JPH10335084A - Inverter transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve safety and to achieve miniaturization and reduction of costs. SOLUTION: In an inverter transformer 1 in which a primary side coil 2 is connected to an inverter circuit 7, and a secondary side coil 4 is connected to a discharge lamp, the secondary side coil 4 is cut on the way of the coil and divided into 4A, 4B, a ballast condenser 8 is interposed between cut terminals of the divided coils, high voltage is generated on the secondary side coil 4 in starting of a discharge lamp 9, and terminal voltage of the secondary side coil is automatically lowered to voltage approximate to the lighting maintaining voltage of the discharge lamp in the stable state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter transformer used in a discharge lamp lighting circuit.

[0002]

2. Description of the Related Art A cold cathode discharge lamp is often used as a backlight for a liquid crystal display device such as a word processor or a notebook personal computer, and an inverter type lighting circuit as shown in FIG. I have.

[0003]

In FIG. 7, reference numeral 20 denotes an inverter transformer, which is composed of a primary winding 211, a base winding 212 and a secondary winding 22, which are cores 23 constituting a closed magnetic circuit. Electrically coupled. An inverter circuit 24 includes two transistors 25 and 26, a capacitor 27, a primary winding 211 and a base winding 212 of the inverter transformer 20, and the emitters of the transistors 25 and 26 are grounded to each other. Capacitor 27 and inverter transformer 2
0 primary windings 211 are connected in parallel. Also,
A base winding 212 of the inverter transformer 20 is connected to the bases of the two transistors 25 and 26. The secondary winding 22 of the inverter transformer 20 has:
A ballast capacitor 28 and a cold cathode discharge lamp 29 are connected in series. In this configuration, when a DC drive voltage is supplied through the choke coil 30 and the resistor 31, the inverter circuit 24 starts operating, and a high-frequency voltage is generated at both ends of the secondary winding 22 of the inverter transformer 20. .

[0004] Here, the cold cathode discharge lamp 29 is in an open state at the time of starting and has an impedance close to infinity, so that a large starting voltage is required to start the lamp. However, when the discharge is started, the impedance is sharply reduced. Therefore, in a stable state, it is necessary to supply a considerably lower voltage than at the start.

Therefore, conventionally, an inverter transformer 20
By connecting a ballast capacitor 28 and a cold cathode discharge lamp 29 in series at both ends of the secondary winding 22 of the first embodiment, when the cold cathode discharge lamp 29 is started, the entire voltage boosted by the secondary winding 22 is cooled. The voltage is applied to the cathode discharge lamp 29, and in a stable state after lighting, the voltage across the secondary winding 22 is divided between the ballast capacitor 28 and the cold cathode discharge lamp 29, and the cold cathode discharge lamp Reference numeral 29 denotes a voltage required to maintain lighting (hereinafter, referred to as a lighting maintenance voltage).

For this reason, the conventional inverter transformer 20
It is necessary to make the number of turns of the secondary side winding 22 suitable for the starting voltage of the cold-cathode discharge lamp 29 and to make the withstand voltage of the inverter transformer 20 sufficiently high according to the starting voltage. The inverter transformer 25
Is inevitably large and the cost is high.
Further, in the above-described configuration, the same high voltage as that at the start is always generated at both ends of the secondary winding 22 of the inverter transformer 20 regardless of the lighting state of the cold cathode discharge lamp 29. However, since the output impedance of the secondary winding 22 is not so large, if the load side of the secondary winding is short-circuited or opened for some reason, large electric energy is generated to cause a fire accident or the like. There were also drawbacks that were prone to occur.

[0007]

According to a first aspect of the present invention, there is provided an inverter transformer in which a primary winding is connected to an inverter circuit and a secondary winding is connected to a discharge lamp.
Cut and split the secondary winding in the middle of the winding,
It is characterized in that a ballast capacitor is interposed between the cut-side terminals of each split winding. In a second solution of the present invention, the primary winding is connected to an inverter circuit,
In an inverter transformer in which a secondary winding is connected to a discharge lamp, the secondary winding is cut in the middle of the winding and divided, and the cut-side terminals of the divided windings are opened to open. It is characterized in that a coupling capacitance formed by a split winding of a secondary winding is interposed between the side terminals. The present invention
According to the first and second solutions, when the discharge lamp is started, the secondary winding generates a high voltage to start the discharge lamp,
It is an object of the present invention to improve the safety of the inverter transformer by automatically lowering the terminal voltage of the secondary winding to a value close to the lighting maintenance voltage of the discharge lamp in a stable state of the discharge lamp. Another object of the second solution is to reduce the size and cost of the inverter circuit in addition to the above object by omitting a ballast capacitor connected to the outside.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are a bottom view of an inverter transformer according to a first embodiment of the present invention and a connection diagram showing an example of a discharge lamp lighting circuit using the inverter transformer. It comprises a base winding 3 and a secondary winding 4, and these windings are wound around a bobbin 5 equipped with a core 6 forming a closed magnetic circuit.
Here, the secondary winding 4 is cut in the middle of the winding and divided into two windings 4A and 4B. The terminals j to n are terminals of the primary winding 2 and the base winding 3, which are planted on a terminal block 51 provided at one end of the bobbin 5, and the terminals are connected to an inverter circuit 7. The inverter circuit 7
Is formed by two transistors, a capacitor, a resistor, and the like. The connection configuration is the same as that of the conventional example of FIG. d and g are terminals on both outer ends of the secondary winding 4 and are planted on a terminal block 52 provided on the opposite side to the terminal block 51, and a discharge lamp 9 is connected between both terminals. e and f are terminals on the cutting side of the secondary winding 4 which are planted on a terminal block 53 provided between the terminal blocks 51 and 52, and a ballast capacitor 8 is interposed at both ends thereof. is there. In the first embodiment, a chip capacitor is used as the ballast capacitor 8, and the chip capacitor is inserted into the concave portion 10 formed at the bottom of the terminal block 53.

