TW201408129A - LED control circuit and lighting device thereof - Google Patents

Abstract

A LED control circuit and a lighting device thereof are disclosed. The LED control circuit includes a rectifier circuit, a first filter circuit and an adjustment circuit. The rectifier circuit rectifies a modulated power signal received from a dimming circuit to a DC power signal. The first filter circuit filters the DC power signal to a filtered power signal. The adjustment circuit generates an adjustment signal to a LED string as a forward voltage. When the filtered power signal is less than a sum of a first threshold voltage and the adjustment signal and larger than a sum of a second threshold voltage and the adjustment signal, the adjustment circuit generates the adjustment signal to allow the forward voltage to increase or decrease synchronously with the modulated power signal and further allows a luminance of the LED string to brighten or darken synchronously.

Description

Light-emitting diode control circuit and light-emitting device thereof

The present invention relates to a light-emitting diode control circuit and a light-emitting device thereof, and more particularly to a light-emitting diode control circuit and a light-emitting device thereof for adjusting the brightness of a light-emitting diode by adjusting a forward voltage of the light-emitting diode.

Compared with conventional incandescent lamps, fluorescent lamps or other illumination sources, Light Emitting Diode (LED) has become a variety of lighting due to its low temperature luminous efficiency, pollution-free and long life. The preferred choice for device light source selection. Also, due to the popularity of the use of light-emitting diodes, many adjustment control methods for the brightness of the light-emitting diode have been developed in the prior art.

In the prior art, the phase cut-off dimming module is usually used with a complicated control circuit, and the brightness of the light-emitting diode is made by the user's visual persistence by blinking the light-emitting diode. Attenuate, thereby adjusting the brightness of the light-emitting diode. However, this dimming method may still cause some users to see that the LEDs are constantly flickering and feel uncomfortable. Moreover, the control circuit in the prior art is complicated, which increases the cost in manufacturing. Moreover, the control circuit in the prior art may also cause electromagnetic interference problems, which require additional cost to handle the electromagnetic interference during manufacturing.

Therefore, there is a need to invent a new light-emitting diode control circuit and a light-emitting device having the light-emitting diode control circuit to solve the problems of the prior art.

The main object of the present invention is to provide a light emitting diode control circuit having the effect of changing the brightness of the light emitting diode by adjusting the forward voltage of the light emitting diode.

Another main object of the present invention is to provide a light-emitting device having the above-described light-emitting diode control circuit.

In order to achieve the above object, the LED control circuit of the present invention is disposed between the dimming circuit and the LED string, wherein the LED string comprises at least one LED, when the voltage is applied to the LED When the forward voltage of the polar body string is greater than the first threshold voltage, the light emitting diode string reaches the maximum light amount; when the forward voltage is less than the first threshold voltage value and greater than the second threshold voltage value, the light emitting diode string The amount of luminescence will be brightened or darkened synchronously with the increase and decrease of the forward voltage; when the forward voltage is less than the second threshold voltage, the illuminating diode string stops emitting light. The LED control circuit includes a rectifier circuit, a first filter circuit, and an adjustment circuit. The rectifier circuit is electrically connected to the dimming circuit, and receives the modulated power signal from the dimming circuit and converts it into a DC power signal, and the DC power signal is synchronously increased or decreased with the modulated power signal. The first filter circuit is electrically connected to the rectifier circuit for converting the DC power signal into a filtered power signal, and the filtered power signal is synchronously increased or decreased with the DC power signal. The adjusting circuit is electrically connected between the first filter circuit and the LED string, the adjusting circuit has a minimum input voltage value, and the adjusting circuit outputs the adjusting signal to the LED string as the forward voltage of the LED string. Wherein, when the adjustment voltage across the adjustment circuit is greater than the minimum input voltage value, the adjustment circuit maintains a substantially stable output adjustment signal. When the filtered power signal is greater than the sum of the first threshold voltage and the minimum input voltage, the adjustment circuit maintains a substantially stable output adjustment signal, and the forward voltage is greater than the first threshold voltage, so that the LED string is maintained. The maximum amount of luminescence. When the filtered power signal is less than the sum of the first threshold voltage and the adjusted voltage, but greater than the sum of the second threshold voltage and the adjusted voltage, the adjusting circuit outputs an adjustment signal such that the forward voltage is greater than the second threshold voltage but less than the first A threshold voltage value, and the forward voltage will be synchronously increased or decreased with the modulation power signal, so that the amount of illumination of the LED string can be simultaneously brightened or darkened. When the filtered power signal is less than the sum of the second threshold voltage and the adjusted voltage, the adjusting circuit cuts off the output adjusting signal so that the forward voltage is less than the second threshold voltage, so that the LED string stops emitting light.

