JPH0518878Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a discharge lamp lighting device that operates switching elements such as transistors at high frequencies to achieve small size, light weight, and high efficiency.

[Background Art] A conventional discharge lamp lighting device of this type is shown in FIG. In this discharge lamp lighting device, an AC power supply 1 is rectified by a diode bridge DB ₁ and smoothed by a smoothing capacitor C ₁ to obtain a DC voltage _{. 1} , coil L ₁
The voltage is converted to a predetermined voltage by a separately excited chopper circuit 5, which is a voltage conversion circuit composed of a capacitor _C2 and a capacitor C2.

In the above chopper circuit 5, the transistor Q ₁ is switched at high frequency by the first control circuit 8, and when the transistor Q ₁ is turned on, the transistor Q ₁ , the coil L ₁ , and the capacitor C ₂ are connected by a DC voltage.
At the same time _, the energy stored in _{the coil L 1 is} used to charge _the capacitor C ₂ through the path of
A capacitor C ₂ is further charged through the path of the diode D ₁ , and a voltage obtained by boosting the DC voltage generated across the capacitor C ₂ is supplied to the discharge lamp 2 and the igniter 4 as a power source. Here, the coil _L1 of the chopper circuit 5 is small because the transistor _Q1 is switched at a high frequency. Further, since the high frequency components contained in the current flowing through the coil _L1 of the chopper circuit 5 are bypassed by the capacitor _C2 , a DC voltage with few high frequency components is applied to the discharge lamp 2 and the igniter 4.

The igniter 4 starts the discharge lamp 2.
It consists of a pulse transformer PT ₁ , a bidirectional thyristor (hereinafter simply referred to as thyristor) Q ₂ , a capacitor C ₃ , and a resistor R ₁ . This igniter 4
The thyristor _Q2 is turned on and off by the second control circuit 6, and when the thyristor _Q2 is turned off, the output of the chopper circuit 5 is used to connect the primary winding _L3 of the pulse transformer _PT1 , the capacitor _C3 , and the resistor R. ₁ , the capacitor _C3 is charged, and when the thyristor _Q2 is turned on, the charge in the capacitor _C3 is rapidly discharged through the path of the primary winding _L3 of the pulse transformer _PT1 and the thyristor _Q2 . At this time, the primary winding L ₃ of pulse transformer PT ₁
The current flowing through induces a high voltage in the secondary winding _L2 of the pulse transformer _PT1 , and this high voltage is applied to the discharge lamp 2 to start it.

Here, when the discharge lamp 2 is started, it is not necessary to apply high voltage to the discharge lamp 2 from the igniter 4, but there is a problem such as deterioration of the discharge lamp 2, so it is preferable to apply a high voltage pulse. do not have.

Therefore, a high voltage is applied from the igniter 4 to the discharge lamp 2 only during the period (starting period) from immediately after the power is turned on until the discharge lamp 2 transitions from glow discharge to arc discharge (starting period).
This control is performed by controlling the second control circuit 6 with the detection circuit 3.

The detection circuit 3 is composed of a current transformer CT ₁ , a diode D ₂ and a capacitor C ₄ , and the discharge lamp 2
When the engine starts, the load current increases, so the detection circuit 3 detects this load current and controls the second control circuit 6.

The second control circuit 6 consists of a resistor R ₃ and a capacitor C ₅
A charging circuit consisting of a capacitor of this charging circuit
Trigger element Q ₄ turns on when the voltage across C ₅ reaches the breakover voltage, and when this trigger element Q ₄ turns on, current flows to the primary winding, and the trigger voltage of thyristor Q ₂ is applied to the secondary winding. It is composed of a pulse transformer PT ₃ that induces , and a transistor Q ₃ that is turned on and off by the output of the detection circuit 3 provided through a resistor R ₂ .

In this second control circuit 6, from the time the power is turned on until the discharge lamp 2 starts, a trigger is activated to continuously turn on the thyristor _Q2 at a cycle determined by the charging time constant of the resistor _R3 and the capacitor _C5 . Generates voltage.

Then, when the discharge lamp 2 starts, the voltage across the capacitor C ₄ of the detection circuit 3 rises to the voltage that turns on the transistor Q _{3, which turns on the transistor Q 3 and} shorts both ends of the capacitor C ₅ . This stops the generation of the trigger voltage.

By the way, the reason why the detection output of the current transformer CT ₁ is rectified and smoothed by the diode D ₂ and the capacitor C ₄ in the detection circuit 3 is that the output of the current transformer CT ₁ changes after the discharge lamp 2 starts. If the transistor Q varies by ₃
so that the igniter 4 does not turn off.
This is to ensure that the operation is stopped.

