JP2005044674A - Lamp driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to easily control brightness without affecting the action of a lamp at all by applying a sufficiently high voltage and high current to both ends of the lamp by controlling duty ratio in a lamp driving device to control illumination. <P>SOLUTION: This device comprises a duty control part 10 to output low frequency rectangular signals (LP) in which the duty ratio is variable according to illumination control voltage (Vdim), a very high frequency generation part 20 to output high frequency oscillation signals (HP), a lamp control driving part 30, and an inverter 40. The lamp control driving part 30 receives these signals (LP, HP), and outputs a first driving signal (PUL1) by selecting the high frequency oscillation signals (HP) and converting them into the rectangular signals in the passivation zone of low frequency rectangular signals (LP), and a second driving signal (PUL2) into which the first driving signal (PUL1) is reversed. Responding to the first and the second driving signals (PUL1, PUL2), a first and a second switching parts (M1, M2) of the inverter 40 are turned on and turned off. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a lamp driving device, and more particularly to a lamp driving device capable of adjusting the brightness of an external electrode discharge lamp according to the magnitude of an illumination control voltage.

  External electrode discharge lamps do not have electrodes inside the lamp, and high voltage and high current are applied to the external electrodes formed at both ends of the lamp, and the gas inside the lamp is discharged by a strong electric field, and the lamp is lit. As a result, since there is no electrode inside, the pole loss due to ion bombardment (sputtering) can be reduced and the life of the lamp can be extended, and since it has capacitive load characteristics, it has excellent luminance maintenance characteristics.

  Conventional lamp illumination control methods for controlling the brightness of the lamp include a frequency control method and a burst method.

The frequency control method is used for general fluorescent lamp inverters, and adjusts the brightness of the lamp by controlling the current flowing in the lamp tube by changing the resonance frequency in the impedance matching coil and capacitance resonance region of the inverter section. This is suitable for a lamp driving device having a large resonance bandwidth.
JP 2000-78857 A

  However, the external electrode discharge lamp requires a high voltage and a high current at the time of starting, and does not disclose discharge unless the high voltage is maintained even after lighting. Therefore, a high voltage is not applied by a transformer having a high step-up ratio. Therefore, resonance by the coil and capacitance must be induced for impedance matching. Accordingly, since the resonance bandwidth must be set very narrow, the frequency control method cannot be used.

  FIG. 1 shows a block diagram of a burst system. The burst method is mainly used in an inverter of a cold cathode discharge lamp used as a light source of a liquid crystal display backlight (LCD's back light). As shown in FIG. 1, the inverter 1 and a DC power supply (Vdc) are used. As a method of adjusting the lamp illumination by changing the duty ratio of the frequency at which the switching transistor (S1) is turned on or off, this method is a cold cathode discharge lamp. It is suitable for use in lamps that operate with low voltage and low current.

  However, the power consumption of the external electrode discharge lamp is several to several tens of times or more than that of the cold cathode discharge lamp. Therefore, when the burst method is used, the power loss of the switching transistor (S1) is large and the entire system is reduced. When the burst method is used in the illumination control method of the external electrode discharge lamp, there is a problem that electromagnetic interference and heat are generated due to frequent switching noise caused by on / off. Therefore, the external electrode discharge lamp cannot use the burst method.

  An object of the present invention is to apply a sufficiently high voltage and high current to both ends of the external electrode discharge lamp by controlling the lamp point and the duty ratio within one cycle when the lamp is extinguished. An object of the present invention is to provide a lamp driving device that can easily control the brightness of a lamp without any influence.

