JP2854632B2 - Discharge lamp lighting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a discharge lamp lighting device in which a discharge lamp is turned on by an output of an inverter having a switching element for interrupting an output of a DC power supply at a high frequency.

[Prior art]

As a discharge lamp lighting device of this type, for example, a circuit configuration as shown in FIG. 4 is known. That is, an AC power source AC is full-wave rectified by a rectifier DB, rectifier and smoothed by the smoothing capacitor C to the output of the DB includes a DC power supply for generating a DC supply voltage V _0, a switching element output of the DC power source The frequency is converted to a high frequency by the inverter 1, and the discharge lamp is turned on by the output voltage of the inverter 1. Inverter 1, to interrupt the DC power supply voltage V ₀ by four switching elements Q ₁ to Q _4, current limiting inductance L
The power is supplied to the discharge lamp 2 via the. The discharge lamp 2 has a high-frequency bypass capacitor C _1.
Are connected in parallel. That is, the four switching elements Q _{1 to} Q ₄ are connected in series by _two (Q ₁ and Q ₃ , Q ₂ and Q ₄ ), and each series circuit is connected between both ends of the DC power supply. The series circuit of the current limiting inductance L and the discharge lamp 2 is connected between the connection points of the switching elements Q ₁ , Q ₃ , Q ₂ , Q ₄ of each series circuit. Further, each of the switching elements Q ₁ to Q ₄ diodes D ₁ to D ₄ are connected in antiparallel. Switching elements Q ₁ and Q ₂ are turned on at high frequency (several + kHz).
Is turned off, and the switching elements Q ₃ and Q _4
1, is turned on and off at a sufficiently low frequency (hundreds Hz) than Q _2. As shown in FIGS. 5 (c) and 5 (d), the switching elements Q ₃ and Q ₄ are turned on and off alternately, and as shown in FIGS. 5 (b) and 5 (c), During the period when ₃ is on, the switching element Q ₂ turns on and off,
As shown in FIGS. 5 (a) and (d), the switching element
Q ₄ is the period is on has been set operation timing as the switching element Q ₁ is turned on and off. Therefore, when the switching element Q ₄ is on, the switching element Q ₁ is is on, DC power source → the switching element Q ₁ → current limiting inductance L → discharge lamp 2 and a capacitor C ₁ → switching element Q ₄ → resistor R
→ Current flows through the path of DC power supply, and the switching element
When Q ₁ is turned off, the energy accumulated in the current limiting inductance L, a path of the current limiting inductance L → discharge lamp 2 and a capacitor C ₁ → switching element Q ₄ → resistor R → diode D ₃ → current limiting inductance L Electric current flows. On the other hand, when the switching element Q ₃ is turned on, the switching element Q ₂ is on, DC power source → the switching element Q ₂ → discharge lamp 2 and a capacitor C ₁ → current limiting inductance L → switching element Q ₃ → resistor R → Current flows through the path of DC power supply,
When the switching element Q ₂ is turned off, the energy accumulated in the current limiting inductance L, current limiting inductance L → switching element Q ₃ → resistor R → diode D ₄
A current flows through a path of discharge lamp 2 and capacitor C ₁ → current-limiting inductance L. By the operation as described above, the high frequency current _IL flows through the current limiting inductance L as shown in FIG. 5 (e). Capacitor C _1, as shown in FIG. 5 (f), from being set to pass the high-frequency components I _C1 flowing through the current limiting inductance LD, the lamp current Il flowing through the discharge lamp 2, FIG. 5 As shown in (g), a high-frequency ripple component of the ON / OFF cycle of the switching elements Q ₁ and Q ₂ is superimposed on a rectangular wave corresponding to the ON / OFF cycle of the switching elements Q ₃ and Q ₄ . By the way, in the above circuit, a current corresponding to the lamp current is detected as a voltage across the resistor R, and the switching element Q is controlled via the control circuit 3 via the control circuit 3 so that the lamp current becomes constant according to the magnitude of the voltage across the resistor R. has a _1, Q ₂ on-duty so that feedback control. The control circuit 3 includes a lamp current detection circuit 11, a high frequency generation circuit 12, a low frequency generation circuit 13, a gate circuit 14, a drive circuit
Composed of 15 ₁ to 15 _4. For example, as shown in FIG. 6, the high-frequency generation circuit 12 is set by a saw-tooth wave generation circuit 16 capable of obtaining an oscillation output of several tens of kHz, an output of the lamp current detection circuit 11, and resistors R ₁ and R ₂ . It comprises a differential amplifier circuit 17 that outputs a difference from the reference voltage, and a comparison circuit 18 that compares the output of the sawtooth wave generation circuit 16 with the output of the differential amplifier circuit 17. The output level of the differential amplifier circuit 17 is set to decrease as the output level of the lamp current detection circuit 11 increases. Comparison circuit 18, as shown in FIG. 7 (a), the output level V _X sawtooth wave generating circuit than 16 of the differential amplifier circuit 17
The output level is set to “H” during the period when the output level is low. The lamp current detection circuit 11 outputs the average value of the voltage across the resistor R. When the lamp current increases, the output level of the differential amplifier circuit 17 decreases, so that the ON period of the comparison circuit 18 decreases. is there. The low-frequency generation circuit 13 generates two outputs whose on-duty is slightly smaller than 50%, so that both outputs are turned on alternately. The gate circuit 14 includes a pair of NOR circuits 19a and 19b,
Each of the NOR circuits 19a and 19b inverts the output of the high frequency generating circuit 12 only for the NOR circuits 19a and 19b to which the other output is input when one output level of the low frequency generating circuit 13 is "H". The output is made available. Drive circuit 15 ₁ to 15 ₄ receives the output of the NOR circuit 19a, 19b of the output and the low frequency generation circuit 13 is to control the switching element Q ₁ to Q _4. As described above, in the control circuit 3, when the lamp current increases, the on-duty of the output of the high-frequency generation circuit 12 is reduced to shorten the on-periods of the switching elements Q ₁ and Q ₂ to make the lamp current substantially constant. Limit it to keep it.

