JPH0679520B2 - Discharge lamp lighting device - Google Patents

Description

Description: TECHNICAL FIELD The present invention uses a resonant circuit including a discharge lamp as a load circuit, and feeds back a load current to switch a switching element of a self-excited inverter circuit to light the discharge lamp. The present invention relates to an electric lamp lighting device.

BACKGROUND ART Conventionally, in a discharge lamp lighting device that uses a resonant circuit composed of a discharge lamp, a choke coil, and a capacitor as a load circuit, there are many devices that make the lamp current constant by detecting the lamp current and applying feedback. It is considered. Especially in the separately excited inverter circuit, the lamp current is detected and the switching frequency is changed from the sum of the signals to make the lamp current constant, or a switch circuit is provided in the power supply section of the inverter circuit to change the size of the power supply. It is considered that the lamp current is made constant by controlling the above.

However, a resonant circuit consisting of a choke coil and a capacitor is used as a load, and current feedback is performed by a drive transformer having a primary winding through which a load current flows, and switching transistors, which are two switching elements, are switched to perform oscillating operation. In a discharge lamp lighting device including an excitation type serial inverter circuit or a half-bridge inverter circuit, one having a load current fluctuation compensating function is rarely considered.

FIG. 6 shows the structure of the above-mentioned conventional discharge lamp lighting device. DC power supply (including rectified voltage of AC power supply) E,
Transistors Q ₁ and Q ₂ are connected in series, and diodes D ₁ and D ₂ are connected in antiparallel to these transistors Q ₁ and Q ₂ , respectively (however, diodes D ₁ and D ₂ are not always necessary). . Capacitor C ₁ and discharge lamp l in parallel with transistor Q ₁
, And a series circuit of the primary winding n ₁ of the drive transformer T ₁ are connected to form a series inverter circuit or a half bridge inverter circuit. A drive transformer T ₁ having a primary winding n ₁ comprises secondary windings n ₂ and n ₃ ,
The secondary winding n ₂ is connected to the control resistor R ₁ of the transistor Q _{1 and} the secondary winding n _2.
n ₃ is connected to the control resistor R ₂ of transistor Q ₂ . The resonance circuit A is composed of a choke coil L ₁ , a capacitor C ₂ and a discharge lamp l. The starting circuit ST that starts the inverter circuit 1 is composed of a switch element Q ₃ , a capacitor C ₃ , a diode D ₃ , a resistor R _{3 and the} like.

Now, when the power switch SW is turned on, the capacitor C ₃ is charged via the resistor R ₃ . The voltage of the capacitor C ₃ is, for example, reaches the breakover voltage of the switching element Q ₃ consisting of a diac or SBS and the like, a capacitor
The charge charged in C ₃ is the switching element Q ₃ and the transistor.
It is discharged through the base and emitter of Q ₂ . Therefore a base current is supplied to the transistor Q _2, the transistor Q ₂
Turns on. When the transistor Q ₂ turns on, the DC power supply E
→ a current flows through the primary winding n ₁ → transistor Q ₂ → DC power source E of the capacitor C ₁ → resonant circuit A → drive transformer T _1, the capacitor C ₁ is charged. At this time the drive transformer
Since current flows through the winding n ₁ of T _1, the voltage on the secondary winding n ₃ is induced. Since the transistor Q ₂ is sequentially biased by the voltage induced in the secondary winding n ₃ , the transistor Q ₂
Maintains continuity. After that, the current increases in an attempt to charge the capacitor C ₁ , but the current gradually decreases as the charging progresses, and when the current flowing through the resonance circuit A and the drive transformer T ₁ approaches zero, the feedback voltage due to the drive transformer T ₁ is changed. When inverted, the transistor Q ₁ is forward biased and the transistor Q ₂ is reverse biased, so that the transistor Q ₂ is turned off and the transistor Q ₁ is turned on. Then the resonant circuit A, driving the primary winding n ₁ of the transformer T _1, and the capacitor C ₁ at closed circuit of the transistor Q ₁ is started to discharge. This capacitor
Off the transistors Q ₁ and subsequent vibration caused by discharge of C _1, the transistor Q by the charging and discharging are repeated as such to ₂ is turned on, the transistors Q _1, Q ₂ were alternately turned on and off a current in the resonant circuit A And the voltage of the capacitor C ₂ is applied to the discharge lamp l to light it. Drive transformer
T ₁ is a current transformer, and the current flowing in the primary winding n ₁ of the drive transformer T ₁ via the choke coil L ₁ is applied to the secondary winding.
The current is fed to the transistors Q ₁ and Q ₂ via n ₂ and n ₃ , and both transistors Q ₁ and Q ₂ are driven by current feedback.

