Patent Publication Number: US-2022240361-A1

Title: Led driving circuit, light tube and illumination device

Description:
TECHNICAL HELD 
     The embodiments of the present invention relate to the field of illumination technology, and in particular to an LED driving circuit, a light tube and an illumination device. 
     BACKGROUND 
     Ballast mainly includes two types: instant start ballast and program start ballast. Ballast has resonance circuit, and its driving circuit is matchable with the characteristics of the load of fluorescent lamp, which outputs high frequency and high voltage (50-100 KHZ, 600-1200V) when starting. In the prior art, in order to meet the requirement of energy saving, LED light tube may be replaced by the fluorescent lamp. Because most of the lamp holder of the fluorescent lamp is a standard lamp holder, and most of the lamp holder of the LED light tube is also a standard lamp holder, the LED light tube is structurally matchable with the lamp holder of the conventional illumination device. 
     LED light tube includes TYPE A replacement type, TYPE B wire shearing type and TYPE A+B compatible type. Among them, TYPE A replacement type and TYPE A+B compatible type are applicable for ballast, while TYPE B wire shearing type is only applicable for AC power supply. In use of the illumination device, there will be a risk of damage and failure of the electronic components, and misapplication or misconnection of the type B wire shearing type to the ballast, as well as safety problem. 
     SUMMARY 
     Embodiments of the present invention provide an LED driving circuit, a light tube and an illumination device, to improve the safety of the illumination device. 
     In a first aspect, an embodiment of the present invention provides an LED driving circuit, including a first AC input end, a second AC input end, a driving module, a first protection unit, a first DC output end and a second DC output end. 
     The driving module includes a first input end, a second input end, a first output end and a second output end, and wherein the first input end of the driving module is electrically connected to the first AC input end, the second input end of the driving module is electrically connected to the second AC input end, the first output end of the driving module is electrically connected to the first DC output end, and the second output end of the driving module is electrically connected to the second DC output end; the driving module is configured to convert an AC voltage inputted from the first AC input end and the second AC input end into a DC voltage, and output the DC voltage through the first DC output end and the second DC output end. 
     The first protection unit includes a voltage detection subunit and an abnormality cutoff subunit, and wherein the voltage detection subunit is connected in parallel between two corresponding voltage nodes of the driving module, and the voltage detection subunit is configured to detect a voltage value of the driving module; and the abnormality cutoff subunit is connected in series between the second input end of the driving module and the second AC input end; the first protection unit is configured to cut off a circuit of the driving module when a voltage abnormality of the driving module is detected. 
     Optionally, the driving module includes a rectifying unit and a filtering unit. 
     The rectifying unit includes a first input end, a second input end, an output end and a grounding end, and wherein the first input end of the rectifying unit is the first input end of the driving module, the second input end of the rectifying unit is electrically connected to the second input end of the driving module, and the grounding end of the rectifying unit is electrically connected to a first earth wire. 
     The filtering unit includes a first input end, a second input end, a first output end and a second output end, and wherein the first input end of the filtering unit is electrically connected to the output end of the rectifying unit, the second input end of the filtering unit is electrically connected to the first earth wire, the first output end of the filtering unit is the first output end of the driving module, and the second output end of the filtering unit is the second output end of the driving module. 
     The voltage detection subunit is connected in parallel between the first input end and the second input end of the rectifying unit. 
     Alternatively, the voltage detection subunit is connected in parallel between the first output end and the second output end of the rectifying unit. 
     Alternatively, the voltage detection subunit is connected in parallel between the first output end and the second output end of the filtering unit. 
     Optionally, the voltage detection subunit includes a varistor, and temperature of the varistor increases with voltage. 
     Optionally, the abnormality cutoff subunit includes a temperature fuse. 
     Optionally, the LED driving circuit further includes a spike voltage absorbing unit which is connected between the first AC input end and the second AC input end. 
     Optionally, the spike voltage absorbing unit includes a first capacitor which is connected between the first AC input end and the second AC input end. 
     Optionally, the driving module further includes a rectifying unit, a filtering unit and a voltage regulating unit. 
     The rectifying unit includes a first input end, a second input end, an output end and a grounding end, and wherein the first input end of the rectifying unit is the first input end of the driving module, the second input end of the rectifying unit is electrically connected to the second input end of the driving module, and the grounding end of the rectifying unit is electrically connected to a first earth wire. 