  The lamp driving device of the present invention that achieves the above object includes a duty control unit that outputs a low-frequency rectangular signal having a duty ratio variable according to an illumination control voltage, and a high-frequency oscillation signal having a higher frequency than the low-frequency rectangular signal. A high-frequency generator that outputs a low-frequency rectangular signal and a high-frequency oscillation signal, select a high-frequency oscillation signal during the inactive period of the low-frequency rectangular signal, and convert the selected high-frequency oscillation signal into a rectangular wave signal The converted first drive signal and the second drive signal obtained by inverting the first drive signal are output, and the first drive signal and the second drive signal are inactivated during the activation period of the low-frequency rectangular signal. A lamp drive control unit; and inverter means for turning on / off the lamp. The inverter means is activated when the first drive signal is activated and the second drive signal is activated. A second switching unit that is turned on each time it is turned on, a coil having one terminal connected to a DC supply voltage, and a transformer, and the transformer includes primary side first and second coils, It is composed of a secondary coil in which a high voltage is induced at both ends of the lamp by currents induced in the primary side first and second coils, and one terminal of the primary side first and second coils is connected in common. The other terminals of the primary side first and second coils are connected to the first switching unit and the second switching unit, respectively, and the first switching unit is activated and is not connected. When activated, a back electromotive force is generated in the DC supply voltage from the primary side first coil, a high voltage is induced in the secondary side coil, and the second switching unit is activated and inactivated. And back electromotive force from the primary side second coil to the DC supply voltage Wherein the high voltage to the secondary coil generated is intended to be induced.

  In the present invention, a sufficient high voltage and high current are applied to both ends of the lamp by controlling the duty ratio within one cycle of turning on and off the lamp according to the voltage value of the illumination control voltage. The brightness of the lamp can be easily controlled without any effect.

  Hereinafter, a lamp driving device of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 2 is a block diagram showing the lamp driving device of the present invention, and FIG. 3 is a block diagram of the duty control unit of FIG.

  2 includes a duty control unit 10 that outputs a low-frequency rectangular signal (LP) having a duty ratio variable according to an illumination control voltage (Vdim), and a low-frequency rectangular signal (LP). A high-frequency generator 20 that outputs a high-frequency oscillation signal (HP) having a faster (higher) frequency, a lamp drive controller 30, and an inverter 40 that turns on and off the lamp 50 are included. The lamp drive control unit 30 receives the low frequency rectangular signal (LP) and the high frequency oscillation signal (HP) from the lamp drive control unit 30, and during the inactive period of the low frequency rectangular signal (LP), the high frequency oscillation signal ( HP), the first drive signal (PUL1) obtained by converting the selected high-frequency oscillation signal (HP) into a rectangular wave signal, and the second drive signal (PUL2) obtained by inverting the first drive signal (PUL1). And the first drive signal (PUL1) and the second drive signal (PUL2) are inactivated during the activation period of the low-frequency rectangular signal (LP). The inverter 40 is turned on each time the first drive signal (PUL1) is activated, and second switching is turned on each time the second drive signal (PUL2) is activated. A part (M2), a coil (L) whose one terminal is connected to a DC supply voltage (Vdc), and a transformer (T). This transformer (T) is high at both ends of the lamp 50 by currents induced in the primary side first and second coils (T11, T12) and the primary side first and second coils (T11, T12). The secondary side coil (T2) for inducing voltage is constructed, and one terminal of the primary side first and second coils (T11, T12) is connected in common to the other terminal of the coil (L). The other terminals of the primary side first and second coils (T11, T12) are connected to the first switching unit (M1) and the second switching unit (M2), respectively. When M1) is activated and deactivated, a back electromotive force is generated in the DC supply voltage (Vdc) from the primary side first coil (T11), and a high voltage is induced in the secondary side coil (T2). The second switching unit (M2) is activated and deactivated. When a high voltage is induced in the primary side of the second coil (T12) from the counter electromotive force is generated in the DC supply voltage (Vdc) 2 primary coil (T2).

  The duty control unit 10 includes a charging unit 11, a discharging unit (TR 1), and a low frequency generating unit 12. The charging unit 11 has one end connected to the DC supply voltage (Vdc) and the other end connected to the first node (N1), and one end connected to the first node (N1) and the other end. Is composed of a second resistor (R2) connected to the second node (N2), and a charging capacitor (CAP) having one end connected to the second node (N2) and the other end connected to the ground voltage (Vss). The charging capacitor (CAP) is charged with a voltage according to the time constants of the first resistor (R1), the second resistor (R2), and the charging capacitor (CAP). The discharge unit (TR1) receives the switching control signal (SWC) and discharges the voltage charged in the charging capacitor (CAP) of the charging unit 11 when the switching control signal (SWC) is activated. If the voltage charged in the charging capacitor (CAP) is higher than the first reference voltage (Vref1) smaller than the DC supply voltage (Vdc), the low-frequency generator 12 performs switching control input to the discharging unit (TR1). The signal (SWC) is activated to discharge the voltage charged in the charging capacitor (CAP) by the discharging unit (TR1), and the voltage charged in the charging capacitor (CAP) by discharging by the discharging unit (TR1) Is smaller than a second reference voltage (Vref2) that varies according to the voltage value of the illumination control voltage (Vdim), the switching control signal (SWC) input to the discharge unit (TR1) is deactivated to charge the capacitor. (CAP) is charged again, and the charging capacitor (CAP) is charged according to the variable voltage value of the second reference voltage (Vref2). To change that time, the duty ratio outputs the low-frequency rectangular signal (LP) for varying in accordance with the voltage value of the illumination control voltage (Vdim).

