JPH09190892A - Electric discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the overvoltage of a switching transistor in half-wave discharge by inserting an auxiliary inductor in series with the primary winding of a current feedback transformer, and by connecting an auxiliary capacitor across the primary winding and the auxiliary inductor. SOLUTION: Part of a high (a) current flows into an auxiliary inductor 13 to store electromagnetic energy. In reducing the (a) current, the electromagnetic energy is discharged to charge an auxiliary capacitor 12 in a polarity shown in a diagram. Eliminating the (a) current and flowing a low (b) current, it discharges the polarlized electric charge of the auxiliary capacitor 12 shown in the diagram through the auxiliary inductor 13. The (b) current flows counterclockwise through the primary winding 81. A discharge circuit (c) from the auxiliary capacitor 12 flows counterclockwise through the primary winding 81 as well. Viewing from the location of the primary winding 81, the current (c) is added to the (b) current to relax an influence evolved by the (b) current accordingly. The influence is exerted on a base circuit at the secondary winding 82 side. Thus, an overvoltage evolved on a switching transistor 4 is relaxed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is connected in parallel with a switching transistor and a vibration inductor to which a DC power supply voltage is intermittently applied via a switching transistor or one of a switching transistor and a vibration inductor. The present invention relates to a discharge lamp lighting device of a single-stone inverter type, which includes a vibration capacitor, and a lighting circuit including a series circuit of a discharge lamp / ballast inductor is connected to both ends of the vibration inductor.

[0002]

2. Description of the Related Art A conventional device of this type will be described with reference to FIG. Vibration inductor 3 and switching transistor 4 to which voltage of DC power supply 1 is intermittently applied via switching transistor 4 and switching transistor 4
A vibration capacitor 2 connected in parallel with one of the vibration inductors 3 is provided. Vibration inductor 3
A lighting circuit including a series circuit of the discharge lamp 10 and the ballast inductor 9 is connected to both ends of the. The primary coil 81 of the saturable current feedback transformer 8 is inserted in series with the lighting circuit.
The base circuit includes the base-emitter junction of the switching transistor 4, the secondary coil 82 of the current feedback transformer 8, and the base capacitor 14. A charge discharging circuit (5, 6) is provided for slowly discharging the electric charge of the base capacitor 14 accumulated when a base current flows through the base circuit. The charge discharging circuit (5, 6) is a series circuit including a diode 5 and a resistor 6 having a required polarity. Reference numeral 7 is a starting resistance. Reference numeral 11 is a preheating capacitor connected between the non-power supply side terminals of the discharge lamp 10. The operation of the apparatus shown in FIG. 2 will be described. When the DC power supply 1 is turned on, the starting resistance 7
A base current flows to the base of the switching transistor 4 via the, and the inverter operation proceeds. Discharge lamp 10
Is preheated through the preheating capacitor 11 and is turned on. After lighting, it becomes as follows. Switching transistor 4
During the ON period, the DC power supply 1 voltage is applied to the vibration inductor 3 to accumulate electromagnetic energy in the vibration inductor 3. At the same time, current flows through the discharge lamp 10, the ballast inductor 9, and the primary coil 81 of the current feedback transformer 8. A current substantially proportional to this current is generated in the secondary coil 82, positive feedback is applied to the base of the switching transistor 4, and the switching transistor 4 continues to be in the ON state. When the current feedback transformer 8 is saturated, the voltage of the secondary coil 82 thereof becomes 0 and the voltage of the base capacitor 14 reversely biases the switching transistor 4, so that the switching transistor 4 is turned off.
During the off period, a vibration action mainly occurs due to the vibration inductor 3, the vibration capacitor 2, and the ballast inductor 9. On the other hand, the electric charge of the base capacitor 14 is slowly discharged through the diode 5 and the resistor 6 to prepare for the next turn-on. Then, when the oscillating action around the ballast inductor 9 progresses and the leftward current is formed again in the ballast inductor 9, the switching transistor 4 is turned on again. The following will be repeated.

[0003]

When the discharge lamp 10 in the conventional apparatus shown in FIG. 2 falls into a half-wave discharge state at the end of its life, the output of the secondary coil 82 of the current feedback transformer 8 becomes asymmetrical, which causes the influence. The ON period of the switching transistor 4 becomes long, and an overvoltage may be applied to the switching transistor 4. An object of the present invention is to mitigate an overvoltage that threatens the withstand voltage of a switching transistor.

