JP3197167B2 - Lighting circuit of discharge lamp - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a novel discharge lamp lighting circuit capable of improving control accuracy by obtaining a control line for constant power control of a discharge lamp by approximating the constant power curve with a broken line. What you want to do.

[0002]

2. Description of the Related Art In recent years, small metal halide lamps have attracted attention as light sources replacing incandescent light bulbs.
2. Description of the Related Art There has been known an apparatus in which a DC power supply is used as a power supply, and a DC input voltage is boosted, converted to an AC voltage, and then applied to a metal halide lamp.

FIG. 5 shows an example a of a lighting circuit. The voltage is supplied from a battery b as a power supply to a DC power supply circuit d via a lighting switch c, and then converted to an AC voltage by a DC-AC conversion circuit e. It is configured to convert and apply to the metal halide lamp f.

An igniter circuit g generates a high-voltage pulse when the metal halide lamp f is activated, and superimposes the high-voltage pulse on the output of the DC-AC conversion circuit e to supply the pulse to the metal halide lamp f. It is provided after the circuit e.

[0005] h is a control unit, which detects the output voltage and current of the DC power supply circuit d and performs lighting control according to a predetermined control line that defines the lamp voltage-lamp current characteristics.
The control output is sent to the DC power supply circuit d to control the output of the DC power supply circuit d. For example, since the metal halide lamp f has a disadvantage that the starting time becomes longer when the metal halide lamp f is turned on from a cold state, by temporarily supplying power exceeding the rated power at the initial stage of lighting of the metal halide lamp f, Control is performed so as to improve the rising characteristics of the luminous flux, and finally to shift to constant power control at the rated power.

FIG. 6 shows an example of a control line related to constant power control. The horizontal axis indicates a lamp voltage (this is referred to as "VL"), and the vertical axis indicates a lamp current (this is "IL"). ).

[0007] In the figure, i indicates a constant power curve, "V
As is clear from the relationship of “L · IL = constant”, it has a hyperbolic shape.

The control line j at the time of the constant power control is obtained by performing a first-order linear approximation to the constant power curve i, and is a straight line falling to the right where the IL decreases with a certain slope as the VL increases. The range indicated by ΔVt indicates the rated voltage range of the metal halide lamp f.

The control unit h is configured to perform control in accordance with the control line j when controlling the constant power of the metal halide lamp f.

[0010]

In the above-described circuit, since the degree of approximation to the constant power curve is coarse, the error between the constant power curve i and the control line j can be ignored. There is a problem that can not be.

That is, as shown in FIG. 6, the rated voltage range Δ
At the positions near both ends of Vt, the difference becomes noticeable as shown by ΔI1 and ΔI2.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a DC power supply circuit for performing DC voltage step-up and / or step-down control, and converts the output voltage of the DC power supply circuit to an AC voltage. A DC-AC conversion circuit for conversion, a lamp voltage detection circuit for detecting a voltage applied to the discharge lamp or a signal corresponding thereto, a lamp current detection circuit for detecting a current flowing in the discharge lamp or a corresponding signal thereof, and a lamp A control circuit for controlling the output voltage of the DC power supply circuit in accordance with signals from the voltage detection circuit and the lamp current detection circuit, wherein the control circuit defines a characteristic between the lamp voltage and the lamp current A lighting circuit for a discharge lamp in which lighting control is performed according to a line has the following configuration.
It is. The control circuit has a constant power control unit, and the constant power control unit
Detection signals from the pump voltage detection circuit and the lamp current detection circuit
The constant power curve with multiple straight lines
Abbreviation according to control line obtained by performing line approximation
A control signal is sent to the DC power supply circuit to perform lighting control with electric power.
To control the output voltage. ・ The constant power control unit detects the detection signal of the lamp voltage detection circuit and
With the detection signal of the pump current detection circuit at a predetermined ratio.
And the detection signal of the lamp voltage detection circuit.
A detection circuit for obtaining an output multiplied by a constant coefficient,
When the lamp voltage is lower than the predetermined voltage, the output of the adder circuit is
Control so that the lamp voltage exceeds the specified voltage
The sum of the output of the addition circuit and the output of the detection circuit
Control to be constant.

[0013]

According to the present invention, constant power control of a discharge lamp can be performed in accordance with a control line obtained by performing a polygonal line approximation using a plurality of straight lines on a constant power curve. It is possible to improve the accuracy by reducing the error between the lines.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a lighting circuit of a discharge lamp according to the present invention will be described in detail with reference to the illustrated embodiments. The illustrated embodiment shows an example in which the present invention is applied to a lighting circuit of a vehicular discharge lamp.

