JP2007173697A - Light-emitting diode-driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the flexibility of light-emitting driving control, by making a total electrostatic capacity of a capacitor to be connected in a light emitting diode driving device which alternately switches and connects a capacitor to the power supply and a light-emitting diode and drives it in a form of discharging the charge of the capacitor to the light-emitting diode side. <P>SOLUTION: Capacitors C1, C2 for driving a light emitting diode 2 are disposed parallel mutually, as viewed from a charge/discharge line 4. A plurality of capacitors C1, C2 which can switch connection/disconnection each to a charge/discharge line 4 by means of electrostatic capacity changeover switches P1, P2 are used. The total electrostatic capacity of the capacitors C1, C2 to be connected to the charge/discharge line 4 is adjusted, based on changeover of the electrostatic capacity changeover switches P1, P2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light emitting diode driving device.

JP-A-9-97925

In recent years, light emitting diodes (Light
Emitting Diode (hereinafter also referred to as LED) is widely used for illumination as well as an indicator. An example of a conventional LED driving circuit is shown in FIG. + V is a power supply voltage, and Sig is a signal for LED ON / OFF and dimming control. When a voltage is applied to Sig, the base current of the transistor Tr flows through the resistor R1, and the transistor Tr is turned on. The LED emits light when a current flows through the current limiting resistor R2. Since the luminance of the LED is substantially proportional to the current i flowing, the emission luminance I of the LED can be expressed as follows when the forward voltage of the LED is V _F and the collector-emitter voltage when the transistor is ON is Vce.
I≈Ai = A (+ V−V _F −Vce) / R2 (1)
Usually, the light emission luminance I is determined by setting the power supply voltage + V and the electric resistance value of the current limiting resistor R2. Such a drive circuit is not efficient because power is always consumed by the current limiting resistor R2. In particular, when a large number of LEDs are used, the amount of heat radiation increases, which causes a problem in designing a circuit board and a housing. If the current limiting resistor R2 is reduced to reduce the amount of voltage drop due to the current limiting resistor R2, the LED driving efficiency itself is improved. Since the voltage Vf is greatly affected by variations and fluctuations, there is a limit in reducing the current limiting resistance R2.

  Therefore, in Patent Document 1, a capacitor with a switch is connected between the light emitting diode and the driving power source, and the switch is alternately switched between the state in which the driving power source is connected to the capacitor and the state in which the light emitting diode is connected. A configuration for driving is disclosed. When the capacitor is connected to the driving power supply, the capacitor enters a charging mode, and accumulates a constant charge according to the power supply voltage and its own capacitance. When the connection is switched from this state to the light emitting diode side, the light emitting diode becomes a load and the capacitor is discharged, and a current corresponding to the accumulated charge amount flows to the light emitting diode to emit light. The instantaneous current value flowing through the light emitting diode is determined by the amount of charge stored in the capacitor discharged at one time. Therefore, by appropriately selecting the capacitance of the capacitor to be used according to the power supply voltage (for example, the battery voltage in the case of an automobile) so that the instantaneous current value does not exceed the maximum current value that can be passed through the light emitting diode. Even if the current limiting resistor is not used, even if it is used, the electrical resistance value can be significantly reduced, and the light emission driving efficiency can be improved.

  In Patent Document 1, there is a problem that the total capacitance of capacitors connected to a power supply or a light emitting diode is constant, and the degree of freedom in light emission drive control is lacking. For example, Patent Document 1 discloses that the emission luminance can be adjusted (dimmed) by controlling the number N of connection switching between the power source of the capacitor and the light emitting diode. However, this connection switching frequency has a lower limit value from the viewpoint of preventing flickering of the light emitting diode, and on the other hand, there is a limit to the upper limit value of the frequency from the charging time constant of the capacitor. Bandwidth cannot be taken as wide as expected. Considering that the power supply voltage is stable, when the total capacitance of the capacitor is constant, the amount of discharge charge of the capacitor per time, and hence the amount of light emission per pulse of the light emitting diode, is also substantially constant. Therefore, the light control range of the light emission luminance itself cannot be made so wide only by connection switching frequency control.

