JP2003208994A - Electric discharge lamp lighting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric discharge lamp lighting circuit which can manage correctly the lighting operation time, which continues generating of the high-voltage pulse impressed on an electric discharge lamp, and the discontinuation time of operation, which interrupts generating of the high-voltage pulse. <P>SOLUTION: The high-voltage pulse impressed to the electric discharge lamp 3 is generated by making the electric charge of a capacitor C1 charged through a diode D1 with the output of an alternate current power supply 1 discharge through a thyristor Th1 for electric discharge, and a primary coil of a boosting transformer 5. The lighting operation time and the discontinuation time of operation are correctly set by providing a thyristor Th2 for giving triggers, which gives the trigger signal to the thyristor Th1, and a thyristor Th1, which give a side way to the trigger signal of the transistor TR1 and by controlling ON-OFF of the transistor TR1 by a timer 9a. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting circuit used for lighting a discharge lamp such as a metal halide lamp.

[0002]

2. Description of the Related Art When lighting a discharge lamp that requires a high starting voltage, such as a metal halide lamp, a discharge lamp lighting circuit that generates a starting voltage having a waveform in which a high frequency AC voltage and a high voltage pulse are superimposed is used. The discharge lamp is started by applying a starting voltage from the lighting circuit to the discharge lamp.

FIG. 3 shows a conventional discharge lamp lighting circuit of this type. This discharge lamp lighting circuit has a pair of input terminals 2a, to which an output of a high frequency AC power source 1 including a high frequency generator is applied. 2b, a pair of output terminals 4a, 4b to which the discharge lamp 3 is connected, a step-up transformer 5 having a primary coil 5p and a secondary coil 5s, a capacitor C1 provided on the primary side of the step-up transformer 5, and an alternating current The output of one half cycle of the power supply 1, the capacitor C through the diode D1, the primary coil 5p of the step-up transformer and the feedback diode D2.
1 to one polarity, a discharge thyristor Th1 provided to discharge the charge of the capacitor C1 through the primary coil 5p of the step-up transformer when conducting, and the other half cycle of the AC power supply. By passing a current through the diode D3, the resistors R1 to R3 and the feedback diode D4 at the output voltage, the resistor R3
Is thermally coupled to the iron core of the step-up transformer 5, and a discharge thyristor trigger circuit that gives a trigger signal between the gate and cathode of the discharge thyristor Th1 when the voltage generated across both ends of the zener diode ZD1 exceeds the zener voltage of the zener diode ZD1. And a thermistor (a temperature-sensitive resistance element having a negative temperature coefficient) Rth connected between the gates and cathodes of the thyristor Th1.

In this discharge lamp lighting circuit, a step-up transformer 5, a charging circuit for charging the capacitor C1 with the output of one half cycle of the capacitor C1 and the AC power supply 1, a discharging thyristor Th1 and an AC power supply for the other. A high voltage pulse generation circuit is configured by a circuit that triggers a thyristor when a voltage of a half cycle is generated.

In this discharge lamp lighting circuit, the high voltage pulse induced in the secondary coil 5s of the step-up transformer when the electric charge of the capacitor is discharged through the primary coil 5p of the step-up transformer is also applied between the input terminals 2a and 2b. A voltage obtained by superimposing the output voltage of the AC power supply is a pair of output terminals 4a,
4b, the pair of input terminals 2a, 2b, the secondary coil 5s of the step-up transformer 5, and the pair of output terminals 4a, 4b.
And are connected to each other.

In the discharge lamp lighting circuit shown in FIG. 3,
When the AC power supply 1 outputs the voltage V1p for one half cycle, the capacitor C1 is charged to the polarity shown in the figure. Next, when the AC power supply 1 outputs the voltage V1n in the other half cycle, a trigger signal is given to the discharging thyristor Th1, so that the thyristor becomes conductive and the electric charge of the capacitor C1 is discharged through the primary coil of the step-up transformer 5. Since a large magnetic flux change occurs in the iron core of the step-up transformer 5 due to the discharge of this capacitor, the secondary coil 5s
A high voltage pulse Vh is generated at. These operations are repeated in synchronization with the output of the AC power supply, and each time the AC power supply outputs the voltage of the other half cycle, a high voltage pulse is induced in the secondary coil of the step-up transformer (the high voltage pulse generation circuit Oscillates).

