JP4924916B2 - LED driving device - Google Patents

Description

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

JP-A-8-78731

In recent years, light emitting diodes (hereinafter also referred to as LEDs) have been widely used for lighting as well as indicators. An example of a conventional LED driving circuit is shown in FIG. 14 (FIG. 1 of Patent Document 1 as an example based on the literature). + 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 flowing current i, the emission intensity I of the LED can be expressed as follows, assuming that the forward voltage drop 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 (0)
Usually, the emission intensity I is determined by setting the power supply voltage + V and the electric resistance value of the current limiting resistor R2.

However, the drive circuit as described above 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. it means that largely affected by the variation or fluctuation of the voltage drop V _F, to reduce the current limiting resistor R2 is limited.

  An object of the present invention is to provide a high-efficiency light-emitting diode driving device that can significantly reduce power loss due to a current limiting resistor.

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 main drive line for driving the light emitting diode;
An inductor inserted in series with the light emitting diode on the main drive line;
A power supply line for supplying a main drive current from the drive power supply to the light emitting diode;
An auxiliary closed current path forming line that forms an auxiliary closed current path that does not include a power supply line for the light emitting diode together with the main drive line; and
While the energization state for the light emitting diode is from the power supply line to the main drive line, the first energization state for supplying the main drive current while accumulating magnetic energy in the inductor, and the supply of the main drive current to the main drive line is cut off, An energization state switching means for alternately switching between a second energization state in which the magnetic energy stored in the inductor is discharged through the auxiliary closed current path as an auxiliary drive current of the light emitting diode ;
A plurality of the inductors are prepared, and an inductor switching mechanism is provided that connects one or two or more of the inductors to the main drive line so that the total inductances can be switched in different combinations .

  According to the light emitting diode driving device of the present invention, an inductor is connected in series to the light emitting diodes on the main driving line, the first energization state for supplying the main driving current while storing the magnetic energy in the inductor, and the main driving current Light-emitting diodes emit light by alternately switching to the second energized state where the magnetic energy stored in the inductor is released through the auxiliary closed current path as the auxiliary drive current of the light-emitting diodes while cutting off the supply to the drive line To drive. In the first energized state, a part of current energy flowing through the main drive line is stored as magnetic energy in the inductor, so that the drive current of the light emitting diode can be limited. In the second energization state, the energy stored in the inductor for current limitation in the first energization state can be used for driving the light emitting diode in the form of an auxiliary drive current without waste. In other words, the power that was wasted in the current limiting resistor in the conventional circuit is temporarily stored in the inductor in the first energization state to limit the current, and the energy stored in the inductor drives the light emitting diode in the second energization state. Is extremely efficient. As a result, wasteful power consumption is suppressed, so there is little heat generation, and the heat dissipation design of the circuit board and the housing can be simplified.

  According to the configuration of the present invention, the current adjustment resistor for adjusting the energization current to the light emitting diode is excluded from the energization path of the light emitting diode including the power supply line, the main drive line, and the auxiliary closed current path forming line. Can do. This essentially eliminates wasted power consumption at the current adjustment resistor.

  Next, the energization state switching means can be configured to include a drive switch that switches the power supply line and the main drive line between a connected state and a disconnected state. In this case, the auxiliary closed current path forming line is branched from the main drive line on the side closer to the drive switch than either the light emitting diode or the inductor, and the power line is connected to the auxiliary closed current path forming line by the drive switch. When connected to the main drive line, the main drive current is prevented from flowing through the auxiliary closed current path forming line, and when the power supply line is disconnected from the main drive line, the auxiliary closed current path forming line is assisted. A rectifying element (for example, a diode) that allows a drive current to flow can be provided. A mechanism for switching between the first energized state and the second energized state can be easily and inexpensively realized by a simple circuit configuration in which the drive switch and the rectifying element are combined.

  The drive switch can be composed of a transistor switch. By inputting a drive signal to the drive terminal of the transistor switch, the supply of the main drive current to the light emitting diode and the inductor via the power line is periodically switched, so that the first energized state and the second energized state Can be easily and rapidly switched. On the other hand, when the drive power supply supplies a square wave power supply output with a predetermined cycle to the power supply line, the drive switch allows the main drive current to be conducted to the main drive line and to the power supply line side. The diode that cuts off the conduction of the auxiliary drive current can be configured at a lower cost.

