JPH0336280B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter-type discharge lamp lighting device.

[Conventional technology]

FIG. 1 shows a circuit diagram of a conventional discharge lamp lighting device. This discharge lamp lighting device uses a direct current power supply voltage obtained by rectifying a commercial power supply 1 with a rectifier bridge 2 and smoothing it with a smoothing capacitor 4, using a leakage type oscillation transformer 7, transistors 8 and 9, a chiyoke coil 3, and a resistor 5. , 6, and a capacitor 10, and the discharge lamps 19 and 20 are lit at high frequency by the inverter output obtained from the main secondary winding _N2 of the oscillation transformer 7.

Another main secondary winding Nf of the oscillation transformer 7 is wound in the opposite direction to the main secondary winding _N2 , and is a preheating compensation winding for the lamp filament, and is a preheating compensation winding for the saturable reactor 17, which is a switch element. At saturation, a preheating current is applied to the discharge lamps 19 and 20 via the preheating transformer 18. Capacitor 21 is a sequence capacitor for sequential lighting, and N _B is a feedback winding of an oscillation transformer.

The aforementioned saturable reactor 17 is controlled by a DC power supply voltage obtained by rectifying and smoothing the voltage generated in the auxiliary winding N _C of the oscillation transformer 7 with a diode 11 and a capacitor 12, a timer circuit 16, and a transistor 15. Specifically, when the commercial power supply 1 is turned on, the timer circuit 16 is activated and supplies base current to the transistor 15 for a certain period of time (for example, 1 second) to make the transistor 15 conductive. Since the exciting current flows through the primary winding and saturates the iron core, the filaments of the discharge lamps 19 and 20 are preheated. After a certain period of time has elapsed, when the timer circuit 16 times up and the transistor 15 turns off, the excitation current of the saturable reactor 17 is cut off and the secondary winding of the saturable reactor 17 has a large inductance, so the preheating current is cut off. is,
The output of the oscillation transformer 7 is applied to the discharge lamps 19 and 20, and the discharge lamps 19 and 20 are started.

Note that the resistor 14 is a base resistance of the transistor 15, and the diode 13 is a protection diode.

[Problem to be solved by the invention]

In such a conventional circuit, when the commercial power supply 1 is cut off and then turned on again, if the cut-off time is long and the driving power supply voltage of the timer circuit has fallen below the reset level of the timer circuit, then the commercial power supply 1 is turned on again.
The timer circuit is reset, and as described above, preheating and lighting are repeated, but if the cut-off time is short and the timer circuit is turned on again before the drive voltage has fallen to the timer circuit reset level, the timer circuit will be reset. Since the transistor 15 does not conduct when the power is turned on again, preheating is not performed.
The discharge lamps 19 and 20 are lit by cold cathode discharge. In such a case, especially when multiple lamps are lit in series or the ambient temperature is low, it may be difficult for the discharge lamps 19, 20 to restart, and in such a situation, the conductance of the discharge lamps 19, 20 may become unstable. As a result, the inverter circuit may cause abnormal oscillation, causing abnormal noise or flickering, and further impeding the reliability of the lighting device.

SUMMARY OF THE INVENTION An object of the present invention is to provide a discharge lamp lighting device that can improve reliability by preventing abnormal oscillations and restart failures of an inverter circuit when a commercial power supply is quickly switched on and off.

[Means to solve the problem]

The discharge lamp lighting device of the present invention is provided with an oscillation transformer having a main secondary winding and a preheating compensation winding wound in the opposite direction to the main secondary winding at the output stage,
an inverter circuit supplied with power from a commercial power supply; a discharge lamp connected between both ends of a main secondary winding of an oscillation transformer of the inverter circuit; a main secondary winding of the oscillation transformer, a filament of the discharge lamp, and the It is connected to form a loop circuit with the preheating compensation winding of the oscillation transformer.
When turned on, the voltage applied from the inverter circuit to the discharge lamp is lowered and a preheating current is passed through the filament of the discharge lamp, and when turned off, the voltage applied from the inverter circuit to the discharge lamp is increased and the filament A switch element that cuts off the supply of preheating current to the inverter circuit, and a DC power supply voltage obtained by rectifying and smoothing the output of the inverter circuit is supplied as a drive power supply voltage, and turns on the switch element for a certain period of time after application of the drive power supply voltage. A timer circuit that is reset when the drive power supply voltage drops below a certain voltage when the drive power supply voltage is turned off and the DC power supply voltage obtained by rectifying and smoothing the output of the inverter circuit drops below a threshold value close to the voltage value during normal lighting. The configuration includes a voltage detection circuit that sometimes turns on the switch element.

