JPS6111438B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a discharge lamp lighting device which uses an AC power source having a voltage comparable to the rated voltage of the discharge lamp and which is capable of lighting the discharge lamp satisfactorily.

FIG. 1 shows an example of a basic circuit that is the premise of the present invention, and shows an AC power supply V _AC having a voltage approximately equal to or slightly lower than the rated voltage of the discharge lamp L _A.
and capacitor C ₁ and inductance L ₁ and discharge lamp L _A
are connected in series to form a first closed circuit, and the _AC power source VAC, the capacitor _C1 , the auxiliary inductance _L2 , and the switching element _S1 are connected in series, partially overlapping the first closed circuit. This is a discharge lamp lighting device in which a second closed circuit is formed connected to the switching element S1, and the switching element _S1 is made conductive for a certain period of time once every half cycle of _{the AC} power source _VAC . This is an example of a circuit using. However, the basic circuit of the discharge lamp lighting device shown in FIG. 1 operates as shown in the time chart of FIG. Discharge lamp L
In this figure, _A is the voltage waveform of the AC power supply V _AC , B is the waveform of the input current Iin, C is the waveform of the lamp current I _LA , and D is the lamp voltage V _LA. waveform, E is the switching element
This is the waveform of the current I _S flowing through _S1 . In the circuit of Fig. 1, the main circuit composed of the AC power supply V _AC , the capacitor C ₁ , the inductance L ₁ and the discharge lamp L _A is phase leading, and therefore the input current Iin is AC as shown in Fig. 2 B. The phase is ahead of the power supply V _AC . Now _, if _the switching element _S1 is turned on at time _t0 as shown in FIG.
Since the second closed circuit consisting of L ₂ and the switching element S ₁ is LC oscillatory, a current I _S as shown in FIG. 2(e) flows through the switching element S ₁ . At this time, the voltage across the capacitor C ₁ is increased by the oscillatory charging current I _S when the switching element S ₁ is turned on, and after the switching element S ₁ is turned off at time t ₁ , this voltage is increased. The terminal voltage of the capacitor C ₁ and the voltage of the AC power supply V _AC are superimposed, and the discharge lamp L _A remains lit until time t ₀ in the next half cycle. After time _t0 , the same operation as described above is repeated, and the discharge lamp _LA is kept constantly lit. Note that even during the ON period of the switching element _S1 , a continuous current flows through the first closed circuit, and the lamp current I _LA has an extremely smooth waveform as shown in FIG. The input current Iin is the lamp current _ILA and the switching element.
The waveform shown in Fig. 2 (b) is obtained by superimposing the S ₁ current I _S and e, and in this Fig. 2 (b), the shaded area is the oscillatory charging current I of the capacitor C ₁ when the switching element S ₁ is on. This is _{the S} part. Thus, the basic circuit shown in Fig. 1 operates as described above, and it becomes possible to maintain the discharge lamp L _A in a steady lighting state with the AC power supply V _AC voltage that is approximately equal to or slightly lower than the rated voltage of the discharge lamp L _A. , it is possible to provide a discharge lamp lighting device that is smaller and lighter, since the inductance L ₁ and the power capacity of the capacitor C ₁ do not need to be small.

