CN101959340A - LED circuit - Google Patents

Abstract

The present invention provides a light-emitting diode circuit. The light-emitting diode circuit includes an AC power supply, a rectifier, a voltage limiting circuit and a light-emitting diode module. The AC power supply provides an AC voltage. The rectifier can generate a first rectified voltage according to the AC voltage. The voltage limiting circuit can limit the upper limit value of the first rectified voltage to a rated voltage to generate a second rectified voltage, wherein the second rectified voltage is lower than the rated voltage. The light-emitting diode module can receive the second rectified voltage. In this way, when the AC voltage is unstable, the amplitude difference of the current flowing through the light-emitting diode module can be reduced.

Description

LED circuit

technical field

The invention relates to a light-emitting diode circuit, and in particular to a light-emitting diode circuit which can prevent the current flowing through the light-emitting diode from changing drastically.

Background technique

Light Emitting Diodes (LEDs for short) have advantages such as long life, small size, high shock resistance, low heat generation, and low power consumption, so they have been widely used as indicators or light sources in household and various equipment. In recent years, light-emitting diodes have developed towards multi-color and high brightness, so their application fields have been extended to large outdoor signage, traffic lights and related fields. In the future, light-emitting diodes may even become the main lighting source with both power saving and environmental protection functions.

FIG. 1 is a schematic diagram of an existing LED circuit. FIG. 2 is a waveform diagram of an existing AC voltage. FIG. 3 is a waveform diagram of a conventional rectified voltage. Please refer to FIGS. 1-3 together. The AC power supply Vac can provide the AC voltage AS1 to the rectifier BD1. The rectifier BD1 can provide the rectified voltage DS1 to the light-emitting diodes LED1-LEDN according to the AC voltage AS1. The current limiting resistor R1 is, for example, 896Ω. The number of light emitting diodes LED1 - LEDN is 34, for example.

It should be noted that when the AC voltage AS1 provided by the AC power supply is unstable, the current flowing through the LEDs LED1-LEDN will also change drastically, which will cause large brightness differences and color temperature shifts of the LEDs. For example, ideally, the AC power supply Vac would provide the AC voltage AS1 of 110V, but actually the AC voltage AS1 should oscillate between 100V˜120V.

FIG. 4 is a waveform diagram of conventional rectified voltages under different AC voltages. Please refer to FIG. 1 and FIG. 4 together. When the AC voltage AS1 oscillates between 100V-120V, the rectified voltage DS1 also oscillates between the curves C1 and C2 in FIG. 4 . The severe oscillation of the rectified voltage DS1 will cause the currents flowing through the LEDs LED1-LEDN to change drastically, wherein the difference of the RMS currents flowing through the LEDs LED1-LEDN reaches (26.53/15.194)=1.75 times. This will cause large brightness difference and color temperature shift of the light emitting diodes LED1 - LEDN.

Table 1 Experimental data in Figure 1

To sum up, how to improve the LED current difference and stabilize the voltage under different supply voltages, so that the power supply can continuously provide quality and stable voltage to the LEDs, so as to improve the brightness difference and color temperature shift of the LEDs, etc., becomes a problem. This is the goal that the German industry in the field of light-emitting diodes urgently needs to work hard on.

Contents of the invention

The invention provides a light-emitting diode circuit, which can prevent the current flowing through the light-emitting diode from changing drastically.

The invention proposes a light emitting diode circuit, which includes an AC power supply, a rectifier, a voltage limiting circuit and a light emitting diode module. The AC power supply provides AC voltage. The rectifier is connected to the AC power supply and can generate a first rectified voltage according to the AC voltage. The voltage limiting circuit is connected to the rectifier and can limit the upper limit of the first rectified voltage to the rated voltage to generate the second rectified voltage, wherein the second rectified voltage is lower than the rated voltage. The LED module is connected to the voltage limiting circuit and can receive the second rectified voltage.

In an embodiment of the present invention, the LED circuit further includes a triac dimmer. The triac dimmer is connected between the AC power source and the rectifier.