  Furthermore, Patent Document 1 says that it can be used stably even with respect to in-vehicle battery voltages, etc., where voltage fluctuations are significant. However, on the premise that no voltage stabilization circuit is provided, the battery voltage for charging the capacitor varies greatly. In this case, if the capacitance of the capacitor is constant, the amount of discharge charge per pulse to the light emitting diode also greatly varies. This not only leads to fluctuations in the light emission luminance, but when the battery voltage is shifted to a higher side due to, for example, superposition of an alternator voltage, an excessive current may flow through the light emitting diode, leading to a reduction in life. In Patent Document 1, there is a description in FIG. 5 that the capacitances of the two capacitors 9 and 9 may be different from each other. However, in this circuit, two capacitors are connected in series. Even if the capacitances are different, there is no change in the combined capacitance of the capacitors inserted in the charge / discharge lines being constant. In addition, as shown in FIG. 6, there is a description that the current level of the light emission pulse can be made constant by driving with the voltage from the sawtooth wave generation circuit superimposed, but this is only during the discharge period of one pulse. It is intended to flatten the instantaneous current value and not to stabilize the light emission drive current value against fluctuations in the power supply voltage. (Of course, an additional sawtooth wave generation circuit synchronized with the switch drive is required. Needless to say, this leads to circuit complexity and cost increase).

  An object of the present invention is to provide a light emitting diode driving device in which a capacitor is alternately connected to a power source and a light emitting diode, and the charged charge of the capacitor is discharged to the light emitting diode side to drive the capacitor. This is to make the total capacitance variable, and to increase the degree of freedom of light emission drive control.

Means for Solving the Problems and Effects of the Invention

In order to solve the above problems, a light-emitting diode driving device of the present invention includes:
A drive line for driving the light emitting diode;
A capacitor constituting a drive current source of each light emitting diode;
A charge / discharge line constituting the charge / discharge path of the capacitor;
The capacitor connected to the charge / discharge line is charged in the first state by alternately switching the charge / discharge line between the first state connected to the drive power supply side and the second state connected to the drive line side. On the other hand, in the second state, the capacitor is discharged to the drive line side, and includes a drive switch that causes the light emitting diode to emit light with a discharge current corresponding to the charge of the capacitor.
As the capacitor, a plurality of capacitors are arranged in parallel with each other as viewed from the charge / discharge line, and a capacitance changeover switch for connecting the plurality of capacitors to the charge / discharge line so as to be connectable / disconnectable is provided. The total capacitance of the capacitors connected to the charge / discharge line is adjusted based on switching of the capacitance changeover switch.

  According to the present invention, the capacitors for driving the light emitting diodes are arranged in parallel with each other as viewed from the charge / discharge line, and can be switched to / from the charge / discharge line by the capacitance changeover switch. The total capacitance of the capacitors connected to the charge / discharge line is adjusted based on the switching of the capacitance changeover switch. Thereby, the structure which makes variable the total electrostatic capacitance of the capacitor | condenser connected can be implement | achieved simply, and the freedom degree of light emission drive control can be raised more.

  As the plurality of capacitors, capacitors having different capacitances can be used. Thereby, the total capacitance of the capacitors connected to the charge / discharge line can be easily changed according to which of the plurality of capacitors is used. In particular, if one of a plurality of capacitors is selectively connected to the charge / discharge line based on the switching of the capacitance changeover switch, the specific capacitance for each capacitor is directly added to the total capacitance. It can be employed as a capacity setting value.

  On the other hand, two or more of a plurality of capacitors arranged in parallel can be combined and connected to the charge / discharge line based on switching of the capacitance changeover switch. In this way, various settings of the total capacitance can be made by combining a limited number of capacitors. In this case, the plurality of capacitors can have the same capacitance of two or more capacitors. By connecting a plurality of capacitors having the same capacitance in combination, a fine total capacitance can be set in units of the capacitance of the capacitors.

  When the fluctuation of the power supply voltage is not so rapid, the total discharge charge amount from the capacitor is changed based on the adjustment of the total capacitance of the capacitor connected to the charge / discharge line. The amount of emitted light can be adjusted. In other words, the light emission luminance of the light emitting diode can be adjusted by adjusting the total capacitance of the capacitor.

