JPH01167995A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To stop the oscillation operation of a switching circuit immediately when it comes to an emitterless condition by providing a triple-terminal control element to stop a current to drive a transistor flowing from a driving circuit of the switching circuit by the current flowing in to a control terminal. CONSTITUTION:When a fluorescent lamp 7 becomes to an emitterless condition, the lamp 7 is discharged with difficulty to increase the impedance, a large current flows through a positive property of thermistor 21, and when the temperature exceeds the Curie temperature, the resistance value increases suddenly. As a result, the potential at the contact of the thermistor 21 and a capacitor rises, and a current flows into the control terminal of a transistor 23 which is a tripleterminal control element through a Zener diode 22 which is a voltage response switching element. And, by this current, the triple-terminal control element is operated to stop the current to drive the transistor 6 of a circuit 11 from the driving circuit of a switching circuit 11. Consequently, the oscillation operation of the circuit 11 is stopped immediately.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a discharge lamp lighting device for starting and lighting a discharge lamp at high frequency.

2. Description of the Related Art A conventional discharge lamp lighting device is disclosed in, for example, Japanese Patent Application Laid-open No. 62-20
Publication No. 2494 and National Technlc
al Report Vol., 33 No., 3 p.
296, the circuit was as shown in Figure 2.

That is, in FIG. 2, 4 is a power supply circuit whose output voltage has a constant polarity and is composed of a commercial power supply 1, a rectifier bridge 2, and a smoothing capacitor 3, 5 is a capacitor connected in series to the output, and 6 is a capacitor. 5 and the power supply circuit 4, a series circuit of a fluorescent lamp 7 and an inductance 8 is connected in parallel to the capacitor 5, and a starting circuit is connected in parallel to the opposite end of the fluorescent lamp 7 on the source side. A certain capacitor 9 and an inductance 10 are connected.

11 is a self-excited switching circuit consisting of a capacitor 5, a transistor 6, a capacitor 9, an inductance 8, and an inductance 10. Reference numeral 12 denotes an inductance which is a driving inductance with one end connected to the base of the transistor 6, and a series circuit of an inductance 80 secondary winding 8b and a capacitor 13 which is a driving capacitor is connected between the other end and the emitter. . 1.7 is a timer circuit consisting of a voltage dividing resistor 14.15 connected to the output end of the power supply circuit 4 and a capacitor 16 with one end connected to the midpoint thereof; 18 is a timer circuit with the other end of the capacitor 16 connected to the base; A transistor 19 is a short-circuiting transistor connected in parallel to the inductance 12, and a diode 19 has a cathode connected to the base of the transistor 6 and the other end connected to the emitter of the transistor 6 through a resistor 20.

The operation of the conventional circuit configured as above will be explained.

When the power is turned on, voltage is generated in the power supply circuit 4 and the timer starts! 117 resistor 14, capacitor 16 and transistor 1
The starting current flows through the base of transistor 18.
conducts, and at the same time, its base current causes transistor 6 to conduct.

Initially, the fluorescent lamp 7 is not lit, and current flows from the power supply circuit 4 through the transistor 6 via the inductance 8, the filament electrode of the fluorescent lamp 7, the capacitor 9, and the inductance 10. At this time, inductance 8
A positive voltage is generated in the secondary winding 8b of the transistor 6, and the base current of the transistor 6 is supplied through the capacitor 13 and the inductance 12, thereby keeping the transistor 6 on. At this time, the current flowing through the primary winding 8a of the inductance 8 is a resonant current between the capacitor 9 and the inductance 8. Here, the current flowing due to the positive voltage generated in the secondary winding 8b of the inductance 8 is a series resonant current at the natural vibration frequency of the inductance 12 and the capacitor 13.
In reality, since the transistor 18 is conductive, the current flows to some extent in the opposite direction from the emitter to the collector of the transistor 18, so the resonance state is weak and the inductance 12 hardly functions, so its oscillation period is close to the charging/discharging time of the capacitor 13. It becomes shorter.