In an embodiment of the invention, the rectifier is a full bridge rectifier.

In an embodiment of the invention, the voltage limiting circuit includes a transistor. The collector of the transistor is connected to the output of the rectifier. The emitter of the transistor is connected to the input terminal of the LED module. The base terminal of the transistor is connected to a voltage.

In an embodiment of the invention, the voltage limiting circuit includes a transistor, a current limiting resistor and a Zener diode. The collector of the transistor is connected to the output of the rectifier. The emitter of the transistor is connected to the input terminal of the LED module. The first end of the current limiting resistor is connected to the output end of the rectifier. The second terminal of the current limiting resistor is connected to the base terminal of the transistor. The anode terminal of the Zener diode is connected to the output terminal of the LED module. The cathode terminal of the Zener diode is connected to the base terminal of the transistor.

Based on the above, in another embodiment, the voltage limiting circuit may further include a variable resistor. The variable resistor is connected between the base terminal of the transistor and the cathode terminal of the Zener diode. In yet another embodiment, the voltage limiting circuit may further include a thermistor. The thermistor is connected between the base terminal of the transistor and the cathode terminal of the Zener diode.

In an embodiment of the present invention, the voltage limiting circuit includes several transistors, a current limiting resistor and a Zener diode. The collector of each transistor is connected to the output terminal of the rectifier. The emitters of each transistor are connected to the input ends of several LED strings in the LED module. The first end of the current limiting resistor is connected to the output end of the rectifier. The second terminal of the current limiting resistor is connected to the base terminal of each transistor. The anode terminals of the Zener diodes are connected to the output terminals of each LED string. The cathode terminal of the Zener diode is connected to the base terminal of each transistor.

In an embodiment of the present invention, the LED module includes a series of resistors and LEDs. The first end of the resistor is connected to the voltage limiting circuit. The input end of the light emitting diode series is connected to the second end of the resistor. The output terminals of the LED strings are connected to a voltage.

In an embodiment of the invention, the LED module includes Zener diodes and LED series. The cathode terminal of the Zener diode is connected to the voltage limiting circuit. The input end of the LED string is connected to the anode of the Zener diode, and the output end of the LED string is connected to a voltage.

In an embodiment of the present invention, the LED module includes a constant current diode and a series of LEDs. The anode terminal of the constant current diode is connected to the voltage limiting circuit. The input end of the light emitting diode series is connected to the cathode end of the constant current diode. The output terminals of the LED strings are connected to a voltage.

In an embodiment of the present invention, the LED module includes a variable resistor and a series of LEDs. The first end of the variable resistor is connected to the voltage limiting circuit. The input terminal of the light emitting diode series is connected with the second terminal of the variable resistor. The output terminals of the LED strings are connected to a voltage.

In an embodiment of the present invention, the LED module includes a thermistor and a series of LEDs. The first end of the thermistor is connected to the voltage limiting circuit. The input end of the LED series is connected to the second end of the thermistor. The output terminals of the LED strings are connected to a voltage.

In an embodiment of the present invention, the LED module includes a resistor, LED strings and transistors. The first end of the resistor is connected to the voltage limiting circuit. The input end of the light emitting diode series is connected to the second end of the resistor. The drains of the field effect transistors are connected to the output ends of the LED strings. The source of the field effect transistor is connected to a voltage. The gate terminal of the field effect transistor receives the pulse width modulation signal.

Based on the above, the present invention utilizes the voltage limiting circuit to limit the upper limit of the voltage provided to the LED module to the rated voltage. In this way, the current flowing through the light-emitting diodes can be prevented from changing drastically, so as to improve problems such as brightness differences and color temperature shifts of the light-emitting diodes.

In order to make the above-mentioned features and advantages of the present invention more comprehensible, the following specific embodiments are described in detail with reference to the accompanying drawings.

Description of drawings

FIG. 1 is a schematic diagram of an existing LED circuit.

FIG. 2 is a waveform diagram of an existing AC voltage.

