JPS5926116B2 - DC discharge lamp lighting device - Google Patents

Description

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

Generally, in order to light a DC discharge lamp, such as a xenon short arc lamp, a DC discharge lamp lighting device commonly called a ballast is used.

In the past, this ballast had a major drawback of being heavy, but recently, ultra-compact and lightweight ballasts that employ a semiconductor element opening/closing control system have been developed. An example of the design of the above-mentioned ballast that employs the current semiconductor device opening/closing control system will be explained with reference to FIG. 1.
Inverter 10 composed of transformer Ti
One of the two secondary output parts of the transformer Ti, 2A, is connected to a rectifier DIVC, and this rectifier D1 has a
A smoothing circuit 4 consisting of a high frequency choke coil Li and a capacitor C is connected to the current detection element 3 connected to the negative side of the smoothing circuit 4.
is connected, and its positive output terminal is connected to the discharge lamp 6 via the starter 5.
The negative output terminal is connected to the negative side of the discharge lamp 6.

Here, since the inverter 10 outputs a high frequency alternating current of 20 to 100 KHz, a choke coil suitable for high frequencies is used as the smoothing circuit 4. The discharge lamp 6 is
During stable lighting, the inverter 10, the rectifier,
Since it is lit by the main circuit composed of D1 and the smoothing circuit 4, in order to design this main circuit most economically, the output voltage of the main circuit during stable lighting is equal to the rated voltage of the discharge lamp 6. or something close to it.

However, if this is done as it is, the transition from glow discharge to arc discharge seen at the beginning of discharge lamp startup, that is, the ignitability of the discharge lamp at startup cannot be said to be good, so a high voltage superimposition circuit is connected to both ends of the capacitor C. . This high voltage superimposition circuit is usually composed of a transformer, a rectifier, a resistor, and a superposition capacitor, but in the example shown in FIG. One end thereof is connected to the positive side of the capacitor C constituting the smoothing circuit 4 through a series circuit of a rectifier diode D2 and a resistor R1, and the other end is connected to the negative side of the capacitor C. There is. That is, in this example, the transformer T1 is commonly used for the main circuit and the high voltage superimposing circuit, and the capacitor C is commonly used for the smoothing circuit 4 and the high voltage superimposing circuit. On the other hand, the signal from the current detection element 3 is applied as a feedback signal to a pulse width control circuit 8VC consisting of an error amplifier EA connected to a reference voltage source Refvc, and a pulse width converter PWM connected to an oscillator 0SCIIC, and is driven The switching pulse width of the semiconductor switching elements TRl and TR2 is increased or decreased through the circuit 9,
Discharge lamp 6! The current supplied to the IC is controlled to be constant.

When the starter 5 is activated and the discharge lamp 6 undergoes dielectric breakdown, a large amount of charge is instantly released from the capacitor C, causing a transition from the glow discharge seen at the beginning of lighting to arc discharge, and the discharge lamp 6 , and then enters a stable lighting state.

However, the DC discharge lamp lighting device V having such a conventional configuration
However, it has been found that the transition from glow discharge to arc discharge is not always achieved smoothly and reliably, and so-called extinction occurs.

To explain this, when the discharge lamp 6 is started up, the lamp voltage Ef:. As shown in Fig. 2A, the starter 5
The time T when the was activated. Additionally, due to the rapid discharge of the capacitor C charged by the high voltage superimposition circuit,
As a result, the lamp current 1L becomes lower than the superimposed voltage at time T, as shown at the beginning of FIG. The current suddenly rises from 0 to 1, reaches the peak current 1p at time Tlvc immediately after time TO, and then decreases. Then, at time T2vc, the lamp voltage 1 becomes a voltage approximately 1.5 to 3 times higher than the rated lamp voltage 3, and the lamp rectifier 1L becomes a current smaller than the rated lamp current 1B, and then at time T2vc. , the discharge lamp 6 enters a stable lighting state according to its rating. During the period from time T2 to time T3, so-called extinction occurs and the discharge lamp 6 is turned off. After examining various causes of this phenomenon, it was concluded that it is because the peak current 1p appears too early.