  Specifically, the first dimming is performed by switching the driving switch between the first state and the second state at a predetermined frequency, and changing the number of light emission pulses per unit time by changing the frequency. Control means and second dimming control means for uniformly changing the light emission amounts of the plurality of light emission pulses output continuously at the frequency by switching of the capacitance changeover switch can be provided. With this configuration, finer dimming is possible based on both the switching frequency between the power supply / light emitting diode (first state / second state) of the capacitor and the amount of light emission pulse by changing the capacitance of the capacitor. It becomes.

  For example, the plurality of capacitors include a first capacitor and a second capacitor having a smaller capacitance than the first capacitor, and the flicker described above is used for switching the drive switch by the first dimming control means. When the lower limit frequency is predetermined from the viewpoint of prevention, etc., the second dimming control means and the first dimming control means use the first capacitor to drive the light emitting diode at the lower limit frequency. The output of the light emission luminance smaller than the average light emission luminance obtained in the above can be cooperatively controlled by driving the light emitting diode at a frequency higher than the lower limit frequency using the second capacitor. That is, with only the first capacitor having a large capacitance, the average emission luminance when driven at the lower limit frequency is the limit emission luminance from the viewpoint of preventing flickering, whereas the second capacitor having a smaller capacitance than that. By switching to the capacitor, it is possible to achieve an average light emission luminance smaller than the limit light emission luminance of the first capacitor by driving at a frequency higher than the lower limit frequency. As a result, the dimming range of the emission luminance can be greatly expanded while preventing flickering. Note that the plurality of capacitors may include three or more capacitors having different capacitances. In this case, any two capacitors that can specify the magnitude relationship are used as the first capacitor and the second capacitor. Can be considered. The concept of the first capacitor and the second capacitor includes a case where each is a combination of a plurality of parallel capacitors. In this case, it is only necessary that the total capacitance in the combination of the parallel capacitors is different from each other, and common (that is, the same) is used for each parallel capacitor combination corresponding to the first capacitor and the second capacitor. A capacitor may be included (for example, the first capacitor is composed of unit capacitors A, B and C connected in parallel, and the second capacitor is composed of unit capacitors A and D connected in parallel). .

  On the other hand, in the light emitting diode driving device of the present invention, voltage detecting means for detecting the voltage of the driving power supply can be provided, and the capacitance of the capacitor connected to the charge / discharge line increases as the detected voltage increases. The capacitance switching switch can be switched so as to be lowered. In this way, the higher the drive power supply voltage supplied, the lower the capacitance of the capacitor used for charging. For example, even when the drive power supply voltage suddenly rises, the capacitance of the capacitor is reduced, so that the light emitting diode It is possible to suppress a sudden increase in the amount of discharge charge to the side, and it is possible to prevent an excessive instantaneous current from flowing through the light emitting diode. In addition, since the amount of charged electric current itself is reduced by changing the capacitance of the capacitor, there is less Joule heat loss compared to a configuration in which current is limited by a voltage drop using a current limiting resistor, and there is a concern that light emission drive efficiency may be reduced. There is no.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 conceptually shows an example of a light emitting diode driving device of the present invention. The light-emitting diode driving device 1 includes a drive line 3 for driving the light-emitting diode 2, capacitors C1 and C2 constituting drive current sources for the light-emitting diode 2, and charging / discharging paths constituting capacitors C1 and C2. Discharge line 4 is provided (signs “C1, C2” may also indicate the capacitance of the capacitor). In addition, the charge / discharge line 4 is alternately connected between the first state connected to the drive power supply 5 side and the second state connected to the drive line 3 side, thereby connecting to the charge / discharge line in the first state. While the charged capacitors C1 and C2 are charged, in the second state, the capacitors C1 and C2 are discharged to the drive line 3 side, and the light emitting diode 2 is pulsed with a discharge current corresponding to the charge of the capacitors C1 and C2. (In FIG. 1, the drive switches S1 and S2 are drawn by one SPDT switch that is functionally equivalent to the set of the drive switches S1 and S2. However, the general structure is not limited to this). The drive line 3 has a first end connected to a positive power source 5 and the second end is grounded. The light emitting diode 2 is connected on the drive line 3 so that the anode side is grounded (the polarity of the power source 5 can be reversed, and in this case, the insertion direction of the light emitting diode 2 into the drive line 3 is also reversed. ).