  Next, in the present invention, the intensity of the light emission pulse generated in the light emitting diode in one switching period between the first energized state and the second energized state by the energized state switching means is the continuation of the first energized state in the switching period. A pulse intensity adjusting means that adjusts by changing the time can be provided. According to this configuration, for example, when the drive power supply voltage is constant, the intensity of the light emission pulse generated in the light emitting diode in one switching cycle can be increased by increasing the duration of the first energization state. Further, when the drive power supply voltage fluctuates, the light emission pulse intensity fluctuation due to the drive power supply voltage is changed to cancel (for example, when the drive power supply voltage fluctuates in the increasing direction, the duration of the first energization state is shortened). The light emission intensity of the light emitting diode can be stabilized.

  When the switching frequency between the first energized state and the second energized state by the energized state switching unit is fixed, the pulse intensity adjusting unit emits light by changing the duty ratio of the first energized state in one switching cycle. It can function as a light control means for adjusting the average light emission intensity of the diode. In addition, if a voltage detection means for detecting the voltage of the drive power supply is provided, the above-described pulse intensity adjustment means causes the first emission period in one switching cycle to obtain the same emission intensity as the detected voltage increases. It can function as a light emission intensity stabilizing means for setting the duty ratio in the energized state small. In these configurations, switching control between the first energization state and the second energization state can be easily performed based on a known PWM control signal, and dimming control or light emission intensity can be achieved by changing the duty ratio of the control signal. Stabilization control can be performed with high accuracy.

  On the other hand, in the present invention, there is provided pulse number adjusting means for adjusting the number of light emitting pulses per unit time generated in the light emitting diode by changing the switching frequency between the first energized state and the second energized state by the energized state switching means. It can also be provided. This configuration can also be effectively used for dimming control of light emitting diodes or emission intensity stabilization control. For example, in the former case, the pulse number adjusting unit may function as a dimming unit that adjusts the average light emission intensity of the light emitting diode by changing the switching frequency. In the latter case, if voltage detection means for detecting the voltage of the drive power supply is provided, and the pulse number adjustment means functions as light emission intensity stabilization means for setting the switching frequency to be smaller as the detected voltage is higher. Good.

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 is configured with the following requirements.
Main drive line 3: A light emitting diode LED2 is provided.
Inductor L1: The light emitting diode LED2 is inserted in series on the main drive line 3.
Power supply line 6: The main drive current from the drive power supply 5 is supplied to the light emitting diode LED2.
Auxiliary closed current path forming line 4: An auxiliary closed current path 7 that does not include the power supply line 6 for the light emitting diode LED2 is formed together with the main drive line 3.
Energization state switching means: The energization state of the light emitting diode LED2 is transmitted from the power supply line 6 to the main drive line 3, and magnetic energy is applied to the inductor L1 (the symbols “L1 and L2” represent inductances of the inductors) The first energized state S1 for supplying the main drive current while storing it, and closing the supply of the main drive current to the main drive line 3 while assisting the magnetic energy stored in the inductor L1 as an auxiliary drive current for the light emitting diode LED2 It switches alternately with 2nd electricity supply state S2 discharged | emitted via the current path 7. FIG. In FIG. 1, a switch for conceptually realizing this function (in this case, an SPDT switch is used, but if the function as a whole is equivalent, the switch form is not limited to this) 10 and its switching This is realized by a CPU (not shown) (noted by reference numeral 8 in FIG. 7) which is a control main body.

The drive line 3 has a first end connected to the power supply line 6 via the switch 10 and a second end connected to the ground. The power supply line 6 (in the present embodiment, the power supply voltage is an in-vehicle battery + V _B) drive power source 5 is connected. Further, the end of the auxiliary closed current path forming line 4 is also grounded. The switch 10 serves to connect the main drive line 3 to either the power supply line 6 (S1 side) or the auxiliary closed current path forming line 4 (S2 side) in a switchable manner. When the switch 10 is tilted toward the auxiliary closed current path forming line 4, the auxiliary closed current path forming line 4 and the main drive line 3 are connected in a ring shape through the ground, thereby forming the auxiliary closed current path 7. It will be. The light emitting diode LED2 is connected on the drive line 3 so that the anode side is grounded. However, the polarity of the power source 5 can be reversed. In this case, the direction of insertion of the light emitting diode LED2 into the drive line 3 is also reversed. Become.

