JPH0745389A - Lighting circuit and illuminator - Google Patents

Abstract

PURPOSE:To downsize a circuit and cut down the cost and raise reliability and elongate the life by suppressing the change of electric properties by the dispersion of parts used for a lighting circuit, and setting a lamp current and a preheating current to optimum values with little dispersion, and lessening the margin of used parts. CONSTITUTION:This device is made in such structure that an inverter circuit 9 on lamp side and a preheating circuit 12 are turned on or turned off alternately, and this is provided with circuit means 14 and 15 which detect the lamp current of the inverter circuit 9 and the preheating current of the preheating current 12, respectively, and selectively feed the detected voltage back to a constant voltage circuit 4. The lamp current and the preheated current are controlled to be optimum values by feeding back the detection signal by the lamp current during the on period of the inverter circuit 9 and the detection signal by the preheating current during the on period of the preheating current 12 to the said constant voltage circuit 4 so as to control the output voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting circuit and a lighting device, and particularly to detecting a main discharge current during a main discharge period and a preheat current during a preheating period, and feeding back to a constant voltage circuit during each period. The present invention relates to a lighting circuit and a lighting device that control a main discharge current and a preheating current to have optimum values.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a lighting circuit of a conventional hot cathode discharge lamp.

In FIG. 2, reference numeral 1 is a constant voltage power source or a DC power source such as a battery (including a commercial AC power source rectified and smoothed), and the power source voltage is smoothed by a smoothing capacitor 3 via a fuse 2. , Is supplied to the constant voltage circuit 4. The illustrated constant voltage circuit 4 constitutes a step-down chopper, and includes a chopper control (PWM control) transistor 41, a constant voltage control circuit 42, and a resistor 4.
3, 44, a commutation diode 45, a rectifier circuit including a coil 46 and a smoothing capacitor 47. A resistor 43 is connected between the emitter and base of the control transistor 41, and a PWM control pulse is supplied to the base from the constant voltage control circuit 42 driven by the DC power supply 1 via the resistor 44. The smoothed voltage from the smoothing capacitor is chopper-controlled (PWM control). The diode 45 is for supplying the voltage generated in the coil 46 to the load during the off period of the control transistor 41. Here, the output voltage of the constant voltage circuit 4 is lower than the DC power supply voltage input by the control of the constant voltage control circuit 42. A series circuit of output voltage detecting resistors 5 and 6 is connected in parallel to both ends of the constant voltage circuit 4, and the voltage at the connection point (voltage dividing point) of the resistors 5 and 6 is a constant voltage control circuit. The control terminal 42 is connected to the control terminal 42a, and the constant voltage control circuit 42 detects the output voltage of the constant voltage circuit 4 and controls the ON period of the control pulse supplied to the base of the control transistor 41 according to the voltage fluctuation. As a result, the output voltage of the constant voltage circuit 4 is controlled to be always constant. The switching frequency of the control transistor 41 is, for example, about 20 kHz.

The output voltage of the constant voltage circuit 4 is supplied to the inverter circuit 9 constituting the main discharge circuit via the lamp side PWM control section of the PWM system dimming circuit 7.

The PWM type dimming circuit 7 comprises a PWM dimming control circuit 71, a lamp side PWM control section, and a preheating side PWM control section. The PWM dimming control circuit 71 is
Driven by the output voltage of the constant voltage circuit 4, the circuit 7
A switching element (not shown) in the output section in 1 is turned on and off at a constant frequency (for example, 1 kHz), and its output terminal 7
The potential of 1a is controlled to be short-circuited (on) and opened (off) with respect to the earth line GND. The lamp-side PWM control unit controls to turn on / off the output terminal of the PWM dimming control circuit 71 in response to turning on / off, and cut off (off) or pass (on) the voltage from the constant voltage circuit 4. To do. The preheating side PWM control unit is
The M dimming control circuit 71 is turned on / off in response to the turning on / off of the output terminal, and the voltage from the constant voltage circuit 4 is controlled to pass (on) or cut off (off).

The lamp-side PWM control unit controls the output voltage of the constant voltage circuit 4 by PWM control, a resistor 73 connected between the emitter and base of the control transistor 42, and a base, respectively. 7
4 and a resistor 7 connected to the base of the control transistor 72
4 and the ground line GND, a collector / emitter path is connected between the control transistor 75 and ON / OFF of the transistor 72 and OFF / ON according to ON / OFF of the output terminal 71a of the PWM dimming control circuit 71. Switch diode 76, and output terminal 7 of PWM dimming control circuit 71
A switch diode 77 that turns on and off in response to turning on and off of 1a, resistors 78 and 79 that form switching means together with the diodes 76 and 77, and a voltage generated in the coil 91 are supplied to the load during the off period of the control transistor 72. It is composed of a diode 80 for operating.

