JP2020161383A - Load drive device - Google Patents

Abstract

To suppress flicker even when an LED load is composed of a plurality of LEDs with different numbers of stages.SOLUTION: The characteristics of an LED load 60 to be driven are stored in a load drive device 10, and a duty ratio Ti is calculated by adding the characteristics to each of the load drive devices 10. As a result, it is possible to suppress flicker even when the plurality of LED loads 60 have different numbers of LED stages.SELECTED DRAWING: Figure 1

Description

The present invention relates to a load driving device that drives an LED load such as LED lighting composed of a light emitting diode (hereinafter referred to as LED: light emitting diode).

Conventionally, Patent Document 1 discloses a load drive circuit that drives a load using a filament type lamp as a load. This load drive circuit drives the lamp with a duty ratio calculated from the power supply voltage applied to the lamp to keep the illuminance of the lamp within a certain range and prevent the lamp from flickering.

On the other hand, Patent Document 2 proposes a technique for preventing flicker by driving an LED with a duty ratio calculated from a power supply voltage in a drive device for driving an LED load, as in Patent Document 1. In this drive device, the voltage drop width in the forward direction of the LED is Vf [V], the power supply voltage is VB [V], the duty ratio is 100%, and the illuminance when the LED is driven at the target voltage Vx [V]. The duty ratio to be such is set based on the following equation for Ti. The voltage drop width Vf [V] in the forward direction of the LED is a fixed value stored in advance in a memory or the like.

(Equation 1)
Ti = (Vx-Vf) / (VB-Vf)

Japanese Unexamined Patent Publication No. 2011-119236 JP-A-2018-6187

However, in the case of an LED, since it is affected by the diode characteristics, it is not possible to accurately prevent flicker even if the duty ratio is simply calculated based on the power supply voltage applied to the LED as in Patent Document 1.

Further, even if the duty ratio is set only by the power supply voltage VB [V] and the voltage drop width Vf [V] stored in advance as a fixed value as in Patent Document 2, the drop voltage in the LED is actually set. Has an LED stage number and voltage temperature dependence, so an appropriate duty ratio cannot be set. Therefore, when an LED lamp with a plurality of LEDs having different numbers of stages is used as a load, the illuminance cannot be kept constant.

In view of the above points, the present invention makes it possible to suppress flicker in a load drive device for driving an LED load composed of LEDs even if the LED load is composed of a plurality of LEDs having different numbers of stages. The purpose is.

In order to achieve the above object, the invention according to claim 1 is a load drive used to drive a load (60) composed of a predetermined number of stages of LEDs based on a power supply voltage when a drive instruction signal is input. A voltage detection unit (23) that detects the power supply voltage, a storage unit (25) that stores voltage-dependent data of the voltage drop width of the LED, and a voltage detection unit when a drive instruction signal is input. The control unit (21) that calculates the duty ratio of the drive signal based on the voltage detection result in the unit and the voltage-dependent data stored in the storage unit, and the drive signal with the duty ratio calculated by the control unit. A load drive output unit (22) that outputs, and a drive device (22) that applies a power supply voltage to the load by performing on / off drive according to the duty ratio based on the drive signal so that illumination by the LED is performed. 50), and the storage unit stores the voltage drop width of the LED as Vf, the voltage dependence as ΔVfv, and the target voltage when the LED has a constant illuminance as Vx as the voltage-dependent data. The control unit is characterized in that the duty ratio Ti is calculated by the equation 3 described later, where the power supply voltage is VB.

In this way, the characteristics of the LED load to be driven are stored in the load drive device, and the duty ratio Ti is calculated by taking into account the amount of change in the voltage drop width corresponding to the fluctuation of the power supply voltage. As a result, it is possible to suppress flicker even if a plurality of LED loads have different numbers of LED stages.

In the invention according to claim 2, the storage unit uses Vf as the voltage drop width of the LED, ΔVfv as the voltage dependence, Vx as the target voltage when the LED has a constant illuminance, and the LED as voltage-dependent data. The number of stages is stored as n, and the control unit is characterized in that the power supply voltage is VB and the duty ratio Ti is calculated by the equation 4 described later.