Since the above-mentioned high voltage pulse Vh is superimposed on the AC voltage V1n applied between the input terminals 2a and 2b from the AC power source 1 and applied to the discharge lamp 3, discharge is started in the discharge lamp 3 and is discharged. The light turns on.

When the discharge lamp 3 is activated, the voltage across the discharge lamp 3 decreases, and the voltage between the input terminals 2a and 2b also decreases. This also lowers the voltage across resistor R3,
The Zener diode ZD1 cannot be conducted, and the thyristor Th1 is not supplied with the trigger signal. Therefore, the thyristor Th1 cannot be conducted, and the generation of the high voltage pulse (oscillation of the high voltage pulse generation circuit) is stopped. After the generation of the high voltage pulse is stopped, the output voltage of the AC power supply 1 is applied to the discharge lamp,
The discharge in the discharge lamp is maintained.

In the discharge lamp lighting circuit shown in FIG. 3, since the discharge lamp cannot be started for some reason, when the high voltage pulse is repeatedly generated, the temperature of the step-up transformer rises, causing the discharge thyristor to discharge. The temperature also rises. If this state is left as it is, the winding of the step-up transformer may be burned or the thyristor may be damaged. Therefore, in the circuit shown in FIG. 3, the thermistor Rth thermally coupled to the iron core of the step-up transformer is connected to the thyristor T.
It is connected between the gate and cathode of h1. If the thermistor is provided in this way, the resistance value of the thermistor Rth decreases when the temperature of the step-up transformer rises excessively,
Since the voltage between the gate and the cathode of the thyristor Th1 cannot reach the trigger level of the thyristor,
The generation of high voltage pulse stops. When the temperature of the step-up transformer 5 decreases, the resistance value of the thermistor increases, and the voltage between the gate and the cathode of the thyristor Th1 can reach the trigger level of the thyristor, the oscillation operation is restarted,
The generation of the high voltage pulse is restarted. The duration of oscillation and the duration of oscillation of the high voltage pulse generation circuit are determined by the resistance-temperature characteristics of the thermistor.

[0010]

In the discharge lamp lighting circuit shown in FIG. 3, the trigger voltage is applied to the discharging thyristor Th1 through the Zener diode ZD1 by the low voltage across the resistor R3. In the case of the configuration, a sufficient gate current may not flow in the thyristor Th1 and the thyristor Th1 may not be reliably triggered.

In the discharge lamp lighting circuit shown in FIG. 3, the generation time of the high voltage pulse (the time during which the high voltage pulse continues to be generated) is determined by the characteristics of the thermistor, but the thermistor has a large variation in the characteristics. There is a problem that the generation time of the high voltage pulse varies greatly depending on the product.

Furthermore, in the discharge lamp lighting circuit shown in FIG.
Since the generation time of the high voltage pulse depends on the characteristics of the thermistor with large variations, it is not possible to manage the generation time of the high voltage pulse accurately, and it is possible to properly protect the boost transformer and the discharge thyristor. There was a problem that I could not.

A thyristor having a large current capacity and a step-up transformer may be used so that the thyristor having a large current capacity can be used so as to withstand a long generation time of the high voltage pulse, but a thyristor having a large current capacity is large and expensive. In order to increase the current capacity of the step-up transformer, it is necessary to increase the cross-sectional area of its winding. Therefore, if a thyristor or step-up transformer with a large current capacity is used, the lighting circuit becomes large and expensive, which is not preferable. .

It is an object of the present invention to provide a discharge lamp lighting circuit capable of reliably triggering a discharge thyristor.

Another object of the present invention is to provide a discharge lamp lighting circuit capable of accurately controlling the generation time of a high voltage pulse.

