JP2011060703A - Lamp lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lamp lighting device for achieving smooth dimming by suppressing a sudden change in the light quantity. <P>SOLUTION: The lamp lighting device includes: a control part for switching-controlling a switching element to which DC voltage is input; a converter transformer having a secondary winding in which AC voltage is excited with the switching output of the switching element; a lamp to be lit by using the AC voltage excited in the secondary winding; a control voltage-generating part for generating control voltage to dim the lamp; a dimming circuit for driving the switching element in a voltage dimming or burst dimming mode, the dimming circuit including an error amplifier for comparing the control voltage with the output DC voltage of the converter transformer to feedback an error signal to the control part; and a gain control part for controlling the gain of the error amplifier in response to the selection of the voltage dimming or burst dimming mode to suppress a sudden change in the light quantity of the lamp during the selection of the mode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lamp lighting device using a switching power supply circuit, and more particularly to a lamp lighting device capable of preventing a sudden change in the amount of light during lamp dimming and performing smooth dimming.

  Conventionally, a switching power supply circuit is used to drive a load such as a halogen lamp. The switching power supply circuit has a switching element and a converter transformer, switches the switching element at a high frequency to convert a DC voltage into a high-frequency AC voltage, and supplies the high-frequency AC voltage to a load circuit such as a lamp. .

  On the other hand, a dimming circuit is provided to control the brightness of the lamp. There are two methods for controlling the brightness of the lamp: a voltage dimming method that adjusts the voltage (or current) supplied to the lamp for dimming, and a burst control that turns on the lamp intermittently using PWM (Pulse Width Modulation) pulses. There is a light system. In general, both methods are combined, and the lamp is continuously driven by the voltage dimming method in the region where the lamp dimming voltage is high, and the lamp is intermittently driven by the burst dimming method in the region where the lamp dimming voltage is low. I am doing so.

  Patent Document 1 discloses a lighting control device for a discharge lamp driven by an inverter circuit. In the example of Patent Document 1, a circuit that includes a voltage dimming circuit and a PWM dimming circuit (burst dimming circuit) and that reduces a rush current generated when switching from the voltage dimming circuit to the burst dimming circuit is described. ing.

  However, in the example of the prior art and Patent Document 1, since two-stage dimming, voltage dimming and burst dimming, is performed, the amount of light suddenly changes when switching from voltage dimming to burst dimming due to the difference in dimming control. There was a change. For this reason, there was a problem that dimming could not be performed smoothly.

JP 2008-91082 A

  Conventionally, in lamp lighting devices that perform two-stage dimming, voltage dimming and burst dimming, the amount of light may change abruptly when switching from voltage dimming to burst dimming due to differences in dimming control. There was a problem that dimming was not possible.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a lamp lighting device capable of smoothly adjusting light while suppressing a sudden change in light amount.

  According to a first aspect of the present invention, there is provided a lamp lighting device according to the present invention, wherein a switching element that receives a DC voltage from a DC power source, a control unit that controls the switching of the switching element, and a switching output from the switching element are supplied. A converter transformer having a secondary winding, a secondary winding in which an AC voltage is excited by the switching output, and an AC voltage connected to the secondary winding of the converter transformer and excited in the secondary winding A lamp that is turned on, a control voltage generator that generates a control voltage for dimming the lamp, and the control voltage and the output DC voltage of the converter transformer are compared and an error signal is fed back to the controller And an error amplifier that drives the switching element in a voltage dimming mode or a burst dimming mode according to the control voltage. A gain control unit that controls a gain of the error amplifier in accordance with the mode switching between the voltage dimming and the burst dimming and suppresses a sudden change in the light amount of the lamp in the mode switching. It is characterized by.

  In the lamp lighting device of the present invention according to claim 5, a DC voltage from a DC power source is input to a switching element, the switching element is switching-controlled by a control unit, and a switching output from the switching element is supplied to a converter transformer. Supply to the secondary winding, excite an AC voltage in the secondary winding of the converter transformer by the switching output, use the AC voltage excited in the secondary winding of the converter transformer to light the lamp, A control voltage for dimming the lamp is generated, the control voltage and the output DC voltage of the converter transformer are compared by an error amplifier, and an error signal is fed back to the control unit, and the switching element according to the control voltage Drive in voltage dimming or burst dimming mode, and the voltage dimming and burst dimming Controlling a gain of the error amplifier in accordance with the over de switching, which comprises suppressing the sudden change of the light amount of the lamp in the switching of the mode.

  In the lamp lighting device of the present invention, even when switching from voltage dimming to burst dimming at the time of lamp dimming, by changing the feedback gain by the gain control unit, it is possible to avoid a sudden change in the light amount of the lamp, Dimming can be performed smoothly.