In this way, by calculating the duty ratio Ti in consideration of the number of LED stages in addition to the amount of change in the voltage drop width corresponding to the fluctuation of the power supply voltage VB, it is possible to further suppress the flicker.

The invention according to claim 3 has a temperature detection unit (24) for detecting the ambient temperature, the storage unit also stores temperature-dependent data of the LED, and the control unit receives a drive instruction signal. Then, in addition to the voltage detection result in the voltage detection unit and the voltage-dependent data stored in the storage unit, the duty ratio of the drive signal is calculated based on the temperature-dependent data, and the duty ratio is temperature-dependent. The property is ΔVft, the ambient temperature is Tx, the target temperature when the LED is a constant illuminance is Ta, and the denominator of the formula for calculating the duty ratio is the value obtained by subtracting ΔVfv (VB-Vx). , The duty ratio Ti is calculated.

In this way, the duty ratio Ti can be calculated by taking into account the amount of change in the voltage drop width corresponding to the temperature fluctuation in addition to the fluctuation of the power supply voltage and the number of LED stages. By doing so, it is possible to further suppress flicker.

The load drive devices according to claims 1 to 3 can be provided one by one according to the load, for example, as described in claim 4.

Further, as described in claim 5 or 6, the load driving device according to claims 1 to 3 may be a common one used for driving a plurality of loads composed of LEDs having different stages. good.

In that case, as shown in claim 5, the number of drive devices corresponding to each of the plurality of loads is provided, the storage unit stores data for each of the plurality of loads, and the control unit stores the data for each of the plurality of loads. The duty ratio Ti is calculated, and a plurality of loads and the calculated duty ratio Ti are linked and output to the load drive output unit, and the load drive output section links the calculated duty ratios for each of the plurality of loads. By outputting the drive signal with Ti, the corresponding drive device can be driven on and off.

Further, as shown in claim 6, a number of load drive output units and drive devices corresponding to each of the plurality of loads are provided, data is stored for each of the plurality of loads in the storage unit, and a plurality of load drive output units and drive devices are stored in the control unit. The duty ratio Ti is calculated for each load, and the duty ratio Ti corresponding to the load is output to the load drive output unit used to drive the corresponding load among multiple loads, and the load drive output unit By outputting a drive signal with a duty ratio of Ti, the corresponding drive device can be driven on and off.

The reference reference numerals in parentheses attached to each component or the like indicate an example of the correspondence between the component or the like and the specific component or the like described in the embodiment described later.

It is a figure which showed the block structure of the load drive device which concerns on 1st Embodiment. It is a circuit diagram of the LED load when the LED has one stage. It is a circuit diagram of the LED load when the LED has 3 stages. It is a figure which shows the result of having investigated the relationship of the current change amount with respect to the fluctuation of a power supply voltage by changing the number of LED stages constituting an LED load. It is a figure which shows the result of having investigated the relationship of the current change amount with respect to the fluctuation of an ambient temperature by changing the number of LED stages constituting an LED load. It is a figure which showed the block structure of the load drive device which concerns on 2nd Embodiment. It is a figure which showed the block structure of the load drive device which concerns on 3rd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each of the following embodiments, parts that are the same or equal to each other will be described with the same reference numerals.

(First Embodiment)
The load driving device according to the first embodiment of the present invention will be described. FIG. 1 is a diagram showing a block configuration of the load drive device 10. First, the configuration of the load drive device 10 will be described with reference to this figure. In this embodiment, a mode in which the load drive device 10 is provided for each LED load will be described. FIG. 1 shows only the load drive device 10 provided for one of the LED loads, but each load drive device 10 has the same configuration.

The load drive device 10 shown in FIG. 1 is provided for each of a plurality of LED loads 60 provided, and includes an integrated circuit for control (hereinafter referred to as a control IC) 20, a voltage detection circuit 30, a temperature detection circuit 40, and a drive device 50. It is said that it has a structure.