[Problems to be solved by the invention]

By the way, as in the above conventional configuration, the switching element
When Q ₃ and Q ₄ are driven at several hundred Hz, FIG.
As shown in (1), the impedance of the discharge lamp 2 is high immediately after the reversal of the polarity of the lamp current, and gradually decreases thereafter. That is, during the discharge half cycle, the discharge lamp 2
The impedance of this changes. On the contrary,
Since the on-duty of the switching elements Q ₁ and Q ₂ is controlled based on the average value of the lamp current, the on-duty of the switching elements Q ₁ and Q ₂ is substantially constant during a half cycle of the discharge. As a result, the peak value of the current flowing through the current limiting inductance L is relatively small immediately after the polarity reversal, and gradually increases thereafter. When the current flowing through the current-limiting inductance L changes in this manner, the ripple component of the lamp current increases, causing a problem that the discharge lamp 2 flickers. The present invention is aimed at solving the above problems,
An object of the present invention is to provide a discharge lamp lighting device in which a change in a lamp current during a half cycle is suppressed to prevent flicker of the discharge lamp.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides an inverter having a switching element for intermittently switching the output of a DC power supply at a high frequency and obtaining an output obtained by superimposing the high frequency on a multi-polar rectangular wave having a frequency covered by the high frequency. A control circuit for controlling the on-duty of the switching element so that the lamp current to the discharge lamp lit by the envelope output of the inverter is substantially constant. The on-duty is gradually reduced for a certain period of time after the inversion of the polarity of the lamp current so that the lamp current becomes substantially constant with respect to the change in impedance within the half cycle of the lamp current.

[Action]

According to the above configuration, the on-duty is gradually reduced for a certain period of time after the polarity reversal of the lamp current so that the lamp current becomes substantially constant with respect to the change in impedance within a half cycle of the lamp current to the discharge lamp. Because the lamp current is kept almost constant with respect to the change in impedance within a half cycle of the lamp current, the increase in the ripple component is suppressed and the flicker of the discharge lamp is prevented. It is.

Embodiment 1 The basic configuration is the same as the conventional configuration shown in FIG. 4, and only a part of the control circuit 3 is different. Therefore, only the differences will be described. As shown in FIG. 1, the high-frequency generation circuit 12 of the control circuit 3
1, the correction circuit 4 for superimposing the output of the low-frequency generation circuit 13 is provided between the differential amplifier circuit 17 and the comparison circuit 18. The correction circuit 4 includes a pair of capacitors C ₃ and C ₄ and a pair of resistors R
_3, R _{4, 3} pieces of composed of the diode D ₃ to D ₅ for preventing reverse flow. Each of the capacitors C ₃ and C ₄ and each of the resistors R ₃ and R ₄ are connected in series, and each output terminal of the low-frequency generation circuit 13 is connected to each series circuit. The diodes D ₃ and D ₄ are provided between the connection point of each of the capacitors C ₃ and C ₄ and each of the resistors R ₃ and R ₄ and one input terminal of the comparison circuit 18 so that the comparison circuit 18 side becomes a cathode. Is inserted into. The diode D ₅ is the cathode is connected to the connection point of the comparator circuit 18 and the diode D _3, D _4, the anode is connected to the output terminal of the differential amplifier circuit 17. According to this configuration, both outputs of the low frequency generating circuit 13 are turned on alternately as shown in FIGS. 2A and 2B, and each of the capacitors C ₃ and C ₄ and each of the resistors R _3, the potential at the connection point between R ₄ will vary as FIG. 2 (c) (d). Here, the output level of the low frequency generation circuit 13 is
Figure 2 relative to the output level V _X of the differential amplifier circuit 17 (c)
The level is adjusted so that the relationship as shown in (d) is obtained. As a result, a signal as shown in FIG. 2 (e) is inputted to the positive input terminal of the comparison circuit 18. That is, the level to be compared with the output of the sawtooth wave generating circuit 16 changes during a half cycle of the discharge as shown in FIG. 2 (e).
If one input to the comparison circuit 18 to be compared with the departure of the sawtooth generation circuit 16 changes in this way, the on-periods of the switching elements Q ₁ and Q ₂ become longer immediately after the polarity inversion, and then gradually become shorter. After a certain period of time, the operation state changes to the same operation state as the conventional one. Accordingly, control is performed so that the lamp current is increased immediately after the polarity reversal and the lamp current is decreased to the normal level after a predetermined time.
Since the change is opposite to the change tendency of the lamp current shown in (1), the lamp current is kept almost constant as a result. In this manner, the lamp current becomes substantially constant during the half cycle of the discharge, so that an increase in the ripple component is suppressed and flicker is prevented.