[0016]

The present invention is a step-up transformer having a pair of input terminals to which an output of an AC power source is applied, a pair of output terminals to which a discharge lamp is connected, a primary coil and a secondary coil. A capacitor provided on the primary side of the step-up transformer, and a capacitor charging circuit that charges the capacitor to one polarity with the output of one half cycle of the AC power supply,
A discharge thyristor provided to discharge the electric charge of the capacitor through the primary coil of the step-up transformer when conducting, and a discharge thyristor trigger circuit that gives a trigger signal to the discharge thyristor at the output voltage of the other half cycle of the AC power supply. And a high voltage pulse induced in the secondary coil of the step-up transformer when the electric charge of the capacitor is discharged through the primary coil of the step-up transformer and a voltage obtained by superimposing the output voltage of the AC power supply applied between the input terminals. The discharge lamp lighting circuit includes a pair of input terminals, a secondary coil of a step-up transformer, and a pair of output terminals that are connected to each other so as to output from between the output terminals.

According to the present invention, when the discharge thyristor trigger circuit is provided between the anode and the gate of the discharge thyristor with the anode facing the anode side of the discharge thyristor, the charge of the capacitor is reduced. A trigger thyristor that partially discharges between the gate and cathode of the discharge thyristor, and a trigger thyristor trigger circuit that gives a trigger signal to the trigger thyristor when the output voltage of the other half cycle of the AC power supply reaches the set value. Is equipped with.

With the above configuration, when the voltage of the other half cycle generated by the AC power supply reaches the set value, a part of the charge of the capacitor passes through between the gate cathode of the trigger thyristor and the gate cathode of the discharge thyristor. Since the discharge is performed, a large gate current can be passed through the discharge thyristor to reliably trigger the discharge thyristor.

In a preferred aspect of the present invention, a pair of input terminals to which the output of the AC power supply is applied, a pair of output terminals to which a discharge lamp is connected, a step-up transformer having a primary coil and a secondary coil, and a step-up transformer. A capacitor whose one end is connected to one end of the primary coil of the transformer, a capacitor charging diode whose cathode is connected to the capacitor side between the other end of the capacitor and one of the input terminals of the pair, and a primary coil An anode and a cathode are respectively connected to the other end, the first and second feedback diodes whose anodes are commonly connected and whose cathodes are respectively connected to one and the other of the pair of input terminals, and the other end of the capacitor and the other end of the primary coil, respectively. , And the discharge thyristor with the anode and cathode facing the anode side and the gate side of the discharge thyristor, respectively. Of the trigger thyristor, which is connected between the anode gates of the capacitors through a current limiting resistor and discharges some of the charge of the capacitor through the gate and cathode of the discharging thyristor when conducting, and the other of the pair of input terminals. A discharge lamp lighting circuit is configured by a trigger thyristor trigger circuit that applies a trigger signal from the side to the gate of the trigger thyristor.

In addition to the above structure, the discharge lamp lighting circuit according to the present invention is further provided so as to bypass the trigger signal provided to the trigger thyristor when it becomes conductive from the trigger thyristor. Turns on and off the trigger signal side switch, and when the AC power output is applied to the input terminal, starts the timing operation and turns on the trigger signal side switch when the set allowable limit operation time is measured. It is preferable that the lighting operation stop timer holds the ON state of the trigger signal side switch while the output of the AC power supply is applied between the pair of input terminals.

When the trigger signal side switch and the timer are provided as described above, the trigger of the discharge thyristor is stopped when the set allowable limit operation time elapses after the AC power supply is turned on. Therefore, when the discharge lamp does not light up even after the allowable limit operation time elapses, the generation of the high voltage pulse can be stopped to protect the step-up transformer and the discharge thyristor. Since the allowable limit operation time can be determined by a timer, it is possible to manage it accurately.