In the second embodiment of the present invention, a ballast capacitor is formed between the secondary windings by cutting in the middle of the winding instead of the ballast capacitor in the first embodiment. Is to utilize the coupling capacity. FIG. 3 is a sectional structural view showing an example of the inverter transformer according to the second embodiment, and FIG. 4 is a schematic connection diagram of a discharge lamp lighting circuit using the inverter transformer according to the second embodiment. . 3 and 4, the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals. 3 and 4, the secondary winding 4 is wound around a bobbin 5, cut in the middle, and divided into two parts, 4A and 4B. One split winding 4
A part of B is coaxially wound around an outer periphery of a part of the previously wound divided winding 4A via an insulating tape 11. At this time, the terminals e and f on the cutting side of each of the divided windings 4A and 4B are insulated and open. Cc is a coupling capacitance formed between the divided windings 4A and 4B wound via the insulating tape 11. In the present embodiment, a part of each of the divided windings 4A and 4B constituting the secondary winding 4 is wound coaxially, but the winding method is limited as long as a predetermined coupling capacity is obtained. Never. Further, in the first and second embodiments, the number of windings of each of the divided windings 4A and 4B is selected such that a voltage of about half of the starting voltage of the discharge lamp 9 is generated.

[0010]

For example, in FIG. 2, when a driving voltage is supplied to the inverter circuit 7, a high-frequency voltage having the oscillation frequency of the inverter circuit 7 is generated in the primary winding 2 of the inverter transformer 1, and the secondary winding is generated. The voltage is boosted on line 4. At this time,
Split windings 4A and 4B of the secondary winding 4 are provided at both ends of the discharge lamp 9.
Are applied via a ballast capacitor 8. Here, since the divided windings 4A and 4B each generate a voltage of about half of the starting voltage of the discharge lamp 9, a voltage equal to the starting voltage is applied to both ends of the discharge lamp 9. The electric lamp 9 starts lighting. When the discharge lamp 9 is in a stable state, the impedance decreases, and the terminal voltage of the secondary winding 4 becomes substantially equal to the lighting maintenance voltage of the discharge lamp 9 accordingly, so that the discharge lamp 9 is continuously lit. That is, since the ballast capacitor 8 is connected between the divided windings 4A and 4B, when the discharge lamp 9 is in a stable state, the output impedance of the secondary winding 4 increases by the amount of the ballast capacitor. Therefore, the secondary winding 4
The output voltage decreases as the impedance of the discharge lamp 9 decreases, and becomes a value close to the lighting maintenance voltage of the discharge lamp. In the inverter transformer of the present invention, when starting the discharge lamp, the secondary winding generates a high voltage to start the discharge lamp, and
In the stable state of the discharge lamp, the terminal voltage of the secondary winding is automatically reduced to a value close to the lighting maintenance voltage of the discharge lamp, so that the safety of the inverter transformer can be improved.

