JP5260226B2 - Discharge lamp lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device capable of preventing lamp lighting from becoming unstable even if a constant power control is performed for obtaining an identical power value for any direction of a lamp current in order to eliminate luminance variation. <P>SOLUTION: The discharge lamp lighting device is provided with a half-bridge type inverter circuit 20 having two smoothing capacitors 32, 34 and two inverter switching elements 36, 38 and a controlling circuit 52 controls an alternating period of the inverter switching elements 36, 38 so that an intermediate potential of the two smoothing capacitors 32, 34 can come near a set-up potential, and at a time of capacity variation of the two smoothing capacitors 32, 34, the set-up potential is shifted in accordance with the capacity ratio. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a discharge lamp lighting device, and more particularly to an improvement of a lamp power stabilization mechanism.

In order to start discharge (that is, dielectric breakdown between lamp electrodes) at the start of the discharge lamp and to limit the current after the start of discharge, it is necessary to use a so-called discharge lamp lighting device.
When the discharge lamp is sine-waved at the frequency of the commercial power source, flickering is likely to occur, and recently, rectangular wave lighting by an inverter-type discharge lamp lighting device has become mainstream.
By the way, the inverter type discharge lamp lighting device adopts a full bridge type inverter circuit that supplies a rectangular wave power of a desired frequency to the lamp by alternating four switching elements, and desired by alternating two switching elements. Some use a half-bridge inverter circuit that supplies power at a frequency to the lamp. The latter has a simple circuit configuration and a small number of parts, and is useful from the viewpoint of cost or miniaturization requirements ( Patent Documents 1 to 3).
When a half-bridge inverter circuit is used, a lamp is installed between the connection point of two inverter switching elements and the connection point of two smoothing capacitors. Current is passed through a loop formed by a capacitor. And, if the supplied power is different for each direction of the lamp current, pulsation occurs in the lamp light amount, and it is preferable to perform constant power control. However, due to a slight difference in capacitance between the two smoothing capacitors, the potential at the capacitor connection point with respect to the ground fluctuates, and the lighting operation of the lamp becomes unstable and sometimes goes out.
In addition, when the lamp is lit with a proportional relationship to the voltage applied to each smoothing capacitor for each direction of the lamp current, the midpoint potential between the two capacitors does not fluctuate, Although stable lighting is possible, the input power to the lamp differs depending on the direction of the lamp current, which causes a problem that the light fluctuates.
Furthermore, the method of lighting the lamp with a proportional relationship to the voltage applied to each smoothing capacitor is not a problem when there is little difference in the capacitance of each capacitor, but the difference in capacitance is large. Then, the consumption of one side of the electrode of the lamp becomes severe, and there is a problem that the life of the lamp is remarkably shortened.
JP 2006-147368 A JP 2006-147367 A JP-A 64-72496

  The present invention has been made in view of the prior art, and the problem to be solved is that even if constant power control is performed such that the same power value is obtained for each direction of the lamp current in order to eliminate fluctuations in light, An object of the present invention is to provide a discharge lamp lighting device capable of preventing the lighting of the lamp from becoming unstable.

In order to solve the above problems, a discharge lamp lighting device according to the present invention employs a half-bridge type inverter circuit having two smoothing capacitors and two inverter switching elements,
The control circuit controls the alternating period of the inverter switching element so that the midpoint potential of the two smoothing capacitors approaches the set potential ,
It counts which inverter switching element drive period becomes longer every cycle, and sets the set potential so that the potential difference between both ends of the inverter switching element having a large count value in the long drive period becomes larger every fixed period. It is preferable to change.
In the present invention, the unit for extending the alternating period is preferably 1 msec or less, particularly preferably 0.
About 1 to 0.5 msec is preferable. If the extension unit is too large, the switching elements are alternately driven for a long period of time, making it difficult to stabilize, and if the extension unit is too small, it takes time to control.
For the same reason, the moving unit of the set potential is 0.2 V or more and 3 V or less, preferably 0.5 V.
It is preferable that there is about ˜1V.

According to the present invention, even if there is a difference in capacitance between the smoothing capacitors C ₁ and C ₂ due to secular change or the like, the direction of the lamp current can be adjusted without impairing the stability of the lighting state by adjusting the midpoint potential. It is possible to perform constant power control so that the same power value is obtained every time.

Preferred embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a circuit configuration of a half-bridge type discharge lamp lighting device 10 according to an embodiment of the present invention.
In the figure, a lighting device 10 includes a rectifier circuit 14 that rectifies and converts AC power supplied from a commercial power supply 12 into a DC voltage, and a power factor correction circuit 16 that converts the output of the rectifier circuit 14 to a constant voltage and increases the power factor. And an inverter circuit 20 that supplies the DC power output from the power factor correction circuit 16 to the lamp 18 at a desired frequency.

