JPH0313998Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Field of Application) This invention relates to a discharge lamp lighting device, particularly to a discharge lamp lighting device used as a power supply device for a high frequency inverter.

(Prior Art) A means for lighting a discharge lamp using a DC power source, such as a battery, as an operating power source and a high frequency inverter that generates high frequency output is well known. In such a configuration, it is well known that the current flowing from the battery to the high frequency inverter increases momentarily just before the discharge lamp starts up. Even in such a case, the base current of the transistor constituting the high frequency inverter is usually set so that a sufficient current flows through the discharge lamp.

However, the base current set in this way is higher than the base current required for the current flowing to the high frequency inverter after the discharge lamp reaches the lighting state,
Naturally, the loss due to the base current increases. Such an increase in loss increases the consumption of the DC power source used as a power source, and therefore, it is required to reduce the base current loss as much as possible.

(Problem that the invention attempts to solve) This invention allows sufficient base current to flow through the transistors that make up the high-frequency inverter in order to cope with the increase in input current just before the discharge lamp starts. Note that the purpose is to suppress the increase in loss due to base current.

(Means for solving the problem) This idea uses a Hall element to detect the input current flowing into the high-frequency inverter, and when an increase in the input current is detected, the base circuit of the transistor constituting the high-frequency inverter detects an increase in the input current. A resistor inserted in the discharge lamp is short-circuited, and after the discharge lamp is lit, the short-circuit of the resistor is released upon detection of the return of the input current. Further, the Hall element is installed in a magnetic field formed by a choke for preventing inrush current connected between the battery and the high-frequency inverter, and the strength of the magnetic field varies in response to increases and decreases in input current. Increases and decreases in input current are detected from the output of the Hall element based on .

(Function) When the Hall element detects an increase in the input current and shorts the resistor, the base current increases, causing the transistor to oscillate in the saturation region, causing sufficient current to flow through the discharge lamp and Lighting becomes easy. After lighting, the short circuit of the resistor is released,
The base current returns to a value appropriate for a steady input current. As a result, the loss due to the base current becomes sufficiently small compared to the conventional configuration. Furthermore, since the Hall element is placed within the magnetic field generated by the choke through which the input current flows, an increase or decrease in the input current can be detected as a change in the output voltage of the Hall element based on a change in the strength of the magnetic field.

(Example) An example of this invention will be explained using figures. In Figure 1, 1 is a discharge lamp, 2 is a ballast capacitor, 3 is a high frequency inverter, and output transformer 4
and a pair of transistors 5 and 6. 7 is a battery as a power source, and 8 is a choke for preventing rush current. The output transformer 4 is composed of a primary coil 9, a secondary coil 10, and an auxiliary coil 11. A battery 7 and a choke 8 are connected in series between an intermediate tap 12 of the primary coil 9 and the emitters of both transistors 5 and 6. The circuit is connected. The auxiliary coil 11 is connected to the bases of both transistors 5 and 6 and turns both transistors on and off alternately. The battery 7 is also connected to the base of each transistor 5, 6 via a base resistor 13, 14. These structures are not particularly different from conventional discharge lamp lighting devices of this type.

According to this idea, the battery 7 and the base of each transistor 5, 6 (base resistors 13, 14 in the figure)
A resistor 21 is inserted between the two. A switching element 22 is connected in parallel to the resistor 21. 23 is a drive circuit for the switching element 22, and 24 is a Hall element for detecting input current.

FIG. 2 shows a specific circuit example of the main part of FIG. 1. In the figure, 25 is a terminal for the Hall current of the Hall element 24, and 26 is a terminal for the Hall electromotive force signal of the Hall element 24. When a constant current flows between the terminals 24, when the strength of the magnetic field interlinked with the current changes, the voltage between the terminals 26 changes. Such a structure and operation are already well known. The voltage between the terminals 26 of the Hall element 24 is amplified by an amplifier 27 and is applied to a comparator 28 as a comparison input. A Zener voltage from a Zener diode 29 is applied to the comparator 28 as a reference voltage. When the output from the amplifier 27 exceeds the reference voltage, an output is output from the comparator 28 and the switching element (transistor switch in the figure) is activated.
22 is turned on.