FIG. 1 is a circuit block diagram showing the overall configuration of the lighting circuit 1. As shown in FIG.

The battery 2 has DC voltage input terminals 3, 3 '.
The lighting switch 4 is connected between the DC booster circuit 5
Is provided on a line connecting the positive side input terminal of the battery and the DC voltage input terminal 3 (connected to the positive electrode of the battery 2). Note that the DC booster circuit 5 may be configured to perform not only boosting but also buck-boost control.

Reference numeral 6 denotes a DC-AC conversion circuit, which is provided for converting the DC output voltage of the DC booster circuit 5 into a rectangular wave voltage and outputting it.

Reference numeral 7 denotes an igniter circuit which generates a trigger pulse when the metal halide lamp 8 is started, and superimposes the trigger pulse on the AC output of the DC-AC conversion circuit 6 to connect the metal halide lamp 8 to the AC output terminals 9 and 9 '. 8 is applied.

Reference numeral 10 denotes a control circuit for controlling the output voltage of the DC booster circuit 5, which includes a current detection unit 11, a voltage detection unit 12, a light emission promotion control unit 13, a constant power control unit 14, a PWM
(Pulse width modulation) control section 15 is provided.

The current detecting section 11 and the voltage detecting section 12 are provided for detecting signals corresponding to the lamp current and the lamp voltage. That is, a current detection signal corresponding to the output current of the DC booster circuit 5 is provided to the current detector 11 by a current detection resistor 16 provided on a ground line connecting the DC booster circuit 5 and the DC-AC converter circuit 6. Is input in a voltage-converted form. Further, the output voltage of the DC booster circuit 5 is input to the voltage detector 12. The lamp voltage and lamp current may be detected directly, but in the present embodiment, signals corresponding to these are detected.

The light emission promotion control unit 13 is provided for temporarily supplying power equal to or higher than the rated power to the metal halide lamp 8 to promote light emission when the metal halide lamp 8 is turned on from a cold state. Detection signals from the detection unit 11 and the voltage detection unit 12 are input.

The constant power control section 14 is in charge of constant power control of the metal halide lamp 8, and
1. A detection signal from the voltage detection unit 12 is input. The constant power control unit 14 is configured to perform constant power control of the metal halide lamp 8 according to a control line obtained by applying a polygonal line approximation to a constant power curve using a plurality of straight lines.

Light emission promotion control unit 13 and constant power control unit 14
Are output to the PWM control unit 15 after being added.
A control signal generated by the PWM control unit 15 is fed back to the DC boosting circuit 5.

FIG. 2 shows a current detector 11, a voltage detector 12,
The constant power control unit 14 is taken out and schematically shows the configuration thereof.

The voltage detector 12 is configured as a voltage buffer using an operational amplifier. The output voltage of the DC booster 5 is divided by the voltage dividing resistors 17 and 17 ', and then the non-inverting input of the operational amplifier 18 is supplied. Sent to the terminal.

The current detecting section 11 is adapted to send the terminal voltage of the current detecting resistor 16 to an operational amplifier 19 having a differential amplifier configuration. That is, one end of the current detection resistor 16 is connected to the inverting input terminal of the operational amplifier 19 via the resistor 20, the other end of the current detection resistor 16 is grounded via the resistors 21 and 21 ', and Nineteen non-inverting input terminals are connected between the resistors 21 and 21 '. A feedback resistor 22 is interposed between the output terminal of the operational amplifier 19 and the inverting input terminal.

The constant power control unit 14 includes two operational amplifiers 2
3 and 24. That is, the operational amplifier 2
Reference numeral 3 designates a buffer (ideal diode circuit) by providing a diode 25 at its output stage, and the output voltage of the DC booster circuit 5 is divided at its non-inverting input terminal by resistors 26 and 26 '. A voltage is supplied. The output terminal of the operational amplifier 23 is connected to the anode of the diode 25, and the cathode of the diode 25 is connected to the inverting input terminal of the operational amplifier 23 and grounded via the resistors 27 and 28.

The operational amplifier 24 has a configuration of a differential inverting amplifier. The output of the current detecting section 11 and the output of the voltage detecting section 12 are added and input to the inverting input terminal thereof.
That is, the output terminal of the operational amplifier 19 of the current detector 11 is grounded via the resistors 29 and 30, and the output terminal of the operational amplifier 18 of the voltage detector 12 is connected to the resistors 29 and 30 via the resistor 31. Between the resistor 30
Is supplied to the inverting input terminal of the operational amplifier 24. The non-inverting input terminal of the operational amplifier 24 is supplied with a reference voltage from the constant voltage source E1. Note that a feedback resistor 24a is interposed between the output terminal and the inverting input terminal of the operational amplifier 24.

