TWI437914B - Led control circuit and method - Google Patents

Description

LED control circuit and method

The present invention relates to a light emitting diode (LED), and more particularly to an insect resistant LED control circuit and method.

Insects such as flies and mosquitoes are extremely harmful to human quality of life, but the most direct insecticides are harmful to the human body and the environment. Therefore, fly paper, mosquito traps, etc. are all kinds of insects for odor, humidity, light, etc. Characteristic de-worm products are constantly being developed. Light has a great influence on the ecology of insects. For example, fireflies rely on the flash frequency of their abdominal fluorescence in the dark as a tool to attract heterosexual mating and communication. Many insects can perceive the flash frequency much higher than the human eye, and the swing pattern in some flash frequencies can make the insects anxious and uncomfortable.

LEDs are devices that illuminate current through a semiconductor p-n junction, typically with a double heterojunction and a quantum well structure. In 1962, General Electric (GE) commercialized red LEDs for the first time using GaAsP. The initial red LED had a luminous flux of 0.11 m/W, which is about 1/150 of that of ordinary light, and its luminous efficiency is about every 10 years. Increase by an order of magnitude. Recently, with the practical application of blue and green LEDs, white LEDs with high power have also appeared on the market. LEDs have gradually shifted from decorative applications to applications, and are moving toward the goal of replacing traditional light bulbs. In addition to environmentally friendly, power-saving features, LEDs can be controlled to flicker at very high frequencies, with switching frequencies up to over MHz. In the prior art, there have been many methods of controlling the brightness of an LED light source using PWM.

One of the objects of the present invention is to provide an LED control circuit and method for generating an LED driving signal for driving an insect resistant LED lamp.

According to the present invention, an LED control circuit includes a pulse edge generator generating a clock according to a frequency control signal, and a duty cycle ratio controller generating an LED driving signal according to the brightness control signal and the clock, the frequency of which is determined by the frequency of the clock. The duty cycle is determined by the brightness control signal.

According to the present invention, a method for generating an LED driving signal includes generating a clock according to a frequency control signal, and generating an LED driving signal according to the brightness control signal and the clock, the frequency of which is determined by the frequency of the clock, and the duty cycle is determined by the brightness Control signal decision.

Referring to FIG. 1, at a fixed duty cycle, the human eye can distinguish the flash frequency f _L or less, f _L vary, generally in the vicinity of about 60Hz. When the flash frequency of the light source exceeds the human eye's perception range, that is, above f _L , the human eye automatically averages the brightness of the flash as a stable light source, and the brightness of the light source is proportional to the duty cycle and is independent of the flash frequency. . However, the upper limit f _H of the flash frequency that the insect can distinguish is higher than that of the human, and therefore the LED control circuit and method of the present invention can be used for the insect-resistant LED lamp for the foregoing reasons. The LED control circuit and method of the present invention maintains the range of the flash frequency swing beyond the sensing range of the human eye during the frequency swing, and maintains the fixed brightness pulse width modulation (PWM) duty cycle so that the average brightness is almost the same, Such illumination is equivalent to a fixed-light source for the human eye, so that the effect of eviction, confusion or trapping of insects can be achieved without affecting humans. Preferably, the brightness PWM duty cycle can be set or planned, but remains fixed until the next adjustment.

2 is an embodiment of the present invention, wherein the LED control circuit 38 has two control signal inputs 40 and 42 respectively receiving the frequency control signal VF and the brightness control signal VD provided by the microcontroller 36, and accordingly generating an LED driving signal I _LED. . The frequency control signal VF is used to control the frequency f _{PWM of the} LED driving signal I _LED , and the brightness control signal VD is used to control the duty cycle D of the LED driving signal I _LED . In the LED control circuit 38, an edge pulse generator 44 is connected to a control signal input terminal 40 and the reception frequency control signal VF is generated according to the CLK clock, the frequency f _CLK by the frequency number VF decision control, duty ratio controller 46 is connected The control signal input terminal 42 and the pulse edge generator 44 generate the LED driving signal I _LED according to the clock CLK and the brightness control signal VD. LED drive signal I _LED frequency f _PWM is determined by the frequency f _{CLK of the} clock CLK, so the frequency f _{PWM of the} LED drive signal I _LED will be determined by the frequency control signal VF, and the duty cycle D of the LED drive signal I _LED is controlled by the brightness Signal VD decided. I _LED LED drive signal operating time (on-time) and the non-working time (off-time) are t1 and t2, thus obtained signal I _LED LED driving frequency f _PWM and the duty cycle D is

