Abstract:
A linear light-emitting diode (LED)-based solid-state lamp comprises an LED driving circuit, LED arrays, at least one rectifier, and an electric current flow control module. The LED driving circuit comprises a control loop compensation device with a control loop correction signal to precisely control an electric current to flow into the LED arrays. The electric current flow control module uses the control loop correction signal in a way that it detects and determines if the linear LED-based solid-state lamp is operated in a normal mode or in an electric shock hazard mode. When an electric shock hazard is identified, the electric current flow control module shuts off a return current flow from the LED arrays to reach the at least one rectifier, thus eliminating an overall through-lamp electric shock current. The scheme can effectively prevent a through-lamp electric shock from occurring during relamping or maintenance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present disclosure is part of a continuation-in-part (CIP) application of U.S. patent application Ser. No. 15/444,536, filed 28 Feb. 2017 and currently pending, which is a CIP application of U.S. patent application Ser. No. 15/362,772, filed 28 Nov. 2016 and currently pending, which is a CIP application of U.S. patent application Ser. No. 15/225,748, filed 1 Aug. 2016 and currently pending, which is a CIP application of U.S. patent application Ser. No. 14/818,041, filed 4 Aug. 2015 and issued as U.S. Pat. No. 9,420,663 on 16 Aug. 2016, which is a CIP application of U.S. patent application Ser. No. 14/688,841, filed 16 Apr. 2015 and issued as U.S. Pat. No. 9,288,867 on 15 Mar. 2016, which is a CIP application of U.S. patent application Ser. No. 14/465,174, filed 21 Aug. 2014 and issued as U.S. Pat. No. 9,277,603 on 1 Mar. 2016, which is a CIP application of U.S. patent application Ser. No. 14/135,116, filed 19 Dec. 2013 and issued as U.S. Pat. No. 9,163,818 on 20 Oct. 2015, which is a CIP application of U.S. patent application Ser. No. 13/525,249, filed 15 Jun. 2012 and issued as U.S. Pat. No. 8,749,167 on 10 Jun. 2014. Contents of the above-identified applications are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND 
     Technical Field 
       [0002]    The present disclosure relates to linear light-emitting diode (LED) lamps and more particularly to a linear LED lamp with electric shock detection and prevention, configured to shut off an accidental LED current to reach ground through a person&#39;s body. 
       Description of the Related Art 
       [0003]    Solid-state lighting from semiconductor light-emitting diodes (LEDs) has received much attention in general lighting applications today. Because of its potential for more energy savings, better environmental protection (no hazardous materials used), higher efficiency, smaller size, and much longer lifetime than conventional incandescent bulbs and fluorescent tubes, the LED-based solid-state lighting will be a mainstream for general lighting in the near future. As LED technologies develop with the drive for energy efficiency and clean technologies worldwide, more families and organizations will adopt LED lighting for their illumination applications. In this trend, the potential safety concerns such as risk of electric shock become especially important and need to be well addressed. 
         [0004]    In today&#39;s retrofit application of a linear LED tube (LLT) lamp to replace an existing fluorescent tube, consumers may choose either to adopt a ballast-compatible LLT lamp with an existing ballast used to operate the fluorescent tube or to employ an AC mains-operable LED lamp by removing/bypassing the ballast. Either application has its advantages and disadvantages. In the former case, although the ballast consumes extra power, it is straightforward to replace the fluorescent tube without rewiring, which consumers may have a first impression that it is the best alternative to fluorescent tube lamps. But the fact is that total cost of ownership for this approach is high regardless of very low initial cost. For example, the ballast-compatible LLT lamps work only with particular types of ballasts. If the existing ballast is not compatible with the ballast-compatible LLT lamp, the consumers will have to replace the ballast. Some facilities built long time ago incorporate different types of fixtures, which requires extensive labor for both identifying ballasts and replacing incompatible ones. Moreover, a ballast-compatible LLT lamp can operate longer than the ballast. When an old ballast fails, a new ballast will be needed to replace in order to keep the ballast-compatible LLT lamps working. Maintenance will be complicated, sometimes for lamps and sometimes for ballasts. The incurred cost will preponderate over the initial cost savings by changeover to the ballast-compatible LLT lamps for hundreds of fixtures throughout a facility. When the ballast in a fixture dies, all the ballast-compatible tube lamps in the fixture go out until the ballast is replaced. In addition, replacing a failed ballast requires a certified electrician. The labor costs and long-term maintenance costs will be unacceptable to end users. From energy saving point of view, a ballast constantly draws power, even when the ballast-compatible LLT lamps are dead or not installed. In this sense, any energy saved while using the ballast-compatible LLT lamps becomes meaningless with the constant energy use by the ballast. In the long run, ballast-compatible LLT lamps are more expensive and less efficient than self-sustaining AC mains-operable LLT lamps. 