  The low frequency generation unit 12 includes a reference voltage generation unit 13, an illumination control unit 14, a first comparison unit (COMP 1), a second comparison unit (COMP 2), and a set / reset flip-flop 15. The reference voltage generator 13 includes third, fourth and fifth resistors (R3, R4, R5) sequentially connected in series between a DC supply voltage (Vdc) and a ground voltage (Vss). The DC supply voltage (Vdc) is distributed at a constant ratio, and the third node (N3), in which the third resistor (R3) and the fourth resistor (R4) are commonly connected, is supplied from the DC supply voltage (Vdc). The first reference voltage (Vref1), which is a low voltage, is output, and the fourth node (N4) in which the fourth resistor (R4) and the fifth resistor (R5) are connected in common is supplied from the first reference voltage (Vref1). The second reference voltage (Vref2), which is a low voltage, is output. The illumination control unit 14 includes a sixth resistor (R6) and a seventh resistor (R7), and a transistor (TR2) having an emitter end, a base end, and a collector end. In the illumination control unit 14, the illumination control voltage (Vdim) is set at a constant ratio by the sixth resistor (R6) and the seventh resistor (R7) connected in series between the illumination control voltage (Vdim) and the ground voltage (Vss). The voltage (Va) distributed in step (5) is output. The base end of the transistor (TR2) is connected to the distributed voltage (Va) of the sixth resistor (R6) and the seventh resistor (R7), and the collector end is connected to the first end. 1 is connected to the first reference voltage (Vref1), and the emitter end is connected to the second reference voltage (Vref2). Thus, as the illumination control voltage (Vdim) increases, the second reference voltage (Vref2) is increased to the first reference voltage (Vref2). It increases to the voltage (Vref1). The first comparator (COMP1) receives the voltage of the second node (N2) and the first reference voltage (Vref1) and is activated if the voltage of the second node (N2) is greater than the first reference voltage (Vref1). The first comparison signal (CP1) is output. The second comparator (COMP2) receives the voltage of the second node (N2) and the second reference voltage (Vref2) and is activated if the voltage of the second node (N2) is smaller than the second reference voltage (Vref2). The second comparison signal (CP2) is output. The set / reset flip-flop 15 has a reset terminal (R), a set terminal (S), a first output terminal (Q), and a second output terminal (QB) that outputs an inverted signal of the first output terminal (Q). The reset terminal (R) is connected to the first comparison signal (CP1), the set terminal (S) is connected to the second comparison signal (CP2), and the second comparison signal (CP2) is activated. Then, the first output terminal (Q) outputs a high logic value, and when the first comparison signal (CP1) is activated, the first output terminal (Q) outputs a low logic value. When the first comparison signal (CP1) and the second comparison signal (CP2) are all inactivated, the first output terminal (Q) latches the previous logic value and outputs a low frequency rectangular signal (LP). The second output terminal (QB) outputs a switching control signal (SWC).

  The discharge part (TR1) includes a transistor having a collector end, a base end, and an emitter end. The collector end is connected to the first node (N1), the emitter end is connected to the ground voltage (Vss), and the base is connected. The end is connected to the switching control signal (SWC) and is turned on when the switching control signal (SWC) is activated.