The control IC 20 is composed of, for example, a microcomputer equipped with a CPU, ROM, RAM, I / O, etc., and is driven by a predetermined voltage (for example, 5 V). In the case of the present embodiment, the control IC 20 has a control unit 21, a load drive output unit 22, a voltage detection unit 23, a temperature detection unit 24, a non-volatile memory 25, and the like, and drives the LED load 60 based on the drive instruction signal. To do.

The control unit 21 calculates the duty ratio based on, for example, a drive instruction signal from the vehicle, and outputs a control signal indicating the calculated duty ratio to the load drive output unit 22 in order to drive the LED load. .. Specifically, the control unit 21 determines the duty ratio based on the voltage detection result of the voltage detection unit 23, the temperature detection result of the temperature detection unit 24, and various data stored in the non-volatile memory 25. It is set. The details of this duty ratio calculation method will be described later.

The load drive output unit 22 drives the LED load 60 by outputting a drive signal for on / off driving the drive device 50 according to the duty ratio calculated by the control unit 21. As will be described later, since the drive device 50 is composed of switching elements, the load drive output unit 22 drives a voltage or current having a predetermined duty ratio for driving the switching elements constituting the drive device 50. Output as a signal.

The voltage detection unit 23 detects the power supply voltage VB by converting the monitor voltage Vs corresponding to the power supply voltage VB detected by the voltage detection circuit 30 into a digital value, and is composed of an AD conversion circuit or the like. .. Since the input allowable voltage of the control IC 20 is 5 V or less, the power supply voltage VB is divided to 5 V or less by the voltage detection circuit 30 described above to generate the monitor voltage Vs. The voltage detection unit 23 converts the monitor voltage Vs indicated by the analog value generated by the voltage detection circuit 30 into a digital value, and inputs it to the control unit 21.

The temperature detection unit 24 inputs a temperature detection signal according to the ambient temperature transmitted from the temperature detection circuit 40 and converts it into a digital value, and is composed of an AD conversion circuit or the like.

The non-volatile memory 25 corresponds to a storage unit and is a non-transitional tangible recording medium such as a flash memory that constitutes a ROM or the like built in the control IC 20 so that various data can be stored and read by the control unit 21. It has become. Specifically, the non-volatile memory 25 stores Vf [V], Vx [V], Tx [° C.], ΔVfv [V / V], and ΔVft [V / ° C.] as the characteristics of the LED load 60. There is. Vf is the voltage drop width in the forward direction of the LED. Vx is a target voltage when the illuminance of the LED load 60 is constant, and it is assumed that the illuminance is constant when the duty ratio is driven by 100% at the target voltage Vx. Tx is a target temperature at which the illuminance of the LED load 60 is constant, and it is assumed that the illuminance when the duty ratio is 100% driven at the target temperature Tx is constant. ΔVfv is the voltage dependence of Vf, that is, the amount of change in Vf when the power supply voltage fluctuates by 1 V. ΔVft is the temperature dependence of Vf, that is, the amount of change in Vf when the ambient temperature fluctuates by 1 ° C.

In the case of the present embodiment, the characteristics of the LED load 60 stored in the non-volatile memory 25 are those of the LED load 60 to be driven by the load drive device 10. Therefore, the non-volatile memory 25 of each load drive device 10 separately stores the characteristics corresponding to the LED load 60 to be driven.

The voltage detection circuit 30 converts the power supply voltage VB into the monitor voltage Vs corresponding to the power supply voltage VB and inputs it to the voltage detection unit 23. For example, the voltage detection circuit 30 is composed of a voltage dividing resistor, and the power supply voltage VB is divided by the voltage dividing resistor to generate a monitor voltage Vs. The monitor voltage Vs generated by the voltage detection circuit 30 is an input allowable voltage to the control IC 20, for example, 5 V or less.

