JPS6226159B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a transistor inverter type discharge lamp lighting device for lighting a discharge lamp such as a fluorescent lamp at high frequency.

[Background technology]

As shown in FIG. 1, a conventional transistor inverter type discharge lamp lighting device connects a transistor inverter 4 to a DC power source, which is made up of an AC power source 1 connected to a full-wave rectifier 2, via a discharge lamp ballast 3.
A discharge lamp 5 is connected as a load to this transistor inverter 4. In this case, the transistor inverter 4 is connected to the primary winding 6 of the oscillation transformer 6.
Oscillation transistors 7 and 8 are connected to the series circuit of a and 6b.
are connected in parallel with the waveform shaping capacitor 9, and the oscillation transistors 7,
8 are commonly connected via base resistors 10 and 11, and the connection points of the primary windings 6a and 6b are further commonly connected, and this common connection point is connected to the full-wave rectifier 2 through the discharge lamp ballast 3. The common emitter of the oscillating transistors 7 and 8 is connected to the negative output terminal of the full-wave rectifier 2, and both ends of the base winding 6c are connected to the bases of the oscillating transistors 7 and 8, respectively. are doing. The discharge lamp 5 is connected to the secondary winding 6d of the oscillation transformer 6 and the preheating windings 6e and 6f.

Next, the operation of this transistor inverter type discharge lamp lighting device will be explained. When the AC power supply 1 is turned on, one of the oscillation transistors 7 and 8 is made conductive by the base resistors 10 and 11, and then the oscillation transistors 7 and 8 are made conductive alternately by the feedback action of the base winding 6c to continue oscillation. . This oscillation output lights up the discharge lamp 5 at high frequency. The lamp voltage of the discharge lamp 5 at this time is shown in FIG.
As shown, it is symmetrical. However, if the emitter of the discharge lamp 5 is exhausted, the lamp current will only flow in one direction, and the lamp voltage will therefore become asymmetrical as shown in FIG. 2B. When the lamp current only flows in one direction,
The secondary winding 6d of the oscillation transformer 6 becomes biased, and the lamp current flows by about 1.5 to 2 times compared to the normal state.As a result, a large current also flows in the primary windings 6a and 6b, causing excessive parts When stress is applied, the temperature rise rate of the oscillation transformer 6 and the oscillation transistors 7 and 8 increases, and if the discharge lamp 5 is lit for a long time, the allowable temperature of those parts will be exceeded, significantly shortening the life of the parts. There was a problem.

On the other hand, in order to solve this inconvenience,
As seen in No. 74095 and JP-A-56-22583,
A system has also been proposed in which an abnormality in a discharge lamp is detected, the base signal of an oscillating transistor is limited in response to the detected output, and the transistor inverter is disabled in the event of an abnormality. However, simply controlling the base will leave the voltage applied between the collector and emitter of the oscillation transistor, and as a result, the base current will be small depending on the performance of the element, the circuit specifications, the environment in which the device is used, etc. flows, and in response, a collector current multiplied by hfe (amplification factor) flows, causing the oscillation transistor to generate heat. Due to the heat generated by the oscillation transistor, hfe increases, causing an even larger collector current to flow, and this process is repeated. It was found that so-called thermal runaway occurs.

In this way, in a discharge lamp lighting device using a transistor inverter, if the base of the oscillation transistor is simply controlled to protect the components, the oscillation transistor will cause thermal runaway, which poses a serious problem in terms of component protection. It was hot.

[Purpose of the invention]

An object of the present invention is to provide a transistor inverter type discharge lamp lighting device that can protect components from excessive component stress when an abnormality occurs in the discharge lamp without causing the problem of thermal runaway of the oscillation transistor of the transistor inverter. It is to be.

