JP2000012258A - Lighting control circuit for high illumination discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely and stably light a discharge lamp according to the state of the lamp by detecting lamp extinguished time, controlling the term setting of one period of applying AC voltage soon after lighting, and controlling lamp current setting. SOLUTION: A control circuit 5 detects the time elapsed after operation of lights-out based on the terminal voltage of a capacitor with a time detecting circuit comprising a CR charge/discharge circuit. Since the shorter lights-out, the hotter a lamp, a driver 6 of an inverter 3 is controlled, the term of one period of AC voltage soon after lighting, supplied to the lamp is lengthened, lamp voltage information and lamp current information are inputted, a D/D converter 1 is controlled, and the shorter the lights-out, the lower the lamp current of one period soon after lighting. Thereby, excess power supply in the hot state is prevented. In a lamp cooled state after long lights-out, the term of one period is set shorter, and lamp current is set higher to surely keep lighting at the activation of the lamp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting control circuit for a high-intensity discharge lamp used for a vehicle headlight or the like.

[0002]

2. Description of the Related Art In recent years, studies have been made on the use of a high-intensity discharge (HID) lamp, which has higher luminous efficiency and higher illuminance than a halogen lamp, as a headlight of an automobile. When the lighting of a high-intensity discharge lamp is controlled, the brightness largely depends not only on the power consumption of the lamp but also on the temperature of the lamp (steam therein). In other words, when the high-intensity discharge lamp is lit with constant power, the luminous flux is small in the cold state of the lamp immediately after starting, and the luminous flux gradually increases as the temperature rises and shifts to a stable lighting state (steady mode), and the lamp is steadily lit. In this state, the luminous flux is substantially constant.

For this reason, in order to use a high-intensity discharge lamp in applications requiring rapid rise of light flux and stability of light speed, such as a headlight of an automobile, for example, electric power is appropriately adjusted according to the temperature of the lamp. Need to be controlled. However, since it is difficult to directly monitor the temperature of the lamp, instead of monitoring the temperature of the lamp, the elapsed time after turning on and off the lamp is detected, and the power of the lamp is controlled accordingly.

In this case, in a cold start in which the power is turned on by a lighting switch or the like to start lighting when the lamp is cold, the temperature of the lamp can be estimated from the time since the power was turned on. In a hot start in which the lamp in the lighting state is once turned off and then turned on again without a long interval, the state before turning off and the length of the turning-off time are indicators of the lamp temperature at restart.

As a method for estimating such a temperature, FIG.
There is known a device which counts the on / off time of a power supply using a CR charge / discharge circuit using a capacitor C and a resistor R as shown in FIG. In the charge / discharge circuit of FIG. 6, when the power supply Vcc is supplied, the terminal voltage Vc of the capacitor C changes as shown in the voltage waveform diagram of the capacitor of FIG. That is, when the power supply Vcc is turned on, charging of the capacitor C is started, and when the power supply Vcc is turned off, the charge stored in the capacitor C is discharged.

That is, the terminal voltage Vc of the capacitor C changes with time except for the period from the end of charging to the start of discharging (stable lighting state).
The on / off time of the power supply can be obtained from the terminal voltage Vc, and the lamp temperature can be estimated.

On the basis of the lamp temperature thus obtained, power control is performed such that when the temperature of the lamp is low, a large amount of electric power is supplied and the electric power is decreased as the temperature rises. By the way, after the lamp is turned on, the power is controlled as described above, so that the lighting operation is stably maintained, but is unstable immediately after lighting, and the lamp is turned on once if necessary and sufficient power is not supplied in a short time. Even so, it can happen that they disappear quickly.

Therefore, in Japanese Patent Application Laid-Open No. 2-136342, the lamp current at the time of starting the lighting of the discharge lamp or at the time of restarting is controlled in accordance with the extinguishing time of the high-pressure discharge lamp to obtain a specified brightness. The time it takes to become is shortened.

There is also a method in which a period during which power is supplied at a frequency different from a normal lighting frequency is provided immediately after the lamp is turned on in order to reliably maintain lighting immediately after the lamp is turned on. The power supplied during this period is determined according to the length of the period and the value of the current flowing through the lamp.