The temperature detection circuit 40 is composed of a temperature sensor or the like, and inputs a temperature detection signal corresponding to the ambient temperature to the temperature detection unit 24. The ambient temperature referred to here is the ambient temperature of the LED load 60 that correlates with the temperature of the LED load 60 to be driven. It is preferable that the temperature of the LED load 60 can be directly measured, but since it is difficult to directly measure the temperature, the ambient temperature of the LED load 60 is measured by the temperature detection circuit 40, and this is used as the temperature of the LED load 60. Of course, instead of using the ambient temperature as the temperature of the LED load 60, for example, the temperature is corrected by multiplying it by a predetermined coefficient, or the LED load corresponding to the ambient temperature is used by using a correlation diagram investigated in advance by an experiment. The temperature of the LED load 60 may be obtained more accurately by obtaining the temperature of 60. For example, the temperature sensor is composed of diodes arranged in multiple stages, and outputs a temperature detection signal according to the ambient temperature based on the change in the voltage drop width Vf in the forward direction of the diodes depending on the temperature characteristics.

The drive device 50 supplies a drive current for driving the LED load 60 based on a drive signal from the load drive output unit 22. For example, the drive device 50 is composed of MOSFETs, transistors, IPDs (intelligent power devices), and the like. By duty-driving the drive device 50 based on the drive signal, the average current value of the drive current supplied to the LED load 60 is controlled to a value that keeps the illuminance of the LED load 60 constant. There is.

The LED load 60 performs LED lighting by duty-driving the drive device 50. Specifically, the LED load 60 performs LED illumination by applying a power supply voltage VB when the drive device 50 is turned on. The illuminance of the LED lighting changes according to the average current value supplied to the LED load 60, that is, the magnitude of the current value per unit time, and the larger the average current value, the higher the illuminance. Since the average current value is variable according to the duty ratio of the drive current of the drive device 50, the illuminance of the LED load 60 is adjusted based on the duty ratio set by the control unit 21. There is.

Although only one LED load 60 is shown in FIG. 1, a plurality of LED loads 60 having different numbers of stages are actually provided, and in the case of the present embodiment, each of them is a separate load drive device 10. Driven by. FIG. 2A shows a configuration in which the first load 61 is provided as the LED load 60, and FIG. 2B shows a configuration in which the second load 62 is provided as the LED load 60. The first load 61 and the second load 62 are different in the number of stages of the LED 61a and the number of stages of the LED 62a, respectively. Further, a limiting resistor 61b is connected in series to the LED 61a to the first load 61, and a limiting resistor 62b is connected in series to the LED 62a to the second load 62. Therefore, the current is limited so that an excessive current does not flow through the LEDs 61a and 62a.

As described above, the load drive device 10 according to the present embodiment is configured. Subsequently, the operation of the load drive device 10 of the present embodiment will be described.

The load drive device 10 shown in FIG. 1 is driven based on, for example, a drive instruction signal from a vehicle. For example, when the user switches the lighting switch provided in the vehicle from off to on, a drive instruction signal for driving the LED load 60 to turn on the LED lighting is input to the load driving device 10. .. As a result, in the control unit 21, the duty ratio is set based on the voltage detection result of the voltage detection unit 23, the temperature detection result of the temperature detection unit 24, and various data stored in the non-volatile memory 25, and the load drive is performed. A drive signal of a voltage or current having a duty ratio is output from the output unit 22. As a result, the drive device 50 is duty-driven based on the drive signal, the LED load 60 is driven, and the LED illumination is turned on.

Here, the details of the duty ratio calculation method by the control unit 21 will be described.

As described above, the control unit 21 has a duty ratio based on the following equation based on the voltage detection result of the voltage detection unit 23, the temperature detection result of the temperature detection unit 24, and various data stored in the non-volatile memory 25. Ti is calculated.

(Number 2)
Ti = (Vx-nVf) /
{VB-nVf-ΔVfv (VB-Vx) -ΔVft (Ta-Tx)}
In the LED load 60, the current value flowing through the LED changes depending on the number of LED stages configured, even if the power supply voltage VB has the same voltage value. As shown in FIG. 2, FIG. 3 measures the amount of current change when the power supply voltage VB is changed for each of the first load 61 having the LED 61a in one stage and the second load 62 having the LED 62a in three stages. The result is shown. Here, the amount of change in current from the power supply voltage VB is illustrated with reference to the case of 13V. Further, FIG. 4 shows the results of measuring the amount of current change when the ambient temperature Ta is changed for each of the first load 61 having the LED 61a in one stage and the second load 62 having the LED 62a in three stages. .. Here, the ambient temperature Ta is assumed to be −30 ° C. to 80 ° C. as the usage environment of the vehicle, and the amount of current change from the temperature of −30 ° C. is shown as a reference.

