JPS63110491A - Leak detection circuit for high frequency lighting apparatus for neon sign discharge tube - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a lighting device for lighting a neon sign discharge tube using high-frequency current, in which an IJ-resistance occurs between the load circuit of the neon sign discharge tube or the like and the ground. The present invention relates to a leak detection circuit that detects this leak and obtains a signal to stop the operation of the lighting device in order to prevent the lighting device from being damaged.

2. Description of the Related Art High frequency lighting devices that supply a high frequency current of several to several dozen kilohertz have been used for small neon sign discharge tubes used for indoor decoration. This high-frequency lighting device lights a neon sign discharge tube via a high-voltage transformer using a high-frequency inverter using transistors as switching elements, and is not provided with a special protection circuit.

Further, a high-output high-frequency lighting device for large neon sign discharge tubes used for outdoor ominous purposes has not yet been put to practical use.

Problems to be Solved by the Invention If the above-mentioned high frequency lighting device for a small neon sign discharge tube is enlarged as it is and used for a large neon sign discharge tube for outdoor use, the following problems will occur. That is,
If the insulation of the neon sign discharge tube cable deteriorates due to long-term use, or if the lead wire of the neon sign discharge tube comes into contact with the mounting plate, leakage current may flow between the secondary side of the high voltage transformer and ground. When this leak occurs, the high frequency inverter's transistors become abnormally heated and are damaged. This is one of the reasons why a high frequency lighting device for large neon sign discharge tubes has not yet been realized.

Therefore, in order to realize a high-frequency lighting device for a large neon sign discharge tube, the present invention provides a detection circuit that detects the occurrence of a leak so that when the leak occurs, the device can be stopped before the transistor is damaged. .

Means for Solving the Problems The present invention provides a lighting device that lights a neon sign discharge tube via a high-voltage transformer using a high-frequency inverter that uses transistors as switching elements, and detects the occurrence of unsaturated voltage in the transistor. This is a leak detection circuit in a high-frequency lighting device for a neon sign discharge tube, which is designed to detect leakage between the secondary side of a high-voltage transformer and ground.

In a working high-frequency inverter, under normal conditions, the phase of the collector current of the transistor that repeatedly turns on and off is almost in phase with the pace current. Therefore, during the period when the collector current flows, the transistor is in a saturated state, and the IE power loss of the transistor is reduced. Continues stable operation with very little effort.

However, if a leak occurs between the secondary side of the high-voltage transformer and the ground, the phase difference between the collector current and the pace current increases, and as a result, the collector current flows without saturation, and the power loss of the transistor becomes extremely large. The transistor suddenly heats up and is destroyed.

The circuit of the present invention monitors the collector voltage of the transistor, detects that the collector current flows in an unsaturated state due to the increase in the phase difference, and generates an unsaturated voltage, thereby detecting the occurrence of leakage.

EXAMPLES Below, examples illustrating the present invention will be specifically described.

FIG. 1 shows a high-frequency lighting device 10 for a neon sign discharge tube, in which 11 is a high-frequency inverter and 12 is a leak detection circuit.

The high frequency inverter 11 includes transistors Tr1 and Tr2.
is the voltage VBI from the base circuit (not shown), V
B2 alternately turns on and off, and the coil Lo,
A high frequency current is supplied to the primary windings P1 to P2 of the high voltage transformer T1 together with the capacitor CO*CO, and the high voltage transformer T
A high-voltage, high-frequency current is output from the secondary windings P3 and P4 of 1 to the output ends 13 and 13, and a discharge tube for a neon sign is connected to the output ends 13 and 13 to light up the neon sign.

The leak detection circuit 12 monitors the collector voltage of the transistor Trz and issues a high level signal to the terminal OUT when an unsaturated voltage is generated.

That is, the voltage VA at point A located at the collector of the transistor Trz is divided to an appropriate magnitude by the resistors R1+R2, and this is added to the circuit consisting of the resistors R3+R4 and the transistor Tr3. It is set so that it is in the off state and in the on state when it is unsaturated (see VA and VB in Figure 2). Note that by doing this, when the transistor Trz is in the off state, Tra
Needless to say, it is in the on state. The voltage VB at point B located at the collector of the transistor Tra is alternately switched between high and low levels as the transistor Tr3 turns on and off, but when an unsaturated state occurs in the transistor Tr2, the off-state period of the transistor Trs The proportion of low-level periods increases.

A capacitor is connected to point B via a diode D, and the voltage at point B is smoothed to a DC voltage, which is then connected to a resistor R.
5 to discharge the battery. Therefore, the voltage VC at point C at the end of this resistor R5 decreases as the proportion of the low level period at point B increases (see VC in FIG. 2).

A circuit consisting of resistors R6+R7 and a transistor Tr4 is connected to point C, so that when the voltage Vc at point C decreases, transistor Tr4 is turned on. At this time, the values of the resistors R41R5 are appropriately selected, and when an unsaturated voltage is generated in the transistor Trz and a dangerous situation occurs, the point C
The voltage Vc is set so as to drop beyond a threshold value TL for turning on the transistor Tr4. In this way, an output voltage VOUT which becomes high level when an unsaturated voltage is generated in the transistor Trz is obtained at the output terminal OUT connected to the collector of the transistor 'l'r4 (see VOUT in FIG. 2).

Although not shown in the drawings, this output terminal OUT is connected to a device that is connected to a power supply circuit, a high frequency inverter, etc., and stops the high frequency inverter using this no-repel output.

In Fig. 1, yt indicates connection to a DC power supply,
In Figure 2, IA indicates the current at point A, H is high level,
L indicates a low level, and t indicates time.

In the above embodiment, the occurrence of unsaturated voltage is detected and output using a decrease in the time ratio of the saturation period of the transistor, but the occurrence of unsaturated voltage of the transistor may be detected using any other method. Needless to say, it can be used as the leak detection circuit of the present invention.

Effects of the Invention As mentioned above, the leak detection circuit of the present invention takes advantage of the fact that an unsaturated voltage is generated in the switching transistor of a high-frequency inverter when a leak occurs between the secondary side of a high-voltage transformer and the ground, and detects this unsaturated voltage. Since the voltage generation is detected, the structure can be extremely simple, and leakage can be reliably detected and damage to the transistor due to leakage can be prevented. Therefore, the present invention is useful for realizing a high frequency lighting device for a large neon sign discharge tube.

Furthermore, in addition to leakage, unsaturated voltage is generated in the transistor when the length of the neon sign discharge tube connected to the secondary side of the high-voltage transformer is too short or too long, resulting in an overload condition. The circuit can also detect this overload condition, which is of great practical advantage.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a graph showing voltage and current at various parts in the circuit diagram. 10... High frequency lighting device for neon sign discharge tube, 11... High frequency inverter, 12...
...Leak detection circuit, T1...High voltage transformer.

Claims (1)

[Claims] 1. In a lighting device that lights a neon sign discharge tube via a high-voltage transformer using a high-frequency inverter that uses transistors as switching elements, it detects the occurrence of unsaturated voltage in the transistor and detects the occurrence of leakage between the secondary side of the high-voltage transformer and the ground. A leak detection circuit in a high frequency lighting device for neon sign discharge tubes.