JP2017045592A - LED dimming device and LED dimming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED dimming device capable of performing dimming at a low light level without requiring a high-speed switching circuit and without increasing the capacity of an inductor.SOLUTION: In an LED dimming method, a PWM signal with a predetermined duty in a predetermined cycle is generated in accordance with a dimming level, an input voltage is switched in a switching circuit that operates by the PWM signal, and the voltage obtained by the switching is rectified and smoothed to be output to an LED lighting system. In the LED dimming method, the cycle of the PWM signal is switched in accordance with the dimming level.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an LED dimming device and an LED dimming method that are improved with respect to dimming control when the dimming level is low.

  In recent years, efficient switching power supplies for LED lighting have been used. Among these, a digital control type switching power supply using a digital control circuit configured by using a microprocessor or a DSP is attracting attention. This digital control type switching power supply device can perform PWM control on the current and voltage output to the LED, and can generate a PWM signal having a duty corresponding to a dimming level set externally.

  In the digital control type switching power supply device, the current / voltage supplied to the LED lighting device is applied by rectifying and smoothing the voltage generated in the inductor when the switching element of the switching circuit is turned on / off. The switching element is controlled by a PWM signal. At this time, as shown in FIG. 5, the light amount of the LED lighting device can be increased or decreased by controlling the ON time of the PWM signal whose cycle is T1 according to the dimming level (for example, see Patent Document 1). ).

JP 2009-026544 A

  However, when the light amount set according to the dimming level is lowered, the on-time is shortened. If the on-time falls below the time corresponding to the limit response speed of the switching operation of the switching circuit, the switching circuit cannot operate corresponding to the on-time, and the target light quantity cannot be realized.

  As a solution to this, there are a method using a high-speed switching circuit capable of dealing with a short on-time, and a method of increasing the on-time with the same duty by increasing the period of the PWM signal.

  However, a method using a high-speed switching circuit causes an increase in cost. Also, the method of extending the PWM signal cycle to increase the on-time increases the maximum current that flows to the inductor when the dimming level is set high. Problems such as increased costs and increased equipment size occur.

  An object of the present invention is to provide an LED dimming device and an LED dimming method that do not require a high-speed switching circuit and enable dimming with a low amount of light without increasing the capacity of an inductor.

  To achieve the above object, an LED dimming device according to a first aspect of the present invention generates a PWM signal having a predetermined duty at a predetermined cycle by a digital control circuit in accordance with a dimming level, and operates with the PWM signal. A switching power supply that switches an input voltage by a switching circuit that performs rectification and smoothing and outputs the voltage obtained by the switching, an LED lighting device connected to an output side of the switching power supply, and the digital control circuit In the LED dimming device including the dimming setting device for inputting the dimming level, the digital control circuit switches the cycle of the PWM signal according to the dimming level input from the dimming setting device. It is characterized by that.

  According to a second aspect of the present invention, in the LED dimming device according to the first aspect, when the on-time of the PWM signal falls below a time corresponding to a limit response speed of the switching circuit, the digital control circuit The period of the signal is extended.

  According to a third aspect of the present invention, in the LED dimming device according to the first or second aspect, the switching power supply device includes a current detection unit that detects an output current flowing through the LED lighting device, and the digital control circuit includes: The PWM signal is generated such that the current value detected by the current detection means becomes a value corresponding to the dimming level.

  According to a fourth aspect of the present invention, there is provided an LED dimming method that generates a PWM signal having a predetermined duty at a predetermined cycle according to a dimming level, switches an input voltage by a switching circuit that operates based on the PWM signal, and performs the switching. In the LED dimming method of rectifying and smoothing the voltage obtained in step 1 and outputting the rectified voltage to the LED lighting device, the period of the PWM signal is switched according to the dimming level.

  According to a fifth aspect of the present invention, in the LED dimming method according to the fourth aspect, when the on-time of the PWM signal falls below a time corresponding to a limit response speed of the switching circuit, the period of the PWM signal It is characterized by extending.

  The invention according to claim 6 is the LED dimming method according to claim 4 or 5, wherein the PWM signal is generated such that the value of the current flowing through the LED lighting device is a value corresponding to the dimming level. It is characterized by that.

