JPH04255697A - Discharge lamp lightening device - Google Patents

Abstract

PURPOSE:To protect a circuit from abnormal conditions of a discharge lamp with a simple and cheap construction in a discharge lamp lightening device, which illuminates the discharge lamp by a high frequency inverter. CONSTITUTION:The second inductor 19 and a positive characteristic thermistor 20 for the purpose of bypassing a direct current component are connected in series to each other between both electrode terminals 17a, l7b of the discharge lamp 16 of a discharge lamp lightening device which lightes the discharge lamp by feeding resonance current thereto directly after connecting both electrode terminals 17a, l7b of a discharge lamp 16 in series to a capacitor 8 and the first inductor 9 both of which comprise a resonance circuit. When the discharge lamp 16 is damaged or become emitter-less, at the end of life, direct current component flowing into the first and second inductors 9 and 19 are suppressed, by the characteristic of the positive characteristic thermister 20, and then discharge is stopped so as to provide protection function for preventing any damage of the circuit.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device for lighting a discharge lamp such as a fluorescent lamp using a high frequency inverter.

0002

[Prior Art] In recent years, discharge lamp lighting devices have become highly efficient and
In order to reduce weight, many systems have been adopted in which lights are lit using high-frequency inverters made of semiconductor elements. In particular, with the recent release of compact fluorescent lamps, there is a demand for smaller lighting devices using high-frequency inverters.

A conventional discharge lamp lighting device will be explained below with reference to the drawings. FIG. 3 shows a circuit diagram of a conventional discharge lamp lighting device, in which 1 is a power supply circuit, 2 is an inverter circuit, and 3 is a discharge lamp load circuit. The power supply circuit 1 includes an AC power supply 4, a rectifier circuit 5, and a capacitor 6. To explain the configuration of the inverter circuit 2, the emitter of the transistor 7 is connected to the negative side of the rectifier circuit 5, and the collector is connected to the positive side of the rectifier circuit 5 via a resonance capacitor 8.

The collector of the transistor 7 is connected to the discharge lamp load circuit 3 through a resonance inductor 9. The resonance inductor 9 has a feedback winding 10.
is provided, one terminal of which is connected to the negative side of the rectifier circuit 5, and the other terminal is connected to the base of the transistor 7 through a series circuit of an inductor 11 and a capacitor 12. Further, a starting resistor 13 is connected between the base and the positive side of the rectifier circuit 5, and a diode 14 and a resistor 15 connected in series from the emitter of the transistor 7 to the base. One filament electrode 17a of the discharge lamp 16 of the discharge lamp load circuit 3 is connected to the positive side of the rectifier circuit 5, and the other filament electrode 17b is connected to the inductor 9.

In addition, on the non-power-supplied terminal side of the filament electrodes 17a and 17b, there is a capacitor 18 for preheating and stabilizing the discharge after lighting, and a capacitor 18 for passing the starting current and bypassing the DC component flowing to the discharge lamp during lighting. An inductor 19 is connected in parallel.

The operation of the conventional discharge lamp lighting device constructed as described above will be explained below.

When the AC power source 4 is applied, the DC current is rectified by the rectifier circuit 5 and smoothed by the capacitor 6, and then supplied to the inverter circuit 2. Resistor 1 from the positive side of power supply circuit 1
3 to the base of the transistor 7, and the transistor 7 becomes conductive. Therefore, the current flows from the positive side of the rectifier circuit 5, passes through the filament electrode 17a of the discharge lamp 16, passes through the inductor 19, the filament electrode 17b, and the inductor 9, and then flows to the collector of the transistor 7. Current flows.

On the other hand, the base of the transistor 7 is connected to the feedback winding 10 of the inductor 9 so as to provide positive feedback of changes in the current flowing to the inductor 9 via a series resonant circuit of an inductor 11 and a capacitor 12. When the power is turned on, the inverter circuit 2 enters an oscillating state. In the oscillation state, the diode 14 and the resistor 15 are connected for the purpose of discharging the charge in the capacitor 12 when the transistor 7 is off.