That is, as mentioned above, the lamp current 1L has a peak current of 1L.
, appears at the time T, vc immediately after the actuation of the starter 5, and at this time, even if the lamp voltage VL is sufficiently high, only a discharge occurs, and the cathode of the discharge lamp 6 is also sufficiently high. Since it is not in a heated state, the effect of the peak current 1p flowing is on the surface Vc of the cathode.
This only increases the area of the glow discharge generation region where the current density is constant, and does not contribute to the generation of arc bright spots necessary for transition to arc discharge. In other words, in order to facilitate the transition from glow discharge to arc discharge, it is not enough to simply supply a large amount of charge from the high voltage superimposition circuit to the discharge lamp at the initial stage of startup as in the past. The ignitability of the discharge lamp is not necessarily good, and unless the discharge time of the capacitor C is taken into consideration, the discharge lamp cannot be lit reliably. The present invention relates to an improvement of a DC discharge lamp lighting device that employs a semiconductor element opening/closing control system, and facilitates the transition from glow discharge to arc discharge in a discharge lamp FC at the time of lighting start-up of a DC discharge lamp. An object of the present invention is to provide a DC discharge lamp lighting device that can reliably light a discharge lamp after starting the electric lamp.

An embodiment of the present invention will be described below with reference to the drawings.
Regarding the present invention, as shown in FIG. 3, for example, a DC power supply 1 configured in the same manner as in FIG.
and a smoothing circuit 4 consisting of a transformer T1, a rectifier D1, a current detection element 3, a high frequency choke coil L1 and a capacitor C, a high voltage superimposition circuit, a pulse width control circuit 8, and a drive circuit 9. The positive output side of the 4VC capacitor C is connected to the discharge lamp 6 via the starter 5.
A parallel circuit of a discharge time delay resistor R2 and a thyristor THR is connected to the negative output side of the capacitor C to delay the discharge time of the capacitor C, and the lamp voltage of the discharge lamp 6 is connected to the positive side of the capacitor C. is detected and its magnitude is considerably lower than the superimposed voltage by the high voltage superimposing circuit, for example, when the lamp voltage reaches or is close to the rated lamp voltage of the discharge lamp 6, the thyristor THR is activated. Thyristor trigger circuit 1 for conduction
1 will be provided.

FIG. 4 shows an example of the thyristor trigger circuit 11 together with the thyristor THR, etc. This example! In terms of the IC, a series circuit of trigger resistors R3 and R4 is connected to both ends of the capacitor C, and the gate electrode G of the thyristor THR is connected to the connection point a between the trigger resistors R3 and R4.
A series circuit of voltage dividing resistors R5 and R6 is connected to both ends of the capacitor C, and a connection point BVC between voltage dividing resistors R5 and R6 is connected to the base of a transistor TR3 via a Zener diode DZ. A thyristor trigger circuit 11 is constructed by connecting the collector to the connection point a between the trigger resistors R3 and R4 and connecting the emitter to the negative side of the capacitor C.

Regarding the thyristor trigger circuit 11 having such a configuration,
The voltage across the capacitor C is applied as a supply voltage, and a voltage obtained by dividing the supply voltage by the voltage dividing resistors R5 and R6 appears at the connection point BVC between the voltage dividing resistors R5 and R6, and these voltages are used as the detection voltage. This detection voltage is applied to the Zener diode DZ.
When the zener diode DZVC current flows to the base of the transistor TR3, the transistor TR3 is activated, and the potential at the connection point a between the trigger resistors R3 and R4 is equal to or higher than the capacitor C. The thyristor T becomes the same potential as the negative side of
No voltage is applied to the gate electrode GVC of HR, so the thyristor is rendered non-conductive. However, when the detected voltage is lower than the Zener potential, the Zener diode DZ
Transistor TR3 is inactive because no current ilC flows, so the connection point Avc between trigger resistors R3 and R4 is such that the supply voltage is
A divided voltage appears and is applied to the gate electrode GVC, making the thyristor THR conductive. The operation of the embodiment configured as above is as follows.

That is, as the capacitor C is charged by the high voltage superimposition circuit, the supply voltage across the capacitor C increases. is the fifth
As shown in Figure A, this supply voltage V gradually increases. The detection voltage (voltage at connection point b) VO of the thyristor trigger circuit 11 to which VO is applied is a voltage as shown at the beginning of FIG. gradually increases in response to However, this detection voltage V. Since the Zener diode DZ does not conduct until the potential V2K of the Zener diode DZ reaches the Zener diode DZ, the transistor TR3 is in the inactive (0FF) state as shown in FIG. Al
The driving voltage VE of fC is a voltage as shown in FIG.
When the voltage corresponds to the FC, the thyristor THR becomes conductive, but at this time, the discharge lamp 6 is in an insulated state, so no current flows through the thyristor THRVC and it is unrelated to the operation of the discharge lamp 6. Next, supply power Ff. When Vc becomes higher and the detection voltage o reaches the Zener potential V2, the transistor TR3 becomes activated (ON) as shown in FIG.