Therefore, when the capacitor 13 is charged to near the voltage generated in the secondary winding 8b and the base current of the transistor 6 stops flowing, the base current of the transistor 6 is slightly pulled in the opposite direction due to the influence of the inductance 12.
is about to turn off, so the inductance 8b
When the voltage generated in the capacitor 13 becomes smaller, the charge accumulated in the capacitor 13 is fed back to the base and emitter of the transistor 6 in the opposite direction, and the transistor 6 is quickly turned off. When the transistor 6 is turned off, the energy stored in the series resonant circuit of the capacitor 9 and inductance 8 and the inductance 25 is released to the capacitor 5, the fluorescent lamp 7, the capacitor 9, the inductance 8, and the inductance 10, causing vibration, and preheating the fluorescent lamp 7. It becomes an electric current. At this time, settings are made so that the fluorescent lamp 7 is not started by the voltage generated in the capacitor 9. The oscillating current flowing through the primary winding 8a of the inductance 8 when the transistor 6 is off generates a negative voltage in the secondary winding 8b of the inductance 8. At this time, transistor 18 conducts in the forward direction and inductance 1-2 does not function at all, so this voltage causes diode 19 and resistor 2 to
A reverse voltage is applied between the base and emitter of the transistor 6 through 0 to keep the transistor 6 off. When the oscillating current passes a negative peak, a positive voltage is gradually generated in the secondary winding 8b of the inductance 8, and the voltage that was charged in the reverse direction in the capacitor 13 during the off period of the transistor 6 is transferred to the base of the transistor 6. The transistor 6 is turned on when the voltage is applied in the direction.

At this time, immediately after turn-on, the current in inductance 8 is still flowing in the opposite direction, so diode 19 and resistor 2
Current flows from the base to the collector through 0. The reverse current in the inductance 8 gradually decreases, and a forward current begins to flow through the transistor 6, and the above operation is repeated thereafter. Due to the above oscillation operation, the temperature of the preheating electrode of the fluorescent lamp 7 increases with the passage of time.

Note that the timer circuit M17 accumulates charge in the capacitor 16 via the resistor 14 after the power is turned on, and the transistor 18
When the capacitor 16 is charged to the voltage of the resistor 14.15 after a predetermined period of time, it is no longer charged, so from this point on, the power is cut off and the charge in the capacitor 16 is released via the resistor 14.15. No current flows to the base of transistor 18 until the current is reached. Therefore, when transistor 18 turns off after a predetermined time, transistor 6
When turned on, a positive voltage is generated in the secondary winding 8b of the inductance 8, and the base current of the transistor 6 is supplied via the capacitor 13 and the inductance 12. This base current is a resonant current of the capacitor 13 and the inductance 12, and around the half cycle, the base current of the transistor 6 changes from positive to negative, and when the accumulated charge of the transistor 6 is released, the transistor 6 is turned off. Before starting the fluorescent lamp 7, the inductance 8 and the capacitor 9 are in a series resonant state, and the capacitor 9 has a voltage which is much larger than when the lamp is turned on and larger than during preheating before the timer circuit operates.
Each inductance and capacitor is set to generate sufficient voltage to start the fluorescent lamp 7t'. Therefore, the fluorescent lamp 7 is started.

After starting, the operation of the circuit is almost the same as after the operation of the timer circuit 17, but since the impedance of the fluorescent lamp 7 is connected in parallel with the impedance of the capacitor 9 and the inductance 10, the current of the capacitor 9 decreases and the fluorescent lamp 7 Current flows. Therefore, the resonance between the inductance 8 and the capacitor 9 is almost eliminated, and the 2nd half of the inductance 8
Positive and negative voltages are generated in the next winding 8b according to the difference between the output voltage of the power supply circuit 4 and the lamp voltage, and the transistor 6
On/off control is performed to keep the fluorescent lamp 7 lit. Note that the inductance 10 is for removing the DC component of the current of the fluorescent lamp 7.

Further, when the fluorescent lamp 7 cannot be lit normally, such as at the end of its life, the circuit becomes in the same operating state (resonant state) as when the starting voltage is generated after the timer circuit 17 operates. Furthermore, when the fluorescent lamp 7 is removed, no current flows through the inductance 8, so the transistor 6 is not turned on and does not oscillate.

Problems to be Solved by the Invention However, in the above configuration, when the fluorescent lamp 7 is started or in an abnormal state such as at the end of its life, the impedance of the fluorescent lamp 7 is large and changes rapidly and irregularly. Therefore, not only does the resonance generated between the series resonant circuit of the capacitor 9 and the inductance 8 and the inductance 5 increase, but also periodic deviations occur due to changes in the inductance value of the inductance 12 and changes in the storage time of the transistor 6. causing abnormal oscillation,
There is a problem in that the loss of the transistor 6 becomes large, and if this state continues as at the end of its life, the temperature of the transistor 6 may rise rapidly and be destroyed.