[0004]

According to the present invention, an auxiliary inductor is inserted in series with a primary coil of a current feedback transformer, and an auxiliary capacitor is connected to a position across the primary coil and the auxiliary inductor.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The embodiment of the present invention shown in FIG. 1 will be described. The same reference numerals as those in FIG. 2 are used in FIG. 1 as they are, and the redundant description is omitted as appropriate. The auxiliary inductor 13 is inserted in series with the primary coil 81 of the current feedback transformer 8. The auxiliary capacitor 12 is connected to a position that straddles the primary coil 81 and the auxiliary inductor 13. The basic operation of the discharge lamp lighting device is the same as in FIG. 1 discharge lamp 1
It is assumed that 0 is at the end of life, and the half-wave discharge state is in which the a-direction current is large and the b-direction current is small (a large / b small if narrowed). For convenience of explanation, it is assumed that the auxiliary capacitor 12 and the auxiliary inductor 13 are ignored for a while, and the circuit is similar to that shown in FIG. The influence of the light rectification characteristics (large a / small b) generated in the discharge lamp 10 is reflected in the primary coil 81 of the current feedback transformer 8. It is also reflected in the secondary coil 82. 2
The current on the side of the next coil 82 also tends to be large 'and small'.
A small a'current flows through the base circuit during the ON period of the switching transistor 4. Since the a'current is small, the indicated polarity voltage of the base capacitor 14 slowly rises. The voltage of the primary coil 81 and the secondary coil 82 of the current feedback transformer 8 also slowly rises. Current feedback transformer 8
Magnetic flux also rises slowly. The timing of magnetic saturation of the current feedback transformer 8 is delayed. The ON period of the switching transistor 4 becomes longer. A large amount of electromagnetic energy is stored in the vibration inductor 3 during a long ON period. When the switching transistor 4 is turned off, a large amount of electromagnetic energy of the vibration inductor 3 is transferred to the vibration capacitor 2 and a voltage having a large polarity is generated in the vibration capacitor 2. The illustrated polarity voltage of the vibration capacitor 2 is added to the voltage of the DC power supply 1 and applied to the switching transistor 4. Therefore, the voltage of the switching transistor 4 becomes excessive and threatens its withstand voltage.

If the auxiliary capacitor 12 and the auxiliary inductor 13 shown in FIG. Part of the large a current flows into the auxiliary inductor 13, and the auxiliary inductor 1
Store electromagnetic energy in 3. In the process of decreasing the current a, the electromagnetic energy of the auxiliary inductor 13 is released to charge the auxiliary capacitor 12 to the polarity shown in the figure. Eventually the a current disappears and a small b current begins to flow. At this stage, the illustrated polar charges of the auxiliary capacitor 12 are discharged through the auxiliary inductor 13. A small b current flows through the primary coil 81 to the left. The discharge current c of the auxiliary capacitor 12 also flows to the left in the primary coil 81. When viewed from the position of the primary coil 81, the discharge current c is added to the small b current, and the influence of the small b current is reduced accordingly. The effect of the relaxation extends to the base circuit on the secondary coil 82 side. Therefore, the overvoltage generated in the switching transistor 4 is mitigated. Supplement the operation when the lamp is normally lit. The a-direction current and the b-direction current during normal lighting are substantially equal. For this reason, the functions of the auxiliary capacitor 12 and the auxiliary inductor 13 are almost neutral, and they do not act to enhance only the rightward current or the leftward current of the primary coil 81.

[0007]

According to the present invention, the auxiliary inductor is inserted in series with the primary coil of the current feedback transformer, and the auxiliary capacitor 12 is placed at the position where it crosses over the primary coil 81 and the auxiliary inductor 13.
Are connected. According to this, the overvoltage of the switching transistor generated at the half-wave discharge of the discharge lamp can be alleviated, and the reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of the device of the present invention.

FIG. 2 is a circuit diagram of a conventional device.

[Explanation of symbols]

 1: DC power supply 2: Vibration capacitor 3: Vibration inductor 4: Switching transistor 5.6: Charge discharge circuit 8: Current feedback transformer 81: Primary coil 82: Secondary coil 9: Ballast inductor 10: Discharge lamp 13 : Auxiliary inductor 12: Auxiliary capacitor

Claims (1)

[Claims] 1. A switching transistor (4) and a vibration inductor (3) to which a DC power supply (1) voltage is intermittently applied via the switching transistor (4), the switching transistor (4), and vibration. A vibration capacitor (2) connected in parallel with any one of the vibration inductors (3), and the vibration inductor (3)
Discharge lamp (10) and ballast inductor (9) on both ends of
Connecting a lighting circuit including a series circuit, inserting a primary coil (81) of a saturable current feedback transformer (8) in series with the lighting circuit, and connecting a base-emitter junction of the switching transistor (4). And a base circuit including a secondary coil (82) of the current feedback transformer (8) and a base capacitor (14), and the base capacitor (14) accumulated by the base current flowing through the base circuit. ), A discharge lamp lighting device comprising a charge discharge circuit (5, 6) for slowly discharging the forward polarity charge of the auxiliary inductor (1) in series with the primary coil (81).
3) is inserted, and the auxiliary capacitor (1) is placed at a position where the auxiliary coil (81) and the auxiliary inductor (13) are straddled.
A discharge lamp lighting device characterized in that 2) is connected.