FIG. 3 is a waveform diagram of a conventional rectified voltage.

FIG. 4 is a waveform diagram of conventional rectified voltages under different AC voltages.

FIG. 5 is a schematic diagram of an LED circuit according to the first embodiment of the present invention.

FIG. 6 is a waveform diagram of rectified voltages under different AC voltages according to the first embodiment of the present invention.

FIG. 7 is a schematic diagram of an LED circuit according to a second embodiment of the present invention.

FIG. 8 is a schematic diagram of a light emitting diode circuit according to a third embodiment of the present invention.

FIG. 9 is a schematic diagram of a light emitting diode circuit according to a fourth embodiment of the present invention.

FIG. 10 is a schematic diagram of a light emitting diode circuit according to a fifth embodiment of the present invention.

FIG. 11 is a schematic diagram of a light emitting diode circuit according to a sixth embodiment of the present invention.

FIG. 12 is a schematic diagram of an LED circuit according to a seventh embodiment of the present invention.

FIG. 13 is a schematic diagram of an LED circuit according to an eighth embodiment of the present invention.

FIG. 14 is a schematic diagram of a light emitting diode circuit according to a ninth embodiment of the present invention.

FIG. 15 is a waveform diagram of the AC voltage AS2 when the triac dimmer in FIG. 14 is fully output.

FIG. 16 is a waveform diagram of the rectified voltage DS4 when the triac dimmer in FIG. 14 is fully output.

FIG. 17 is a waveform diagram of AC voltage AS2 when the triac dimmer in FIG. 14 is at half output.

FIG. 18 is a waveform diagram of the rectified voltage DS4 when the triac dimmer in FIG. 14 is at half output.

FIG. 19 is a waveform diagram of the AC voltage AS2 when the triac dimmer in FIG. 14 outputs a quarter.

FIG. 20 is a waveform diagram of the rectified voltage DS4 when the triac dimmer in FIG. 14 outputs a quarter.

Description of main component symbols:

Light-emitting diode circuit-10～18; Voltage limiting circuit-30～33;

Light-emitting diode module-50～55; Triac dimmer-70;

Terminals - A, B; AC voltage - AS1, AS2;

Rectifier-BD1; Curve-C1～C4;

Constant current diode-CRD1; rectified voltage-DS1～DS4;

Transistor-Q1～Q4; Current limiting resistors-R1, R2, R2-1～R2-3;

AC power supply - Vac; Reference voltage - VCC;

Variable resistor-VR1; Zener diode-ZD1, ZD2;

Light-emitting diodes - LED1~LEDN, LED11~LED1N, LED21~LED2N, LED31~LED3N.

Detailed ways

FIG. 5 is a schematic diagram of an LED circuit according to the first embodiment of the present invention. Referring to FIG. 5 , in this embodiment, the LED circuit 10 includes an AC power source Vac, a rectifier BD1 , a voltage limiting circuit 30 and a LED module 50 . The AC power Vac is connected to the rectifier BD1, and can provide the AC voltage AS1 as shown in FIG. 2 to the rectifier BD1. The rectifier BD1 is connected to the voltage limiting circuit 30 . The rectifier BD1 can be, for example, a full bridge rectifier (Full Bridge Rectifier), which can rectify the AC voltage AS1 to provide the rectified voltage DS1 as shown in FIG. 3 to the voltage limiting circuit 30.

It should be noted that the voltage limiting circuit 30 is connected to the LED module 50 . The voltage limiting circuit 30 can limit the upper limit of the rectified voltage DS1 to the rated voltage, and accordingly provide the rectified voltage DS2 lower than the rated voltage to the LED module 50 .

In this embodiment, the voltage limiting circuit 30 includes a current limiting resistor R1, a transistor Q1 and a Zener diode (Zener Diode) ZD1. The current limiting resistor R1 is, for example, 10KΩ. The transistor Q1 is, for example, a bipolar junction transistor. The reverse breakdown voltage of Zener diode ZD1 is, for example, 132V. In this way, the transistor Q1 can provide the rectified voltage DS2 with a voltage less than 131.3V to the LED module 50 . In other words, the rated voltage of this embodiment is 131.3V.