  As apparent from FIG. 1, a current adjusting resistor for adjusting the energization current to the light emitting diode LED <b> 2 from the energization path of the light emitting diode LED <b> 2 including the power supply line 6, the main drive line 3 and the auxiliary closed current path forming line 4. Has been completely eliminated.

An outline of the operation of the circuit of FIG. 1 will be described.
First, when the switch 10 falls to the S1 side and enters the first energization state, a main drive current, which is a direct drive current from the power source, starts to flow through the light emitting diode LED2. When the light emitting diode LED2 is directly connected to the drive power supply 5 and the current adjustment resistor is omitted, and continuously energized, the current value I flowing through the light emitting diode LED2 instantaneously becomes a very large value as is apparent from the equation (0). This leads to destruction of the light emitting diode LED2.

However, in FIG. 1, the inductor L1 is connected in series with the light emitting diode LED2. When connecting a light emitting diode LED2 of the inductance L1 resistor R0 and the forward voltage drop V _F to the supply voltage V, the transient equations of the current flowing through the circuit I, is shown in the following equation (1).

  When the current adjusting resistor is omitted, the resistor R0 included in the circuit is only the direct current resistance inherently provided in the energization path of the light emitting diode LED2, and the value of the direct current resistance is, for example, an expression (1 in the conventional circuit). ) Is small enough to be ignored (for example, 1/100 or less). Therefore, by setting R0 to approximately zero and solving the equation 1 by setting the current value I0 at the start of energization to zero, the current I (main drive current) flowing through the light emitting diode LED2 is obtained as in the following equation (1). . The main drive current I flowing through the light emitting diode LED2 increases linearly from zero as the energization time t elapses as shown in FIG. 2 due to the accumulation of magnetic energy in the inductor L1.

When the interval between the first energized states is τon, the maximum current value Ip is expressed by the following equation (2).

  Next, when the switch 10 falls to the S2 side from the above state and enters the second energized state, the current I does not immediately become zero, but the magnetic energy stored in the inductor L1 is released and the auxiliary closed current path is released. 7, the auxiliary drive current I ′ (t) represented by the following equation (3) flows while being attenuated.

  As apparent from the equation (2), the auxiliary drive current Ip decreases linearly with time t (FIG. 2), and after switching to the second energization state, the critical time τk represented by the following equation (4) passes. Will be zero.

  Since the light emission intensity IL of the light emitting diode LED2 is proportional to the integral value of the flowing current, if the switching frequency between the first energization state and the second energization state (S1 / S2) is F, the luminance IL is expressed by the following equation (5). It is expressed as That is, it can be seen that the light emission intensity IL of the light emitting diode LED2 can be controlled by the power supply voltage V, the inductance L1, the duration τon of the first energization state, and the switching frequency F.

  Theoretically, there is a current saturation value corresponding to the inherent DC resistance of the energization path, but this value is much larger than the maximum current value that can be energized in a general light emitting diode. Therefore, switching from the first energized state to the second energized state needs to be performed before the current I flowing through the light emitting diode LED2 reaches the maximum current value. In other words, because the switching is performed before reaching the maximum current value, the current flowing through the light emitting diode LED2 can be limited even though the current adjustment resistor is eliminated.

  FIG. 3 shows a more specific circuit example. The circuit is provided with a drive switch Tr1 for switching the power supply line 6 and the main drive line 3 between a connected state and a disconnected state. Further, the auxiliary closed current path forming line 4 branches from the main drive line 3 on the side closer to the drive switch Tr1 than either the light emitting diode LED2 or the inductor L1. Then, when the power supply line 6 is connected to the main drive line 3 by the drive switch Tr1 on the auxiliary closed current path forming line 4, the main drive current is prevented from flowing through the auxiliary closed current path forming line 4. In the state where the power supply line 6 is disconnected from the main drive line 3, a rectifying element Di 1 (here, a diode) that allows the auxiliary drive current to flow through the auxiliary closed current path forming line 4 is provided.

  In FIG. 3, the drive switch Tr1 is a transistor switch (here, it is a bipolar transistor, but it may be an FET: a mechanical switch such as a relay can be substituted). By inputting the drive signal SC to the drive terminal of the transistor switch Tr1, the supply of the main drive current to the light emitting diode LED2 and the inductor L1 via the power supply line 6 is periodically switched, so that The second energized state can be switched. The bipolar transistor constituting the drive switch Tr1 is driven to be switched by the drive signal SC through the auxiliary transistor Tr2. The resistors R1 and R3 are for adjusting the drive input voltages of the transistors Tr2 and Tr1, and the resistor R2 functions to extract the residual charge of the auxiliary transistor Tr2 and improve the switching speed.