The Hall element 24 is placed within the magnetic field of the choke 8. FIG. 3 shows its specific configuration.
The choke 8 shown in the figure has a structure in which a coil 31 is wound around a ferrite core 30, and the Hall element 8 is installed near the coil 31, specifically, near the axial center of the ferrite core 30. Direct current from the battery 7 flows through the choke 8 . The direct current increases or decreases in accordance with the increase or decrease in the current flowing from the battery to the high frequency inverter 3. Therefore, as the direct current increases or decreases, the strength of the magnetic field in the vicinity increases or decreases.

In the above configuration, when the direct current from the battery 7 increases immediately before the discharge lamp 1 is started, the output voltage of the Hall element 24 increases. When the output of the amplifier 27 based on this becomes equal to or higher than the reference voltage generated by the Zener diode 29, the switching element 22 is turned on and the resistor 21 is short-circuited. This causes battery 7
Since the current flowing to the base of each transistor 5, 6 increases, the transistors 5, 6 oscillate in the saturation region, and a sufficient collector current flows. As a result, sufficient current also flows through the discharge lamp 1, making it easy to start it up.

After the discharge lamp 1 is started, the current flowing from the battery 7 to the high frequency inverter 3 returns to the predetermined value, so the output of the amplifier 27 becomes below the reference voltage and the switching element 22 is turned off. Therefore, the base current is reduced compared to before, and returns to the base current that is optimal for flowing the lamp current necessary to keep the discharge lamp 1 lit. As a result of the above, the loss due to the base current is sufficiently reduced compared to the conventional case.

The above explanation was for dealing with an increase in the input current just before starting the discharge lamp 1, but even at the end of the discharge lamp's life, the input current may increase abnormally. Ideas can help. That is, in the case of such an abnormal increase, in the conventional configuration, the base current becomes insufficient, so that the collector current of the transistor abnormally increases. As a result, the transistor may generate abnormal heat and may even be destroyed. However, in this invention, in such a case, the switching element 22 is turned on, and the transistors 5 and 6 are turned on.
Unless a sufficient base current is supplied to cause oscillation in the saturation region, abnormal heat generation of the transistor can be suppressed to a minimum.

(Effects) (1) When the input current increases just before starting the discharge lamp, base current is supplied so that sufficient current flows through the discharge lamp, and after lighting, the base current is returned to the optimum value, so a large base current is constantly flowing. This is no longer necessary, and the base current loss can be reduced accordingly.

(2) Since a Hall element is used to detect increases and decreases in the input current, there is almost no loss in the current flowing here, and increases and decreases in the DC current from the power supply can be reliably and easily detected as changes in the strength of the magnetic field. .

(3) The magnetic field that acts on the Hall element uses the magnetic field generated in the choke for preventing inrush current, so
In particular, it is not necessary to create a magnetic field for the Hall element, especially a magnetic field whose strength changes in response to increases and decreases in input current. Therefore, the configuration becomes simpler.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an embodiment of this invention, Figure 2 is a circuit diagram showing an embodiment of this invention.
The figure is a circuit diagram showing some details of FIG. 1, and FIG. 3 is a sectional view of the choke. 1...Discharge lamp, 3...High frequency inverter, 4...
...Output transformer, 5, 6...Transistor, 7
...Battery, 8...Choke, 21...Resistor, 22
... Switching element, 23 ... Drive circuit, 24
……Hall element.

Claims (1)

[Scope of utility model registration request] a high-frequency inverter including a pair of transistors that are turned on and off alternately and an output transformer that outputs high-frequency waves by turning the transistors on and off; a discharge lamp that is lit by the high-frequency output from the output transformer; In the discharge lamp lighting device comprising a DC power source for the high frequency inverter, a parallel circuit including a resistor and a switching element is connected between the base of the transistor and the DC power source, and the DC power source is supplied to the high frequency inverter. A Hall element is disposed within a magnetic field of a choke for preventing inrush current through which an input current flows, and further, when an output voltage based on a change in the strength of the magnetic field of the Hall element exceeds a reference value, the switching element is activated. A discharge lamp lighting device that includes a drive circuit that turns on the discharge lamp.