The preheat side PWM control section controls the output voltage of the constant voltage circuit 4 by PWM control, and a resistor 82 connected between the emitter and base of the control transistor 81 and the base. , 8
3, the output end 71a of the PWM dimming control circuit 71 is turned on,
Switch diode 84 that turns on and off according to the off state
And a diode 85 for supplying the load with the voltage generated in the coil 121 during the off period of the control transistor 81.

The collector output of the control transistor 72 of the lamp side PWM control section is supplied to the inverter circuit 9. The inverter circuit 9 is composed of a constant current push-pull type self-excited inverter circuit, and the control transistor 7
The collector output of No. 2 is supplied to the center tap of the primary coil 92a of the transformer 92 via the choke coil 91, the capacitors 93 are connected in parallel to both ends of the primary coil 92a, and one end of the primary coil 92a is a switching transistor. Ground line G via 94 collector-emitter path
ND, the other end of the primary coil 92a is connected to the ground line GND through the collector / emitter path of the switching transistor 95, and both ends of the feedback coil 92c provided in the transformer 92 are connected to the bases of the transistors 94 and 95, respectively. The bases of the transistors 94 and 95 are connected by a series circuit of resistors 96 and 97, and the series connection point is connected to the output end of the choke coil 91. The feedback coil 92c allows the switching transistor 94,
Positive feedback is applied to 95, and the switching transistor 94,
95 is oscillated by a resonance circuit composed of the primary coil 92a and the capacitor 93 (for example, 20 kHz), and the transformer 9
The boosted high frequency voltage is output to both ends of the second secondary coil 92b.

The high frequency voltage output from the secondary coil 92b of the transformer 92 is applied to the filaments 11a and 11a 'at both ends of the discharge lamp 11 via the capacitor 10.

The collector output of the control transistor 81 of the preheating side PWM control section is supplied to the preheating circuit 12. The preheating circuit 12 is also composed of a constant current push-pull type self-exciting inverter, like the inverter circuit 9. The collector output of the control transistor 81 is passed through the choke coil 121 to the primary coil 12 of the transformer 122.
2a, and a capacitor 123 is connected in parallel to both ends of the primary coil 122a.
One end of 2a is connected to the earth line GND through the collector-emitter path of the switching transistor 124,
The other end of the primary coil 122a is connected to the ground line G via the collector-emitter path of the switching transistor 125.
Feedback coil 12 connected to ND and provided in transformer 122
Both ends of 2c are connected to the bases of the transistors 124 and 125, respectively, the bases of the transistors 124 and 125 are connected by a series circuit of resistors 126 and 127, and the series connection point is connected to the output end of the choke coil 121. There is. Positive feedback is applied to the switching transistors 124 and 125 by the feedback coil 122c, and the switching transistors 124 and 125 are caused to self-oscillate in a resonance circuit formed by the primary coil 122a and the capacitor 123 (for example, 2
0 kHz), two secondary coils 122 of the transformer 122
The stepped down or stepped up high frequency voltage is output to both ends of b and 122b '.

Two secondary coils 122 of the transformer 122
The high frequency voltage output from each of b and 122b 'is
Two filaments 11a, 11a 'of the discharge lamp 11
Is supplied to both ends of each of the filaments 11a,
11a 'is preheated.

On the other hand, in the PWM dimming control circuit 71,
The timer circuit 13 driven by the output voltage of the constant voltage circuit 4 is connected, and the PWM dimming control circuit 71 has its output end 71a short-circuited (for example, 3 seconds) set by the timer circuit 13. The output terminal 71a is turned on and off at a constant frequency (for example, 1 kHz) in order to perform the switching operation for the normal PWM control after the set time has elapsed, whereby the control transistor 72, Reference numeral 81 is adapted to perform switching for PWM control.

In the circuit configured as described above, after the DC power supply 1 is turned on, the output of the PWM dimming control circuit 71 is maintained until the fixed time (for example, 3 seconds) set by the timer circuit 13 elapses. The terminal 71a is short-circuited to the earth line GND, and a current flows from the constant voltage circuit 4 to the earth line GND through the resistors 82 and 83 and the diode 84, so that the transistor 81 is turned on for the timer setting time. From voltage circuit 4 to preheating circuit 1
A constant voltage is simultaneously supplied to the center tap of the primary coil 122a of No. 2 and both bases of the switching transistors 126 and 127 to start self-excited oscillation.
A high frequency voltage is supplied to 1a and 11a 'for a preset time of the timer to preheat them. During the timer setting time, in the lamp side PWM control unit, current flows from the constant voltage circuit 4 to the ground line GND through the resistor 78 and the diode 77, and no current flows through the resistor 78, the diode 76 and the resistor 79. Therefore (due to high impedance), the transistor 72 is not turned on, the lamp side inverter circuit 9 as the main discharge circuit does not operate at all, and the high frequency voltage is not applied to the discharge lamp 11.