     The filtering unit includes a first input end, a second input end, a first output end and a second output end, and wherein the first input end of the filtering unit is electrically connected to the output end of the rectifying unit, the second input end of the filtering unit is electrically connected to the first earth wire, the first output end of the filtering unit is the first output end of the driving module, and the second output end of the filtering unit is the second output end of the driving module. 
     The voltage regulating unit includes a first input end, a second input end, a first output end and a second output end, and wherein the first input end of the voltage regulating unit is electrically connected to the first output end of the filtering unit, the second input end of the voltage regulating unit is electrically connected to the second input end of the filtering unit, the first output end of the voltage regulating unit is electrically connected to the first DC output end, and the second output end of the voltage regulating unit is electrically connected to the second DC output end. 
     Optionally, the voltage regulating unit includes a first control chip and a transformer. 
     A first end of a primary coil of the transformer is electrically connected to the first output end of the filtering unit through a first diode, and a second end of the primary coil is electrically connected to the second DC output end. 
     A signal input end of the first control chip is electrically connected to the first end of the primary coil of the transformer, and a signal output end of the first control chip is electrically connected to the second output end of the filtering unit; the first control chip is configured to control voltage output by the voltage regulating unit. 
     Optionally, the driving module further includes a frequency detection unit and a switch unit; the first control chip further includes a control signal input end. 
     An input end of the frequency detection unit is electrically connected to the second AC input end, and a control signal output end of the frequency detection unit is electrically connected to the control signal input end of the first control chip and a control end of the switch unit. 
     A first end of the switch unit is electrically connected to the second end of the primary coil of the transformer, and the second end of the switch unit is electrically connected to the first earth wire. 
     Optionally, the LED driving circuit further includes a second protection unit which includes an input end and a grounding end, wherein the input end of the second protection unit is electrically connected to the second input end of the filtering unit; the second protection unit is configured to detect an impedance of the second input end of the filtering unit to ground; the second input end of the filtering unit is connected or disconnected to the ground depending on the detected impedance. 
     In a second aspect, an embodiment of that present invention also provide a light tube including a first pin, a second pin and the LED driving circuit as described in any embodiments of the present invention, wherein the first pin is electrically connected to the first AC input end of the driving circuit, and the second pin is electrically connected to the second AC input end. 
     In a third aspect, an embodiment of the invention also provides an illumination device including a ballast and the light tube as described in any embodiments of the present invention. The ballast includes a first connection end, a second connection end, a first output end and a second output end, and wherein the first connection end and the second connection end of the ballast are connected to a mains, the first output end of the ballast is electrically connected to the first pin of the light tube, and the second output end of the ballast is electrically connected to the second pin of the light tube. 
     In the embodiments of the invention, the LED driving circuit includes a first protection unit. The first protection unit includes a voltage detection subunit and an abnormality cutoff subunit, and wherein the voltage detection subunit is connected in parallel between two corresponding voltage nodes of the driving module, and the voltage detection subunit is configured to detect a voltage value of the driving module; and the abnormality cutoff subunit is connected in series between the second input end of the driving module and the second AC input end; the first protection unit is configured to cut off a circuit of the driving module when a voltage abnormality of the driving module is detected. It can be seen that the first protection unit can detect the high voltage output by the ballast through the voltage detection subunit. When the high voltage is detected for a long time, the first protection unit is capable of cutting off the input circuit of the LED driving circuit by the abnormality cutoff subunit so that the LED driving circuit stops operating, and the LED driving circuit is disconnected from the power grid, thereby disconnecting the LED driving circuit from other devices, which improves the safety of the LED driving circuit and thus the safety of the illumination device. In addition, in the present embodiments of the invention, the LED driving circuit is protected by detecting the abnormal voltage value, and the driving module is disconnected when the LED driving circuit is protected, so that the LED driving circuit is applicable to detect more abnormal conditions, and is compatible with various types of illumination device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram of an LED driving circuit according to an embodiment of the present invention; 
         FIG. 2  is a circuit diagram of another LED driving circuit according to an embodiment of the present invention; 
         FIG. 3  is a circuit diagram of another LED driving circuit according to an embodiment of the present invention; 
         FIG. 4  is a circuit diagram of another LED driving circuit according to an embodiment of the present invention; 
         FIG. 5  is a circuit diagram of another LED driving circuit according to an embodiment of the present invention; 
         FIG. 6  is a circuit diagram of another LED driving circuit according to an embodiment of the present invention; 
         FIG. 7  is a schematic structural diagram of a light tube according to an embodiment of the present invention; and 
         FIG. 8  is a schematic structural diagram of an illumination device according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The invention will be further described in detail with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are for the purpose of explaining the present invention only and are not intended to limit the present invention. It should also be noted that, for ease of description, only some, but not all, of the structures related to the present invention are shown in the drawings. 