By the way, Fig. 3 shows the discharge lamp L in the circuit shown in Fig. 1.
This shows the time chart when _A is removed, and the operation in this case will be explained below.
In Fig. 3, when the AC power supply V _AC is turned on at time Ton and the AC power supply V _AC voltage as shown in Fig. 3A is applied to the circuit, the switching element S ₁ is turned on at time t ₀ of the first half cycle. Assuming that is turned on,
A series vibration system consisting of the AC power supply V _AC , the capacitor C ₁ , the auxiliary inductance L ₂ , and the second closed circuit of the switching element S ₁ is formed, and the switching element
An oscillating current I _S as shown in FIG. 8B flows through _S1 . Therefore, at time t ₁ when this oscillating current I _S is about to reverse, the switching element S ₁ is turned off, but at this time, the capacitor C ₁ is charged as shown in FIG. ₀
Maintain this charging voltage until On the other hand, in the next half cycle, the switching element S ₁ is turned on again at time t ₀ .
is turned on and the series oscillation system described above is formed again, but at this time the voltage of capacitor C ₁ is equal to AC power supply V _A
Therefore, the oscillation is stronger than that in the previous half cycle, and as shown in Figure 3B, _the current has a larger peak value than the previous half cycle current I _S. I _S flows, and the capacitor C ₁ is charged to a higher voltage than in the previous half cycle, as shown in FIG. At time t ₁ when this current I _S is about to reverse, the switching element S ₁ is turned off again, and the capacitor C ₁ remains charged to a higher voltage than the previous half cycle until time t ₀ of the next half cycle. do. Thus, the voltage V _C1 across the capacitor C ₁ increases exponentially every half cycle of the AC power supply V _AC , as shown in Figure 3C, and finally reaches several times to ten times the voltage of the AC power supply V _AC . It will reach several times as many. However, as shown above, the terminal voltage V _C1 of capacitor C ₁
When C increases, the voltage V _S applied across the switching element S ₁ also increases exponentially, as shown in FIG. 3D, and eventually the capacitor C ₁
In order to prevent _this , there is no choice but to use the above-mentioned element with extremely high withstand voltage, which is undesirable in terms of cost and performance. Ta. In other words, the basic example circuit shown in Fig. 1 has the great advantages mentioned above, but on the other hand, when the discharge lamp L _A is removed or due to the life of the discharge lamp L _A , the discharge lamp L _A may go into a non-lighting state. There is a problem in that an abnormally high voltage is applied to the switching element S ₁ and the capacitor C ₁ when the temperature increases.

Therefore, conventionally, as shown in Fig. 4, the voltage across the secondary side terminals Ia ₁ and Ia ₂ to which the discharge lamp L _A is connected is controlled by resistors R ₆ ,
It is detected by the circuit of _R7 , resistors _R4 , _R5 , and capacitor _C3 , and when it is determined that there is no load, the auxiliary switch elements _S2 , _S3 for the positive direction and negative direction are turned on. A circuit has been proposed in which this prevents the switching element _S1 of the second closed circuit from turning on, thereby preventing abnormal voltage boosting during no-load conditions. In the conventional circuit shown in FIG. 4, auxiliary switch elements S ₂ and S ₃ are formed by SCR and PUT, respectively, and S ₄ is a switch for controlling the auxiliary switch element S ₃ which is PUT. A time chart showing the waveform of is shown in FIG. In Fig. 5, A is the voltage waveform of the AC power supply V _AC , B is the waveform of the current I _S flowing through the switching element _S1 ,
C shows the waveform of the voltage V _C1 across the capacitor C ₁ in the main circuit, and the waveform of the no-load secondary voltage V _O2 occurring at the secondary side terminals Ia ₁ and Ia ₂ , respectively. However, in the conventional example shown in FIG. 4, the auxiliary switch element _S2 constituted by the SCR has no trigger input during normal lighting, and as shown in FIG. 5D, the no-load secondary voltage V
When _O2 has been increasing as described in the basic circuit example above, at time _t1 when the no-load secondary voltage V _O2 reaches the predetermined detection level V _L , a trigger pulse is input to the gate and the conduction state is established. Resistors R ₄ , R ₅ ,
A circuit consisting of a capacitor C ₃ and a trigger element S ₆ is set up. If the auxiliary switching element S ₂ becomes conductive at time t ₁ after power-on, this will short-circuit the positive trigger of the switching element S ₁ and the switching element S ₁ will remain in the off state. The voltage V _C1 across the capacitor C ₁ is not inverted, and the no-load secondary voltage V _O2 has a voltage waveform obtained by subtracting the voltage V _C1 across the capacitor C ₁ , which is a negative voltage at this time, from the AC power supply V _AC voltage. Even during a period when the voltage of the AC power supply V _AC is negative, the no-load secondary voltage has a positive potential. Therefore, at this time, switch _S4 , which is a PNP transistor, is in the off state, so PUT
The auxiliary switching element S3 using the auxiliary switching element _S3 conducts when a trigger is input during its own forward bias period when the AC power supply V _AC becomes negative, and the negative polarity trigger signal inputted to the switching element _S1 is also short-circuited. will be done. In this way, no trigger signal is input to the switching element _S1 in either the positive or negative polarity direction, and the voltage V _C1 across the capacitor _C1 does not invert at all, and the resistor _R8 gradually increases. At this time, no load 2
The next voltage V _O2 is the voltage V _C as shown between time t ₁ and t ₂
No load 2 due to the voltage difference between ₁ and V _AC
This prevents an abnormal rise in the secondary voltage. However, in such a conventional example, when the voltage across the capacitor _C1 gradually discharges and the no-load secondary voltage drops below the above-mentioned detection level _VL , the auxiliary switch element S composed of the above-mentioned SCR ₂ shifts to the off state again, and a positive trigger signal is again input to the switching element _S1 at time _t2 . Therefore, the charge on the capacitor C ₁ flows through the switching element S ₁ and the voltage V _C1 across the capacitor C ₁ is reversed, which also returns the auxiliary switching element S ₃ using PUT to the OFF state, and at time t ₃ A negative trigger signal is also input to the switching element S ₁ , and the voltage V _C1 across the capacitor C ₁ and the no-load secondary voltage V _O2 are inverted again, so that the no-load secondary voltage V _{O2 becomes the detection level V O2} again. _L or higher, the auxiliary switch element S ₂ turns on, and the operation from time t ₁ to time t ₃ is repeated, resulting in the problem that the no-load secondary voltage V _O2 cannot be kept low enough. It was hot. In other words, in the conventional circuit shown in FIG. 4, when the no-load secondary voltage V _O2 becomes lower than the detection level V _L , as shown in the time chart of _FIG . There is a problem that it is not possible to lower this voltage V _{O2, and if you try to lower this voltage V O2} , you have no choice but to lower the detection level V _L itself, and if you lower this detection level V _L too much, there is a risk that it will operate with the secondary voltage when lighting. A problem arose.

