LED current control circuit and LED lighting device

Abstract

To provide a technology that suppresses "flickering" when outputting low power.SOLUTION: An LED current control circuit includes an on-width generation unit 21 that generates a Ton value (FB) for each unit time period on the basis of a current setting value and a current detection value of an LED current, an on-width holding unit 25 that holds the Ton value (FB) as a Ton value (Hold), a PWM generation unit 26 that generates a PWM signal of an on-width specified by the Ton value (Hold) held in the on-width holding unit 25 for each unit time period, a comparison unit 23 that compares the Ton value (FB) generated by the on-width generation unit 21 with the previous Ton value (Hold) that has specified the on-width of the PWM signal, and a counter 24 that counts the comparison result by the comparison unit 23 and increases or decreases the Ton value (Hold) held in the on-width holding unit 25 when the count value of the comparison result reaches +th or -th.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present disclosure relate to an LED current control circuit and an LED lighting device.

Background Art

[0002] The conventional drive circuit disclosed in Patent Document 1 reconverts the digital value of the input dimming pulse into an output dimming pulse, and controls the on and off of the drive current supplied to the light source, thereby reducing the "flickering" in PWM dimming caused by jitter and noise.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, LED lighting devices have been required to comply with the DALI (registered trademark) (Digital Addressable Lighting Interface) standard. The DALI standard indicates an international standard (IEC62386) for a communication method for lighting-specific control. In the case of LED lighting devices, dimming control by stepwise digital values such as in 1% units is required.

[0005] Since digital control is not continuous control, the dimming control becomes a stepwise control as shown in FIG. 7. FIG. 7 shows an example where the resolution of the on-width in the PWM signal is 100 gradations. In the region with a large output (the upper right region X shown in FIG. 7), the change rate of the output (out) per gradation (digit) is about 1% (for example, 99% / 98%), and since the rate of change is small, even if it changes by one step, it seems like continuous control without being noticeable. On the other hand, in the region with a small output (the lower left region Y shown in FIG. 7), the change rate of the output per gradation is about 100% (for example, 2% / 1%), and since the rate of change becomes large, when it changes by one step, the output changes greatly.

[0006] On the other hand, when controlling the current at low output, since the voltage to be handled (the voltage generated across the current detection resistor) is small, the control circuit becomes sensitive to noise etc., and furthermore the control becomes unstable. For example, when feedback controlling the output to 1% of the minimum value, due to the influence of noise etc., the output cannot be locked at 1%, and the current amount may become an unstable state where it repeats 1 mA (1%) and 2 mA (2%). In this case, the amount of change becomes large, from 1 mA to 2 mA (2 times), and from 2 mA to 1 mA (1 / 2). And since the sensitivity of the human eye to changes in light amount is better in the dark region, the large change at low output is felt as a very large "flicker" due to the multiplicative effect.

[0007] The present disclosure aims to provide a technique for suppressing the "flicker" at low output.

Means for Solving the Problem

[0008] The LED current control circuit of the present disclosure is an LED current control circuit that generates a PWM signal for controlling the LED current supplied to the LED light source unit, and includes: an on-width generation unit that generates an on-width specified value for each cycle of a unit time based on a current set value and a current detection value of the LED current; an on-width holding unit that holds the on-width specified value as an on-width holding value; a PWM generation unit that generates the PWM signal having an on-width specified by the on-width holding value held in the on-width holding unit for each cycle of the unit time; a comparison unit that compares the on-width specified value generated by the on-width generation unit with the previous on-width holding value that specified the on-width of the PWM signal; and an arithmetic unit that accumulates the comparison result by the comparison unit and increases or decreases the on-width holding value held in the on-width holding unit when the accumulated value of the comparison result reaches a change threshold value. The PWM generation unit continuously generates the PWM signal with the previous on-width holding value until the accumulated value of the comparison result reaches the change threshold value, and generates the PWM signal with the on-width holding value increased or decreased by the arithmetic unit when the accumulated value of the comparison result reaches the change threshold value.

Effects of the Invention

[0009] According to the present invention, "flickering" at low output can be suppressed.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Best Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, components having the same function are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0012] Referring to FIG. 1, the LED lighting device 1 of the present embodiment uses a DC power supply Vin as an input power supply, and includes an LED power supply device 2 and an LED light source unit 3.