     According to an embodiment of the present invention, an LED driving circuit is provided.  FIG. 1  is a circuit diagram of an LED driving circuit according to an embodiment of the present invention. Referring to  FIG. 1 , the LED driving circuit includes a first AC input end, a second AC input end, a driving module  100 , a first protection unit  200 , a first DC output end VO+ and a second DC output end V 0 −. As exemplarily shown in  FIG. 1 , the first AC input end includes two short-circuited connection ends, i.e., a connection end X 1  and a connection end X 2 , and the second AC input end includes two short-circuited connection ends, i.e., a connection end X 3  and a connection end X 4 . 
     The driving module  100  includes a first input end, a second input end, a first output end and a second output end. The first input end of the driving module  100  is electrically connected to the first AC input end. The second input end of the driving module  100  is electrically connected to the second AC input end. The first output end of the driving module  100  is electrically connected to the first DC output end VO+. The second output end of the driving module  100  is electrically connected to the second DC output end VO−. The driving module  100  is configured to convert the AC voltage inputted from the first AC input end and the second AC input end into a DC voltage, and output the DC voltage through the first DC output end VO+ and the second DC output end VO−. 
     The first protection unit  200  includes a voltage detection subunit  210  and an abnormality cutoff subunit  220 . The voltage detection subunit  210  is connected in parallel between two corresponding voltage nodes of the driving module  100  for detecting the voltage value of the driving module  100 . The abnormality cutoff subunit  220  is connected in series between the second input end of the driving module  100  and the second AC input end. The first protection unit  200  is configured to cut off the circuit of the driving module  100  when the voltage abnormality of the driving module  100  is detected. 
     The two corresponding voltage nodes of the driving module  100  refer to nodes of the driving module  100  for transmitting AC voltage or DC voltage. As an example, as shown in  FIG. 1 , the driving module  100  includes a first rectifying subunit DB 1 . The first rectifying subunit DB 1  includes a first input end, a second input end, an output end and a grounding end. The first input end of the first rectifying subunit DB 1  functions as the first input end of the driving module  100 , and the second input end of the first rectifying subunit DB 1  is electrically connected to the second input end of the driving module  100 . The voltage between the first input end of the first rectifying subunit DB 1  and the second input end of the first rectifying subunit DB 1  is an AC voltage, and the voltage between the output end of the first rectifying subunit DB 1  and the grounding end of the first rectifying subunit DB 1  is a DC voltage. Therefore, the first input end of the first rectifying subunit DB 1  and the second input end of the first rectifying subunit DB 1  can be used as the two corresponding voltage nodes, and the output end of the first rectifying subunit DB 1  and the grounding end of the first rectifying subunit DB 1  can be used as the two corresponding voltage nodes. The voltage detection subunit  210  can be connected in parallel between the first input end and the second input end of the first rectifying subunit DB 1  or between the output end and the grounding end of the first rectifying subunit DB 1 . 
     As an example, the first DC output end V 0 + and the second DC output end V 0 − can be connected to LED beads of the light tube.  FIG. 1  exemplarily shows a plurality of LED beads of the light tube which are connected in series. AC voltage output by a ballast is transmitted to the first AC input end and the second AC input end of the LED driving circuit. The ballast outputs high frequency and high voltage (50-100 KHZ, 600-1200V) when starting. After starting, the LED driving circuit can clamp the output voltage of the ballast at the normal working voltage of about 100V. However, in case where the electronic components of the LED driving circuit are damaged or failed or where the LED bead is damaged, the LED driving circuit could not clamp the voltage output by the ballast at the normal working voltage of about 100V. Then the high voltage of 600-1200V output by the ballast will be applied to the whole circuit for a long time until exceeding the stress of the electronic components of the LED driving circuit, so that the electronic components will suffer from overvoltage or overcurrent to generate heat and even being damaged, resulting in fire risk. 