The present invention has been provided in view of the above-mentioned points, and is such that once the no-load secondary voltage reaches or exceeds a predetermined detection level, the switching element is kept in the OFF state regardless of a slight drop in the no-load secondary voltage. The object of the present invention is to provide a discharge lamp lighting device that can always limit the no-load secondary voltage to below the detection level and set the detection level itself low. It is something.

An embodiment of the present invention will be described in detail below with reference to the drawings.
FIG. 6 shows a circuit diagram of an embodiment of the present invention, and FIG.
The figure is a time chart showing the waveforms of each part.
The circuit according to the embodiment shown in FIG. 6 differs from the conventional example shown in FIG. 4 in that a forward bias is constantly applied to the auxiliary switch element _S2 , which is made up of an SCR, in order to supply its holding current. It is. In other words, the voltage obtained by half-wave rectifying the AC power supply V _AC with the diode D ₄ is applied to the capacitor C ₄ through the resistor R ₂ .
charge the voltage across this capacitor C ₄ resistor
Auxiliary switch element via R ₃ and diode D ₃
By applying _S2 to the anode and cathode,
When the auxiliary switch element _S2 turns on, _the auxiliary switch element
A current higher than the holding current is passed through _S2 to maintain the on state of the auxiliary switch element _S2 .
In Fig. 7, A shows the waveforms of the AC power supply V _AC , B shows the current I _S flowing through the switching element _S1 , C shows the voltage V _C1 across the capacitor _C1 , and D shows the waveforms of the no-load secondary voltage V _O2 . It is.