In this case, the effect is higher if the threshold voltage is as close as possible to the voltage value during normal lighting.

[Effect]

According to the configuration of the present invention, when the drive power supply voltage of the timer circuit drops to a certain extent due to interruption of the commercial power supply, the switch element is turned on to shift the discharge lamp to the preheating state. Therefore, even if the commercial power supply is turned on again before the drive power supply voltage of the timer circuit drops below the reset level, the discharge lamp can be preheated. Therefore, the discharge lamp can be easily restarted to prevent restart failure, and reliability can be improved by preventing abnormal oscillation of the inverter circuit due to instability of lamp conductance. .

〔Example〕

Hereinafter, embodiments will be described based on the drawings.

FIG. 2 shows a circuit diagram of a discharge lamp lighting device according to an embodiment of the present invention. This discharge lamp lighting device is
A voltage detection circuit 22 consisting of a transistor 24, a Zener diode 25, and resistors 23, 26, and 27 is added to the circuit shown in FIG. This voltage detection circuit 22 is connected to the auxiliary winding of the oscillation transformer 7.
The saturable reactor 17 is controlled by comparing the level of the DC power supply voltage obtained by rectifying and smoothing the voltage generated at the N _C with a threshold value. Specifically, when the above-mentioned DC power supply voltage is higher than the Zener voltage (threshold) of the Zener diode 25, the transistor 24 becomes conductive and its collector voltage becomes low level, and when it is lower than the Zener voltage. In this case, the transistor 24 is non-conductive and its collector voltage becomes high level. This threshold (Zener voltage) is set at V ₂ in FIG. As a result of the above, when the DC power supply voltage obtained across the capacitor 12 is higher than V ₂ , the transistor 24 is on and its collector voltage is at a low level, so the base current from the voltage detection circuit 22 to the transistor 15 is supply is cut off, transistor 15 is connected to timer circuit 1
The saturable reactor 17, which is a switch element, is turned on and off in accordance with the output of the switch element 6. On the other hand, when the DC power supply voltage obtained across the capacitor 12 is lower than the voltage _V2 , the transistor 24 is off and its collector voltage is at a high level, so the output of the timer circuit 16 is at a low level even if it is at a low level. Even if transistor 1
5 is turned on, and the saturable reactor 17 becomes conductive.

The vertical axis in FIG. 3 shows the DC voltage level of the capacitor 12 mentioned above, and the horizontal axis shows time. V ₀ is the DC voltage level during normal operation of the inverter circuit, V ₁
is the reset level of the timer circuit 16, and _t0 on the horizontal axis
indicates the time when the commercial power supply 1 is cut off, _t1 indicates the time when the voltage detection circuit 22 is reversed, and _t2 indicates the time when the DC voltage across the capacitor 12 reaches the reset level.
This shows the time when the timer circuit 16 is reset by falling below _V1 .

Voltage detection circuit 2 with thresholds set in this way
2, the discharge lamp lighting device of this embodiment operates as follows.

When the commercial power supply 1 is turned on, the inverter circuit is driven in the same manner as described in the conventional example, and the voltages of the main secondary winding N ₂ and the preheating compensation winding N _f of the oscillation transformer are changed to the discharge lamps 19, 20, Saturable reactor 1
7. The additions to the preheating transformer 18 and the capacitor 21 are similar to those in FIG.

The control operation of the saturable reactor 17 differs from that in FIG. This point will be explained below.

