JP2000058284A - Ballast for discharge lamp - Google Patents

Abstract

(57) [Problem] To provide a ballast for a discharge lamp, which is practically capable of obtaining high power efficiency and excellent in starting performance of the discharge lamp. A ballast for a discharge lamp according to the present invention converts a low DC voltage obtained from a power supply into a high DC voltage V1, and a drive that converts the high DC voltage V1 from the booster circuit into a substantially rectangular voltage. A large-capacity capacitor, a coil, and a small-capacitance capacitor are connected in series to the output side of the drive circuit, and a discharge lamp is connected in parallel to both ends of the small-capacity capacitor to form a resonance circuit. A lighting detection circuit for detecting that the discharge lamp has been lit; a lighting state of the discharge lamp being detected by the lighting detection circuit; a boosting circuit being controlled when the discharge lamp is in a non-lighting state; The voltage is boosted to a starting voltage V2 higher than the DC voltage V1 of the booster circuit when the discharge lamp is in a steady lighting state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ballast for a discharge lamp for stably lighting a discharge lamp.

[0002]

2. Description of the Related Art Generally, a ballast for a discharge lamp has a simple circuit configuration, high power efficiency of the circuit, and can be downsized as a whole. It is suitably used as a lighting device in such a case. For example, in a lighting device for a hot-cathode fluorescent lamp, at the time of starting, a heating current is supplied to a filament constituting a hot cathode of a discharge lamp through a parallel circuit of small capacitors. It can be easily turned on with a low starting voltage.

On the other hand, a lighting device for lighting a cold cathode fluorescent lamp or a high-intensity discharge lamp is often provided with a high voltage generating circuit for applying a high voltage to a resonance circuit to start the discharge lamp. ing. This is because, in order to start the discharge lamp without a high-voltage generating circuit, it is necessary to increase the Q value of the resonance circuit and drive the discharge lamp at a frequency close to the resonance frequency.

[0004]

In order to obtain high power efficiency in a conventional ballast for a discharge lamp,
It is effective to reduce the voltage of the rectangular wave supplied to the drive circuit within a range where the lighting state of the discharge lamp is stably maintained. In this case, the supply voltage to the drive circuit is reduced. Due to the low value, good startability of the discharge lamp cannot be obtained.

[0005] On the other hand, in order to improve the startability of the discharge lamp in the lighting device, it is effective to increase the supply voltage to the drive circuit.
High power efficiency cannot be obtained, which is uneconomical. As described above, in the conventional ballast for a discharge lamp, there are conflicting demands in terms of power efficiency and startability of the discharge lamp.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a ballast for a discharge lamp which is practically capable of obtaining high power efficiency and excellent in starting properties of the discharge lamp. Aim.

[0007]

SUMMARY OF THE INVENTION A ballast for a discharge lamp according to the present invention comprises a booster circuit for converting a low DC voltage obtained from a power supply into a high DC voltage V1, and a substantially rectangular DC voltage V1 from the booster circuit. A drive circuit for converting to a voltage,
A large capacity capacitor, a coil, and a small capacity capacitor are connected in series on the output side of the drive circuit, and a discharge lamp is connected in parallel to both ends of the small capacity capacitor to form a resonance circuit. A lighting detection circuit for detecting that the lamp has been lit, the lighting state of the discharge lamp being detected by the lighting detection circuit, and controlling the booster circuit when the discharge lamp is in a non-lighting state; Is increased to a starting voltage V2 higher than the DC voltage V1 of the booster circuit when the discharge lamp is in a steady lighting state.

In the above ballast, it is preferable that an intermittent operation circuit for controlling the drive circuit to intermittently drive when the discharge lamp is in a non-lighting state is provided. Further, it is preferable that the resonance circuit is configured to resonate at an odd harmonic higher than or equal to three times the drive frequency.