     In the present embodiment of the invention, the voltage detection subunit  210  is connected in parallel between the two corresponding voltage nodes of the driving module  100  to detect the high voltage output by the ballast. When the high voltage is detected for a long time, the abnormality cutoff subunit  220  will be cut off. That is, the abnormality cutoff subunit  220  will cut off the input circuit of the LED driving circuit so that the LED driving circuit stops operating, and the LED driving circuit is disconnected from the power grid, thereby disconnecting the LED driving circuit from other devices, which improves the safety of the LED driving circuit and thus the safety of the illumination device. In addition, in the present embodiments of the invention, the LED driving circuit is protected by detecting the abnormal voltage value, and the driving module  100  is disconnected when the LED driving circuit is protected, so that the LED driving circuit is applicable to detect more abnormal conditions, and is compatible with various types of illumination devices. 
       FIG. 2  is a circuit diagram of another LED driving circuit according to an embodiment of the present invention. Referring to  FIG. 2 , on the basis of the above embodiments, the voltage detection subunit  210  optionally includes a varistor RV 1 . The temperature of the varistor RV 1  increases with the increase of the voltage, and gradually increases under a high voltage. When the ballast is started, the output high voltage of the ballast is remained for a short time, and the temperature of the varistor RV 1  is low. When the output high voltage of the ballast is remained for a long time, the temperature of the varistor RV 1  is high, and the abnormality cutoff subunit  220  is triggered to be cut off. In the present embodiment of the invention, the LED driving circuit has the advantages of simple structure, low cost and easy implementation. 
     Referring to  FIG. 2  again, on the basis of the above embodiments, the abnormality cutoff subunit  220  optionally includes a temperature fuse F 3 . The temperature fuse F 3  is also known as thermal links, and is a temperature-sensing circuit-cutoff device. The temperature fuse F 3  can sense the heat generated by the varistor RV 1  and the temperature of the varistor RV 1 . When the temperature of the varistor RV 1  reaches the working temperature of the temperature fuse F 3 , the temperature fuse F 3  is opened to cut off the input circuit of the LED driving circuit, so that the LED driving circuit stops operating. In the present embodiment of the invention, the LED driving circuit has the advantages of simple structure, low cost and easy implementation. 
     Referring to  FIG. 1  and  FIG. 2 , on the basis of the above embodiments, optionally, the LED driving circuit further includes a spike voltage absorbing unit  300  that is connected between the first AC input end and the second AC input end. The spike voltage absorbing unit  300  is connected between the output lines of the ballast for absorbing the high-frequency and high-voltage spike output by the ballast when the ballast is started, so that the voltage received by the driving module  100  can be maintained within the stress range of the components of the circuit, thereby protecting the electronic components of the driving module  100  and thus further improving the safety of the LED driving circuit. 
     Referring to  FIG. 1  and  FIG. 2  again, on the basis of the above embodiments, the spike voltage absorbing unit  300  optionally includes a first capacitor CX 2  connected between the first AC input end and the second AC input end. The first capacitor CX 2  can pass AC and block DC, and is a non-polarised electronic component resisting high-voltage and high-current impact. When the ballast is started, the high frequency and high voltage is absorbed and coupled by the first capacitor CX 2 , so that the voltage flowing into the rectifying unit of the driving module  100  is greatly reduced (about 400 V). By absorbing the high-frequency and high-voltage spike through the first capacitor CX 2 , the output voltage of the ballast is within the stress range of the electronic components of the LED driving circuit, which advantageously prevents early failure and premature damage of the electronic components caused by high voltage. 
     It should be noted that, in the above embodiments, it is exemplarily shown that the voltage detection subunit  210  of the first protection unit  200  is connected in parallel between the first output end and the second output end of the first rectifying subunit DB 1 , which is not intended to limit the invention. In other embodiments, the voltage detection subunit  210  can be arranged at other positions. The voltage detection subunit  210  of the driving module  100  regarding the connection position thereof will be described below. 