Next, when a predetermined timer preheat time elapses after the power is turned on, the output terminal 71 of the PWM dimming control circuit 71
a starts short-circuiting (on) and opening (off) at a constant frequency (for example, 1 kHz) (starts PWM control). Output terminal 71
When a is turned on and off in a constant cycle, the transistor 81 is turned on during the on period as in the above timer setting period, whereby a constant voltage is supplied from the constant voltage circuit 4 to the preheating circuit 12, and the preheating circuit 12 is turned on. Self-oscillates to supply high frequency voltage to the filaments 11a and 11a 'for preheating.

Further, the output terminal 7 of the PWM dimming control circuit 71
During the off period of 1a, the resistors 82 and 83 and the diode 84 are
Since no current flows through the transistor 81, the preheating circuit 12 does not oscillate and filament preheating is not performed, but no current flows from the constant voltage circuit 4 to the ground line GND through the resistor 78, the diode 76 and the resistor 79. Then, the transistor 75 is turned on, and thus the transistor 72 is turned on, so that the constant voltage is supplied from the constant voltage circuit 4 to the lamp side inverter circuit 9. Therefore, a constant voltage is simultaneously supplied from the constant voltage circuit 4 to the center tap of the primary coil 92a of the inverter circuit 9 and both bases of the switching transistors 94 and 95, and self-excited oscillation (for example, 20 kHz) is started, and 2 A boosted high frequency voltage is obtained across the secondary coil 92b and is applied to the filaments at both ends of the discharge lamp 11 only during the off period of the output terminal 71a (that is, during the on period of the transistor 72).
The discharge lamp 11 is lit at high frequency.

After that, during lighting, the PWM dimming control circuit 7
Since the output terminal 71a of No. 1 is repeatedly turned on and off at a constant cycle, the transistors 72 and 81 are alternately turned on and off repeatedly. During the on period of the transistor 81, the preheating circuit 12 operates so that the filaments 11a and 11a 'are preheated. And the inverter circuit 9 operates during the ON period of the transistor 72 to supply the lamp current to the discharge lamp 11. Thereby, the lighting state is maintained.

By the way, in the above-mentioned hot cathode discharge lamp lighting circuit, the constant voltage control method by the constant voltage circuit 4 detects the output voltage of the constant voltage circuit 4 and feeds back the detected voltage to the constant voltage control circuit 42. Since it is controlled, it is not possible to suppress fluctuations in the electrical characteristics due to variations in the components of the inverter circuit 9 and the preheating circuit 12 in the subsequent stage of the constant voltage circuit 4. That is, there is a problem in that variations in the lamp current and the preheating current of the discharge lamp 11 can be suppressed and these currents cannot be controlled so as to always have optimum values. Further, since these current variations cannot be suppressed, it is not possible to secure a large margin for the parts used, which is a factor that hinders circuit miniaturization, cost reduction, high reliability, and long lamp life.

[0018]

As described above, in the prior art,
Since the output voltage of the constant voltage circuit was feedback-controlled, it was not possible to suppress changes in electrical characteristics due to variations in parts such as the inverter circuit and preheating circuit, and to suppress fluctuations in the lamp current and preheating current to obtain optimum values. Because you can't
There are problems that the circuit is downsized, the cost is reduced, the reliability is increased, and the life of the lamp is extended.

Therefore, the present invention has been made in view of the above problems.
Changes in electrical characteristics due to variations in parts such as the inverter circuit and preheating circuit can be suppressed, and the lamp current and preheating current can be set to optimal values with little variation.
It is an object of the present invention to provide a lighting circuit and a lighting device that can reduce the margin of parts used and can achieve circuit miniaturization, cost reduction, high reliability, and long lamp life.

[0020]

A lighting circuit according to the present invention comprises a DC power supply, a voltage circuit for controlling the voltage of the DC power supply by a feedback voltage, and a main discharge circuit driven by the voltage circuit. A preheat circuit driven by the voltage circuit, and a signal for controlling on / off of the main discharge circuit and the preheat circuit in a predetermined cycle, and the preheat circuit when the main discharge circuit is on Is turned off, a control circuit for controlling the preheating circuit to turn on when the main discharge circuit is off, and a main discharge current of the main discharge circuit and a preheating current of the preheat circuit are respectively detected to the voltage circuit. Which is fed back, and selectively switches the detection signal by the main discharge current during the ON period of the main discharge circuit and the detection signal by the preheat current during the ON period of the preheating circuit, It is obtained; and a circuit for feeding back the pressure circuit.