[0013] The LED power supply device 2 includes a power supply circuit 10 and a control unit 20 that generates a PWM signal for driving the power supply circuit 10, and supplies an LED current controlled by the PWM signal to the LED light source unit 3.

[0014] The power supply circuit 10 shown in FIG. 1 is a buck converter and is connected to the output terminal of the DC power supply Vin. The power supply circuit 10 may employ a boost converter or a buck-boost converter, and may be of either a non-isolated type or an isolated type.

[0015] The power supply circuit 10 includes a switching element Q1, an inductor L1, a diode D1, a capacitor C1, a current detection circuit 11, and a drive circuit 12. The switching element Q1 is composed of, for example, an N-channel MOSFET. The capacitor C1 is composed of, for example, an electrolytic capacitor.

[0016] A series circuit composed of the switching element Q1, the inductor L1, and the capacitor C1 is connected across the DC power supply Vin. The drain of the switching element Q1 is connected to the positive electrode of the DC power supply Vin, and the source is connected to one end of the inductor L1. The positive electrode of the capacitor C1 is connected to the other end of the inductor L1, and the negative electrode is connected to the negative electrode of the DC power supply Vin.

[0017] Diode D1 is connected in parallel to inductor L1 and capacitor C1. The anode of diode D1 is connected to the negative electrode of capacitor C1, and the cathode is connected to one end of inductor L1.

[0018] The LED light source unit 3 is composed of a plurality of LEDs (light-emitting diodes) and is connected between the output terminals of the power supply circuit 10. The anode side of the LED light source unit 3 is connected to the positive electrode of capacitor C1, and the cathode side is connected to the negative electrode side of capacitor C1 via the current detection circuit 11.

[0019] The current detection circuit 11 includes a current detection resistor R1 connected between the cathode side of the LED light source unit 3 and the negative electrode side of capacitor C1, and an amplifier AMP1 that amplifies the potential difference across both ends of the current detection resistor R1. The current detection circuit 11 detects the LED current flowing through the LED light source unit 3 and outputs it as a current detection value.

[0020] The control unit 20 is an LED current control circuit that generates a PWM signal for controlling the LED current supplied to the LED light source unit 3. The control unit 20 includes a detection signal input terminal T1 to which a current detection signal detected by the current detection circuit 11 is input, a dimming signal input terminal T2 to which a dimming signal is input, and a PWM signal output terminal T3 that outputs a PWM signal. The control unit 20 generates a Ton value that specifies the on-width of the PWM signal based on the current detection signal input from the detection signal input terminal T1 and the dimming signal input from the dimming signal input terminal T2. The control unit 20 outputs a PWM signal with an on-width specified by the generated Ton value from the PWM signal output terminal T3 to the drive circuit 12 of the power supply circuit 10.

[0021] The control unit 20 is an arithmetic processing circuit such as a microcomputer equipped with a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc. A control program for controlling the operation of the UPS1 is stored in the ROM. The control unit 20 reads out the control program stored in the ROM and expands the control program in the RAM, thereby functioning as an on-width generation unit 21, a small-output determination unit 22, a comparison unit 23, a counter 24, an on-width holding unit 25, and a PWM generation unit 26.

[0022] The current detection signal input from the detection signal input terminal T1 and the dimming signal input from the dimming signal input terminal T2 are respectively converted into a current detection value and a current setting value, which are digital signals, by an A / D converter (ADC).

[0023] The on-width generation unit 21 functions as an error amplifier and generates a Ton value (FB) that specifies the on-width of the PWM signal so that the current detection value becomes the current setting value. That is, the Ton value (FB) generated by the on-width generation unit 21 is obtained by a feedback operation using the current detection signal input from the detection signal input terminal T1 as a feedback signal.

[0024] The small-output determination unit 22 compares the current setting value with a preset small-output threshold value to determine whether it is a small output. When the small-output determination unit 22 determines that it is not a small output, the Ton value (FB) generated by the on-width generation unit 21 is output to the on-width holding unit 25 and the PWM generation unit 26. When the small-output determination unit 22 determines that it is a small output, the Ton value (FB) generated by the on-width generation unit 21 is output to the comparison unit 23.