The circuit diagram which shows the structure of the lamp lighting device which concerns on one Embodiment of this invention. The circuit diagram which shows an example of the light control circuit in the embodiment. The wave form diagram explaining operation | movement of the light control discrimination circuit in the embodiment. The characteristic view which shows the change of a lamp current when the control voltage for light control is varied. The circuit diagram which shows the modification of a light control circuit.

  Hereinafter, an embodiment of a lamp lighting device of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram showing a configuration of a lamp lighting device 100 of the present invention. The lamp lighting device 100 includes an AC power supply 11, a full-wave rectifier circuit 12, a PFC (Power Factor Correction) circuit 13, a resonant converter 15, a lamp 17 such as a halogen lamp, and a dimming circuit 20. The AC power supply 11, the full-wave rectifier circuit 12, the PFC circuit 13, and the converter 15 constitute a switching power supply circuit.

  The AC power supply 11 is full-wave rectified by a full-wave rectifier circuit 12 and supplies a DC voltage to the PFC circuit 13. The PFC circuit 13 is a power factor correction circuit that boosts the DC voltage rectified by the full-wave rectifier circuit 12. The PFC circuit 13 includes a boost converter including an inductance element L1 and a diode D1, a switching element Q1 connected to a connection point between the inductance element L1 and the diode D1, a smoothing capacitor C1, and a control IC.

  The voltage across the smoothing capacitor C1 is proportional to the output voltage of the PFC circuit 13, and this output voltage is fed back to the control IC 14. A control pulse for driving the switching element Q1 is output from the control IC 14, and the output voltage is stabilized by controlling the switching element Q1 on and off according to the feedback voltage. Such a PFC circuit 13 is also called an active filter. The PFC circuit 13 constitutes a DC voltage source for the converter 15.

  Converter 15 includes switching elements Q2 and Q3 connected in series between the output terminal of PFC circuit 13 and a reference potential point (ground). The DC voltage from the PFC circuit 13 is input to the drain of the switching element Q2, the source is connected to the drain of the switching element Q3, and the source of the switching element Q3 is connected to the reference potential point (earth). A series resonance circuit including a primary winding T1 of a converter transformer T and a capacitor C2 is connected between the connection point of the switching elements Q2 and Q3 and the ground. Further, the PWM signal from the control unit 16 is supplied to the gates of the switching elements Q2 and Q3, and the switching elements Q2 and Q3 perform a complementary switching operation at a predetermined frequency (or a constant frequency) by the PWM signal.

  A switching output is obtained at the connection point of the switching elements Q2 and Q3, and the series circuit of the primary winding T1 of the transformer T and the capacitor C2 is current-resonated by this switching output, and an AC voltage is applied to the secondary winding T2 of the transformer T. Is excited. For example, a lamp 17 is connected to both ends of the secondary winding T2 of the transformer T as a load circuit, and the lamp 17 is AC lit by the AC voltage of the secondary winding T2. Further, the AC voltage VA of the secondary winding T2 is supplied to the dimming circuit 20.

  The tertiary winding T3 of the transformer T is connected to a rectifying / smoothing circuit composed of a diode D2 and a capacitor C3. By dividing the rectified / smoothed output voltage by a series circuit of resistors R1 and R2, a converter is obtained. An output DC voltage VB of the transformer T can be obtained. The voltage VB is fed back to the dimming circuit 20.

  The dimming circuit 20 includes a variable resistor (volume) that generates a control voltage for dimming, and the light amount of the lamp 17 can be adjusted by adjusting the volume. The dimming circuit 20 controls the control unit 16 according to changes in the control voltage by adjusting the volume, the AC voltage VA of the secondary winding T2 of the transformer T, and the output DC voltage VB divided by the resistors R1 and R2. An error amplifier that feeds back an error signal is included, and the controller 16 is controlled in accordance with the control voltage V1. For example, the lamp 17 is dimmed by changing the AC voltage VA by controlling the ON / OFF cycle of the switching elements Q2, Q3. Further, burst dimming is performed by operating the switching elements Q3 and Q4 in a pause period and a driving period. The control unit 16 is configured by an integrated circuit (IC).

  Thus, the converter 15 operates as a current resonance type, and the frequency of the output AC voltage of the secondary winding T2 of the transformer T is changed by controlling on / off of the switching elements Q2, Q3 by the PWM signal.