Further, in the above ballast, there is provided an oscillation circuit which receives a frequency signal from the resonance circuit and oscillates at a frequency close to the resonance condition of the resonance circuit, and an oscillation output from the oscillation circuit is driven. Preferably, it is transmitted to a circuit. Further, the lighting detection circuit, in a state where a DC bias voltage is applied to the discharge lamp via a resistor,
It is preferable to detect a decrease in the voltage across the discharge lamp caused by the lighting of the discharge lamp.

In the above ballast, there is provided an oscillation stop circuit for stopping the supply of the drive voltage to the resonance circuit after a lapse of a predetermined time from the detection of the non-lighting state of the discharge lamp. Is preferred.

[0011]

According to the ballast for a discharge lamp having the above configuration, in a steady lighting state in which the discharge lamp is stably lit, a lighting state maintaining operation with high power efficiency can be obtained, and the discharge lamp is started. At times, a high starting voltage is supplied to the drive circuit, so that good starting properties of the discharge lamp can be obtained. Then, the time during which the starting voltage is supplied to the drive circuit is extremely short as compared with the entire lighting use time of the discharge lamp, so that the degree to which high power efficiency is sacrificed is small, In practice, high power efficiency is obtained as a whole.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a specific embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. FIG. 1 is a block circuit diagram of a ballast for a discharge lamp according to one embodiment of the present invention, and FIG. 2 is a circuit diagram showing a specific configuration thereof. The ballast in this example is
The rated lamp voltage is 70 ± 10V and the rated lamp current is 0.
It is for lighting a metal halide lamp having a rated power consumption of 20 W at 3 A.

[0013] As shown in FIG.
A rectifier circuit C1, a booster circuit C2, a half-bridge circuit C3 forming a drive circuit, and a resonance circuit C4 are connected in this order to a 00V commercial power supply PS, and a discharge lamp DL is connected to the resonance circuit C4. Connected. Commercial power supply P
Instead of the rectifier circuit C1 connected to S, a DC power source using an appropriate battery or the like may be used.

A lighting detection circuit C5 is provided, and an intermittent operation circuit C6 and a starting compensation circuit C7 for receiving a signal from the lighting detection circuit C5 are provided. The intermittent operation circuit C6 is connected to the half bridge circuit C3. And
The starting compensation circuit C7 is connected to the booster circuit C2. Further, an oscillation circuit C8 to which a frequency signal from the resonance circuit C4 is supplied is provided, and a signal from the oscillation circuit C8 is fed back to the half bridge circuit C3. The oscillation stop timer circuit C9 is further connected to the half bridge circuit C3.

The alternating current of the commercial power supply PS is rectified by a rectifier circuit C1 including a semiconductor rectifier 1 and a smoothing capacitor 2. This rectified voltage or the low DC voltage of the battery is converted into a high DC voltage V1 by the booster circuit C2 including the inverter circuit 5 and at the same time, the harmonics are reduced. Is obtained, and this is the half-bridge circuit C
3 is supplied. In the booster circuit C2, 3 and 4 are resistors, 6 is a coil, and 7 is a field effect transistor (FE).
T), 8 is a resistor, 9 is a diode, 10 and 11 are resistors, 12 is a comparison resistor connected to the transistor 13, and the starting compensation circuit C7 is
And resistors 14 and 15.

At the midpoint N between the two switching elements 20 and 21 of the half bridge circuit C3, a substantially rectangular wave voltage swinging around zero (V) is generated. At this midpoint N,
A series circuit of a large-capacity capacitor 23, a coil 26, and a small-capacity capacitor 29 is connected, and these constitute a resonance circuit C4 for voltage amplification. Then, a discharge lamp DL is connected in parallel to both ends of the small capacity capacitor 29 of the resonance circuit C4.

The large capacity capacitor 2 of the resonance circuit C4
A DC bias resistor 24 is connected to a connection point A between
Is connected to the DC bias resistor 24 and the resistors 14 and 1 of the starting compensation circuit C7.
5 constitutes a lighting detection circuit C5.