Means for Solving the Problems In order to solve the above problems, the present invention includes a power supply whose output voltage has a constant polarity, and at least one transistor, inductance, and capacitor connected to the output terminal of the power supply. a switching circuit having a self-excited drive circuit for starting and lighting a discharge lamp connected to an output terminal by turning on and off a forward current of the power source and the transistor; a series circuit of a positive temperature coefficient thermistor and a starting circuit, the positive temperature coefficient thermistor being connected to the opposite side of the power supply, and a voltage responsive switching element having one end connected to a connection point between the positive temperature coefficient thermistor and the starting circuit; and a three-terminal control element that stops the current that drives the transistor from the drive circuit of the switching circuit by a current flowing into a control terminal connected to the other end of the voltage responsive switching element.

Operation The present invention has the above-described configuration, so that when the fluorescent lamp 7 enters a so-called emitterless state in which the emitters of the electrodes on one or both sides disappear at the end of its life, the fluorescent lamp 7 becomes difficult to discharge and its impedance becomes high. When a large current flows through the characteristic thermistor and the temperature of the positive characteristic thermistor rises and exceeds the Curie temperature, the resistance value increases rapidly. Therefore, the potential at the connection point between the positive temperature coefficient thermistor and the capacitor becomes high, and the current flowing into the control terminal of the three-terminal control element through the voltage-responsive switching element operates the three-terminal control element, causing the drive circuit of the switching circuit to The current driving the transistor of the switching circuit is stopped, and the oscillation operation of the switching circuit is immediately stopped. Furthermore, when the negative voltage side of the power supply or the electrodes on both sides are emitterless, a larger current flows through the positive thermistor, and the resistance value of the thermistor increases, and almost no current flows directly from the power supply through the lamp, resulting in an inductance of 8. Since the base of the transistor 6 flowing through the current is eliminated, the oscillation operation of the switching circuit is stopped more reliably. In this way, when the fluorescent lamp 7 enters the emitterless state that occurs at the end of its life, the oscillation operation of the switching circuit can be stopped immediately, and the transistor 6 is prevented from being destroyed due to a sudden temperature rise. .

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings. FIG. 1 is a circuit diagram showing an embodiment of the discharge lamp lighting device of the present invention. In Figure 1, from commercial power supply 1 to resistor 20
Up to this point, the configuration and operation are the same as the conventional example. What is different from the conventional example is that the positive temperature coefficient thermistor 21 is connected in series between the non-power supply side and anti-transistor side electrode of the fluorescent lamp 7, which is a discharge lamp, and the capacitor 9, which is the starting circuit. A current flows from the drive circuit of the switching circuit 11 to the transistor 6 by the current flowing into the Zener diode 22, which is a voltage-responsive switching element whose one end is connected to the connection point A with the Zener diode 9, and the base connected to the other end of the Zener diode 22. This is because the transistor 23 is a three-terminal control element that stops the operation. In this lighting device, the operation of the circuit of the embodiment in which the drive circuit is configured as 0 or more, in which the drive circuit is constituted by an inductance 8, an inductance 12, and a capacitor 13, will be explained. The operation from when the power is turned on until the fluorescent lamp 7 lights up normally is the same as in the conventional example, so the explanation will be omitted, and the operations different from the conventional example will be explained below. When the electrode 7a of the fluorescent lamp 7 is emitterless and the electrode 7b has an emitter, when the power source 1f is turned on, the switching circuit 11 starts oscillating as in the conventional example. However, since the electrode 7a of the fluorescent lamp 7 is emitterless, the lamp current flows from the electrode 7a to the electrode 7b, but not in the opposite direction. Therefore, a large current corresponding to the lamp current flows through the PTC thermistor 21 via the capacitor 9, and the temperature of the PTC thermistor 21 rises, and when the temperature approaches the Curie temperature, the resistance value increases rapidly. FIG. 2 shows the change in voltage at the connection point A between the PTC thermistor 21 and the capacitor 9 when the resistance value of the PTC thermistor 21 changes in this manner. In FIG. 2, before t, the resistance value of the positive characteristic thermistor 21 is low, and the voltage at the connection point A is almost equal to the output voltage of the power supply circuit 4 because there is almost no potential difference with the positive voltage side of the power supply circuit 4. The voltage is close. After t1, the resistance value of the positive characteristic thermistor 21 increases, and as the resistance value increases, the resonance voltages of the capacitor 9 and the inductance 8 are superimposed, and the peak voltage increases. When the peak voltage at connection point A reaches the operating voltage of Zener diode 22, current flows from connection point A to the base of transistor 23 via Zener diode 22, transistor 23 operates, and the connection point between capacitor 13 and inductance 12 B and the negative voltage side of the power source 4 are short-circuited. Therefore, the supply of base current to the transistor 6 is stopped, and the operation of the switching circuit is stopped.

