discharge lamp; an OR circuit for selecting a maximum value among the voltage between both ends detected by these voltage detection circuits; A control circuit for controlling an output frequency of the high-frequency power supply so that a maximum voltage between both ends of the high-frequency power supply is equal to or higher than a lamp starting voltage. .