As shown in these figures, the slope of the amount of change in the current with respect to the change in the power supply voltage VB and the change in the ambient temperature Ta is different between the case of the one-stage LED61a and the case of the three-stage LED62a. In this way, when the power supply voltage VB or the ambient temperature Ta fluctuates, the amount of change in the current changes. Therefore, even if the power supply voltage VB is simply detected and the duty ratio Ti is calculated using the above equation 1, the LED It is not possible to deal with fluctuations in the number of stages, power supply voltage VB, and ambient temperature Ta.

Therefore, in the present embodiment, the duty ratio Ti is calculated based on the above-mentioned mathematical formula 2 in consideration of the case where the number of LED stages, the power supply voltage VB, and the ambient temperature Ta fluctuate.

Specifically, the voltage drop width according to the number of stages is obtained by multiplying Vf in each term by the number of stages n. Further, by multiplying the difference between the power supply voltage VB and the target voltage Vx by ΔVfv, when there is a voltage difference between the power supply voltage VB and the target voltage Vx, the voltage drop width corresponding to the voltage difference can be obtained. The amount of change is obtained. Similarly, by multiplying the difference between the ambient temperature Ta and the target temperature Tx by ΔVft, when there is a temperature difference between the ambient temperature Ta and the target temperature Tx, the voltage drop width corresponding to the temperature difference The amount of change in is obtained. Therefore, the voltage drop width Vf corresponding to the number of LED stages is subtracted from the target voltage Vx, and the voltage drop width Vf corresponding to the number of LED stages is subtracted from the power supply voltage VB, and the amount of change in the voltage drop width corresponding to the voltage difference or temperature difference. The duty ratio Ti is calculated by dividing by the value obtained by subtracting.

The duty ratio Ti is calculated for each of the first load 61 and the second load 62, and the target voltage Vx is the same voltage. For example, in the law, in consideration of LED life and the like, it is stipulated that the LED is driven at a voltage lower than that when the LED is driven at a voltage of 13.5 V at a duty ratio of 100%. .. Therefore, for example, 13.0 V, which is lower than that, is set as the target voltage Vx. Then, if the power supply voltage VB is larger than the target voltage Vx, the voltage difference VB-Vx is obtained, and by multiplying it by the amount of change in the voltage drop width corresponding to the voltage difference, the third term of the denominator of Equation 2 Is required.

As described above, the load driving device 10 stores the characteristics of the LED load 60 to be driven, and each load driving device 10 takes the characteristics into consideration to calculate the duty ratio Ti. Therefore, it is possible to suppress flicker for a plurality of LED loads 60 even if the number of LED stages is different.

(Second Embodiment)
The second embodiment will be described. This embodiment is designed so that a plurality of LED loads 60 are driven by a common load drive device 10 with respect to the first embodiment, and the other aspects are the same as those of the first embodiment. , Only the part different from the first embodiment will be described.

As shown in FIG. 5, the load drive device 10 of the present embodiment includes a number of drive devices 50 corresponding to the LED load 60, and a drive signal is output from the load drive output unit 22 to each drive device 50. It is supposed to be done.

In such a form, all the characteristics of each LED load 60 are stored in the non-volatile memory 25, and the control unit 21 separately calculates the duty ratio Ti according to the characteristics of each LED load 60. Then, the calculation result for each LED load 60 is linked to indicate which LED load 60 has the duty ratio Ti, and is transmitted to the load drive output unit 22, and the load drive output unit 22 corresponds to the LED load 60. A drive signal corresponding to the calculated duty ratio Ti is output to the drive device 50.

