JP3300786B2 - Discharge lamp lighting circuit - 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 circuit for lighting a plurality of discharge lamps, and more particularly to a discharge lamp lighting circuit for lighting all discharge lamps without an unlit discharge lamp.

[0002]

2. Description of the Related Art When a plurality of cold-cathode discharge lamps (discharge lamps) are lit by one inverter, it is usually determined whether each discharge lamp is lit or not lit by using an operational amplifier or a comparator. Is integrated by an operational amplifier, and then applied to an inverter control circuit to continuously apply a high voltage at which discharge can be started until all the discharge lamps are turned on, and after lighting, a circuit is used to reduce to a normal discharge sustaining voltage. .

FIG. 2 shows an example of such a lighting circuit.
1 and 2 are discharge lamps respectively, 3 is a transistor Q1,
A self-excited oscillating inverter by Q2 serves as a lighting power supply for energizing the discharge lamps 1 and 2. A part of the current passing through Q1 and Q2 is rectified by D3 to generate a voltage at point C,
When all the discharge lamps are turned on, Q4 changes from off to on, the voltage at point C decreases, and is input to the control unit 4 via D4.

The control unit 4 controls the output of the inverter 3 to be either the discharge starting voltage or the discharge sustaining voltage.
3 is changed so as to generate a sustaining voltage.

[0005] Reference numeral 5 denotes a judgment circuit using an operational amplifier or a comparator, which judges lighting based on a voltage drop of a resistor R due to a load current of a discharge lamp, and controls to turn on Q4 when all lamps are lit. It is.

[0006]

In the lighting circuit as described above, if there is no lighting based on the signal from the determination circuit 5, a high discharge starting voltage is applied and continues until all of the lighting are performed. In order to determine the operation of the discharge lamp, a comparator, an operational amplifier, and the like for each lamp are required, which causes a problem that the cost is increased and a circuit space is required.

The present invention has been made in view of such a problem, and an object of the present invention is to solve a conventional problem by simplifying a lighting determination circuit in a lighting circuit for lighting a plurality of discharge lamps. An object of the present invention is to provide a lighting circuit.

[0008]

In order to achieve the object of the present invention as described above, the present invention provides a self-excited inverter circuit which serves as a power source for a predetermined number of cold cathode discharge lamps connected in parallel. In the discharge lamp lighting circuit for applying a discharge starting voltage and applying a discharge maintaining voltage to the predetermined number of cold cathode discharge lamps connected in parallel, wherein the predetermined number of cold cathode discharge lamps are confirmed to be lit, Using a load current detection circuit provided in each of the discharge lamps to extract the amount of current flowing through these discharge lamps as a voltage, and a diode AND circuit using a reference voltage, a combined voltage of the load current detection circuits is input. A transistor that is applied and turned on by the combined voltage of the load current detection circuit in a state where a predetermined number of discharge lamps are turned on, and is turned off by a combined voltage in a state where even one lamp is not lit; In the off state, the inverter circuit applies a discharge starting voltage to the discharge lamp, and when the transistor is on, the self-excited inverter circuit includes voltage control means for applying a sustaining voltage to the discharge lamp. Disclosed is a discharge lamp lighting circuit.

[0009]

According to the present invention, it is determined whether or not all of the voltages of the detection circuit for detecting the load current of the discharge lamp have been turned on using a diode AND circuit, and the inverter serving as a power supply is controlled in accordance with the result. And the cost is reduced.

[0010]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of a discharge lamp lighting circuit according to the present invention. In this figure, the same parts as those in FIG. 2 described above are denoted by the same reference numerals, and description thereof will be omitted.

D1 and D2 are cold cathode discharge lamps (discharge lamps)
Is a diode connected to a point A or A 'at one end of a resistor R serving as a detecting means that changes in accordance with the load current, and connected to an AND circuit of a logic circuit. The voltage at the point A 'is checked, and when it is determined that both are turned on, the operation of the transistor Q5 is changed from off to on.

The operation of this embodiment constructed as described above will be described. When the power is turned on and the discharge lamps 1 and 2 are not lit, the reference voltage Vre of the control unit 4 via R1 is output.
Since f is about 0.8 V at the point B, the points A and A 'are 0.1 V. Therefore, Q5 is turned off, and the control unit 4 controls the inverter 3 to output the discharge start voltage.

Next, when only the discharge lamp 1 is turned on, the point A is about 5 V due to the load current, but the point A 'is about 0.1 V when the lamp is not lit, and the point B is 0 V as described above. .
Since the voltage is 8 V, Q5 is turned off, and the discharge start voltage is continued.

Next, when the discharge lamp 2 is turned on to be fully lit, both the points A and A 'become 5V, and the point B becomes about 1.4V when D1 and D2 are in the reverse bias state. For this reason, Q5 is turned on, and the operation of Q3, which is the output of the control unit 4, is changed to control the inverter 3 to output a predetermined discharge sustaining voltage, so that the discharge lamps 1, 2 continue stable lighting. Will do.

Although the present invention has been described with reference to the above embodiment, various modifications are possible within the scope of the present invention, and these modifications are not excluded from the scope of the present invention.

[0017]

According to the present invention as in the above embodiment,
When lighting multiple discharge lamps with a single inverter, all the lightings are determined using a diode AND circuit based on the voltage from the resistor that detects the load current of each discharge lamp, and the inverter is controlled to maintain discharge. Switching to voltage eliminates the need for a comparator or an operational amplifier in the discriminating circuit, thereby simplifying the circuit, reducing the circuit space, and reducing the cost.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a discharge lamp lighting circuit according to the present invention.

FIG. 2 is a circuit diagram of an example of a conventional lighting circuit.

[Explanation of symbols]

 1, 2, discharge lamp 3, inverter 4, control unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-52-93181 (JP, A) JP-A-3-118514 (JP, A) JP-A-60-74391 (JP, A) JP-A 63-93181 160197 (JP, A) Japanese Utility Model Showa 61-15164 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 41/24-41/298 H05B 41/38-41/42

Claims (1)

(57) [Claims] 1. A discharge start voltage is applied from a self-excited inverter circuit serving as a power supply to a predetermined number of cold cathode discharge lamps connected in parallel, and lighting of the predetermined number of cold cathode discharge lamps is confirmed. In a discharge lamp lighting circuit for applying a discharge sustaining voltage to the predetermined number of cold cathode discharge lamps connected in parallel, a load current provided for each of the discharge lamps and extracting a current amount flowing through these discharge lamps as a voltage and detection circuit, using a diode aND circuit using the reference voltage, the combined voltage of each of the load current detection circuit is input application, the load current detection times in the state in which a predetermined number of the discharge lamp is lit
A transistor that is turned on by the combined voltage of the path and is turned off by the combined voltage in a state where at least one lamp is not lit; and an inverter circuit applies a discharge starting voltage to the discharge lamp when the transistor is off, and the transistor is turned off. A self-excited inverter circuit in a turned-on state, comprising: voltage control means for applying a discharge sustaining voltage to the discharge lamp;