  Further, as the capacitors C1 and C2, a plurality of capacitors C1 and C2 are provided in parallel with each other when viewed from the charge / discharge line 4. Further, electrostatic capacity changeover switches P1 and P2 for connecting the plurality of capacitors C1 and C2 to the charge / discharge line 4 so as to be connectable / disconnectable are provided. The terminals on the opposite side of the capacitors C1 and C2 connected to the switches P1 and P2 are grounded.

  Based on the switching of the capacitance changeover switches P1 and P2, the total capacitance of the capacitors C1 and C2 connected to the charge / discharge line 4 can be adjusted. This will be described in detail below. As the plurality of capacitors C1 and C2, capacitors having different capacitances are used. Here, C1> C2. One of the plurality of capacitors C1 and C2 is alternatively connected to the charge / discharge line 4 based on the switching of the capacitance changeover switches P1 and P2. As a result, depending on which capacitor is used, the amount of charge and thus the driving charge of the light emitting diode 2 changes, and the amount of light emitted per light emission pulse also changes.

  The drive switches S1 and S2 are switched and driven between a first state and a second state at a predetermined frequency, and change the number of light emission pulses per unit time by changing the frequency (first dimming control). means). By switching the capacitance changeover switches P1 and P2, the light emission amounts of the plurality of light emission pulses continuously output at the above frequency can be uniformly changed (second dimming control means).

As described above, the capacitances of the plurality of capacitors C1 and C2 are set such that C1> C2. For example, consider a state in which the capacitor C1 is connected to the discharge line 4, as shown in FIG. 2, when the switch S1 is turned ON, the capacitor C is charged to the supply voltage + V _B. Next, when the switch S2 is turned on, the electric charge charged in the capacitor C1 is discharged through the light emitting diode 2. When a forward voltage drop of the light emitting diode 2 and V _F, the charge amount Q switch S2 is discharged to ON is as follows.
Q = (+ V _B −V _F ) C1 (2)
The light emission intensity of the light emitting diode 2 is substantially determined by the flowing current. When the switch S2 is turned on once, the light emission intensity of the light emitting diode 2 is proportional to the integral value of the flowing current, that is, the charge amount Q discharged from the capacitor C1. When the switching frequency of the switches S1 and S2 is f, the luminance I of the LED is as follows.
I≈AfQ = Af (+ V _B −V _F ) C1: A is a constant (3)
Therefore, it can be seen that the luminance of the LED can be controlled by the repetition frequency f, the power supply voltage + V, and the capacitor capacitance C. The same applies when the capacitor C2 is used.
I≈AfQ = Af (+ V _B −V _F ) C2: A is a constant (4)
If the frequency f is the same, the luminance I can be changed almost in proportion to the capacitance of the capacitor. In FIG. 1, protective resistors R1 and R2 are provided on the power supply line and the drive line. However, the protective resistors R1 and R2 can be omitted in terms of driving principle (particularly, When the ON resistance of the switches S1 and S2 is sufficiently high).

  FIG. 3 shows a more specific circuit. The drive switches S1 and S2 are both analog semiconductor switches that are turned on / off by a control signal SC1 from the ECU. The control signal SC1 is a digital square wave signal output from a port of the ECU, and its frequency f can be arbitrarily changed by a known signal generation program. The control signal SC1 is directly input to the switch S1, while being inverted and input to the switch S2 via the inverter 10. As a result, the drive switches S1 and S2 are exclusively turned on / off, and operate equivalent to the SPDT switch of FIG. Then, the exclusive on / off operation of the drive switches S1 and S2 is repeated for each period of the square wave.

  The capacitance changeover switches P1 and P2 are also configured by analog semiconductor switches that are turned on / off by a control signal SC2 from the ECU (however, switches such as mechanical relays can also be used). . The control signal SC2 is directly input to the switch P1, while being inverted and input to the switch P2 via the inverter 10. As a result, the drive switches S1 and S2 are exclusively turned on / off. As a result, the capacitors C1 and C2 are selected with respect to the charge / discharge line 4 depending on which of the drive switches S1 and S2 is on. Will be connected together.