_{f PWM = 1 / (t1 +} t2) = f (VF),

as well as

D = t1/(t1 + t2) = f (VD).

Therefore, the frequency control signal VF only controls the frequency f _{PWM of the} LED driving signal I _LED , and the brightness control signal VD only controls the duty cycle D of the LED driving signal I _LED .

The LED drive signal I _LED can be used to drive the LED light. Since the frequency f _PWM and the duty cycle D of the LED driving signal I _LED are controlled only by the frequency control signal VF and the brightness control signal VD, respectively, the frequency control signal VF and the brightness control signal VD respectively determine the blinking frequency of the driven LED lamp. And brightness, this control structure is to facilitate the user to adjust the brightness of the LED light, does not change the flashing characteristics of the LED light, or does not change the brightness of the LED light when adjusting the blinking frequency of the LED light. For example, in a particular mode, setting the VD to be fixed and the VF to change over time, the LED lamp will produce a flash characteristic as shown in FIG. The duty cycle D of the LED drive current I _LED can be set or planned by the brightness control signal VD, but remains fixed until it is adjusted, in other words, the brightness of the LED lamp will remain fixed unless VD changes. The frequency control signal VF allows the LED lamp to emit a flash of a dynamic sample at a certain frequency, for example, a frequency change between f _L and f _H .

As shown in FIG. 3, the frequency control signal VF may include a PWM signal, an analog level signal, or an encoded signal. If the frequency control signal VF includes a PWM signal, the pulse edge generator 44 includes a Low-Pass Filter (LPF) 48 to filter the PWM signal to generate an analog level signal V1, and the voltage controlled oscillator (Voltage Controlled Oscillator) The VCO 50 generates an oscillation signal OSC according to the analog level signal V1, and the edge detector 52 detects the pulse edge of the oscillation signal OSC to generate the clock CLK. If the frequency control signal VF includes an analog level signal, it can be directly sent to the VCO 50, and the edge detector 52 thus generates the clock CLK. If the frequency control signal includes an encoded signal, the pulse edge generator 44 includes a digital-to-analog converter (DAC) 58 to convert the encoded signal to generate an analog level signal V1 for the VCO 50 and the edge detector. 52 generates the clock CLK. In the edge detector 52, the short delay device 54 temporarily delays the oscillation signal OSC to generate a delayed oscillation signal OSCD, and the digital logic gate 56 generates the clock CLK based on the oscillation signal OSC and its delayed signal OSCD.

In another embodiment, as shown in FIG. 4, if the frequency control signal VF includes a PWM signal, the pulse edge generator 44 may only include the edge detector 52 to detect the pulse edge of the PWM signal to generate the clock CLK.