For example, the power supply voltage V 12V, 2V forward voltage drop _{V F} of the light-emitting diodes LED2, when the inductance of the inductor L1 and 2 mH, after Tr1 is turned on (first energized state) 10 [mu] s light emitting diode LED2 of the current Increase to 50 mA. Here, when the control signal SC is set to “L” and Tr1 is turned off, the auxiliary drive current flows through the auxiliary closed current path 7 formed by the diode Di1, the inductor L1, and the light emitting diode LED2 by the energy stored in the inductor L1. As can be seen from equation (4), this auxiliary drive current becomes zero after about 50 μs (critical time τk). The switching frequency F of the control signal SC “H / L (first energization state / second energization state)” is fixed to 10 KHz, and the duration τon of the first energization state is 10 μs (duty ratio η is 0.1). When the luminance at the time is 100%, the luminance is controlled from 1% to 100% by controlling τon from 1 μs to 10 μs (that is, the duty ratio η is from 0.01 to 0.1) from the equation (5). it can.

  As shown in FIG. 4, when the switching frequency between the first energized state and the second energized state is fixed at F0, the light emission is obtained by changing the duty ratio η of the first energized state in one switching cycle T0. The average light emission intensity IL of the diode LED2 can be adjusted. Since η = τon · F 0, the light emission intensity IL increases in proportion to the square of the duty ratio η if the drive power supply voltage V is constant, as is apparent from substituting this into the above equation (5). Further, the duty ratio η when the target light emission intensity IL is given can be calculated by the following equation (6).

On the other hand, the voltage V (here, car battery voltage is V _B) of the drive power source 5 when the fluctuating detects the power supply voltage V, the more the detected voltage becomes higher, to obtain the same luminous intensity IL If the control is performed so that the duty ratio η in the first energization state in one switching cycle T0 is set to be small, the light emission intensity IL can be stabilized. In this case, the duty ratio η corresponding to the detected power supply voltage V can be calculated by the above equation (6) with the light emission intensity IL being a fixed value.

  Next, as another method, the number of light emission pulses per unit time generated in the light emitting diode LED2 can be adjusted by changing the switching frequency F between the first energization state and the second energization state. As shown in FIGS. 5A, 5B, and 6C, the duration τon of the first energized state is constant, and the duration τoff of the second energized state is set to the critical time described above. If it is set to τk or more, the amount of emitted light per pulse can be made constant, and light control in proportion to the switching frequency F is possible. Note that the duration τoff of the second energized state can be set to be equal to the critical time τk, as shown in FIG. 6C, and light is emitted by continuously generating a triangular wave-like light emission pulse. Strength can be increased. When the duration of the first energization state is fixed at τon0, the switching frequency F when the target light emission intensity IL is given can be calculated by the following equation (7).

Voltage V of the drive power source 5 (in this case, the vehicle-mounted battery voltage is V _B) if varies detects the power supply voltage V, the more the detected voltage becomes higher, the frequency for obtaining the same emission intensity IL If the F is controlled to be set small, the emission intensity IL can be stabilized. In this case, the switching frequency F corresponding to the detected power supply voltage V can be calculated by the above equation (7) with the emission intensity IL as a fixed value. That is, the switching frequency F corresponding to the target light emission intensity IL is the power supply voltage (e.g., detected vehicle battery voltage + V _B) is set as inversely proportional to the value obtained by subtracting the forward voltage drop V _F of the light emitting diode LED2 from I understand that

  Note that the duration τoff of the second energized state can be set shorter than the critical time τk. In this case, as shown in FIG. Can be lit continuously. In this case, since the magnetic energy stored in the inductor in the second energized state period of the previous cycle is not completely released, the first energized state is transferred to the next cycle. It is necessary to determine the duty ratio η so that the energization current value reached in the period does not exceed the allowable maximum current value of the light emitting diode LED2.

