JPH039279Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a discharge lamp lighting device that uses a DC power supply, and in particular, it facilitates the start of lighting of a discharge lamp and constantly maintains the lighting output of the discharge lamp regardless of fluctuations in input voltage. The purpose is to stabilize.

An example of a discharge lamp lighting circuit in a conventional device of this type is shown in FIG. Inverter section 1 of this circuit
0 consists of a first transistor 1, a resistor 2 for passing a starting current through it, current limiting capacitors 3, 6, an oscillating transformer 4, and a rectifying diode 5.
A discharge lamp 7 is connected between the end and one end of the capacitor 6.

In this circuit configuration, when the lighting power of the discharge lamp 7 is particularly low, the starting current flowing to the base of the transistor 1 via the resistor 2 is determined by the resistor 2, so normal lighting may not be possible depending on the value of the resistor 2. The discharge lamp 7 may also be affected by fluctuations in input voltage.
Since the structure directly affects the discharge current of the lamp, there was a drawback that the lighting output fluctuated greatly. The second method of stabilizing the lighting output is
DC power supply 8 and DC voltage stabilization unit 9 shown in the figure
A circuit consisting of an inverter section 10 and an inverter section 10 is generally known. However, according to this method, the power loss in the voltage stabilizing section 9 is large, and it is difficult to put it into practical use, especially in a device using a battery as a power source.

In order to eliminate these drawbacks, the present invention has provided second and third transistors 16 and 18, diodes 12, 19, The circuit configuration that includes the capacitor 13 and resistors 14, 15, and 17 ensures that the lighting starts normally, and also greatly improves the conversion efficiency against fluctuations in input voltage compared to conventional circuits and stabilizes the lighting output. It has become. This will be explained in detail below with reference to the drawings.

In FIG. 3, in order to light up the discharge lamp 7, when the switch 11 is closed, a charging current flows from the DC power source 8 to the capacitor 13 via the resistor 14 and the emitter/base of the second transistor 16. Therefore, the emitter and collector of the second transistor 16 become conductive, and a starting current is supplied to the base of the first transistor 1 via the resistor 15.
Therefore, by appropriately selecting the values of the resistors 14 and 15 and the capacitor 13, a sufficient starting current necessary to start lighting the discharge lamp 7 can be supplied to the base of the first transistor 1. capacitor 13
When the potential of the second transistor 16 reaches a predetermined value, the charging current stops flowing, and the emitter and collector of the second transistor 16 become non-conductive. Therefore, while the discharge lamp 7 is lit, no current flows through the second transistor 16, and the minimum starting current determined by the resistor 2 to continue lighting flows. .

Also, when switch 11 is opened to turn off the light, the charge stored in capacitor 13 is transferred to diode 1.
2. It is released through the first transistor 1 and quickly returns to the initial state.

Next, the stabilization function will be explained.

The basic operation is to detect the emitter current of the first transistor 1, and to stabilize the output of the inverter by controlling the base of the transistor 1 so that this value remains constant against fluctuations in the input voltage. .

The value of the resistor 17 is determined so that the voltage waveform across the resistor 17 when the power supply voltage is the lowest and a predetermined lighting output is obtained becomes a sawtooth waveform as shown by the solid line in FIG. That is, the peak value of the voltage waveform is made to be the on-voltage of the third transistor 18.
When the power supply voltage increases, the emitter current of the first transistor 1 increases, so that the voltage across the resistor 17 tends to take the sawtooth waveform shown by the dotted line in FIG. However, at the point where the voltage across the resistor 17 exceeds the on-voltage of the third transistor 18, the collector and emitter of the transistor 18 become conductive, so that the current to be supplied to the base of the first transistor 1 is reduced. It flows to ground via the diode 19 and the third transistor 18. Therefore, the first transistor 1 is quickly turned off. This operation shortens the conduction time of the first transistor 1, so that even if the power supply voltage increases, constant power is supplied to the discharge lamp, and the lighting output is stabilized.
Here, the role of the diode 19 will be supplementarily explained.
19 is for backflow prevention, and without it, the first
When the transistor 1 is off, a current flows in the path from the base of the third transistor 18 to the collector to the capacitor 3, which destroys the reverse bias condition of the transistor 1 and deteriorates the conversion efficiency by the amount of current.

Furthermore, when the power supply voltage decreases, the operation described above is reversed, the conduction time of the first transistor 1 becomes longer, and the lighting output is stabilized.

FIG. 5 shows changes in output power with respect to fluctuations in input voltage. Curve a is based on the conventional circuit, and the output power increases in proportion to the increase in input voltage, making it unstable. On the other hand, according to the present invention, even if the input voltage fluctuates (increases or decreases) as shown in curve b, the lighting output is significantly stabilized by only changing almost smoothly.

As explained above, according to the discharge lamp lighting circuit of the present invention, the discharge lamp can be reliably lit with a sufficient starting current. Furthermore, it is possible to greatly improve conversion efficiency against fluctuations in input voltage compared to conventional methods, and to obtain stable lighting output.
The practical effects are remarkable.

[Brief explanation of the drawing]

Fig. 1 is an example of a conventional discharge lamp lighting circuit, Fig. 2 is a configuration example diagram of a conventional stabilization method, Fig. 3 is a circuit diagram showing an embodiment of the present invention, and Fig. 4 is a discharge lamp lighting circuit. FIG. 5, which is a diagram for explaining the output stabilization operation, is a relationship diagram of input voltage versus output power, where a is a characteristic curve according to the conventional circuit and b is a characteristic curve according to the present invention. 1, 16, 18...First, second, and third transistors, 2, 14, 15, 17...Resistor, 3,
6.13...Capacitor, 4...Oscillation transformer,
5, 12, 19...Diode, 7...Discharge lamp,
8...DC power supply, 9...DC voltage stabilization section, 10
...Inverter section, 11...Switch.

Claims (1)

[Scope of utility model registration request] In order to light the discharge lamp, a rectifying diode and a capacitor for limiting the filament heating current of the discharge lamp are installed on the secondary side of the oscillation transformer, and a first
In a discharge lamp lighting device having a transistor, a resistance for supplying a starting current of the first transistor, and a capacitor for limiting a base current of the first transistor, a series connected element of a diode and a capacitor is connected in parallel with a DC power supply. And the second
The base of the transistor is connected to the connection point between the diode and the capacitor, and when the second transistor is activated, a charging current from the DC power supply is caused to flow into the capacitor through the resistor and the emitter of the second transistor. The second transistor is activated to supply a starting current to the base of the first transistor via a resistor connected to the collector of the second transistor, and the second transistor is activated while the discharge lamp is lit. becomes non-conductive, and the starting current for continuing the lighting is passed through the starting current supplying resistor of the first transistor, and the emitter of the first transistor and one end of the resistor are connected to the base of the third transistor. The other end of the resistor is connected to the emitter of the third transistor, and a backflow blocking diode is connected between the collector of the third transistor and the base of the first transistor. 1
When the transistor is non-conductive, current flows through the base and collector of the third transistor and the base current limiting capacitor of the first transistor, stabilizing the lighting output of the discharge lamp against fluctuations in input voltage. Characteristic discharge lamp lighting device.