JP2001051007A - Grounding protector circuit for cold cathode discharge tube lighting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the manufacturing of a step-up transformer for igniting neon tubes and provide a coil for detecting the grounding. SOLUTION: The step-up transformer is disposed in a case 52 on a wiring board 51 on which an inverter for converting a commercial a-c power into a high frequency power, and a grounding detector circuit, etc., are mounted, lead wires (cables) 53, 54 for leading out a high voltage output of the step-up transformer are erected on the wiring board 51, coils 57, 58 are wound around air-core bobbins 55, 56, lead wires 53, 54 pass through the air-core bobbins 55, 56, and outputs of the coils 51, 58 are fed to a grounding detector circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground fault protection circuit for detecting a ground fault on a high voltage side in a lighting circuit for lighting a cold cathode discharge tube such as a neon tube or an argon tube with a high voltage output of a step-up transformer.

[0002]

2. Description of the Related Art A ground fault protection circuit of this type has been proposed, for example, in Japanese Patent Application No. 7-71831 (Japanese Patent Application Laid-Open No. 8-271566). This ground fault protection circuit will be briefly described with reference to FIG. One end of the primary winding 12 of the step-up transformer 11 is connected to the input terminal 13, and the other end is connected to the input terminal 15 via the triac 14, and the secondary windings 16 and 17 on the high-voltage output side of the step-up transformer 11. Are connected to each other and connected to a transformer case, and each other end is connected to an output terminal 1.
8 and 19 respectively. A cold cathode discharge tube 20 such as a neon tube is connected to the output terminals 18 and 19. A power input between the input terminals 13 and 15 is rectified and smoothed by a rectifying and smoothing circuit 26, and its output is made a constant voltage by a Zener diode 27. The constant voltage is divided by a voltage dividing circuit 28 to generate a reference voltage Er. And supplied to the inverting input terminal of the comparator 29. The output side of the comparator 29 is connected to the gate of the thyristor 31 through a voltage dividing circuit, and both ends of the zener diode 27 are connected through the release switch 32 to the thyristor 31.
Are connected to both ends. One ends of the first and second tertiary windings 21 and 22 magnetically coupled to the secondary windings 16 and 17 are connected to each other, and the other ends are input terminals of a full-wave rectifier circuit 33 in the detection circuit 23. , And the output terminal of the full-wave rectifier circuit 33 is connected to the non-inverting input terminal of the comparator 29 through the smoothing circuit 34.

For example, if the induced voltages of the first and second tertiary windings 21 and 22 are connected so as to cancel each other,
In a normal state, voltages equal to the first and second tertiary windings 21 and 22 are induced, the input of the detection circuit 23 is 0, and the voltage of the non-inverting input terminal of the comparator 29 is also 0. . However, if one of the first and second secondary windings 16 and 17, for example, 16 is grounded, the induced voltage of the tertiary winding induced by the secondary winding, 21 in this example, becomes almost zero. , A relatively large positive voltage appears at the non-inverting end of the comparator 29, which exceeds the reference voltage Er, the output of the comparator 29 is inverted and a large positive level is output, the thyristor 31 is turned on, and a ground fault occurs. Is detected.

In FIG. 4, the primary winding 1 is detected by the detection output.
2 is automatically cut off, and a triac 1 as a switch 24 is connected in series with the primary winding 12.
4, a series circuit of a Zener diode 36 and a resistor 37 is connected between both ends of a series circuit of the thyristor 31 and the switch 32, and one end and a gate of the triac 14 are connected between both ends of the resistor 37. Therefore, in a normal state, the thyristor 31 is turned off, the triac 14 is turned on through the Zener diode 36, and AC power is supplied to the primary winding 12. However, as described above, when one of the secondary windings is grounded, the output of the comparator 29 is inverted and the thyristor 31 is turned on,
As the gate voltage of the triac 14 drops, the triac 14 is turned off, and the supply of AC power to the primary winding 12 is cut off.

[0005]

The tertiary windings 21 and 22 for detecting a ground fault are wound on a bobbin 42 through which a magnetic core 41 is inserted, as shown in FIG. An insulating film 43 such as a polyester tape was wound thereon, and the secondary windings 16 and 17 were further wound thereon.

In this way, the tertiary windings 21 and 22 are wound,
Further, after winding the insulating film 43, the secondary windings 16, 1
7 and a tertiary winding 2
It took a relatively long time to manufacture the step-up transformer 11 from the viewpoint of the number of lead wires for forming the step-up transformers 1 and 22 and the insulation between the tertiary windings 21 and 22 and the secondary windings 16 and 17. In particular, in the case of the step-up transformer 11 in which the high-frequency high voltage is generated by the inverter to turn on the cold cathode discharge tube 20,
Since the size was small, winding of the tertiary windings 21 and 22, winding of the insulating film 43, and lead wire processing were difficult.