The rectifier circuit 14 is composed of a full-wave rectifier diode bridge, and is connected to both ends of the output end of a commercial AC power supply 12 which is a low-frequency (for example, 50 Hz) power supply.
The power factor correction circuit 16 includes a coil 22 having one end connected to one output end (+ voltage output end in the figure) of the rectifier circuit 14, and the other end of the coil 22 and the other end of the rectifier circuit 14. A high-frequency switching element Q ₁ 26 having a drain and a source connected through a resistor 24 between output terminals (in the figure, a voltage output terminal), and a capacitor 28 as a high-frequency component passing filter associated with the switching of the switching element Q ₁ 26 A commutation diode 30 having an anode connected to a connection point between the coil 22 and the switching element Q ₁ 26, and a negative voltage output terminal of the rectifier circuit 14 through a cathode of the commutation diode 30 and a resistor 24. A series circuit of smoothing capacitors C ₁ 32 and C ₂ 34 is provided. The power factor correction circuit 16 functions as an active filter circuit that receives the full-wave rectified output from the rectifier circuit 14 and generates a stabilized DC voltage with a constant amplitude at a high power factor, or a DC power source.

An inverter circuit 20 is connected to the subsequent stage of the power factor correction circuit 16. The inverter circuit 20 includes high-frequency switching elements Q ₂ 36 and Q ₃ 38 connected in parallel to both ends of a series circuit of smoothing capacitors C ₁ 32 and C ₂ 34 of the power factor correction circuit 16, and switching elements Q ₂ 36 and Q ₃ and element _Q 2 36 in parallel to each _{38, Q} 3 38 direction of the current between the diodes 40, 42 connected in the opposite direction, a connection point of the series circuit of the switching element _Q 2 _{36, Q} 3 38 A series circuit of a coil 44 as an inductor, a winding of an HID lamp 18 and a step-up transformer 46 connected between connection points of the series circuit of the smoothing capacitors C ₁ 32 and C ₂ 34; Are connected in parallel to each other, and the high-frequency switching by high-frequency switching of the switching elements Q ₂ 36 and Q ₃ 38 is performed from the current flowing through the HID lamp 18. A capacitor 48 for bypassing the component and a resistor 50 for detecting the current value flowing through the HID lamp 18 are provided.

When FETs are used as the switching elements Q ₂ 36 and Q ₃ 38, parasitic diodes built in the FETs are used for the reverse current conducting diodes 40 and 42, so that diodes are connected specially. do not have to.
In the present embodiment, on / off control of each switching element Q ₁ 26, Q ₂ 36, Q ₃ 38 is performed by the control circuit 52.
That is, when an AC power supply is turned on in the discharge lamp lighting device of FIG. 1, the voltage obtained by dividing the rectified voltage by a resistance voltage dividing circuit (not shown) connected to both ends of the full-wave rectified output terminal of the rectifier circuit 14 is And the rectified voltage of the rectifier circuit 14 is supplied to the power factor correction circuit 16, so that the switching element Q ₁ 26 of the power factor improvement circuit 16 performs an on / off switching operation at a high frequency (several tens of kHz). Start.

The control circuit 52 controls the on-period of the switching element Q ₁ 26 for high-frequency switching according to the output voltage of the series circuit of the smoothing capacitors C ₁ 32 and C ₂ 34 on the output side of the power factor correction circuit (boost chopper circuit) 16. Thus, feedback control is performed so that the output voltage becomes a constant value, and the control is performed by monitoring the full-wave rectified voltage amplitude level of the rectifier circuit 14 (detecting the voltage at the + voltage output terminal of the rectifier circuit) and the resistor 24. control of by controlling the oN period of the switching element Q ₁ 26 in accordance with the amplitude level of the full-wave rectified voltage on the basis of the monitoring of the current level, the power factor correction to match the input AC current to the input AC voltage of the phase flowing Is also going. As a result, the power factor correction circuit 16 converts the full-wave rectified voltage into a stabilized DC voltage with a high power factor. The switching frequency of the switching element Q ₁ 26 is usually several tens of KHz.