The discharge lamp lighting circuit according to the present invention, in addition to the trigger signal side switch and the timer for stopping the lighting operation, further permits when the output of the AC power supply is applied to the input terminal. Timing that measures the lighting operation time by alternately performing the timing operation that measures the lighting operation time that is set shorter than the limit operation time and the time measurement operation that measures the operation interruption time that is set shorter than the allowable limit operation time. A lighting operation in which the trigger signal side path switch is held in the off state while the time operation is performed, and the trigger signal side path switch is held in the on state while the timing operation for measuring the operation interruption time is performed. It is preferable to employ a configuration including a gating timer.

With this configuration, the lighting operation period and the lighting operation interruption period that are accurately managed by the timer are alternately generated, and the lighting operation of the discharge lamp is performed while suppressing the temperature rise of the step-up transformer and the discharging thyristor. Since it can be performed, it is possible to proceed with the lighting operation of the discharge lamp while accurately protecting the step-up transformer and the discharge thyristor without being affected by the variations in the characteristics of the circuit elements.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a configuration example of a discharge lamp lighting device according to the present invention. In FIG. 1, 1 is a high-frequency AC power source including a high-frequency generator and 2a and 2b are high-current power sources. Is the pair of input terminals to which the output of is input. 3 is a high-pressure discharge lamp such as a metal halide lamp, 4a and 4b are output terminals of a pair to which the discharge lamp 3 is connected, and 5 is a step-up transformer configured by winding a primary coil 5p and a secondary coil 5s around an iron core. One end of the secondary coil 5s of the transformer 5 is connected to one output terminal 4a.

Further, 6 is a primary current control circuit for controlling the primary current of the step-up transformer, 7 is a constant voltage power supply circuit for converting the output of the AC power supply into a constant DC voltage, 8 is a timer for stopping the lighting operation, and 9 is a lighting operation. This is an intermittent timer.

At one end of the primary coil of the step-up transformer 5,
One end of the capacitor C1 is connected, and a capacitor charging diode D1 is connected between the other end of the capacitor C1 and the one input terminal 2a with its cathode facing the capacitor C1 side.

The other end of the primary coil 5p of the step-up transformer is grounded and the first and second feedback diodes D are provided.
Commonly connected to the anodes of 2 and D4, and the cathodes of the feedback diodes D2 and D4 are connected to the input terminals 2a and 2b, respectively. The anode and cathode of the discharging thyristor Th1 are connected to the other end of the capacitor C1 and the other end of the primary coil 5p, respectively, and when the thyristor Th1 conducts, the charge of the capacitor C1 is changed to the thyristor Th.
It discharges through the anode coil of No. 1 and the primary coil of the step-up transformer 5.

The trigger thyristor Th is connected to the anode of the thyristor Th1 through the current limiting resistors R4 and R5.
Two anodes are connected to each other, and a cathode of the thyristor Th2 is connected to a gate of the discharging thyristor through a diode D5 in which the anode is directed to the cathode side of the thyristor Th2. A resistor R6 and a capacitor C2 are connected in parallel between the anode of the diode D5 and the other end of the primary coil of the step-up transformer 5, and the thyristor T for triggering is connected.
A resistor R7 and a thermistor Rt are placed between the gate and cathode of h2.
and h are connected in parallel. The thermistor Rth is thermally coupled to the iron core of the step-up transformer 5.

The anode of the diode D3 is connected to the input terminal 2b, and the resistor R1 is provided between the cathode of the diode D3 and the other end (ground) of the primary coil of the step-up transformer 5.
To R3 are sequentially connected in series. Resistors R2 and R
A Zener diode ZD1 having its anode directed to the gate side of the thyristor Th2 is connected between a connection point with the third thyristor Th2 and the gate of the trigger thyristor Th2, and the voltage across the resistor R3 exceeds the Zener voltage of the Zener diode ZD1. A trigger signal is sometimes applied to the trigger thyristor Th2.

In this example, diode D3, resistors R1 to R3, resistors R6 and R7, capacitor C2,
The zener diode ZD1 constitutes a trigger thyristor trigger circuit that applies a trigger signal from the input terminal 2b side to the gate of the trigger thyristor Th2.