  The lamp drive control unit 30 includes a constant voltage generation unit 31 that outputs a constant reference voltage (Vr) that is smaller than the DC supply voltage (Vdc), and a reference voltage (Vr) that has one terminal as the output of the constant voltage generation unit 31. And the other terminal is connected to the other terminal of the eighth resistor (R8), and at the same time, the low-frequency rectangular signal (LP) ) Connected to the ninth resistor (R9), the comparison unit 32, and the current amplification unit 33. The comparison unit 32 receives the low-frequency rectangular signal (LP) and the high-frequency oscillation signal (HP) that swing based on the distribution voltage of the eighth resistor (R8) and the ninth resistor (R9), and compares them to generate a high-frequency signal. If the oscillation signal (HP) is larger than the low frequency rectangular signal (LP), it is activated and outputs a rectangular wave driving signal (DP). The current amplifier 33 amplifies the drive signal (DP), which is the output of the comparator 32, to increase the drive capability of the drive signal (DP), and the first drive signal (PUL1) and the first drive signal (PUL1) Is output as a second drive signal (PUL2).

  The operation of the lamp driving device of the present invention having the above-described configuration is as follows. The illumination control voltage (Vdim) that is an input of the duty control unit 10 varies from 0V to 5V as an externally applied voltage. For example, if the illumination control voltage (Vdim) is 0 V, the transistor (TR2) of the illumination control unit 14 is turned off, and the reference voltage generation unit 13 has a third resistor (R3), a fourth resistor (R4), and a fifth resistor (R5). ), A first reference voltage (Vref1) smaller than the DC supply voltage (Vdc) and a second reference voltage (Vref2) smaller than the first reference voltage (Vref1) are output. If the illumination control voltage (Vdim) increases sequentially from 0V, the distribution voltage (Va) of the sixth resistor (R6) and the seventh resistor (R7) increases, and the current flowing through the base of the transistor (TR2) increases. The on-resistance of the transistor (TR2) decreases. The second reference voltage (Vref2) increases to the first reference voltage (Vref1) due to a decrease in the on-resistance of the transistor (TR2). If the illumination control voltage (Vdim) increases to 5V, the second reference voltage (Vref2) becomes a voltage obtained by subtracting the threshold voltage of the transistor (TR2) from the first reference voltage (Vref1).

  FIG. 4a shows an operation waveform diagram of the lamp driving device of the present invention when the illumination control voltage (Vdim) is 0V. FIGS. 4b and 4c show that the illumination control voltage (Vdim) is sequentially increased from 0V. FIG. 4B is an operation waveform diagram when the second reference voltage (Vref2 ′) of FIG. 4B is larger than the second reference voltage (Vref2) of FIG. 4A. (Vref2 ″) is an operation waveform diagram when the voltage is higher than the second reference voltage (Vref2 ′) of FIG. 4B.