  In the configuration of FIG. 1, a first capacitor C1 and a second capacitor C2 having a smaller capacitance than that of the first capacitor C2 are provided. As shown in FIG. 4, switching of the drive switches S1 and S2 On the other hand, the lower limit frequency fm is determined in advance from the viewpoint of flicker prevention. At this time, the output of the light emission luminance smaller than the average light emission luminance Im obtained when the light emitting diode 2 is driven to emit light at the lower limit frequency fm using the first capacitor C1 is output using the second capacitor C2. Can be obtained by driving at a frequency higher than the lower limit frequency fm (this effect can be received up to a frequency fq at which the luminance is equal to the average light emission luminance Im, for example). Note that the light emission brightness Im may be obtained by driving the light emitting diode 2 at the lower limit frequency fm using the first capacitor C1.

  Assuming that the switching frequency of the switches S1 and S2 is f, it is desirable to set the lower limit frequency fm to about 50 Hz (preferably 100 Hz), for example, so that flicker is not normally recognized. On the other hand, the upper limit of the switching frequency f is determined by the charging time constant of the capacitor. For example, if the capacitor is disconnected from the power supply before it is sufficiently charged, or if it is disconnected from the light emitting diode 2 before the capacitor is sufficiently discharged, it is impossible to ensure a sufficient amount of discharge charge per pulse and thus sufficient emission luminance. Since the desired light emission luminance cannot be obtained, the switching frequency needs to be set to be appropriately long so that this does not occur, and the corresponding frequency becomes the upper limit frequency.

  Assuming that the upper limit frequency is 1 KHz, if only one capacitor is provided, the brightness that can be dimmed is about 10% at 100 Hz if the brightness is 1% and the maximum brightness is only 10 times the minimum brightness. . However, if two types of capacitors having different capacitances are prepared and switched as shown in FIG. 4, the dimming range can be greatly expanded. For example, if the capacitance of the second capacitor C2 is 1/10 of that of the first capacitor C1, the luminance can be reduced to 1/10 by switching from the first capacitor C1 to the second capacitor C2 even at the same frequency. . Therefore, assuming that the luminance when the repetition frequency is 1 KHz with the first capacitor C1 is 100%, the luminance can be reduced to 10% by reducing the repetition frequency to 100 Hz. Next, when switching to the second capacitor C2 and setting the repetition frequency to 1 KHz, the luminance is 10%. By reducing the repetition frequency to 100 Hz, the luminance can be reduced to 1%, and the maximum luminance can be taken up to 100 times the minimum luminance. It becomes like this. Since the luminance can be easily changed by providing and switching a plurality of capacitors C in this way, a wide dimming range can be realized by combining with the control of the switching frequency f.

  The above functions can be realized, for example, by the ECU (configured by a microcomputer) in FIG. 3 performing the following signal output processing according to a program. That is, the correspondence between the setting value of the switching frequency f for realizing the emission luminance and the information specifying the type of capacitor to be used is previously stored in a ROM or the like as shown in FIG. Remember. Then, as shown in the flowchart of FIG. 6, in S1, the command value of the emission luminance is acquired from the outside, and in S2, the correspondence relationship in FIG. The capacitor is specified, and the switch control signals SC1 and SC2 are set to corresponding states and output in S3.

  Hereinafter, other embodiments of the present invention will be described. FIG. 7 shows an example in which two or more of a plurality of capacitors C0 to C5 arranged in parallel can be combined and connected to the charge / discharge line 4 based on switching of the capacitance changeover switches P1 to P5. Is. Here, all of the switches P1 to P5 can be turned on / off independently, and the corresponding capacitors C0 and C2 to C5 can be connected in parallel to the charge / discharge line 4 in any combination. The capacitor C1 is always connected to the charge / discharge line 4 without a switch.

  Capacitor C0 has a larger capacitance than capacitors C1 to C5. Specifically, the capacitors C1 to C5 are set to values CA having the same capacitance, while the capacitance of the capacitor C0 is set equal to the total capacitance of the capacitors C1 to C5 (here, 5CA). The ECU independently controls on / off of the switches P1 to P5 by a bit control signal (PC1 to PC5) corresponding to the number of switches. As a result, as shown in the lower table of FIG. 7, the connection of the capacitors C1 to C5 to the charge / discharge line 4 can be changed in any combination corresponding to the control signal bit input to the switches P1 to P5, and the total The capacitance can be set using the capacitance CA of the capacitors C1 to C5 as an increase / decrease unit. Specifically, when all the switches P1 to P5 are turned off, the minimum capacitance value CA is set by the directly connected capacitor C1, and when all the switches P1 to P5 are turned on, the maximum capacitance value CA is set. A capacitance value 10CA is set. That is, the capacitor C0 having a large capacitance plays a role of carry. For each capacitance value set by switching the switches P1 to P5 (second dimming control means), dimming control according to the switching frequency f of the switches S1 and S2 is possible (first Dimming control means).