According to a second aspect of the present invention, there is provided a lighting device including a DC power supply, a voltage circuit for controlling the voltage of the DC power supply by a feedback voltage, a main discharge circuit driven by the voltage circuit, and a voltage circuit driven by the voltage circuit. Preheat circuit, a discharge lamp that is preheated by a preheat current from the preheat circuit, and is turned on by a main discharge current from the main discharge circuit, and an on / off control for the main discharge circuit and the preheat circuit in a predetermined cycle. A control circuit for controlling the preheating circuit to turn off when the main discharge circuit is on, and to turn on the preheating circuit when the main discharge circuit is off, and The main discharge current of the main discharge circuit and the preheat current of the preheat circuit are respectively detected and fed back to the voltage circuit, and the main discharge current is supplied during the ON period of the main discharge circuit. A detection signal that, during the ON period of the preheating circuit is selectively switched signal detected by the preheating current is obtained by including a circuit for feeding back the voltage circuit.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the main discharge circuit is composed of an inverter circuit for converting the voltage of the voltage circuit into an alternating current.

The invention according to claim 4 is the same as claims 1 to 3.
In any one of the inventions, the preheating circuit is configured by an inverter circuit that converts the voltage of the voltage circuit into an alternating current.

According to a fifth aspect of the present invention, in the invention according to any one of the first and second aspects, the control circuit is configured by a PWM control circuit capable of controlling an ON period of ON / OFF control. is there.

[0025]

In the present invention, the main discharge circuit and the preheat circuit are alternately turned on and off, and the main discharge current of the main discharge circuit and the preheat current of the preheat circuit are detected and the detected voltage is selectively applied. A circuit for returning to the voltage circuit is provided, and the detection signal by the main discharge current is supplied during the ON period of the main discharge circuit, and the detection signal by the preheating current is supplied during the ON period of the preheating circuit to the voltage circuit to output the output voltage. By controlling, the main discharge current and the preheating current can be set to the optimum values, the margin of the components used can be suppressed to be small, and the circuit can be downsized and the cost can be reduced.

[0026]

EXAMPLES Examples will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a lighting circuit and a lighting device according to an embodiment of the present invention. The present embodiment relates to a lighting circuit of a hot cathode discharge lamp having a constant voltage control function and a PWM dimming control function, and the same parts as those in FIG.

The difference between the embodiment of FIG. 1 and the conventional example of FIG. 2 is that the secondary coil 92 of the transformer 92 of the inverter circuit 9 is different.
b and the secondary coil 12 of the transformer 122 of the preheating circuit 12
2b 'is provided with a feedback circuit 14 for detecting the lamp current and the filament preheating current, respectively, and the detection voltage of the lamp current from the feedback circuit 14 and the filament preheating current are provided in the subsequent stage of the constant voltage circuit 4. A feedback switching circuit 15 for selectively switching between the detection voltage and the feedback to the control terminal 42a of the constant voltage control circuit 42 is provided, and the lamp current is supplied during the lamp lighting period and the filament preheating current is supplied during the filament preheating period. The configuration is such that the output voltage of the constant voltage circuit 4 is controlled so as to be set to the optimum value. Since the constant voltage circuit 4 is controlled so that the lamp current value and the filament preheating current value become constant, in order to detect the output voltage of the constant voltage circuit 4 arranged in the circuit of the conventional example of FIG. The resistors 5 and 6 are deleted. As described above, the resistors 5 and 6 for detecting the output voltage of the constant voltage circuit 4 are deleted. In the lighting circuit of the hot cathode discharge lamp, the lamp current of the discharge lamp 11 and the filament preheating current are optimized. This is because it is most important to control the The configuration of this embodiment will be described below.

In FIG. 1, reference numeral 1 is a constant voltage power source or a DC power source such as a battery (including a commercial AC power source rectified and smoothed), and the power source voltage is smoothed by a smoothing capacitor 3 via a fuse 2. , Is supplied to the constant voltage circuit 4. The illustrated constant voltage circuit 4 constitutes a step-down chopper, and includes a chopper control (PWM control) transistor 41, a constant voltage control circuit 42, and a resistor 4.
3, 44, a commutation diode 45, a rectifier circuit including a coil 46 and a smoothing capacitor 47. A resistor 43 is connected between the emitter and base of the control transistor 41, and a PWM control pulse is supplied to the base from the constant voltage control circuit 42 driven by the DC power supply 1 via the resistor 44. The smoothed voltage from the smoothing capacitor is chopper-controlled (PWM control). The diode 45 is for supplying the voltage generated in the coil 46 to the load during the off period of the control transistor 41. Here, the output voltage of the constant voltage circuit 4 is lower than the DC power supply voltage input by the control of the constant voltage control circuit 42. The switching frequency of the control transistor 41 is, for example, about 20 kHz.