As shown in FIG. 5, the brightness control signal VD may include a PWM signal, an analog level signal, or an encoded signal. If the brightness control signal VD includes a PWM signal, the duty cycle ratio controller 46 includes the LPF 60 to filter the PWM signal to generate an analog level signal Va, and the LPF 62 filters the LED drive signal I _{LED to} generate an analog level signal Vd, and the voltage control current source ( Voltage Controlled Current Source; VCCS) 64 generates current I according to the difference Va-Vd. The transistor M1 has an input terminal receiving the first reference voltage VREF1, a control terminal receiving clock CLK, and an output terminal preset node voltage VC, and the capacitor C is connected to the battery. The output of crystal M1 and VCCS 64, and PWM generator 66 generate LED drive signal I _LED based on voltage VC. In one embodiment, the PWM generator 66 includes a comparator 68 comparing the voltage VC and the reference voltage VREF2 to generate an LED drive signal I _LED . When the clock CLK so that when transistor M1 is turned on (turn on), the voltage VC equals the reference voltage VREF1, thereby triggering the LED driving signal of the operating time t1 I _LED. When the pulse CLK causes the transistor M1 to turn off, the capacitor C is discharged by the discharge current I of the VCCS 64, so the voltage VC drops from the reference voltage VREF1, and the LED drive signal when the voltage VC falls below the reference voltage VREF2. The working time t1 of the I _LED ends. The discharge current I determines the falling slope of the voltage VC, and thus determines the width of the operating time t1. The discharge current I is a function of the difference Va-Vd and has a negative rate of change with respect to the difference Va-Vd. Preferably, the discharge current I has a proportional relationship with the difference Va-Vd. In other embodiments, the PWM generator 66 may include a hysteresis comparator 70 (which may have a single input or multiple inputs) or an inverter string 72 that generates an LED drive signal I _LED based on the voltage VC. If the brightness control signal VD includes an analog level signal, it can be provided directly to the VCCS 64 as the signal Va. If the brightness control signal VD includes an encoded signal, it is converted to a signal Va using the DAC 74.

In another embodiment, as shown in FIG. 6, if the brightness control signal VD includes a PWM signal, the duty cycle ratio controller 46 includes the comparator 76 to compare the PWM signal and the LED driving signal I _{LED to} generate a comparison signal Sc, and the LPF. The filter comparison signal Sc generates an analog level signal Vx, and the analog level signal Vx controls the current I provided by the VCCS 64. The current I and the analog level signal Vx have a positive rate of change.

As shown in FIG. 7, another circuit can be used to control the voltage VC, in which the transistor M1 is connected between the capacitor C and the ground, and the VCCS 64 provides the charging current I. When the pulse CLK turns on the transistor M1, the capacitor C is grounded to reset the voltage VC, thereby triggering the LED driving signal I _LED . When the pulse CLK causes the transistor M1 to be non-conducting, the capacitor C is charged by the VCCS 64, so the voltage VC rises. When the voltage VC rises above the reference voltage VREF2, the operating time t1 of the LED driving signal I _LED ends. The charging current I determines the duty cycle D of the LED driving signal I _LED .

There are many equivalent circuits that can replace the circuits in the above embodiments. For example, the pulse edge detector can be implemented with a high-pass filter and can be combined with other circuits. The hysteresis comparator can also use a Smith-trigger circuit. )achieve. Further, the foregoing embodiments and other embodiments may be constituted by a separate element, an integrated circuit, a combination of a separate element and an integrated circuit, or a single-wafer integrated circuit.

The above description of the preferred embodiments of the present invention is intended to be illustrative, and is not intended to limit the scope of the invention. It is possible to modify or change the teachings of the present invention, and the embodiments are described and illustrated in the practical application of the present invention in various embodiments. The technical idea of the present invention is intended to be determined by the following claims and their equals.

36. . . Microcontroller

38. . . LED control circuit

40. . . Control signal input

42. . . Control signal input

44. . . Pulse edge generator

46. . . Accountability cycle ratio controller

48. . . Low pass filter

50. . . Voltage controlled oscillator

52. . . Edge detector

54. . . Ephemeral delay device

56. . . Digital logic gate

58. . . Digital analog converter

60. . . Low pass filter

62. . . Low pass filter

64. . . Voltage controlled current source

66. . . PWM generator

68. . . Comparators

70. . . Hysteresis comparator

72. . . Inverter string

74. . . Digital analog converter

76. . . Comparators

78. . . Low pass filter

Figure 1 is a schematic diagram showing the relationship between the flash frequency range of the human eye and the insect perception and the flash mode to be implemented;

Figure 2 is an embodiment of the invention;

Figure 3 provides three embodiments of the pulse edge generator of Figure 2;

Figure 4 is a fourth embodiment of the pulse edge generator of Figure 2;

Figure 5 provides three embodiments of the duty cycle ratio controller of Figure 2;

Figure 6 is a fourth embodiment of the duty cycle ratio controller of Figure 2;

Figure 7 is a fifth embodiment of the duty cycle ratio controller of Figure 2.