FIG. 7 shows the change of the resonance current I of the resonance circuit A with respect to the switching frequency when the impedance of the discharge lamp 1 of FIG. 6 is changed, in the same figure (a), and the transistor Q ₁ (Q ₂ ) with respect to the switching frequency. The change of the flowing current I _Q2 (I _Q1 ) is shown in FIG. The operating frequency of the inverter circuit 1 determined by the saturable drive transformer T ₁ is set to the frequency f ₁ so as to be lower than the resonance frequency f ₀ of the series resonance circuit of the capacitors C ₁ , C ₂ and the choke coil L _1. If so, the resonance circuit A, which is the load of the inverter circuit 1, is set to be capacitive. The operating frequency of the inverter circuit 1 determined by the driving saturable transformer T ₁ is set to the capacitor C ₁ ,
If the frequency f ₂ is set to be higher than the resonance frequency f ₀ of the series resonance circuit of C ₂ and the choke coil L ₁ , the resonance circuit A is set to be inductive.

When the operating frequency of the inverter circuit 1 is set to f ₁ , the resonance current I is I ′ and the current flowing in the transistor Q ₂ is I _Q2 ′. Here, the fluctuation of the power supply voltage,
When the current flowing through the transistor Q ₂ by the self heat generation of the transistor Q ₂ is increased (but also increases the resonant current I),
The primary winding n ₁ of the current increase of the transformer T ₁ → increase in current secondary winding n ₃ of the transformer T ₁ (the base current increases of the transistor Q ₂₎
→ increase collector current of transistor Q ₂ → increase current of transformer T ₁ → increase resonance current I, etc.
The current flowing in the discharge lamp l also changes due to Q ₁ ), and the light output of the discharge lamp l changes or flicker occurs. That is, by operating the frequency f ₁ of the inverter circuit 1 by repeating the above operation is shifted towards the series resonance frequency f _0, and proceeds in the direction of the collector current of the transistor Q _1, Q ₂ is increased, the discharge lamp l There is a problem in that the current flowing through the discharge lamp l increases due to the increase in the current flowing through the discharge lamp l and the fluctuations in the power supply voltage and the heat generation of the transistors Q ₁ and Q ₂ (or the increase in ambient temperature).

[Object of the Invention] The present invention has been made in view of the above points of the present invention. A resonance circuit including a choke coil, a capacitor, and a discharge lamp is used as a load circuit, and a load current is fed back to switch a self-excited inverter circuit. In a discharge lamp lighting device that lights a discharge lamp by switching elements, it is an object to prevent fluctuation or flicker of the light output of the discharge lamp due to fluctuations in power supply voltage, changes in ambient temperature, and the like.

DISCLOSURE OF THE INVENTION FIG. 1 is a basic circuit diagram of the present invention. Since the basic circuit configuration is the same as that of the conventional example, only the characteristic points will be described. The present invention is a transistor of the inverter circuit 1.
The discharge lamp current detection circuit D for detecting the current flowing through the discharge lamp l is provided with a switching control means for increasing / decreasing the base current of Q ₂ contrary to the increase / decrease of the current flowing through the discharge lamp l. And a comparison circuit C for comparing the output of the discharge lamp current detection circuit D with the output of the reference voltage circuit E.
And a base current variable circuit B for controlling the output of the comparison circuit C so as to increase or decrease the base current of the transistor Q ₂ .

