JPS58121594A - Circuit for firing cold cathode discharge lamp for vehicle - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for lighting a cold cathode discharge lamp for an automobile by boosting an alternating current voltage obtained from a direct current power supply via an inverter.

Conventional circuits of this type simply convert direct current to alternating current using an inverter, step up the voltage using a step-up transformer, and apply the voltage to the discharge lamp, so they are easily affected by fluctuations in the direct current power supply voltage. That is, when the DC power supply voltage fluctuates, the inverter output voltage fluctuates, and the brightness of the discharge lamp fluctuates. In addition, discharge lamps generally have extremely high impedance at low temperatures, making them difficult to start, but conventional circuits simply have the above-mentioned configuration, so they have the disadvantage of poor startability at low temperatures. Ta.

The present invention has been made to eliminate the above-mentioned drawbacks, and is a discharge lamp for automobiles that does not vary in brightness even when the DC power supply voltage fluctuates, and has excellent starting performance at low temperatures. The purpose of this invention is to provide a lighting circuit for a cold cathode discharge lamp.

The present invention will be described in detail below with reference to FIGS. 1 and 2. FIG. 1 is a diagram schematically showing an embodiment of a lighting circuit for a cold cathode discharge lamp for an automobile according to the present invention, in which B is a positive connection terminal of a battery whose negative electrode is grounded, G is a ground terminal,
1 is N, which is the main component of the inverter that converts direct current to alternating current.
A PN type booster transistor, 2 a step-up transformer for boosting the alternating current voltage output from the inverter, and 3 a cold cathode discharge lamp provided with a secondary side voltage of the step-up transformer 2. In addition, 4 is a constant voltage circuit that makes the battery voltage constant;
Reference numeral 5 denotes a starting circuit provided between the constant voltage circuit 4 and the inverter, which increases the drive voltage of the inverter to increase the inverter output voltage when starting the discharge lamp 3, and after starting the inverter increases the inverter output voltage. The output voltage of the constant voltage circuit 4 is controlled so that it is driven at a constant voltage with a relatively small voltage. Reference numeral 6 denotes a backflow prevention circuit inserted in the power supply line extending from the positive connection terminal B to the primary side of the step-up transformer 2.

That is, in the present invention, the constant voltage circuit 4 drives the inverter at a constant voltage so that the brightness of the discharge lamp 3 does not change even if the battery voltage fluctuates, and the starting circuit 5 drives the inverter at a constant voltage to prevent the brightness of the discharge lamp 3 from changing when starting the discharge lamp 3. This circuit is designed to improve the startability of the discharge lamp 3 at low temperatures by increasing the applied voltage.Hereinafter, a specific example of the circuit of the present invention will be explained based on FIG. 2.

In FIG. 2, B and G respectively indicate the positive connection terminal and the ground terminal of the battery as in FIG. 1. Reference numeral 7 denotes a diode constituting the backflow prevention circuit 6, whose anode is connected to the positive terminal BK and whose cathode is grounded via the capacitor 8. 9 is a resistor whose one end is connected to the cathode of diode 7, and 10 is a resistor 9 whose base is connected to the cathode of diode 7.
An NPN type transistor is connected to the other end, and the collector is connected to the cathode of the diode 7, 11 is a Zener diode connected between the base of the transistor 10 and the ground, and 12 is connected between the emitter of the transistor 10 and the ground. These capacitors constitute the constant voltage circuit 4. 13 is a resistor whose one end is connected to the emitter of the transistor 10, and 14 is a resistor whose emitter is connected to the emitter of the transistor 10 and whose base is the resistor 13.
A PNP type transistor is connected to the other end, 15 is a capacitor connected between the base of the transistor 14 and ground, and 16 is a resistor connected between the emitter and collector of the transistor 14. Configure.

17 has one end connected to the collector of the transistor 14,
The other end is a resistor that is grounded via a capacitor 18.

19, 20 and 21 are power transistors, step-up transformers and discharge lamps similar to 1.2 and 3 in FIG. 1, respectively. In this case, the power transistor 19 has a collector connected to the cathode of the diode 7 via the first primary winding 20a of the step-up transformer 20, and a base connected to the resistor 17 and the cathode of the diode 7 via the second primary winding 20b of the step-up transformer 20. It is connected to the connection point of the capacitor 18 and its emitter is grounded, and forms the main structure of an inverter that converts the DC voltage from the positive connection terminal B into an AC voltage. Further, the discharge lamp 2
1 is a step-up transformer 20 whose one end is grounded as in Fig. 1.
is connected between both ends of the secondary winding 20c.