In this embodiment, the light emitting diode module 50 may include a current limiting resistor R2 and light emitting diodes LED1 ˜ LEDN, wherein the light emitting diodes LED1 ˜ LEDN form a series of light emitting diodes. The current limiting resistor R2 is, for example, 218Ω. For example, there are 34 light-emitting diodes LED1-LEDN. It should be noted that, in other embodiments, the number is not limited.

FIG. 6 is a waveform diagram of rectified voltages under different AC voltages according to the first embodiment of the present invention. Please refer to FIG. 5 and FIG. 6 together. When the AC voltage AS1 oscillates between 100V-120V, the rectified voltage DS2 will only oscillate between curves C3 and C4 in FIG. 6 . It can be clearly seen from Table 2 below that when the AC voltage AS1 oscillates between 100V and 120V, the difference (27.78/22.1) of the RMS current value flowing through the light-emitting diodes LED1 to LEDN is about 1.26 times, compared with Table 1 has been substantially reduced. It should be noted that the lower the voltage value of the Zener diode (Zener Diode) ZD1 used in the present invention, the smaller the difference in current when the input AC voltage AS1 changes, but it will also cause greater energy loss at the same time, so the difference in current and energy loss Can make a trade-off.

Experimental data in Table 2 and Figure 5

Those skilled in the art should know that the brightness of a light emitting diode is positively correlated with the current flowing through the light emitting diode. In this embodiment, when the AC voltage AS1 oscillates between 100V and 120V, the difference in the root mean square current value flowing through the light-emitting diodes LED1 to LEDN is only about 1.26 times, compared with the prior art, this embodiment can effectively Improve problems such as brightness differences and color temperature shifts of LEDs.

Although a possible form of the light-emitting diode circuit has been described in the above-mentioned embodiment, those skilled in the art should know that each manufacturer has different designs for the light-emitting diode circuit, so the application of the present invention should not be limited to this possible form. In other words, as long as the upper limit of the voltage supplied to the LED module is limited to the rated voltage by the voltage limiting circuit, the spirit of the present invention is met. Several implementation modes are given below so that those skilled in the art can further understand the spirit of the present invention and implement the present invention.

In the above embodiments, although the current limiting resistor R1, the current limiting resistor R2 and the Zener diode ZD1 can be implemented by a single component, the present invention is not limited thereto. In other embodiments, the current-limiting resistor R1 , the current-limiting resistor R2 and the Zener diode ZD1 can also be composed of a plurality of components connected in series or in parallel. Although the rectifier BD1 is an example of a full-bridge rectifier, the present invention is not limited thereto. In other embodiments, the rectifier BD1 can also be implemented in other ways. For example, it can also be implemented using a half-bridge rectifier with capacitors. Although the current limiting resistor R1 is 10KΩ as an example. Although the current limiting resistor R2 is 218Ω as an example. But the present invention is not limited thereto. In other embodiments, the current limiting resistors R1 and R2 can also be replaced by current limiting resistors with other resistance values.

In addition, although the rated voltage is described by taking 131.3V as an example, the present invention is not limited thereto. In other embodiments, those skilled in the art can also change the rated voltage according to their needs. For example, the reverse breakdown voltage of the Zener diode ZD1 can be changed to change the rated voltage. For another example, the reference voltage provided to the base of the transistor Q1 can be changed to change the rated voltage.

Specifically, in the first embodiment, the voltage limiting circuit 30 and the LED module 50 shown in FIG. 5 are only an optional embodiment, and the present invention is not limited thereto. In other embodiments, those skilled in the art can change the implementations of the voltage limiting circuit 30 and the LED module 50 according to their needs.