The output of the detection circuit 3 is also used to keep the power flowing to the discharge lamp 2 constant. For this purpose, a comparator 10 is provided to compare the output power of the detection circuit 3 with a reference voltage V _ref . The first control circuit 8 is controlled by the output of 10.

Here, the first control circuit 8 is controlled by the time constant of the resistor _R6 and the capacitor _C6 , for example, from 20kHz to
Triangular wave oscillation circuit 12 that generates a 50kHz triangular wave
A comparator 9 compares the output of the triangular wave oscillation circuit 12 with the output of the comparator 10.
, a flip-flop 11 that generates a pulse signal that turns on and off the transistor Q ₁ according to the output of the comparator 9, and a transistor Q ₅ that is turned on and off by the output of the flip-flop 11.
According to the current flowing to the primary winding when transistor Q ₅ is turned on or off, transistor Q ₁ is connected to the secondary winding.
A pulse transformer PT ₂ that generates a drive signal with a potential that can turn on and turn off, and a diode that quickly turns off bias resistors R ₄ and R ₅ and transistor Q _1.
It is composed of _D3 . Also, a triangular wave oscillation circuit 12, a comparator 9 and a flip-flop 11
constitutes a so-called PWM circuit section 8a that generates a pulse signal with variable on-duty.

Until the discharge lamp 2 starts, the voltage across the capacitor _C4 does not reach the reference voltage _Vref , and the flip-flop 11 is controlled by the output obtained by comparing the output of the comparator 10 and the output of the triangular wave oscillation circuit 12 at this time. Ru.

When the discharge lamp 2 starts, the voltage across the capacitor _C4 increases. Here, when the voltage across the capacitor _C4 exceeds the reference voltage _Vref due to an increase in the load current, the output of the comparator 10 is inverted, so that the on-duty of the pulse signal that is the output of the flip-flop 11 becomes narrower. This results in
The load current of the discharge lamp 2 is reduced, and the load current is prevented from exceeding a certain value. In other words, the detection circuit 3, the comparator 10 and the PWM circuit section 8
At point a, feedback is applied to control the load current to a constant value.

However, in the conventional circuit described above, the load current is detected by the current transformer CT ₁ and the output of this current transformer CT ₁ is smoothed by the capacitor C ₄ . When an abnormality occurs, it takes time for the voltage across capacitor _C4 to change accordingly.
The switching control of transistor _Q1 is delayed,
Transistor _Q1 was subjected to stress such as overcurrent flowing, and in severe cases, transistor _Q1 could be damaged.

Therefore, in order to prevent damage to the transistor _Q1 , the circuit shown in FIG. 5 has been proposed. Only the main parts of this circuit are shown, and the parts not shown have the same structure as the circuit of FIG. 4. In the case of FIG. 5, constant control of the load current is achieved by comparing the voltage across the resistor _R7 inserted between the discharge lamp 2 and the smoothing capacitor _C1 with the reference voltage _Vref using the comparator 10. This is done by operating the first control circuit 8 using the output. In other words, a non-smooth DC voltage depending on the load current is generated across the resistor _R7 , so this resistor
The voltage across R ₇ is set to the reference voltage V _ref and the comparator 10
By comparing the above, switching control of the transistor _Q1 of the chopper circuit 5 can be performed in immediate response to the load current. Therefore, in the event of an abnormality, the on-duty of the transistor _Q1 can be shortened to prevent excessive current from flowing, thereby preventing damage to the transistor _Q1 .

Further, the operation of the igniter 4 is controlled by operating the second control circuit 6 in accordance with the output obtained by rectifying and smoothing the output of the current transformer CT ₁ using the diode D ₂ and the capacitor C ₄ , as in the circuit shown in FIG. 4 described above. I'm going.

However, in this case transistor Q ₁
Although this method does not cause a control delay, it requires two detection means for detecting the load current, making the circuit configuration complicated.

As another method, as shown in FIG. 6, it is conceivable to use both the voltage across the resistor _R7 to control the operation of the igniter 4 and constant control of the load current.

However, in this case, the voltage across the resistor _R7 must be increased, and the second control circuit 6 will not operate reliably, so the resistance value of the resistor _R7 must be increased. Therefore, there is a problem in that the loss due to the resistor _R7 increases.