[0025] The comparison unit 23 compares the Ton value (FB) generated by the on-width generation unit 21 with the Ton value (Hold) held in the on-width holding unit 25, and calculates the difference between the Ton value (FB) and the Ton value (Hold). When the Ton value (FB) is greater than the Ton value (Hold), the comparison unit 23 outputs a count increment signal (+1) instructing to add 1 to the count value, and when the Ton value (FB) is less than the Ton value (Hold), the comparison unit 23 outputs a count decrement signal (-1) instructing to subtract 1 from the count value to the counter 24 respectively.

[0026] The counter 24 is an arithmetic unit that accumulates the comparison results by the comparison unit 23. The count value counted by the counter 24 is the accumulated value obtained by accumulating the comparison results by the comparison unit 23. The counter 24 increases or decreases the count value according to the count increment signal (+1) and the count decrement signal (-1), and determines whether the increased or decreased count value has reached the positive-side change threshold (+th) or the negative-side change threshold (-th). When the count value after addition reaches the positive-side change threshold (+th), the counter 24 outputs a Ton value addition signal (+1) instructing to raise the Ton value (Hold) by one step (1 digit) to the on-width holding unit 25. When the count value after subtraction reaches the negative-side change threshold (-th), the counter 24 outputs a Ton value subtraction signal (-1) instructing to lower the Ton value (Hold) by one step (1 digit) to the on-width holding unit 25. When the count value reaches the positive-side change threshold (+th) or the negative-side change threshold (-th), the counter 24 initializes the count value to 0.

[0027] The on-width holding unit 25 holds (holds) the Ton value (FB) input from the small output determination unit 22 as the Ton value (Hold), and outputs the held Ton value (Hold). When the Ton value addition signal (+1) is input, the on-width holding unit 25 outputs the Ton value (Hold) obtained by raising the held Ton value (Hold) by one step (1 digit). When the Ton value subtraction signal (-1) is input, the on-width holding unit 25 outputs the Ton value (Hold) obtained by lowering the held Ton value (Hold) by one step (1 digit).

[0028] When the small output determination unit 22 determines that the output is not a small output, the PWM generation unit 26 generates a PWM signal with a pulse width specified by the Ton value (FB) input from the small output determination unit 22. When the small output determination unit 22 determines that the output is a small output, the PWM generation unit 26 generates a PWM signal with a pulse width specified by the Ton value (Hold) output from the pulse width holding unit 25. The PWM generation unit 26 controls the on / off of the switching element Q1 by outputting the generated PWM signal from the PWM signal output terminal T3 to the drive circuit 12 of the power supply circuit 10.

[0029] The control unit 20 acquires the current detection signal for each predetermined clock (for each cycle of the unit time) and generates a Ton value (Hold) that specifies the pulse width of the PWM signal. Hereinafter, the generation operation of the Ton value (Hold) by the control unit 20 will be described in detail with reference to FIGS. 2 and 3. FIG. 2 shows the generation operation of the Ton value (Hold) executed for each predetermined clock (unit time). In FIG. 3, (a) shows an example of the generation of the Ton value (FB), (b) shows the transition of the Ton value (Hold), and (c) shows the transition of the count value.

[0030] The pulse width generation unit 21 generates a Ton value (FB) that specifies the pulse width of the PWM signal so that the current detection value becomes the current set value (step S101).

[0031] Next, the small output determination unit 22 determines whether or not it is in the small output region by comparing the current set value with a preset small output threshold value (step S102). If it is determined in step S102 that it is not in the small output region, the small output determination unit 22 outputs the Ton value (FB) generated by the pulse width generation unit 21 to the pulse width holding unit 25 and holds it as the Ton value (Hold) (step S103). In this case, normal control is performed, and the pulse width holding unit 25 outputs the Ton value (FB) generated by the pulse width generation unit 21 to the PWM generation unit 26 as the Ton value (Hold).