FIG. 8 is provided with voltage detection means for detecting the voltage of the drive power supply 5, and the higher the detected voltage, the lower the capacitance of the capacitor (one of C1 to C3) connected to the charge / discharge line 4. In this example, the capacitance changeover switches P1 to P3 are switched. Since the discharge charge Q per pulse from the capacitor having the capacitance C is (+ V _B −V _F ) C from the equation (2), if the capacitance C is constant, When the voltage, that is, the battery voltage + V _B becomes very high, the instantaneous current value of the light emitting diode 2 becomes considerably large. For example, if you are traveling at high speed at light load condition, may output the voltage of the battery is not depleted alternator voltage is superimposed will rise to + 18V longitudinal, if V _F is 2V longitudinal, battery voltage + V _B The instantaneous current value of the light-emitting diode 2 is increased by nearly 60% as compared with the case where is around the standard voltage + 12V.

In this case, the instantaneous current value of the light emitting diode 2 on the basis of the maximum value of the battery voltage + V _B, for example, when you try to regulation by the protective resistor R2 as shown in FIG. 3, the battery voltage + V _B standard voltage (+ 12V) or less in In this case, the luminance of the light emitting diode 2 is significantly reduced, and the light emission driving efficiency is unavoidably reduced. Therefore, in the configuration of FIG. 8, as shown in FIG. 9, the assumed fluctuation range of the battery voltage + V _B is divided into a plurality of sections (in FIG. 9, V1 to V2, V2 to V3, V3 to V4 (V1>V2>V3> V4), but may be two, or may be four or more;), and capacitors C1 to C3 having capacitance values corresponding to the respective sections are switched to switches P1 to P3. The control signal is alternatively switched by PC1 to PC3 and connected to the charge / discharge line 4. Incidentally, the battery voltage + V _B is input to the ECU as a monitor voltage Vm via the resistor divider. The ECU compares and determines which of the sections the monitor voltage Vm belongs to, and performs a process of turning on the corresponding capacitor and connecting it to the charge / discharge line 4.

The capacitance of the capacitor C1>C2> a C3, C1 when the battery voltage + _{V B} takes a value of the section V3~V4 is, the C2 in the case of taking the value of the section V2～V3, section V4~ When taking the value of V3, C3 is used. The values of C1, C2, and C3 are equal to, for example, the battery voltage + V _{B as} a representative value in each section (for example, the median values Vn1, Vn2, and Vn3, but any boundary value in the section may be adopted). In this case, the discharge charge amounts according to the equation (2) can be determined to be substantially equal to each other. As a result, the amount of discharge charge, that is, the instantaneous current value per pulse, is reduced in the difference between the voltage sections (respectively equal to each other). As a result, when the switching frequency f is constant, an excessive instantaneous current value can be prevented from being generated in the light-emitting diode 2 even when the battery voltage + V _B is increased, and the battery voltage + V _B is decreased. Even when it fluctuates to the side, it is possible to prevent the light emission luminance from significantly decreasing. In addition, the light emission driving efficiency is hardly lowered. In FIG. 8, the protective resistors used in FIG. 3 and the like are omitted.

  In the configuration of FIG. 10, the first capacitor C1 and the second capacitor C2 (C1> C2) in the configuration of FIG. 3 are alternately switched for each pulse and connected to the charge / discharge line 4. It is. In this way, a high luminance pulse by the first capacitor C1 and a low luminance pulse by the second capacitor C2 are alternately output. For example, when dimming on the low-brightness side, even if the output cycle of the high-brightness pulse is long, the output waveform has a low-brightness pulse inserted between them. Can be supplemented with pulses. Note that the control signal SC1 (square wave) of the switches S1 and S2 is distributed to the frequency divider circuit 11 to the switches P1 and P2 for switching between the first capacitor C1 and the second capacitor C2, and the frequency is halved. The above-described operation is realized by outputting the control signal SC1 ′ to the switches P1 and P2.