In other words, if the detection output of the current transformer CT ₁ is smoothed by the capacitor C ₄ as shown in FIG. There is a problem that the response is delayed and the stress on the transistor _Q1 increases, and if separate load current detection means are provided for the first and second control circuits 8 and 6 as shown in FIG. Although _it is possible to prevent delay in response to abnormalities that occur in the
Furthermore, if the first and second control circuits ₈ and 6 are operated by the detection output from the resistor _R7 as shown in FIG. 6, the resistance value of the resistor _R7 will be increased. However, there is a problem in that the loss caused by this resistor _R7 increases.

[Purpose of the invention] The present invention was devised in view of the above points, and its purpose is to reliably prevent stress from being applied to the switching element during transient abnormalities, and to prevent the discharge lamp from being stressed. To provide a discharge lamp lighting device which can simplify the configuration of a circuit for detecting a flowing current, can perform reliable operation control of an igniter, and does not cause loss in the circuit for detecting a current flowing to a discharge lamp.

[Disclosure of the invention] (Embodiment) FIG. 1 is a diagram showing an embodiment of the invention, and this embodiment is basically similar to that explained in FIG. is started, the discharge lamp 2 is kept lit by the tipper circuit 5, and the tipper circuit 5 is turned on.
The first control circuit 8 performs on/off control of the transistor Q ₁ of the igniter 4, and the thyristor Q ₂ of the igniter 4
The second control circuit 6 performs on/off control. In the case of this embodiment, the load current is detected by the resistor _R7 , and the detected output is sent to the amplifier circuit 1.
In response to the output amplified in step 4, the first control circuit 8 performs an operation to control the load current to a constant value. The second control circuit 6 controls the operation of the igniter 4 using the output of the amplifier circuit 14 delayed by the delay circuit 13. Here, the amplifier circuit 14 includes an operational amplifier 7, resistors R ₈ and R ₉ , and a delay circuit 1
3 is composed of a diode D ₄ , a capacitor C ₇ and a resistor R ₁₀ .

The operation of the embodiment will be described below, but parts that overlap with the conventional example will be omitted. When the igniter 4 applies a high voltage to the discharge lamp 2 to start the discharge lamp 2 immediately after the power is turned on, the load current i ₁ flowing through the resistor R ₇ increases as described above. The voltage V ₇ (R ₇ , i ₁ ) across the resistor R ₇ is amplified by the amplifier circuit 14, and the output E ₂ of the amplifier circuit 14 becomes E ₂ =(R ₈ +R ₉ )V ₇ /R ₉ . Here, the resistance value of the resistor R ₈ of the amplifier circuit 14 is, for example, on the order of several times to hundreds of times that of the resistor R ₉ . In this way, by amplifying the voltage across the resistor _R7 with the amplifier circuit 14, the resistance value of the resistor _R7 can be reduced, and the loss due to the resistor _R7 does not increase as in the case of Fig. 6. .

The output of the amplifier circuit 14 is input to the comparator 9 of the first control circuit 8. Here, when the load current increases, the output of the amplifier circuit 14 also increases, so the time point at which the output of the comparator 9 which compares this output with the output of the triangular wave oscillation circuit 12 is inverted is delayed, and the flip-flop 11 The period when _Q1 is turned on becomes shorter. Therefore, in the case of this embodiment as well, the load current can be controlled to be constant in the same manner as in the case of FIG.

Moreover, in the case of this embodiment, since the first control circuit 8 is operated with the voltage across the resistor R ₇ , that is, the non-smooth DC voltage, the corresponding voltage is applied to the PWM circuit in the event of a transient abnormality. 8a,
Therefore, switching of the transistor _Q1 can be quickly controlled, and excessive current can be prevented from flowing through the transistor _Q1 .

On the other hand, the amplifier circuit 14 input to the delay circuit 13
The output is applied to capacitor C ₇ via diode D ₄ and resistor R ₁₀ . This delay circuit 13 includes
Since the resistor _R10 is provided, the capacitor _C6 is slowly charged, and when the voltage across the capacitor _C6 reaches the base-emitter voltage of the transistor _Q3 , the transistor _Q3 is turned on.
The operation of the igniter 4 is stopped. That is, resistance
If the time constants of R ₁₀ and capacitor C ₆ are set so that transistor Q ₃ is turned on when discharge lamp 2 transitions from glow discharge to arc discharge, then The operation of the igniter 4 can be stopped. Note that the delay circuit 1
Since the output of the amplifier circuit 14 is smoothed in step 3, the igniter 4 will not operate when the load current fluctuates.

By adopting the above-mentioned configuration, this embodiment can quickly control the transistor _Q1 in the event of a transient abnormality as described above, but it also requires two detection means for detecting the load current as in the circuit shown in FIG. Therefore, the detection means can be simplified, the operation of the igniter 4 can be controlled reliably, and there is no loss caused by the resistor _R7 .