For example, FIG. 7 is a schematic diagram of an LED circuit according to a second embodiment of the present invention. Please refer to FIG. 7 and FIG. 5 together, the LED circuit 11 is similar to the LED circuit 10 . The difference is that the light emitting diode circuit 11 is a multi-level parallel structure, which includes a voltage limiting circuit 31 and a light emitting diode module 51 . In this embodiment, the voltage limiting circuit 31 may include a current limiting resistor R1 , a Zener diode ZD1 and a plurality of transistors, and this embodiment takes three transistors Q1 - Q3 as an example. The LED module 51 may include a plurality of LED strings, and this embodiment takes three strings as an example. The first series of light emitting diodes can be composed of a current limiting resistor R2-1 and light emitting diodes LED11˜LED1N. The second series of light emitting diodes may be composed of a current limiting resistor R2-2 and light emitting diodes LED21˜LED2N. The third series of light emitting diodes may be composed of a current limiting resistor R2-3 and light emitting diodes LED31˜LED3N. In this way, the effect similar to that of the first embodiment can also be achieved.

FIG. 8 is a schematic diagram of a light emitting diode circuit according to a third embodiment of the present invention. Please refer to FIG. 8 and FIG. 5 together, the LED circuit 12 is similar to the LED circuit 10 . The difference lies in the voltage limiting circuit 32 of the LED circuit 12 . In this embodiment, the voltage limiting circuit 32 may include a transistor Q1, wherein the transistor Q1 is connected between the rectifier BD1 and the LED module 50, and the base of the transistor Q1 is connected to a reference voltage VCC. In addition, by adjusting the voltage of the reference VCC , but also adjust the brightness of LED1 ~ LEDN.

FIG. 9 is a schematic diagram of a light emitting diode circuit according to a fourth embodiment of the present invention. Please refer to FIG. 9 and FIG. 5 together, the LED circuit 13 is similar to the LED circuit 10 . The difference lies in the LED module 52 . In this embodiment, the light emitting diode module 52 includes a constant current diode (Current Regulative Diode, CRD) CRD 1 and light emitting diodes LED1-LEDN. The constant current diode CRD1 can replace the current limiting resistor. In other embodiments, multiple constant current diodes can also be used in series or in parallel, and this element can keep the current of the LED module 52 below the set current. The Zener diode ZD1 can limit the voltage within a certain appropriate range, so that the cross-voltage of the constant current diode will not be too large, causing the components to burn out.

FIG. 10 is a schematic diagram of a light emitting diode circuit according to a fifth embodiment of the present invention. Please refer to FIG. 10 and FIG. 5 together, the LED circuit 14 is similar to the LED circuit 10 . The difference lies in the LED module 53 . In this embodiment, the light emitting diode module 53 includes a Zener diode ZD2 and light emitting diodes LED1 -LEDN. Zener diode ZD2 can replace the current limiting resistor. The current-limiting resistor R2 is replaced by a Zener diode ZD2, which can absorb excess cross-voltage between terminal A and terminal B, so as to prevent the light-emitting diode module 53 from being burned due to excessive cross-voltage.

FIG. 11 is a schematic diagram of a light emitting diode circuit according to a sixth embodiment of the present invention. Please refer to FIG. 11 and FIG. 5 together, the LED circuit 15 is similar to the LED circuit 10 . The difference lies in the LED module 54 . In this embodiment, the LED module 54 includes a variable resistor (Variable Resistor) VR1 and LEDs LED1-LEDN. Variable resistor VR1 can be used as a current limiting resistor. In addition, by adjusting the variable resistor VR1, the brightness of the light-emitting diodes LED1-LEDN can be further adjusted. In this way, not only the effect similar to that of the first embodiment can be achieved, but also the brightness adjustment function of the light emitting diodes LED1 - LEDN is added.

Please note that in another embodiment, the variable resistor VR1 in FIG. 11 can also be replaced by a thermistor. In this way, not only the effects similar to those of the first embodiment can be achieved, but also the brightness of the light-emitting diodes LED1 - LEDN can be adjusted according to the ambient temperature.

