JPS6232597B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a discharge lamp lighting device.

An object of the present invention is to shorten the preheating time when the preheating current is large and to lengthen the preheating time when the preheating current is small, thereby optimally preheating the filament to improve startability and extend the lamp life. be.

A conventional discharge lamp lighting device is constructed as shown in FIG. In Fig. 1, when the switch SW is turned on at time t ₀ in Fig. 2, the inductance element L, the filament F ₁ of the discharge lamp La, and the full-wave rectifier BD ₁
The voltage of the power supply V _S is applied to the switch element Q via the switch element Q. On the other hand, this voltage charges the capacitor C ₁ through the resistor R ₁ , and after several cycles of the supply voltage, the charge is sufficient to make the switch element Q conductive, and a resistor R ₂ is connected to the base of the switch element Q. A base current is passed through the switch element Q to turn on the switch element Q. At this moment, a preheating current flows through the filaments F ₁ and F ₂ , and an induced voltage is generated across the secondary winding L' of the inductance element L. From now on, the capacitor C ₁ is connected mainly to this voltage through the full-wave rectifier BD ₂ . Charged by induced voltage. Therefore, capacitor _C1 acts as a control power supply necessary to control switch element Q. However, since the emitter potential of the transistor Q ₁ is limited by the Zener voltage V _Z1 of the Zener diode ZD ₁ , this control power supply is a constant voltage power supply. Once the switch element Q is turned on, a DC voltage appears across the capacitor _C1 as described above. At the next moment, the state of the switch element Q is until the transistor _Q2 is turned on, that is, the state of the switch element Q is the same as that of the capacitor.
During the charging period until the voltage of _C2 reaches the Zener voltage of the Zener diode _ZD2 , the transistor _Q3 is off, so the switch element Q obtains a base current and continues to be on. Therefore, filaments F ₁ and F ₂ are preheated during this period. Next, when transistor _Q2 is turned on, transistor _Q3 is turned on, and the subsequent state of switch element Q is determined by transistor _Q4 . Here, the transistor
Q Explain the condition of ₄ .

The capacitor C ₃ is charged from the control power supply via the resistor R ₃ , but while the filaments F ₁ and F ₂ are being preheated, that is, the transistor Q ₃ is off and the switch element Q is on. During this period, a large base current is supplied from the control power source to the switch element Q, and only a voltage less than the Zener voltage of the Zener diode _ZD3 is generated. Therefore, no base current flows through transistor _Q5 , and since it is off, capacitor _C4 is charged via resistor _R4 .
On the other hand, transistor Q ₆ serves as a charge discharger for capacitor C ₄ . During the preheating period, the collector potential of the switch element Q is almost zero, so the transistor
Since Q ₇ is turned off and transistor Q ₆ remains off, the charging voltage of capacitor C ₄ reaches the Zener voltage of Zener diode ZD ₄ and the transistor
_Q4 is on. In this state transistor _Q3
When turned on, the collector potential of the transistor _Q4 becomes almost zero at time _t1 as shown in Fig. 2b, and the switch element Q is turned off at that moment, the preheating current flowing through the inductance element L is cut off, and the inductance element A kick voltage is generated from L as shown in FIG. 2c and applied between both filaments F ₁ and F ₂ of the discharge lamp La, and the discharge lamp La is lit. When the discharge lamp La is turned on, a current flows through the discharge lamp La, and since the base current of the switch element Q does not flow, a voltage higher than that during the preheating period is obtained in the capacitor _C1 .
Therefore, resistor R ₅ becomes increasingly biased, as shown by the dotted line in FIG. 2a.

Next, when the lamp voltage becomes zero at time t ₂ in Figure 2 due to the phase reversal of the power supply V _S , the transistor
A trigger pulse is applied to _{the transistor Q 6 as} shown in Fig. 2d, and the capacitor C ₄ is connected to the second
As shown in Figure a, the battery is instantly discharged. Then, the transistor Q ₆ turns off, so the capacitor C ₄ is charged again, but after being discharged, the transistor Q ₄ remains off until the charging voltage reaches the Zener voltage of the Zener diode ZD ₄ , and the switch element Q turns on. This period is called the on period T as shown in FIG. 2b. As mentioned above, this on-period T depends on the charging period of the capacitor _C4 , but this is due to the bias of the resistor _R5 , that is, the transistor _Q5
Determined by the base potential of this is a transistor
Since Q ₅ turns on with the bias of resistor R ₅ and instantaneously charges capacitor C ₄ to approximately this base potential, the constant time constant charging from resistor R ₄ dominates after this and therefore the resistor The bias on _R5 will determine the charging period of capacitor _C4 .