[0007]

According to the present invention, there are provided first and second coils which are electromagnetically coupled to respective lead wires for leading a high voltage of a step-up transformer to the outside.
The output of the second coil is supplied to a ground fault detection circuit.

[0008]

FIG. 1 shows an embodiment of the present invention.
Although not shown in FIG.
And the step-up transformer 11 is covered with a case 52. Although not shown in the drawing on the wiring board 51,
An inverter that converts commercial AC power into high-frequency power, a ground fault detection circuit, and the like are configured. Secondary output leads (cables) 53 and 54 for leading the high voltage output of the step-up transformer 11 to the outside are set up with respect to the wiring board 51.

In this embodiment, the air-core bobbins 55,
First and second coils 57 and 58 are wound around 56, respectively.
The bobbins 55, 56 are passed over the leads 53, 54, and the first and second coils 57, 58 and the leads 53, 54
Are electromagnetically coupled. Both ends of the first and second coils 57 and 58 are connected to a ground fault detection circuit (not shown) formed on the wiring board 51. First and second coils 5
The number of turns of 7, 58 is relatively large, for example, 1000 turns, so that as large an output as possible, for example, about 10 V is obtained.

FIG. 2 shows an example of a cold cathode discharge tube lighting circuit to which the present invention is applied. In this example, commercial power is converted to high-frequency power, and the cold-cathode discharge tube is turned on by high-frequency power. Input terminal 1 to be connected to commercial power supply 61
3 and 15 are full-wave rectifier circuits 63 via a power switch 62.
The output side of the rectifier circuit 63 is connected to the smoothing circuit 64, one end of the smoothing circuit 64 is grounded, the other end is connected to the middle point of the primary winding 12, and the resistance element 65,
The other end of the Zener diode 67 is grounded. The voltage between both ends of the Zener diode 67 is divided by the resistance element 68 and the Zener diode 69, and is connected between the both ends of the Zener diode 69 to the voltage dividing resistors 71 and 72. The pressure point is connected to each gate of the switching elements 73 and 74 of the FET, and is connected to both ends of a feedback winding 75 electromagnetically coupled to the primary winding 12.

Both ends of the primary winding 12 are grounded through switching elements 73 and 74, respectively.
Is connected between both ends of the capacitor. Primary winding 1
2. A self-excited oscillation circuit (push-pull inverter) 77 is constituted by the switching elements 73 and 74, the feedback winding 75, and the capacitor 76. For example, a high-frequency signal of 10 kHz to 30 kHz is generated. Are obtained as a high-voltage output at both ends of the discharge tube 20. This high-voltage output is applied to the discharge tube 20, and the discharge tube 20 is turned on.

Both ends of the secondary winding 16 and the output terminals 18, 1
The outputs of the coils 57 and 58 that are electromagnetically coupled to the lead wires 53 and 54 between the coils 9 are supplied to full-wave rectifier circuits 81 and 82, respectively. Each rectified output of the rectifier circuits 81 and 82 is supplied to a smoothing circuit 8.
3,84 in the smooth, the two smoothed output difference voltage V _D of each other in the difference circuit 85 is detected. The differential voltage V _D is supplied to the window comparator 86. That is, it is supplied to the non-inverting input terminal of the comparator 87 and is compared with the reference voltage V3, and is also supplied to the inverting input terminal of the comparator 88 and is compared with the reference voltage V1. Comparators 87, 88
Are supplied to the gate of the thyristor 92 through the backflow blocking diodes 89 and 91, respectively. The thyristor 92 is connected between the resistance points of the resistance elements 65 and 66 and the ground.

In a normal state, the first and second coils 5
Voltages of the same magnitude are induced at 7, 58 and the difference circuit 85
The output voltage V _D of becoming the virtual zero potential V2. At this time, the difference voltage V _D = V2 and the reference voltage V
3 is larger than the reference voltage V1 of the comparator 88.
Is smaller and V1 <V2 <V3 so that V1 <V2 <V3.
1, V3 is selected, each output of each of the comparators 87 and 88 becomes a negative voltage, no voltage is applied to the gate of the thyristor 92, the thyristor 92 is in a non-conductive state, the inverter 77 is in an oscillating state, and The power of the power supply 61 is converted to high-frequency power, and the discharge tube 20 is turned on.

However, for example, wiring on the lead wire 53 side,
When the discharge tube, the wiring connection point, or the like comes into contact with, for example, the building material of the neon tower, a current flows to the ground, the voltage induced in the first coil 57 decreases, and the output voltage V of the difference circuit 85 decreases. _D becomes positive, this positive V _D becomes larger than the reference voltage V3, and the output of the comparator 89 becomes positive. The positive voltage is applied to the gate of the thyristor 92, and the thyristor 92 becomes conductive, and the FETs 73, 74 Becomes zero, and the inverter 77 stops operating.