The light-emitting device of the present invention comprises a power supply terminal, a dimming circuit, a light-emitting diode string and a light-emitting diode control circuit. The power supply terminal is used to input a power signal. The dimming circuit is configured to receive a power signal for conversion to a modulated power signal. The light emitting diode string includes at least one light emitting diode, wherein when the forward voltage across the light emitting diode string is greater than the first threshold voltage, the light emitting diode string reaches the maximum light amount; when the forward voltage When the value is smaller than the first threshold voltage and greater than the second threshold voltage, the amount of illumination of the LED string is synchronously brightened or darkened as the forward voltage increases or decreases; when the forward voltage is less than the second threshold voltage At the time, the light-emitting diode string stops emitting light. The LED control circuit is electrically connected between the dimming circuit and the LED string. The LED control circuit includes a rectifier circuit, a first filter circuit, and an adjustment circuit. The rectifier circuit is electrically connected to the dimming circuit, and receives the modulated power signal from the dimming circuit and converts it into a DC power signal, and the DC power signal is synchronously increased or decreased with the modulated power signal. The first filter circuit is electrically connected The rectifier circuit is configured to convert the DC power signal into a filtered power signal, and the filtered power signal is synchronously increased or decreased with the DC power signal. The adjustment circuit is electrically connected between the first filter circuit and the LED string, the adjustment circuit has a minimum input voltage value, and the adjustment circuit outputs an adjustment signal to the LED string as a forward voltage of the LED string. Wherein, when the adjustment voltage across the adjustment circuit is greater than the minimum input voltage value, the adjustment circuit maintains a substantially stable output adjustment signal. When the filtered power signal is greater than the sum of the first threshold voltage and the minimum input voltage, the adjustment circuit maintains a substantially stable output adjustment signal, and the forward voltage is greater than the first threshold voltage, so that the LED string is maintained. The maximum amount of luminescence. When the filtered power signal is less than the sum of the first threshold voltage and the adjusted voltage, but greater than the sum of the second threshold voltage and the adjusted voltage, the adjusting circuit outputs an adjustment signal such that the forward voltage is greater than the second threshold voltage but less than the first A threshold voltage value, and the forward voltage will be synchronously increased or decreased with the modulation power signal, so that the amount of illumination of the LED string can be simultaneously brightened or darkened. When the filtered power signal is less than the sum of the second threshold voltage and the adjusted voltage, the adjusting circuit cuts off the output adjusting signal so that the forward voltage is less than the second threshold voltage, so that the LED string stops emitting light.

The above and other objects, features and advantages of the present invention will become more <

Please refer to FIG. 1 for a schematic diagram of the structure of the illuminating device of the present invention.

The light-emitting device 1 of the present invention can be a bulb, a lamp, or any other A device having a light-emitting diode is provided, and the present invention is not limited to this. The light-emitting device 1 includes a power supply terminal 10, a dimming circuit 20, a light-emitting diode string 30, and a light-emitting diode control circuit 40. The power supply terminal 10 can be connected to the device for supplying the mains, or can be connected to the battery device for inputting the power signal to the dimming circuit 20, so that the dimming circuit 20 can generate the modulated power signal. In the embodiment of the present invention, the power signal is taken as an example, but the power supply terminal 10 of the present invention is not limited to input only the AC signal. The dimming circuit 20 can be a Triode for Alternating Current (TRIAC) module for the user to control to generate different modulated power signals according to the brightness to be adjusted. Since the mode of operation of the phase-cutting dimming module has been familiar to those of ordinary skill in the art, it will not be repeated here.

The LED string 30 can include at least one light emitting diode. As shown in FIG. 3, the LED string 30 can be connected in series with the LEDs 301, 302 to 30n, but the plurality of LEDs of the present invention. The body can also be connected in parallel or in series and parallel. The LED string 30 has its first threshold voltage value and a second threshold voltage value. When the forward voltage input to the LED string 30 is greater than the first threshold voltage value, the LED string 30 can reach the maximum. The amount of luminescence. When the forward voltage input to the LED string 30 is less than the second threshold voltage, the LED string 30 stops emitting light. When the forward voltage input to the LED string 30 is between the first threshold voltage and the second threshold voltage, the LED string 30 will be simultaneously brightened or decreased as the forward voltage increases or decreases. darken.