  According to the present invention, since the cycle of the PWM signal is switched according to the ON time of the PWM signal having a predetermined duty, the ON time set according to the dimming level is the limit response speed of the switching circuit. If the time corresponding to the above is exceeded, the required dimming can be achieved without increasing the capacity of the inductor and increasing the speed of the switching circuit by extending the PWM signal cycle. Dimming can be realized.

It is a circuit diagram which shows the structure of the LED light modulation apparatus of 1st Example of this invention. It is a flowchart of the light control by the digital control circuit of the LED light control apparatus of FIG. It is an operation | movement waveform diagram of the LED light control apparatus of FIG. It is a flowchart of the light control by the digital control circuit of the LED light control apparatus of the 2nd Example of this invention. It is an operation | movement waveform diagram of the conventional LED light control apparatus.

<First embodiment>
FIG. 1 shows the configuration of a digitally controlled LED dimmer according to a first embodiment of the present invention. Reference numeral 10 denotes a switching power supply device composed of a DC / DC converter, 20 denotes an LED lighting device in which a plurality of LEDs driven by voltage / current output from the switching power supply device 10 are connected in series, and 30 denotes a voltage applied to the switching power supply device 10. , 40 is a dimming setting device for setting the light quantity of the LED lighting device 20. Input terminals P11 and P12 of the switching power supply device 10 are connected to the input power supply 30, and output terminals P21 and P22 are connected to the LED lighting device 20.

  The switching power supply device 10 includes a switching circuit 11 including a transistor Q1 that switches an input voltage and a drive circuit 111 that PWM-drives the transistor Q1, a digital control circuit 12 that performs PWM control of the switching circuit 11, and an LED lighting device 20. The current detection circuit 13 detects a flowing output current and feeds back a detection signal to the digital control circuit 12, a boosting inductor L1, a rectifying diode D1, and a smoothing capacitor C1.

  The digital control circuit 12 inputs the output current signal detected by the current detection circuit 13, and has a specific period so that the current becomes a predetermined value corresponding to the dimming level set by the dimming setting device 40. Based on the duty of the PWM signal, the on-time and off-time of the transistor Q1 of the switching circuit 11 are calculated and output to the drive circuit 111.

  FIG. 2 shows a flowchart of one program of dimming control executed by the microprocessor or DSP CPU incorporated in the digital control circuit 12. In this embodiment, the period of the PWM signal is updated according to the ON time of the PWM signal.

  The output current signal detected by the current detection circuit 13 is converted into a digital signal by the A / D converter built in the digital control circuit 12 as a signal used for the update process (step S1), and the dimming setting is performed. The dimming level input from the device 40 is acquired (step S2).

  Then, a predetermined value that is a current value supplied to the LED lighting device 20 is calculated so that the output current matches the dimming level (step S3). Next, the period of the PWM signal output to the switching circuit 11 from the predetermined value is determined (step S4). The period at this time is a constant value.

  Next, the ON time and the OFF time of the switching element Ql are calculated from the determined period of the PWM signal (step S5).

  If the calculated on time is longer than the time corresponding to the limit response speed of the switching circuit 11 (step S6-YES), the digital value of the calculated on / off time is the digital control circuit 12. Is transmitted as a PWM signal to the drive circuit 111 of the switching circuit 11 via the built-in PWM module (step S7). Thereby, the output current is set to a predetermined value, and the light amount of the LED lighting device 20 is adjusted to the set dimming level.

  On the other hand, when the ON time calculated in step S5 is less than the time corresponding to the limit response speed of the switching circuit 11 (step S6-NO), the period of the PWM signal is increased and extended by a predetermined time from the current time, The on / off time in the new cycle is calculated (S5), and the determination is again made in step S6.

  As a result, if step S6 becomes YES, the PWM signal of the on / off time calculated in the cycle increased by the predetermined time is transmitted to the drive circuit 111 (step S7). However, when step S6 becomes NO, the PWM cycle is further increased by a fixed time, and the same processing is repeated until step S6 becomes YES.

  As described above, in the process shown in FIG. 2, the PWM period can be extended as much as necessary by setting the predetermined period of the PWM period in step S8 to a small time.

  When the PWM cycle is lengthened as described above, from the viewpoint of flicker prevention, the cycle length is set so that the on-time does not exceed the on-time at the time of setting a high amount of light (for example, a dimming level of about 50% or more). It is preferable to determine the thickness.