FIG. 7 shows an example of a circuit in which the above functions are realized by software processing by the CPU. The drive power supply voltage (vehicle battery voltage) + V _B is input to the A / D conversion port of the CPU 8, while the target light emission intensity IL is also input to another port of the CPU 8. The CPU 8 performs light emission drive control according to the program processing flow shown in FIG. First, in U1 and U2, each value of the input drive power supply voltage + V _B and the target light emission intensity IL is read, and in the case of PWM control, the duty ratio η is calculated according to the above equation (6). In the case of frequency control, the set frequency F is calculated according to the aforementioned equation (7). In U4, a square wave control signal SC having the calculated duty ratio η or switching frequency F is output from the designated port. As shown in FIG. 9, the set duty ratio η or the switching frequency F is stored as the two-dimensional table B1 or B2 in accordance with the combination of the values of the target light emission intensity IL and the drive power supply voltage V _B and acquired. The duty ratio η or the switching frequency F corresponding to the target emission intensity IL and the drive power supply voltage V _B may be acquired from the table B1 or B2.

If the target light emission intensity IL is always constant, step U2 in FIG. 8 is omitted, and the duty ratio η or the switching frequency F may be calculated in U3 with the target light emission intensity IL as a constant (even if a table is used). A one-dimensional table corresponding to this may be used). Calculating the other hand, such as when the stabilized power supply may be used, if the drive power supply voltage + V _B is constant, omitting the step U1 in FIG. 8, the duty ratio η to switching frequency F the drive power supply voltage V _B as a constant in the U3 (If a table is used, a corresponding one-dimensional table may be used).

As another method, the target emission intensity IL is set by changing the duty ratio η, and the luminance stabilization corresponding to the drive power supply voltage + V _B is handled by changing the switching frequency F, or It is also possible to employ a composite control method that combines frequency control and duty ratio control, such as the reverse.

Next, FIG. 10 shows an example in which a control signal SC generation unit for performing duty ratio control is configured by analog hardware. In this case, a signal conversion unit configured by a dedicated IC that calculates the duty ratio η according to the equation (6) based on each input value of the drive power supply voltage + V _B and the target light emission intensity IL and outputs it as an analog value is provided. The instruction voltage of the duty ratio η and the oscillation output from the sawtooth wave generation circuit 26 can be input to the comparator 27 to output the PWM control signal SC.

In FIGS. 3, 7 and 10, the drive switch is constituted by a transistor switch Tr1 (which may be either a bipolar transistor or an FET). However, as shown in FIG. 11, the drive power supply 5 is a square wave. When the power supply voltage waveform is input to the power supply line 6 in a pre-switched state, the drive switch allows the main drive current to be connected to the main drive line 3, and the auxiliary drive current is supplied to the power supply line 6 side. It is also possible to configure with a diode Di2 that cuts off. When the power input is + _{V B} diode Di2, the main drive current flows through the inductor L1. This main drive current is expressed by equation (2) if the forward voltage drop Di2 of the diode is ignored. When the power supply voltage becomes zero after a certain time, the auxiliary drive current flows through the auxiliary closed current path formed by Di2, L1, and the light emitting diode LED2 by the energy stored in the inductor L1. That is, if there is a square wave output power source, the same operation can be realized only by the diode Di2. The period when the power source is + V is the duration τon of the first energized state, and the period of 0 V corresponds to the duration τoff of the first energized state. In this case, if the frequency of the square wave power supply voltage is F, the light emission intensity of the light emitting diode LED2 is expressed in exactly the same manner by the equation (5).

  Also, as shown in FIGS. 12 and 13, there is provided an inductor switching mechanism in which a plurality of inductors are prepared and one or two or more of these inductors are connected to the main drive line 3 so as to be switchable in combinations with different total inductances. It can also be added. Thereby, the structure which makes the inductance connected to a main drive line variable is easily realizable, and the freedom degree of light emission drive control can be raised more. For example, if the inductance can be switched between the first inductance L1 and the second inductance larger than the first inductance L1 (L1 + L2 in FIG. 12, L2 in FIG. 13), When the variable range of the switching frequency F of the duration τon or the first energization state / second energization state is set to be the same, the dimming range that is impossible in one of the first inductance and the second inductance is set to the other Can be covered with a dimming range that is possible, and the dimming range that is possible for the entire apparatus can be effectively expanded.