FIG. 12 is a schematic diagram of an LED circuit according to a seventh embodiment of the present invention. Please refer to FIG. 12 and FIG. 5 together, the LED circuit 16 is similar to the LED circuit 10 . The difference lies in the voltage limiting circuit 33 . In this embodiment, the voltage limiting circuit 33 includes a variable resistor VR1, a current limiting resistor R1, a transistor Q1 and a Zener diode ZD1. By adjusting the variable resistor VR1, the voltage value of the base of the transistor Q1 can be changed, and then the brightness of the light-emitting diodes LED1-LEDN can be adjusted. In this way, not only the effect similar to that of the first embodiment can be achieved, but also the brightness adjustment function of the light emitting diode is added.

Please note that in another embodiment, the variable resistor VR1 in FIG. 12 can also be replaced by a thermistor. In this way, not only the effects similar to those of the first embodiment can be achieved, but also the brightness of the light-emitting diodes LED1 - LEDN can be adjusted according to the ambient temperature.

FIG. 13 is a schematic diagram of an LED circuit according to an eighth embodiment of the present invention. Please refer to FIG. 13 and FIG. 5 together, the LED circuit 17 is similar to the LED circuit 10 . The difference lies in the LED module 55 . In this embodiment, the LED module 55 includes a transistor Q4, a current limiting resistor R2, and LEDs LED1-LEDN. The gate terminal of the transistor Q4 can receive a pulse width modulation (PWM) signal, and the brightness of the light-emitting diodes LED1-LEDN can be adjusted by changing the pulse width modulation period. In this way, not only the effect similar to that of the first embodiment can be achieved, but also the brightness adjustment function of the light emitting diodes LED1 - LEDN is added.

FIG. 14 is a schematic diagram of a light emitting diode circuit according to a ninth embodiment of the present invention. Please refer to FIG. 14 and FIG. 5 together, the LED circuit 18 is similar to the LED circuit 10 . The difference is that the LED circuit 18 also includes a triac dimmer (Triac Dimmer) 70 . The triac dimmer 70 is connected between the AC power Vac and the rectifier BD1. In this way, the brightness of the light emitting diodes LED1 - LEDN can also be adjusted. FIG. 15 is a waveform diagram of the AC voltage AS2 when the triac dimmer 70 in FIG. 14 is fully output. FIG. 16 is a waveform diagram of the rectified voltage DS4 when the triac dimmer 70 in FIG. 14 is fully output. FIG. 17 is a waveform diagram of the AC voltage AS2 when the triac dimmer 70 in FIG. 14 is at half output. FIG. 18 is a waveform diagram of the rectified voltage DS4 when the triac dimmer 70 in FIG. 14 is half output. FIG. 19 is a waveform diagram of the AC voltage AS2 when the triac dimmer 70 in FIG. 14 outputs a quarter of the output. FIG. 20 is a waveform diagram of the rectified voltage DS4 when the output of the triac dimmer 70 in FIG. 14 is quarter output.

Then compare the test results in Figures 15 to 20. When the full output of the triac dimmer 70 reaches a quarter output, it can be seen from the figure that the present invention can produce a dimming effect under the AC voltage AS2.

To sum up, the present invention utilizes the voltage limiting circuit to limit the upper voltage limit provided to the LED module to the rated voltage, thus preventing the current flowing through the LED from changing drastically. Embodiments of the present invention also have the following effects in addition:

1. Add a variable resistor to the voltage limiting circuit or LED module to adjust the brightness of the LED.

2. Adding a thermistor to the voltage limiting circuit or the LED module can adjust the brightness of the LED according to the ambient temperature.

3. A transistor is added to the light-emitting diode module, and the brightness of the light-emitting diode can be adjusted in conjunction with the pulse width modulation signal.