       FIG. 3  is a circuit diagram of another LED driving circuit according to an embodiment of the present invention. Referring to  FIG. 3 , on the basis of the above embodiments, the driving module optionally includes a rectifying unit  110  and a filtering unit  120 . The rectifying unit  110  includes a first input end, a second input end, an output end and a grounding end. The first input end of the rectifying unit  110  functions as the first input end of the driving module, the second input end of the rectifying unit  110  is electrically connected to the second input end of the driving module, and the grounding end of the rectifying unit  110  is electrically connected to a first earth wire. The filtering unit  120  includes a first input end, a second input end, a first output end and a second output end. The first input end of the filtering unit  120  is electrically connected to the output end of the rectifying unit  110 , the second input end of the filtering unit  120  is electrically connected to the first earth wire, the first output end of the filtering unit  120  functions as the first output end of the driving module, and the second output end of the filtering unit  120  functions as the second output end of the driving module. 
     The rectifying unit  110  can be a rectifying circuit unit commonly used in the art, such as a bridge rectifier circuit unit. Optionally, the rectifying unit  110  includes a first rectifying subunit DB 1  and a second rectifying subunit DB 2 . The first rectifying subunit DB 1  includes two input ends (both input ends are denoted by AC) and two output ends denoted by V+ and V−, respectively. The two input ends of the first rectifying subunit DB 1  are electrically connected to a first AC input end (denoted by L 1  and N 1 , as shown in  FIG. 3 ) and a second AC input end (which includes two short-circuited connection ends denoted by AC 2  and AC 3 , respectively, as shown in  FIG. 3 ) of the LED driving circuit, respectively. One of the two output ends of the first rectifying subunit DB 1  is electrically connected to the first input end of the filtering unit  120 , and the other is electrically connected to the first earth wire. The two input ends (both input ends are denoted by AC) of the second rectifying subunit DB 2  are both electrically connected to the second AC input end of the LED driving circuit. One of the two output ends (denoted by V+ and V− respectively) of the second rectifying subunit DB 2  is electrically connected to the first input end of the filtering unit  120 , and the other is electrically connected to the first earth wire. 
     Optionally, the filtering unit  120  includes a second capacitor C 1 , a third capacitor C 2 , a first inductor L 1 , a second inductor L 2 , a first resistor R 10 , and a second resistor R 7 . The second capacitor C 1  is electrically connected between the output end of the rectifying unit  110  and the first earth wire, and the third capacitor C 2  is electrically connected between the first output end and the second output end of the filtering unit  120 . The second output end of the filtering unit  120  is electrically connected to the second earth wire. The first inductor L 1  and the first resistor R 10  are connected in parallel. The first end of the first inductor L 1  is electrically connected to the second input end of the filtering unit  120 , and the second end of the first inductor L 1  is electrically connected to the second earth wire. The second inductor L 2  and the second resistor R 7  are connected in parallel. The first end of the second inductor L 2  is electrically connected to the first output end of the rectifying unit  110 , and the second end of the second inductor L 2  is electrically connected to the first output end of the filtering unit  120 . The filtering unit  120  functions to eliminate EMI interference in the circuit. 
     Referring to  FIG. 3  again, in one embodiment of the present invention, optionally, the voltage detection subunit  210  is connected in parallel between the first output end and the second output end of the rectifying unit  110 . That is, the voltage detection subunit  210  is connected in parallel between the first output end and the second output end of the second rectifying subunit DB 2 . The second rectifying subunit DB 2  functions to rectify and output the AC voltage inputted thereto, and the voltage outputted from the second rectifying subunit DB 2  increases as the AC voltage inputted thereto. Therefore, the input AC voltage can be detected by detecting the output voltage of the second rectifying subunit DB 2 . 
       FIG. 4  is a circuit diagram of another LED driving circuit according to an embodiment of the present invention. Referring to  FIG. 4 , in an embodiment of the present invention, optionally, the voltage detection subunit  210  is connected in parallel between the first input end and the second input end of the rectifying unit  110 . That is, the voltage detection subunit  210  is connected in parallel between the first input end and the second input end of the first rectifying unit  110  DB 1 , so as to detect the inputted AC voltage. 