  In the configuration of FIG. 12, a first inductor L1 and a second inductor L2 having an inductance larger than that of the first inductor L1 are inserted in series with the main drive line 3. The inductor switching mechanism includes a bypass line 18 that short-circuits both ends of the second inductor L2, and a changeover switch SW that is provided on the bypass line 18 and switches conduction / cutoff of the bypass line 18. If both ends of the second inductor L2 are short-circuited by the operation of the changeover switch SW, the inductance connected to the light emitting diode LED2 is only a value derived from the first inductor L1, while the bypass line 18 is opened to open the second inductor L2. If the short-circuit state of the second inductor L2 is eliminated, the inductance connected to the light emitting diode LED2 becomes the value when the first inductor L1 and the second inductor L2 are combined in series, and the inductance can be easily changed. Can do. In this configuration, the switch SW only needs to have a function of switching the bypass line 18 between open and short, and there is an advantage that it can be simply configured by an SPST switch or the like. In FIG. 12, the switch SW is composed of two transistors Tr3 and Tr4 and peripheral resistors R5 and R4, and is switched according to the input level of the switching control signal SK.

  The operating characteristics when the switch SW is in the on state are the same as the configuration of FIG. Assuming that the emission intensity when the duration τon of the first energization state is 10 μs is 100%, the luminance can be controlled from 1% to 100% by controlling τon from 1 μs to 10 μs from the equation (5). Here, in order to further reduce the emission intensity, τon may be shortened. However, the frequency characteristics of the transistors and diodes, particularly the on / off times of Tr1 and Tr2, and the on / off time of the diode Di1 cannot be ignored. Leads to a decline. Further, since switching is performed at a high frequency, noise may be a problem. Therefore, if the inductance of the inductor L2 is set to 99 times that of the inductor L1, for example, and the switch SW is opened, the combined inductance becomes 100 times. As can be seen from the equation (5), the emission intensity (IL) is reduced to 1/100 even when τon = 10 μs. If τon is decreased to 1 μs from this state, the emission intensity is further reduced to 1/100, so that it can be reduced to 1/10000 of the initial emission intensity. In this way, by adding an inductor switching mechanism, the dimming range can be greatly expanded, and efficiency problems and noise problems can be avoided compared with control using only τon (duty ratio η) and frequency F. become.

  As shown in FIG. 13, a plurality of inductors L1 and L2 may be provided in parallel with each other on the main drive line, and the inductors may be selectively switched and connected to the power line by the switch SX. Good. In this case, the switch SX needs to use a multi-throw switch corresponding to the number of switchable inductors L1 and L2. In FIG. 13, the switch SX is configured as an SPDT switch using analog semiconductor switches σ1 and σ2 corresponding to the inductors L1 and L2. The level signal SK for switch control is directly input to one analog semiconductor switch σ1, and is input to the other analog semiconductor switch σ2 with its level inverted by an inverter 9.

The conceptual diagram which shows one 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 1st example which actualized the light emitting diode drive device of FIG. 1 more. Explanatory drawing in the case of carrying out PWM control of the light emitting diode drive device of FIG. FIG. 4 is a first explanatory diagram when the frequency of the light emitting diode driving device of FIG. 3 is controlled. Similarly second explanatory diagram. FIG. 4 is a circuit diagram showing an example in which the light emitting diode driving device of FIG. 3 is further embodied. The figure which shows an example of the control flow in the light emitting diode drive device of FIG. FIG. 8 is a conceptual diagram of a duty ratio or frequency conversion table used in the light emitting diode driving device of FIG. 7. FIG. 4 is a circuit diagram showing another example in which the light emitting diode driving device of FIG. 3 is further embodied. The circuit diagram which shows the 2nd example which actualized the light emitting diode drive device of FIG. 1 more. The circuit diagram which shows the 3rd example which actualized the light emitting diode drive device of FIG. 1 more. The circuit diagram which shows the 4th example which actualized the light emitting diode drive device of FIG. 1 more. 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 Main drive line 4 Auxiliary closed current path formation line 6 Power supply line 7 Auxiliary closed current path 8 CPU (energization state switching means, pulse intensity adjusting means, emission intensity stabilizing means, pulse number adjusting means , Dimming means)
18 Bypass line L1, L2 Inductor Tr1, Tr2, Di2 Drive switch SW changeover switch (inductor changeover mechanism)

Claims (13)