becomes zero, and the thyristor THR is rendered non-conductive.
And the supply voltage remains in this state. When TOvc becomes even higher, the starter 5 is activated, the discharge lamp 6 causes dielectric breakdown and current begins to flow, and the lamp voltage 1
is the supply voltage at time TOvc, as shown in FIG. The superimposed voltage 1 begins to drop, which is approximately equal in magnitude to
Starts to stand up rapidly. However, since the thyristor THR is in a non-conducting state at this time, the resistor R2 prevents a large amount of the charge from the capacitor C from being released instantly, and the time constant is determined by the capacitance of the capacitor C and the value of the resistor R2. The discharge time is delayed or extended depending on the time, and therefore the lamp current 1L does not suddenly decrease after reaching the peak value at time T4IIC immediately after time TO, but gradually decreases. .

Then, the voltage across the capacitor C, that is, the supply voltage V, is increased due to charge release. This supply voltage VOIIC naturally decreases, but the corresponding detection voltage V. At the time T,vc becomes lower than the zener potential 2, the transistor TR3 of the thyristor trigger circuit 11 becomes inactive (0FF), thereby causing the driving voltage o to become the supply voltage. Since the size corresponds to the current value, the thyristor THR is triggered and becomes conductive.
After the thyristor THR is triggered in this way, the resistor R2 that suppresses the discharge of the capacitor C is short-circuited, and as a result, at this time T, Vc, the lamp current 1
A pulse Ps appears in L, although it is not very large. As a result of the above, unlike the conventional case where most of the charge charged by the high voltage superimposition circuit of the capacitor C is discharged during glow discharge when the lamp voltage 1 is sufficiently high, the supply voltage.

Lamp current 1L when the lamp voltage is sufficiently high, which is approximately equal to
is suppressed to a relatively small value, a glow discharge occurs only at the minute tip of the discharge lamp 6, and the cathode is heated.Moreover, the discharge time of the capacitor C is extended, so the cathode heating time becomes longer, and the cathode heats up. As a result of efficiently forming an arc bright spot at the minute tip, a pulse Ps of 1 L of lamp current at time T5&c is generated, as shown in Figure 6 (a) and (a), and the glow discharge smoothly occurs. The state shifts to the arc discharge state, and at time T6, which occurs after time T, the discharge lamp 6 reliably enters the stable lighting state. The scale of FIG. 6 is not the same as that of FIG.
In short, when the lamp voltage 1 (Vc) after activation of the starter 5 is high, the lamp current 1L is suppressed by the resistor R2, and when the lamp voltage VL decreases, this is detected by the detection voltage V. By detecting this with a Zener diode DZ and making the thyristor THR conductive, conditions are created in which an arc bright spot is easily formed, thereby facilitating the transition from glow discharge to arc discharge at the initial stage of discharge lamp lighting. It is something. Here, the Zener diode DZ
And voltage dividing resistors R5 and R6 are detection voltages corresponding to the lamp voltage 1 when the lamp voltage 1 of the discharge lamp 6 decreases to the vicinity of the lamp rated voltage 3.

It suffices if the voltage is set to have a characteristic such that the potential of the Zener diode DZ is the same as that of the Zener diode DZ, and the normal time T. The time from T to time T is about 300 μsec or more. The resistor R2 may be any resistor that can suppress the lamp current IL to an appropriate level until time T. In the above embodiment, the parallel circuit of the resistor R2 and the thyristor THR is connected to the capacitor C. Although the capacitor C is inserted between the negative side and the discharge lamp 6, the same effect can be obtained by inserting it between the positive side of the capacitor C and the discharge lamp 6 instead. .

In addition to the thyristor trigger circuit shown in Figure 4, the supply voltage. It is also possible to use a known circuit having another configuration that generates a trigger signal when the voltage falls below a certain level. In order to make the thyristor conductive, the Vc of the present invention monitors the voltage across the discharge lamp and detects when the voltage has dropped below the superimposed voltage by the high voltage superimposition circuit and has reached a level near the rated voltage of the discharge lamp. However, since this triggers the thyristor, the discharge lamp causes dielectric breakdown and glow discharge occurs.Furthermore, this glow discharge is maintained and the cathode is sufficiently heated, that is, if the pulse current If the voltage is added, even if it is small, the thyristor will become conductive when a condition that inevitably causes arc discharge actually occurs.