By doing so, when a plurality of LED loads 60 are driven by the common load driving device 10, flicker can be suppressed even if the plurality of LED loads 60 have different numbers of LED stages. It will be possible.

(Third Embodiment)
A third embodiment will be described. This embodiment is also designed so that a plurality of LED loads 60 are driven by a common load drive device 10 with respect to the first embodiment, and the other aspects are the same as those of the first embodiment. , Only the part different from the first embodiment will be described.

As shown in FIG. 6, the load drive device 10 of the present embodiment also includes a number of drive devices 50 corresponding to the LED load 60 as in the second embodiment, but the load drive output unit 22 also has LEDs. There are a number corresponding to the load 60. In the case of the present embodiment, a plurality of load drive output units 22 are provided as external components independent of the control IC 20, so that the number of LED loads 60 can be easily matched, but a plurality of load drive output units 22 are provided in the control IC 20. You may be prepared.

In this way, the load drive output unit 22 and the drive device 50 may be provided in a number corresponding to the number of LED loads 60. Also in this case, as in the second embodiment, all the characteristics of each LED load 60 are stored in the non-volatile memory 25, and the control unit 21 separately sets the duty ratio Ti according to the characteristics of each LED load 60. Calculate to. Then, the calculation result for each LED load 60 is transmitted to the load drive output unit 22 used for driving the LED load 60, and the load drive output unit 22 sends a drive signal corresponding to the duty ratio Ti of the calculation result to the corresponding drive device 50. Is output. Even in this way, the same effect as that of the second embodiment can be obtained.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and can be appropriately modified within the scope of the claims.

For example, in the above embodiment, the first load 61 and the second load 62 are given as examples of the LED load 60, but the number of the LED load 60 is arbitrary, and the number of LED stages constituting each LED load 60 is arbitrary. Is also optional.

Further, in the above embodiment, an example is shown in which the number of LED stages constituting the LED load 60, the power supply voltage VB, and the ambient temperature Ta can be all changed. However, even if all of these cannot be dealt with, it is sufficient that the duty ratio Ti can be set in consideration of at least the amount of change in the voltage drop width corresponding to the fluctuation of the power supply voltage VB.

For example, when the duty ratio Ti is set in consideration of only the amount of change in the voltage drop width corresponding to the fluctuation of the power supply voltage VB, the duty ratio Ti may be calculated by the mathematical formula 3. Further, if the number of LED stages is taken into consideration in addition to the amount of change in the voltage drop width corresponding to the fluctuation of the power supply voltage VB, the duty ratio Ti may be calculated by Equation 4. Further, if the amount of change in the voltage drop width corresponding to the fluctuation of the temperature is taken into consideration in addition to the amount of change in the voltage drop width corresponding to the fluctuation of the power supply voltage VB, the duty ratio Ti may be calculated by the equation 5.

(Number 3)
Ti = (Vx-Vf) / {VB-Vf-ΔVfv (VB-Vx)}

(Number 4)
Ti = (Vx-nVf) / {VB-nVf-ΔVfv (VB-Vx)}

(Number 5)
Ti = (Vx-Vf) / {VB-Vf-ΔVfv (VB-Vx) -ΔVft (Ta-Tx)}

10 ... Load drive device, 20 ... Control IC, 21 ... Control unit, 22 ... Load drive output unit, 23 ... Voltage detection unit, 24 ... Temperature detection unit, 25 ... Non-volatile memory, 30 ... Voltage detection circuit, 40 ... Temperature Detection circuit, 50 ... drive device, 60 ... LED load, 61 ... first load, 61a ... LED, 61b ... limiting resistor, 62 ... second load, 62a ... LED, 62b ... limiting resistor

Claims (6)