In the subsequent stage of the constant voltage circuit 4, the detection voltage of the lamp current and the detection voltage of the filament preheating current from the feedback circuit 14 described later are selectively switched and fed back to the control terminal 42a of the constant voltage control circuit 42. Feedback switching circuit 1 for
5 are provided. The feedback switching circuit 15 outputs a detection signal based on the lamp current during the ON period of the lamp side PWM control unit described later, that is, during the operation of the inverter circuit 9, and the ON period of the lamp side PWM control unit described later, that is, the preheating circuit 1.
During the period when 2 operates, the detection signal by the preheating current is switched so as to be fed back to the control terminal 42a of the constant voltage control circuit 42.

The constant voltage control circuit 42 alternately detects the feedback voltage of the lamp current and the feedback voltage of the filament preheating current and controls the ON period of the control pulse supplied to the base of the control transistor 41 according to the voltage fluctuation. Thus, the lamp current and the filament preheating current are controlled so that they are always constant.

The output voltage of the constant voltage circuit 4 is supplied to the inverter circuit 8 constituting the main discharge circuit via the PWM control section of the PWM type dimming circuit 7.

The PWM type dimming circuit 7 comprises a PWM dimming control circuit 71, a lamp side PWM control section, and a preheating side PWM control section. The PWM dimming control circuit 71 is
Driven by the output voltage of the constant voltage circuit 4, the circuit 7
A switching element (not shown) in the output section is turned on / off at a constant frequency (for example, 1 kHz) to short-circuit (on) or open (off) the potential of the output terminal 71a with respect to the ground line GND. . The PWM controller on the lamp side
The PWM dimming control circuit 71 is turned off and on in response to turning on and off, and the voltage from the constant voltage circuit 4 is controlled to be cut off (off) and passed (on). The preheating side PWM control unit turns on and off in response to turning on and off the output end of the PWM dimming control circuit 71, and controls so that the voltage from the constant voltage circuit 4 passes (on) and cuts off (off). It is a thing.

The lamp-side PWM control unit controls the output voltage of the constant voltage circuit 4 by PWM control, a resistor 73 connected between the emitter and base of the control transistor 42, and a base, respectively. 7
4 and a resistor 7 connected to the base of the control transistor 72
4 and the ground line GND, a collector / emitter path is connected between the control transistor 75 and ON / OFF of the transistor 72 and OFF / ON according to ON / OFF of the output terminal 71a of the PWM dimming control circuit 71. Switch diode 76, and output terminal 7 of PWM dimming control circuit 71
A switch diode 77 that turns on and off in response to turning on and off of 1a, resistors 78 and 79 that form switching means together with the diodes 76 and 77, and a voltage generated in the coil 91 are supplied to the load during the off period of the control transistor 72. It is composed of a diode 80 for operating.

The preheat side PWM control section controls the output voltage of the constant voltage circuit 4 by PWM, and the resistor 82 connected between the emitter and base of the control transistor 81 and the base. , 8
3, the output end 71a of the PWM dimming control circuit 71 is turned on,
Switch diode 84 that turns on and off according to the off state
And a diode 85 for supplying the load with the voltage generated in the coil 121 during the off period of the control transistor 81.

The collector output of the control transistor 72 of the lamp side PWM control unit is supplied to the inverter circuit 9. The inverter circuit 9 is composed of a constant current push-pull type self-exciting inverter, and outputs the collector output of the control transistor 72 via the choke coil 91 to the transformer 9.
2 to the center tap of the primary coil 92a, and a capacitor 93 is connected in parallel to both ends of the primary coil 92a.
One end of the next coil 92a is connected to the switching transistor 94.
Of the primary coil 92a is connected to the ground line GND through the collector-emitter path of the switching transistor 95, and the other end of the primary coil 92a is connected to the ground line GND through the collector-emitter path of the switching transistor 95.
Both ends of 2c are connected to the bases of the transistors 94 and 95, respectively, and the resistor 9 is connected between the bases of the transistors 94 and 95.
6, 97 connected in series, and the series connection point is connected to the output end of the choke coil 91. Positive feedback is applied to the switching transistors 94 and 95 by the feedback coil 92c, and the switching transistors 94 and 95 are oscillated by the resonance circuit formed by the primary coil 92a and the capacitor 93 (for example, 20 kHz).
The boosted high frequency voltage is output to both ends of the next coil 92b.