In the present invention, the trigger signal bypass switch 10 is provided between the gate of the trigger thyristor Th2 and the other end of the primary coil of the step-up transformer 5. In the illustrated example, an NPN transistor TR1 having a collector and an emitter connected to the gate of the trigger thyristor Th2 and the other end of the primary coil of the step-up transformer, respectively.
And a resistor R10 connected between the base and emitter of the transistor, and a resistor R11 whose one end is connected to the base of the transistor TR1.
Is configured. This trigger signal side switch 10
, The other end of the resistor R11 is connected to the control signal input terminal 10
A, the control signal input terminal is a diode D
It is connected to the output terminals of the timers 8 and 9 through an OR circuit composed of 6 and D7.

The transistor TR1 maintains the off state when the base current is not supplied from the timer circuit 8 or 9, and turns on when the base current is supplied from the timer circuit 8 or 9. In this example, when the transistor TR1 is in the off state, the trigger thyristor T is passed from the input terminal 2b side through the Zener diode ZD1.
It is allowed that a trigger signal is given to h2. When the transistor TR1 is turned on, the trigger signal given to the trigger thyristor Th2 through the Zener diode ZD1 is bypassed from the thyristor Th2.
The supply of the trigger signal to the trigger thyristor Th2 is stopped. When the trigger of the trigger thyristor Th2 is prohibited in this way, the trigger signal is not given to the discharge thyristor Th1. Therefore, the discharge thyristor Th1 is not supplied.
Is cut off when its anode current becomes equal to or lower than the holding current, and the discharge thyristor is held in the OFF state while the trigger of the trigger thyristor is prohibited thereafter, and the generation of the high voltage pulse is prohibited.

In order to supply the power supply voltage to the timers 8 and 9,
A constant voltage power supply circuit 7 is provided. This power circuit
Resistors R12 and R13 connected in series between the cathodes of the diodes D10 and D11 whose anodes are connected to the input terminals 2a and 2b, respectively, and the resistor R12.
And R13, the collector of which is connected to the NPN transistor TR2, the emitter of the transistor TR2, the capacitor C3 which is connected between the ground, and the transistor TR2.
Zener diode ZD connected between base and ground
2, a resistor R14 connected between the collector and base of the transistor TR2, and a capacitor C4 connected between the collector of the transistor TR2 and ground. In this power supply circuit, the transistor TR2 is turned on when the voltage across the capacitor C3 is less than the Zener voltage of the Zener diode ZD2, and the diode D10 or D11 and the transistor TR2 are output by the output of the AC power supply.
The capacitor C3 is charged through the collector-emitter circuit of the. When the terminal voltage of the capacitor C3 reaches the Zener voltage of the Zener diode ZD2, the transistor TR2 is turned off, so that the charging of the capacitor C3 is stopped. By these operations, a DC voltage substantially equal to the Zener voltage of the Zener diode is obtained across the capacitor C3.

The lighting operation stop timer 8 is composed of a commercially available timer IC 8A and external resistors and capacitors, and starts the time counting operation when the output of the AC power supply 1 is applied to the input terminals 2a and 2b. , When the set allowable limit operating time To is measured, a base current is applied to the transistor TR1 through the diode D6 to turn on the transistor (trigger signal side switch 10). The timer 8 keeps the transistor TR1 (trigger signal bypass switch 10) in the ON state by continuously supplying the base current to the transistor TR1 while the output of the AC power supply is applied between the pair of input terminals 2a and 2b. To do.

The ignition operation on / off timer 9 is composed of a commercially available timer IC 9A, an external resistor and a capacitor, and has an allowable limit operation when the output of the AC power supply is applied to the input terminals 2a and 2b. The lighting operation time T1 is measured by alternately performing the time counting operation for measuring the lighting operation time T1 set shorter than the time To and the time counting operation for measuring the operation interruption time T2 set shorter than the allowable limit operation time. The base current supply to the transistor TR1 is stopped and the transistor TR1 (trigger signal bypass switch) is held in the OFF state during the clocking operation to measure the operation interruption time. A base current is supplied to the inter-transistor TR1 to hold the transistor (trigger signal side switch) in the ON state.