The conceptual diagram which shows 1st embodiment of the light emitting diode drive device of this invention. The timing diagram which shows the operation | movement concept of the light emitting diode drive device of FIG. The circuit diagram which shows the light emitting diode drive device of FIG. 1 in detail. FIG. 4 is a graph conceptually illustrating the function sharing between the first capacitor and the second capacitor in the circuit of FIG. 3. The schematic diagram which shows an example of the table shown to control of the light emitting diode drive device of FIG. The figure which shows an example of the control flow using the table of FIG. The circuit diagram which shows 2nd Embodiment of the light emitting diode drive device of this invention with the operation | movement table | surface of a capacitor | condenser switching. The circuit diagram which shows 3rd embodiment of the light-emitting-diode drive device of this invention. The figure which shows the concept of the capacitor | condenser switching according to a voltage fluctuation in the circuit of FIG. The circuit diagram which shows 4th Embodiment of the light-emitting-diode drive device of this invention with the timing diagram which shows operation | movement. The circuit diagram of the conventional light emitting diode drive device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emitting diode drive device 2 Light emitting diode 3 Drive line 4 Charge / discharge line C1, C2 Capacitor S1, S2 Drive switch P1, P2 Capacitance changeover switch

Claims (9)

A drive line for driving the light emitting diode;
A capacitor that constitutes a drive current source of each of the light emitting diodes;
A charge / discharge line constituting a charge / discharge path of the capacitor;
By alternately switching the charge / discharge line between a first state connected to the drive power supply side and a second state connected to the drive line side, the charge / discharge line is connected to the charge / discharge line in the first state. The capacitor is charged while the capacitor is discharged to the drive line side in the second state, and the light emitting diode is pulsed with a discharge current corresponding to the charge of the capacitor, and a drive switch is provided.
As the capacitor, a plurality of capacitors are arranged in parallel with each other when viewed from the charge / discharge line, and a capacitance changeover switch is provided for connecting the plurality of capacitors to the charge / discharge line so that connection / disconnection can be switched. A light emitting diode driving device characterized in that a total capacitance of capacitors connected to the charge / discharge line is adjusted based on switching of the capacitance changeover switch. The light emitting diode driving device according to claim 1, wherein capacitors having different capacitances are used as the plurality of capacitors. The light emitting diode drive device according to claim 2, wherein one of the plurality of capacitors is selectively connected to the charge / discharge line based on switching of the capacitance changeover switch. The light emission according to claim 1 or 2, wherein two or more of the plurality of capacitors arranged in parallel are connected in combination to the charge / discharge line based on switching of the capacitance changeover switch. Diode drive device. Based on switching of the capacitance changeover switch, two or more of the plurality of capacitors arranged in parallel are connected in combination to the charge / discharge line, and the plurality of capacitors are electrostatic capacitances of two or more. 2. The light emitting diode driving device according to claim 1, wherein the capacities are set to be equal to each other. The light emission amount per pulse of the light emitting diode is adjusted by changing the total discharge charge amount from the capacitor based on the adjustment of the total capacitance of the capacitor connected to the charge / discharge line. The light-emitting diode driving device according to claim 1. A first dimming control for switching the drive switch between the first state and the second state at a predetermined frequency and changing the number of light emission pulses per unit time by changing the frequency Means,
The light-emitting diode according to claim 6, further comprising: a second dimming control unit that uniformly changes each light-emission amount of the plurality of light-emission pulses continuously output at the frequency by switching the capacitance changeover switch. Drive device. The plurality of capacitors include a first capacitor and a second capacitor having a smaller capacitance than the first capacitor, and a lower limit frequency is set in advance for switching the drive switch by the first dimming control means. The second dimming control means and the first dimming control means are defined as an average obtained when the light emitting diode is driven to emit light at the lower limit frequency using the first capacitor. 8. The light emitting diode driving device according to claim 7, wherein the output of the light emitting luminance smaller than the light emitting luminance is cooperatively controlled by driving the light emitting diode at a frequency higher than the lower limit frequency using the second capacitor. The electrostatic capacity changeover switch includes voltage detection means for detecting the voltage of the driving power supply, and the electrostatic capacity of the capacitor connected to the charge / discharge line is decreased as the detected voltage increases. The light-emitting diode driving device according to claim 1, wherein the LED is switched.

Images