The oscillation circuit C8 is connected to the small capacitor 29 of the resonance circuit C4. The oscillation circuit C8 includes an impedance element 27 composed of a diode.
And 28, and the output thereof is fed back to the logic circuit 19 via the capacitor 18 and the resistor 17. Impedance element 27
And 28 may be resistors instead of diodes. 22 is a capacitor.

In the resonance circuit C4, when the discharge lamp DL is not lit, a connection point A between the large-capacity capacitor 23 and the coil 26 via the DC bias resistor 24.
In addition, a considerably high voltage (for example, 200 V) appears due to the operation of the start-up compensation circuit C7. In this period, the high voltage at the connection point A is applied through the resistors 25 and 15, so that the transistor 13 is turned on. The output voltage of the booster circuit C2 is kept high (for example, 400 V) by the comparison resistor 12 of the booster circuit C2.

As a result, a high-voltage resonance voltage (for example, 160) generated across the small-capacity capacitor 29 of the resonance circuit C4.
(0 V or more) is applied to the discharge lamp DL, so that the startability of the discharge lamp DL is very good. Immediately after the discharge lamp DL is turned on, by increasing the current flowing through the discharge lamp DL, the glow discharge generated in the discharge lamp DL can be easily transferred to arc discharge. In the final arc discharge state.

As described above, once the discharge lamp DL
Lights up, the voltage at the connection point A becomes the DC bias resistance 2
4 and lower than a low voltage (for example, 1 V) determined by the magnitude of the supply voltage and the impedance of the discharge lamp. By detecting this voltage difference, it can be detected that the discharge lamp DL has been turned on. More specifically, the lighting state of the discharge lamp DL is detected by comparing the voltage at the connection point A between the resistors 15 and 14 via the resistor 25. As a result, the lighting state is detected. Then, the transistor 13 is turned off.
Since the state becomes F, the start compensation circuit C7 is electrically disconnected.

On the other hand, while the transistor 13 is ON, the voltage applied to the coil 26 of the resonance circuit C4 becomes a high voltage as a result of the operation of the resonance circuit C4. When the resonance frequency is set to, the core of the coil 26 becomes magnetically saturated. To avoid this, it is necessary to increase the size of the coil itself.

However, in the circuit having the illustrated configuration, in the oscillation circuit C8, a frequency signal is supplied to the impedance elements 27 and 28 from a part of the circuit through which the load current flows, and is fed back to the logic circuit 19 via the capacitor 18. This allows the resonance circuit C4 to resonate at a harmonic that is N times the oscillation frequency of the half bridge circuit C3. Therefore, in the resonance circuit C4, the higher harmonic can be made to be an odd multiple of the frequency of the half bridge circuit C3. And as a result,
Since magnetic saturation of the core of the coil 26 of the resonance circuit C4 is prevented, a small-capacity coil 26 can be used.

Further, at the time of resonance of the resonance circuit C4, the coil 26, the capacitors 23 and 29, and the switching elements 20 and 21 generate heat and become high in temperature. However, in the ballast shown in the figure, an intermittent operation circuit C6 is provided. I have. The intermittent operation circuit C6 includes a capacitor 31, a diac element 32, a capacitor 33, a resistor 34, and a field effect transistor (F
ET) 35 and a diode 36, and a circuit including a resistor 38 and a DC power supply 39 connected to the logic circuit 19 of the half-bridge circuit C3 via a switching transistor 37.

The intermittent operation circuit C6 controls the operation of the half-bridge circuit C3 to generate a downtime, thereby preventing those circuit components from becoming high in temperature. Therefore, there is an advantage that small components can be used as those circuit components.

More specifically, the intermittent operation of the half bridge circuit C3 is executed by the switching transistor 37 connected between the logic circuit 19 and the DC power supply 39. That is, in the intermittent operation circuit C6, the voltage at the connection point A causes the capacitor 31
Is charged until the diac element 32 breaks out. When the diac element 32 breaks out, the electric charge of the capacitor 31 is accumulated in the capacitor 33 and the FET is charged.
35 is turned on, the switching transistor 37 is turned off, and the driving of the logic circuit 19 is stopped.