When the discharge tube, the wiring, or the connection point on the lead wire 54 side contacts, for example, the building material of the neon tower,
Earth current flows, the voltage induced in the coil 58 decreases, the output voltage V _D of the difference circuit 85 becomes a negative voltage V2
Smaller than the reference voltage V1, and the output of the comparator 88 becomes a positive potential.
, The thyristor 92 conducts, and the oscillation of the inverter 77 stops.

When such a ground fault has occurred, it is detected and the supply of high-frequency power to the output terminals 18 and 19 is stopped, so that there is no possibility that a disaster or the like will occur. Inverter 77
Is not limited to two switching elements,
It may be composed of four switching elements,
In addition to the self-excited type, the type may be separately excited.

The present invention can be applied not only to an inverter type lighting circuit but also to a lighting circuit using low-frequency AC power. That is, for example, as shown in FIG. 4, the coils 57 and 58 in FIG. 2 may be connected at one end to each other similarly to the tertiary windings 21 and 22, and may be connected to the detection circuit 23 at the other end. In addition to detecting the difference between the induced voltages of the coils 57 and 58, the magnitude of each induced voltage of the coils 57 and 58 is detected to stop the supply of the secondary output of the step-up transformer 11. You may. For example, as shown in FIG. 3 by assigning the same reference numerals to portions corresponding to FIGS. 2 and 4, first and second coils 57 and 58 provided electromagnetically coupled to secondary output lead wires 53 and 54, respectively. Are rectified and smoothed, and compared with the reference voltage VS1 by comparators 94 and 95, respectively, and the coils 57 and 58 are in a normal state.
Are high, the outputs of the comparators 94 and 95 both have a positive potential, and no current flows through the diodes 96 and 97 to the light emitting element 98L of the photocoupler 98.
The terminals 13 and 1 are connected via the light receiving element 98P of the photocoupler 98.
No current flows through the relay 99 connected between the terminals 5, and the terminals 13 and 13 are connected through the normally closed NC of the switching contact 99C of the relay.
15 is connected to the primary winding 12 and the AC voltage is
2.

However, when a ground fault occurs, the induced voltage of the coil 57 or 58 on the side where the ground fault has occurred decreases, the input of the comparator 94 or 95 becomes smaller than the reference voltage VS1, and the output of the comparator becomes low. When the diode 96 or 97 conducts, a current flows through the light emitting element 98L, which emits light, the light receiving element 98P conducts, and the relay 9
9 operates, its switching contact is connected to the normally open side NO, the supply of AC power to the primary winding 12 is cut off, and a holding circuit for the relay 99 is configured.

In the inverter type lighting circuit, FIG.
Alternatively, the supply of power to the secondary winding 16 may be stopped by the detection circuit 23 illustrated in FIG. Conversely, the supply of the commercial power to the primary winding 12 may be controlled using the detection circuit 23 shown in FIG. In this case, the thyristor 92 is inserted in series with one end of the primary winding 12.

[0020]

As described above, according to the present invention, the first and second coils 57 and 58 for detecting a ground fault are provided.
Are connected to a lead wire 53 for supplying a high voltage output to the outside.
54 and the step-up transformer 11
On the other hand, there is no need to provide the tertiary windings 21 and 22, and the manufacture of the step-up transformer 11 becomes extremely simple. The first and second coils 57 and 58 may be produced in parallel with the step-up transformer 11, and the first and second coils 57 and 58 may be inserted through the external lead wires 53 and 54. It is also very simple. The elimination of the provision of the tertiary windings 21 and 22 in the step-up transformer 11 has a great effect that the production of the step-up transformer 11 becomes extremely easy especially when the step-up transformer 11 is downsized as in an inverter type lighting circuit. .

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an outline of a main part of the present invention.

FIG. 2 is a diagram showing an example of an inverter type lighting circuit to which the present invention is applied.

FIG. 3 is a circuit diagram showing an example in which the present invention is applied to a commercial power lighting system.

FIG. 4 is a diagram showing an example of a conventional protection circuit for a discharge tube lighting circuit.

FIG. 5 is a sectional view showing a conventional step-up transformer.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H05B 41/02 H05B 41/02 Z F term (Reference) 2G014 AA04 AB04 AB54 AC18 3K072 AA01 AA19 AB03 BA03 BB01 BC03 BC07 DD04 EB05 GA02 GB12 GB14 GB18 GC03 GC04 5G058 AA02 AB06 5H007 BB03 CA02 CB06 CC32 DC02 FA03 FA14 HA01 HA03

Claims (1)

[Claims] 1. A ground fault protection circuit of a lighting circuit for lighting by applying a high voltage output of a step-up transformer to a cold cathode discharge tube, wherein the high voltage of the step-up transformer is electromagnetically coupled to each lead wire leading out to the outside. A cold-cathode characterized by comprising a first and a second coil, and a ground fault detecting circuit supplied with outputs of the first and second coils and detecting a ground fault on a high voltage output side of the transformer. Ground fault protection circuit for discharge tube lighting circuit.