In the example shown in FIG. 1, the capacitor C1 and
A primary current control circuit 6 is constituted by the discharging thyristor Th1, the diode D5, the trigger thyristor Th2, the resistors R4 to R7, the capacitor C2, and the thermistor Rth.
The step-up transformer 5 and a circuit that gives a trigger signal to the trigger thyristor Th2 from the input terminal 2b side constitute a high voltage pulse generation circuit.

In the discharge lamp lighting circuit shown in FIG. 1, when the output of the AC power supply 1 is applied between the input terminals 2a and 2b, the AC power supply 1 outputs the voltage V1p of one half cycle. 1, the capacitor C1 is charged to the polarity shown by way of the diode D1, the primary coil 5p of the step-up transformer 5 and the diode D2. Next, when the AC power supply 1 outputs the voltage V1n in the other half cycle, a current flows from the AC power supply through the diode D3 and the resistors R1 to R3, and a voltage is generated across the resistor R3. When this voltage exceeds the Zener voltage of Zener diode ZD1,
Since the trigger signal is given to the trigger thyristor Th2, the thyristor becomes conductive, and a part of the charge of the capacitor C1 is discharged through the gate and cathode of the discharge thyristor Th1. As a result, a trigger signal is given to the discharging thyristor Th1, so that the discharging thyristor Th1 becomes conductive, and the charge of the capacitor C1 is discharged through the primary coil 5p of the step-up transformer 5. This allows the secondary coil 5
A high voltage pulse Vh is generated at s, and this high voltage pulse is superimposed on the output voltage of the AC power supply and applied to the discharge lamp 3.
Therefore, discharge is generated in the discharge lamp 3 and the discharge lamp is activated.

When the output of the AC power supply 1 is applied between the input terminals 2a and 2b, the output voltage of the power supply circuit 7 is applied to the power supply terminals of the lighting operation interruption timer 9 and the lighting operation stop timer 8. These timers start operating. The lighting operation on / off timer 9 has an allowable limit operation time To when the output of the AC power supply is applied to the input terminals 2a and 2b.
The timekeeping operation for measuring the lighting operation time T1 by alternately performing the timekeeping operation for measuring the lighting operation time T1 set to be shorter than that and the timekeeping operation for measuring the operation interruption time T2 set to be shorter than the allowable limit operation time. While the operation is being performed, the supply of the base current to the transistor TR1 is stopped to keep the transistor TR1 in the off state, and the base current is supplied to the transistor TR1 while the time measuring operation for measuring the operation interruption time T2 is being performed. Hold the transistor in the on state. Oscillation of the high voltage pulse generation circuit is enabled while the transistor TR1 is held in the off state, generation of the high voltage pulse is allowed, and oscillation of the high voltage pulse generation circuit is maintained while the transistor TR1 is held in the on state. Is disabled and the generation of high voltage pulses is prohibited.

In the discharge lamp lighting circuit of FIG.
Voltage waveforms at points D and D are shown in FIGS. During the period T2 during which the lighting operation interruption timer 9 measures the operation interruption time T2, the potential of the output terminal (point A) of the timer circuit 9 is held at the H level as shown in FIG. Therefore, the potential of the control signal input terminal 10A (point C) of the trigger signal side switch 10 becomes H level. Therefore, the transistor TR1 forming the trigger signal side switch is held in the ON state, and the oscillation of the high voltage pulse generation circuit (generation of high voltage pulse) becomes impossible.

On the other hand, during the period T1 during which the lighting operation on / off timer 9 measures the lighting operation time T1, the output of the timer circuit 9 is held at the L level as shown in FIG. Since the potential of the control signal input terminal (point C) of the signal bypass switch 10 is held at the L level, the transistor TR1 that constitutes the trigger signal bypass switch
Is held off. Therefore, the trigger of the trigger thyristor Th2 is allowed, and the oscillation of the high voltage pulse generation circuit is enabled.