When the inverter circuit 2 starts operating, the discharge lamp does not discharge immediately after the operation, and the high frequency current passes through the filament electrode 17a of the discharge lamp 16, the capacitor 18 connected to the non-power supply side between both electrodes, and the filament electrode 17b. flows. Both filament electrodes 17a, 17b of the discharge lamp 16 are preheated by this current. When the electrode is sufficiently preheated, electrons are actively emitted from the electrodes, making it easier to discharge, and eventually discharge starts and the discharge lamp 16 lights up.

When lit, the filament electrodes 17a and 1
Since the voltage between 7b becomes the tube voltage of the discharge lamp 16,
The high frequency current flowing through the capacitor 18 is significantly reduced and the discharge lamp 16 is turned on. At this time, most of the direct current from the power supply necessary to maintain the oscillation state flows through the inductor 19 in a bypass manner, and does not flow as discharge current of the lamp.

[0011]

However, in the above configuration, when the discharge lamp 16 becomes emitterless at the end of its life, the tube voltage of the discharge lamp 15 increases, the input power increases, and the inductor 9 and the inductor If the current flowing through the transistors 19 increases and burns them out, or if the emitter on the filament electrode 17b side of the discharge lamp 16 is worn out, the oscillation waveform will deteriorate, resulting in increased heat loss of the transistor 7 and damage. There is a problem in that if this occurs and the discharge lamp in use goes into an abnormal state, the function of the discharge lamp lighting circuit will be destroyed.

0012

[Means for Solving the Problems] The discharge lamp lighting device of the present invention is characterized in that the first inductance of a high-frequency inverter, which is constituted by a resonant circuit including a capacitor and a first inductance, and a switching element, is connected to both electrodes of a discharge lamp. The terminals are connected in series so that a resonant electrode flows through both electrode terminals of the discharge lamp, and a second inductor and a positive temperature coefficient thermistor are connected in series between both electrode terminals of the discharge lamp. .

[0013]

[Operation] With the above-described configuration, the present invention has a low tube voltage when the discharge lamp is normal, and the electrode flowing through the series circuit of the second inductor and positive temperature coefficient thermistor connected between both electrode terminals of the discharge lamp is small. The temperature of the positive temperature coefficient thermistor remains lit without increasing. On the other hand, when the emitter of the discharge lamp 15 is lost at the end of its life, the tube voltage of the discharge lamp 15 increases and the direct current flowing through the positive temperature coefficient thermistor increases, causing the temperature to rise due to self-heating and eventually reach the Curie point. The positive temperature coefficient thermistor changes to high resistance. As a result, the current flowing through the inductor is significantly reduced, making it impossible to supply sufficient energy to the resonant circuit, and the oscillation force becomes extremely weak, making it impossible to maintain the lighting state of the discharge lamp and causing it to stop.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A discharge lamp lighting device according to an embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows a discharge lamp lighting device according to an embodiment of the present invention. Regarding the configuration, in order to avoid redundant explanation with the conventional example, the same parts as in the circuit diagram of the conventional example are given the same reference numerals, and different parts will be described. The different parts are
In the discharge lamp load circuit 3, a positive temperature coefficient thermistor 20 is connected in series with an inductor 19 connected between the non-power feeding side terminals of the filament electrodes 17a and 17b of the discharge lamp 16. The operation of the conventional discharge lamp lighting device configured as described above will be described below.

When the AC power source 4 is applied, the DC current is rectified by the rectifier circuit 5 and smoothed by the capacitor 6, as in the conventional example, and then supplied to the inverter circuit 2. Then, the flow flows from the positive side of the power supply circuit 1 through the resistor 13 to the base of the transistor 7, making the transistor 7 conductive, and from the positive side of the rectifying circuit 5 to the filament electrode 17a of the discharge lamp 16.
A current flows through the inductor 19, the positive temperature coefficient thermistor 20, the filament electrode 17b, and the inductor 9 to the collector of the transistor 7. On the other hand, the base of the transistor 7 is connected to the feedback winding 10 of the inductor 9 so as to provide positive feedback of changes in the current flowing to the inductor 9 via a series resonant circuit of an inductor 11 and a capacitor 12. becomes an oscillating state. Most of the direct current from the power supply necessary to maintain the oscillation state flows through the inductor 19 in a bypass manner, and does not flow as discharge current of the lamp.