Further, in this ballast, if the discharge lamp is not lit even after a lapse of a fixed time from the start of the lighting operation of the discharge lamp, the ballast is fixed from the point of detection of the high voltage state at the connection point A. An oscillation stop timer circuit C9 having a timer circuit 44 for stopping the operation of the logic circuit 19 after a lapse of time is added. This oscillation stop timer circuit C
9 is a timer circuit 44, a resistor 42, a transistor 4
3, the resistors 45 and 47, and the capacitor 46.

The oscillation stop timer circuit C9 is capable of controlling the discharge lamp from the lighting state to the non-lighting state,
It works. This oscillation stop timer circuit C9
Is a circuit for preventing the high voltage application operation from being performed repeatedly when the discharge lamp DL is not turned on for some reason, whereby the ballast has high safety.

More specifically, when the discharge lamp DL is not lit, the voltage at the connection point A is high.
The switching transistor 40 is turned on by the voltage applied through the resistor 25 and the resistor 41. Meanwhile, the timer circuit 44 includes a resistor 45 and a capacitor 46.
Oscillation occurs at a predetermined clock frequency for a predetermined time determined by the resistor 47 and the resistor 47. When the set predetermined time elapses, the transistor 43 is turned on. As a result, the switching transistor 37 is turned off and the logic circuit is turned off. 1
9 is stopped.

Since the discharge lamp ballast according to the present invention has the above-described configuration, the discharge lamp DL is not lit at the time of starting the discharge lamp DL, so that the resonance circuit C4 and the discharge lamp In order to drive the load circuit composed of the following, a starting voltage higher than the DC voltage of the booster circuit C2 is supplied by the operation of the starting compensation circuit C7, and as a result, a high starting voltage is applied to the discharge lamp DL, and The lamp DL is easily turned on. As described above, the discharge lamp DL is turned on, and the transition from the glow discharge state to the arc discharge state in the discharge lamp DL is easily realized, so that the discharge lamp DL has good startability.

On the other hand, if such a high starting voltage V2 is continuously supplied, the power efficiency in each circuit for generating the starting voltage V2 becomes low.
However, in the above ballast, when the discharge lamp DL is lit, this is detected by the lighting detection circuit C5, and the starting compensation circuit C7 is electrically cut off. V1 is supplied, and the high DC voltage V1 is equal to the starting voltage V1.
2, the discharge lamp D is maintained in a state where the power efficiency of the entire ballast circuit is maintained high.
The lighting state of L is maintained.

The coils and capacitors constituting the load circuit usually have a capacity large enough to withstand a thermal load in anticipation of a loss when the lighting state of the discharge lamp is in a steady state. If the starting voltage V2 is supplied even temporarily, as described above, the temperature rises due to an increase in the power loss of the coil and the capacitor. It is necessary to use a capacitor with a large capacity that matches. However, in the ballast having the above configuration, the intermittent operation circuit C6 is provided, so that the driving power is intermittently supplied, and as a result, the temperature of the coil and the capacitor does not greatly increase. Sufficiently high reliability can be obtained with a small capacity as a circuit component of (1).

In the load circuit including the large capacity capacitor 23, the coil 26, the small capacity capacitor 29 and the discharge lamp, if the resonance circuit C4 is driven so as to resonate at the drive frequency, the resonance voltage increases. May cause magnetic saturation, but in the above ballast, the coil 2 is resonated with odd harmonics.
No magnetic saturation occurs at 6 and, therefore, the coil 26 may have a small core.

In addition, since the ballast having the above-described configuration includes an oscillation circuit that oscillates at a frequency close to the resonance condition, a feedback from a part of the resonance circuit to the drive circuit reduces the "suck" in the resonance condition. The resonance circuit can be operated stably. On the other hand, if a signal separately oscillated outside is used, adjustment is difficult.