[Disclosure of the invention]

The transistor inverter type discharge lamp lighting device of the present invention includes a DC power supply, a transistor inverter connected to the DC power supply, a discharge lamp serving as a load of the transistor inverter, and a transistor inverter connected to the input power line of the transistor inverter. A switching element inserted in series between the collector and emitter of the oscillation transistor, an abnormality detection circuit for detecting an abnormal state of the discharge lamp, and control for turning off the switching element in response to a detection output of the abnormality detection circuit. It is equipped with a circuit.

According to the configuration of the present invention, power is supplied to the transistor inverter in order to turn off the switching element inserted in the input power supply line of the transistor inverter in series between the collector and emitter of the oscillation transistor of the transistor inverter when an abnormality occurs in the discharge lamp. The oscillation can be stopped, and the components can be protected from excessive component stress when the discharge lamp is abnormal. Moreover, since the input power source of the transistor inverter is quickly cut off by the switching element, the DC power supply voltage applied to the oscillation transistor of the transistor inverter can be lowered, and therefore thermal runaway of the oscillation transistor can be prevented.

Embodiment An embodiment of the present invention will be described based on FIG. As shown in FIG. 3, this transistor inverter type discharge lamp lighting device includes a DC power source, a transistor inverter 4 connected to the DC power source, a discharge lamp 5 serving as a load of the transistor inverter 4, and a transistor inverter 4. A switching element 29 such as a transistor inserted in series between the collector and emitter of the oscillation transistors 7 and 8 of the transistor inverter 4 in the input power supply line of the transistor inverter 4, and an abnormality detection circuit that detects an abnormal state such as emitter exhaustion of the discharge lamp 5. 12, and a control circuit 28 that turns off the switching element 29 in response to the detection output of the abnormality detection circuit 12.

The difference between this transistor inverter type discharge lamp lighting device and that shown in FIG.
Switching element 2 inserted in series between emitters
9, an abnormality detection circuit 12 for detecting the asymmetry of the lamp current of the discharge lamp 5, and this abnormality detection circuit 12.
The other points are the same as in FIG. 1 except that a control circuit 28 is added to turn off the switching element 29 in response to the detection output.

The abnormality detection circuit 12 includes a resistor 14 and a capacitor 15 between both ends of the secondary winding 6d of the oscillation transformer 6.
Connect the parallel circuit of resistor 16 and diode 17 to the series circuit of resistor 16 and diode 17, and connect diode 18 and resistor 1.
9 and a parallel circuit of resistor 20 and capacitor 21, and connect resistor 1 to the connection point of resistor 16 and the parallel circuit of resistor 14 and capacitor 15.
A bridge circuit is constructed by connecting a series circuit of a voltage responsive switch (SBS) 22 and a winding 23 to a connection point between the resistor 9 and the parallel circuit of a resistor 20 and a capacitor 21.

The control circuit 28 connects a thyristor 30 between the base and emitter of a switching element 29 whose collector and emitter are interposed and connected between the common emitters of the oscillation transistors 7 and 8 and the negative output terminal of the full-wave rectifier 2. The anode and cathode are connected, and the winding 31 magnetically coupled to the winding 23 is connected between the gate and cathode of the thyristor 30, and the base resistors 10 and 1 are connected.
A series circuit of a diode 32 and a capacitor 33 is connected between the common connection point of 1 and the negative output terminal of the full-wave rectifier 2, and a resistor 3 is connected from the connection point of this series circuit.
The base current is caused to flow through the switching element 29 through the switching element 29.

Next, the operation of this transistor inverter type discharge lamp lighting device will be explained. During normal operation (when the lamp voltage has the waveform shown in FIG. 2A), the voltages across the capacitors 15 and 21 are approximately equal, the potential difference across the voltage response switch 22 is approximately zero volts, and the voltage response switch 22 is in the non-operational state. It is in a conductive state. Therefore, no current flows through the winding 23 and no voltage is induced in the winding 31. Therefore, the thyristor 30 is in a non-conducting state. At this time, a base current flows through the diode 32 and the resistor 34, making the switching element 29 conductive, causing the transistor inverter 4 to oscillate, and providing an oscillation output to the discharge lamp 5.