The output of the operational amplifier 24 is connected via a resistor 32 to a connection point between the resistor 27 and the resistor 28 (hereinafter referred to as a “point Pa”). It becomes the input potential of the PWM control unit 15. Although not shown, the output of the light emission promotion control unit 13 is also supplied to this point Pa.

In this circuit, the output voltage of the DC booster circuit 5 is set to “Vo”, the voltage conversion value of the output current of the DC booster circuit 5 by the current detecting resistor 16 is set to “Io”, and the output of the voltage detector 12 is set to “Io”. V12 ", the output of the current detection unit 11 is" V11 ", and the amplification factor of the voltage detection unit 12 is" A "and the amplification factor of the current detection unit 11 is" B ". A relationship is obtained.

[0031]

(Equation 1)

The operational amplifier 23 and the diode 25
, And the amplification factor of the circuit including the operational amplifier 23 and the resistors 26 and 26 'is represented by "C".

[0033]

(Equation 2)

In the circuit of FIG. 2, control is performed by the feedback control of the PWM control method so that the potential at the point Pa is always kept constant. When the value of the output voltage Vo exceeds a certain threshold value, the output V23 becomes high. The potential is set to exceed the potential (E1) of the point Pa. That is, in the case of V23 ≦ E1, the following equation is obtained by using the equation [1], assuming that the current flowing through the resistor 28 is equal to the current flowing through the resistor 32 provided at the output stage of the operational amplifier 24. Obtainable.

[0035]

(Equation 3)

In the above equation, "R" represents the resistors 24a, 31,
32, and “R28” is the resistance value of the resistor 28,
“R29” is the resistance value of the resistor 29, and “R30” is the resistor 30
Are shown, respectively.

When V23> E1, it is assumed that the difference between the current flowing through the resistor 28 and the current flowing through the resistor 27 is equal to the current flowing through the resistor 32 provided at the output stage of the operational amplifier 24. The following equation can be obtained by using the equations [1] and [Equation 2].

[0038]

(Equation 4)

Note that R and R28 to R30 in the above equation are as described above, and "R27" indicates the resistance value of the resistor 27.

FIG. 3 shows a constant power curve and two approximate straight lines with respect to Vo, which corresponds to the lamp voltage on the horizontal axis and Io corresponding to the lamp current on the vertical axis. The point Vt on the Vo axis indicates the value of Vo when V23 = E1, and the range indicated by ΔVt indicates the rated voltage range.

In the figure, reference numeral 33 denotes a constant power curve, and the constant power curve 33 is approximated by broken lines using straight lines 34 and 35. That is, a straight line 34 located in a region below Vt in ΔVt is expressed by the following equation (3), and a straight line 3 located in a region exceeding Vt in ΔVt.
5 is represented by [Equation 4]. As can be seen from a comparison between Expression 3 and Expression 4, the straight line 35 has a gentler slope and a smaller intercept value with respect to the Io axis.

The power value at a point on the constant power curve 33 is apparent from the fact that it corresponds to a straight line extending through the point parallel to the vertical and horizontal axes and the area of a rectangle surrounded by the vertical and horizontal axes. By applying a polygonal line approximation to the hyperbolic constant power curve 33 using two straight lines 34 and 35, the lower area of the constant power curve 33 and the lower areas of the straight lines 34 and 35 can be approximated.

It goes without saying that the degree of approximation can be increased by increasing the number of straight lines in such a broken line approximation.

For example, as shown in FIG.
, And a buffer 37, may be connected in parallel. That is, the voltages V11 and V12 are supplied to the resistors 39 and 40, respectively.
0 is grounded via a resistor 41,
Is supplied to the inverting input terminal of the operational amplifier 42 constituting the adding circuit 36. The reference voltage from the constant voltage source 43 is supplied to the non-inverting input terminal of the operational amplifier 42. The output of the operational amplifier 42 is connected to the non-inverting input terminal of the operational amplifier 46 forming the buffer 37 via the resistors 44 and 45. Connected to terminal. Then, the output of the operational amplifier 46 is sent to the PWM control unit 15 via the diode 47, and is returned to the inverting input terminal of the operational amplifier 46.