Next, the operation of the circuit of the present invention configured as described above will be explained. First, when the positive terminal of a battery (not shown) is connected (power is turned on) to the positive terminal B, the transistor 1
When 0 is ON, the emitter voltage of the transistor 10, which is the output voltage of the constant voltage circuit 4, increases instantaneously. When the emitter voltage of transistor 10 increases, capacitor 15 is charged according to a time constant determined by resistor 13 and capacitor 15 of starting circuit 5, and the base potential of transistor 14 gradually increases. Therefore, the transistor 14
The emitter-collector impedance of the inverter gradually changes from zero to infinity, and the base current of the power transistor 19, which constitutes the main component of the inverter, gradually decreases from the maximum until the steady state magnitude determined by the resistors 16 and 17 is reached. It's going to be. By the way, when the base current of the power transistor 19 is large, its collector current, in other words, the inverter output voltage becomes large, and the voltage across the secondary winding 20c of the step-up transformer 20 also becomes large. When starting the discharge lamp 21, a high voltage is applied to the discharge lamp 21 to facilitate its starting (starting of lighting). In addition, in a steady state after starting the discharge lamp 21, the transistor 14 of the starting circuit 5 is OFF, so a voltage regulated by the constant voltage circuit 4 is applied to the power transistor 19. Sahuru. Therefore, even if the power supply voltage (voltage applied to terminal B) changes in a steady state after the discharge lamp 21 is started, the drive voltage and oscillation frequency of the inverter will not change, and the brightness of the discharge lamp 21 will not change. It doesn't change either. In addition, normally, in a circuit using the step-up transformer 20, strong spike noise appears in the primary windings 2Qa, 20b (Ill) of the step-up transformer 20, and this gets on the power supply line and adversely affects other circuits of the automobile.Diode 7 (Noise prevention circuit 6) is to cut such noise, and this diode 7 also has the function of cutting the negative side of noise and surge from the positive terminal terminal B side. It is something.

As described above, the present invention provides a circuit for lighting an automotive cold cathode discharge lamp by boosting an AC voltage obtained from a DC power source via an inverter using a step-up transformer, in which the voltage of the DC power source is made constant. A constant voltage circuit is provided between the constant voltage circuit and the inverter, and when the discharge lamp is started, the drive voltage of the inverter is increased to increase the inverter output voltage, and after the discharge lamp is started, the inverter is Since a starting circuit is provided to control the output voltage of the constant voltage circuit so that the lamp is driven at a constant voltage with a small voltage, the brightness of the discharge lamp does not fluctuate even if the DC power supply voltage fluctuates. However, there are effects such as being able to easily start the discharge lamp.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing an embodiment of a lighting circuit for a cold cathode discharge lamp for an automobile according to the present invention, and FIG. 2 is a diagram showing a specific example of the circuit of the present invention. 1.19... Power transistor, 2.20... Step-up transformer, 3.21... Discharge lamp, 4... Constant voltage circuit, 5... Starting circuit, 6... Backflow prevention circuit, 10B・
...Battery positive connection terminal, G...Ground terminal. Patent applicant: Ichikoh Industries, Ltd.

Claims (1)

[Claims] (1) In a circuit for lighting a cold cathode discharge lamp for an automobile by boosting an AC voltage obtained from a DC power source via an inverter using a step-up transformer, the voltage of the DC power source is made constant. A voltage circuit is provided between the constant voltage circuit and the inverter, and when the discharge lamp is started, the driving voltage of the inverter is increased to increase the inverter output voltage, and after the discharge lamp is started, the inverter is lower than that at the time of starting. 1. A lighting circuit for a cold cathode discharge lamp for an automobile, comprising a starting circuit for controlling an output voltage of the constant voltage circuit so as to be driven at a constant voltage. 2. The lighting circuit for a cold cathode discharge lamp for an automobile according to claim 1, wherein the DC power line leading from the DC power source to the step-up transformer is equipped with a backflow prevention circuit.