Embodiment 1 FIG. 5 shows a discharge lamp lighting circuit using the conventional inverter transformer shown in FIG. 7 and each part of the discharge lamp lighting circuit using the inverter transformer according to the first embodiment of the present invention shown in FIG. D is the voltage between the terminals of the secondary winding 22 in the conventional circuit, E is the voltage between the terminals of the discharge lamp 29, F is the leak voltage generated between the core 23 forming the closed magnetic circuit and the ground, G is a voltage between one divided winding 4B of the inverter transformer and the ground (point fg) in the lighting circuit of FIG. 2 using the inverter transformer of the present invention, and H is a voltage between the ballast capacitor 8 and the divided winding 4B. The voltage J between the series circuit and the ground (point e-g), J is the voltage between the outer terminals (points d-g) of the split windings 4A and 4B connected in series via the ballast capacitor 8, that is, the discharge. Lighting maintenance voltage of the light 9,
K is a leak voltage generated between the core 6 and the ground. In addition,
In the comparative experiment, in the discharge lamp lighting circuit using the conventional inverter transformer and the discharge lamp lighting circuit using the inverter transformer of the first embodiment of the present invention, the inverter circuit connected to the primary winding and the load connected as a load were used. Discharge lamps with the same specifications and characteristics. Further, in the first embodiment of the present invention, the number of windings of each of the divided windings 4A and 4B of the inverter transformer is substantially equal. As is apparent from FIG. 5, in the first embodiment of the present invention, a voltage (G) between the divided winding 4B and the ground (point f-g), a series circuit of the divided winding 4B and the ballast capacitor 8 And the ground (point e-g) and the voltage (J) between the outer terminals of the split windings 4A and 4B (point d-g) by the secondary winding of the conventional inverter transformer. Of the discharge lamps (D) or less, and these voltages could be made very close to the lighting maintenance voltage of the discharge lamp. Further, the leak voltage generated between the core and the ground can be reduced to less than half of the conventional case.

[0011]

Embodiment 2 FIG. 6 shows the second embodiment of the present invention shown in FIGS. 3 and 4, in which the number of windings of each of the divided windings 4A and 4B is five.
00 turns, and the coupling capacitance Cc formed between the divided windings 4A and 4B when the number of turns of the insulating tape 11 wound between the part of the divided winding 4A and the part of 4B is changed. This shows the change of At this time, the oscillation frequency of the inverter circuit was 75 KHz. Generally, the capacitance of a ballast capacitor used in this type of discharge lamp lighting circuit depends on the oscillation frequency of the inverter circuit, but is 10 pF.
To 50 pF, the coupling capacitance Cc formed between the split windings 4A and 4B in the second embodiment of the present invention can sufficiently function as a ballast capacitor. In FIG. 4, the voltage of each part in the lighting state of the discharge lamp 9 having a rated lamp power of about 2 W is 3 volts between the cut terminal of the divided winding 4A and the ground (point e-g).
30v, between the cut terminal of the divided winding 4B and the ground (point fg)
440 V, the voltage at both ends of the discharge lamp 9 was 370 V, and the leak voltage between the core 6 and the ground was 190 V.

[0012]

According to the inverter transformer of the present invention, since the secondary winding is divided into two and a ballast capacitor is interposed in the middle, the discharge lamp side becomes open due to a misfiring accident or the like. However, large electric energy is not stored and it is safe. Also, since the terminal voltage of the secondary winding of the inverter transformer automatically changes according to the lighting state of the discharge lamp, a constant high voltage is always applied regardless of the lighting state of the discharge lamp as in the past. The safety of the inverter transformer can be improved compared to what would occur,
This makes it possible to reduce the size and cost of the inverter transformer. Particularly, in the second embodiment, the effect is great because the ballast capacitor connected to the outside can be omitted.

[Brief description of the drawings]

FIG. 1 is a bottom view showing the structure of the inverter transformer according to the first embodiment of the present invention, and FIG. 2 is a connection diagram showing an example of a discharge lamp lighting circuit using the inverter transformer according to the first embodiment of the present invention. FIG. 3 is a sectional view showing an example of an inverter transformer according to a second embodiment of the present invention, and FIG. 4 is a circuit diagram of a discharge lamp lighting circuit using the inverter transformer according to the second embodiment of the present invention. It is a schematic connection diagram. 5 is a diagram comparing the voltage of each part in the discharge lamp lighting circuit of FIG. 7 using the conventional inverter transformer and the discharge lamp lighting circuit of FIG. 2 using the inverter transformer of the present invention, and FIG. 6 is an insulating tape in FIG. FIG. 7 is a diagram showing the relationship between the number of turns and the change in the coupling capacitance Cc in FIG. 4, FIG. 7 is a connection diagram of a discharge lamp lighting circuit using a conventional inverter transformer,

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Inverter transformer, 2 ... Primary winding 3 ... Base winding, 4 ... Secondary winding, 4A, 4B
... Divided windings 5 ... Bobbins, 6 ... Cores, 7 ... Inverter circuits, 8 ... Ballast capacitors, 9 ... Discharge lamps,
11: insulating tape, Cc: coupling capacity

Claims (2)

[Claims] A primary winding connected to an inverter circuit;
In an inverter transformer whose secondary winding is connected to a discharge lamp, the secondary winding is cut in the middle of the winding and divided, and a ballast capacitor is inserted between the cut-side terminals of each split winding. An inverter transformer characterized by the following. 2. The primary winding is connected to an inverter circuit,
In an inverter transformer in which a secondary winding is connected to a discharge lamp, the secondary winding is cut in the middle of the winding and divided, and the cut-side terminals of the divided windings are opened to open. 2. The inverter transformer according to claim 1, wherein a coupling capacitance formed by a split winding of a secondary winding is interposed between the side terminals.