The high frequency voltage output from the secondary coil 92b of the transformer 92 is applied to the filaments 11a and 11a 'at both ends of the discharge lamp 11 via the capacitor 10. Note that one end of the secondary coil 92b and the filament 11
A lamp current detection resistor 141 is connected between one end of a '.

The collector output of the control transistor 81 of the preheating side PWM control section is supplied to the preheating circuit 12. The preheating circuit 12 is also composed of a constant current push-pull type self-exciting inverter, like the inverter circuit 9. The collector output of the control transistor 81 is passed through the choke coil 121 to the primary coil 12 of the transformer 122.
2a, and a capacitor 123 is connected in parallel to both ends of the primary coil 122a.
One end of 2a is connected to the earth line GND through the collector-emitter path of the switching transistor 124,
The other end of the primary coil 122a is connected to the ground line G via the collector-emitter path of the switching transistor 125.
Feedback coil 12 connected to ND and provided in transformer 122
Both ends of 2c are connected to the bases of the transistors 124 and 125, respectively, the bases of the transistors 124 and 125 are connected by a series circuit of resistors 126 and 127, and the series connection point is connected to the output end of the choke coil 121. There is. Positive feedback is applied to the switching transistors 124 and 125 by the feedback coil 122c, and the switching transistors 124 and 125 are caused to self-oscillate in a resonance circuit formed by the primary coil 122a and the capacitor 123 (for example, 2
0 kHz), two secondary coils 122 of the transformer 122
A high-frequency voltage that is stepped down or stepped up (voltage adjustment) is output to both ends of b and 122b '. This high-frequency voltage is adjusted so that a voltage suitable for the lamp such that a preheating current flows is generated.

Two secondary coils 122 of the transformer 122
The high frequency voltage output from each of b and 122b 'is
Two filaments 11a, 11a 'of the discharge lamp 11
Is supplied to both ends of each of the filaments 11a,
11a 'is preheated.

2 of the transformer 92 of the inverter circuit 9
The feedback circuit 14 is formed between the secondary coil 92b and the secondary coil 122b of the transformer 122 of the preheating circuit 12.

The feedback circuit 14 connects the ground line GND to one end of the filament 11a ',
A lamp current detecting resistor 141 is provided on a line connecting one end of a ′ and one end of the secondary coil 92b of the transformer 92,
Also, both ends of the filament 11a 'and the transformer 122
A filament preheating current detection resistor 142 is provided on a line connecting both ends of the secondary coil 122b ', and an electrolytic capacitor 143 is connected between one end of the secondary coil 92b and the ground line GND to connect the secondary coil 122b'. The electrolytic capacitor 144 is connected between one end of the above and the ground line GND.

The resistor 141 feeds back the voltage generated between the one end of the secondary coil 92b and the ground line GND to the switch transistor 151 of the feedback switching circuit 15 as the lamp current detection voltage, and the resistor 142 puts it in the secondary coil. The voltage generated between one end of 122b 'and the ground line GND is fed back to the switch transistor 155 of the feedback switching circuit 15 as the detection voltage of the filament preheating current.

In the feedback switching circuit 15, the feedback voltage of the lamp current is input to the emitter of the switch transistor 151, the resistor 152 is connected between the emitter and the base of the transistor 151, and the base is switched via the resistor 153 to the switch transistor. 161 is connected to the collector of the transistor 161 and the emitter of the transistor 161 is connected to the ground line GND.
The collector of the transistor 151 is connected to the diode 154.
It is connected to the control terminal 42a of the constant voltage control circuit 42 via. The feedback voltage of the filament preheating current is input to the emitter of the switch transistor 155, a resistor 156 is connected between the emitter and the base of the transistor 155, and the base is PWM-controlled through the resistor 157, the diode 163, and the diode 164 in series. Light control circuit 71
Of the diode 163 and the diode 164 are connected to the base of the transistor 161 and also connected to the ground line GND via the resistor 162. In addition, the output voltage line of the constant voltage circuit 4 is connected in series with the resistor 159 and the diode 160,
It is connected to the connection point between the base of the transistor 161 and the resistor 162 (that is, the connection point between the diode 163 and the diode 164).

On the other hand, in the PWM dimming control circuit 71,
The timer circuit 13 driven by the output voltage of the constant voltage circuit 4 is connected, and the PWM dimming control circuit 71 has its output end 71a short-circuited (for example, 3 seconds) set by the timer circuit 13. The output terminal 71a is turned on and off at a constant frequency (for example, 1 kHz) in order to perform the switching operation for the normal PWM control after the set time has passed, whereby the switching transistors 72 and 81 are controlled by the PWM control. It is designed to switch.