As described above, in the present embodiment, the period in which the generation of the high voltage pulse is allowed and the period in which the generation of the high voltage pulse is prohibited appear alternately, so that the generation of the high voltage pulse takes a long time. It is possible to prevent the temperature of the step-up transformer from rising excessively and the temperature of the discharge thyristor Th1 from rising excessively. Since the lighting operation time and the lighting operation interruption time are accurately determined by the timer, it is possible to accurately manage the time for oscillating the high voltage pulse generation circuit and the time for interrupting the oscillation, and It is possible to properly protect the thyristor.

When the discharge lamp is not started for some reason and the allowable limit operation time To is reached,
As shown in (B), the potential of the output terminal (point B) of the lighting operation stop timer 8 becomes H level, which causes the potential of the control signal input terminal (point C) of the trigger signal side switch 10 to rise. Since it becomes the H level, the transistor TR1 that constitutes the trigger signal side switch is held in the ON state,
Oscillation of the high voltage pulse generation circuit is stopped. This state continues while the output voltage of the AC power supply 1 is applied between the input terminals 2A and 2b.

In the above embodiment, the thermistor Rt.
h is to stop the trigger of the trigger thyristor when the ambient temperature of the discharge circuit rises abnormally for some reason,
It is provided to stop the operation of the circuit in an emergency,
It is not involved in determining the lighting operation time and the operation interruption time during the normal lighting operation.

In the example shown in FIG. 1, the capacitor C1 is connected to one end of the primary coil 5p of the step-up transformer, but in the figure, the same operation is performed even if the positions of the discharging thyristor Th1 and the capacitor C1 are exchanged. Can be done. That is, in FIG. 1, the capacitor C1 may be connected between the cathode of the diode D1 and the ground, and the anode and cathode of the discharging thyristor Th1 may be connected to the cathode of the diode D1 and one end of the primary coil 5p, respectively.

[0045]

As described above, according to the present invention, the capacitor provided on the primary side of the step-up transformer and charged by the voltage of one half cycle of the AC power source is passed through the discharging thyristor to the primary coil of the step-up transformer. At the time of discharging, a part of the electric charge accumulated in the capacitor is discharged through the trigger thyristor provided between the anode gates of the discharging thyristor to give a trigger signal to the discharging thyristor. It is possible to surely perform the trigger of and to surely perform the operation of generating the high voltage pulse.

Further, in the present invention, a trigger signal bypass switch for bypassing the trigger signal to be applied to the trigger thyristor when it is turned on is provided, and the lighting operation time and the operation interruption time are alternated. If a timer for interrupting lighting operation to be measured is provided and the trigger signal thyristor is turned on while the timer is measuring the operation interruption time, the trigger thyristor is turned on. It is possible to prevent the excessive temperature rise of the step-up transformer and the discharge thyristor by alternately generating the period for generating the voltage pulse and the period for stopping the generation of the high voltage pulse. In this case, since the lighting operation time and the operation interruption time are determined by the timer, the time during which the lighting operation is performed and the time during which the lighting operation is interrupted are accurately managed,
The step-up transformer and the discharge thyristor can be properly protected.

Further, in the present invention, a trigger signal bypass switch for bypassing the trigger signal to be given to the trigger thyristor when it is turned on is provided and the trigger signal is measured when the allowable limit operation time is measured. When a lighting operation stop timer that turns on the bypass switch is provided, it prevents the lighting operation from continuing indefinitely and destroying the circuit when an abnormality such as a discharge lamp abnormality occurs. be able to.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a waveform diagram showing signal waveforms of respective parts in FIG.

FIG. 3 is a circuit diagram showing a configuration of a conventional discharge lamp lighting circuit.