Fig. 2 is a graph showing the characteristics of the forward voltage and current of each of the light-emitting diodes 301, 302, ..., 30n in the light-emitting diode string 30 of the present invention. According to the characteristics of the light-emitting diode, each of the light-emitting diodes 301, 302 to 30n has its corresponding typical operating voltage VT and low threshold voltage VL. The typical operating voltage VT, that is, V _1T , V _2T ..., V _{NT of} each of the LEDs 301, 302 to 30n, is a typical forward operating bias recommended for the LED specifications (Typical). The low threshold voltage VL, that is, V _1L , V _2L ..., V _{NL of} each of the light-emitting diodes 301, 302 to 30n, is the minimum forward bias required for the light-emitting diode to conduct light. Pressure.

When each of the light-emitting diodes 301, 302 or 30n in the light-emitting diode string 30 receives a forward voltage that is greater than a respective typical operating voltage VT, the light-emitting diodes 301, 302 or Each of 30n will emit maximum brightness, and the LED string 30 will also emit maximum brightness.

When each of the light-emitting diodes 301, 302 or 30n in the light-emitting diode string 30 receives a forward voltage which is less than a respective low threshold voltage VL, respectively, the light-emitting diodes 301, 302 or The 30n system does not emit light, that is, the light-emitting diode string 30 does not emit light at this time.

Therefore, when the LEDs 301, 302 or 30n are connected in series with each other, the formula of the first threshold voltage value of the LED string 30 can be: the first threshold voltage value = V _1T + V _2T .. .+V _NT . The V _1T , V _2T , and V _NT light-emitting diodes 301, 302 to 30n each have a typical operating voltage.

In addition, the formula of the second threshold voltage value of the LED string 30 may be: the second threshold voltage value = V _1L + V _2L ... + V _NL . The V _1L , V _2L , and V _NL based light-emitting diodes 301, 302 to 30n each have a low threshold voltage.

And when the light-emitting diode 301, 302 or 30n receives the forward voltage When between the typical operating voltage VT and the low threshold voltage VL, the luminance emitted by the light-emitting diodes 301, 302 or 30n changes with the magnitude of the forward voltage.

If it is assumed that the light-emitting diode string 30 has 30 light-emitting diodes, the typical operating voltage VT of each light-emitting diode is 3.2 volts, and the low threshold voltage VL is 2.0 volts, at which time the first of the light-emitting diode strings 30 The threshold voltage value = V _1T + V _2T ... + V _NT = 96 volts; and the second threshold voltage value of the light-emitting diode string 30 = V _1L + V _2L ... + V _NL = 60 volts. Therefore, when the forward voltage across the LED string 30 is greater than the first threshold voltage of 96 volts, the voltage across the LEDs 301, 302 or 30n may exceed the typical operating voltage V. _1T , V _2T , V _NT . Therefore, the light-emitting diodes 301, 302 or 30n emit the maximum amount of light, so that the light-emitting diode string 30 can reach the maximum amount of light.

When the forward voltage is less than the first threshold voltage value of 96 volts and greater than a second threshold voltage value of 60 volts, the cross-voltage obtained by the light-emitting diodes 301, 302 or 30n may be at a typical operating voltage V _1T , V _2T , V _{NT are} between the low threshold voltages V _1L , V _2L , and V _NL . Therefore, the amount of illuminating light of the illuminating diode 301, 302 or 30n changes with the increase or decrease of the voltage across the same. Similarly, the illuminating amount of the illuminating diode string 30 will be simultaneously brightened or decreased as the forward voltage increases or decreases. darken.

Finally, when the forward voltage is less than the second threshold voltage value of 60 volts, the voltage across the representative LED 301, 302 or 30n is less than the low threshold voltages V _1L , V _2L , V _NL . Therefore, the light-emitting diodes 301, 302, or 30n cannot emit light because they cannot receive a sufficient voltage value, so that the light-emitting diode string 30 stops emitting light.