[0010]

It is necessary to set appropriate values for the length of the period and the value of the current flowing through the lamp in accordance with the temperature of the lamp. That is, since it is difficult to maintain lighting immediately after lighting in a cold lamp, it is desirable that the current value be high. However, if the current value is high in a hot lamp, excessive stress may be applied to the lamp. As described above, in the control during this period immediately after the lighting, the necessary current value and the length of the period differ depending on the temperature state of the lamp. There was no control.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a lighting control circuit for a high-intensity discharge lamp which reliably and stably lights a lamp according to the state of the lamp in control immediately after the lamp is turned on. Is to provide.

[0012]

According to the present invention, a DC power supply for supplying a DC voltage, a conversion circuit for converting a DC voltage supplied from the DC power supply to an AC voltage, and In a lighting control circuit for a high-intensity discharge lamp including a high-intensity discharge lamp that is turned on by being supplied with an AC voltage by a conversion circuit, a light-off time detecting means for detecting a time when the lamp is turned off, and the light-off time detecting means When it is detected that the turn-off time of the lamp is short, the period of one cycle immediately after the lamp is turned on of the AC voltage supplied to the lamp is set longer, and the lamp is supplied to the lamp during the one cycle. A setting unit for setting the flowing lamp current to be small.

The setting unit may include a period of the one cycle,
The method is characterized in that the product of the lamp current flowing through the lamp and the current value during the one cycle period is set to a constant value.

[0014] The setting unit may include a period of the one cycle,
The current value of the lamp current flowing through the lamp during the one cycle is set steplessly based on the output of the turn-off time detecting means.

[0015] The setting unit may determine the period of the one cycle when the time during which the lamp is turned off is zero and the period of the one period.
A first setting unit that sets a current value of a lamp current flowing through the lamp during a period; and a period of the one period when the time during which the lamp is turned off is infinite and a period of the one period. A second setting unit configured to set a current value of a lamp current flowing through the lamp; and a current of the lamp current flowing through the lamp during the one cycle period and the one cycle period according to a time during which the lamp is turned off. And an adjusting unit for adjusting the value.

[0016]

Embodiments of the present invention will be described below.

FIG. 1 is a block diagram of a lighting control circuit for a high-intensity discharge lamp according to the present invention. Reference numeral 1 denotes a D / D converter circuit which boosts a DC voltage from a battery power source which is a DC power source to a voltage required for discharging and lighting a lamp 2 which is a high-intensity discharge lamp, and converts the boosted DC voltage to a conversion circuit. Is converted to an AC voltage by the full-bridge inverter circuit section 3 and supplied to the lamp 2. Numeral 5 reads the voltage Vvla applied to the lamp 2 from V and the voltage Vila corresponding to the current flowing through the lamp 2 from I, controls the full-bridge inverter circuit unit 3 via the driver 6, and outputs D / This is a control circuit that controls the boosting of the D converter circuit 1. Reference numeral 7 denotes a lighting switch for switching the lighting state of the lamp 2, and reference numeral 4 denotes an igniter for generating an ignition signal for starting ignition of the lamp 2.

The operation of the lighting control circuit for a high illuminance discharge lamp thus configured will be described with reference to the time chart of FIG. First, as shown in FIG.
Is turned on, the control circuit 5 outputs a waveform signal HFOUT to the D / D converter 1 as shown in FIG.
Converter 1 performs boosting.

Next, as shown in FIG.
Rises to a dischargeable voltage, and at time t2, the discharge and lighting of the lamp 2 are started by the ignition signal from the igniter 4. Immediately after this time t2, as described above, the lighting of the lamp becomes unstable. Therefore, the control signal LFOUT output from the control circuit 5 to the driver 6 normally has a period T of one cycle from time t2 to t3 as shown in FIG. Is set to have a frequency different from that at the time of lighting, so that the AC voltage supplied to the lamp 2 also has a frequency different from the normal frequency. After time t3, the normal lighting mode is set, the control signal LFOUT output from the control circuit 5 to the driver 6 has a constant frequency, and the frequency of the AC voltage supplied to the lamp 2 also becomes constant.