Further, in the lighting detection circuit, a state in which a DC bias voltage is applied to the discharge lamp via a DC bias resistor, and the fact that the lamp voltage is reduced when the discharge lamp is turned on is used for lighting the discharge lamp. Since the presence / absence is detected, the lighting state of the discharge lamp can be reliably detected.

When the discharge lamp does not light,
After a certain period of time, the load circuit is provided with an oscillation stop timer circuit for stopping the supply of the high DC voltage V1, so that a state in which a high voltage is applied to the power supply of the discharge lamp due to an accident or failure of the discharge lamp for a long time. Since the continuation is prevented, high security can be obtained.

FIG. 3 is an equivalent circuit diagram of a driving circuit portion in the above-described example using a half-bridge circuit as a driving circuit for driving a discharge lamp.
These are one output signal and the other output signal of the switching signal generation circuit 48, respectively.
0 and 21. Here, the switching signal generating circuit 48 includes the resistor 17, the capacitor 18 and the logic circuit 19 in the circuit of FIG. However, the ballast of the present invention is not limited to a drive circuit using a half-bridge circuit, and a drive circuit of another method can be used.

For example, FIG. 4 is a circuit diagram when a full bridge circuit is used as a drive circuit connected to a switching signal generation circuit. In this figure, 20
1, 202, switching elements to which one output signal a from the switching signal generating circuit 48 is supplied;
Reference numeral 212 denotes a switching element to which the other output signal b from the switching signal generating circuit 48 is supplied, and a large-capacity capacitor 23 is provided between a connection point between the switching elements 201 and 211 and a connection point between the switching elements 202 and 212. , Coil 26 and small capacitor 29
And a discharge lamp DL is connected in parallel with the small-capacity capacitor 29.

On the other hand, FIG. 5 is a circuit diagram in the case of employing a configuration based on a transformer coupling type push-pull system. In this example, the switching signal generating circuit 48 includes a resonance circuit via the switching elements 20 and 21 and the transformer 50. Are connected. Specifically, a primary winding of a transformer 50 whose middle point is connected to a constant voltage source V is provided between switching elements 20 and 21 receiving one output signal a and the other output signal b from switching signal generating circuit 48. Are connected to each other, and between the large-capacity capacitor 23 and the coil 26 in the series circuit including the large-capacity capacitor 23, the coil 26, and the small-capacity capacitor 29,
The secondary winding of the transformer 50 is interposed.

[0040]

As described above, the ballast for a discharge lamp of the present invention has a high starting voltage V2 only when the discharge lamp is started.
Is supplied to the drive circuit, and after the discharge lamp is turned on, the lamp is driven at a lower voltage, so that high power efficiency can be obtained as a whole and good startability can be obtained.

According to the ballast according to the second aspect, the drive circuit supplies the power intermittently, thereby preventing the coil and the capacitor from becoming high temperature. Small ones can be used. According to the ballast according to the third aspect, a small-sized coil can be used as a coil constituting the resonance circuit by causing the resonance circuit to resonate at an odd-order harmonic higher than or equal to three times the drive frequency. it can.

According to the ballast according to the fourth aspect, by applying feedback from a part of the resonance circuit to the drive circuit, it is possible to stably oscillate in the vicinity of the resonance frequency in a state in which suction occurs.

According to the ballast according to the fifth aspect, the lighting state of the discharge lamp is detected by detecting a decrease in the lamp voltage, so that the detection result is reliable and an operation with high reliability can be obtained. Can be.

According to the ballast according to the sixth aspect, the oscillation stop timer circuit including the timer circuit prevents a state in which a high voltage is applied to the discharge lamp for a long time, thereby achieving high safety. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of a ballast for a discharge lamp according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific configuration of the ballast for a discharge lamp of FIG. 1;

FIG. 3 is an equivalent circuit diagram of a drive circuit portion in the example of FIG.