  Hereinafter, details of the dimming circuit 20 will be described with reference to FIG. The dimming circuit 20 includes a volume circuit 21, a negative feedback circuit 22 including an operational amplifier (error amplifier) A21, and a dimming determination circuit 23. The volume circuit 21 is a series circuit of a variable resistor R21, a resistor 22, and a resistor R25 connected between the voltage source V20 and a reference potential point (earth). The variable resistor R21 is connected to the connection point between the variable resistor R21 and the resistor 22 with the variable resistor R21. A dimming control voltage V1 caused by the change can be obtained. The volume circuit 21 constitutes a control voltage generation unit.

  The negative feedback circuit 22 includes an operational amplifier A21. An output DC voltage VB divided by resistors R1 and R2 is input to the non-inverting input terminal (+) of the operational amplifier A21, and a resistor R23 is input to the inverting input terminal (−). The control voltage V1 for dimming is input via A capacitor C21 and a resistor R24 are connected in parallel between the inverting input terminal (−) of the operational amplifier A21 and the output terminal. A switch SW1 is connected in parallel with the resistor R25. The switch SW1 is preferably composed of an electronic switch such as a transistor. The resistor R25 and the switch SW1 constitute a gain control unit.

  Based on the waveform of the AC voltage VA of the secondary winding T2 of the transformer T, the dimming discrimination circuit 23 switches the control of the lamp 17 from voltage dimming to burst dimming, or from burst dimming to voltage dimming. The switch SW1 is turned on / off according to the detection result.

  The light quantity of the lamp 17 is adjusted by changing the variable resistor R21 of the volume circuit 21. For example, when the dimming control voltage V1 is higher than the output DC voltage VB, the mode is the voltage dimming mode, and the controller 16 is controlled to continuously supply the AC voltage VA to the lamp 17, for example, the frequency of the AC voltage. Change the amount of light. Further, when the dimming control voltage V1 is lower than the output DC voltage VB, the mode is a burst dimming mode, and the control unit 16 is controlled to operate the switching elements Q2 and Q3 intermittently during the pause period and the operation period. Then, the control is performed so that the pause period becomes longer as the dimming control voltage V1 becomes lower.

  FIG. 3 is a waveform diagram showing the operation of the dimming determination circuit 23. 3A shows the waveform of the AC voltage VA of the secondary winding T2 of the transformer T during voltage dimming, and FIG. 3B shows the secondary winding T2 of the transformer T during burst dimming. The waveform of AC voltage VA is shown. The dimming determination circuit 23 determines whether the voltage dimming mode or the burst dimming mode from the change in the peak value of the AC voltage VA. For example, if the period when the peak value is zero continues for a predetermined time or more, it is determined that burst dimming (intermittent driving) is started, and thereafter, the period when the peak value is high and the period when the peak value is zero continue. In this case, it is determined that the mode has shifted to the burst dimming mode. Conversely, when the burst dimming is changed to the voltage dimming mode, the determination is made from the change in the peak value of the AC voltage VA.

  Returning to FIG. 2, the switch SW1 of the gain control unit is turned on / off in response to the discrimination result of the dimming discrimination circuit 23, and is turned off (open) at the time of voltage dimming, and is in series with the resistor R22. R25 is connected and the feedback gain is increased. Further, it is turned on (closed) during burst dimming, the resistor R25 is short-circuited, and the feedback gain is lowered during burst dimming.

  That is, when the switch SW1 is not provided, the feedback gain of the negative feedback circuit 22 is constant, so that the control method changes when the voltage dimming mode is switched to the burst dimming mode, so that the light amount of the lamp 17 changes suddenly. However, in the present invention, when the voltage dimming is switched to the burst dimming, the resistor R25 is connected and the gain is lowered, so that a rapid change in the amount of light can be reduced.

  FIG. 4 is a characteristic diagram showing a change in the current of the lamp 17 when the light control voltage V1 is varied by the volume circuit 21. As shown in FIG. The horizontal axis in FIG. 4 indicates the control voltage V1, and the vertical axis indicates the lamp current IL. On the horizontal axis, t1 represents a burst dimming period, and t2 represents a voltage dimming period. For example, when the lamp 17 is controlled by voltage dimming, when the control voltage V1 falls below a predetermined value, the mode is switched to the burst dimming (intermittent drive) mode.

  Conventionally, the lamp current image changes abruptly as shown by the characteristic A at the moment of switching to burst dimming, and the light quantity of the lamp 17 does not change smoothly. On the other hand, in the present invention, when switching from voltage dimming to burst dimming, the feedback gain of the negative feedback circuit 22 decreases, so that the lamp current IL changes rapidly even when the burst dimming is changed as shown by the characteristic B. You can avoid doing it. Therefore, the light can be adjusted smoothly without abrupt change in the amount of light.