[0032] If it is determined in step S102 that it is a small output area, small output control is performed, and the small output determination unit 22 outputs the Ton value (FB) generated by the on-width generation unit 21 to the comparison unit 23. The comparison unit 23 compares the Ton value (FB) generated by the on-width generation unit 21 with the Ton value (Hold) output before a predetermined clock (unit time) held in the on-width holding unit 25, and calculates the difference component (step S104).

[0033] The comparison unit 23 determines whether the Ton value (FB) is greater than the Ton value (Hold) (step S105).

[0034] If the Ton value (FB) is greater than the Ton value (Hold) in step S105, the comparison unit 23 outputs a count addition signal (+1) instructing an addition of 1 to the count value to the counter 24. The counter 24 adds 1 to the count value by the count addition signal (+1) (step S106), and determines whether the count value after the addition has reached the positive-side change threshold value (+th) (step S107).

[0035] If the count value has not reached the positive-side change threshold value (+th) in step S107, the Ton value (Hold) will not be increased or decreased in the subsequent process, and the on-width holding unit 25 continuously outputs the Ton value (Hold) output before a predetermined clock (unit time) to the PWM generation unit 26.

[0036] If the count value reaches the positive-side change threshold value (+th) in step S107, the counter 24 outputs a Ton value addition signal (+1) instructing an increase of one step (1 digit) of the Ton value (Hold) to the on-width holding unit 25, and initializes the count value to 0 (step S108).

[0037] When the Ton value addition signal (+1) is input, the on-width holding unit 25 raises the held Ton value (Hold) by one step (1 digit) (step S109). As a result, the on-width holding unit 25 outputs the Ton value (Hold) raised by one step (1 digit) from the Ton value (Hold) output before a predetermined clock (unit time).

[0038] If the Ton value (FB) is not greater than the Ton value (Hold) in step S105, the comparison unit 23 determines whether the Ton value (FB) is smaller than the Ton value (Hold) (step S110).

[0039] If the Ton value (FB) is not smaller than the Ton value (Hold) in step S110, that is, if the Ton value (FB) = Ton value (Hold), the Ton value (Hold) will not be increased or decreased in the subsequent process, and the on-width holding unit 25 continuously outputs the Ton value (Hold) output before a predetermined clock (unit time) to the PWM generation unit 26.

[0040] If the Ton value (FB) is smaller than the Ton value (Hold) in step S110, the comparison unit 23 outputs a count subtraction signal (-1) instructing a subtraction of 1 from the count value to the counter 24. The counter 24 subtracts 1 from the count value by the count subtraction signal (-1) (step S111) and determines whether the subtracted count value has reached the negative-side change threshold (-th) (step S112).

[0041] If the count value has not reached the negative-side change threshold (-th) in step S112, the Ton value (Hold) will not be increased or decreased in the subsequent process, and the on-width holding unit 25 continuously outputs the Ton value (Hold) output before a predetermined clock (unit time) to the PWM generation unit 26.

[0042] If the count value has reached the negative-side change threshold (-th) in step S112, the counter 24 outputs a Ton value subtraction signal (-1) instructing a one-step (1 digit) decrease of the Ton value (Hold) to the on-width holding unit 25 and initializes the count value to 0 (step S113).

[0043] When the Ton value subtraction signal (-1) is input to the on-width holding unit 25, the held Ton value (Hold) is decreased by one step (1 digit) (step S114). As a result, the on-width holding unit 25 outputs the Ton value (Hold) decreased by one step (1 digit) from the Ton value (Hold) output before a predetermined clock (unit time).

[0044] In the above small-output control, it can be seen that even if the Ton value (FB) shown in FIG. 3(a) fluctuates finely by feedback control, the fluctuation of the Ton value (Hold) shown in FIG. 3(b) is suppressed although it follows the feedback control. That is, in the feedback control during small output, the current detection signal (potential difference between both ends of the current detection resistor R1) is likely to fluctuate due to the influence of noise or the like, but the Ton value (Hold) that specifies the on-width of the PWM signal does not fluctuate sensitively in response to the change in the current detection signal (potential difference between both ends of the current detection resistor R1). As a result, in the LED lighting device 1, when the output is small with the light amount decreased, the LED current does not change finely, so "flickering" can be suppressed.