Next, the operation of the inverter circuit 20 will be described with reference to FIGS. First, an operation in which the switching element Q ₂ 36 is turned on / off during the half cycle T1 will be described with reference to FIG. And an on-pulse is applied from the control circuit 52 to the gate of the switching element _Q 2 36, when the switching element _Q 2 36 is turned ON, the charging voltage of the smoothing capacitor _C 1 32 as a power supply, a capacitor _C 1 32 → switching element _Q 2 36 → Coil 44 → (Transformer 46) → HID lamp 18 → (Resistance 50) → When a current flows through the capacitor C ₁ 32 and the switching element 32 is turned off, the energy stored in the coil 44 causes the coil 44 → (Transformer 46). → HID lamp 18 → (resistor 50) → capacitor C ₂ 34 → (diode 42) → Current flows through the coil 44. As a result, current flows through the HID lamp 18 in the direction of the coil 44 → the HID lamp 18 during the period T1 during which the switching element Q ₂ 36 is performing high-frequency switching operation (FIG. 3A).

Then, when the period of the next half cycle T2 is reached, the switching element Q ₃ 38 is turned on / off. Switching element _Q 3 38 and an on-pulse is applied from the control circuit 52 to the gate of the switching element _Q 3 38 is turned on, the charging voltage of the smoothing capacitor _C 2 34 as a power supply, a capacitor _C 2 34 → (resistance 50) → HID When the current flows through the lamp 18 → (transformer 46) → coil 44 → switching element Q ₃ 38 → capacitor C ₂ 34 and the switching element Q ₃ 38 is turned off, the energy stored in the coil 44 causes the coil 44 → (diode 40). ) → capacitor C ₁ 32 → (resistor 50) → HID lamp 18 → (transformer 46) → current flows through the coil 44. For this reason, in the next period T2 during which the switching element Q ₃ 38 is performing high-frequency switching operation, a current always flows through the HID lamp 18 in the direction of (resistor 50) → HID lamp 18 → coil 44 (FIG. 3). (B)). Therefore, a low-frequency lamp current as shown in FIG. 3C flows through the HID lamp 18 while being driven at a high frequency.

Next, with reference to FIG. 4, the control operation of the switching elements Q ₂ 36 and Q ₃ 38 characteristic of the present invention will be described.
Until the end of the period of the half cycle T, the lamp lighting maintenance is controlled. The control circuit 52 determines whether the intermediate potential of the capacitors C ₁ 32 and C ₂ 34 is a target potential (set value) between the end of the half cycle T and the start of the period of the next half cycle T. If the intermediate potential is higher than the target potential (set value), the operation period T2 during which the switching element Q ₃ 38 is turned on / off is lengthened, or the operation in which the switching element Q ₂ 36 is turned on / off. Control is performed to shorten the period T1, and when the intermediate potential is lower than the target potential (set value), the period T1 of the operation in which the switching element Q ₂ 36 is turned on / off is lengthened, or the switching element Q ₃ 38 Control is performed to shorten the period T2 of the operation of turning on / off. As a result, the intermediate potential of the capacitors C ₁ 32 and C ₂ 34 is brought close to the target potential (set value), and constant power is achieved in the range of normal operation. Usually, the capacitances c ₁ and c ₂ of the capacitors are the same, and it is preferable that the periods T1 and T2 have the same power value, so that T1 = T2.
However, variations in manufacture of the capacitance of the capacitor _C 1 _{32, C} 2 34, depending on the temperature condition at the time of use, there is the capacitor _C 1 _{32, C} 2 34 is aging in different capacities.

In this case, if the HID lamp current is lit at the same power value for each direction of the HID lamp current, the capacity of the capacitor C ₁ 32 is less than C ₂ due to the difference in the amount of power (energy) stored in the capacitors C ₁ and C _2. the potential of the midpoint to a higher direction, when the capacitance of the capacitor C ₁ is larger than C ₂ potential at the midpoint is moved to a lower direction, HID lamp lighting becomes unstable, which may result in off soon.

Therefore, in the present embodiment, when the driving time of one of the switching elements becomes long over several cycles, the time period from the end of the capacitor half cycle T to the start of the period of the next half cycle T is shown in FIG. As shown, the number of times the switching element Q ₃ 38 is turned on / off is increased (Q3count), and the number of times the switching element Q ₂ 36 is turned on / off is increased (Q2count). It is determined which count value is larger (after several seconds).

When the number of times the switching element Q ₃ 38 is turned on / off is longer (Q3count) than the number of times the switching element Q ₂ 36 is turned on / off is longer (Q2count), the capacitors C ₁ and C ₂ The intermediate potential increases the target potential (set value) and decreases if it is small.
By repeating this, the midpoint potential converges to the optimum value as shown in FIG. 5, and stable lighting with constant power is achieved.