  Note that when the gain is switched at the moment when the voltage dimming is switched to the burst dimming, the lamp current (voltage) may change suddenly to cause an unnecessary oscillation phenomenon. Therefore, the dimming discrimination circuit 23 has a hysteresis characteristic. It is preferable to switch the switch SW1 with a predetermined delay time from the moment of switching from voltage dimming to burst dimming (or burst dimming to voltage dimming).

  FIG. 5 is a diagram illustrating a modification of the light control circuit 20. In FIG. 5, the switch SW1 is turned on / off by the dimming control voltage V1. That is, since the dimming circuit 20 switches from the voltage dimming mode to the burst dimming mode when the voltage V1 at the connection point between the variable resistor R21 and the resistor R22 of the volume circuit 21 becomes equal to or lower than a predetermined voltage, the voltage V1 The switch SW1 is turned on when the value becomes equal to or less than a preset value, and the switch SW1 is turned off when the value becomes equal to or greater than a preset value. In the example of FIG. 5, the same characteristics as in FIG. 4 can be obtained.

  As described above, in the present invention, even when the voltage dimming is switched to the burst dimming when the lamp 17 is dimmed, the feedback gain of the negative feedback circuit 22 is changed, so that the light quantity of the lamp 17 is prevented from changing rapidly. Can be dimmed smoothly.

  The embodiment of the present invention is not limited to the configuration described above. Various modifications can be made without departing from the scope of the claims.

DESCRIPTION OF SYMBOLS 100 ... Lamp lighting device 11 ... AC power supply 12 ... Full wave rectifier circuit 13 ... PFC circuit 14 ... Control IC
DESCRIPTION OF SYMBOLS 15 ... Converter 16 ... Control part 17 ... Lamp 20 ... Dimming circuit 21 ... Volume circuit (control voltage production | generation part)
22 ... Negative feedback circuit 23 ... Dimming discrimination circuit Q2, Q3 ... Switching element T ... Converter transformer T1 ... Primary winding,
T2 ... secondary winding C2 ... capacitor A21 ... operational amplifier (error amplifier)
R21 ... Variable resistors R22 to R25 ... Resistor SW1 ... Switch (gain control unit)

Claims (5)

A switching element that receives a DC voltage from a DC power supply;
A control unit that performs switching control of the switching element;
A primary transformer to which a switching output from the switching element is supplied; a converter transformer having a secondary winding in which an alternating voltage is excited by the switching output;
A lamp connected to the secondary winding of the converter transformer and lit using an alternating voltage excited by the secondary winding;
A control voltage generating unit that generates a control voltage for dimming the lamp; and an error amplifier that compares the control voltage with an output DC voltage of the converter transformer and feeds back an error signal to the control unit. A dimming circuit that drives the switching element in voltage dimming or burst dimming mode according to
A gain control unit that controls the gain of the error amplifier in accordance with the mode switching between the voltage dimming and the burst dimming, and suppresses a sudden change in the light amount of the lamp in the mode switching. Lamp lighting device to do. The control voltage generation unit includes a series circuit of a variable resistor, a first resistor, and a second resistor connected between a voltage source and a reference potential point, and is generated at a connection point between the variable resistor and the first resistor. Supplying a control voltage to the input of the error amplifier;
2. The gain control unit includes a switch connected in parallel to one of the first and second resistors, and turns on / off the switch in response to switching of the mode. Lamp lighting device. Based on the alternating voltage waveform excited in the secondary winding, comprising a determination unit for determining a change in mode of the voltage dimming and the burst dimming with a hysteresis characteristic,
The lamp lighting device according to claim 2, wherein the switch of the gain control unit is turned on / off according to a determination result of the determination unit.   3. The lamp lighting device according to claim 2, wherein when the control voltage for dimming the lamp reaches a preset voltage value, the switch of the gain control unit is turned on / off. Input the DC voltage from the DC power supply to the switching element,
The switching control of the switching element by the control unit,
A switching output from the switching element is supplied to a primary winding of the converter transformer, and an alternating voltage is excited in the secondary winding of the converter transformer by the switching output;
The lamp is turned on using the AC voltage excited in the secondary winding of the converter transformer,
Generating a control voltage for dimming the lamp;
The control voltage and the output DC voltage of the converter transformer are compared by an error amplifier, an error signal is fed back to the control unit, and the switching element is driven in a voltage dimming mode or burst dimming mode according to the control voltage. And
A lamp lighting device characterized by controlling the gain of the error amplifier in accordance with the mode switching between the voltage dimming and the burst dimming to suppress a sudden change in the light amount of the lamp at the mode switching.

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