JPH0362499A - Discharge lamp lighting circuit - Google Patents

Abstract

PURPOSE:To prevent an overcurrent and prevent the exothermic of a transistor at the time of part failure by providing an overcurrent detecting circuit in an inverter lighting circuit. CONSTITUTION:At the time of normal lighting, a transistor 6 is turned on and off at a duty corresponding to the input level of a comparator 7 to supply an electric power of a certain ratio to an inverter part. When a capacitor 3 is short circuited or the emitter or base of transistors 4, 5 is opened to stop oscillation, a current I rapidly increases. If this state is continued, a transistor 6 and the transistor having no failure of the transistors 4, 5 will be exothermic. According to this circuit, when the both end voltages of a resistance 8 is increased to VBE enough to turn on a transistor 9 by the overcurrent, the current is sent to the transistor 9 and also to the gate of a thyristor 10, and the transistor 6 is turned off regardless of the level of light control signal to prevent the exothermic of the transistors 4, 5, 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to safety in the event of component failure in a discharge lamp lighting circuit.

[Conventional technology]

Conventional devices do not take into account overcurrent in the event of component failure, as described in JIER-009r Practical Application Research Survey on Electronic Lighting Circuits (Illuminating Engineering Society of Japan), page 26.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take into account heat generation of the transistor due to overcurrent when oscillation is stopped, and there is a problem in terms of safety in the event of component failure.

SUMMARY OF THE INVENTION An object of the present invention is to provide a discharge lamp lighting circuit that monitors power supply current and cuts off current flowing into an inverter in case of overcurrent when one component fails.

[Means to solve the problem]

To achieve the above objective, a resistor was inserted into the inverter's power supply line so that current could be detected as voltage.

In addition, a thyristor was used to turn it off instantly.

[Operation] The resistor generates voltage due to overcurrent, turning on the transistor. This causes current to flow through the gate of the thyristor, cutting off the power supply. Since a thyristor is used, the power is cut off momentarily.

Also, it is not something that can be blown like a fuse, so
The overcurrent detection circuit can be reused as long as the cause of the failure is removed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, 1 is a push-pull inverter section, 2 is a dimming circuit section, 3 is a capacitor that limits the lamp current, 4, 5
1 is a transistor for oscillation, 6 is a transistor for dimming, 7 is a comparator, and 8, 9, and 10 are overcurrent detection circuits.

During normal lighting, the transistor 6 is turned on and off with a duty according to the input level of the comparator 7, and a certain ratio of power is supplied to the inverter section 1. However, when the capacitor 3 is short-circuited or when the emitter or base of the transistor 4 or 5 becomes open and oscillation stops, the current I increases rapidly. If this continues, the transistor 6 and the one of the transistors 4 and 5 that has not failed will generate heat. However, according to this circuit,
When the voltage across the resistor 8 rises to VBE enough to turn on the transistor 9 due to overcurrent, current flows through the transistor 9, current flows through the gate of the thyristor 10, and the anode and cathode of the thyristor O is turned on. Then, the input level of the comparator becomes high, turning off the transistor 6 regardless of the level of the dimming signal, and it is possible to prevent the transistor 4.5.6 from generating heat.

In addition, as shown in Fig. 2, the overcurrent detection circuits 8, 9゜10 are
Insert between the base and emitter of the dimming transistor 61. When an overcurrent occurs, the VBE of transistor 6 is changed to thyristor 10.
The same effect can be obtained even if the transistor 6 is turned off by lowering the current and the current is cut off.

〔Effect of the invention〕

According to the present invention, since overcurrent can be prevented, heat generation of the transistor in the event of component failure can be prevented. Additionally, since a thyristor is used, the overcurrent detection circuit can be reused by turning the power back on.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG. 2 is a circuit diagram of another embodiment of the present invention. l...Push-pull inverter section, 2...Dimmer circuit, 3...Capacitor, 4, 5...Transistor, 6
...Transistor, 7...Comparator, 8...Resistor,
9...Transistor, 10...Thyristor, 11.
12...Resistance.

Claims (1)

[Scope of Claims] 1. A discharge lamp lighting circuit comprising an inverter lighting circuit comprising a high-frequency transformer, a transistor for oscillating the high-frequency transformer, and a capacitor for limiting lamp current, characterized in that an overcurrent detection circuit is provided. 2. In a lighting circuit using the above inverter, a thyristor,
2. The discharge lamp lighting circuit according to claim 1, further comprising an overcurrent detection circuit comprising a transistor or the like.