[Explanation of symbols]

1 ... AC power supply, 2A, 2b ... Input terminal, 3 ... Discharge lamp, 4
a, 4b ... Output terminals, 5 ... Step-up transformer, 6 ... Primary current control circuit, 10 ... Trigger signal side switch, C1 ... Capacitor, Th1 ... Discharge thyristor, Th2 ... Trigger thyristor, TR1 ... Transistor.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 3K083 AA01 AA05 AA13 AA28 AA41                       AA46 AA48 AA66 BA12 BC15                       BC33 BC42 BC47 BD09 BD15                       BE05 BE17 BE22 BE28 CA33

Claims (4)

[Claims] 1. A step-up transformer having a pair of input terminals to which an output of an AC power source is applied, a pair of output terminals to which a discharge lamp is connected, a primary coil and a secondary coil, and a primary side of the step-up transformer. And a capacitor charging circuit that charges the capacitor to one polarity with the output of one half cycle of the AC power supply, and discharges the electric charge of the capacitor through the primary coil of the step-up transformer when conducting. And a discharge thyristor trigger circuit that gives a trigger signal to the discharge thyristor at the output voltage of the other half cycle of the AC power supply, the charge of the capacitor being the primary coil of the step-up transformer. High-voltage pulse induced in the secondary coil of the step-up transformer when discharged through the input terminal. In a discharge lamp lighting circuit in which the input terminal of the pair, the secondary coil of the step-up transformer and the output terminal of the pair are connected to each other so as to be superimposed on the output voltage of the current source and output from between the output terminals of the pair. The discharge thyristor trigger circuit is provided between the anode and the gate of the discharge thyristor with the anode facing the anode side of the discharge thyristor, and a part of the electric charge of the capacitor when conducting. And a trigger thyristor trigger circuit that gives a trigger signal to the trigger thyristor when the output voltage of the other half cycle of the AC power supply reaches a set value. And a discharge lamp lighting circuit. 2. A pair of input terminals to which an output of an AC power supply is applied, a pair of output terminals to which a discharge lamp is connected, a step-up transformer having a primary coil and a secondary coil, and a primary coil of the step-up transformer. A capacitor whose one end is connected to one end of the capacitor, a capacitor charging diode whose cathode is connected between the other end of the capacitor and one of the pair of input terminals, and the other of the primary coil An anode is commonly connected to an end and a cathode is connected to one and the other of the pair of input terminals, respectively, and first and second feedback diodes, and the other end of the capacitor and the other end of the primary coil are anodes. And a discharge thyristor to which the cathode is connected, with the anode and the cathode facing the anode side and the gate side of the discharge thyristor, respectively. A trigger thyristor which is connected between the anode gates of the discharging thyristor through a current limiting resistor and discharges a part of the electric charge of the capacitor through the gate and cathode of the discharging thyristor when conducting; A discharge lamp lighting circuit, comprising: a trigger thyristor trigger circuit for applying a trigger signal to the gate of the trigger thyristor from the other side of the input terminal of. 3. A trigger signal bypass switch capable of on / off control, which is provided so as to bypass the trigger signal provided to the trigger thyristor when the trigger thyristor is turned on. When the output of the AC power supply is applied to the terminals, the timing operation is started, and when the set allowable limit operation time is measured, the trigger signal bypass switch is turned on and the AC power supply is provided between the pair of input terminals. 3. The discharge lamp lighting circuit according to claim 1, further comprising a lighting operation stopping timer that holds the ON state of the trigger signal side switch while the output of FIG. 4. A switch for a trigger signal bypass, which is provided so as to bypass a trigger signal provided to the trigger thyristor when the switch is turned on from the trigger thyristor, and the input. When the output of the AC power supply is applied to the terminals, the timekeeping operation is started, and when the set allowable limit operation time is measured, the trigger signal side switch is turned on and the AC is applied between the pair of input terminals. A lighting operation stop timer for holding the ON state of the trigger signal side switch while the output of the power supply is applied;
When the output of the AC power supply is applied to the input terminal, a timed operation for measuring a lighting operation time set to be shorter than the allowable limit operation time and an operation interruption time set to be shorter than the allowable limit operation time By alternately performing the timing operation for measuring the lighting operation time, the trigger signal bypass switch is held in the OFF state while the timing operation for measuring the lighting operation time is performed, and the time interrupt operation for measuring the operation interruption time is performed. 3. The discharge lamp lighting circuit according to claim 1, further comprising a lighting operation interrupting timer that holds the trigger signal side switch in an ON state while performing.