(Embodiment 2) FIG. 2 shows another embodiment of the present invention.
In this embodiment, a full-bridge type inverter circuit 5' is used instead of the chopper circuit 5 as a voltage conversion circuit.

The full bridge inverter circuit 5' has a series circuit of transistors Q ₆ and Q ₈ and a series circuit of transistors Q ₇ and Q ₉ connected across a smoothing capacitor C ₁ , and a coil L between the connection point of the transistors of both series circuits. A discharge lamp 2 and an igniter 4 are connected through a capacitor ₁ , and a capacitor is connected to both ends of the igniter 4.
C ₂ is connected. Here, the diodes D ₅ to _{D 8}
is a freewheeling diode.

This full bridge type inverter circuit 5' alternately turns on and off diagonally located transistors Q ₆ and Q ₉ and transistors Q ₇ and Q ₈ as a set.
In addition, the transistors Q ₈ and Q ₉ are turned on and off at a low frequency of several hundred Hz, and these transistors are
When Q ₈ , Q ₉ are turned on, the transistors Q ₆ ,
This turns _Q7 on and off at a high frequency of 20 to 50kHz, for example. This full bridge type inverter circuit 5' has an alternating period (low frequency) of transistors Q ₈ and Q ₉ .
A rectangular wave voltage corresponding to the voltage is applied to the discharge lamp 2, and the discharge lamp 2 is lit in a so-called rectangular wave. Here, the coil
L ₁ suppresses the high frequency components contained in the above square wave voltage, capacitor C ₂ bypasses the high frequency components,
It has the function of applying a rectangular wave voltage with few high frequency components to the discharge lamp 2 and the igniter 4.

The first transistor controls switching of transistors Q ₆ to _{Q 9} of this full bridge type inverter circuit 5'.
The control circuit 8' has the following configuration. This first control circuit 8' is a timer IC that oscillates a low frequency.
(555 type) oscillation circuit 20 consisting of 21,
a frequency divider circuit 19 that divides the output of the oscillation circuit 20;
It is composed of a drive circuit 17 that switches transistors Q ₈ and Q ₉ according to mutually inverted outputs of this frequency dividing circuit 19, a triangular wave oscillation circuit 12, a comparator 9, and a flip-flop 11 as explained in FIG. PWM circuit section 8a and this
A NOR circuit 15 that takes the NOR of the output of the PWM circuit section 8a and the output of the frequency divider circuit 19;
It is composed of a drive circuit 18 that switches transistors Q ₆ and Q ₇ according to the output. Further, the frequency dividing circuit 19 has a D flip-flop 22.
and two NAND circuits 16. Here, the oscillation circuit 20 and the frequency dividing circuit 19 function as a low frequency oscillation section, and the PWM circuit section 8a functions as a high frequency oscillation section.

In the case of this embodiment, the load current is detected by a resistor _R7 connected between the connection point of the emitters of the transistors _Q8 and _Q9 and the smoothing capacitor _C1 .
Here, a current i ₁ flows through the resistor R ₇ in the direction indicated by the arrow in the figure even when the transistors Q ₆ and Q ₉ or the transistors Q ₇ and Q ₈ are operating. The first control circuit 8' controls the load current to be constant using the output of the amplifier circuit 14 which amplifies the voltage across the resistor _R7 . However, in this embodiment, the load current is controlled to be constant by controlling the on-duty of transistors Q ₆ and Q ₇ that perform switching operations at high frequencies. Further, the second control circuit 6 controls the operation of the igniter 4 based on the output of the delay circuit 13 that delays the output of the amplifier circuit 14.

(Embodiment 3) FIG. 3 shows still another embodiment of the present invention. In the case of the second embodiment, the operation of the igniter 4 is controlled in accordance with the output delayed by the delay circuit 13.
However, in this embodiment, the bidirectional control circuit 6 is used instead of the thyristor _Q2 .
Using an igniter 4' equipped with a terminal thyristor (for example SSS, hereinafter simply referred to as thyristor) Q2 _' ,
The present invention is characterized in that the oscillation circuit 20 is controlled by the output obtained by delaying the output of the amplifier circuit 14 by the delay circuit 13, and the operation of the igniter 4' is stopped.

The igniter 4' closes the thyristor when the voltage across the thyristor _Q2 ' reaches the breakover voltage.
Q ₂ ' is turned on, generating a high voltage in the secondary winding L ₂ of the pulse transformer PT ₁ .