The operation of the basic circuit will be described below. Now, due to fluctuations in power supply voltage or self-heating of transistors Q ₁ and Q ₂ (or increase in ambient temperature),
If the current flowing through Q ₁ and Q ₂ increases, the drive transformer T
Increasing the current flowing through the _first primary winding n ₁ is → 2 winding n _2, the current of n ₃ is increased driving transformer T ₁ (transistor Q _1, the base current Q ₂ 'is increased) → transistor Q _1, The operation of increasing the collector current of Q ₂ → increasing the current of the driving transformer T ₁ → increasing the resonance current I is repeated. In this way, when the load current increases, the current flowing through the discharge lamp 1 also increases and the output voltage of the discharge lamp current detection circuit D also increases. At this time, the output of the discharge lamp current detection circuit D and the output of the reference voltage circuit E are compared by the comparison circuit C. When the output of the discharge lamp current detection circuit D becomes larger than the output of the reference voltage circuit E, the output of the comparison circuit C becomes Get higher At this time, the base current variable circuit B suppresses the base current of the transistor Q _{2 by} the output of the comparison circuit C.
Therefore, the collector current of the transistor Q ₂ is also suppressed, the increase of the load current and the increase of the current of the discharge lamp l can be suppressed, and the current of the discharge lamp l does not increase remarkably as in the conventional case. .

(Embodiment 1) FIG. 2 is a diagram showing a specific circuit of FIG. 1. In this embodiment, a discharge lamp current detection circuit D is composed of a current transformer T ₂ , a capacitor C ₄ and a diode D ₂ , and a reference voltage is set. Connect circuit E to resistor R ₅ ,
A zener diode ZD ₁ , a comparison circuit C is composed of an operational amplifier (OP amplifier) IC ₁ , resistors R _{7 to} R ₁₀ , and a base current variable circuit B is composed of a transistor Q ₄ and resistors R ₄ and R ₆ . A comparison circuit C composed of an operational amplifier IC ₁ and resistors R _{7 to} R ₁₀ .
Is a differential amplifier circuit, the output voltage V ₁ of the reference voltage circuit E is input to the non-inverting input, and the output voltage V ₂ of the discharge lamp current detection circuit D is input to the inverting input. The output voltage V ₃ of the comparison circuit C is input to the transistor Q ₄ via the resistor R ₆ , and the series circuit of the resistor R ₄ and the transistor Q ₄ is connected to both ends of the secondary winding n ₃ of the driving transformer T _1. I am doing it.

The operation will be described below. When a current having a normal current value is flowing, the output voltage V ₂ of the discharge lamp current detection circuit D becomes smaller than the output voltage V ₁ of the reference voltage circuit E, and the comparison circuit C
The output voltage V ₃ = 0 next, since no flow base current to the transistor Q _4, the transistor Q ₄ are in a non-conductive state. Now, it is assumed that the current flowing through the discharge lamp 1 has increased due to a rise in the power supply voltage or the like. At this time, the output voltage V _{2 of the} discharge lamp current detection circuit D also rises and the output voltage of the reference voltage circuit E increases.
When it rises above V _1, the output of the comparison circuit C becomes V ₃ = R ₇ (V ₂ −V ₁ ) / R ₈ . The output voltage V ₃ of this comparison circuit C causes a transistor
The base current flows in Q _4, and the secondary winding n ₃ of the drive transformer T ₁
Resistor R _4, the transistors Q _4, 2 winding n ₃ of the closed circuit the collector current of the transistor Q ₄ flows in, 2 normally at winding n ₃ in the voltage induced through the resistor R ₂ transistor Q _Although the base current is flowing through ₂ , the base current of the transistor Q ₂ is reduced because the current flows through the transistor Q _4, and the increase of the collector current of the transistor Q ₂ can be prevented.

This point will be described in more detail. For example, when the current flowing through the discharge lamp 1 decreases, it is detected by the discharge lamp current detection circuit D. Here, the detection voltage of the discharge lamp current detection circuit D corresponds to the degree of decrease in the current of the discharge lamp 1. Accordingly, the base current I _R6 of the auxiliary switching element Q ₄
Decreases, and the collector current I _Q4 also decreases. The collector current I _Q4, since reduced by the relationship _{I Q4 (= I R4) =} I R6 × hfe ( DC amplification factor), the degree of decrease also is in accordance with the degree of decrease of the current of the discharge lamp l. With such collector current decreases, the base current decreases diverted transistor Q _2, then increases the base current of the transistor Q ₂ is, transistors Q ₂ to which the on a predetermined base current is the ON period It becomes longer, the operating frequency of the inverter circuit 1 becomes lower, the impedance of the choke coil L ₁ lowers, and the load current increases. In this way, the load current is increased in accordance with the decrease in the current of the discharge lamp l, that is, the load current increase / decrease control is performed by continuous control.