[0045] In the above small-output control, since the fluctuation due to the feedback control is suppressed, the responsiveness decreases. The responsiveness of the feedback control can be improved by changing the increase / decrease value of the count value in the counter 24 according to the magnitude of the difference between the Ton value (FB) and the Ton value (Hold).

[0046] Hereinafter, the generation operation of the Ton value (Hold) with improved responsiveness will be described in detail with reference to FIGS. 4 and 5. The same steps as the generation operation shown in FIG. 2 will be omitted as appropriate. FIG. 4 shows the generation operation of the Ton value (Hold) executed for each predetermined clock. In FIG. 5, (a) shows an example of the generation of the Ton value (FB), (b) shows the transition of the Ton value (Hold), and (c) shows the transition of the count value.

[0047] Referring to FIG. 4, when the Ton value (FB) is larger than the Ton value (Hold) in step S105, the comparison unit 23 determines whether the difference between the Ton value (FB) and the Ton value (Hold) is larger than a predetermined amount set in advance (step S201).

[0048] If the difference amount in step S201 is not greater than a predetermined amount, the comparison unit 23 outputs a count increment signal (+1) instructing an increment of 1 to the counter value to the counter 24. The counter 24 increments the counter value by 1 by the count increment signal (+1) (step S106), and determines whether or not the incremented counter value has reached the positive change threshold value (+th) (step S107).

[0049] If the difference amount in step S201 is greater than a predetermined amount, the comparison unit 23 weights the comparison result by the difference amount and outputs a count increment signal (+2) instructing an increment of 2 to the counter value to the counter 24. The counter 24 increments the counter value by 2 by the count increment signal (+2) (step S202), and determines whether or not the incremented counter value has reached the positive change threshold value (+th) (step S107).

[0050] If the Ton value (FB) is smaller than the Ton value (Hold) in step S110, it is determined whether or not the difference amount between the Ton value (FB) and the Ton value (Hold) is greater than a preset predetermined amount (step S203).

[0051] If the difference amount in step S201 is not greater than a predetermined amount, the comparison unit 23 outputs a count decrement signal (-1) instructing a decrement of 1 from the counter value to the counter 24. The counter 24 decrements the counter value by 1 by the count decrement signal (-1) (step S111), and determines whether or not the decremented counter value has reached the negative change threshold value (-th) (step S112).

[0052] If the difference amount in step S201 is greater than a predetermined amount, the comparison unit 23 weights the comparison result by the difference amount and outputs a count decrement signal (-2) instructing a decrement of 2 from the counter value to the counter 24. The counter 24 decrements the counter value by 2 by the count decrement signal (-2) (step S204), and determines whether or not the decremented counter value has reached the negative change threshold value (-th) (step S112).

[0053] It can be seen that the variation of the Ton value (Hold) shown in Fig. 5(b) has improved responsiveness compared to the Ton value (Hold) shown in Fig. 3(b). Note that the increase / decrease amplitude of the count value in the counter 24 may be set to 3 or more according to the difference amount.

[0054] The small output control shown in Fig. 2 and the small output control shown in Fig. 4 may be switched according to the dimming signal. In this case, the small output region where the small output control is executed is divided into a darker first region and a brighter second region. The first region executes the small output control shown in Fig. 2, and the second region executes the small output control shown in Fig. 4. Thereby, the "flickering" of the small output can be surely suppressed in the first region, and the responsiveness can be improved while suppressing it in the second region.

[0055] Also, in the counter 24, the responsiveness of the feedback control can be changed by changing the absolute values of the positive-side change threshold value (+th) and the negative-side change threshold value (-th) compared with the count value. In this case, +th1 and +th2 smaller than +th1 are set as the positive-side change threshold value, and -th1 and +th2 having an absolute value smaller than -th1 are set as the negative-side change threshold value (-th). Then, the first region may use the positive-side change threshold value (+th1) and the negative-side change threshold value (-th1), and the second region may use the positive-side change threshold value (+th2) and the negative-side change threshold value (-th2). Thereby, the "flickering" during small output can be surely suppressed in the first region, and the responsiveness can be improved while suppressing it in the second region.