The timer circuit 16 _,
The transistor 15, voltage detection circuit 22, etc. control conduction/cutoff of the saturable reactor 17, which is a switch element.

Specifically, when the commercial power supply 1 is turned on, the DC power supply voltage (voltage
V ₀ ), the timer circuit 16 is activated and the output is at a high level for a certain period of time (for example, about one second), supplying base current to the transistor 15 and making the transistor 15 conductive. As a result, an exciting current flows through the primary winding of the saturable reactor 17 and the iron core is saturated, that is, the saturable reactor 17 becomes conductive, so that the filaments of the bar electric lamps 19 and 20 are preheated. At this time, since the voltage is higher than the DC power supply voltage V ₂ obtained across the capacitor 12, the transistor 24 of the voltage detection circuit 22 is on and the collector voltage is at a low level. 15
Since it is connected to the base of transistor 24
Even if the transistor 15 is turned on, the transistor 15 will not be turned off. As a result, even if the voltage detection circuit 22 is added, the saturable reactor 17 can be turned on and the discharge lamps 19 and 20 can be preheated by turning on the commercial power supply 1.

After that, when the timer circuit 16 times up and its output becomes low level, the transistor 15
is turned off. As a result, the excitation current of the saturable reactor 17 is cut off and the secondary winding of the saturable reactor 17 has a large reactance, that is, the saturable reactor 17 is cut off, so the preheating current is cut off, and the discharge lamp 19, Oscillation transformer 7 in 20
The discharge lamps 19 and 20 are started and lit up by applying the output.

While the commercial power supply 1 is turned on and the inverter circuit is operating normally, the DC power supply voltage obtained across the capacitor 12 also remains higher than the voltage _V2 , and the transistor 24 is in the on state, that is, the voltage detection circuit 22 to the transistor 15, and the output of the voltage detection circuit 22 prevents problems such as the discharge lamps 19 and 20 going into a preheating state while they are being lit. do not have.

When the commercial power supply 1 is cut off at subsequent time t ₀ , the voltage of the smoothing capacitor 4 also gradually decreases, and the output of the transistor inverter also decreases. At this time, the DC power supply voltage obtained across the capacitor 12 also decreases. Then, at time _t1 , the voltage falls below _V2 . As a result, after time _t1 , the transistor 24 of the voltage detection circuit 22 is cut off, and its collector potential becomes high level, passing through the resistors 23 and 27 of the voltage detection circuit 22 to the transistor 15.
The base current is supplied to the timer circuit 16, and the timer circuit 16
Although the output is at a low level due to time-up, the transistor 15 is turned on, and the saturable reactor 17 is driven to conduct by the DC power supply voltage across the capacitor 12, and the discharge lamps 19, 20 are turned on. becomes preheated. At this time, the discharge lamps 19 and 20 are preheated by the output of the inverter circuit using the residual charge of the smoothing capacitor 4.

Thereafter, after time _t2 , the DC power supply voltage across the capacitor 12 falls below the voltage _V1 , and the timer circuit 16 is reset.

When the commercial power supply 1 is turned on again before time t ₂ (after time t ₁ ), the DC power supply voltage is still higher than the reset level V ₁ and the timer circuit 16 has not been reset, so the timer circuit 1
6 is not performed for a certain period of time (for example, about 1 second), but the DC power supply voltage across the capacitor 12 drops from voltage V ₂ and rises again to voltage V ₂ when the commercial power supply 1 is turned on again. Until then, the voltage detection circuit 22 works to preheat the capacitor 12, and when the DC power supply voltage of the capacitor 12 exceeds the voltage _V2 , the saturable reactor 17 shuts off and the discharge lamp 1
9 and 20 start and turn on.

On the other hand, when the commercial power supply 1 is turned on again after time _t2 , the DC power supply voltage is already lower than the reset level _V1 and the timer circuit 16 has been reset, so the power supply is reset in the same way as when the power was initially turned on. , the timer circuit 16 operates, and the discharge lamps 19,
After the lamp 20 is preheated for a certain period of time (for example, about 1 second), it starts and lights up.