Embodiment 2 As shown in FIG. 3, a low-frequency generation circuit 13 in this embodiment includes a pulse generation circuit 20, a flip-flop circuit 21,
It is composed of a pair of NAND circuits 22a, 22b and the like. That is, a pulse signal is output from the pulse generation circuit 20,
The flip-flop circuit 21 and the NAND circuits 22a and 22b convert the output into a pair of outputs that are turned on alternately. Therefore, the polarity is inverted each time the output of the pulse generation circuit 20 rises. The correction circuit 4 is configured to receive the output of the pulse generation circuit 20 and obtain an output in which only the positive output in FIGS. 2C and 2D is synthesized. That is, the correction circuit 4 includes a monostable multivibrator 23 which is triggered by the rise of the output of the pulse generating circuit 20, a time constant circuit consisting of a capacitor C ₆ and a resistor R ₆ connected to the output terminal of the monostable multivibrator 23 When, is constituted by a diode D ₆ whose anode is connected to a connection point between the capacitor C ₆ and the resistance R _6, the cathode of the diode D ₆ is input of the comparator circuit 18 and the output terminal of the differential amplifier circuit 17 in FIG. 6 It is designed to be connected between the ends. However, each time the polarity of the lamp current by inverting the output of the low frequency generation circuit 13 is inverted, a pulse of a predetermined time width is output from the monostable multivibrator 23, the connection point between the capacitor C ₆ and a resistor R ₆ The change in potential is diode D ₆
Is input to the comparison circuit 18 via the. Thus,
A signal obtained by synthesizing the positive signal in FIGS. 2C and 2D can be obtained. Example 1 for other operations
In the same manner as above, during the half cycle of the lamp current, control is performed so as to increase the lamp current immediately after the polarity reversal, and then gradually decrease the lamp current and return the lamp current to a normal state after a certain period of time. You can do it. In each of the above embodiments, the inverter 1 shown in FIG. 4 has been exemplified. However, the same effect can be obtained by using a half-bridge type inverter. Also, an example in which the lamp state is detected based on the average value of the lamp current has been described. However, the present invention is not limited to this, and the present invention may be applied to a configuration in which the lamp voltage or light output level is detected. The technical idea of the invention is applicable.

【The invention's effect】

As described above, an inverter that includes a switching element that interrupts the output of a DC power supply at a high frequency and obtains an output obtained by superimposing the high frequency on a multipolar rectangular wave having a frequency lower than the high frequency, and is turned on by an envelope output of the inverter. A control circuit for controlling the on-duty of the switching element such that the lamp current to the discharge lamp becomes substantially constant. The on-duty is gradually reduced for a certain time after the polarity reversal of the lamp current so that the lamp current becomes substantially constant with respect to the change in impedance of the lamp current. The lamp current is kept almost constant against the change, and the increase of the ripple component is suppressed. There is an advantage that flicker of the discharge lamp is prevented.

[Brief description of the drawings]

FIG. 1 is a main part circuit diagram showing an embodiment of the present invention, FIG. 2 is an operation explanatory view of the same, FIG. 3 is a main part circuit diagram showing a second embodiment of the present invention, and FIG. 5, FIG. 5 is an operation explanatory diagram of the above, FIG. 6 is a main part circuit diagram of the above, and FIGS. 7 and 8 are operation explanatory diagrams of the above. 1 ...... inverter, 2 ...... discharge lamp, 3 ...... control circuit, 4 ...... correction circuit, Q ₁ to Q ₄ ...... switching element.

Claims (1)

(57) [Claims] 1. An inverter having a switching element for interrupting the output of a DC power supply at a high frequency and providing an output obtained by superposing the high frequency on a multipolar rectangular wave having a frequency lower than the high frequency, and lighting by an envelope output of the inverter. And a control circuit for controlling the in-duty of the switching element so that the lamp current to the discharge lamp becomes substantially constant, wherein the control circuit operates within a half cycle of the lamp current to the discharge lamp. A discharge lamp lighting device characterized in that the on-duty is gradually reduced for a certain period of time after the reversal of the polarity of the lamp current so that the lamp current becomes substantially constant with respect to a change in impedance of the discharge lamp.