       FIG. 5  is a circuit diagram of another LED driving circuit according to an embodiment of the present invention. Referring to  FIG. 5 , in an embodiment of the present invention, optionally, the voltage detection subunit  210  is connected in parallel between the first output end and the second output end of the filtering unit  120 . The filtering unit  120  functions to filter the signal output by the rectifying unit  110 . If the input AC voltage is higher, the voltage output by the second rectifying subunit DB 2  will be higher, and then the voltage output by the filtering unit  120  will be higher. In other words, the greater the output voltage of the filtering unit  120  detected by the voltage detection subunit  210  is, the greater the input AC voltage will be. Therefore, the input AC voltage can be detected by detecting the output voltage of the filtering unit  120 . 
       FIG. 6  is a circuit diagram of another LED driving circuit according to an embodiment of the present invention. Referring to  FIG. 6 , on the basis of the above embodiments, optionally, the driving module further includes a voltage regulating unit  130 . The voltage regulating unit  130  includes a first input end, a second input end, a first output end and a second output end. The first input end of the voltage regulating unit  130  is electrically connected to the first output end of the filtering unit  120 , the second input end of the voltage regulating unit  130  is electrically connected to the second output end of the filtering unit  120 , the first output end of the voltage regulating unit  130  is electrically connected to the first DC output end VO+, and the second output end of the voltage regulating unit  130  is electrically connected to the second DC output end VO−. The voltage regulating unit  130  is configured to convert the DC voltage inputted from the first input end and the second input end thereof into another one or more DC voltage. 
     Referring to  FIG. 6  again, optionally, the voltage regulating unit  130  includes a first control chip U 1  and a transformer. A first end of a primary coil of the transformer is electrically connected to the first output end of the filtering unit  120  through a first diode D 3 , and a second end of the primary coil is electrically connected to the second DC output end VO−. A secondary coil of the transformer functions to supply power to the first control chip U 1 . A signal input end (hereinafter, drain end indicated as Drain) of the first control chip U 1  is electrically connected to the first end of the primary coil of the transformer, a signal output end of the first control chip U 1  is electrically connected to the second output end of the filtering unit  120 . The first control chip U 1  is configured to control the output voltage of the voltage regulating unit  130 . 
     Specifically, the first control chip U 1  can be a PWM control chip. Due to the energy storage effect of the transformer T 1 , the node voltage in the first control chip U 1  will slowly rise. By SNP sampling and comparing with the reference voltage in the first control chip U 1 , when the reference voltage is reached, the first control chip U 1  will send a PWM signal to cut off the switch transistor between the drain end Drain and the grounding end GND. The anode of the first diode D 3  and the second earth wire are disconnected. Due to the energy storage effect of the transformer T 1 , the load will be further charged through the first diode D 3 . When the voltage for the resistance in the first control chip U 1  is 0, the first control chip U 1  finishes one work cycle and starts the next cycle. The transformer T 1  has the function of preventing current change, so that if the switching frequency of the switch transistor in the first control chip U 1  is high enough, for example, up to 50K-80K, the current can be made stable enough to allow the LED light tube to work in flicker-free. 
     Referring to  FIG. 6  again, on the basis of the above embodiments, optionally, the driving module further includes a frequency detection unit  140  and a switch unit Q 2 . The first control chip U 1  further includes a control signal input end EN. An input end of the frequency detection unit  140  is electrically connected to the second input end of the rectifying unit  110 . The control signal output end of the frequency detection unit  140  is electrically connected to the control signal input end EN of the first control chip U 1  and a control end of the switch unit Q 2 . A first end of the switch unit Q 2  is electrically connected to the second end of the primary coil of the transformer, and the second end of the switch unit Q 2  is electrically connected to the first earth wire. 
     The working process of the LED driving circuit will be exemplarily described here. The ballast is started and outputs high frequency and high voltage of 50-100 KHZ and 600-1200V for 100-600 milliseconds, during which, the high-frequency and high-voltage current first flows through the circuit anterior to the rectifying unit  110 . The first capacitor CX 2  is connected anterior to the rectifying unit  110 . In other words, the first capacitor CX 2  is directly connected between the output lines of the ballast. The first capacitor CX 2  can pass the alternating current and block the direct current, and can resist the high-voltage and high-current impact without polarity. When the ballast is started, the high frequency and high voltage is absorbed and coupled by the first capacitor CX 2 , and flows into the rectifying unit  110 . The voltage is greatly reduced (about 400V). After being absorbed by the first capacitor CX 2 , the high frequency and high voltage is within the stress range of the electronic components of the LED driving module, which advantageously prevents early failure and premature damage of the electronic components of the LED driving module caused by high voltage. 