However, in the embodiment circuit of FIG. 6, the no-load secondary voltage V _O2 after power-on is set to
As shown in FIG. 2, the voltage is gradually increased and when it reaches a preset detection level V _L at time t ₁ , a trigger signal is input to the auxiliary switch element S ₂ and the auxiliary switch element S ₂ is turned on. Therefore, the auxiliary switching element _S2 short-circuits the capacitor _C2 in the positive direction to prevent the generation of a trigger signal to the switching element _S1 , but at the same time, the capacitor _C4 is connected to the resistor _R3 and the diode. A current greater than the holding current flows through _D3 to this auxiliary switch element _S2 , and the auxiliary switch element _S2 is thereafter held in the on state regardless of its gate input. Therefore, in this embodiment circuit of FIG. 6, once the no-load state is detected, the auxiliary switching element _S2 remembers this and maintains the conductive state, and thereafter the switching element _S1 When a positive trigger signal is not input to , and once the input of this positive trigger signal stops, the voltage V _C1 across the capacitor C ₁ is not inverted and its voltage polarity is maintained, so the no-load secondary voltage V _O2 becomes a positive potential as shown in Figure 7 D,
As a result, the auxiliary switch element _S3 using PUT also becomes conductive. Thus, after time _t1 , no trigger signal is input to the switching element _S1 , and it maintains an off state as shown in Figure 7B, and the voltage V _C1 gradually decreases as shown in Figure 7C. It will continue to discharge. At this time, the no-load secondary voltage V _O2
becomes the voltage obtained by subtracting the above voltage V _C1 from the voltage of the AC power supply V _AC , and eventually at time t ₂ the voltage V _O2
When enters the negative region, the auxiliary switching element _S3 consisting of PUT turns off, and as a result, a negative trigger signal is applied to the switching element _S1 , making the switching element _S1 conductive. The voltages applied to element S ₁ are voltages V _AC and V
This is the voltage difference between _C1 and C1, and since it is very small, the voltage across capacitor _C1 is hardly boosted either. Thereafter, the no-load secondary voltage V _O2 repeats the cycle from t ₂ to _{t 3} as described above, and is kept at a sufficiently low voltage.

As described above, the present invention provides a sequence in which the auxiliary switch element is formed by a circuit element having a self-holding function such as a thyristor, and a holding current of the degree necessary to self-maintain the conduction state is supplied to the auxiliary switch element. Since the bias is constantly applied, the circuit has the function of detecting and memorizing the no-load state. Therefore, once the no-load secondary voltage exceeds the detection level, the voltage will be sufficiently low below this detection level. It is possible to suppress the no-load secondary voltage,
This also makes it possible to set the detection level to a sufficiently low voltage within a range that does not cause malfunctions when lighting, which has the effect of ensuring that the no-load secondary voltage has a stable waveform after the overvoltage prevention operation during no-load operation. It is something that you have.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a basic circuit example that is the premise of the present invention, Fig. 2 is a time chart when the same as above is normally lit, Fig. 3 is a time chart when the same as above is under no load,
Fig. 4 is a circuit diagram of the conventional example, Fig. 5 is a time chart of the same without load, Fig. 6 is a circuit diagram of an embodiment of the present invention, and Fig. 7 is a time chart of the same with no load. , L _A is a discharge lamp, V _AC is an AC power supply, C ₁ is a capacitor, L ₁ is an inductance, L _A is a discharge lamp, L ₂ is an auxiliary inductance, and S ₂ and S ₃ are each auxiliary switch elements.

Claims (1)

[Claims] 1. A first closed circuit formed by connecting in series a discharge lamp, an AC power supply having a voltage approximately equal to or slightly lower than the rated voltage, a capacitor, an inductance, and the discharge lamp, and the AC power supply, the capacitor, the auxiliary inductance, and switching. A second closed circuit is formed by connecting the switching element in series, and the switching element is made conductive for a certain period of time once every half cycle of the AC power supply, so that the switching element is connected in series, and the switching element is made conductive for a certain period of time once every half cycle of the AC power supply. In a discharge lamp lighting device that detects an abnormally boosted circuit voltage, detects no load, and conducts an auxiliary switch element to forcibly cut off conduction of the switching element during no load, the auxiliary switch element is used like a thyristor. A discharge lamp lighting device characterized in that it is formed of circuit elements having a self-holding function, and a forward bias is constantly applied to the auxiliary switch element to supply a holding current necessary to self-maintain its conductive state. Device.