In the circuit configured as described above, the output terminal of the PWM dimming control circuit 71 is turned on until the fixed time (for example, 3 seconds) set by the timer circuit 13 elapses after the DC power supply 1 is turned on. 71a is short-circuited to the earth line GND, and a current flows from the constant voltage circuit 4 through the resistors 82 and 83 and the diode 84 to the earth line GND, so that the transistor 81 is turned on for the timer setting time. From circuit 4, preheat circuit 12
A constant voltage is simultaneously supplied to the center tap of the primary coil 122a and the bases of the switching transistors 126 and 127 to start self-excited oscillation, and the filament 11
A high frequency voltage is supplied to a and 11a 'for a preset time of the timer to be preheated. During the timer setting time, in the lamp side PWM control unit, the transistor 72 is not turned on and the lamp side inverter circuit 9 as the main discharge circuit does not operate at all in the lamp side PWM control unit as in the conventional example of FIG. No high frequency voltage is applied to 11.

Next, when a predetermined timer preheat time has passed since the power was turned on, the output terminal 71 of the PWM dimming control circuit 71
a starts short-circuiting (ON) and opening (OFF) (PWM start) at a constant frequency (for example, 1 kHz). When the output terminal 71a is turned on and off in a constant cycle, the transistor 81 is turned on during the on period as in the above timer setting period, whereby the constant voltage is supplied from the constant voltage circuit 4 to the preheating circuit 12, and the preheating is performed. The circuit 12 self-oscillates and supplies a high frequency voltage to the filaments 11a and 11a 'to preheat it.

Further, the output terminal 7 of the PWM dimming control circuit 71
During the off period of 1a, the resistors 82 and 83 and the diode 84 are
Since no current flows through the transistor 81, the preheating circuit 12 does not oscillate and filament preheating is not performed, but no current flows from the constant voltage circuit 4 to the ground line GND through the resistor 78, the diode 76 and the resistor 79. Then, the transistor 75 is turned on, and thus the transistor 72 is turned on, so that the constant voltage is supplied from the constant voltage circuit 4 to the lamp side inverter circuit 9. Therefore, a constant voltage is simultaneously supplied from the constant voltage circuit 4 to the center tap of the primary coil 92a of the inverter circuit 9 and both bases of the switching transistors 94 and 95, and self-excited oscillation (for example, 20 kHz) is started, and 2 A boosted high frequency voltage is obtained across the secondary coil 92b and is applied to the filaments at both ends of the discharge lamp 11 only during the off period of the output terminal 71a (that is, during the on period of the transistor 72).
The discharge lamp 11 is lit at high frequency.

After that, during lighting, the PWM dimming control circuit 7
Since the output terminal 71a of No. 1 is repeatedly turned on and off at a constant cycle, the transistors 72 and 81 are alternately turned on and off repeatedly. During the on period of the transistor 81, the preheating circuit 12 operates so that the filaments 11a and 11a 'are preheated. The inverter circuit 9 operates during the ON period of the transistor 72 to supply a lamp current to the discharge lamp 11. Thereby, the lighting state is maintained.

By the way, the ON period of the transistor 72 of the lamp side PWM control section (that is, the PWM dimming control circuit 71
During the off period of the output terminal 71a), since the output terminal 71a is off, a current flows from the output voltage line of the constant voltage circuit 4 to the ground line GND through the resistor 159, the diode 160 and the resistor 162, and the transistor 161 turns on. Due to the voltage of the capacitor 143 connected to both ends of the lamp current detecting resistor 141, a current flows through the resistors 152 and 153 and the transistor 161 to the ground line GND, and as a result, the transistor 151 is turned on and the resistor 1
The lamp current detection voltage detected at 41 is the transistor 1
Constant voltage control circuit 42 through 51 and diode 154
Is fed back to the control terminal 42a. As a result, the constant voltage control circuit 42 compares the fed-back lamp current voltage with the reference value, and if the feedback voltage is large, the ON period of the control pulse supplied to the base of the control transistor 41 is shortened to reduce the constant voltage circuit 4's. The output voltage is controlled to be small, and if the feedback voltage is smaller than the reference value, the control transistor 41
The ON period of the control pulse supplied to the base is increased to increase the output voltage of the constant voltage circuit 4.
As a result, the lamp current is controlled to have a constant value regardless of variations in components used in the lighting circuit.