A load drive device that drives a load (60) composed of light emitting diodes having a predetermined number of stages based on a power supply voltage when a drive instruction signal is input.
The voltage detection unit (23) for detecting the power supply voltage and
A storage unit (25) that stores voltage-dependent data of the voltage drop width of the light emitting diode, and
When the drive instruction signal is input, the control unit (21) calculates the duty ratio of the drive signal based on the voltage detection result in the voltage detection unit and the voltage-dependent data stored in the storage unit. )When,
A load drive output unit (22) that outputs the drive signal with the duty ratio calculated by the control unit, and
A drive device (50) that applies the power supply voltage to the load by performing on / off drive according to the duty ratio based on the drive signal so that illumination by the light emitting diode is performed. Have and
The storage unit stores Vf as the voltage drop width of the light emitting diode, ΔVfv as the voltage dependence, and Vx as the target voltage when the light emitting diode has a constant illuminance as the voltage dependence data. ,
The control unit sets the duty ratio Ti as VB and sets the duty ratio Ti.
Ti = (Vx-Vf) / {VB-Vf-ΔVfv (VB-Vx)}
A load drive device characterized by being calculated by a mathematical formula represented by. A load drive device that drives a load (60) composed of light emitting diodes having a predetermined number of stages based on a power supply voltage when a drive instruction signal is input.
The voltage detection unit (23) for detecting the power supply voltage and
A storage unit (25) that stores voltage-dependent data of the voltage drop width of the light emitting diode, and
When the drive instruction signal is input, the control unit (21) calculates the duty ratio of the drive signal based on the voltage detection result in the voltage detection unit and the voltage-dependent data stored in the storage unit. )When,
A load drive output unit (22) that outputs the drive signal with the duty ratio calculated by the control unit, and
A drive device (50) that applies the power supply voltage to the load by performing on / off drive according to the duty ratio based on the drive signal so that illumination by the light emitting diode is performed. Have and
As the voltage-dependent data, the storage unit sets the voltage drop width of the light emitting diode as Vf, the voltage dependence as ΔVfv, the target voltage when the light emitting diode has a constant illuminance as Vx, and the light emitting diode. The number of stages is stored as n,
The control unit sets the duty ratio Ti as VB and sets the duty ratio Ti.
Ti = (Vx-nVf) / {VB-nVf-ΔVfv (VB-Vx)}
A load drive device characterized by being calculated by a mathematical formula represented by. It has a temperature detection unit (24) that detects the ambient temperature,
The storage unit also stores temperature-dependent data of the light emitting diode.
The control unit
When the drive instruction signal is input, the drive signal is based on the temperature-dependent data in addition to the voltage detection result in the voltage detection unit and the voltage-dependent data stored in the storage unit. Duty ratio is calculated
Let ΔVft be the temperature dependence, Tx be the ambient temperature, and Ta be the target temperature when the light emitting diode has a constant illuminance.
The load according to claim 1 or 2, wherein the duty ratio Ti is calculated by using the denominator of the formula for calculating the duty ratio as a value obtained by further subtracting ΔVfv (VB−Vx). Drive device. The load driving device according to any one of claims 1 to 3, wherein the load driving device is provided one by one corresponding to the load. Used to drive a plurality of the loads composed of the light emitting diodes having different stages.
The drive devices are provided in a number corresponding to each of the plurality of loads.
The storage unit stores the data for each of the plurality of loads, and the storage unit stores the data.
The control unit calculates the duty ratio Ti for each of the plurality of loads, links the plurality of loads with the calculated duty ratio Ti, and outputs the output to the load drive output unit.
The load drive output unit is characterized in that the corresponding drive device is driven on and off by outputting the drive signal with the duty ratio Ti associated with each of the plurality of loads. The load drive device according to any one of 3. Used to drive a plurality of the loads composed of the light emitting diodes having different stages.
The load drive output unit and the drive device are provided in a number corresponding to each of the plurality of loads.
The storage unit stores the data for each of the plurality of loads, and the storage unit stores the data.
The control unit calculates the duty ratio Ti for each of the plurality of loads, and the duty ratio corresponding to the load with respect to the load drive output unit used to drive the corresponding load among the plurality of loads. Output Ti and
The load drive according to any one of claims 1 to 3, wherein the load drive output unit drives the corresponding drive device on and off by outputting the drive signal at the duty ratio Ti. apparatus.

Images