The LED control circuit 40 is configured to adjust according to the modulated power signal The current of the LED string 30. The light-emitting diode control circuit 40 includes a transformer 41, a rectifier circuit 42, a first filter circuit 43, an adjustment circuit 44, a second filter circuit 45, and a discharge circuit 46.

For a detailed operation mode of the LED control circuit 40, please refer to FIG. 3, which is a circuit diagram of the first embodiment of the LED control circuit of the present invention.

In the first embodiment of the present invention, the LED control circuit 40a can select whether or not the transformer 41 is required according to the magnitude of the power signal input by the power supply terminal 10. For example, when the power signal input by the power supply terminal 10 is 220 volts, the transformer 41 can step down the power signal to comply with the applicable voltage of other circuit components in the LED control circuit 40a. Since the mode of operation of the transformer 41 has been familiar to those of ordinary skill in the art to which the present invention pertains, the principles thereof will not be described herein.

The rectifier circuit 42 is electrically connected to the dimming circuit 20 to receive the modulated power signal and converted into a DC power signal, and the DC power signal is synchronously increased or decreased with the modulation power signal. The rectifier circuit 42 can be a full-wave bridge rectifier, but the invention is not limited thereto.

The first filter circuit 43 is electrically connected to the rectifier circuit 42 to receive the DC power signal and convert it into a filtered power signal, thereby obtaining a stable signal. The filtered power signal will increase or decrease synchronously with the DC power signal. The first filter circuit 43 includes capacitor elements C1 and C2 and a resistor element R1. The capacitor elements C1 and C2 are used to shape the waveform of the DC power signal, and the resistor element R1 is used to step down the DC power signal to generate a filtered power signal.

The adjustment circuit 44 is electrically connected between the first filter circuit 43 and the LED string 30. In a first embodiment of the present invention, the adjustment circuit 44 is a variable pressure-based wafer, such as Vendor Model Supertex Inc. ^® CL2 is constant current driven light-emitting diode chip (Constant Current LED Driver IC), in accordance with the received The filtered power signal selectively generates a constant current adjustment signal having a current value of 20 milliamps to the LED string 30. The adjustment signal can be regarded as the forward voltage of the LED string 30. It should be noted that the adjustment circuit 44 can also be connected in parallel with the voltage surge suppressor 441. The voltage surge suppressor 441 can be a Transient Voltage Suppresser (TVS) diode. The voltage surge suppressor 441 can prevent the input power signal from having a too high voltage peak or a sudden surge, which causes the adjustment signal given to the LED string 30 to be unstable.

Based on characteristics of the constant current driving the light emitting diode chip manufacturer Supertex Inc. ^® model CL2 is (Constant Current LED Driver IC) element, the adjustment circuit 44 has a minimum value of the input voltage to 5 volts. When the adjustment voltage across the adjustment circuit 44 is greater than 5 volts, the adjustment circuit 44 can substantially stably output an adjustment signal having a constant current of 20 milliamps. Therefore, when the filtered power signal is greater than 101 volts (the first threshold voltage value is 96 volts and the minimum input voltage value is 5 volts), the adjustment circuit maintains a substantially stable output current of 20 milliamps of regulation signal, and the forward voltage at this time. The first threshold voltage value of the LED string 30 is greater than 96 volts, which causes the LED string 30 to maintain the maximum amount of illumination.

When the filtered power signal input to the adjustment circuit 44 is less than 101 volts (the sum of the first threshold voltage of the LED string 30 and the volt of the voltage of 5 volts) is greater than 65 volts (the second threshold voltage is 60 volts). When adjusting the voltage to 5 volts, the signal is adjusted to make the forward current The voltage is greater than the second threshold voltage value of the light-emitting diode string 30 of 60 volts, but less than the first threshold voltage value of 96 volts. At the same time, the adjustment signal will be synchronously increased or decreased with the modulation power signal, that is, the forward voltage of the LED string 30 is also changed, so that the amount of illumination of the LED string 30 can be adjusted. Change the power signal to be set to brighten or darken simultaneously.

Finally, when the filtered power signal input to the adjusting circuit 44 is less than the sum of the second threshold voltage value of 60 volts and the adjusted voltage, the adjusting circuit 44 cannot stably output the adjusting signal of the constant current of 20 milliamps, and the crossover is carried on the light emitting diode. The forward voltage of the string 30 is reduced to less than the second threshold voltage of 60 volts, so that the LED string 30 cannot receive sufficient voltage values to stop illuminating.