  The operation of FIG. 4a is described below. The charging capacitor CAP is connected to the first resistor R1, the second resistor R2 and the charging capacitor CAP that are connected in series between the DC supply voltage Vdc and the ground voltage Vss. The two nodes (N2) are charged. If the charging voltage (Vcap) charged in the charging capacitor (CAP) is larger than the first reference voltage (Vref1) of the reference voltage generator 13, that is, from t1 to t2, the output of the first comparator (COMP1) A certain first comparison signal (CP1) outputs a high logic value, and a second comparison signal (CP2) output from the second comparison unit (COMP2) outputs a low logic value. The low frequency rectangular signal (LP) at the first output terminal (Q) which is the output of the set / reset flip-flop 15 outputs a low logic value, and the switching control signal (SWC) at the second output terminal (QB) is high. Output a logical value. The discharge unit TR1 including the bipolar transistor is turned on by the switching control signal SWC having a high logic value, and the voltage Vcap charged in the charge capacitor CAP is the second resistor R2 and the discharge unit. The discharge starts to the ground voltage (Vss) through (TR1). If the charging voltage (Vcap) of the charging capacitor (CAP) is smaller than the first reference voltage (Vref1) and larger than the second reference voltage (Vref2) by discharging, that is, from the time t2 to the time t3, the first comparison unit (COMP1). The first comparison signal (CP1), which is the output of the second comparison signal, outputs a low logic value, and the second comparison signal (CP2), which is the output of the second comparison unit (COMP2), outputs a low logic value. Therefore, the low-frequency rectangular signal (LP) at the first output terminal (Q) that is the output of the set / reset flip-flop 15 outputs a low logical value that is the same logical value as the previous state, and the second output terminal ( The switching control signal (SWC) in QB) outputs a high logic value that is the logic value of the previous state. The discharging unit (TR1) is continuously turned on by the switching control signal (SWC) having a high logic value, and the voltage (Vcap) charged in the charging capacitor (CAP) is continuously discharged by the discharging unit (TR1). . If the charging voltage (Vcap) charged in the charging capacitor (CAP) by continuous discharge becomes smaller than the second reference voltage (Vref2), that is, at the time t3, the first output that is the output of the first comparison unit (COMP1). The comparison signal (CP1) outputs the same low logic value as in the previous state, and the second comparison signal (CP2), which is the output of the second comparison unit (COMP2), outputs a high logic value. The low frequency rectangular signal (LP) at the first output terminal (Q) of the set / reset flip-flop 15 outputs a high logic value, and the switching control signal (SWC) at the second output terminal (QB) outputs a low logic value. To do. The discharging unit (TR1) is turned off by the switching control signal (SWC) having a low logic value, and the DC voltage (Vdc) starts to be charged in the charging capacitor (CAP). If the charging voltage (Vcap) of the charging capacitor (CAP) is larger than the second reference voltage (Vref2), the second comparison signal (CP2) that is the output of the second comparison unit (COMP2) outputs a low logic value at time t4. As a result, the low-frequency rectangular signal (LP) at the first output terminal (Q) of the set / reset flip-flop 15 outputs the same high logic value as in the previous state, and the switching control signal at the second output terminal (QB). (SWC) outputs a low logic value. The switching control signal (SWC) continues to have a low logic value until the charging voltage (Vcap) of the charging capacitor (CAP) becomes larger than the first reference voltage (Vref2), that is, from the time t4 to the time t5. Thus, the discharge part (TR1) is continuously turned off.

  The increase of the illumination control voltage (Vdim) from 0V to 5V by the above method will be described. As shown in FIG. 4b, when the second reference voltage (Vref2 ′) has a voltage higher than the second reference voltage (Vref2) of FIG. 4a, the low frequency rectangular signal (LP) is t1 to t3 time. Since it has a low logic value during this period, the interval having a low logic value is reduced compared to the low frequency rectangular signal (LP) of FIG. 4a. As shown in FIG. 4c, when the illumination control voltage (Vdim) is further increased from that of FIG. 4b, the second reference voltage (Vref2 ″) has a voltage larger than the second reference voltage (Vref2 ′) of FIG. 4b. Accordingly, the interval of the low-frequency rectangular signal (LP) having the low logic value is further reduced, that is, the low-frequency rectangular signal (LP) is increased as the illumination control voltage (Vdim) is increased from 0V to 5V. ) Of the low frequency rectangular signal (LP) having a low logic value is decreased.

  Therefore, the duty control unit 10 changes the charge / discharge of the charging voltage (Vcap) of the charging capacitor (CAP) and the illumination control voltage (Vdim) so that the duty ratio of several hundreds Hz can be changed. LP) is output.