[0056] Also, during external fluctuations such as changes in the dimming signal and fluctuations in the DC power supply Vin, it must be quickly changed to the set illuminance even in the small output region. Therefore, during a period when the difference amount between the Ton value (FB) and the Ton value (Hold) fluctuates greatly during external fluctuations, normal control may be executed even in the small output region.

[0057] FIG. 6 shows the transition of the difference between the Ton value (FB) and the Ton value (Hold) when the current set value (dimming signal) is changed. When external fluctuations start at time t1, the difference component fluctuates greatly. Even when the external fluctuations end at time t2, the large fluctuations in the difference component continue for a while. Therefore, when the small output determination unit 22 detects that external fluctuations have started at time t1 based on the current set value (dimming signal), it determines that the period from time t1 to the time t3 when the difference component stabilizes is not the small output region and performs normal control. The period from time t2 to time t3 may be a preset period, or the stabilization of the difference component may be detected by the feedback of the difference component from the comparison unit 23. Thereby, even in the small output region, the illuminance can be quickly changed to the set value.

[0058] The following summarizes the key points in the above embodiment. This embodiment is a control unit 20 (LED current control circuit) that generates a PWM signal for controlling the LED current supplied to the LED light source unit 3, and based on the current set value and the current detection value of the LED current, generates a Ton value (FB) (on-width specified value) for each cycle of the unit time. An on-width generation unit 21 (on-width generation unit), an on-width holding unit 25 (on-width holding unit) that holds the Ton value (FB) as the Ton value (Hold) (on-width holding value), and a PWM generation unit 26 that generates a PWM signal with an on-width specified by the Ton value (Hold) held by the on-width holding unit 25 for each cycle of the unit time. A comparison unit 23 that compares the Ton value (FB) generated by the on-width generation unit 21 with the previous Ton value (Hold) that specifies the on-width of the PWM signal, and counts (accumulates) the comparison result by the comparison unit 23. When the count value (accumulated value) of the comparison result reaches the change threshold (+th or -th), a counter 24 (arithmetic unit) that increases or decreases the Ton value (Hold) held by the on-width holding unit 25. The PWM generation unit 26 continuously generates a PWM signal with the previous Ton value (Hold) until the count value reaches the change threshold, and when the count value reaches the change threshold, generates a PWM signal with the Ton value (Hold) increased or decreased by the counter 24. Due to this feature, this embodiment can suppress the "flickering" during small output.

[0059] Furthermore, this embodiment includes a small-output determination unit 22 that determines whether it is a small output based on the current set value. When it is determined by the small-output determination unit 22 that it is not a small output, the PWM generation unit 26 generates a PWM signal with the Ton value (FB) generated by the on-width generation unit 21. Due to this feature, this embodiment can execute normal control with good responsiveness when it is not a small output.

[0060] Furthermore, in this embodiment, the counter 24 counts by weighting the count value with the difference between the Ton value (FB) and the Ton value (Hold). Due to this feature, this embodiment can improve responsiveness while suppressing "flickering".

[0061] Furthermore, in this embodiment, there is provided a small-output determination unit 22 that determines whether it is a small output based on the current set value and divides the small-output region determined to be a small output into a darker first region and a brighter second region for determination. When it is determined by the small-output determination unit 22 that it is the second region, the counter 24 counts by weighting the count value with the difference between the Ton value (FB) and the Ton value (Hold). Due to this feature, this embodiment can surely suppress "flickering" in the first region and can improve responsiveness while suppressing "flickering" in the second region.

[0062] Furthermore, in this embodiment, when the small-output determination unit 22 detects that an external fluctuation has started, it determines that it is not a small output until the difference between the Ton value (FB) and the Ton value (Hold) stabilizes. Due to this feature, even if there is an external fluctuation in the small-output region, the illuminance can be quickly changed to the set value.

[0063] Furthermore, this embodiment includes a small-output determination unit 22 that determines whether it is a small output based on the current set value and divides the small-output region determined to be a small output into a darker first region and a brighter second region for determination, and switches the change threshold between the first region and the second region. Due to this feature, in the first region, "flickering" can be reliably suppressed, and in the second region, responsiveness can be improved while suppressing "flickering".