     The input AC current flows through the abnormality cutoff subunit  220 , and is then absorbed and coupled by the first capacitor CX 2 , and flows into the first rectifying subunit DB 1  and the second rectifying subunit DB 2  of the rectifying unit  110  to be rectified, whereby the high-frequency AC is converted into a direct current. The voltage detection subunit  210  is posterior to the second rectifying subunit DB 2 , the voltage detection subunit  210  does not work at a normal voltage (about 300-400 V). The current is filtered through the second capacitor, the third capacitor, the first inductor, and the second inductor, and becomes a stable direct current through the fourth capacitor CD 1  (as an example, the fourth capacitor CD 1  is an electrolytic capacitor), which is output via the first DC output end VO+, and input to the circuit of the LED driving circuit via the second DC output end VO−, and then flows through the second diode D 5  and the transformer T 1 . If the frequency detection unit  140  detects the high frequency and high voltage of 50-100 KHZ and 600-1200V under the working mode of the ballast, the switch unit Q 2  is directly turned on (Q 1 -D as shown in  FIG. 6  is used to indicate the connection point of the transformer T 1  and the switch unit Q 2 , and HIF is used to indicate the connection point of the frequency detection unit  140  and the second input end of the rectifying unit  110 ), the first control chip U 1  does not work, the current flows through the switch unit Q 2  to the ground, and then to the first earth wire of the rectifying unit  110 , thereby forming a complete circuit for the LED driving circuits. If the frequency detection unit  140  detects a normal working voltage of about 100V, the first control chip U 1  works via the control signal input end EN to adjust the output DC voltage, thereby forming a BUCK circuit. 
     In case where the LED driving circuit is out of the service life thereof, or where the LED driving circuit is opened due to the damaged electronic component or the damaged LED bead, the LED driving circuit cannot work normally and clamp the voltage, so that the ballast will output high frequency and high voltage. The high frequency and high voltage flows through the first rectifying subunit DB 1  and the second rectifying subunit DB 2 , with the DC voltage being 600-1200V. At this time, the varistor RV 1  of the voltage detection subunit  210  detects the high voltage and generates heat. When the heat and the temperature reaches the working temperature of the temperature fuse F 3  of the abnormality cutoff subunit  220 , the temperature fuse F 3  is opened, thereby cutting off the input circuit of the LED driving circuit. The LED light tube and the circuit stop working. Therefore, the embodiments of the invention prevent the high frequency and high voltage output by the ballast from exceeding the stress of the electronic components, thereby avoiding over-voltage, over-current, heat generation and damage of the electronic components. The fire risk is avoided and the safety of the LED driving circuit is improved. 
     Referring to  FIG. 6  again, on the basis of the above embodiments, optionally, the LED driving circuit further includes a second protection unit  400  which includes an input end and a grounding end. The input end of the second protection unit  400  is electrically connected to a second input end of the filtering unit  120 . The second protection unit  400  is configured to detect an impedance of the second input end of the filtering unit  120  to ground. The second input end of the filtering unit  120  is connected or disconnected from ground depending on the detected impedance. For example, when an operator gets an electric shock, the resistance of the human body at the contact is connected to the circuit of the LED driving circuit. Specifically, a circuit is formed from the first AC input end, the rectifying unit  110 , the filtering unit  120  to the human body. The impedance of the second input end of the filtering unit  120  to the first earth wire is abnormal. When the second protection unit  400  detects the impedance abnormality of the second input end of the filtering unit  120  to the first earth wire, the input end of the second protection unit  400  is disconnected from the ground, that is, the second input end of the first filtering unit  120  is disconnected from the first earth wire, and the circuit from the live wire L, the rectifying unit  110 , the first filtering unit  120  to the human body is disconnected, thereby realizing electric shock protection and ensuring personal safety. Since the input end of the second protection unit  400  is disconnected from the grounding end, the circuit formed through the electric shock of the human body is cut off, thereby realizing electric shock protection. 