It should be noted that the LED string 30 can also be connected in parallel to the second filter circuit 45 and the discharge circuit 46. The second filter circuit 45 can be a capacitive component for rectifying the adjustment signal input to the LED string 30 to avoid flickering of the LED string 30. The discharge circuit 46 can be a resistive component. When the adjustment signal stops inputting to the LED string 30, the discharge circuit 46 enables the LED string 30 to be discharged at a relatively fast speed, so as to prevent the user from completely turning off the power. Supply, but because the charge stored in the capacitor element of the second filter circuit 45 is discharged, the remaining light of the LED string 30 is maintained for a while before disappearing. The discharge circuit 46 can also be used with the diode D1 as a fine adjustment, but the invention is not limited thereto.

The control result of the light-emitting diode control circuit 40a for the light-emitting diode string 30 is as shown in FIG. 4. FIG. 4 is a voltage value corresponding diagram of the light-emitting diode control circuit of the present invention in the first embodiment. The power signal input from the power supply terminal 10 is 110 volts alternating current of 20 milliamperes of current. It is assumed that the resistance element R1 of the first filter circuit 43 is 560 ohms. In this case, the voltage value of the DC power signal outputted by the rectifier circuit 42 is the root mean square value of the power signal, that is, about 154 volts. Therefore, in the case of a constant current of 20 milliamperes, the voltage across the first filter circuit 43 is approximately 11.2 volts.

If the number of the light-emitting diode strings 30 is 30 light-emitting diodes, the typical operating voltage VT of each light-emitting diode is 3.2 volts, so the forward voltage of the light-emitting diode string 30 will require 96 volts. That is, the first threshold voltage value = V _1H + V _2H ... + V _NH = 3.2 volts ^* 30 = 96 volts.

As such, the voltage across the adjustment circuit 44 is: 154 volts - 11.2 volts - 96 volts = 46.8 volts.

Therefore, the adjustment circuit 44 adjusts the voltage value of its output so that the voltage across the adjustment circuit 44 is adjusted to 46.8 volts. The 46.8 volts is higher than the minimum input voltage of the constant current LED driver of the Supertex Inc. ^® model CL2, so the constant current LED driver of the CL2 model maintains a substantially stable output. A milliamperes of constant current adjustment signal is applied to the LED string 30 to maintain the LED string 30 at maximum brightness. Therefore, when the filtered power signal is greater than the sum of the first threshold voltage and the minimum input voltage, the LED string 30 maintains the maximum amount of illumination.

When the luminance of the LED string 30 is adjusted to 50%, the voltage value of the DC power signal will become 120 volts due to the change of the modulation power signal outputted by the dimming circuit 20, and is illuminated. The required crossover voltage of the light-emitting diode at 50% brightness is about 2.73 volts, so the forward voltage required for the LED string 30 is about 82 volts, so the power is adjusted. The path 44 will thus adjust its output voltage value synchronously such that the voltage across the adjustment circuit 44 will be adjusted to: 120 volts - 11.2 volts - 82 volts = 26.8 volts.

When the luminance of the light-emitting diode string 30 is adjusted to 20%, the required voltage across the light-emitting diode at a luminance of 20% is about 2.27 volts, so the light-emitting diode string The required forward voltage is about 68 volts, and the voltage value of the DC power signal becomes 95 volts due to the change of the modulated power signal outputted by the dimming circuit 20, so the adjustment circuit 44 adjusts its output synchronously. The voltage value causes the voltage across the adjustment circuit 44 to be adjusted to: 95 volts - 11.2 volts - 68 volts = 15.8 volts.

Therefore, when the filtered power signal input to the adjusting circuit 44 is smaller than the sum of the first threshold voltage and the adjusted voltage of the LED string 30, but greater than the sum of the second threshold voltage and the adjusted voltage, the LED string 30 The brightness of the light can be brightened or dimmed simultaneously with the modulated power signal of the adjustment circuit 44.