[0064] As described above, the present invention has been described based on the embodiments. It is understood by those skilled in the art that these embodiments are illustrative, and various modifications are possible for combinations of their respective components and the like, and such modifications are also within the scope of the present invention.

Explanation of Reference Numerals

[0065] 1 LED lighting device 2 LED power supply device 3 LED light source unit 10 Power supply circuit 11 Current detection circuit 12 Drive circuit 20 Control unit 21 On-width generation unit 22 Small output determination unit 23 Comparison unit 24 Counter 25 On-width holding unit 26 PWM generation unit Q1 Switching element R1 Current detection resistor Vin DC power supply

Claims

1. An LED current control circuit that generates a PWM signal for controlling an LED current supplied to an LED light source unit, an on-width generation unit that generates an on-width specified value for each cycle of a unit time based on a current set value and a current detection value of the LED current; an on-width holding unit that holds the on-width specified value as an on-width holding value; a PWM generation unit that generates the PWM signal having an on-width specified by the on-width holding value held in the on-width holding unit for each cycle of the unit time; a comparison unit that compares the on-width specified value generated by the on-width generation unit with the previous on-width holding value that specified the on-width of the PWM signal; an arithmetic unit that accumulates the comparison result by the comparison unit and increases or decreases the on-width holding value held in the on-width holding unit when the cumulative value of the comparison result reaches a change threshold value, and the PWM generation unit continuously generates the PWM signal with the previous on-width holding value until the cumulative value of the comparison result reaches the change threshold value, and when the cumulative value of the comparison result reaches the change threshold value, generates the PWM signal with the on-width holding value increased or decreased by the arithmetic unit. An LED current control circuit characterized by that.

2. comprising a small-output determination unit that determines whether it is a small output based on the current set value, wherein when it is determined by the small-output determination unit that it is not the small output, the PWM generation unit generates the PWM signal with the on-width specified value generated by the on-width generation unit. The LED current control circuit according to claim 1.

3. The arithmetic unit of the LED current control circuit according to claim 1, wherein the arithmetic unit weights and accumulates the comparison result by a difference component between the on-width specified value and the on-width holding value.

4. comprising a small-output determination unit that determines whether it is a small output based on the current set value and divides a small-output region determined to be the small output into a darker first region and a brighter second region for determination, wherein when it is determined by the small-output determination unit that it is the second region, the arithmetic unit weights and accumulates by a difference component between the on-width specified value and the on-width holding value. The LED current control circuit according to claim 3.

5. The small-output determination unit of the LED current control circuit according to claim 4, wherein when detecting that an external fluctuation has started, the small-output determination unit determines that it is not the small output until the difference component between the on-width specified value and the on-width holding value stabilizes.

6. A small-output determination unit that determines whether it is a small output based on the current set value, and divides the small-output region determined to be the small output into a darker first region and a brighter second region for determination is provided. The LED current control circuit according to claim 1, wherein the change threshold is switched between the first region and the second region.

7. An LED light source unit, A power supply circuit that supplies an LED current generated by on / off control of a switching element to the LED light source unit, An LED lighting device including an LED current control circuit that generates a PWM signal for on / off control of the switching element, The LED current control circuit, An on-width generation unit that generates an on-width specified value for each cycle of a unit time based on the current set value and the current detection value of the LED current, An on-width holding unit that holds the on-width specified value as an on-width holding value, A PWM generation unit that generates the PWM signal having an on-width specified by the on-width holding value held in the on-width holding unit for each cycle of the unit time, A comparison unit that compares the on-width specified value generated by the on-width generation unit with the previous on-width holding value that specified the on-width of the PWM signal, An arithmetic unit that accumulates the comparison result by the comparison unit and increases or decreases the on-width holding value held in the on-width holding unit when the cumulative value of the comparison result reaches a change threshold is provided. The LED lighting device is characterized in that the PWM generation unit continuously generates the PWM signal with the previous on-width holding value until the cumulative value of the comparison result reaches the change threshold, and when the cumulative value of the comparison result reaches the change threshold, generates the PWM signal with the on-width holding value increased or decreased by the arithmetic unit.

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