A main drive line for driving the light emitting diode;
An inductor inserted in series with the light emitting diode on the main drive line;
A power supply line for supplying a main drive current from a drive power supply to the light emitting diode;
An auxiliary closed current path forming line that forms an auxiliary closed current path not including the power supply line for the light emitting diode together with the main drive line; and
The energization state of the light emitting diode is changed from the power supply line to the main drive line, the first energization state for supplying the main drive current while storing magnetic energy in the inductor, and the main drive current to the main drive line. Energization state switching means for alternately switching between the second energization state in which the magnetic energy stored in the inductor is released through the auxiliary closed current path as the auxiliary drive current of the light emitting diode , equipped with a,
A light emitting device comprising: an inductor switching mechanism that includes a plurality of the inductors, and that connects one or more of the inductors to the main drive line in a switchable combination with different total inductances. Diode drive device. In the inductor, a first inductor and a second inductor having an inductance larger than that of the first inductor are inserted in series with the main drive line, and the inductor switching mechanism is configured to connect both ends of the second inductor. 2. The light emitting diode driving device according to claim 1 , further comprising: a bypass line that is short-circuited; and a changeover switch that is provided on the bypass line and switches between conduction and interruption of the bypass line . A plurality of the inductors are provided in parallel with each other on the main drive line,
2. The light emitting diode driving device according to claim 1, wherein the inductor switching mechanism is a switch that selectively switches and connects the plurality of inductors to the power supply line . The current adjustment resistor for adjusting the energization current to the light emitting diode is excluded from the energization path of the light emitting diode including the power line, the main drive line, and the auxiliary closed current path forming line. The light-emitting-diode drive device of any one of Claim 3 . The energization state switching means includes a drive switch for switching the power supply line and the main drive line between a connected state and a disconnected state, and is closer to the drive switch than either the light emitting diode or the inductor. The auxiliary closed current path forming line branches off from the main drive line, and the auxiliary closed current path forming line is on the auxiliary closed current path forming line when the power switch is connected to the main drive line by the drive switch. Rectification that prevents the main drive current from flowing through the current path forming line and allows the auxiliary drive current to flow through the auxiliary closed current path forming line when the power supply line is disconnected from the main drive line. The light-emitting diode driving device according to claim 1, further comprising an element . The drive switch is configured by a transistor switch, and by inputting a drive signal to the drive terminal of the transistor switch, the supply of the main drive current to the light emitting diode and the inductor through the power supply line is periodically performed. 6. The light emitting diode driving device according to claim 5, which performs switching . The drive power supply supplies a square wave power output having a predetermined period to the power supply line, and the drive switch allows conduction of the main drive current to the main drive line, and the power supply line 6. The light emitting diode driving device according to claim 5, wherein the light emitting diode driving device is a diode that blocks conduction of the auxiliary driving current to the side . The light emission pulse intensity generated in the light emitting diode in one switching cycle between the first energized state and the second energized state by the energized state switching means is changed, and the duration of the first energized state in the switching cycle is changed. The light-emitting diode driving device according to claim 1, further comprising a pulse intensity adjusting unit that adjusts by performing the adjustment . The switching frequency between the first energized state and the second energized state by the energized state switching unit is fixed, and the pulse intensity adjusting unit changes the duty ratio of the first energized state in the one switching cycle. 9. The light emitting diode driving device according to claim 8 , wherein the light emitting diode driving device functions as dimming means for adjusting an average light emission intensity of the light emitting diode. Voltage detection means for detecting the voltage of the drive power supply, and the pulse intensity adjustment means is configured to perform the first energization in the one switching cycle to obtain the same light emission intensity as the detected voltage increases. 9. The light emitting diode driving device according to claim 8, wherein the light emitting diode driving device functions as light emission intensity stabilizing means for setting a state duty ratio to a small value . The pulse number adjusting means for adjusting the number of light emitting pulses per unit time generated in the light emitting diode by changing a switching frequency between the first energized state and the second energized state by the energized state switching means. The light emitting diode driving device according to claim 1 . 12. The light emitting diode driving device according to claim 11, wherein the pulse number adjusting unit functions as a dimming unit that adjusts an average light emission intensity of the light emitting diode by changing the switching frequency . The voltage detection means for detecting the voltage of the drive power supply, wherein the pulse number adjustment means functions as a light emission intensity stabilization means for setting the switching frequency to be smaller as the detected voltage is higher. Item 13. A light-emitting diode driving device according to Item 12 .

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