Since the second threshold voltage value of the LED string 30 = V _1L + V _2L ... + V _NL = 2 volts ^* 30 = 60 volts, when the voltage value of the DC power signal is adjusted due to the output of the dimming circuit 20 When the change of the power supply signal is reduced to less than 50 volts, the forward voltage of the LED string 30 must be less than the second threshold voltage of 60 volts, and the voltage across the adjustment circuit 44 must be reduced to less than 5 volts. Since the voltage across the trimming circuit 44 is less than 5 volts, i.e., below the minimum input voltage value of the constant current LED driving wafer of the model CL2, the trimming circuit 44 turns off the output voltage value. At the same time, the cross-voltage system obtained by each of the light-emitting diodes is less than the low threshold voltage VL of 2 volts, and the light-emitting diode string 30 does not emit light. Therefore, when the filtered power signal is less than the sum of the second threshold voltage and the adjusted voltage, the LED string 30 stops emitting light.

It should be noted that the forward voltage required for the above-mentioned LED string 30 at different brightness is actually measured, so the forward voltage required for different types or different types of LED strings 30 may be The above numerical values are merely illustrative, and the present invention is not limited to the above numerical values.

Finally, please refer to FIG. 5, which is a circuit diagram of a second embodiment of the LED control circuit of the present invention.

In the second embodiment of the present invention, the adjustment circuit 44 of the LED control circuit 40b may also be a pulse width modulation switching circuit 442 for generating different pulse width modulation signals according to the filtered power signal, and the adjustment circuit 44 is The adjustment signal is obtained by generating a switching pulse width modulation signal. Therefore, the pulse width modulation signal can also be adjusted to increase or decrease in synchronization with the modulation power signal to further change the forward voltage applied to the LED string 30 to control the brightness of the LED string 30. Since the adjustment mode when the adjustment circuit 44 is the pulse width modulation switching circuit 442 is similar to the adjustment method when the adjustment circuit 44 is a variable voltage chip, the principle will not be described herein.

As can be seen from the above description, the light-emitting device 1 of the present invention can control the brightness emitted by the light-emitting diode string 30 by using the simple light-emitting diode control circuit 40, 40a or 40b, and can prevent the light-emitting diode string 30 from blinking. The problem of electromagnetic interference can be avoided. In addition, the LED strings 30 can be controlled by the LED control circuit 40, 40a or 40b regardless of whether they are connected in series, in parallel or in series or in parallel, without replacing other control circuits.

To sum up, the present invention, regardless of its purpose, means and efficacy, shows its distinctive features of the prior art. You are requested to review the examination and express the patent as soon as possible. It should be noted that the various embodiments described above are merely illustrative for ease of explanation, and the scope of the invention is intended to be limited by the scope of the claims.

1‧‧‧Lighting device

10‧‧‧Power supply

20‧‧‧ dimming circuit

30‧‧‧Lighting diode strings

301, 302, 30n‧‧‧Lighting diodes

40, 40a, 40b‧‧‧Lighting diode control circuit

41‧‧‧Transformers

42‧‧‧Rectifier circuit

43‧‧‧First filter circuit

44‧‧‧Adjustment circuit

441‧‧‧Voltage spur suppressor

442‧‧‧ Pulse width modulation switching circuit

45‧‧‧Second filter circuit

46‧‧‧Discharge circuit

C1, C2‧‧‧ capacitor components

D1‧‧‧ diode

R1‧‧‧resistive components

VT‧‧‧ typical operating voltage

VL‧‧‧low threshold voltage

1 is a schematic view showing the structure of a light-emitting device of the present invention.

2 is a graph showing the characteristics of forward voltage and current of each of the light-emitting diodes in the light-emitting diode string of the present invention.

3 is a circuit diagram of a first embodiment of a light-emitting diode control circuit of the present invention.

Fig. 4 is a view showing a voltage value corresponding to the light-emitting diode control circuit of the present invention in the first embodiment.

Figure 5 is a circuit diagram of a second embodiment of the LED control circuit of the present invention.