  FIG. 3 shows a waveform for changing the waveform and cycle of the PWM signal in accordance with the dimming level. In FIG. 3, in the state where the light is adjusted with the PWM signal having the period T1, the period is T2 (> T1) when the light control level is 0.1%, and 0.01%. Switching to T3 (> T2).

  Here, the dimming level at which the ON time corresponds to the limit response speed of the switching circuit 11 is set to 0.1%, and the PWM signal cycle is changed from T1 to T2 and further to T3 at a predetermined value below this level. By extending the time, the on-time is extended.

  As a result, the on-time of the transistor Q1 can be set so that it falls within the time range corresponding to the limit response speed of the switching circuit 11. Therefore, even if the dimming level is 0.1%, 0. Even if it is 01%, the LED lighting device 20 can be normally lit.

  In this way, by adjusting the period of the PWM signal and lengthening the ON time so that the ON time of the PWM signal does not fall below the time corresponding to the limit response speed of the switching circuit 11, Normal light control is possible even with a low light amount of 0.01% without requiring an increase in the capacity of the inductor L1.

<Second embodiment>
FIG. 4 shows a flowchart of the program of the second embodiment of the dimming control executed by the digital control circuit 12. This is an example in which the PWM cycle when the on-time is less than the time corresponding to the limit response speed of the switching circuit 11 is extended using a LUT (look-up table) in a normal PWM cycle. The same components as those described with reference to FIG.

  In the present embodiment, when the ON time is less than the time corresponding to the limit response speed of the switching circuit 11 in the determination in step S6 (step S6-NO), the difference between the ON time and the time corresponding to the limit response speed is calculated. Calculate (step S9), read a preset PWM cycle from the LUT according to the difference (step S10), calculate an on / off time according to the read cycle (step S11), and obtain the obtained PWM A signal is transmitted to the drive circuit 111 (step S7).

  In the processing method in the first embodiment, when the ON time is less than the time corresponding to the limit response speed of the switching circuit 11, the steps of S6 → S8 → S5 are repeated until the optimum PWM cycle is determined. In some cases, the optimum PWM cycle can be determined at one time according to the processing method of the second embodiment.

DESCRIPTION OF SYMBOLS 10: Switching power supply device, 11: Switching circuit, 111: Drive circuit, 12: Digital control circuit, 13: Current detection circuit, P11, P12: Input terminal, P21, P22: Output terminal 20: LED lighting device 30: Input power supply 40: Dimming setting device

Claims (6)

A digital control circuit generates a PWM signal with a predetermined duty in a predetermined cycle according to the dimming level, switches an input voltage with a switching circuit that operates with the PWM signal, and rectifies and smoothes the voltage obtained by the switching An LED dimming device comprising: a switching power supply device that outputs power; an LED lighting device connected to the output side of the switching power supply device; and a dimming setting device that inputs the dimming level to the digital control circuit;
The LED control device, wherein the digital control circuit switches the period of the PWM signal in accordance with the light control level input from the light control setting device. The LED light control device according to claim 1,
The LED dimming device, wherein the digital control circuit extends the period of the PWM signal when an ON time of the PWM signal falls below a time corresponding to a limit response speed of the switching circuit. The LED light control device according to claim 1 or 2,
The switching power supply device includes current detection means for detecting an output current flowing through the LED lighting device, and the digital control circuit has a current value detected by the current detection means corresponding to the dimming level. An LED dimmer that generates the PWM signal. An LED lighting device that generates a PWM signal having a predetermined duty in a predetermined cycle according to a dimming level, switches an input voltage by a switching circuit that operates based on the PWM signal, and rectifies and smoothes the voltage obtained by the switching. In LED dimming method to output to
An LED dimming method, wherein the period of the PWM signal is switched according to the dimming level. The LED dimming method according to claim 4,
The LED dimming method, wherein the period of the PWM signal is extended when the ON time of the PWM signal falls below a time corresponding to a limit response speed of the switching circuit. In the LED light control method according to claim 4 or 5,
The LED dimming method, wherein the PWM signal is generated such that a value of a current flowing through the LED lighting device becomes a value corresponding to the dimming level.

Images