     On the basis of the embodiments described above, optionally, the second protection unit  400  includes a second control chip U 2 , a third resistor R 1 , a fourth resistor R 2 , a fifth resistor R 3 , a sixth resistor R 4 , a seventh resistor R 5 , an eighth resistor R 6 , a ninth resistor R 7 , a tenth resistor R 8 , an eleventh resistor R 9  and a twelfth resistor RS 1  (a sampling resistor). The second control chip U 2  includes a power input end Vcc, a first voltage monitoring end VS, a second voltage monitoring end TRG, a current monitoring end CS, an isolation input end DRN, and a grounding end GND. The first power input end Vcc is electrically connected to the output end of the rectifying unit  110  through the third resistor R 1 , the fourth resistor R 2  and the fifth resistor R 3 . The first voltage monitoring end VS is electrically connected to the isolation input end DRN through the sixth resistor R 4 , the seventh resistor R 5  and the eighth resistor R 6 . The current monitoring end CS is electrically connected to the first earth wire through the twelfth resistor RS 1 . The second control chip U 2  can control the circuit between the isolation input end DRN thereof and the grounding end GND thereof to be turned on or off (Vbus− in  FIG. 6  is used to indicate the connection point between the isolation input end DRN and the second input end of the filtering unit  120 , and by Vbus+ is used to indicate the connection point between the second protection unit  400  and the second output end of the rectifying unit  110 ). 
     Illustratively, the first pow input end Vcc normally receives the working voltage, and when the light tube works normally, the current monitoring end CS of the second control chip U 2  constantly collects the current between the second input end of the filtering unit  120  and the first earth wire (Vbus− in  FIG. 6  is used to indicate the signal at the second input end of the filtering unit  120 ), and the first voltage monitoring end VS and the second voltage monitoring end TRG constantly collect the voltage between the second input end of the filtering unit  120  and the first earth wire, thereby calculating the power grid impedance between the second input of the filtering unit  120  and the first earth wire. If the impedance is determined to be within the normal range, the isolation input end DRN and the current monitoring end Cs are connected, and the current flows through the sampling resistor at the current monitoring end Cs and is connected to the first earth wire. On the contrary, if the impedance is determined to be within the abnormal range, the isolation input end DRN is disconnected from the current monitoring end Cs, and the second input end of the filtering unit  120  is disconnected from the first earth wire, thereby realizing electric shock protection and ensuring personal safety. 
     In the embodiments of the invention, the LED driving circuit itself can realize the electric shock protection, and once the electric shock is detected, the whole circuit can be cut off, thereby reducing the potential risk when a user uses the light tube, and thus further improving the safety of the LED driving circuit. 
     According to an embodiment of the present invention, a light tube is further provided, which can be, for example, an LED straight tube light or a U tube light.  FIG. 7  is a schematic structural diagram of a light tube according to an embodiment of the present invention. Referring to  FIG. 7 , the light tube includes a first pin A, a second pin B and the LED driving circuit  10  according to any embodiments of the present invention. The first pin A is electrically connected to a first AC input end of the driving circuit, and the second pin B is electrically connected to the second AC input end. The light tube according to the embodiment of the present invention includes the LED driving circuit  10  according to any embodiments of the present invention as described above, and therefore the technical principle and the advantages thereof will not be described in detail. 
     According to an embodiment of the present invention, an illumination device is further provided.  FIG. 8  is a schematic structural diagram of an illumination device according to an embodiment of the present invention. Referring to  FIG. 8 , the illumination device includes a ballast  2  and a light tube  1  according to any embodiments of the present invention. The ballast  2  includes a first connection end L, a second connection end N, a first output end, and a second output end. The first connection end L and the second connection end N of the ballast  2  are connected to the mains (e.g., AC120-277V/60 HZ). The first output end of the ballast  2  is electrically connected to the first pin of the light tube, and the second output end of the ballast  2  is electrically connected to the second pin of the light tube. The ballast  2  includes at least one of an electronic ballast and an inductive ballast. The illumination device according to the embodiment of the present invention includes the LED driving circuit according to any embodiments of the present invention as described above, and therefore the technical principle and the advantages thereof will not be described in detail. 
     It should be noted that the above embodiments only show the preferred embodiments of the present invention and the preferred technical principle thereof. Those skilled in the art will appreciate that the present invention is not limited to the specific embodiments described herein, and the various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited only to the above embodiments, but can include other equivalent embodiments without departing from the inventive concept. The scope of the invention is determined by the scope of the appended claims.