1‧‧‧Lighting device

10‧‧‧Power supply

20‧‧‧ dimming circuit

30‧‧‧Lighting diode strings

40‧‧‧Lighting diode control circuit

41‧‧‧Transformers

42‧‧‧Rectifier circuit

43‧‧‧First filter circuit

44‧‧‧Adjustment circuit

45‧‧‧Second filter circuit

46‧‧‧Discharge circuit

Claims (17)

An LED control circuit is disposed between a dimming circuit and a LED string, wherein the dimming circuit outputs a modulated power signal, wherein the LED string comprises at least one LED When the forward voltage of one of the strings of the light-emitting diodes is greater than a first threshold voltage, the light-emitting diodes are connected to a maximum amount of light; when the forward voltage is less than the first threshold voltage and When the value is greater than a second threshold voltage, the amount of illumination of the LED string is synchronously brightened or darkened as the forward voltage is increased or decreased; when the forward voltage is less than the second threshold voltage, The LED diode circuit stops emitting light; the LED control circuit includes: a rectifying circuit electrically connected to the dimming circuit, receiving the modulated power signal and converting the signal into a DC power signal, and the DC power signal is Synchronously increasing or decreasing with the modulated power signal; a first filter circuit is electrically connected to the rectifier circuit for converting the DC power signal into a filtered power signal, and the filtered power signal will follow DC power supply And an adjustment circuit is electrically connected between the first filter circuit and the LED string, the adjustment circuit has a minimum input voltage value, and the adjustment circuit outputs an adjustment signal to The LED string serves as the forward voltage of the LED string, wherein the adjustment circuit maintains a substantially stable output when the voltage across one of the adjustment circuits is greater than the minimum input voltage. a signal; wherein, when the filtered power signal is greater than a sum of the first threshold voltage and the minimum input voltage, the adjusting circuit maintains a substantially stable output of the adjustment signal, and the forward voltage is greater than the first threshold voltage a value, such that the LED string maintains the maximum amount of illumination; wherein, the filtered power signal is less than a sum of the first threshold voltage and the adjustment voltage, but greater than the second threshold voltage and the adjustment voltage In the sum of the adjustment circuit, the adjustment circuit outputs the adjustment signal such that the forward voltage is greater than the second threshold voltage but less than the first threshold voltage, and the forward voltage is synchronized with the modulated power signal Increasing or decreasing, the illuminating amount of the illuminating diode string can be simultaneously brightened or darkened; wherein, when the filtered power signal is less than the sum of the second threshold voltage and the adjusted voltage, the adjusting circuit is cut off The adjustment signal is output such that the forward voltage is less than the second threshold voltage, and the LED string stops emitting light. The illuminating diode control circuit of claim 1, further comprising a second filter circuit connected in parallel to the illuminating diode string for adjusting the input to the illuminating diode string The signal is rectified. The illuminating diode control circuit of claim 1 or 2 further includes a discharge circuit connected in parallel to the illuminating diode string, wherein when the adjustment signal stops inputting, the discharging circuit is The light emitting diode string is discharged. The light-emitting diode control circuit of claim 1, wherein the rectifier circuit and the dimming circuit are further electrically connected to a transformer, and the transformer is configured to step down the modulated power supply signal. The illuminating diode control circuit of claim 1, wherein the adjusting circuit is further connected in parallel with a voltage surge suppressor for avoiding the adjustment signal spur. The illuminating diode control circuit of claim 1, wherein the adjusting circuit comprises a pulse width modulation switching circuit electrically connected to the first filtering circuit for switching pulse width modulation The way of the signal to get the adjustment signal. The illuminating diode control circuit of claim 1, wherein the illuminating diode control circuit is electrically connected to the plurality of illuminating diodes, each of the illuminating diodes having a typical operating voltage. When the voltage across each of the light-emitting diodes is greater than the corresponding typical operating voltage, the plurality of light-emitting diode systems output the maximum light-emitting amount; wherein the first threshold voltage value of the light-emitting diode string is The first threshold voltage value is V _1T + V _2T ... + V _NT ; wherein V _1T , V _2T , V _NT are the typical operating voltages of the plurality of light-emitting diodes. The illuminating diode control circuit of claim 1, wherein the illuminating diode control circuit is electrically connected to the plurality of illuminating diodes, each of the illuminating diodes having a low threshold voltage. When the voltage across each of the light-emitting diodes is less than the corresponding low threshold voltage, the plurality of light-emitting diode systems stop emitting light; wherein the formula of the second threshold voltage value of the light-emitting diode string is: The second threshold voltage value = V _1L + V _2L ... + V _NL ; wherein V _1L , V _2L , V _NL are the low threshold voltages of the plurality of light-emitting diodes. A lighting device includes: a power supply