FIG. 4 is a circuit diagram in a case where a full bridge circuit is used as a drive circuit.

FIG. 5 is a circuit diagram when a configuration based on a transformer-coupled push-pull system is employed.

[Explanation of symbols]

 PS Commercial power supply C1 Rectifier circuit C2 Boost circuit C3 Half bridge circuit C4 Resonance circuit DL Discharge lamp C5 Lighting detection circuit C6 Intermittent operation circuit C7 Start-up compensation circuit C8 Oscillation circuit C9 Oscillation stop timer circuit 1 Semiconductor rectifier 2 Smoothing capacitors 3, 4 Resistance 5 Inverter circuit 6 Coil 7 Field effect transistor (FET) 8 Resistor 9 Diode 10, 11 Resistance 12 Comparison resistance 13 Transistor 14, 15 Resistance 16 Lighting capacitor 17 Resistance 18 Capacitor 19 Logic circuit 20, 21 Switching element 22 Capacitor 23 Large Capacitor 24 DC bias resistor 25 Resistance 26 Coil 27, 28 Impedance element 29 Small capacity capacitor 30 Resistance 31 Capacitor 32 Diac element 33 Capacitor 34 Resistance 35 FE 36 Diode 37 Switching transistor 38 Resistance 39 DC power supply 40 Switching transistor 41, 42 Resistance 43 Transistor 44 Timer circuit 45 Resistance 46 Capacitor 47 Resistance 48 Switching signal generation circuit a One output signal b The other output signal 201, 202, 211 , 212 Switching element 50 Transformer V Constant voltage source

Continuation of the front page (72) Inventor Tetsuo Shimizu F-term in Osaka Takanami Co., Ltd. 3-3-15 Nihonbashi Higashi, Naniwa-ku, Osaka City, Osaka 3K072 AA11 BA03 BA05 BB01 BB10 BC01 BC03 CA11 DD04 EB01 EB05 GA02 GB01 GB12 GB14 GB18 GC04 HB03

Claims (6)

[Claims] 1. A booster circuit for converting a low DC voltage obtained from a power supply into a high DC voltage V1, and a drive circuit for converting a higher DC voltage V1 from the booster circuit into a substantially rectangular voltage, the drive circuit comprising: A large-capacity capacitor, a coil, and a small-capacity capacitor are connected in series on the output side of the capacitor, and a discharge lamp is connected in parallel to both ends of the small-capacity capacitor to form a resonance circuit, and the discharge lamp is lit. The lighting detection circuit detects the lighting state of the discharge lamp, controls the booster circuit when the discharge lamp is in a non-lighting state, and discharges the output voltage of the discharge lamp. A ballast for a discharge lamp, which boosts a starting voltage V2 higher than a DC voltage V1 of a boosting circuit when the lamp is in a steady lighting state. 2. The discharge lamp stabilization device according to claim 1, further comprising an intermittent operation circuit that controls the drive circuit to intermittently drive the discharge lamp when the discharge lamp is in a non-lighting state. vessel. 3. The ballast for a discharge lamp according to claim 1, wherein the resonance circuit is configured to resonate at an odd harmonic higher than or equal to three times a driving frequency. 4. An oscillation circuit which receives a frequency signal from the resonance circuit and oscillates at a frequency close to the resonance condition of the resonance circuit is provided, and an oscillation output from the oscillation circuit is transmitted to a drive circuit. Claims 1 to 3 characterized in that:
The ballast for a discharge lamp according to any one of the above. 5. The lighting detection circuit according to claim 1, wherein a DC bias voltage is applied to said discharge lamp via a resistor.
5. The ballast for a discharge lamp according to claim 1, wherein the ballast detects a decrease in voltage across the discharge lamp caused by lighting of the discharge lamp. 6. An oscillation stop circuit for stopping supply of a drive voltage to a resonance circuit after a lapse of a predetermined time from detection of a non-lighting state of the discharge lamp. The ballast for a discharge lamp according to any one of claims 1 to 5.