4. A triac dimmer is added to the light-emitting diode circuit to adjust the brightness of the light-emitting diode.

5. A transistor is added to the LED module, the base of the transistor is connected to a reference voltage, and the brightness of the LED can be adjusted by adjusting the reference voltage.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (14)

1. A light emitting diode circuit, comprising: an AC power source for providing an AC voltage; A rectifier, connected to the AC power supply, generates a first rectified voltage according to the AC voltage; A voltage limiting circuit, connected to the rectifier, limits the upper limit of the first rectified voltage to a rated voltage for generating a second rectified voltage, wherein the second rectified voltage is lower than the rated voltage; and A light emitting diode module is connected to the voltage limiting circuit and receives the second rectified voltage. 2. The LED circuit of claim 1, further comprising: A three-terminal bidirectional thyristor switch dimmer is connected between the AC power supply and the rectifier. 3. The LED circuit according to claim 1, wherein the rectifier is a full bridge rectifier. 4. The LED circuit according to claim 1, wherein the voltage limiting circuit comprises: A transistor is suitable for connecting a collector to an output end of the rectifier, an emitter of the transistor to an input end of the light-emitting diode module, and a base of the transistor to a voltage. 5. The LED circuit according to claim 1, wherein the voltage limiting circuit comprises: a transistor adapted to have a collector connected to an output terminal of the rectifier, and an emitter of the transistor connected to the input terminal of the light emitting diode module; a current limiting resistor, with a first terminal connected to the output terminal of the rectifier, and a second terminal of the current limiting resistor connected to the base terminal of the transistor; and A zener diode is adapted to have an anode terminal connected to the output terminal of the LED module, and a cathode terminal of the zener diode is connected to the base terminal of the transistor. 6. The LED circuit according to claim 5, wherein the voltage limiting circuit further comprises: A variable resistor is connected between the base terminal of the transistor and the cathode terminal of the Zener diode. 7. The LED circuit according to claim 5, wherein the voltage limiting circuit further comprises: A thermistor is connected between the base terminal of the transistor and the cathode terminal of the Zener diode. 8. The LED circuit according to claim 1, wherein the voltage limiting circuit comprises: Several transistors, wherein a collector of each transistor is connected to the output terminal of the rectifier, and an emitter of each transistor is connected to the input terminals of several LED strings in the LED module; a current limiting resistor, the first terminal of which is connected to the output terminal of the rectifier, and the second terminal of the current limiting resistor is connected to the base terminal of each of the transistors; and A zener diode, the anode end of which is connected to the output end of each light-emitting diode series, and the cathode end of the zener diode is connected to the base end of each transistor. 9. The LED circuit according to claim 1, wherein the LED module comprises: a resistor, the first end of which is connected to the voltage limiting circuit; and A series of light emitting diodes, the input end of which is connected to the second end of the resistor, and the output end of the series of light emitting diodes is connected to a voltage. 10. The LED circuit according to claim 1, wherein the LED module comprises: a zener diode, the cathode of which is connected to the voltage limiting circuit; and A series of light emitting diodes, the input end of which is connected to the anode of the zener diode, and the output end of the series of light emitting diodes is connected to a voltage. 11. The LED circuit according to claim 1, wherein the LED module comprises: a constant current diode, the anode of which is connected to the voltage limiting circuit; and A series of light emitting diodes, the input terminal of which is connected to the cathode terminal of the constant current diode, and the output terminal of the series of light emitting diodes is connected to a voltage. 12. The LED circuit according to claim 1, wherein the LED module comprises: a variable resistor, the first end of which is connected to the voltage limiting circuit; and A series of light emitting diodes, the input end of which is connected to the second end of the variable resistor, and the output end of the series of light emitting diodes is connected to a voltage. 13. The LED circuit according to claim 1, wherein the LED module comprises: a thermistor, the first end of which is connected to the voltage limiting circuit; and A series of light emitting diodes, the input end of which is connected to the second end of the thermistor, and the output end of the series of light emitting diodes is connected to a voltage. 14. The LED circuit according to claim 1, wherein the LED module comprises: a resistor, the first end of which is connected to the voltage limiting circuit; a series of light emitting diodes, the input end of which is connected to the second end of the resistor; and The drain of the field effect transistor is connected to the output terminal of the light-emitting diode series, the source of the field effect transistor is connected to a voltage, and the gate terminal of the field effect transistor receives a pulse width modulation signal.

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