When the discharge lamp 16 enters the oscillation state, the discharge lamp 16 enters the lighting state in the same manner as in the conventional example. If the discharge lamp 16 is normal, the current flowing through the series circuit of the inductor 19 and the positive temperature coefficient thermistor 20 will be as shown in FIG. 2(a). On the other hand, when the emitter disappears or cracks at the end of its life and becomes abnormal, the tube voltage increases and the input power increases compared to the normal case, and the current flowing through the series circuit of the inductor 19 and the positive temperature coefficient thermistor 20 decreases. (b) in Figure 2.
). Therefore, this positive characteristic thermistor 20
The characteristics are set so that the discharge lamp 16 does not operate with a normal current, but operates with an abnormal current such as at the end of its life when the temperature rises to the Curie point. If the discharge lamp 16 is normal, the positive temperature coefficient thermistor 20
Since the resistance value of the lamp hardly changes, the lamp will remain lit, but if something goes wrong, the current will increase and the lamp will self-heat. When the temperature eventually rises to the Curie point, the resistance value of the positive temperature coefficient thermistor 20 increases significantly and becomes high in resistance. Then, the direct current component of the current flowing through the inductor 19 becomes extremely small, making it impossible to supply sufficient energy to the resonant circuit, and the oscillation force becomes extremely weak.

As a result, the discharge lamp 16 cannot be maintained in a lit state and stops. After stopping, the input power becomes an extremely weak oscillation state of about 2 watts, and a protective operation state is entered. In order to recover the function of the discharge lamp lighting device from this state, it is sufficient to turn off the power, replace it with a normal discharge lamp, and then turn on the power again.

Although this embodiment has been described in which a series circuit of an inductor 19 and a positive temperature coefficient thermistor 20 is connected between the electrodes of the discharge lamp 16 on the non-power feeding side,
The same effect can be obtained when connected to the power supply side.

[0020]

[Effects of the Invention] As described above, both electrode terminals of a discharge lamp are connected in series with the first inductor of the resonant circuit of the high-frequency inverter, which is composed of a resonant circuit consisting of a capacitor and a first inductor, and a switching element. By connecting a second inductor and a positive temperature coefficient thermistor in series between both electrode terminals of the discharge lamp, Accordingly, it is possible to provide a discharge lamp lighting device having a protection function to prevent circuit destruction when the discharge lamp enters an abnormal state at the end of its life, etc., with a simple, compact, and inexpensive configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a discharge lamp lighting device according to an embodiment of the present invention.

[Figure 2] (a) is a waveform diagram of the current flowing through the inductor 19 of the same device when a normal discharge lamp is lit; (b) is a waveform diagram of the current flowing through the inductor 19 of the same device when an abnormal discharge lamp is lit;

[Figure 3] Circuit diagram of conventional discharge lamp lighting device

[Explanation of symbols]

1 Power supply circuit 2 Inverter circuit 3 Discharge lamp load circuit 4 AC power supply 16 Discharge lamp 17a, 17b Filament electrode 18 Capacitor 19 Inductor 20 Positive characteristic thermistor

Claims (1)

[Claims] 1. Both electrode terminals of a discharge lamp are connected in series to the first inductance of a high-frequency inverter comprising a resonant circuit including a capacitor and a first inductance, and a switching element, so that a resonant current is directly applied to the discharge. A discharge lamp lighting device characterized in that the discharge lamp is configured to flow through both electrode terminals of the lamp, and a second inductor and a positive temperature coefficient thermistor are connected in series between both electrode terminals of the discharge lamp.