On the other hand, when the emitter of the discharge lamp 5 is exhausted and the lamp current flows only in one direction (when the lamp voltage has the waveform shown in FIG. 2B), the capacitor 1
The amounts of charge charged in capacitors 5 and 21 are different, and a difference occurs in the voltages across capacitors 15 and 21. for example,
When the voltage across the capacitor 15 is higher,
Capacitor 15 → Voltage response switch 22 → Winding 2
3 → Current flows through the path of capacitor 21,
This current induces a voltage in the winding 31. The induced voltage in the winding 31 causes the thyristor 30 to conduct, and the base current no longer flows through the switching element 29, causing the switching element 29 to become non-conductive.
Oscillation of transistor inverter 4 stops.

As described above, in the transistor inverter type discharge lamp lighting device of this embodiment, the abnormality detection circuit 12 detects the asymmetry of the lamp current, and the control circuit 28 turns off the switching element 29 based on the detection output, and the transistor inverter 4 is turned off. Since the power supply is stopped and the oscillation operation is stopped, excessive component stress due to the asymmetry of the lamp current when the emitter of the discharge lamp 5 is exhausted is eliminated, and components such as the oscillation transformer 6 and the oscillation transistors 7 and 8 are protected. This can prevent shortening of their lifespan. Further, since the discharge lamp 5 is turned off by stopping the oscillation of the transistor inverter 4, it is possible to notify the time to replace the discharge lamp 5, and furthermore, it is possible to prevent wastage of power consumption when the emitter is exhausted.

Moreover, since the input power source of the transistor inverter 4 is cut off by the switching element 29 inserted in series between the collectors and emitters of the oscillation transistors 7 and 8, the oscillation transistors 7 and 8 of the transistor inverter 4 are switched off. The voltage applied between the collector and emitter can be lowered, and thermal runaway of the oscillation transistors 7 and 8 can be prevented.

Note that even if the switching element 29 is a transistor, the DC power supply voltage is divided between the oscillation transistors 7 and 8 and the switching element 29, and the oscillation transistors 7 and 8 and the switching element 29
The applied voltages applied to each of the transistors become lower, and destruction of the oscillation transistors 7 and 8 and the transistor serving as the switching element 29 due to thermal runaway can be prevented.

〔Effect of the invention〕

According to the transistor inverter type discharge lamp lighting device of the present invention, in order to turn off the switching element inserted in the input power supply line of the transistor inverter in series between the collector and emitter of the oscillation transistor of the transistor inverter when an abnormality occurs in the discharge lamp. , the transistor inverter is no longer supplied with power and its oscillation can be stopped, and the components can be protected from excessive component stress when the discharge lamp is abnormal. Moreover, since the input power supply of the transistor inverter is cut off by the switching element, the DC power supply voltage applied to the oscillation transistor of the transistor inverter can be lowered, and therefore thermal runaway of the oscillation transistor can be prevented. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional transistor inverter type discharge lamp lighting device, FIG. 2 is a lamp voltage waveform diagram thereof, and FIG. 3 is a circuit diagram of an embodiment of the present invention. ...DC power supply, 4...Transistor inverter, 5...Discharge lamp, 7,8...Oscillation transistor, 12...Abnormality detection circuit, 28...Control circuit, 29...Switching element.

Claims (1)

[Scope of Claims] 1. A DC power supply, a transistor inverter connected to the DC power supply, a discharge lamp serving as a load of the transistor inverter, and a collector of the oscillation transistor of the transistor inverter connected to the input power line of the transistor inverter.・
A transistor comprising a switching element inserted in series between the emitters, an abnormality detection circuit that detects an abnormal state of the discharge lamp, and a control circuit that turns off the switching element in response to a detection output of the abnormality detection circuit. Inverter type discharge lamp lighting device. 2. The transistor inverter discharge lamp lighting device according to claim 1, wherein the abnormality detection circuit detects an asymmetry in the lamp current of the discharge lamp.