36. . . Microcontroller

38. . . LED control circuit

40. . . Control signal input

42. . . Control signal input

44. . . Pulse edge generator

46. . . Accountability cycle ratio controller

Claims (48)

An LED control circuit includes: a first control signal input end receiving a frequency control signal; a second control signal input end receiving a brightness control signal; a pulse edge generator connected to the first control signal input end for generating a clock, The frequency of the pulse is determined by the frequency control signal; and the duty cycle ratio controller is connected to the second control signal input terminal and the pulse edge generator for generating an LED driving signal, and the frequency of the LED driving signal is determined by the frequency of the clock It is decided that the duty cycle of the LED driving signal is determined by the brightness control signal. The LED control circuit of claim 1, wherein the frequency control signal comprises a pulse width modulation signal. The LED control circuit of claim 2, wherein the pulse edge generator comprises: a low pass filter connected to the first control signal input terminal, filtering the pulse width modulation signal to generate an analog level signal; and the voltage controlled oscillator connection The low pass filter generates an oscillation signal according to the analog level signal; and an edge detector is connected to the voltage controlled oscillator to detect a pulse edge of the oscillation signal to generate the clock. The LED control circuit of claim 3, wherein the edge detector comprises: a short delay device connected to the voltage controlled oscillator, and a short delay of the oscillation signal to generate a delayed oscillation signal; The digital logic gate is connected to the voltage controlled oscillator and the short delay device, and the clock is generated according to the oscillation signal and the delayed oscillation signal. The LED control circuit of claim 2, wherein the pulse edge generator comprises an edge detector connected to the first control signal input for detecting a pulse edge of the pulse width modulation signal to generate the clock. The LED control circuit of claim 5, wherein the edge detector comprises: a short delay device connected to the first control signal input terminal, a short delay delaying the pulse width modulation signal to generate a delayed pulse width modulation signal; and a digital logic gate The short delay device is connected to generate the clock according to the pulse width modulation signal and the delayed pulse width modulation signal. The LED control circuit of claim 1, wherein the frequency control signal comprises an analog level signal. The LED control circuit of claim 7, wherein the pulse edge generator comprises: a voltage controlled oscillator connected to the first control signal input end, generating an oscillation signal according to the analog level signal; and an edge detector connecting the voltage controlled oscillation The detector detects the pulse edge of the oscillation signal to generate the clock. The LED control circuit of claim 8, wherein the edge detector comprises: a short delay device connected to the voltage controlled oscillator, a short delay of the oscillation signal to generate a delayed oscillation signal; and a digital logic gate connected to the voltage controlled oscillator and the Short delay The clock is generated according to the oscillation signal and the delayed oscillation signal. The LED control circuit of claim 1, wherein the frequency control signal comprises an encoded signal. The LED control circuit of claim 10, wherein the pulse edge generator comprises: a digital analog converter connected to the first control signal input end, the encoded signal is converted into an analog level signal; and the voltage controlled oscillator is connected to the digital analog conversion And generating an oscillation signal according to the analog level signal; and an edge detector connecting the voltage controlled oscillator to detect a pulse edge of the oscillation signal to generate the clock. The LED control circuit of claim 11, wherein the edge detector comprises: a short delay device connected to the voltage controlled oscillator for temporarily delaying the oscillation signal to generate a delayed oscillation signal; and a digital logic gate connected to the voltage controlled oscillator And the ephemeral delay device generates the clock according to the oscillating signal and the delayed oscillating signal. The LED control circuit of claim 1, wherein the frequency of the LED driving signal is swung above 60 Hz. The LED control circuit of claim 1, wherein the brightness control signal comprises a pulse width modulation signal. The LED control circuit of claim 14, wherein the duty cycle ratio controller comprises: the transistor has an input terminal to receive the first reference voltage, and the control terminal receives The clock from the pulse edge generator and the output terminal provide a voltage; the capacitor is connected to the output end of the transistor; the first low pass filter is connected