As a specific method of controlling the oscillation circuit 20 to stop the operation of the igniter 4', a method of increasing the oscillation frequency of the full bridge type inverter circuit 5' is adopted. Here, in order to increase the oscillation frequency of the full bridge type inverter circuit 5', a switching circuit b consisting of transistors Q ₃ and Q ₁₀ which are turned on and off by the output of the delay circuit 13 is provided, and the oscillation frequency of the timer IC 21 is increased. The resistor _R13 , which determines the voltage, is short-circuited and opened when the transistor _Q10 is turned on and off.

Now, when the voltage across the capacitor _C7 rises above the base-emitter voltage of the transistor _Q3 , both the transistors _Q3 and _Q10 turn on, and the transistor _Q10 short-circuits the resistor _R13 . This increases the oscillation frequency of the timer IC 21.

Here, in the above igniter 4', the thyristor
The point at which the voltage across Q ₂ ' reaches the breakover voltage is determined by the voltage applied to the igniter 4', the resistance R ₁ ,
It is determined by the breakover voltage of capacitor C ₃ and thyristor Q ₂ '. Now, if the oscillation frequency of the full-bridge inverter circuit 5' is increased as described above, the period of voltage application time to the igniter 4' becomes shorter, and each half cycle is performed by the capacitor.
The process ends before the voltage on _C3 reaches the breakover voltage. Therefore, the thyristor Q ₂ ' is no longer turned on, and the operation of the igniter 4' is stopped.

By the way, in the above explanation, the case where the voltage conversion circuit is a chopper circuit or a full-bridge type inverter circuit is explained, but the same effect can be obtained with a single-stone inverter circuit, a half-bridge type inverter circuit, a push-pull type inverter circuit, etc. .

[Effects of the invention] As described above, the present invention includes a voltage conversion circuit that converts a DC voltage into a predetermined voltage by switching a switching element, a discharge lamp that receives power from this voltage conversion circuit, and a discharge lamp that converts the DC voltage into a predetermined voltage by switching the switching element. There is an igniter that starts the discharge lamp by continuously applying a high voltage until the discharge lamp transitions from glow discharge to arc discharge, a resistor that detects the current flowing through the discharge lamp, and a non-smooth electric current detected by this resistor. an amplifier circuit that amplifies the DC voltage; a first control circuit that controls the on-duty of the switching element to be reduced when the output of the amplifier circuit changes in an increasing direction; a delay circuit that outputs a voltage obtained by smoothing the output of the amplification circuit after the transition to the igniter, and a second delay circuit that receives the output of the delay circuit and holds the igniter in an off state.
Since the first control circuit is operated with a non-smooth DC voltage, the first control circuit can be made to respond immediately in response to a transient abnormal condition. This prevents excessive current from flowing through the switching element, and since the load current is detected only by the resistor, the means for detecting the load current can be simplified, and the voltage across the resistor can be amplified by an amplifier circuit. Because of this, the resistance value of the resistor can be made small, and the loss due to the resistor does not become large.Furthermore, the output of the amplifier circuit is smoothed by the delay circuit, so the igniter is activated by fluctuations in the load current after the discharge lamp is lit. There is an advantage that this is not the case.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the main parts of one embodiment of the present invention, Fig. 2 is a circuit diagram showing another embodiment of the invention, and Fig. 3 is a circuit diagram showing still another embodiment of the invention. Circuit configuration diagram, FIG. 4 is a circuit configuration diagram showing a conventional example,
FIGS. 5 and 6 are circuit configuration diagrams showing main parts of other conventional examples, respectively. 2 is a discharge lamp, 4 is an igniter, 5 is a chopper circuit, 5' is a full bridge type inverter circuit, 6 is a second control circuit, 8 is a first control circuit 8, 13 is a delay circuit, 14 is an amplifier circuit, R ₇ is resistance.

Claims (1)

[Scope of utility model registration request] There is a voltage conversion circuit that converts DC voltage into a predetermined voltage by switching a switching element, and a discharge lamp that receives power from this voltage conversion circuit. An igniter that continuously applies voltage to the discharge lamp to start it, a resistor that detects the current flowing through the discharge lamp, an amplifier circuit that amplifies the non-smooth DC voltage detected by this resistor, and the output of this amplifier circuit. a first control circuit that controls the on-duty of the switching element in a direction to decrease when the on-duty of the switching element changes in an increasing direction; and a voltage that smoothes the output of the amplifier circuit after the discharge lamp shifts from glow discharge to arc discharge a delay circuit that outputs,
A discharge lamp lighting device comprising: a second control circuit that receives the output of the delay circuit and maintains the igniter in an off state.