JPH0364996B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a discharge lamp lighting device equipped with an inverter having an oscillation transformer to perform high frequency lighting.

Conventionally, it has been common practice to use an inverter with an oscillation transformer to perform high-frequency lighting, but when a discharge lamp reaches the end of its life, one of the emitters of the filament wears out, causing the discharge lamp to discharge DC. At this time, the oscillation transformer and the transistors of the inverter may be destroyed due to the increase in the tube current of the discharge lamp, and the power consumption may increase due to the increase in input power. In particular, in high-frequency lighting, the secondary voltage is higher than the commercial frequency voltage, so even lamps at the end of their lifespan that would not turn on at commercial frequencies will continue to be lit.

An example of such an operation is shown in Fig. 1, in which an inverter including two transistors Q ₁ and Q ₂ and an oscillation transformer T is connected to a clear current circuit S connected to a commercial power supply P. A discharge lamp L is connected to the secondary winding _N2 of this oscillation transformer T. The state in which the discharge lamp L reaches the end of its life and is discharging direct current is illustrated using a diode. Further, the leakage inductance of the oscillation transformer T functions as a current limiting reactor for the lamp current. However, when the discharge lamp L reaches the end of its life and discharges direct current, the oscillation transformer T causes biased magnetization, the current limiting reactor decreases, and the input power increases, causing the oscillation transformer T and the transistor Q ₁ ,
Q ₂ may be destroyed.

There is a device shown in FIG. 2 that solves these drawbacks. From FIG. 2 onwards, the temporary side circuit of the oscillation transformer T is completely omitted from illustration. In the case shown in FIG. 2, a series circuit of a discharge lamp and a capacitor C is formed on the secondary side of an oscillation transformer T. Now, when the discharge lamp L is in half-wave mode and the capacitor C is charged in the loop of ○A, the flow of direct current is blocked and the discharge lamp L stops discharging. This provides safety. In an actual lamp at the end of its life, a slight discharge current also flows in the blocking direction of the diode. The equivalent circuit at this time is a diode and a resistor connected in parallel. However, the voltage in the blocking direction is
The voltage Vc across the capacitor C is added to the voltage Vs of Ns, and the discharge lamp L is forced to consume power through the resistor (equivalent value) in parallel with the diode, increasing the input power. This is dangerous.

Next, another example will be explained based on FIG. In the case shown in FIG. 3, a parallel circuit of an inductor CH and a discharge lamp L is connected to the secondary side of an oscillation transformer T. This inductor CH has sufficient inductance when the oscillating transformer T is under no load or when the discharge lamp L is normal, and when the oscillating transformer T is biased when the discharge lamp L is at half-wave (the current direction is ○○). To do this, set saturable characteristics such that magnetic saturation occurs, the inductance decreases, and current flows through the inductor CH. This provides safety.

Therefore, normally, the saturable characteristic eliminates the air gap in the core, reduces the magnetic resistance of this air gap, and determines the saturation point by appropriately selecting the magnetic flux density of the core. However, it is difficult to manage the saturable characteristics as desired due to variations in the B-H characteristics of the core and variations in the magnetic properties of the air gap. In particular, the oscillation transformer T
If the voltage Vs is low, when the saturation point of the inductor varies widely, sufficient saturation current will not flow through the inductor CH when the discharge lamp L is half-wave,
Power is forced to be consumed in the direction of blocking the half-wave lamp, resulting in an increase in input power, which is dangerous.

The present invention has been made in view of the above points, and an object of the present invention is to obtain a highly reliable device that prevents an increase in input power at the end of a lamp's life.

A first embodiment of the present invention will be explained based on FIG. In this embodiment, a capacitor C is connected in series to a parallel circuit of a discharge lamp L and a saturable inductor CH on the secondary side of an oscillation transformer T. As a result, a charging voltage Vc is generated in the capacitor C, and a voltage of Vc + Vs is generated in the discharge lamp L in the blocking direction ○○.
and inductor CH. At this time,
When the inductor CH is saturated, the inductor CH
Since current flows through the discharge lamp L, an excessive current does not flow through the discharge lamp L compared to that shown in FIG.

Furthermore, even if the saturation point of the saturable characteristic of the inductor CH varies widely, a voltage higher by Vc is applied to the inductor CH than in the case shown in FIG. A saturation characteristic of is obtained. Therefore, even if the voltage Vs of the oscillation transformer T is low, the saturation characteristics of the inductor CH can be obtained relatively easily by the action of Vc.

Here, the meaning of "high" or "low" Vs is that when Vs is applied in the blocking direction of a lamp at the end of its life, a relatively large tube current is said to be "high", and a relatively small tube current is said to be "high". The one that flows is called ``low''. This is the size of discharge lamp L,
It is determined by the relationship between the type, number of lamps, etc., and the secondary voltage of the oscillation transformer T required to start and maintain the discharge lamp L.

Incidentally, the impedance of the capacitor C may be as low as to allow the operation of the inductor CH to be sufficiently performed.

Next, a second embodiment of the present invention will be described based on FIG. In this embodiment, a discharge lamp L, a capacitor C, and a saturable inductor are installed on the secondary side of an oscillation transformer T.
This is a parallel circuit connected to CH. Here, the impedance of the capacitor C is set to be sufficiently higher than the impedance of the discharge lamp L. However, when the current flows in the blocking direction ○○,
Capacitor C is rapidly charged and the rebound voltage of Vc promotes saturation of inductor CH.

As described above, the present invention is equipped with an inverter having an oscillation transformer to perform high-frequency lighting, and in which a step-up capacitor is provided in the secondary winding of the oscillation transformer together with a parallel circuit of a saturable inductor and a discharge lamp. Because of this connection, when the discharge lamp reaches the end of its life and starts discharging DC, the voltage of the capacitor acts when the current is generated in the direction of blocking it, promoting the saturation of the saturable inductor, which causes the current to flow into the discharge lamp. It is also possible to ensure saturation even if the saturation point of the inductor varies, making it easier to design and manufacture saturable inductors and using core materials with poor saturability characteristics. This has the effect of making it possible to

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a high frequency lighting circuit equipped with an inverter having an oscillation transformer, Figures 2 and 3 are
The figure is a circuit diagram that eliminates the drawbacks of the circuit shown in Figure 1, Figure 4 is a circuit diagram showing the first embodiment of the invention, and Figure 5 is a circuit diagram showing the second embodiment of the invention. It is. T...Oscillation transformer, Ns...Secondary winding, CH...
...Saturable inductor, L...Discharge lamp, C...Capacitor.

Claims (1)

[Claims] 1. In an inverter having an oscillation transformer for high-frequency lighting, the transformer is polarized by half-wave discharge at the end of the life of the discharge lamp in the secondary winding of the oscillation transformer. 1. A discharge lamp lighting device characterized in that a boosting capacitor is connected to a parallel circuit of the discharge lamp and a saturable inductor that magnetically saturates when the voltage is applied. 2. The discharge lamp lighting device according to claim 1, characterized in that a boosting capacitor is connected in series with a parallel circuit of a saturable inductor and a discharge lamp. 3. The discharge lamp lighting device according to claim 1, characterized in that a boosting capacitor is connected in parallel with a parallel circuit of a saturable inductor and a discharge lamp.