to the second control signal input terminal, and the pulse width modulation signal is filtered. a type of comparison level signal; a second low pass filter is connected to the output of the duty cycle ratio controller, and the LED driving signal is filtered to generate a second analog level signal; the voltage controlled current source is connected to the output end of the transistor, according to the a difference between the first and second analog level signals provides a current, thereby causing the capacitor to be charged or discharged when the transistor is non-conducting; and a pulse width modulation generator is coupled to the output of the transistor, The voltage at the output of the transistor produces the LED drive signal. The LED control circuit of claim 15, wherein the pulse width modulation generator comprises a comparator connected to the output end of the transistor, and comparing the output voltage of the transistor with the second reference voltage to generate the LED driving signal. The LED control circuit of claim 15, wherein the pulse width modulation generator comprises a hysteresis comparator connected to the output end of the transistor, and the LED driving signal is generated according to the output voltage of the transistor. The LED control circuit of claim 15, wherein the pulse width modulation generator comprises an inverter string connected to the output end of the transistor, and the LED driving signal is generated according to the output voltage of the transistor. The LED control circuit of claim 14, wherein the duty cycle ratio controller comprises: The transistor has an input end receiving the first reference voltage, the control terminal accepting the clock from the pulse edge generator, and the output terminal providing a voltage; the capacitor is connected to the output end of the transistor; and the comparator is connected to the second control signal input end And the duty cycle compares the pulse width modulation signal and the LED driving signal to generate a comparison signal; the low pass filter is connected to the comparator, and the comparison signal is filtered to generate an analog level signal; a current source is coupled to the output of the transistor, the current is supplied according to the analog level signal, thereby causing the capacitor to be charged or discharged when the transistor is not conducting; and a pulse width modulation generator is coupled to the output of the transistor, The LED drive signal is generated based on its voltage. The LED control circuit of claim 19, wherein the pulse width modulation generator comprises a second comparator connected to the output end of the transistor, comparing the output voltage of the transistor and the second reference voltage to generate the LED driving signal . The LED control circuit of claim 19, wherein the pulse width modulation generator comprises a hysteresis comparator connected to the output end of the transistor, and the LED driving signal is generated according to the output voltage of the transistor. The LED control circuit of claim 19, wherein the pulse width modulation generator comprises an inverter string connected to the output end of the transistor, and the LED driving signal is generated according to the output voltage of the transistor. The LED control circuit of claim 1, wherein the brightness control signal comprises an analog level signal. The LED control circuit of claim 23, wherein the duty cycle ratio controller comprises: the transistor having an input receiving the first reference voltage, the control receiving the clock from the pulse edge generator, and the output providing a voltage; the capacitor Connecting the output end of the transistor; a low-pass filter that filters the LED driving signal to generate a second analog level signal; and a voltage-controlled current source connected to the output end of the transistor, according to the first and second analog level signals The difference between the currents provides a current, thereby causing the capacitor to be charged or discharged when the transistor is non-conducting; and a pulse width modulation generator is coupled to the output of the transistor to generate the LED drive based on the output voltage of the transistor Signal. The LED control circuit of claim 24, wherein the pulse width modulation generator comprises a comparator connected to the output end of the transistor, and comparing the output voltage of the transistor with the second reference voltage to generate the LED driving signal. The LED control circuit of claim 24, wherein the pulse width modulation generator comprises a hysteresis comparator connected to the output end of the transistor, and the LED driving signal is generated according to the output voltage of the transistor. The LED control circuit of claim 24, wherein the pulse width modulation generator comprises an inverter string connected to an output end of the transistor, according to the The output voltage of the crystal produces the LED drive signal. The LED control circuit of claim 1, wherein the brightness control signal comprises an encoded signal. The LED control