With this arrangement, when the collector currents of the transistors Q ₁ and Q ₂ try to shift to the larger side due to fluctuations in the power supply voltage, etc., the base current of the transistor Q ₂ acts to reduce the switching control means. Therefore, the collector currents of the transistors Q ₁ and Q ₂ can be prevented from increasing, and the operating frequency of the inverter circuit 1 settles at a predetermined frequency.

The operation will be described more specifically. This embodiment is the seventh
An inverter circuit 1 including a discharge circuit 1 having a resonance curve as shown in the figure and a resonance circuit including a choke coil L ₁ and capacitors C ₁ and C ₂ as a load circuit is provided.
When the operating frequency is set to f ₁ , the resonance current I ₁ of the resonance circuit A is I ₁ ′. Here, due to fluctuations in power supply voltage, self-heating of transistor Q ₁ , etc.
When the current flowing in Q ₁ increases (resonance current I also increases), the current flowing in transistors Q ₁ and Q ₂ increases → the current in secondary windings n ₂ and n ₃ of drive transformer T ₁ increases → the transistor Q ₁ ,
Due to the heat generated by the excessive current of Q ₂ ,
Q _1, Q ₂ to the flowing current increases → transistor Q _1, the transistor so that the current flowing to the Q ₂ increases Q _1, the operating frequency Q ₂ 'is transferred (f ₁ in FIG. 7 is the operating frequency from f ₁ + △ f ₁
Move to). When the operating frequency of the transistor Q _1, the transistor Q ₁ so that Q ₂ is increased, Q ₂ is shifted, (the current flowing through the = discharge lamp l) the load current in the resonant circuit A
Becomes large, and the switching control means including the base current variable circuit B and the like controls the base current of the transistor Q ₂ to be small as described above. The same applies when the operating frequency in FIG. 7 is set to f ₂ . As described above, in the self-excited inverter circuit 1 having the resonance circuit A including the discharge lamp 1, the base current of the transistor Q ₂ operates so as to decrease as the load current of the resonance circuit A increases. Can be prevented from changing to a resonance frequency, an excessive current flows through the inverter circuit 1, and the load current, that is, the current flowing through the discharge lamp l, can be largely changed. Flickering can be prevented. A choke coil including a discharge lamp 1 having a resonance curve as shown in FIG.
An inverter circuit 1 having a resonant circuit A composed of L ₁ , capacitors C ₁ , C ₂ etc. as a load circuit is provided, and a current flowing through the resonant circuit is fed back by a drive transformer T ₁ etc. This is particularly effective in a discharge lamp lighting device that drives certain transistors Q ₁ and Q ₂ .

(Embodiment 2) FIG. 3 shows another embodiment of the present invention in which a push-pull inverter circuit 1'is used. In this embodiment, the base current variable circuit B is composed of the transistor Q ₄ .
Similar to the above-mentioned embodiment, the base current of the transistor Q ₂ is reduced as the load current increases. In this embodiment, the conversion circuit F for converting the fluctuation of the load current detected by the discharge lamp current detection circuit D into the change of the base current of the transistor Q ₄ is used, and the reference voltage circuit E is omitted. .

The operation will be briefly described. As the load current increases,
The base current of transistor Q ₄ also increases,
Since the collector current of Q ₄ increases, the base potential of the transistor Q ₂ is suppressed, so that the collector current of the transistor Q ₂ is also suppressed. As a result, the load current, that is, the current flowing through the discharge lamp l is suppressed from increasing, and the same effect as that of the first embodiment can be obtained.

(Embodiment 3) FIG. 4 is also another embodiment of the present invention, which uses a one-stone inverter circuit 1 ″. The configuration and operation are substantially the same as those of the second embodiment. The description is omitted.
Even in this case, the same effect can be obtained.