In this way, when the discharge lamp is actually in a state where it can sufficiently transition to arc discharge, the thyristor is made conductive and the pulse Ps
Therefore, the transition to arc discharge can be achieved very rationally and reliably, even if there is some variation in the characteristics of the discharge lamp due to factors such as the manufacturing process, or Even if the characteristics of the discharge lamp change slightly due to an increase in usage time or lighting frequency, the thyristor conduction timing will change accordingly, making it possible to always achieve reliable lighting. . As described above, the DC discharge lamp lighting device of the present invention includes two semiconductor switching elements connected to a DC power source and whose switching pulse width is controlled by a pulse width control circuit, and a primary coil connected between these semiconductor switching elements. An inverter consisting of a transformer, a rectifier circuit connected to the secondary coil of the transformer of this inverter, a smoothing circuit connected to this rectifier circuit, and a DC discharge lamp connected to the output side of this smoothing circuit are connected in parallel. a high voltage superimposition circuit connected to the capacitor, a parallel circuit of a thyristor and a discharge time delay resistor that delays the discharge time of the capacitor, connected between the capacitor and the DC discharge lamp; and a thyristor trigger circuit that receives a voltage across the discharge lamp and makes the thyristor conductive when the voltage falls below the superimposed voltage by the high voltage superimposition circuit and becomes close to the rated voltage of the DC discharge lamp. Therefore, the discharge of the capacitor can be temporarily suppressed and the discharge time can be extended, and the transition from glow discharge to arc discharge can easily occur. The electric charge flows in without being suppressed, and the transition from glow discharge to arc discharge is reliably performed, and the discharge lamp can eventually be lit reliably.

[Brief explanation of drawings]

FIG. 1 is an explanatory circuit diagram of a conventional DC discharge lamp lighting device, and FIG. ,
FIG. 3 is an explanatory circuit diagram of the DC discharge lamp lighting device of the present invention, FIG. 4 is an explanatory circuit diagram showing an example of a thyristor trigger circuit used in the present invention together with a thyristor, etc., and FIG.
2 is an explanatory diagram showing the supply voltage, detection voltage, operating state of the transistor, and driving voltage over time in the thyristor trigger circuit of FIG. 4, and FIG. 6 is an embodiment of the present invention. FIG. 3 is an explanatory diagram showing lamp voltage time characteristics and lamp current time characteristics of a discharge lamp with a Vc value. 1... DC power supply, T1... Transformer, D1... Rectifier, L1... High frequency choke coil, C... Capacitor, 4... Smoothing circuit, 5... Starter, 6...
Discharge lamp, 8... Pulse width control circuit, 9... Drive circuit, 10... Inverter, R2... Resistor, THR
... Thyristor, 11... Thyristor trigger circuit, R3, R4... Triker resistor, R5, R6... Voltage dividing resistor, DZ... Zener diode, TR3...
transistor.

Claims (1)

[Scope of Claims] 1. An inverter comprising two semiconductor switching elements connected to a DC power source and whose switching pulse width is controlled by a pulse width control circuit, and a transformer having a primary coil connected between these semiconductor switching elements; A rectifier circuit connected to the secondary coil of the transformer of this inverter, a smoothing circuit connected to this rectifier circuit, and a capacitor connected in parallel to the DC discharge lamp connected to the output side of this smoothing circuit. a high voltage superimposition circuit connected between the capacitor and the DC discharge lamp, a parallel circuit of a thyristor and a discharge time delay resistor for delaying the discharge time of the capacitor; A DC discharge lamp lighting device comprising: a thyristor trigger circuit that makes the thyristor conductive when the voltage is lower than the superimposed voltage by the high voltage superimposition circuit and becomes close to the rated voltage of the DC discharge lamp. . 2. The thyristor trigger circuit receives a voltage corresponding to the voltage across the DC discharge lamp from a trigger resistor connected between the gate electrode of the thyristor and the capacitor, and the voltage reaches a level close to the rated voltage of the DC discharge lamp. a Zener diode that becomes conductive when the size is equal to or greater than the corresponding one; and a Zener diode that is connected to this Zener diode, becomes activated when the Zener diode becomes conductive, and applies an electric current to the gate electrode of the thyristor via the trigger resistor. 2. The DC discharge lamp lighting device according to claim 1, further comprising a transistor for dissipating a trigger voltage.