terminal for inputting a power signal; and a dimming circuit for receiving the power signal for conversion to a modulation power supply a light-emitting diode string comprising at least one light-emitting diode, wherein the light-emitting diode string is connected when a forward voltage of one of the light-emitting diode strings is greater than a first threshold voltage a maximum illuminating amount; when the forward voltage is less than the first threshold voltage value and greater than a second threshold voltage value, the illuminating amount of the illuminating diode string is synchronously brightened as the forward voltage increases or decreases Or dimming; when the forward voltage is less than the second threshold voltage, the LED string stops emitting light; and a light emitting diode control circuit is electrically connected to the dimming circuit and the light emitting diode The LED control circuit includes: a rectifying circuit electrically connected to the dimming circuit to receive the modulated power signal from the dimming circuit and converted into a DC power signal, the DC The power signal is synchronously increased or decreased along with the modulated power signal; a first filter circuit is electrically connected to the rectifier circuit for converting the DC power signal into a filtered power signal, and the filtered power signal is With the DC The signal is synchronously increased or decreased; and an adjustment circuit is electrically connected between the first filter circuit and the LED string, the adjustment circuit has a minimum input voltage value, and the adjustment circuit outputs an adjustment signal to The LED string serves as the forward voltage of the LED string, wherein the adjustment circuit maintains a substantially stable output when the voltage across one of the adjustment circuits is greater than the minimum input voltage. a signal; wherein, when the filtered power signal is greater than a sum of the first threshold voltage and the minimum input voltage, the adjusting circuit remains substantially stable And outputting the adjustment signal, and the forward voltage is greater than the first threshold voltage value, so that the LED string maintains the maximum illumination amount; wherein, when the filtered power signal is less than the first threshold voltage value When the sum of the adjusted voltages is greater than the sum of the second threshold voltage and the adjusted voltage, the adjusting circuit outputs the adjusting signal such that the forward voltage is greater than the second threshold voltage but less than the first threshold voltage a value, and the forward voltage is synchronously increased or decreased with the modulated power signal, so that the illuminating amount of the LED string can be simultaneously brightened or darkened; wherein, when the filtered power signal is smaller than the When the second threshold voltage value is the sum of the adjusted voltages, the adjusting circuit cuts off the adjustment signal so that the forward voltage is less than the second threshold voltage, so that the LED string stops emitting light. The illuminating device of claim 9, wherein the illuminating diode control circuit further comprises a second filtering circuit connected in parallel to the illuminating diode for inputting to the illuminating diode The adjustment signal is rectified. The illuminating device of claim 9 or 10, wherein the illuminating diode control circuit further comprises a discharging circuit connected in parallel to the illuminating diode, wherein the discharging is performed when the adjusting signal stops inputting The circuit is capable of discharging the light emitting diode. The illuminating device of claim 9, wherein the rectifier circuit and the dimming circuit are further electrically connected to a transformer, and the transformer is configured to step down the modulated power signal. The illuminating device of claim 9, wherein the adjusting circuit is further connected in parallel with a voltage surge suppressor for preventing the adjusting signal spur. The illuminating device of claim 9, wherein the adjusting circuit comprises a pulse width modulation switching circuit electrically connected to the first filtering circuit for switching the pulse width modulation signal by Get the adjustment signal. The illuminating device of claim 9, wherein the illuminating diode string has a plurality of illuminating diodes, and the plurality of illuminating diodes are connected to each other in series, in parallel or in series and parallel, wherein each The light-emitting diodes respectively have a typical operating voltage and a low threshold voltage; and when the voltage across each of the light-emitting diodes is greater than the corresponding typical operating voltage, the plurality of light-emitting diode systems output the maximum light-emitting When the voltage across each of the light-emitting diodes is less than the corresponding low threshold voltage, the plurality of light-emitting diode systems stop emitting light. The illuminating device of claim 15, wherein when the illuminating diode string has a plurality of illuminating diodes connected in series, the formula of the first threshold voltage value of the illuminating diode string is: The first threshold voltage value = V _1T + V _2T ... + V _NT ; wherein V _1T , V _2T , V _NT are the typical operating voltages of the plurality of light-emitting diodes. The illuminating device of claim 15, wherein when the illuminating diode string has a plurality of illuminating diodes connected in series, the formula of the second threshold voltage value of the illuminating diode string is: The second threshold voltage value = V _1L + V _2L ... + V _NL ; wherein V _1L , V _2L , V _NL are the low threshold voltages of the plurality of light-emitting diodes.