In the control circuit 52, the switching elements Q ₂ 36 and Q ₃ 38 are controlled by the control mechanism shown in FIG.
As shown in the figure, on / off timing of each of the switching elements Q ₂ 36 and Q ₃ 38 in the drive period is performed by a pulse setter 60.
The pulse setter 60 includes an OSC oscillator 62 that oscillates at 10 MHz to 500 MHz, a counter 64 that counts a signal output from the oscillator 62, and a comparison that compares a preset pulse width specified value t1 with the count value of the counter 64. A comparator 66, a comparator 68 for comparing the preset one cycle specified value t2 with the count value, and an RS flip-flop 70 for inputting the outputs of the comparators 66 and 68 to the R and S terminals, respectively.
The pulse setter 60 outputs a pulse train having a pulse width t1 and a pulse period t2.

The driving cycle of the switching element 36 is set by the switching command device 72. The switching command device 72 includes a pulse counter 74 output from the pulse setting device 60, a comparator 76 for comparing a specified on / off duration T1 with a count value, and an RS flip-flop 78, and a count value. Until the designated duration is reached, the RS flip-flop 78 continues the on signal.
A similar configuration is adopted in the switching command device 80 of the switching element 38, and includes a counter 82, a comparator 84, and an RS flip-flop 86.

The switching commanders 72 and 80 are alternately operated every set time, whereby the switching elements Q ₂ 36 and Q ₃ 38 are alternately driven with a predetermined driving time.
Therefore, the command for extending or shortening T1 to T2 in FIG. 4 is performed by designating the ON / OFF duration time to the comparators 76 and 84.

In the above control, the number of times that the period becomes longer is counted, but the number of times that the period becomes shorter may be counted. In this case, the operation for the determination result is reversed.
In the present invention, it is also possible to detect the capacitances of the capacitors C ₁ 32 and C ₂ 34 and obtain the set potential by calculation.
That is, assuming that the capacitances of the capacitors C ₁ and C ₂ are c ₁ and c ₂ and the voltages applied to the capacitors C ₁ and C ₂ are V _C1 and V _C2 , respectively, become that way.

Accordingly, the ratio V _C1 / V _C2 of the DC voltages of the smoothing capacitors C1 ₃₂ and C2 ₃₄ is set to the square root (c ₂ / c ₁ ) ^1/2 of the ratio of the reciprocals of the capacitances of the capacitors C ₁ and C _2. The set potential can be changed.
By performing constant power control as described above, the lamp life is extended, and even a resource-saving high-pressure discharge lamp lighting device with a reduced number of parts as shown in FIG. It becomes possible.
The present invention can be applied to high-pressure discharge lighting devices including xenon lamps in addition to HID lamps such as mercury lamps, metal halide lamps, and high-pressure sodium lamps.
It can be applied to high pressure discharge lighting devices for industrial ultraviolet applications.
Furthermore, the discharge lamp lighting device according to the present invention can be used for lighting equipment for offices and stores.

It is explanatory drawing of the schematic circuit structure of the discharge lamp lighting device concerning one Embodiment of this invention. It is explanatory drawing of the inverter operating state of the circuit shown in FIG. It is explanatory drawing of the on / off state of the switching element for inverters of the circuit shown in FIG. It is explanatory drawing of the constant power conversion process and potential setting value change process of the circuit shown in FIG. FIG. 5 is a conceptual diagram of setting value change of a smoothing capacitor midpoint potential by the control mechanism shown in FIG. 4. It is explanatory drawing of the principal part detailed structure of the control circuit of the switching element for inverters used for this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Discharge lamp lighting device 14 Rectifier circuit 16 Power factor improvement circuit 18 Lamp 20 Inverter circuit 32, 34 Smoothing capacitor 36, 38 Inverter switching element 52 Control circuit

Claims (1)

A rectifier circuit that rectifies AC power and converts it to DC;
A power factor correction circuit having a series circuit of two smoothing capacitors C1, C2 connecting both output terminals of the rectifier circuit;
A half-bridge inverter circuit in which two switching elements that are driven alternately are connected in parallel with the smoothing capacitor series circuit;
A control circuit for controlling the alternating switching elements for the inverter;
In a discharge lamp lighting device in which a lamp is connected between a connection point of the two inverter switching elements and a connection point of the two smoothing capacitors,
The control circuit controls an alternating period of the inverter switching element so that an intermediate point potential of the two smoothing capacitors approaches a set potential,
Each cycle counts which of the two inverter switching elements has a longer driving period, and the potential difference between both ends of the inverter switching element having a large driving period count value increases every certain period. The discharge lamp lighting device is characterized in that the set potential is changed .

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