At this time, the change in the current value ILA flowing through the lamp 2 is as shown in the following, and the product T * ILA of the period T of one cycle and the amount of current ILA flowing through the lamp 2 during that period.
That is, the energy supplied to the lamp is set to be constant regardless of the state of the lamp.

Next, the details of the control circuit 5 of FIG. 1 will be described with reference to FIG.

FIG. 3 is a block diagram showing the details of the control circuit 5. Reference numeral 11 denotes a time constituted by a CR charge / discharge circuit having a capacitor C and a resistor R between the power supply Vcc and the ground Gnd shown in FIG. This is a count circuit that outputs a terminal voltage Vc of the capacitor C. As described above, since the terminal voltage Vc of the capacitor C changes with the time during which the power supply voltage is applied to the capacitor C, the on / off time of the power supply can be obtained from the terminal voltage Vc of the capacitor C.

When the lamp is turned on and off by operating the power switch by operating the lighting switch, the elapsed time after the lighting operation and the light-off operation can be determined from the terminal voltage Vc of the capacitor C. That is, it can be seen that the smaller the terminal voltage Vc of the capacitor C, the longer the power-off time, the lower the lamp temperature, and the longer the lamp extinguishing time. Therefore, the time during which the lamp 2 is turned off is detected by the time counting circuit 11, and the time counting circuit 11 serves as a turning-off time detecting unit.

Reference numeral 12 denotes a power calculation circuit, which inputs a lamp current value Vila and a lamp voltage value Vvla to calculate the current lamp power, and outputs the calculated value to the D / D converter control circuit 1.
Output to 3. Reference numeral 14 denotes a period setting circuit corresponding to a setting unit, which is based on the terminal voltage value Vc of the capacitor C detected by the time counting circuit 11, that is, based on the turn-off time of the lamp 2 detected by the time counting circuit 11. A period T, which is one cycle immediately after the lamp is turned on, and a lamp current amount ILA flowing through the lamp 2 during that period are set. Then, in accordance with the set period T, the full-bridge inverter control circuit 15 operates the driver 6 shown in FIG.
And the set lamp current amount ILA is
Output to the / D converter control circuit 13.

The D / D converter control circuit 13 sets the voltage to be supplied to the lamp 2 based on the lamp temperature state known from the output value from the time count circuit 11, and sets the current calculated by the power calculation circuit 12. In general, a control signal for controlling the boosting according to the difference is output to the D / D converter 1 in comparison with the lamp voltage of the lamp voltage. A control signal for controlling the boosting based on the lamp current ILA set by the above is output to the D / D converter.

Next, details of the period setting circuit 14 in FIG. 3 will be described with reference to FIG. FIG. 4 is a circuit diagram showing details of the period setting circuit, and is composed of three blocks (1), (2), and (3).

First, the circuit configuration of the block (1) will be described.

The transistors Q13, Q14 and Q15 are
In each case, the emitter is connected to the voltage source and a well-known current mirror circuit is formed.
The collector of Q4 has a capacitor C1 connected to the ground, and the collector of Q15 has a resistor R4 connected to the ground.
Is connected.

The collector of the transistor Q12 is connected to the collector of the transistor Q13, and the resistor R3 is connected between the emitter and the ground. Here, a predetermined reference voltage Vref is applied to the base of the transistor Q12, and the voltage between the base and the emitter is set to V12be.
Then, the collector current I12 flowing to the collector of the transistor Q12 is I12 = (Vref-V12be)
/ R3. A current equal to the collector current I12 is applied to the transistors Q13, Q14 and Q15 by the action of the current mirror circuit.
To the capacitor C1 and the transistor Q
15 flows to the resistor R4 from the collector.

A predetermined reference voltage Vref is input to the inverting input terminal of the COMP1, and the non-inverting input terminal of the COMP1 is connected to the capacitor C1.
Is a comparator to which the terminal voltage Vc1 of the capacitor C1 is input.
and outputs the result as an output signal A.
The output signal A of the comparator COMP1 corresponds to a signal corresponding to a period T outputted from the period setting circuit 14 to the full bridge inverter control circuit 15 in FIG. 3, and if the amount of current flowing through the capacitor C1 is large, the capacitor C1 Is shortened, and accordingly, the period T changes to be shorter.

An output signal B of a voltage between the transistor Q15 and the resistor R4 is supplied from the period setting circuit 14 in FIG.
Lamp current IL output to D converter control circuit 13
A, and if the amount of current flowing through the resistor R4 is large,
The D / D converter control circuit 1 of FIG. 3 increases the potential between the collector of the transistor Q15 and the resistor R4, and correspondingly increases the lamp current flowing through the lamp.
3 is output.

Next, the circuit configuration of the block (2) will be described.

The transistors Q9, Q10 and Q11 all have an emitter connected to a voltage source and constitute a current mirror circuit. A diode Q7 is connected between the collector of the transistor Q10 and the resistor R4. The diode Q8 is connected between the collector of the transistor Q11 and the capacitor C1.

The transistor Q6 has a collector connected to the collector of the transistor Q9, and a resistor R2 connected between the emitter and the ground. Here, given that a predetermined reference voltage Vref is applied to the base of the transistor Q6 and the voltage between the base and the emitter is V6be, the collector current I6 flowing through the collector of the transistor Q6 is I6 = (Vref-V6be) / R2 Is set by Then, the transistors Q9, Q10, Q11
The current mirror circuit consisting of
Current, that is, (Vref-V6be) / R2
Are respectively supplied from the transistor Q10 to the resistor R4 via the diode Q7 and the transistor Q1
1 flows into the capacitor C1 via the diode Q8.

Further, the circuit configuration of the block (3) will be described.

The transistors Q1 and Q2 have their emitters connected to a voltage source and constitute a current mirror circuit. The collector of the transistor Q2 is connected to transistors Q3, Q4,
Connected to the collector of transistor Q3 of Q5,
The emitter of transistor Q3 is grounded. The transistor Q4 has a collector connected between the transistor Q11 and the diode Q8 and an emitter grounded, and the transistor Q5 has a collector connected to the transistor Q10.
And the diode Q7, and the emitter is grounded.

The transistor Q16 has a collector connected to the collector of the transistor Q1, and a resistor R1 connected between the emitter of the transistor Q16 and the ground. The AMP1 has an inverting input terminal connected between the transistor Q16 and the resistor R1, and has a non-inverting input terminal connected to the output voltage V of the time count circuit 11 in FIG.
c is input and the output terminal is an amplifier connected to the base of transistor Q16.

(1) (2) (3)
The circuit operation of the block will be described.

First, the output voltage Vc from the time count circuit 11 is input to the non-inverting input terminal of the amplifier AMP1, and a collector current I16 having a current amount represented by Vc / R1 flows through the collector of the transistor Q16. . By the action of transistors Q1 and Q2 and transistors Q3, Q4 and Q5 forming a current mirror, a current equal to this collector current I16 is applied to transistor Q10.
Through the transistor 5 and from the collector of the transistor Q11 to the ground through the transistor Q4.

As described above, in the circuit of the block (2), the current I6 represented by (Vref-V6be) / R2 is supplied from the transistor Q10 to the diode Q10.
7 to the resistor R4, and from the transistor Q11 to the capacitor C1 via the diode Q8, but the current I16 represented by Vc / R1 in the circuit of the block (3).
From the collector of transistor Q10 to transistor Q
5 and from transistor Q11 to ground through transistor Q4, the amount of current flowing to resistor R4 and capacitor C1 through diode Q7 and diode Q8 is (Vref-V6be) / R2-Vc / R
It becomes 1.

Further, as described above, in the circuit of block (1), the current I12 of the current amount represented by (Vref-V12be) / R3 is supplied from the collector of the transistor Q14 to the capacitor C1 and from the collector of the transistor Q15, respectively. Since the current flows through the resistor R4, the current flowing through the capacitor C1 and the resistor R4 is (Vref-V12be) / R3
+ (Vref-V6be) / R2-Vc / R1.

In the state where t is infinite and the lamp is completely cooled, where t is an extinguishing time after the lamp is turned off, the capacitor C of the time counting circuit 11 in FIG. 3 is disconnected from the power supply. Since a considerable amount of time has elapsed, the battery is discharged, and its terminal voltage Vc becomes zero. And t =
0 and the lamp is hot, (Vre
When f−V6be) / R2 = Vc / R1, the current I flowing through the capacitor C1 and the resistor R4 changes as follows in (a), (b), and (c) according to the turn-off time t of the lamp. (A) When t = 0: I = (Vref−V12be) / R
3 (b) 0 <t <infinity: I = (Vref−V12be)
/ R3 + (Vref-V6be) / R2-Vc / R1 (c) When t = infinity: I = (Vref-V12be)
/ R3 + (Vref-V6be) / R2 As described above, the amount of current flowing through the capacitor C1 corresponds to the period T, and the amount of current flowing through the resistor R4 corresponds to the lamp current flowing through the lamp during the period T. are doing.

Therefore, when the lamp in which the lamp extinguishing time t is 0 is in a hot state, I = I in the above equation (a)
(Vref-V12be) / R3, the period T and the lamp current flowing through the lamp during the period T are set. I = (Vref−V1) in equation (c)
2be) / R3 + (Vref-V6be) / R2, the period T and the lamp current flowing through the lamp during the period T are set.

In the above equation (b), I = (Vref-V1
2be) / R3 + (Vref-V6be) / R2-Vc /
In accordance with R1, when the lamp extinguishing time t is in the range of 0 <t <infinity, the capacitor C is set according to the lamp extinguishing time t.
1. The current flowing through the resistor R4 changes, so that the period T and the lamp current flowing through the lamp during the period T are set to change.

That is, as the terminal voltage Vc of the capacitor C input to the amplifier AMP1 becomes smaller, that is, as the lamp turning-off time t becomes longer, the current flowing through the capacitor C1 and the resistor R4 becomes larger. As described above, the capacitor C
The larger the amount of current flowing to the comparator COMP1,
The output signal A is a signal in which the period T is shortened, and the output signal B is a signal in which the lamp current increases as the amount of current flowing through the resistor R4 increases.

Therefore, the period setting circuit 14 composed of three blocks (a), (b) and (c) shown in FIG. 4 receives the signal corresponding to the lamp extinguishing time t from the time counting circuit 11, and The larger the value of t, the shorter the period T, that is, the period of one cycle immediately after lighting of the lamp of the AC voltage supplied to the lamp, and the larger the lamp current flowing through the lamp during that period.

Accordingly, when the lamp is in a hot state in which the lamp is turned off for a short time and the temperature of the lamp is high so that the lamp is turned on immediately after the lamp is turned off, the lamp current flowing through the lamp during one period immediately after the lamp is turned on is Although a higher value is originally desirable, setting a lower value can prevent stress or flashing of the lamp due to excessive current supply, and can set a longer period of the one cycle for supplying the current.

In a state where the lamp has been turned off for a long time and the lamp has cooled down, the current flows to the lamp during the one cycle without excessive current supply as compared with a state where the lamp is hot. The lamp current can be set large and the period of the one cycle for supplying the current can be set short.

As described above, the period T and the lamp current flowing through the lamp during the period T are set by dividing the block into three blocks (a), (b), and (c) in accordance with the lamp extinguishing time t. It is possible to accurately set the period T and the lamp current value according to the turn-off time t when the turn-off time t = 0 and t = infinity.

Incidentally, such a change is as shown in FIG. FIG. 5 is a diagram showing the relationship between the period T and the lamp current with respect to the lamp extinguishing time t. In this figure, the horizontal axis represents the lamp turning-off time t, and the vertical axis represents the period T and the lamp current flowing through the lamp during the period T. The period T changes steplessly so as to have a shorter period as the lamp extinguishing time t increases, that is, as the lamp changes from a hot state to a cold state. Further, the current value of the lamp current flowing through the lamp during the period T changes steplessly so as to increase as the lamp turning-off time t increases. In this way, by setting such that it changes steplessly, the period T and the lamp current flowing through the lamp during the period T can be set with high accuracy according to the lamp extinguishing time t.

[0051]

As described above, according to the first aspect of the present invention, when it is detected that the turn-off time of the lamp is short, the period of one cycle of the AC voltage supplied to the lamp immediately after the lamp is turned on is set to be long. In addition, since the lamp current flowing to the lamp during the one cycle period is set to be small, when the lamp is turned off, the lamp is turned off for a short time so that the lamp is quickly turned on again. It is originally desirable that the lamp current flowing in the lamp during one cycle immediately after lighting be high, but by setting the lamp current low, it is possible to prevent the lamp from being stressed or flashing due to excessive current supply, and to respond accordingly. 1 that supplies the current
The period of the cycle can be set longer.

In the state where the lamp has been turned off for a long time and the lamp has cooled down, the current flows to the lamp during the one cycle without excessive current supply as compared with the state where the lamp is hot. The lamp current can be set large, and the period of the one cycle for supplying the current can be set short accordingly. Therefore, in any case, it is possible to reliably maintain lighting of the lamp at the time of starting while preventing stress on the lamp.

According to the second aspect of the present invention, the product of the period of the one cycle and the current value of the lamp current flowing through the lamp during the period of the one cycle is set to be a constant value.
The energy supplied to the lamp during this period can be kept constant.

According to a third aspect of the present invention, the period of the one cycle and the current value of the lamp current flowing through the lamp during the one cycle are set steplessly based on the output of the turn-off time detecting means. Therefore, the period and the current value can be accurately set according to the lamp extinguishing time.

According to a fourth aspect of the present invention, according to the lamp extinguishing time, when the extinguishing time of the lamp is 0, when it is infinite, and when the extinguishing time of the lamp is between 0 and infinity. In this case, the lamp is divided into three blocks, and the period of the one cycle and the lamp current flowing through the lamp during the period are set in each block.
In this case, the period of one cycle at infinity and the lamp current can be set with high accuracy, and the set values are shifted due to the influence of component variations and the like, and flashing and lighting failure can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram of a lighting control circuit of a high-intensity discharge lamp.

FIG. 2 is a time chart illustrating an operation of a lighting control circuit of a high-intensity discharge lamp.

FIG. 3 is a block diagram showing details of a control circuit 5;

FIG. 4 is a circuit diagram showing details of a period setting circuit.

FIG. 5 is a diagram illustrating a relationship between a period T and a lamp current with respect to a lamp extinguishing time t.

FIG. 6 is a diagram showing a CR charge / discharge circuit.

FIG. 7 is a voltage waveform diagram of a capacitor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 D / D converter 2 Lamp 3 Full bridge inverter circuit part 4 Igniter 5 Control circuit 6 Driver 7 Switch

Claims (4)

[Claims] 1. A direct-current power supply for supplying a direct-current voltage, a conversion circuit for converting a direct-current voltage supplied from the direct-current power supply to an alternating-current voltage, and a high-intensity discharge lamp that is supplied with an alternating-current voltage and lit. A lighting control circuit for a high-intensity discharge lamp, comprising: a light-off time detecting means for detecting a time when the lamp is turned off; and when the light-off time detecting means detects that the light-off time of the lamp is short, A setting unit that sets a longer period of one cycle of the AC voltage supplied to the lamp immediately after the lamp is turned on, and sets a smaller lamp current flowing to the lamp during the one cycle period. Lighting control circuit for high-intensity discharge lamps. 2. The method according to claim 1, wherein the setting unit sets the product of the period of the one cycle and a current value of a lamp current flowing through the lamp during the period of the one cycle to be a constant value. 2. The lighting control circuit for a high illuminance discharge lamp according to 1. 3. The method according to claim 1, wherein the setting unit sets the current value of the lamp current flowing through the lamp during the one cycle period and the lamp current during the one cycle period in a stepless manner based on an output of the turn-off time detecting means. 3. The lighting control circuit for a high illuminance discharge lamp according to claim 1, wherein 4. The method according to claim 1, wherein the setting unit is configured to set a period of the one cycle when the time when the lamp is turned off is 0 and a current value of a lamp current flowing through the lamp during the one cycle. And a second setting unit that sets the period of the one cycle when the time during which the lamp is turned off is infinite and the current value of the lamp current flowing through the lamp during the one cycle. And a controller that adjusts a current value of a lamp current flowing through the lamp during the one cycle according to a time when the lamp is turned off. 4. The lighting control circuit for a high illuminance discharge lamp according to any one of claims 1 to 3.