circuit of claim 28, wherein the duty cycle ratio controller comprises: the transistor having an input receiving the first reference voltage, the control receiving the clock from the pulse edge generator, and the output providing a voltage; the capacitor Connecting the output end of the transistor; the digital analog converter is connected to the second control signal input end, and converting the coded signal into a first analog level signal; the low pass filter is connected to the output of the duty ratio ratio controller, Filtering the LED driving signal to generate a second analog level signal; the voltage control current source is connected to the output end of the transistor, and supplying a current according to a difference between the first and second analog level signals, thereby causing the capacitor to be in the The transistor is charged or discharged when not conducting; and the pulse width modulation generator is coupled to the output of the transistor to generate the LED driving signal according to the voltage thereof. The LED control circuit of claim 29, wherein the pulse width modulation generator comprises a comparator connected to the output end of the transistor, and comparing the output voltage of the transistor with the second reference voltage to generate the LED driving signal. The LED control circuit of claim 29, wherein the pulse width modulation generator comprises a hysteresis comparator connected to the output end of the transistor, according to the The output voltage of the transistor generates the LED drive signal. The LED control circuit of claim 29, wherein the pulse width modulation generator comprises an inverter string connected to the output end of the transistor, and the LED driving signal is generated according to the output voltage of the transistor. A method for generating an LED driving signal, comprising: (a) receiving a frequency control signal and a brightness control signal; (b) generating a clock whose frequency is determined by the frequency control signal; and (c) controlling the clock according to the clock and the brightness The signal generates the LED driving signal, the frequency of which is determined by the frequency of the clock, and the duty cycle is determined by the brightness control signal. The method of claim 33, wherein the frequency control signal controls the frequency of the LED driving signal to swing above 60 Hz. The method of claim 33, wherein the frequency control signal comprises a pulse width modulation signal. The method of claim 35, wherein the step b comprises: filtering the pulse width modulation signal to generate an analog level signal; generating an oscillation signal according to the analog level signal; and detecting a pulse edge of the oscillation signal to generate the time pulse. The method of claim 35, wherein the step b comprises detecting a pulse edge of the pulse width modulation signal to generate the clock. The method of claim 33, wherein the frequency control signal comprises an analog level signal. The method of claim 38, wherein the step b comprises: generating an oscillation signal according to the analog level signal; The pulse is detected by detecting the edge of the pulse of the oscillation signal. The method of claim 33, wherein the frequency control signal comprises an encoded signal. The method of claim 40, wherein the step b comprises: converting the encoded signal into an analog level signal; generating an oscillation signal according to the analog level signal; and detecting a pulse edge of the oscillation signal to generate the clock. The method of claim 33, wherein the brightness control signal comprises a pulse width modulation signal. The method of claim 42, wherein the step c includes: filtering the pulse width modulation signal to generate a first analog level signal; filtering the LED driving signal to generate a second analog level signal; and according to the first and the The difference between the two analog level signals determines the duty cycle of the LED drive signal. The method of claim 42, wherein the step c includes: comparing the pulse width modulation signal and the LED driving signal to generate a comparison signal; filtering the comparison signal to generate an analog level signal; and determining the analog signal according to the analog level signal The duty cycle of the LED drive signal. The method of claim 33, wherein the brightness control signal comprises an analog level signal. The method of claim 45, wherein the step c comprises: Filtering the LED driving signal to generate a second analog level signal; and determining a duty cycle of the LED driving signal according to a difference between the first and second analog level signals. The method of claim 33, wherein the brightness control signal comprises an encoded signal. The method of claim 47, wherein the step c comprises: converting the encoded signal into a first analog level signal; filtering the LED driving signal to generate a second analog level signal; and according to the first and second analog bits The difference between the quasi-signals determines the duty cycle of the LED drive signal.