The filament preheating current is also controlled in the same manner. Filament preheating period is PW on preheating side
Since the transistor 81 of the M control unit is on, that is, the output terminal 71a of the PWM dimming control circuit 71 is on, the resistor 159 and the diode 1 are connected from the output voltage line of the constant voltage circuit 4.
A current flows through the ground line GND through the diode 60, the diode 164 and the output terminal 71a, and at the same time, the resistors 144, 157, the diodes 163, 164 and the output terminal 71a are controlled by the voltage of the capacitor 144 connected across the filament preheating current detecting resistor 142. A current flows through the ground line GND through the transistor 155, and as a result, the transistor 155 is turned on, and the filament preheating current detection voltage detected by the resistor 142 is fed back to the control terminal 42a of the constant voltage control circuit 42 through the transistor 155 and the diode 158. As a result, the constant voltage control circuit 42 compares the fed-back filament preheating current voltage with the reference value, and if the feedback voltage is large, the ON period of the control pulse supplied to the base of the control transistor 41 is shortened to reduce the constant voltage circuit 4. Control to reduce the output voltage of the constant voltage circuit 4, and to increase the output voltage of the constant voltage circuit 4 by increasing the ON period of the control pulse supplied to the base of the control transistor 41 if the feedback voltage is smaller than the reference value. To do. As a result, the filament preheating current is controlled to have a constant value regardless of variations in components used in the lighting circuit.

As described above, changes in the electrical characteristics due to variations in the components of the inverter circuit 9 and the preheating circuit 12 in the subsequent stage of the constant voltage circuit 4 are suppressed, and the lamp current and preheating current of the discharge lamp 11 are set to optimum values. can do. Since the fluctuation of these currents is small, it is possible to reduce the margin of the parts used, and it is possible to downsize the circuit, reduce the cost, improve the reliability, and extend the life of the lamp.

[0051]

As described above, according to the present invention, it is possible to suppress changes in the electrical characteristics due to variations in the components used in the lighting circuit, and to set the lamp current and preheating current to optimum values with little variations. Therefore, it is possible to reduce the margin of the parts used, and to reduce the size of the circuit, reduce the cost, increase the reliability, and extend the life of the lamp.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a lighting circuit and a lighting device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a lighting circuit of a conventional hot cathode discharge lamp.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... DC power supply 4 ... Constant voltage circuit 7 ... PWM system light control circuit 9 ... Inverter circuit (main discharge circuit) 11 ... Discharge lamp 11a, 11a '... Filament 12 ... Preheating circuit 14 ... Feedback circuit 15 ... Feedback switching circuit 42 ... Constant voltage control circuit 71 ... PWM dimming control circuit 141 ... Lamp current detection resistor 142 ... Filament preheating current detection resistor 151 ... Lamp current feedback switching transistor 155 ... Filament preheating current feedback switching transistor

[Procedure amendment]

[Submission date] August 10, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

Claims (5)

[Claims] 1. A DC power supply, a voltage circuit for controlling the voltage of the DC power supply by a feedback voltage, a main discharge circuit driven by this voltage circuit, a preheating circuit driven by the voltage circuit, and the main discharge. A signal for controlling ON / OFF of the circuit and the preheating circuit in a predetermined cycle, wherein the preheating circuit is turned off when the main discharge circuit is on, and the preheating is performed when the main discharge circuit is off. A control circuit for controlling the circuit to be turned on, which detects the main discharge current of the main discharge circuit and the preheat current of the preheat circuit, respectively, and feeds back to the voltage circuit, and during the ON period of the main discharge circuit. A circuit for selectively switching the detection signal based on the main discharge current and the detection signal based on the preheating current during the ON period of the preheating circuit and feeding back the voltage to the voltage circuit. Lighting circuit. 2. A DC power supply, a voltage circuit for controlling the voltage of the DC power supply by a feedback voltage, a main discharge circuit driven by the voltage circuit, a preheating circuit driven by the voltage circuit, and the preheating circuit. A discharge lamp which is preheated by a preheating current from the main discharge circuit and is turned on by a main discharge current from the main discharge circuit, and which outputs a signal for ON / OFF controlling the main discharge circuit and the preheat circuit at a predetermined cycle. A control circuit for controlling the preheating circuit to turn off when the main discharge circuit is on and to turn on the preheating circuit when the main discharge circuit is off; and a main discharge current of the main discharge circuit and the The preheat current of the preheat circuit is detected and fed back to the voltage circuit, and a detection signal based on the main discharge current is supplied to the preheat circuit during the ON period of the main discharge circuit. Period switches the detection signal by the preheating current selectively, the illumination apparatus being characterized in that comprises a circuit for feeding back the voltage circuit. 3. The lighting circuit or the lighting device according to claim 1, wherein the main discharge circuit is composed of an inverter circuit that converts the voltage of the voltage circuit into an alternating current. 4. The lighting circuit or the lighting device according to claim 1, wherein the preheating circuit is composed of an inverter circuit that converts the voltage of the voltage circuit into an alternating current. 5. The lighting circuit or the lighting device according to claim 1, wherein the control circuit comprises a PWM control circuit capable of controlling an ON period of ON / OFF control. .