  The constant voltage generator 31 of the lamp drive controller 30 outputs 5V, which is a constant reference voltage (Vr) smaller than the DC supply voltage (Vdc), and the low-frequency rectangular signal (LP) is the reference voltage (Vr). The eighth resistor (R8) and the ninth resistor (R9) connected in series between the ground voltage (Vss) swing based on a distribution voltage determined by a ratio of resistance values of these resistors. For example, if the eighth resistor (R8) and the ninth resistor (R9) have the same value, the low-frequency rectangular signal (LP) becomes a rectangular wave signal that swings with 2.5V as a reference. The comparison unit 32 compares the high frequency oscillation signal (HP) of about 50-60 kHz output from the high frequency generation unit 20 with the low frequency rectangular signal (LP), and the high frequency oscillation signal (HP) is compared with the low frequency rectangular signal (HP). If it is greater than (LP), it is activated and outputs a rectangular wave drive signal (DP). That is, as shown in FIG. 4a, the drive signal (DP) that is the output of the comparison unit 32 is in a section where the low-frequency rectangular signal (LP) has a low logic value in the section from t1 to t3. The high-frequency oscillation signal (HP) is output as it is, and the low-frequency rectangular signal (LP) has a low logic value in the interval where the low-frequency rectangular signal (LP) has a high logic value, which is from t3 to t5. The current amplification unit 33 of the lamp drive control unit 30 amplifies the drive signal (DP) that is the output of the comparison unit 32 to increase the drive capability of the drive signal (DP), and the first drive signal (PUL1), A second drive signal (PUL2) obtained by inverting the first drive signal (PUL1) is output. The first switching unit (M1) and the second switching unit (M2) of the inverter 40 are turned on or off by the first driving signal (PUL1) and the second driving signal (PUL2), respectively, and the first switching unit (M1) is turned on. When turned from on to off, a counter electromotive force is generated in the primary side first coil (T11) of the transformer (T), and the counter electromotive force causes the secondary side coil (T2) of the transformer (T). A high voltage is induced and the lamp 50 is lit during the period t1 to t3 as shown in FIG. 4a. Similarly, counter electromotive force is generated in the primary second coil (T12) of the transformer (T) by turning on or off the second switching unit (M2), and the transformer (T ) Is induced in the secondary coil (T2), and the lamp 50 is lit in the period from t1 to t3. In the period from t3 to t4 in which the drive signal (DP) has a low logic value, the first drive signal (PUL1) and the second drive signal (PUL2) all have a low logic value, and the lamp 50 Turns off.

  Accordingly, the lamp driving device of the present invention adjusts the brightness of the lamp 50 by changing the voltage value of the illumination control voltage (Vdim) to adjust the duty ratio within one cycle when the lamp 50 is turned on / off. be able to.

It is a block diagram of the lamp drive device which uses the conventional burst system. It is a block diagram of the lamp drive device of this invention. It is a block diagram of the low frequency generation part of FIG. It is an operation | movement timing diagram of the lamp drive device of this invention. The case where the illumination control voltage is 0V is shown. It is a figure similar to FIG. 4a which shows the case where an illumination control voltage is increased. It is a figure similar to FIG. 4a-4b which shows the case where an illumination control voltage is further increased.

Explanation of symbols

10: duty controller 20: high frequency generator 30: lamp drive controller 40: inverter 50: lamp Vdim: illumination control voltage LP: rectangular signal HP: high frequency oscillation signal PUL1: first drive signal PUL2: second drive signal M1: 1st switching part M2: 2nd switching part

Claims (5)