Next, the case where the electrode i7b of the fluorescent lamp 7 is emitterless and the electrode 7a has an emitter, and the case where the electrode 7a, the electrode 7b
In both cases, the emitterless case will be explained. In these cases, since almost no current flows directly from the power supply circuit 4 through the lamp, the current flows directly from the power supply circuit 4 through the positive temperature coefficient thermistor 21, rapidly increasing the resistance value of the positive temperature coefficient thermistor, and then switching the switching circuit by the transistor 23. At the same time as stopping the oscillation operation of 11, the power supply circuit 4
From the fluorescent lamp 7 and the capacitor 97Ir: Since almost no current flows through it, the base of the transistor 6 flowing through the inductance 8 disappears,
The oscillation operation of the switching circuit 11 is stopped more reliably.

Furthermore, since the timer circuit 17 is provided in this embodiment, when the oscillation operation of the -degree switching circuit 11 stops,
The oscillation operation of the switching circuit 11 will not start unless the power supply circuit 4 is turned off and then turned on again.

In this embodiment, a fluorescent lamp is used as the discharge lamp, but similar effects can be obtained with other lamps such as a high-pressure discharge lamp that does not require preheating. Further, the self-excited switching circuit section may be of the one-stone type or the two-stone type. Further, the voltage responsive switching element may be any other element such as a varistor or diac as long as the current flows when the voltage exceeds a specific voltage, and the timer circuit 17 may be any other element. Further, although the secondary winding 8b with the inductance 8 is used as the power source for driving, the same effect can be obtained even if the power is supplied from another inductance.

As described in detail, according to the present invention, it is possible to quickly stop the oscillation operation of a switching circuit when the emitterless state that occurs at the end of a fluorescent lamp's life occurs with a simple and inexpensive circuit configuration. Therefore, it is possible to realize a discharge lamp lighting device that can prevent the transistor 6 from being destroyed due to a sudden temperature rise.

[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, and FIG. 2 shows the voltage at the connection point A between the PTC thermistor 21 and the capacitor 9 when the resistance value of the PTC thermistor 21 changes. FIG. 3, which shows the changes, is a circuit diagram of a conventional discharge lamp lighting device. DESCRIPTION OF SYMBOLS 1... Commercial power supply, 4... Power supply circuit, 8... Inductance, 7... Fluorescent lamp, 6... Main transistor, 12... Drive inductance, 13... Drive capacitor, 21...Positive characteristic thermistor, 22...
・Zener diode, 23...Transistor Name of agent: Patent attorney Toshio Nakao (1 person) Figure 2 Timetable

Claims (1)

[Claims] A power supply whose output voltage has a constant polarity, and at least one transistor, an inductance, and a capacitor connected to the output terminal of the power supply, and a forward current to the power supply is turned on and off by the transistor, and the output terminal is connected to the output terminal of the power supply. a switching circuit having a self-excited drive circuit for starting and lighting a discharge lamp connected to the discharge lamp; and a positive temperature coefficient thermistor connected to the non-power supply side of the discharge lamp so that the positive coefficient thermistor is on the side opposite to the transistor of the power supply. The switching is performed by a current flowing into a series circuit with a starting circuit, a voltage responsive switching element having one end connected to a connection point between the positive temperature coefficient thermistor and the starting circuit, and a control terminal connected to the other end of the voltage responsive switching element. A discharge lamp lighting device comprising: a three-terminal control element that stops a current that drives the transistor from a drive circuit of the circuit.