According to the discharge lamp lighting device of this embodiment, when the DC power supply voltage on both sides of the capacitor 12 drops below the voltage _V2 , the saturable reactor is turned on by turning on the transistor 15 regardless of the output of the timer circuit 16. 17 is made conductive and the discharge lamps 19, 20
Since the discharge lamps 19 and 20 are preheated, even if the commercial power supply 1 is turned on again after the commercial power supply ₁ is cut off and before the timer circuit 16 is reset after the DC power supply voltage falls below the reset level V1, the discharge lamps 19, 20 Can preheat the discharge lamp without cold cathode discharge 1
9, 20 is easy to restart, and restart failure can be prevented. Further, it is possible to prevent abnormal oscillation of the inverter circuit due to instability of lamp conductance. As a result of the above, reliability can be improved. In this case, it is more effective to set the voltage V ₂ to a value close to V ₀ because preheating can be performed sufficiently.

Furthermore, by making the saturable reactor 17 conductive based on the output of the voltage detection circuit 22, the residual charge in the capacitor 12 can be quickly released, and the DC power supply voltage across the capacitor 12 can be quickly lowered. The circuit 16 can be reset quickly, and the resetability of the timer circuit 16 can be improved.

〔Effect of the invention〕

The discharge lamp lighting device of the present invention turns on a switch element to shift the discharge lamp to a preheating state when the drive power supply voltage of the timer circuit drops to a certain extent due to interruption of commercial power supply. Even if the commercial power is turned on again before the voltage drops below the reset level, the discharge lamp can be preheated, making it easy to restart the discharge lamp and preventing restart failure. , abnormal oscillation of the inverter circuit due to instability of lamp conductance can be prevented and reliability can be improved.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional discharge lamp lighting device, Figure 2 is a circuit diagram of a conventional discharge lamp lighting device.
The figure is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a characteristic diagram showing voltage changes in the main parts thereof. 1... Commercial power supply, 2... Rectifier bridge, 3...
Chi York coil, 4... Smoothing capacitor, 5, 6
... Resistor, 7 ... Oscillation transformer, 8, 9 ... Transistor, 10 ... Capacitor, 11 ... Diode, 12 ... Capacitor, 13 ... Diode, 14 ... Resistor, 15 ... Transistor, 16
...Timer circuit, 17...Saturable reactor, 18
...Preheating transformer, 19,20...Discharge lamp,
21... Capacitor, 22... Voltage detection circuit, 2
3, 26, 27...Resistor, 24...Transistor, 25...Zener diode.

Claims (1)

[Scope of Claims] 1. An inverter circuit that is provided with an oscillation transformer having a main secondary winding and a preheating compensation winding wound in the opposite direction to the main secondary winding in the output stage, and is powered from a commercial power supply. and a discharge lamp connected between both ends of the main secondary winding of the oscillation transformer of this inverter circuit, together with the main secondary winding of the oscillation transformer, the filament of the discharge lamp, and the preheating compensation winding of the oscillation transformer. connected to form a loop circuit,
When turned on, the voltage applied from the inverter circuit to the discharge lamp is reduced and a preheating current is passed through the filament of the discharge lamp, and when turned off, the voltage applied from the inverter circuit to the discharge lamp is increased and the filament A switch element that cuts off the supply of preheating current to the inverter circuit, and a DC power supply voltage obtained by rectifying and smoothing the output of the inverter circuit is supplied as a drive power supply voltage, and turns on the switch element for a certain period of time after application of the drive power supply voltage. A timer circuit that is reset when the drive power supply voltage drops below a certain voltage when the drive power supply voltage is turned off and the DC power supply voltage obtained by rectifying and smoothing the output of the inverter circuit drops below a threshold value close to the voltage value during normal lighting. A discharge lamp lighting device comprising: a voltage detection circuit that sometimes turns on the switch element. 2. The discharge lamp lighting device according to claim 1, wherein the switch element is a saturable reactor. 3. The discharge lamp lighting device according to claim 1, wherein the discharge lamps are connected in series, and a sequence capacitor for sequential starting is additionally connected.