(Embodiment 4) FIG. 5 shows still another embodiment of the present invention, and is different from the case of FIG. 1 in the following points. As the DC power supply, a rectified voltage obtained by full-wave rectifying the AC power supply AC with the rectifier circuit Rec is used. Of course, this rectified voltage may be smoothed. The inverter circuit 1 is a half-bridge configuration, to insulate the input power source and the discharge lamp l at the transformer T _3, the transistors Q _1, Q ₂ saturable drive transformer T ₁ of the to drive the discharge lamp l Are connected in series. It should be noted that even if any element (for example, the resonance capacitor C ₂ ) in the resonance circuit A is connected to the drive transformer T _{1 in} series, there is essentially no difference from the case of FIG. 1 and the same effect can be obtained. Further, the discharge lamp current detection circuit D is composed of a current transformer T ₃ having two secondary winding image lines n ₄ and n ₅ , and both the transistors Q ₁ and Q _{2 have} a variable base current of the circuit shown in FIG. Circuits B ₁ and B ₂ are provided. By providing the switching control means for both the transistors Q ₁ and Q ₂ as described above, the effects of the present invention can be further obtained from the circuits of FIGS. 1 to 4.

As described above, the present invention is connected between a DC power supply, a self-excited inverter circuit that is connected to this DC power supply and outputs a rectangular wave voltage between the output terminals, and an output terminal of the self-excited inverter circuit. A choke coil, a capacitor, and a load circuit including a resonance circuit of a discharge lamp, and a discharge current is lit by switching a switching element of the self-excited inverter circuit by feeding back a load current of the load circuit to obtain a control current. In the discharge lamp lighting device, an auxiliary switching element connected in parallel between the control terminals of the switching element,
A discharge lamp current detection circuit that generates a detection voltage that increases or decreases according to an increase or decrease in the current of the discharge lamp, and controls the auxiliary switching element in an active region according to the detection voltage of the discharge lamp current detection circuit. Since the switching control means for controlling the shunt is provided so as to increase / decrease the control current of the switching element in reverse to the increase / decrease of the current of the discharge lamp, for example, fluctuation of the power supply voltage or self-heating of the switching element (change of ambient temperature (Including), the load current fluctuates greatly due to an increase in the current flowing through the switching element of the inverter circuit.However, by increasing or decreasing the control current of the switching element, contrary to the increase or decrease of the load current,
The load current can be kept constant, and therefore, there is an effect that the discharge lamp does not fluctuate in light output or flickering due to fluctuations in the power supply.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a basic circuit of the present invention, FIG. 2 is a specific circuit configuration diagram showing a first embodiment of the present invention, and FIG. 3 is a circuit configuration showing a second embodiment of the present invention. Fig. 4 and Fig. 3
FIG. 5 is a circuit diagram showing a fourth embodiment, FIG. 5 is a circuit diagram showing a conventional example, and FIG.
(A) and (b) are operation | movement explanatory drawings same as the above, respectively. Q ₁ and Q ₂ are transistors, 1-1 are inverter circuits, T ₁
Is a drive transformer, n ₁ is a primary winding, n ₂ and n ₃ are secondary windings, L ₁
Is a choke coil, C ₁ and C ₂ are capacitors, l is a discharge lamp,
A is a resonance circuit, B is a base current variable circuit, C is a comparison circuit, D is a discharge lamp current detection circuit, and F is a conversion circuit.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Akinori Hiramatsu 1048, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works, Ltd. (72) Masataka Mitani, 1048, Kadoma, Kadoma City, Osaka Matsushita Electric Works, Ltd. (56) References JP-A-51-8779 (JP, A) JP-A-62-76297 (JP, A)

Claims (1)

[Claims] 1. A DC power supply, and a self-excited inverter circuit which is connected to the DC power supply and outputs a rectangular wave voltage between output terminals.
A load circuit including a choke coil connected between the output terminals of the self-excited inverter circuit, a capacitor, and a resonance circuit of a discharge lamp, and the load current of the load circuit is fed back to be a control current to switch the self-excited inverter circuit. In a discharge lamp lighting device that lights a discharge lamp by switching elements, an auxiliary switching element connected in parallel between the control terminals of the switching element and a detection voltage that increases or decreases according to an increase or decrease in the current of the discharge lamp. And a discharge lamp current detection circuit that generates a discharge lamp current detection circuit, and controls the auxiliary switching element in an active region according to the detection voltage of the discharge lamp current detection circuit, and the control current of the switching element is opposite to the increase / decrease of the discharge lamp current. 2. A discharge lamp lighting device, comprising: a switching control means for controlling a diversion so as to increase / decrease.