In the lamp driving device that controls the illumination of the lamp according to the illumination control voltage,
Duty control means for outputting a low-frequency rectangular signal having a duty ratio variable according to the illumination control voltage;
High-frequency generating means for outputting a high-frequency oscillation signal having a higher frequency than the low-frequency rectangular signal;
First, the low-frequency rectangular signal and the high-frequency oscillation signal are received, the high-frequency oscillation signal is selected during the inactive period of the low-frequency rectangular signal, and the selected high-frequency oscillation signal is converted into a rectangular wave signal. A ramp that outputs a driving signal and a second driving signal obtained by inverting the first driving signal, and the first driving signal and the second driving signal are inactivated during the activation period of the low-frequency rectangular signal. Drive control means;
Comprising inverter means for turning on and off the lamp,
The inverter means includes a first switching unit that is turned on each time the first drive signal is activated, a second switching unit that is turned on each time the second drive signal is activated, and one terminal having a direct current. Consists of a coil connected to the supply voltage and a transformer,
The transformer includes a primary side first and second coils and a secondary side coil in which a high voltage is induced at both ends of the lamp by currents induced in the primary side first and second coils. The terminals of the primary side first and second coils are connected in common and connected to the other terminal of the coil, and the other terminals of the primary side first and second coils are respectively connected to the first terminal. When the first switching unit is activated and deactivated, a back electromotive force is generated from the primary side first coil to the DC supply voltage when connected to the switching unit and the second switching unit. When a high voltage is induced in the secondary side coil and the second switching unit is activated and deactivated, a back electromotive force is generated in the DC supply voltage from the primary side second coil, A high voltage is induced in the secondary coil. Lamp driving device for. The duty control means includes
A first resistor having one end connected to the DC supply voltage and the other end connected to the first node, a second resistor connected to the first node and one end connected to the second node, and one end connected to the first node Charging means connected to two nodes and connected to the ground voltage at the other end, and charging means for charging the charging capacitor with a voltage according to a time constant of the first resistor, the second resistor and the charging capacitor;
Discharging means for receiving a switching control signal and discharging a voltage charged in a charging capacitor of the charging means when the switching control signal is activated;
If the voltage charged in the charging capacitor is greater than a first reference voltage smaller than a DC supply voltage, a voltage charged in the charging capacitor by the discharging means by activating a switching control signal input to the discharging means. If the voltage charged in the charging capacitor by the discharging by the discharging means is smaller than the second reference voltage that varies according to the voltage value of the illumination control voltage, the switching control signal input to the discharging means is The charging capacitor is reactivated and the charging capacitor is charged again, and the charging time of the charging capacitor is changed according to the variable voltage value of the second reference voltage, and the duty ratio is varied according to the voltage value of the illumination control voltage. The lamp driver according to claim 1, further comprising low-frequency generating means for outputting a low-frequency rectangular signal. Apparatus. The low frequency generation means includes
The third and fourth resistors are sequentially connected in series between the DC supply voltage and the ground voltage, and the DC supply voltage is distributed at a certain ratio, and the third resistor A first reference voltage, which is lower than the DC supply voltage, is output to a third node having a fourth resistor connected in common, and a fourth node having the fourth resistor and a fifth resistor connected in common to the third node. Reference voltage generating means for outputting a second reference voltage that is lower than the first reference voltage;
The sixth resistor and the seventh resistor connected in series between the illumination control voltage and the ground voltage output a voltage obtained by distributing the illumination control pre-pressure at a constant ratio, and have an emitter end, a base end, and a collector end. The base terminal is connected to the distributed voltage of the sixth resistor and the seventh resistor, the collector terminal is connected to the first reference voltage, the emitter terminal is connected to the second reference voltage, and the illumination control voltage is connected. Illumination control means comprising a transistor in which the second reference voltage increases to the first reference voltage as the voltage increases.
First comparison means for receiving the voltage of the second node and the first reference voltage and outputting an activated first comparison signal if the voltage of the second node is greater than the first reference voltage;
Second comparison means for receiving the second node voltage and the second reference voltage and outputting an activated second comparison signal if the second node voltage is lower than the second reference voltage;
A reset terminal, a set terminal, a first output terminal, and a second output terminal for outputting an inverted signal of the first output terminal; the reset terminal is connected to the first comparison signal; and the set terminal is the second comparison terminal When the second comparison signal is activated, the first output terminal outputs a high logic value, and when the first comparison signal is activated, the first output terminal outputs a low logic value. When the first comparison signal and the second comparison signal are all inactivated, the first output terminal latches the previous logical value, the first output terminal outputs a low-frequency rectangular signal, and the second output 3. The lamp driving apparatus according to claim 2, wherein the terminal includes a set / reset flip-flop that outputs a switching control signal.   The discharge means has a collector end, a base end, and an emitter end. The collector end is connected to the first node, the emitter end is connected to a ground voltage, and the base end is connected to a switching control signal. 3. The lamp driving device according to claim 2, wherein the lamp driving device comprises a transistor that is turned on when activated. The lamp drive control means includes
Constant voltage generating means for outputting a constant reference voltage smaller than the DC supply voltage;
An eighth resistor having one terminal connected to a reference voltage that is an output of the constant voltage generating means;
A ninth resistor having one terminal connected to a ground voltage, the other terminal connected to the other terminal of the eighth resistor, and simultaneously connected to the low frequency rectangular signal;
The low-frequency rectangular signal and the high-frequency oscillation signal that swing based on the distribution voltage of the eighth resistor and the ninth resistor are received and compared, and activated if the high-frequency oscillation signal is larger than the low-frequency rectangular signal. Comparing means for outputting a rectangular wave drive signal;
A current amplifying means for amplifying the drive signal output from the comparison means to increase the drive capability of the drive signal and outputting a first drive signal and a second drive signal obtained by inverting the first drive signal; The lamp driving device according to claim 1, further comprising a lamp driving device.

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