The circuits 38, 38,
.. Are set so that the addition ratios to the detection voltages V11 and V12 are different from each other.
By taking the R output and sending it to the PWM control unit 15,
The line approximation to the constant power curve can be performed by the number of straight lines corresponding to the number of the circuits 38, 38,.

Incidentally, in the circuits 38, 38,..., When it is desired to increase the number of straight lines constituting the control line related to the constant power control, circuits of the same configuration differing only in the circuit constant are arranged in series. Although there is an advantage that it can be done, resistances 41 and 4
The adjustment of the resistance values of 1,... Leaves the trouble of having to adjust the rated power of the control line separately, but the configuration of the constant power control unit 14 shown in FIG.
There is an advantage that the resistor 30 can be used as a resistor for adjusting the rated power that is common to V11 and V12 (that is, by simply changing one resistance value R30, the equation (3) or the equation (4) ], The intercept value of the Io axis can be changed.)

[0047]

As is apparent from the above description, according to the first aspect of the present invention, the discharge lamp is fixed in accordance with the control line obtained by the polygonal line approximation using a plurality of straight lines with respect to the constant power curve. Since power control can be performed,
An error between the constant power curve and the approximate control line can be reduced to improve accuracy.

An addition circuit for adding the detection signal of the lamp voltage detection circuit and the detection signal of the lamp current detection circuit at a predetermined ratio, and an output for multiplying the detection signal of the lamp voltage detection circuit by a predetermined coefficient are obtained. And a control circuit for controlling the output of the addition circuit to be constant when the lamp voltage is lower than a predetermined voltage, and for detecting the output of the addition circuit when the lamp voltage exceeds the predetermined voltage. Of the constant power curve can be divided into a plurality of lamp voltage ranges, thereby facilitating power adjustment for the control line.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a configuration of a lighting circuit of a discharge lamp according to the present invention.

FIG. 2 is a circuit diagram showing a main part of a lighting circuit of a discharge lamp according to the present invention.

FIG. 3 is a diagram showing a constant power curve and a control line obtained by applying a polygonal line approximation to the constant power curve.

FIG. 4 is a circuit diagram showing a modification of the constant power control unit.

FIG. 5 is a circuit block diagram illustrating a configuration example of a conventional lighting circuit.

FIG. 6 is a graph for explaining a conventional problem.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discharge lamp lighting circuit 2, 5 DC power supply circuit 6 DC-AC conversion circuit 8 Metal halide lamp (discharge lamp) 10 Control circuit 11 Current detection unit (lamp current detection circuit) 12 Voltage detection unit (lamp voltage detection circuit) 14 Constant Power control unit 23, 25, 26, 26 'Detection circuit 24, 29, 30, 31 Addition circuit

Continuation of the front page (56) References JP-A-4-141988 (JP, A) JP-A-7-263158 (JP, A) JP-A-7-45390 (JP, A) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H05B 41/14-41/298

Claims (1)

(57) [Claims] 1. A DC power supply circuit for performing a step-up and / or step-down control of a DC voltage, a DC-AC conversion circuit for converting an output voltage of the DC power circuit into an AC voltage, and a voltage applied to a discharge lamp or a signal corresponding thereto. A lamp voltage detection circuit for detecting the current flowing through the discharge lamp or a signal corresponding thereto, and a DC power supply circuit in accordance with signals from the lamp voltage detection circuit and the lamp current detection circuit. and a control circuit for controlling the output voltage, in the lighting circuit of the discharge lamp to perform lighting control in accordance with a predetermined control line which define the characteristics between the lamp voltage and the lamp current by the control circuit, (a ) control circuit has a constant power control unit, the constant power control unit receives the detection signal from the lamp voltage detection circuit and the lamp current detection circuit, a plurality of by straight lines to the constant power curve Sends a control signal to the DC power supply circuit to perform a lighting control in Ryakujo power according to the control lines obtained by performing the is line approximation that so as to control its output voltage, (ii) the The constant power controller detects the lamp voltage detection circuit.
A predetermined ratio between the signal and the detection signal of the lamp current detection circuit
Addition circuit to add by detection and detection of lamp voltage detection circuit
A detection circuit for obtaining an output obtained by multiplying the signal by a predetermined coefficient;
When the lamp voltage is equal to or lower than a predetermined voltage, an adding circuit is provided.
Control so that the output of the
If the pressure exceeds the output, the output of the addition circuit and the output of the detection circuit
A lighting circuit for a discharge lamp, characterized in that control is performed so that the sum of the power and the power becomes constant .