By the way, the bias of resistor _R5 is determined by the charging potential of capacitor _C3 from the control power supply through resistor _R3 , but as mentioned above, when the discharge lamp La is lit, the potential of capacitor _C1 increases. , the bias of resistor _R5 increases as shown by the broken line in FIG. 2a and reaches a certain saturation value. When the on-period T ends, a high-voltage pulse is applied to the discharge lamp La by the energy stored in the inductance element L, similarly to when the preheating period ends, and the discharge lamp La is lit again. In this way, the discharge lamp La, which has been lit once, is made conductive for a certain period at the beginning of each half-wave of the power supply V _S , and the voltage required for restriking is not supplemented by the kick voltage of the inductance element L, and the lighting is maintained at a low power supply voltage. let

By the way, in this case, the preheating time is determined by the time constant consisting of resistor R ₆ and capacitor C ₂ .
Under any conditions, it is constant because it is a constant voltage power supply as described above. In this case, when the power supply voltage is low, the preheating current decreases, making starting performance extremely difficult. If the preheating time is set using the above time constant to sufficiently preheat the filaments F ₁ and F ₂ when the power supply voltage is low, if the voltage exceeds the rated voltage, the preheating will be excessive and the time required to start will be too long. It had drawbacks.

The present invention has been made in view of this point, and will be explained in detail below with reference to Examples.

In Figure 3, R ₆ and C ₂ are resistors and capacitors that set the preheating time, and resistor R ₆ is a transistor
Instead of connecting to the emitter of Q ₁ , it is directly connected to capacitor C ₁ , and the preheating current detection means is the secondary winding wound around the current limiting inductance element L.
It is formed by a full-wave rectifier BD ₂ that rectifies the voltage across L' and a capacitor C ₁ . Moreover, the other parts are the same as those in FIG. As mentioned above, the voltage across the capacitor C ₁ increases as the current flowing through the inductance element L increases. There is only an inductance element L that is substantially determined by the power supply frequency, and the current flowing through the inductance element L during preheating increases monotonically with the power supply voltage. Therefore, in FIG. 3, after the switch SW is turned on, the potential of the capacitor _C2 rises faster as the power supply voltage is higher, as shown in FIG. 4, and the preheating time becomes shorter. That is, in Fig. 4, curves a, b, and c are the charging curves of capacitor _C2 . Curve a is the case when the power supply voltage is low, and curves b and c indicate that the power supply voltage increases. Representation, Zener diode
Time Ta to the intersection with Zener voltage V _Z2 of ZD ₂ ,
Tb and Tc are the preheating times for each voltage. In this way, when the preheating current is large, the preheating time is shortened,
By lengthening the preheating time when the preheating current is low, the filaments F ₁ and F ₂ can be optimally preheated.

As described above, the present invention provides a preheating type discharge lamp lighting device in which a preheating current is passed through the discharge lamp for a certain period of time before applying a starting pulse to the discharge lamp, in which a secondary winding is wound around a current limiting inductance element. A preheating current detection means is provided to detect the preheating current based on the output, and when the preheating current is high, the preheating time is shortened, and when the preheating current is low, the preheating time is lengthened to optimally preheat the filament. Since the control means is provided, the filament can be optimally preheated to improve startability, and since there is no excessive preheating, the lamp life can be extended.

[Brief explanation of the drawing]

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.
Figures a to d are time charts of the same as above, Figure 3 is a circuit diagram of an embodiment of the present invention, and Figure 4 is a characteristic diagram of the same. La...discharge lamp, _F1 ...filament, _F2 ...filament, Q...switch element that flows preheating current,
R ₆ , C ₂ ...Resistance and capacitor of the time constant circuit that determines the preheating time.

Claims (1)

[Claims] 1 In an advance preheating type discharge lamp lighting device in which a preheating current is passed through the discharge lamp for a certain period of time before applying a starting pulse to the discharge lamp, the preheating current is determined based on the output of the secondary winding wound around the current limiting inductance element. A preheating current detection means is provided to detect the preheating current, and a preheating control means is formed to optimally preheat the filament by shortening the preheating time when the preheating current is high and lengthening the preheating time when the preheating current is low. A discharge lamp lighting device characterized by: