JP4301015B2 - Discharge lamp lighting device - Google Patents

Description

  The present invention relates to a discharge lamp lighting device that converts and supplies the output of a direct current power source into electric power necessary for stably lighting a discharge lamp.

  To steadily turn on a discharge lamp using a direct current output from a battery or a direct current power supply as a power source, the discharge lamp is equipped with a DC-DC conversion circuit that converts the output of the direct current power into the power required by the discharge lamp. A device is required. FIG. 13 shows a configuration of a conventional discharge lamp lighting device. The discharge lamp lighting device includes a DC power source 1, a DC-DC converter circuit 2, an inverter circuit 3, a starting circuit 4, a discharge lamp 5, And a control circuit 6.

  The DC-DC conversion circuit 2 has a configuration of a flyback converter. The positive electrode of the DC power source 1 is connected to one end of the primary winding of the transformer 21, and the other end of the primary winding is connected to one end of the switching element 22. The other end of the switching element 22 is connected to the negative electrode of the DC power source 1 via the primary side current detection means. The negative electrode of the DC power supply 1 is connected to the circuit ground. One end of the secondary winding of the transformer 21 is connected to the anode of the diode 23, and the cathode of the diode 23 is connected to the positive electrode of the capacitor 24. The negative electrode of the capacitor 24 is connected to the other end of the secondary winding of the transformer 21 via the secondary current detection means. The primary winding and the secondary winding of the transformer 21 are wound in the polarity indicated by the black circles in the drawing. Energy is stored in the transformer 21 during the ON period when the switching element 22 is turned on and the primary current I1 is flowing. When the switching element 22 is turned off, the diode 23 is turned on by the back electromotive force generated by the energy stored in the transformer 21, and the secondary current I2 flows. Thereby, the smoothing capacitor 24 is charged. The voltage induced in the secondary winding of the transformer 21 is rectified by the diode 23 by turning on and off the switching element 22 and is output through the smoothing capacitor 24. The output of the DC power source 1 is discharged to the discharge lamp. 5 is converted to the required power.

  Next, the inverter circuit 3 is a full bridge inverter circuit for converting a DC voltage charged in the capacitor 24 of the DC-DC conversion circuit 2 into an AC voltage, and includes four switching elements 31 to 34 and a drive circuit 35 thereof. And. The switching elements 31 and 33 connected to the positive electrode of the capacitor 24 are connected in series with the switching elements 32 and 34 connected to the negative electrode of the capacitor 24, respectively, and an AC voltage of about several hundred Hz is applied between these connection points. As generated, the period during which the switching elements 31, 34 are turned on and the period during which the switching elements 32, 33 are turned on are controlled to alternate.

  Next, the starting circuit 4 receives the output voltage of the inverter circuit 3 and generates a high voltage pulse for starting the discharge lamp 5 when the discharge lamp 5 is in a no-load state. After that, the generation of the high voltage pulse is stopped.

  Next, the control circuit 6 will be described. In this discharge lamp lighting device, the power supplied to the discharge lamp 5 is controlled by the operation of the DC-DC conversion circuit 2, and the control circuit 6 controls the operation of the DC-DC converter circuit 2. First, the power command value generation circuit 601 generates a lamp power command Wla ′ for determining the output power of the DC-DC conversion circuit 2 (that is, the lamp power supplied to the discharge lamp 5). The current command value calculation unit 602 uses the lamp power command Wla ′ given from the power command value generation circuit 601 and the lamp voltage of the discharge lamp 5 as a lamp current command Ila ′ that is a control target for the output current of the DC-DC conversion circuit 2. Is calculated. For this purpose, the lamp voltage Vla is equivalently detected from the output voltage Vout (voltage of the capacitor 24) of the DC-DC conversion circuit 2 detected by the output voltage detection means, and the lamp voltage Vla is calculated by the current command value via the amplifier 607. This is input to the unit 602. The lamp current command Ila ′ calculated by the current command value calculation unit 602 becomes one input of the error amplifier 603. At the other input of the error amplifier 603, the lamp current Ila detected equivalently by the output current detection means provided between the output of the DC-DC conversion circuit 2 and the input of the inverter circuit 3 is passed through the amplifier 606. Have been entered. In the error amplifier 603, the lamp current command Ila ′ given from the current command value computing unit 602 and the detected value of the lamp current Ila inputted via the amplifier 606 are inputted, and the PWM signal is sent via the proportional-integral computing unit PI. A primary-side peak current command Uipk (ON time adjustment signal) that acts as a command value is created and input to the inverting input terminal of the comparator 610.

  The detection value of the primary current I1 and the detection value of the secondary current I2 of the transformer 21 of the DC-DC conversion circuit 2 are input to the control circuit 6. The detected value of the primary side current I1 is inputted to the non-inverting input terminal of the comparator 610. When the detected value becomes larger than the primary side peak current command Uipk, a forced OFF signal is sent to the Reset terminal of the oscillation circuit 608H. send. The detected value of the secondary current I2 is input to the inverting input terminal of the comparator 609. The non-inverting input terminal of the comparator 609 is connected to circuit ground. Therefore, when the detection value of the secondary side current I2 becomes zero, a compulsory ON signal is sent from the comparator 609 to the Set terminal of the oscillation circuit 608I. The oscillation circuit 608I is configured to include a set / reset flip-flop, and the switching element 22 of the DC-DC conversion circuit 2 is on / off controlled by the Q output. Further, a maximum off time variable signal generation circuit 690 is connected to the oscillation circuit 608I.

  The DC-DC converter circuit 2 uses a flyback converter in FIG. 13, but a choke converter, a chopper circuit, or the like can be used as long as the output of the DC power source 1 can be converted into necessary power by the discharge lamp 5. Good.

  In the above conventional discharge lamp lighting device, the PWM signal output from the oscillation circuit 608I for driving the switching element 22 of the DC-DC converter circuit 2 has a predetermined on-time and a predetermined off-time. The oscillation circuit 608I has a PWM signal forced on / off function. First, when the switching element 22 is turned on and the comparator 610 detects that the primary current I1 flowing through the switching element 22 has reached the primary peak current command Uipk, the comparator 610 outputs a forced-off signal to the oscillation circuit 608I. The oscillation circuit 608I forcibly switches the switching element 22 from on to off. After the switching element 22 is switched from on to off, the secondary current I2 of the transformer 21 flows out and supplies power to the load side via the diode 23. When the magnetic energy stored in the transformer 21 is released to the load side during the ON period of the switching element 22, the secondary current I2 becomes zero. When the comparator 609 detects that the secondary current I2 has reached zero, the comparator 6109 outputs a forced on signal to the oscillation circuit 608I, and the oscillation circuit 608I forcibly switches the switching element 22 from off to on.

  However, in the oscillation circuit 608I, in order to prevent malfunction and to ensure a stable and appropriate switching operation, the oscillation circuit 608I keeps the on state for a predetermined minimum on-time Tonmin, and keeps the off-state for a predetermined minimum off-time Toffmin. Even if the forcible switching signal is input from the comparators 609 and 610 during the minimum on-time Tonmin or the minimum off-time Toffmin, the forcible switching signal until the minimum on-time Tonmin or the minimum off-time Toffmin elapses. Is ignored.

  The oscillation circuit 608I oscillates with a predetermined maximum on-time Tonmax and a predetermined maximum off-time Toffmax, and performs an oscillating operation without the forcible switching signal. Here, the maximum on-time Tonmax is when the power source impedance becomes high for some reason or when the primary peak current command Uipk becomes an excessively large value so that current cannot be supplied due to a sudden change in output. , Provided to enable switching operation.

  Further, in the case of the discharge lamp 5 such as an HID lamp, since the lamp voltage is low when the lamp is cold, it takes a long time to supply the energy stored in the transformer 21 to the load side when the switching element 22 is turned on. Thus, the switching frequency is significantly reduced. Since the decrease in the switching frequency causes the DC-DC converter circuit 2 to be enlarged, the maximum off-time variable signal generation circuit 690 sets the maximum off-time Toffmax so that the switching frequency does not decrease excessively. Accordingly, when the maximum OFF time Toffmax has elapsed, if it is OFF, it is turned ON, and at this time, it operates in a current continuous mode in which it is turned ON again before the secondary current I2 of the transformer 21 becomes substantially zero.

Further, the maximum off time Toffmax set by the maximum off time variable signal generation circuit 690 is made variable by an input / output condition, for example, a primary peak current command Uipk which is an output command. This is because the initial luminous flux is low when the power supply voltage range is wide, or when the lamp voltage fluctuates over a wide range such as an HID lamp, especially when the HID lamp is cold, and the initial luminous flux is low. If the maximum off time Toffmax is fixed to a large value when supplying a large lamp power, the decrease in the switching frequency under the conditions of the low power supply voltage and the low lamp voltage becomes large, and conversely the maximum off time Toffmax is reduced. This is because if the value is fixed to a small value, the switching frequency increases under the conditions of a low lamp voltage and a high lamp power, resulting in an increase in switching loss. (For example, see Patent Document 1)
JP 2000-340385 A (paragraph numbers [0017] to [0036], FIGS. 1 and 2)

  Since the maximum off-time variable signal generation circuit 690 of the conventional example sets a predetermined maximum off-time Toffmax regardless of the on-time of the switching element 22, at the time of a low power supply voltage that is considered to have the lowest switching frequency, It is difficult to uniquely determine the minimum switching frequency in a continuous current mode at a low lamp voltage. Filters that remove switching noise, ripples, etc. are designed in consideration of the minimum switching frequency. However, it is not desirable to set the frequency to an excessively low minimum due to problems such as responsiveness and enlargement of filter parts. . In addition, since it affects the maximum current of inductance elements such as transformers and inductors, the design is difficult unless the minimum frequency is specified, and the core and the like may be larger than necessary. As described above, unless the minimum switching frequency is determined, it is difficult to design a filter and an inductance element.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a discharge lamp capable of individually adjusting the switching on time and the off time of the DC-DC converter circuit and defining the minimum switching frequency by the control circuit. It is to provide a lighting device.

  The invention of claim 1 comprises a DC power source, at least a switching element and an inductance element, and stores energy from the DC power source at least in the inductance element when the switching element is on, and at least in the inductance element when the switching element is off. A DC-DC conversion circuit that converts the output of the DC power source into at least power required by the discharge lamp by discharging the stored energy; and an output state detection unit that detects an output state of the DC-DC conversion circuit; An error amplifying means that receives an output detection signal output from the output state detecting means and a predetermined command value, and adjusting the on-time of the switching element according to the output of the error amplifying means. After switching off, the current through the inductance element reaches approximately zero. The switching element is turned on, and the switching element is controlled so that the OFF time of the switching element continues for at least the first time and does not exceed the second time, and the ON time of the switching element continues for at least the third time. And a control circuit for controlling the operation of the switching element, the switching control means for controlling so as not to exceed a fourth time, the control circuit to the inductance element when the switching element is on The second time is adjusted by a maximum off-time adjustment function having a variable of a first voltage applied and a second voltage generated in the inductance element when the switching element is turned off.

  According to the present invention, the switching on time and the off time of the DC-DC converter circuit can be individually adjusted, and the switching frequency in the current continuous mode at the time of the low power supply voltage and the low lamp voltage at which the switching frequency is the lowest is controlled. It can be defined by the circuit, and the design of each constant, filter, and inductance element of the DC-DC converter circuit can be facilitated.

  According to a second aspect of the present invention, in the first aspect, the control circuit multiplies a value obtained by dividing the first voltage by the sum of the first voltage and the second voltage by the maximum switching period of the switching element. The value is the second time.

  According to the present invention, the maximum off-time adjustment function can be expressed specifically.

  According to a third aspect of the present invention, in the first aspect, the inductance element is a transformer, and the control circuit multiplies the first voltage by a boost ratio of the transformer and a value obtained by multiplying the first voltage by the boost ratio of the transformer. A value obtained by multiplying the value obtained by dividing the sum by the sum of the second value and the second voltage by the maximum switching period of the switching element is defined as the second time.

  According to the present invention, even when a transformer is used as the inductance element, the maximum off-time adjustment function can be expressed specifically.

  According to a fourth aspect of the present invention, in the second or third aspect, the first voltage is replaced with a voltage in the DC-DC conversion circuit capable of obtaining the first voltage equivalently, and the second voltage is The second voltage is replaced with a voltage in the DC-DC conversion circuit which can be obtained equivalently.

  According to the present invention, the maximum off-time adjustment function can be specifically expressed using a voltage signal that is easy to detect.

  According to a fifth aspect of the present invention, in the fourth aspect, the voltage in the DC-DC conversion circuit capable of obtaining the first voltage and the second voltage equivalently is the input voltage of the DC-DC conversion circuit and It is an output voltage.

  According to the present invention, the maximum off-time adjustment function can be specifically expressed using the input voltage and output voltage of the DC-DC conversion circuit that can be easily detected.

  According to a sixth aspect of the present invention, in the fifth aspect, the DC-DC conversion circuit includes a step-up / down converter, and the control circuit converts the input voltage of the DC-DC conversion circuit to the input voltage of the DC-DC conversion circuit. And a value obtained by multiplying the sum of the output voltage of the DC-DC conversion circuit by the maximum switching period of the switching element is defined as the second time.

  According to the present invention, when the DC-DC conversion circuit is configured by a buck-boost converter, the maximum off-time adjustment function is specifically set using the input voltage and output voltage of the DC-DC conversion circuit that are easy to detect. Can be represented.

  A seventh aspect of the present invention is that, in the fifth aspect, the DC-DC conversion circuit is configured by a buck-boost converter or a flyback converter including a transformer as the inductance element, and the control circuit is an input of the DC-DC conversion circuit. The value obtained by multiplying the voltage multiplied by the step-up ratio of the transformer by the sum of the value obtained by multiplying the input voltage of the DC-DC conversion circuit by the step-up ratio of the transformer and the output voltage of the DC-DC conversion circuit A value obtained by multiplying the maximum switching period of the element is defined as the second time.

  According to the present invention, when the DC-DC conversion circuit is composed of a step-up / down converter or a flyback converter including a transformer, the DC-DC conversion circuit can be easily turned off using the input voltage and output voltage of the DC-DC conversion circuit that are easy to detect. The time adjustment function can be expressed specifically.

  According to an eighth aspect of the present invention, in any one of the first to seventh aspects, the control circuit is configured by an analog arithmetic circuit to obtain the second time, and charging the first capacitor and the first capacitor An off-timer circuit that includes a comparator that compares the voltage with a first voltage that is set according to a second time, and that measures a second time, and immediately after the switching element is turned off, The first capacitor whose charging voltage is substantially zero is charged, and the switching element is turned on when the comparator detects that the charging voltage of the first capacitor has reached the first voltage.

  According to the present invention, it is possible to configure an off-timer circuit capable of measuring the maximum off-time of the switching element obtained by the function circuit.

  According to a ninth aspect of the present invention, in any one of the first to seventh aspects, the control circuit analog-converts and outputs the second time obtained using a microcomputer, a first capacitor, and a first An off-timer circuit that includes a comparator that compares a charging voltage of the capacitor with a first voltage that is set in accordance with the analog-converted second time, and that measures the second time, Immediately after the switching element is turned off, the first capacitor whose charging voltage is substantially zero is charged, and if the comparator detects that the charging voltage of the first capacitor has reached the first voltage, the switching element is It is characterized by being turned on.

  According to the present invention, it is possible to configure an off-timer circuit capable of measuring the maximum off-time of the switching element obtained by the function circuit.

  A tenth aspect of the present invention is the control device according to any one of the first to seventh aspects, wherein the control circuit generates a first capacitor, a charging voltage of the first capacitor, and a first voltage set according to a second time. An off-timer circuit that includes a comparator for comparison and measures a second time is provided, and immediately after the switching element is turned off, the first capacitor whose charging voltage is substantially zero is charged, and the first capacitor When the comparator detects that the charging voltage of the first capacitor reaches the first voltage, the switching element is turned on, and the charging current of the first capacitor is the denominator of the maximum off-time adjustment function expressed in fractions. The first voltage is adjusted by at least a variable element among the elements constituting the numerator of the maximum off-time adjustment function expressed in fractions. That.

  According to the present invention, the charging current and the first voltage of the first capacitor can be set by the maximum off-time adjustment function.

  The invention according to claim 11 is the comparator according to claim 7, wherein the control circuit compares the first capacitor and the charging voltage of the first capacitor with the first voltage set according to the second time. And an off-timer circuit for measuring the second time, and immediately after the switching element is turned off, the first capacitor whose charging voltage is substantially zero is charged, and the charging voltage of the first capacitor is If the comparator detects that the first voltage has been reached, the switching element is turned on. The charging current of the first capacitor is obtained by multiplying the input voltage of the DC-DC conversion circuit by the step-up ratio of the transformer. The first voltage is proportional to the value obtained by multiplying the input voltage of the DC-DC conversion circuit by the step-up ratio of the transformer. Voltage And wherein the Rukoto.

  According to this invention, when the DC-DC conversion circuit is configured by a step-up / down converter or a flyback converter including a transformer, the charging current and the first voltage of the first capacitor can be set.

  The invention according to claim 12 is the comparator according to claim 7, wherein the control circuit compares the first capacitor and a charging voltage of the first capacitor with a first voltage set according to a second time. And an off-timer circuit for measuring the second time, and immediately after the switching element is turned off, the first capacitor whose charging voltage is substantially zero is charged, and the charging voltage of the first capacitor is If the comparator detects that the first voltage has been reached, the switching element is turned on. The charging current of the first capacitor is obtained by multiplying the input voltage of the DC-DC conversion circuit by the step-up ratio of the transformer. A current obtained by adding a value proportional to the value and a value proportional to the output voltage of the DC-DC conversion circuit, and the first voltage is obtained by multiplying the input voltage of the DC-DC conversion circuit by the step-up ratio of the transformer. Ratio to value Characterized in that the a voltage.

  According to this invention, when the DC-DC conversion circuit is configured by a step-up / down converter or a flyback converter including a transformer, the charging current and the first voltage of the first capacitor can be set.

  According to a thirteenth aspect of the present invention, in the twelfth aspect, the control circuit includes: a second capacitor; a charging voltage of the second capacitor; a second voltage set according to the third time or the fourth time; And an on-timer circuit for measuring the third time or the fourth time, and a second capacitor whose charging voltage is substantially zero immediately after the switching element is turned on. The comparator detects that the charging voltage of the second capacitor has reached the second voltage, and detects that the third time or the fourth time has passed. The capacitor charging current is a current proportional to a value obtained by multiplying the input voltage of the DC-DC conversion circuit by the step-up ratio of the transformer.

  According to the present invention, when the DC-DC conversion circuit includes a step-up / down converter or a flyback converter including a transformer, the charging current of the second capacitor can be set.

A fourteenth aspect of the present invention is the control device according to any one of the first to thirteenth aspects, wherein the control circuit sets an off time of the switching element while the output voltage of the DC-DC conversion circuit exceeds a third voltage. And setting the on-time of the switching element to the third time while the output voltage of the DC-DC conversion circuit exceeds the fourth voltage higher than the third voltage. Features.

According to the present invention, it is possible to control so that the switching frequency of the switching element does not increase when the output voltage of the DC-DC conversion circuit is overvoltage. Further, even when the output voltage of the DC-DC converter circuit is overvoltage, the switching element has a maximum off time so that the switching element has a minimum on time so that the switching frequency of the switching element does not increase at the time of overvoltage. Can be controlled.

According to a fifteenth aspect of the present invention, in the fourteenth aspect, the control circuit determines whether the output voltage of the DC-DC conversion circuit is a third value based on a determination result of a lighting determination circuit that determines whether or not the discharge lamp is lit. It is characterized by determining whether or not the voltage has been exceeded.

  According to the present invention, by using the lighting determination circuit, it is not necessary to separately provide a means for determining whether or not the output voltage of the DC-DC conversion circuit exceeds the third voltage, and the configuration can be simplified. Can do.

According to a sixteenth aspect of the present invention, in any one of the first to thirteenth aspects, the control circuit sets the off time of the switching element while the output voltage of the DC-DC conversion circuit exceeds a third voltage. And setting the on-time of the switching element to the third time while the output voltage of the DC-DC converter circuit exceeds the fourth voltage higher than the third voltage . It is set to time.

  According to the present invention, when the output voltage of the DC-DC conversion circuit exceeds a predetermined value, the off time of the switching element can be controlled to be constant.

According to a seventeenth aspect of the present invention, in any one of the first to thirteenth aspects, the control circuit controls the on-time adjustment signal when the on-time adjustment signal for adjusting the on-time of the switching element fluctuates in a direction to decrease the on-time. When the ON time of the switching element reaches the first level or less, the ON time of the switching element is fixed to the third time, and when the ON time adjustment signal reaches the second level or less which is the first level or less, the ON time adjustment is performed. The second time is increased according to a difference between the signal and the second level.

  According to the present invention, the short-circuit current can be controlled by increasing the maximum OFF time of the switching element when the load is short-circuited.

According to an eighteenth aspect of the present invention, in any one of the first to thirteenth aspects, the DC-DC conversion circuit includes a current detection unit that detects a current flowing through the switching element, and the control circuit includes a detection output of the current detection unit. The time until the detection output in which the first signal is superimposed as the offset amount and the first signal is superimposed reaches the on-time adjustment signal for adjusting the on-time of the switching element is the on-time of the switching element. When the magnitude of the on-time adjustment signal reaches a predetermined level or less, the second time is increased according to the difference between the on-time adjustment signal and the predetermined level .

  According to the present invention, the short-circuit current can be controlled by increasing the maximum OFF time of the switching element when the load is short-circuited.

The invention of claim 19 is characterized in that, in claim 18 , the magnitude of the first signal is equal to or greater than the predetermined level .

  According to this invention, even when the on-time of the switching element becomes maximum when the load is short-circuited, the short-circuit current can be controlled by increasing the maximum off-time of the switching element.

According to a twentieth aspect of the present invention, in any one of the eighth to twelfth aspects, the DC-DC conversion circuit includes a current detection unit that detects a current flowing through the switching element, and the control circuit includes a current detection unit configured to detect a current. The first signal is superimposed on the signal as an offset amount, and the time until the current detection signal on which the first signal is superimposed reaches the on-time adjustment signal for adjusting the on-time of the switching element is determined by the switching element. When the on-time adjustment signal is set to an on-time and the magnitude of the on-time adjustment signal reaches a predetermined level or less, the first timer includes an off-timer circuit that measures the second time according to a difference between the on-time adjustment signal and the predetermined level . The charging current of the capacitor is reduced.

  According to the present invention, the short-circuit current can be controlled by increasing the maximum OFF time of the switching element when the load is short-circuited.

According to a twenty-first aspect of the invention, in any one of the eighteenth to twentieth aspects, the means for generating the first signal includes a resistor having one end connected to the detection output of the current detecting means, and a predetermined current at the other end of the resistor. And a current source to be supplied.

  According to the present invention, the first signal generating means can have a simple configuration.

  As described above, according to the present invention, the on-time and off-time of switching of the DC-DC converter circuit can be individually adjusted, and in the current continuous mode at the time of the low power supply voltage and the low lamp voltage at which the switching frequency is lowest. The switching frequency can be defined by the control circuit, and there is an effect that each constant of the DC-DC converter circuit, the filter, and the inductance element can be easily designed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 shows a basic configuration of a discharge lamp lighting device according to the present invention. The discharge lamp lighting device includes a DC power supply 1, a DC-DC converter circuit 2 for converting the output of the DC power supply 1 into a desired output, and a DC. A control circuit 6 that controls the operation of the DC converter circuit 2 and a load circuit 10 that includes a discharge lamp to which necessary power is supplied from the DC-DC converter circuit 2. The DC-DC converter circuit 2 includes at least an inductance element 211 such as a transformer or an inductor, a switching element 22, a diode 23, and a capacitor 24 connected in parallel to the load circuit 10, and the control circuit 6 PWMs the switching element 22. To drive. As shown in FIGS. 2A to 2C, when the switching element 22 is turned on, the voltage VL1 is applied to the inductance element 211 in the closed circuit including at least the DC power source 1, the switching element 22, and the inductance element 211. Then, the current I1 flows through the inductance element 211 and energy is accumulated. Next, when the switching element 22 is turned off, the energy accumulated in the inductance element 211 is released to the load circuit 10 side as a current I2, and is closed by at least a parallel circuit of the load circuit 10 and the capacitor 24 and the inductance element 211. A voltage VL2 is generated in the inductance element 211 in the circuit.

  When the control circuit 6 drives the switching element 22 on and off as described above, the maximum off time Toffmax of the switching element 22 is calculated by the maximum off time adjustment function Toffmax = Tmax × {VL1 / (VL1 + VL2)}. Variable based on the result. Tmax is the maximum switching period of the switching element 22. Here, since it is difficult to measure the voltage across the inductance element 211 when the switching element 22 is on and off, the voltages VL1 and VL2 may be obtained and calculated by an equivalent method. That is, if the configuration of the DC-DC converter circuit 2 is determined, the voltages VL1 and VL2 across the inductance element 211 when the switching element 22 is on and off are the input voltage Vin of the DC-DC converter circuit 2, the DC-DC converter. It is possible to replace equivalently using a value that is relatively easy to measure, such as the output voltage Vout of the circuit 2.

  For example, in FIG. 1, when the DC-DC converter circuit 2 has a step-up chopper configuration, when the switching element 22 is on, VL1 = Vin, and when the switching element 22 is off, VL2 = Vout−Vin, and the voltages VL1 and VL2 are the voltages Vin, It becomes possible to replace it with Vout equivalently.

  Next, in FIG. 1, when the DC-DC converter circuit 2 has a step-up / step-down chopper configuration, when the switching element 22 is on, VL1 = Vin, and when the switching element 22 is off, VL2 = Vout, and the voltages VL1 and VL2 become the voltages Vin, It becomes possible to replace it with Vout equivalently.

  Next, in FIG. 1, when the DC-DC converter circuit 2 has a step-down chopper configuration, when the switching element 22 is on, VL1 = Vin−Vout, and when the switching element 22 is off, VL2 = Vout and the voltages VL1 and VL2 become the voltage Vin. , Vout can be equivalently replaced.

  When the inductance element 211 has a transformer structure, if the step-up ratio from the primary side to the secondary side of the transformer is N, the secondary side voltage is converted to the primary side voltage, or the primary side voltage is set to 2 It corresponds by converting to the secondary voltage. For example, in FIG. 1, when the DC-DC converter circuit 2 is a flyback converter using a transformer having a step-up ratio N, the flyback converter is considered to be equivalent to a step-up / down chopper circuit having a transformer configuration. By converting the secondary side voltage to the primary side voltage, when the switching element 22 is on, VL1 = Vin, and when the switching element 22 is off, VL2 = Vout / N, or the primary side voltage is converted to the secondary side voltage. Thus, when the switching element 22 is on, VL1 = N · Vin, and when the switching element 22 is off, VL2 = Vout. Regardless of which conversion is used, the maximum off time Toffmax of the switching element 22 becomes the same value, and is variable based on the result calculated by the maximum off time adjustment function Toffmax = Tmax × {N · Vin / (N · Vin + Vout)}. It becomes.

  As described above, in this embodiment, the ON time and the OFF time of the switching 22 of the DC-DC converter circuit 2 can be individually adjusted, and in the current continuous mode at the time of the low power supply voltage and the low lamp voltage at which the switching frequency is the lowest. The switching frequency can be defined by the control circuit 6, and the design of each constant, filter, and inductance element of the DC-DC converter circuit 2 can be facilitated.

  If the DC-DC converter circuit 2 is of a type that stores energy in an inductance element such as a transformer or an inductor when the switching element 22 is on, and releases the energy accumulated in the inductance element to the load side when the switching element 22 is off, It is not limited to the circuit system of the chopper circuit or the flyback converter, and may be a voltage value that can equivalently replace both-end voltages VL1 and VL2 of the inductance element when the switching element 22 is on and off. For example, the maximum off time adjustment function for calculating the maximum off time Toffmax of the switching element 22 can be converted in the same manner as described above.

(Embodiment 2)
FIG. 3 shows the configuration of the discharge lamp lighting device of the present embodiment. The discharge lamp lighting device includes a DC power source 1, a DC-DC converter circuit 2, an inverter circuit 3, a starting circuit 4, and a discharge lamp 5. And a control circuit 6 for controlling the operation of the DC-DC converter circuit 2, and the same components as those in the conventional example shown in FIG.

  In the present embodiment, the DC-DC converter circuit 2 is a flyback converter using a transformer with a step-up ratio N, and the function circuit 613 included in the control circuit 6 that controls the operation of the DC-DC converter circuit 2 includes the DC-DC converter. The flyback described in the first embodiment is inputted with the input voltage Vin of the converter circuit 2, the output voltage Vout of the DC-DC converter circuit 2, and the maximum periodic signal command Tmax for setting the minimum switching frequency of the switching element 22. The maximum off-time adjustment function Toffmax = Tmax × {N · Vin / (N · Vin + Vout)} of the switching element 22 of the converter is applied. Then, the function circuit 613 outputs a maximum off time adjustment signal to the oscillation circuit 608A according to the calculated maximum off time Toffmax.

  The voltage Vsw across the switching element 22 is input to the inverting input terminal of the comparator 609, and the threshold voltage Vref1 is input to the non-inverting input terminal of the comparator 609.

  Next, specific circuit configurations of the function circuit 613 and the oscillation circuit 608A are shown in FIG. The oscillation circuit 608A charges the capacitor Cs with the current source Js, and the comparator Comp1 detects that the voltage across the capacitor Cs has reached a predetermined value, thereby measuring the off-timer circuit 608a that measures the off-time of the switching element 22. The capacitor Cr is charged by the source Jr, and the comparator Comp2 detects that the voltage across the capacitor Cr has reached a predetermined value, thereby setting the on-timer circuit 608b for measuring the on-time of the switching element 22 and the output of the off-timer circuit 608a. A set / reset flip-flop 608c that inputs to the terminal, inputs the output of the on-timer circuit 608b to the reset terminal, and outputs an on / off signal of the switching element 22.

  If the forced-off signal is not input to the on-timer circuit 608b from the outside of the oscillation circuit 608A, the output of the comparator Comp2 becomes H level when the voltage across the capacitor Cr reaches the voltage Vr2 in the on-timer circuit 608b. The reset flip-flop 608c is reset, and the switching element 22 is turned off. This is the maximum on-time Tonmax. On the other hand, when a forced-off signal is input to the on-timer circuit 608b from the outside of the oscillation circuit 608A, the threshold voltage of the comparator Comp2 is switched from the voltage Vr2 to the voltage Vr1 (Vr1 <Vr2), and the voltage across the capacitor Cr is changed. When the voltage Vr1 is reached, the output of the comparator Comp2 becomes H level, the set / reset flip-flop 608c is forcibly reset, and the switching element 22 is forcibly turned off. Even when the forced off signal is input, the switching element 22 remains on until the voltage across the capacitor Cr reaches the voltage Vr1. That is, this is the minimum on-time Tonmin. The capacitor Cr connects the switch SWr1 in parallel, and turns on the switch SWr1 by the inverted output of the set / reset flip-flop 608c to discharge the charge.

  If the forced on signal is not input to the off timer circuit 608a from the outside of the oscillation circuit 608A, the voltage across the capacitor Cs reaches the voltage input as the maximum off time adjustment signal from the function circuit 613 in the off timer circuit 608a. Sometimes, the output of the comparator Comp1 becomes H level, the set / reset flip-flop 608c is set, and the switching element 22 is turned on. This measures and defines the maximum off time Toffmax, and becomes the maximum off time Toffmax proportional to the voltage of the maximum off time adjustment signal. On the other hand, when a forced on signal is input to the off timer circuit 608a from the outside of the oscillation circuit 608A, the threshold voltage of the comparator Comp1 is switched from the maximum off time adjustment signal to the voltage Vs1 (Vs1 <maximum off time adjustment signal). When the voltage across the capacitor Cs reaches the voltage Vs1, the output of the comparator Comp1 becomes H level, forcibly sets the set / reset flip-flop 608c, and forcibly turns on the switching element 22. Even when the forced on signal is input, the switching element 22 remains off until the voltage across the capacitor Cs reaches the voltage Vs1. That is, this is the minimum off time Toffmin. The capacitor Cs has the switch SWs1 connected in parallel, and the switch SWs1 is turned on by the output of the set / reset flip-flop 608c to discharge the charge. Note that the circuit configurations of the off-timer circuit 608a and the on-timer circuit 608b may have any functions similar to those described above.

  The function circuit 613 that outputs the maximum off-time adjustment signal corresponds to the maximum off-time Toffmax obtained by the maximum off-time adjustment function Toffmax = Tmax × {N · Vin / (N · Vin + Vout)} of the switching element 22 of the flyback converter. 4 outputs a maximum off-time adjustment signal and basically requires a division function. Therefore, in FIG. 4, a multiplication / division circuit 613a using the Vbe (base-emitter voltage) -Ie (emitter current) characteristics of the transistor. A V-I converter 613b that supplies a current Ivin represented by {k · N · Vin} obtained by multiplying the detection signal of the input voltage Vin of the DC-DC converter circuit 2 by N and performing voltage-current conversion; -The detection signal of the output voltage Vout of the DC converter circuit 2 is represented by {k · N · Vout} obtained by voltage-current conversion. A V-I converter 613c that supplies a current Ivout to be generated, a current mirror circuit 613d that receives the supply current Ivin of the V-I converter 613b, and an I-V converter 613e that generates a maximum off-time adjustment signal. Prepare. Here, k is a conversion coefficient of voltage-current conversion.

  The multiplier / divider circuit 613a includes NPN transistors Tr1 to Tr5 having collectors connected to a control power supply Vcc. The emitter of the transistor Tr1 is supplied via a current source J1 that supplies a current corresponding to the maximum switching period Tmax of the switching element 22. Are connected to the circuit ground, and a current I1 flows. The transistor Tr2 has a base connected to the emitter of the transistor Tr1 and an emitter connected to the circuit ground via the output of the VI converter 613b, and a current I2 = k · N · Vin flows. The emitter of the transistor Tr3 is connected to the circuit ground via an NPN transistor Tr6 connected to the emitter of the transistor Tr2 and a current source J2. The emitter of the transistor Tr4 is connected to the circuit ground via the NPN transistor Tr7 and the current source J2, and the current I4 flows. The current I4 is converted into a maximum OFF time adjustment signal by the IV converter 613e. . The transistor Tr5 has a base connected to the emitter of the transistor Tr3, an emitter connected to the circuit ground via the output of the VI converter 613c, and also connected to the circuit ground via the output of the current mirror circuit 613d. A current I3 flows, and the current I3 is the sum of the output currents of the VI converter 613c and the current mirror circuit 613d. A threshold voltage Vref2 is connected to each base of the transistors Tr1, Tr3, Tr4, and a base of the transistor Tr7 is connected to an emitter of the transistor Tr5.

  In the multiplication / division circuit 613a, the relationship is I4 = I1 · I2 / I3, and the IV converter 613e performs current-voltage conversion on the current I4 and outputs a maximum off-time adjustment signal. The lower limit of the switching frequency of the DC-DC converter circuit 2 is defined. Note that the function circuit 613 is not limited to the above-described configuration, and any function circuit that performs the same calculation may be used even if another multiplication circuit or division circuit is used. Further, if the maximum off-time adjustment function changes due to the difference in the circuit system of the DC-DC converter circuit 2, it is necessary to change the circuit configuration of the multiplication / division circuit 613a according to the maximum off-time adjustment function.

  The function circuit 613 shown in FIG. 4 uses an analog arithmetic circuit. However, as shown in FIG. 5, the detection signals of the input voltage Vin and output voltage Vout of the DC-DC converter circuit 2 are converted into A / D converters 613f. The A / D conversion is digitized and taken into the microcomputer 613g, and the results of numerical operations such as multiplication, addition, and division in the microcomputer 613g are D / A converted by the D / A converter 613h, and the maximum off time You may output as an adjustment signal. Alternatively, it may be configured such that the numerical calculation value in the microcomputer is directly set by performing only the measurement of the maximum off time Toffmax with a high-speed digital counter.

(Embodiment 3)
In the second embodiment, the maximum off-time adjustment signal is generated by the function circuit 613 provided with the multiplication / division circuit. However, in this embodiment, the function circuit 613 is deleted and the maximum off-time is added to the oscillation circuit 608B shown in FIG. It incorporates an adjustment function.

  Hereinafter, the oscillation circuit 608B will be described. In the off-timer circuit 608a included in the oscillation circuit 608B, a signal obtained by multiplying the current value of the current source Js that charges the capacitor Cs by N times the detection signal of the input voltage Vin of the DC-DC converter circuit 2, and the DC-DC converter circuit 2 and the detection signal of the output voltage Vout, that is, the maximum off-time adjustment function Toffmax = Tmax × {N · Vin / (N · Vin + Vout)}. Further, when the forced on signal is not input to the off timer circuit 608a from the outside of the oscillation circuit 608B, the threshold voltage to be compared with the voltage across the capacitor Cs by the comparator Comp1 is detected as the input voltage Vin of the DC-DC converter circuit 2. Control is performed by a signal obtained by multiplying the signal by N, that is, a variation amount {N · Vin} constituting a numerator of a maximum off-time adjustment function Toffmax = Tmax × {N · Vin / (N · Vin + Vout)}. By configuring the off-timer circuit 608a in this manner, the maximum off-time adjusting function can be incorporated in the oscillation circuit 608B.

  In the present embodiment, a flyback converter is used for the DC-DC converter circuit 2. However, when another circuit system is used for the DC-DC converter circuit 2, the maximum off-time adjustment function corresponding to the circuit system is used. The current of the current source Js is controlled by the denominator, and the threshold voltage to be compared with the voltage across the capacitor Cs by the comparator Comp1 is controlled by the amount of variation constituting the numerator of the maximum off-time adjustment function corresponding to the circuit system. To do.

  Other configurations are the same as those in the second embodiment, and a description thereof will be omitted.

(Embodiment 4)
In the oscillation circuit 608B of the third embodiment, the charging current of the capacitor Cs is controlled by {N · Vin + Vout}. However, the oscillation circuit 608C in the present embodiment shown in FIG. The signal obtained by multiplying the detection signal of N by N is subjected to voltage-current conversion to supply a current Ivin represented by {k · N · Vin}, and an output voltage Vout of the DC-DC converter circuit 2 Voltage-to-current converted from the detection signal of V−I, a V-I converter 608e that supplies a current Ivout represented by {V · N · Vout}, and a current mirror circuit that inputs a supply current Ivin of the V-I converter 608d 608f, and the sum of the current Ivin and the current Ivout is the charging current Is of the capacitor Cs. Since addition / subtraction of current signals can be performed only by wiring connection, it is not necessary to separately use an addition / subtraction circuit, and a simple configuration can be achieved.

  In the oscillation circuit 608B of the third embodiment, when the forced on signal and the forced off signal are respectively input from the outside in the off timer circuit 608a and the on timer circuit 608b, the comparators Comp1 and Comp2 are connected to the charging voltages of the capacitors Cs and Cr. Each threshold voltage to be compared is a voltage for defining the minimum off time Toffmin from a voltage for defining the maximum off time Toffmax of the switching element 22 and a voltage for defining the maximum on time Tonmax of the switching element 22. The voltage is set to be switched to a voltage for defining the minimum on-time Tonmin.

  On the other hand, the oscillation circuit 608C of the present embodiment inputs resistors Rs1 and Rs2, a series circuit of switches SWs2, and a voltage Vr2 that receive a signal obtained by multiplying the detection signal of the input voltage Vin of the DC-DC converter circuit 2 by N. The resistor Rr1, Rr2 and the switch SWr2 are connected in series. The voltage at the connection point of the resistors Rs1, Rs2 becomes a threshold voltage compared with the voltage across the capacitor Cs by the comparator Comp1, and the resistors Rr1, Rr2 The connection point voltage becomes a threshold voltage that is compared with the voltage across the capacitor Cr by the comparator Comp2. The switches SWs2 and SWr2 are turned on by a forced on signal and a forced off signal, respectively. A voltage N · Vin for defining the maximum off time Toffmax and a voltage Vr2 for defining the maximum on time Tonmax are switched By dividing each of the resistors when SWs2 and SWr2 are turned on, a threshold voltage for defining the minimum off time Toffmin and a threshold voltage for defining the minimum on time Tomin are generated, and each of the comparators Comp1 and Comp2 The threshold voltage is switched.

  Further, in the oscillation circuit 608B of the third embodiment, the maximum on-time Tonmax and the minimum on-time Tonmin defined by the on-timer circuit 608b are fixed times. Here, the on-timer circuit 608b normally has a maximum on-time Tonmax so that the on-time does not become excessive, and a minimum on-time Tonmin so as to obtain a stable continuous oscillation. In the DC-DC converter circuit 2, the on-time Is longer or the power supply voltage of the DC power supply 1 is higher, the current flowing through the switching element 22 in the ON state becomes larger. Therefore, it is desirable that the maximum on-time Tonmax and the minimum on-time Tonmin are variable so as to be inversely proportional to the power supply voltage of the DC power supply 1.

  Therefore, the oscillation circuit 608C of the present embodiment sets the output of the current mirror circuit 608f that receives the current signal Ivin proportional to the input voltage Vin of the DC-DC converter circuit 2 as the charging current Ir of the capacitor Cr. The maximum on-time Tonmax and the minimum on-time Tonmin are variable so as to be inversely proportional to the power supply voltage of the DC power supply 1, and work effectively as a protection function for the primary current I1.

  Other configurations are the same as those of the third embodiment, and a description thereof will be omitted.

(Embodiment 5)
The oscillation circuit 608D of the present embodiment whose configuration is shown in FIG. 8 is obtained by providing an output overvoltage protection circuit of the DC-DC converter circuit 2 in the oscillation circuit 608C of the fourth embodiment. The oscillation circuit 608D receives the comparator Comp4 that detects that the detection signal of the output voltage Vout of the DC-DC converter circuit 2 has reached a predetermined threshold voltage Vn2, and the output of the comparator Comp4 and the forced off signal. An OR element 608i, and while the detection signal of the voltage Vout exceeds a predetermined threshold voltage Vn2, the switch SWr2 of the on-timer circuit 608b is turned on, and the switching element 22 always operates with the minimum on-time Tonmin. The output voltage Vout of the DC-DC converter circuit 2 is controlled so as to decrease. Further, in such overvoltage protection control, when the switching element 22 operates with the minimum on-time Tonmin, the output of the DC-DC converter circuit 2 is a load circuit comprising the inverter circuit 3, the starting circuit 4, and the discharge lamp 5 in FIG. Is set to be smaller than the minimum power consumption.

  Further, when the output overvoltage of the DC-DC converter circuit 2 is exceeded, the time for releasing the energy stored in the transformer 21 (inductance element) when the switching element 22 is turned on is shorter than when the switching element 22 is turned off. Therefore, the forced on signal detected when the secondary current I2 of the transformer 21 becomes substantially zero and input to the oscillation circuit 608D is input after a short OFF period of the switching element 22, The switching frequency is increased. If the switching frequency is high, the output voltage Vout of the DC-DC converter circuit 2 becomes large during the overvoltage protection control, which is disadvantageous for overvoltage protection. Therefore, the oscillation circuit 608D receives the comparator Comp3 that detects that the detection signal of the output voltage Vout of the DC-DC converter circuit 2 has reached a predetermined threshold voltage Vn1, the output of the comparator Comp3, and the forced on signal. When the detection signal of the voltage Vout exceeds the predetermined threshold voltage Vn1, the forced on signal is not transmitted to the switch SWs2 of the off timer circuit 608a, and the switch SWs2 is in the off state. The switching element 22 is controlled so as to always operate at the maximum off time Toffmax. Here, Vn1 ≦ Vn2 is set.

  Further, when a flyback converter as shown in FIG. 8 is used as the DC-DC converter circuit 2, the maximum off-time adjustment function Toffmax = Tmax × {N · Vin / (N · Vin + Vout)}, and the denominator is DC -When the output voltage Vout of the DC converter circuit 2 is present and the output voltage Vout is large as in the case of an overvoltage, the maximum off time Toffmax is shortened, and the switching frequency of the switching element 22 is increased even when operating at the maximum off time Toffmax. Resulting in. Therefore, the oscillation circuit 608D of the present embodiment is represented by {k · N · Vout} obtained by performing voltage-current conversion on the detection signal of the output voltage Vout of the DC-DC converter circuit 2 with respect to the oscillation circuit 608C of the fourth embodiment. The maximum limit value is set for the detection signal of the output voltage Vout before the VI converter 608e that supplies the current Ivout to be supplied, and the current Ivout supplied by the VI converter 608e does not exceed a certain value. Thus, the maximum value limiting circuit 608g is provided to limit the switching frequency of the switching element 22 when the output voltage Vout is overvoltage. Therefore, the overvoltage protection of the output voltage Vout can be stably controlled.

  In the case of a discharge lamp lighting device, the condition that the output voltage Vout of the DC-DC converter circuit 2 becomes an overvoltage is that the DC-DC converter circuit 2 operates with the discharge lamp 5 turned off just before lighting. For example. Further, the difference between the maximum voltage for maintaining the lighting state and the overvoltage at the time of turn-off is relatively large, and the threshold voltage Vn1 is equal to or higher than the voltage corresponding to the maximum voltage at the time of lighting and the threshold voltage Vn2 In a region where the output voltage Vout is set to be lower than the expected value, it is desirable that the maximum value limiting circuit 608g provides a limit so that the current Ivout supplied by the VI converter 608e does not exceed a certain value.

  Other configurations are the same as those of the fourth embodiment, and a description thereof will be omitted.

(Embodiment 6)
The oscillation circuit 608D of the fifth embodiment includes the comparator Comp3, detects that the detection signal of the output voltage Vout of the DC-DC converter circuit 2 has reached the threshold voltage Vn1, and the detection signal of the voltage Vout is a predetermined signal. While the threshold voltage Vn1 is exceeded, the switching element 22 is controlled to always operate at the maximum off time Toffmax. In this embodiment, as shown in FIG. 9, the oscillation circuit 608E and the comparator Comp3 are controlled. Instead, a lighting determination circuit 615 provided in the control circuit 6 is used. The lighting determination circuit 615 includes a hysteresis comparator Comp5 that compares the detection signal of the output voltage Vout of the DC-DC converter circuit 2 with the threshold voltage VLGT and outputs a lighting determination signal. The detection signal of the output voltage Vout is When it is larger than the threshold voltage VLGT, an L level lighting determination signal is output, and when the output voltage Vout detection signal is lower than the threshold voltage VLGT, an H level lighting determination signal is output. If the DC-DC converter circuit 2 is operated when the discharge lamp 5 is extinguished, the output voltage Vout of the DC-DC converter circuit 2 exceeds the maximum voltage at which the discharge lamp 5 maintains the lighting state. The circuit 615 outputs an L level lighting determination signal to the AND element 608h. In the oscillation circuit 608E, the forced on signal is not transmitted to the switch SWs2 of the off timer circuit 608a, the switch SWs2 maintains the off state, and the switching element 22 Control is performed so as to always operate with the maximum off time Toffmax.

  The lighting determination circuit 615 is not only configured to use the detection signal of the output voltage Vout considered to be substantially equivalent to the lamp voltage as described above, but also to a configuration using the output current of the DC-DC converter circuit 2, -The structure which uses the output voltage and output current of the DC converter circuit 2 in combination, or the structure which detects the light output of the discharge lamp 5 may be used.

  Furthermore, in the oscillation circuit 608D of the fifth embodiment, the maximum value limiting circuit 608g provides a limit so that the current Ivout supplied by the VI converter 608e does not exceed a certain value. When the circuit 608g is deleted and the lighting determination circuit 615 determines that the light is turned off immediately before lighting and outputs an L level lighting determination signal, the oscillation circuit 608E is connected in series to the output path of the VI converter 608e. The switch 608j is turned off, and the charging path of the current Ivout to the capacitor Cs provided in the off timer circuit 608a is cut off.

  In addition, a series circuit of the resistor Rs3 and the switch SWs3 is connected in parallel to the series circuit of the resistor Rs2 and the switch SWs2, and the switch SWs3 is turned on by an L level lighting determination signal output from the lighting determination circuit 615. , And turned off by an H level lighting determination signal. The switch SWs3 is turned on when the lighting determination circuit 615 determines that it is in the extinguished state immediately before lighting and outputs an L level lighting determination signal, and the voltage that the comparator Comp1 compares with the voltage across the capacitor Cs is DC A voltage m · N · Vin is obtained by multiplying a voltage obtained by multiplying the detection signal of the input voltage Vin of the DC converter circuit 2 by N times (m <1). Therefore, the OFF time of the switching element 22 when the lighting determination circuit 615 determines that the light is off before lighting is m · Tmax.

  In this embodiment, when the lighting determination circuit 615 determines that the output voltage Vout of the DC-DC converter circuit 2 exceeds a predetermined voltage and is in the extinguished state immediately before lighting, the switching element 22 of the DC-DC converter circuit 2 is used. The off-timer circuit 608a is set so that the denominator and the numerator of the maximum off-time adjustment function cancel each other and become a constant even when the circuit system of the DC-DC converter circuit 2 is different. The same effect can be obtained by adding / subtracting a signal to / from the charging current and threshold voltage of the capacitor.

  Other configurations are the same as those of the fifth embodiment, and a description thereof will be omitted.

(Embodiment 7)
In the discharge lamp lighting device of Embodiments 1 to 6, when the load (inverter circuit 3, starter circuit 4, discharge lamp 5) is short-circuited, the output current of the DC-DC converter circuit 2 increases, but the current command value calculation unit An upper limit value is set for the current command value output from 602 and does not increase beyond a certain value. Therefore, even if the short-circuit current increases, the primary-side peak current command Uipk (ON time adjustment signal) that is the output of the error operational amplifier 603 is reduced, and the ON time of the switching element 22 of the DC-DC converter circuit 2 is reduced. Feedback control is performed so as to shorten the time.

  However, as described above, the oscillation circuit determines the predetermined minimum on-time Tonmin and drives the switching element 22, and the on-time of the switching element 22 cannot be smaller than the minimum on-time Tonmin. If the loss of the inverter circuit 3 or the start circuit 4 connected to the DC-DC converter circuit 2 is large, the short-circuit current can be controlled to some extent, but if the loss is small, the short-circuit current is set to the target value, for example, the upper limit value of the current command value. There is a possibility that it is not possible to control until.

  Therefore, in the discharge lamp lighting device of the present embodiment having the configuration of FIG. 10, the offset amount Vdo1 is superimposed on the primary current detection signal input to the comparator 610 of the control circuit 6. Then, the time until the primary current detection signal on which the offset amount Vdo1 is superimposed reaches the primary peak current command Uipk is set as the ON time of the switching element 22. In this case, the primary peak current command Uipk, which is the output of the error operational amplifier 603, can change the ON time of the switching element 22 when the primary current detection signal input to the comparator 610 is equal to or greater than the offset amount Vdo1. Thus, output control when the load is short-circuited becomes possible.

  However, if the primary-side peak current command Uipk is equal to or less than the offset amount Vdo1 when the load is short-circuited and the on-time of the switching element 22 is minimized, the output current corresponding to the primary-side peak current command Uipk cannot be controlled. The primary peak current command Uipk is further lowered by the action of the amplifier 603.

  Therefore, in the control circuit 6 of the present embodiment, a function circuit 614 is provided. The function circuit 614 multiplies the signal obtained by subtracting the offset amount Vdo2 from the primary peak current command Uipk by a negative coefficient -Kst. If the calculated value is positive (that is, if the primary peak current command Uipk is smaller than the offset amount Vdo2), a signal proportional to the magnitude is output. Then, the signal output from the function circuit 614 is added to the maximum OFF time adjustment signal output from the function circuit 613. That is, the maximum off time Toffmax is controlled to increase as the primary peak current command Uipk falls below the offset amount Vdo2. Here, Vdo1 ≧ Vdo2 is set, and further, Vdo1 <Vdo2 is not set due to circuit variations.

  Therefore, even if the on-time of the switching element 22 is shortened to the minimum on-time Tonmin, the short-circuit current can be controlled to the command value by adjusting the off-time, and the current limit is stabilized even when the load is short-circuited. Circuit protection is achieved by preventing excessive output current.

  In the present embodiment, for output control, the PWM signal width output from the control circuit 6 is adjusted by the primary peak current command Uipk. However, the on-time adjustment of the switching element 22 is performed by triangular wave comparison. However, similarly to the above, it is possible to use a configuration in which the maximum off time Toffmax of the switching element 22 is extended when the output command falls below a predetermined value.

(Embodiment 8)
In the discharge lamp lighting device of the fifth embodiment, the output current control when the load is short-circuited is configured to increase the maximum off-time adjustment amount when the primary peak current command Uipk to be fed back becomes smaller than the offset value Vdo2, In the oscillation circuit 608G of this embodiment shown in FIG. 11 and its peripheral circuits, the short-circuit current control is performed by extending the maximum off time Toffmax by reducing the charging current Is of the capacitor Cs included in the off-timer circuit 608a of the oscillation circuit 608G. Is to do.

  The control circuit 6 according to the present embodiment converts the primary peak current command Uipk into voltage-current and supplies the current Iu, and supplies the current Ido2 by converting the offset amount Vdo2 into voltage-current. A V-I converter 617, a resistor Rip inserted in a path of a primary current detection signal input to the comparator 610, and a current source J3 that supplies a current Iip to a connection point between the resistor Rip and the comparator 610, The current output of the VI converter 616 is connected to the current input of the VI converter 617. Then, the offset amount Vdo1 = Rip · Iip is superimposed on the primary current detection signal, and the comparator 610 compares the added value of the primary current detection signal and the offset amount Vdo1 with the primary-side peak current command Uipk. To output a forced-off signal.

  The oscillation circuit 608G of the present embodiment is configured so that the V-I converter 616 has a connection point between the current output of the VI converter 608d and the current output of the VI converter 608e of the oscillation circuit 608C shown in the fourth embodiment. The diode Ds1 connected in the forward direction toward the current output and the connection point between the current output of the VI converter 608d and the current output of the VI converter 608e were connected in the forward direction toward the capacitor Cs. A diode Ds2, a current Itfx flows through the diode Ds1, and a current Is flows through the diode Ds2.

  In the above circuit, the difference Iu-Ido2 between the current Iu supplied from the VI converter 616 and the current Ido2 supplied from the VI converter 617 is calculated. If Vdo2 <Uipk, the current Iu and the current Ido2 are The difference becomes positive, and this difference current Iu-Ido2 tries to increase the charging current Is to the capacitor Cs in an attempt to flow in the direction of the capacitor Cs, but the current from the VI converter 616 to the capacitor Cs is caused by the diode Ds1. It is blocked and does not affect circuit operation. On the other hand, when the output of the DC-DC converter circuit 2 is short-circuited and the voltage Vdo2> the voltage Uipk, the difference Iu-Ido2 between the current Iu and the current Ido2 is negative, and a part of the charging current Is of the capacitor Cs is As the current Itfx flows into the V-I converter 617 via the diode Ds1, the charging current Is is decreased, and the maximum OFF time Toffmax of the switching element 22 is controlled to increase.

  As described above, in this embodiment, the charging current Is of the capacitor Cs constituting the off-timer circuit 608a is reduced when the output is short-circuited, and the maximum off-time Toffmax is extended. However, the comparator Comp1 constituting the off-timer circuit 608a uses the capacitor Comp1. The threshold voltage to be compared with the voltage across Cs may be increased when the output is short-circuited to extend the maximum off time Toffmax.

  Further, the means for superimposing the offset amount on the primary current detection signal includes a resistor Rip connected in series to the input path of the primary current detection signal and a current source J3 that supplies the current Iip to the output side of the resistor Rip. Composed. By adopting such a configuration, the level of the primary current detection signal is not lowered when the offset amount is superimposed, and the responsiveness is not deteriorated. The offset voltage in this configuration is determined by Rip · Iip.

(Embodiment 9)
FIG. 12 shows specific examples of the oscillation circuit 608H of this embodiment and the lighting determination circuit 615, the short circuit control circuit 618, the offset superimposing circuit 619, the output voltage detection circuit 620, and the input voltage detection circuit 621 that are peripheral circuits thereof. . The oscillation circuit 608 includes an off timer circuit 608a, an on timer circuit 608b, a set / reset flip-flop 608c, a VI conversion circuit 608d, a VI conversion circuit 608e, an overvoltage control circuit 608k, and a lower limit frequency defining circuit 608m.

  The off-timer circuit 608a is connected in parallel to the capacitor Cs, with PNP transistors Trs1 and Trs2 having their emitters connected to the control power supply Vcc and their bases connected, a capacitor Cs connected between the collector of the transistor Trs2 and circuit ground. A comparator Comp1 in which a series circuit of a resistor Rs4 and an NPN transistor Trs3, a collector of the transistor Trs2 is connected to an inverting input terminal, and an output is connected to a set terminal of the set / reset flip-flop 608c, and a non-inverting input terminal of the comparator Comp1 A series circuit of a resistor Rs5 and an NPN transistor Trs4 connected between circuit grounds, resistors Rs6 and Rs7 each having one end connected to the non-inverting input terminal of the comparator Comp1, and a base of the transistor Trs4 An anti-Rs8, an AND element ICs1 that drives the transistor Trs4 via the resistor Rs8, and a NOT element ICs2 connected between the output of the set / reset flip-flop 608c and one input of the AND element ICs1, and the transistor Trs3 The base is connected to the output of the set / reset flip-flop 608c via the resistor Rs9, and the forced ON signal output from the comparator 610 is input to the other input of the AND element ICs1 via the AND element 608n. The base and collector are short-circuited.

  The on-timer circuit 608b is connected in parallel to the capacitor Cr, PNP transistors Trr1 and Trr2 having their emitters connected to the control power supply Vcc and their bases connected to each other, a capacitor Cr connected between the collector of the transistor Trr2 and circuit ground. A comparator Comp2 in which a series circuit of a resistor Rr4 and an NPN transistor Trr3, a collector of the transistor Trr2 is connected to an inverting input terminal, and an output is connected to a reset terminal of the set / reset flip-flop 608c, and a non-inverting input terminal of the comparator Comp2 A series circuit of a resistor Rr5 and an NPN transistor Trr4 connected between circuit grounds, a resistor Rr6 connected between a non-inverting input terminal of the 5V power supply and the comparator Comp1, and a base resistance of the transistor Trr4 Rr8, AND element ICr1 driving transistor Trr4 via resistor Rr8, inverted output of set / reset flip-flop 608c, resistor Rr9 connected between the base of transistor Trr3, and inverted output of set / reset flip-flop 608c A NOT element ICr2 connected between one input of the AND element ICr1, and the other input of the AND element ICr1 is input with a forced OFF signal output from the comparator 609. The emitter of the transistor Trr1 is connected to the collector of the transistor Tr40. The base and collector of the transistor Trr1 are short-circuited.

  The VI conversion circuit 608d performs voltage-current conversion on the detection signal of the input voltage Vin of the DC-DC converter circuit 2 output from the input voltage detection circuit 621, and connects each emitter to the control power supply Vcc and PNP transistors Tr10 and Tr11 having bases connected thereto, and a series circuit of an NPN transistor Tr12 and a resistor Rvi connected between a collector of the transistor Tr11 and circuit ground, and the base and collector of the transistor Tr11 are short-circuited. The output of the input voltage detection circuit 621 is connected to the base of Tr12, and a voltage-current converted current Ivin flows through the transistor Tr12.

  The VI conversion circuit 608e performs voltage-current conversion on the detection signal of the output voltage Vout of the DC-DC converter circuit 2 output from the output voltage detection circuit 620, and connects each emitter to the control power supply Vcc and PNP type transistors Tr13 and Tr14 having bases connected thereto and an NPN type transistor Tr15 connected to the collector of the transistor Tr14, the base and collector of the transistor Tr14 are short-circuited, and the output of the output voltage detection circuit 620 is connected to the base of the transistor Tr15. Are connected, and the current Ivout subjected to voltage-current conversion flows through the transistor Tr13.

  The overvoltage control circuit 608k includes a NOT element IC1 that receives a lighting determination signal output from the lighting determination circuit 615 having the same configuration as that of the sixth embodiment, and NPN transistors Tr16 and Tr18 that are driven by the output of the NOT element IC1. The base resistance R1 of the transistor Tr16, the base resistance R3 of the transistor Tr18, the emitter of the transistor Tr15 of the VI conversion circuit 608e are connected to the non-inverting input terminal, and the threshold voltage Vn2 is connected to the inverting input terminal. Comparator Comp4, transistor Tr17 driven by the output of comparator Comp4, and base resistance R2 of transistor Tr17 are provided. The collector of transistor Tr13 of VI conversion circuit 608e is connected to the collector of transistor Tr18, and the transistor The collector of Tr16 is connected to the off-timer circuit resistance 608a Rs6.

  The lower limit frequency defining circuit 608m connects NPN transistors Tr19 and Tr21 connected between the collector of the transistor Trs1 of the off-timer circuit 608a and the circuit ground, the transistor Tr19 and the base, the transistor Tr13 and the collector, and the base − An NPN transistor Tr20 having a short-circuited collector, an NPN transistor Tr22 having a base connected to the transistor Tr21, a base connected to the collector of the transistor Tr22, a collector connected to the control power source Vcc, and each of the transistors Tr21 and Tr22 An NPN transistor Tr23 whose emitter is connected to the base and the output of the input voltage detection circuit 621 are connected to the base, the control power supply Vcc is connected to the collector, and the emitter is connected to the other end of the resistor Rs7. And a NPN type transistor Tr24, the base of the transistor Tr21,22 is connected to the base of the transistor Tr40.

  Next, the short-circuit control circuit 618 has PNP transistors Tr25 and Tr26, PNP transistors Tr29 and Tr30, PNP transistors Tr33 and Tr34, and collectors of the transistors Tr25, each emitter connected to the control power supply Vcc and the bases connected to each other. A series circuit of a resistor Rsc1 connected between the circuit ground and the PNP transistor Tr27, an NPN transistor Tr28 connected between the collector of the transistor Tr26 and the circuit ground, and a resistor Rsc2 connected between the collector of the transistor Tr29 and the circuit ground And a PNP transistor Tr31, a NPN transistor Tr32 connected between the collector of the transistor Tr30 and the circuit ground, and a PNP transistor Tr32 connected in series to the transistor Tr34. The transistor Tr35 is provided with a resistor Rsc3 which receives the primary peak current command Uipk from one end and is connected to the base of the transistor Tr27 at the other end, and the bases and collectors of the transistors Tr25, Tr28, Tr29 and Tr34 are short-circuited. The base of the transistor Tr31 is connected to the offset voltage Vdo2, and the collectors of the transistors Tr30 and Tr33 are connected to the base of the transistor Tr35.

  The offset superimposing circuit 619 has one end connected to the collector of the transistor Tr36, and PNP-type transistors Tr36 to Tr39 having their emitters connected to the control power supply Vcc and their bases connected to each other. One end is connected to the input of the resistor Rip and the collector of the transistor Tr37, the resistor Rip1 to which the primary peak current command Uipk is input from the other end, and the resistor Rip2 connected between the collector of the transistor Tr37 and the circuit ground And a current source J4 connected between the collector of the transistor Tr39 and the circuit ground to supply the current Iip, the base and the collector of the transistor Tr39 are short-circuited, and the voltage detection across the switching element 22 is detected at the collector of the transistor Tr38. A signal is input. This switching element voltage detection signal is also input to the inverting input terminal of the comparator 610, and the non-inverting input terminal of the comparator 610 is connected to a 5V power source. The collector of the transistor Tr36 is connected to the non-inverting input terminal of the comparator 609, and the collector of the transistor Tr37 is connected to the inverting input terminal of the comparator 609.

  The output voltage detection circuit 620 has an operational amplifier OP1, a resistor Ro1 having one end connected to the non-inverting input terminal of the operational amplifier OP1, and one end connected to the inverting input terminal of the operational amplifier OP1, and the inverting input of the comparator Comp5 of the lighting determination circuit 615. A resistor Ro2 having the other end connected to the terminal and the emitter of the transistor Tr15 of the V-I conversion circuit 608e, and a resistor Ro3 connected between the inverting input terminal of the operational amplifier OP1 and the circuit ground, and the other end of the resistor Ro1 has A voltage obtained by dividing the output voltage Vout of the DC-DC converter circuit 2 by resistors Ro4 and Ro5 is input.

  The input voltage detection circuit 621 includes a series circuit of resistors Ri1 and Ri2 that resistance-divides the input voltage Vin of the DC-DC converter circuit 2, and an operational amplifier OP2 in which a connection point of the resistors Ri1 and Ri2 is connected to a non-inverting input terminal. The inverting input terminal of the operational amplifier OP2 is connected to the emitter of the transistor Tr12 of the VI conversion circuit 608d, and the output of the operational amplifier OP2 is connected to the bases of the transistors Tr12 and Tr24.

  Next, the operation of this embodiment will be described. First, the off-timer circuit 608a of the oscillation circuit 608H detects that the off-time of the switching element 22 has reached a predetermined time by comparing the charging voltage of the capacitor Cs with a threshold value by the comparator Comp1, and the on-timer of the oscillation circuit 608H. The circuit 608b detects that the ON time of the switching element 22 has reached a predetermined time by comparing the charging voltage of the capacitor Cr with a threshold value by the comparator Comp2. The charging current Ir to the capacitor Cr is a current Ivin determined by the input voltage Vin of the DC-DC converter circuit 2, that is, the voltage of the DC power supply 1, and the charging current Is to the capacitor Cs is the current Ivin and the DC-DC converter circuit 2 And the current Ivout determined by the output voltage Vout. The difference from the eighth embodiment is that the current signals Ivin and Ivout to the off-timer circuit 608a and the on-timer circuit 608b are charged by the current mirror circuits inside the off-timer circuit 608a and the on-timer circuit 608b to charge currents Is and Ir to the capacitors Cs and Cr. It is a point that has been converted to.

  The input voltage detection circuit 621 constitutes a buffer amplifier by the operational amplifier OP2 using the voltage of the resistor Rvi as a feedback voltage, and the current flowing through the resistor Rvi, that is, the collector current of the transistor Tr12 is used as the current signal Ivin. At this time, the current signal Ivin = RVin · {Ri2 / (Rvi · (Ri1 + Ri2))}.

  Similarly to the input voltage detection circuit 621, the output voltage detection circuit 620 performs voltage-current conversion by the operational amplifier OP1, the transistor Tr15 connected to the output terminal of the operational amplifier OP1, and the emitter resistors Ro2 and Ro3 of the transistor Tr15. Ro2 is also used as the feedback resistor of the operational amplifier OP1. Note that the circuit configurations of the output voltage detection circuit 620 and the input voltage detection circuit 621 are not limited to the above configurations.

  When the primary peak current command Uipk, which is an adjustment signal for the on-time of the switching element 22, is equal to or less than the offset voltage Vdo2, the adjustment signal Itfx is output from the collector of the transistor Tr35 of the short-circuit control circuit 618 to the off-timer circuit 608a. The charging current Is to the capacitor Cs, that is, the sum current of the current Ivin and the current Ivout is reduced, the charging current Is is reduced, and the maximum off time Toffmax of the switching element 22 is lengthened.

  In the short-circuit control circuit 618, the current signal Iu ′ obtained from the primary peak current command Uipk and flowing through the transistor Tr32 is Iu ′ = {(Vcc−2 · Vbe) / Rsc} − (Uipk / Rsc). The current signal Ido2 'obtained from the offset voltage Vdo2 and flowing through the transistor Tr30 is Ido2' = {(Vcc-2 · Vbe) / Rsc}-{Vdo2 / Rsc}. Here, Vbe is a base-emitter voltage of each transistor constituting the short circuit control circuit 618, and Rsc is a resistance value of the resistors Rsc1 and Rsc2. Then, a difference signal between the current signal Iu 'and the current signal Ido2' is output as the adjustment signal Itfx via the current mirror circuit. If the characteristics of the transistors and resistors constituting the short-circuit control circuit 618 are substantially the same, Itfx = (Vdo2-Uipk) / Rsc. The final-stage current mirror circuit constituting the short-circuit control circuit 618 has an adjustment signal Itfx of substantially zero when Iu ′ <Ido2 ′, that is, when Uipk> Vdo2, and operates in the same manner as in the eighth embodiment. .

  In the offset superimposing circuit 619, the primary current detection signal is input through the resistor Rip, and the current Iip is supplied through the current mirror circuit, whereby the offset voltage Vdo1 = Rip · Iip is set to the primary current detection signal. It is superimposed on.

  Further, the offset voltage is also superimposed on the primary-side peak current command Uipk that is compared with the primary current detection signal by the comparator 609. When the primary-side peak current command Uipk is the offset voltage Vdo1, the comparator 609 It is desirable to set each resistance value of the resistors Rip1 and Rip2 so that the signal input to the non-inverting input terminal becomes the offset voltage Vdo1. Further, since the resistors Rip1 and Rip2 divide the primary peak current command Uipk, when the primary current detection signal is small, the setting of the control gain and the noise resistance can be improved.

  When the discharge lamp 5 is turned off immediately before lighting, the output voltage Vout of the DC-DC converter circuit 2 becomes higher than normal, and the detection signal output from the output voltage detection circuit 620 exceeds the voltage VLGT in the lighting determination circuit 615. When the comparator Comp5 detects this, the comparator Comp5 outputs an L level signal. In the overvoltage control circuit 608k, the transistor Tr18 is turned on via the NOT element IC1, thereby causing the current Ivout from the VI conversion circuit 608e. Is short-circuited to the circuit ground, and the current Ivout is deleted from the charging current Is of the capacitor Cs of the off-timer circuit 608a. Further, an L level signal is also input to one input of the AND element 608n so that the forced on signal is not transmitted to the off timer circuit 608a. The L level signal output from the comparator Comp5 turns on the transistor Tr16 via the NOT element IC1, and the threshold voltage that the comparator Comp1 of the off-timer circuit 608a compares with the charging voltage of the capacitor Cs is fixed to a predetermined value. . Further, in the overvoltage control circuit 608k, when the comparator Comp4 detects that the detection signal output from the output voltage detection circuit 620 exceeds the voltage Vn2, the transistor TR17 is turned on, and the comparator Comp2 of the on-timer circuit 608b charges the capacitor Cr. The on-time of the switching element 22 is fixed to the minimum on-time Tonmin by minimizing the threshold voltage to be compared with the voltage.

  The present invention is not limited to the configuration shown in the above-described embodiment, and any configuration that performs the same operation may be used.

It is a figure which shows the structure of the discharge lamp lighting device of Embodiment 1 of this invention. It is a figure which shows operation | movement same as the above, (a) shows the state of a switching element, (b) shows the current waveform which flows through an inductance element, (c) shows the voltage waveform of an inductance element. It is a figure which shows the structure of the discharge lamp lighting device of Embodiment 2 of this invention. It is a figure which shows the structure of a function circuit and an oscillation circuit same as the above. It is a figure which shows the structure of the functional circuit using the microcomputer same as the above. It is a figure which shows the structure of the oscillation circuit of Embodiment 3 of this invention. It is a figure which shows the structure of the oscillation circuit of Embodiment 4 of this invention. It is a figure which shows the structure of the oscillation circuit of Embodiment 5 of this invention. It is a figure which shows the structure of the oscillation circuit of Embodiment 6 of this invention. It is a figure which shows the structure of the discharge lamp lighting device of Embodiment 7 of this invention. It is a figure which shows the structure of the oscillation circuit of Embodiment 8 of this invention, and its peripheral circuit. It is a figure which shows the structure of the oscillation circuit of Embodiment 9 of this invention, and its peripheral circuit. It is a figure which shows the structure of the conventional discharge lamp lighting device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power supply 2 DC-DC converter circuit 6 Control circuit 10 Load circuit 22 Switching element 23 Diode 24 Capacitor 211 Inductive element VL1, VL2 Inductive element voltage I1, I2 Inductive element current

Claims (21)

DC power supply,
A DC power supply comprising at least a switching element and an inductance element, storing energy from a DC power source at least in the inductance element when the switching element is ON, and discharging at least energy stored in the inductance element when the switching element is OFF. A DC-DC conversion circuit that converts at least the output of power into power required by the discharge lamp;
Output state detection means for detecting an output state of the DC-DC conversion circuit, error amplification means for receiving an output detection signal output from the output state detection means and a predetermined command value, and depending on the output of the error amplification means Adjusting the ON time of the switching element, and when the current flowing through the inductance element reaches approximately zero after the switching element is switched from ON to OFF, the switching element is turned ON, Switching for controlling the off-time to last at least a first time and not to exceed a second time, and to control the on-time of the switching element to last at least a third time and not to exceed a fourth time A control circuit comprising a control means and controlling the operation of the switching element,
The control circuit uses a maximum off-time adjustment function having a variable of a first voltage applied to the inductance element when the switching element is on and a second voltage generated at the inductance element when the switching element is off. A discharge lamp lighting device characterized by adjusting a second time. The control circuit uses the value obtained by dividing the first voltage by the sum of the first voltage and the second voltage multiplied by the maximum switching period of the switching element as the second time. The discharge lamp lighting device according to claim 1. The inductance element is a transformer, and the control circuit divides a value obtained by multiplying the first voltage by the transformer boost ratio by a sum of a value obtained by multiplying the first voltage by the transformer boost ratio and the second voltage. The discharge lamp lighting device according to claim 1, wherein a value obtained by multiplying the calculated value by a maximum switching period of the switching element is used as the second time. The first voltage is replaced with a voltage in the DC-DC conversion circuit capable of obtaining the first voltage equivalently, and the second voltage is replaced with the DC capable of obtaining the second voltage equivalently. 4. The discharge lamp lighting device according to claim 2, wherein the voltage is replaced with a voltage in a DC conversion circuit. 5. The voltage in the DC-DC conversion circuit capable of obtaining the first voltage and the second voltage equivalently is an input voltage and an output voltage of the DC-DC conversion circuit. The discharge lamp lighting device described. The DC-DC conversion circuit includes a step-up / down converter, and the control circuit converts an input voltage of the DC-DC conversion circuit between an input voltage of the DC-DC conversion circuit and an output voltage of the DC-DC conversion circuit. 6. The discharge lamp lighting device according to claim 5, wherein a value obtained by multiplying the sum divided by the maximum switching period of the switching element is used as the second time. The DC-DC conversion circuit includes a step-up / step-down converter or a flyback converter including a transformer as the inductance element, and the control circuit multiplies the input voltage of the DC-DC conversion circuit by a boost ratio of the transformer. A value obtained by multiplying the value obtained by multiplying the input voltage of the DC-DC conversion circuit by the sum of the step-up ratio of the transformer and the output voltage of the DC-DC conversion circuit is multiplied by the maximum switching period of the switching element. 6. The discharge lamp lighting device according to claim 5, wherein the time is two. The control circuit is composed of an analog arithmetic circuit and obtains the second time, a first capacitor, a charging voltage of the first capacitor, and a first voltage set in accordance with the second time And an off-timer circuit for measuring a second time, and immediately after the switching element is turned off, the first capacitor whose charging voltage is substantially zero is charged, 8. The discharge lamp lighting device according to claim 1, wherein the switching element is turned on when the comparator detects that the charging voltage of one capacitor has reached the first voltage. The control circuit responds to the function circuit that analog-converts and outputs the second time obtained using a microcomputer, and the first capacitor and the charging voltage of the first capacitor and the second time subjected to analog conversion. And an off-timer circuit that measures a second time with a comparator that compares the first voltage set to the first voltage, and the charging voltage is substantially zero immediately after the switching element is turned off. 8. The capacitor according to claim 1, wherein the capacitor is charged and the switching element is turned on when the comparator detects that the charging voltage of the first capacitor has reached the first voltage. Discharge lamp lighting device. The control circuit includes a first capacitor and a comparator that compares a charging voltage of the first capacitor and a first voltage set according to a second time, and an off timer that measures a second time. A circuit is provided, and immediately after the switching element is turned off, the first capacitor whose charging voltage is substantially zero is charged, and the comparator indicates that the charging voltage of the first capacitor has reached the first voltage. If detected, the switching element is turned on, and the charging current of the first capacitor is adjusted by an element constituting the denominator of the maximum off-time adjustment function expressed in fraction, and the first voltage is expressed in fraction The discharge lamp lighting device according to any one of claims 1 to 7, wherein the discharge lamp lighting device is adjusted by at least a variable element among elements constituting the numerator of the maximum off-time adjustment function expressed. The control circuit includes a first capacitor and a comparator that compares a charging voltage of the first capacitor and a first voltage set according to a second time, and an off timer that measures a second time. A circuit is provided, and immediately after the switching element is turned off, the first capacitor whose charging voltage is substantially zero is charged, and the comparator indicates that the charging voltage of the first capacitor has reached the first voltage. If detected, the switching element is turned on. The charging current of the first capacitor is obtained by multiplying the input voltage of the DC-DC conversion circuit by the step-up ratio of the transformer and the output voltage of the DC-DC conversion circuit. 8. The current according to claim 7, wherein the first voltage is a voltage proportional to a value obtained by multiplying an input voltage of the DC-DC conversion circuit by a step-up ratio of a transformer. Discharge Lighting device. The control circuit includes a first capacitor and a comparator that compares a charging voltage of the first capacitor and a first voltage set according to a second time, and an off timer that measures a second time. A circuit is provided, and immediately after the switching element is turned off, the first capacitor whose charging voltage is substantially zero is charged, and the comparator indicates that the charging voltage of the first capacitor has reached the first voltage. If detected, the switching element is turned on. The charging current of the first capacitor is proportional to the value obtained by multiplying the input voltage of the DC-DC conversion circuit by the step-up ratio of the transformer, and the DC-DC conversion circuit. The first voltage is a voltage proportional to a value obtained by multiplying the input voltage of the DC-DC conversion circuit by the step-up ratio of the transformer. Claim The discharge lamp lighting device according. The control circuit includes a comparator that compares the second capacitor and a charging voltage of the second capacitor with a second voltage set according to the third time or the fourth time. An on-timer circuit that measures time or a fourth time, and immediately after the switching element is turned on, the second capacitor having a charging voltage of approximately zero is charged, and the charging voltage of the second capacitor is The comparator detects that the voltage of 2 has been reached, thereby detecting that the third time or the fourth time has elapsed. The charging current of the second capacitor is the DC-DC conversion circuit. 13. The discharge lamp lighting device according to claim 12, wherein the current is proportional to a value obtained by multiplying the input voltage by a step-up ratio of the transformer. The control circuit sets the OFF time of the switching element to the second time while the output voltage of the DC-DC conversion circuit exceeds the third voltage, and outputs the output voltage of the DC-DC conversion circuit. 14. The discharge lamp lighting device according to claim 1, wherein an ON time of the switching element is set to the third time while the voltage exceeds a fourth voltage higher than the third voltage. . The control circuit determines whether or not an output voltage of the DC-DC conversion circuit exceeds a third voltage based on a determination result of a lighting determination circuit that determines whether or not the discharge lamp is lit. The discharge lamp lighting device according to claim 14. The control circuit sets the OFF time of the switching element to a fifth time shorter than the second time while the output voltage of the DC-DC conversion circuit exceeds the third voltage, and the DC− The on-time of the switching element is set to the third time while the output voltage of the DC conversion circuit exceeds a fourth voltage higher than the third voltage. The discharge lamp lighting device described. When the on-time adjustment signal reaches a first level or less when the on-time adjustment signal for adjusting the on-time of the switching element fluctuates in the direction of decreasing the on-time, the control circuit detects the on-time of the switching element. Is fixed at the third time, and when the on-time adjustment signal reaches a second level that is less than or equal to the first level, the second time depends on the difference between the on-time adjustment signal and the second level. The discharge lamp lighting device according to claim 1, wherein the time is increased. The DC-DC conversion circuit includes current detection means for detecting a current flowing through the switching element, and the control circuit superimposes a first signal as an offset amount on a detection output of the current detection means, and The time until the detection output on which the signal is superimposed reaches the on-time adjustment signal for adjusting the on-time of the switching element is set to the on-time of the switching element, and the magnitude of the on-time adjustment signal is below a predetermined level. 14. The discharge lamp lighting device according to any one of claims 1 to 13, wherein when it reaches, the second time is increased in accordance with a difference between an on-time adjustment signal and a predetermined level. The discharge lamp lighting device according to claim 18, wherein the magnitude of the first signal is equal to or greater than the predetermined level. The DC-DC conversion circuit includes current detection means for detecting a current flowing through the switching element, and the control circuit superimposes a first signal as an offset amount on a current detection signal of the current detection means, and Is set to the ON time of the switching element, and the magnitude of the ON time adjustment signal is a predetermined level. 9. The charging current of the first capacitor included in the off-timer circuit for measuring the second time is decreased according to a difference between an on-time adjustment signal and a predetermined level when the following is reached: The discharge lamp lighting device of any one of thru | or 12. The means for generating the first signal includes a resistor having one end connected to the detection output of the current detecting unit, and a current source for supplying a predetermined current to the other end of the resistor. 20. The discharge lamp lighting device according to any one of 20.

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