         [0005]    On the contrary, an AC mains-operable LLT lamp does not require a ballast to operate. Before use of an AC mains-operable LLT lamp, the ballast in a fixture must be removed or bypassed. Removing or bypassing the ballast does not require an electrician and can be replaced by end users. Each AC mains-operable LLT lamp is self-sustaining. If one AC mains-operable tube lamp in a fixture goes out, other lamps in the fixture are not affected. Once installed, the AC mains-operable LLT lamps will only need to be replaced after 50,000 hours. In view of above advantages and disadvantages of both ballast-compatible LLT lamps and AC mains-operable LLT lamps, it seems that market needs a most cost-effective solution by using a universal LLT lamp that can be used with the AC mains and is compatible with an electronic ballast so that LLT lamp users can save an initial cost by changeover to such a universal LLT lamp followed by retrofitting the lamp fixture to be used with the AC mains when the ballast dies. 
         [0006]    In the U.S. patent application Ser. No. 14/688,841, filed Apr. 16, 2015, two shock prevention switches and an all-in-one driving circuit are adopted in an LLT lamp such that AC power from either an electronic ballast or the AC mains can operate the lamp without operational uncertainty and electric shock hazards. In other words, no matter what a lamp fixture is configured as the AC mains or an electronic ballast compatible fashion, the LLT lamp automatically detects configurations and works for either one. All of such LLT lamps, no matter whether AC mains-operable or ballast compatible, are electrically wired as double-ended and have one construction issue related to product safety and needed to be resolved prior to wide field deployment. This kind of LLT lamps, if no shock prevention scheme is adopted in, always fails a safety test, which measures a through-lamp electric shock current. Because an AC-mains voltage applies to both opposite ends of the tube when connected to a power source, the measurement of current leakage from one end to the other consistently results in a substantial current flow, which may present a risk of an electric shock during re-lamping. Due to this potential shock risk to the person who replaces the LLT lamps in an existing fluorescent tube fixture, Underwriters Laboratories (UL) uses its safety standard, UL 935, Risk of Shock During Relamping (Through Lamp), to do a current leakage test and to determine if the LLT lamps meet the consumer safety requirement. Although the LLT lamps used with an electronic ballast can pass the current leakage test, some kinds of electric shock hazards do exist. Experimental results show that the skin of the person who touches an exposed bi-pin may be burned due to such an electric shock. Fortunately, a mechanism of double shock prevention switches used in applications with the AC mains is also effective in applications with the ballasts to prevent the electric shock from occurring, thus protecting consumers from such a hazard, no matter whether input voltage is from the AC mains or the electronic ballast. Therefore, a universal LLT lamp that can work with either the AC mains or the electronic ballast makes sense. The effectiveness of using double shock prevention switches for applications in the AC mains has been well addressed in U.S. Pat. No. 8,147,091, issued on Apr. 3, 2012. However, a conventional shock prevention switch has an inherent issue related to an electric arc when operated with an electronic ballast. Unlike an AC voltage of 120 or 277 V/50-60 Hz from the AC mains, the output AC voltage and current from the electronic ballast presents a negative resistance characteristic. The feature that originally supports a fluorescent tube to function properly becomes extremely detrimental to the conventional shock prevention switch due to the electric arc likely occurring between two electrical contacts that have a high electric potential difference with a high frequency, such as 600 V/50 kHz. Once a consumer fails to follow installation instructions to install or uninstall linear LED tube lamps such that one of two ends of the tube lamp is in the fixture socket connected to a powered electronic ballast, and the other end is tweaked to connect to or disconnect from the associated socket, an internal arcing may occur between the electrical contacts in the associated switch. The arcing even in a short period such as several seconds can generate high heat, burning and melting electrical contacts and neighboring plastic enclosures, creating a fire hazard. The AC voltage of 120 or 277 V/50˜60 Hz from the AC mains does not have such an issue because its voltage is relatively low compared with the ballast output voltage of 600 V. Moreover, the AC frequency of 60 Hz automatically extinguishes an arc every 1/60 seconds, if existed. That is why a utility switch can be used in an electrical appliance to turn power on and off without any problem. However, when used with the electronic ballast, the electrical contacts used in the conventional shock prevention switch can easily be burned out due to the high-voltage and high-frequency arcing introduced between each gap of each pair of the electrical contacts in the conventional shock prevention switch when someone tries to abusively tweak to remove the tube lamp from the fixture with the ballast that has a power on it. Although such a situation is rare, an internal arcing, if occurred, does cause burning and even welding of the electrical contacts and melting of the plastic enclosure, so called internal fire, creating consumer safety issues. 
         [0007]    Today, such LLT lamps are mostly used in a ceiling light fixture with a wall-mount power switch. The ceiling light fixture could be an existing one used with fluorescent tubes but retrofitted for LLT lamps or a specific LLT lamp fixture. The drivers that provide a proper voltage and current to LED arrays could be internal or external ones. Not like LLT lamps with an external driver that is inherently electric-shock free if the driver can pass a dielectric withstand test used in the industry, LLT lamps with an internal driver could have a shock hazard during relamping or maintenance, when the substantial through-lamp electric shock current flows from any one of AC voltage inputs through the internal driver connecting to LED arrays to the earth ground. Despite this disadvantage, LLT lamps with the internal driver still receive wide acceptance because they provide a stand-alone functionality and an easy retrofit for an LLT lamp fixture. As consumerism develops, consumer product safety becomes extremely important. Any products with electric shock hazards and risk of injuries or deaths are absolutely not acceptable for consumers. However, commercially available LLT lamps with internal drivers, single-ended or double-ended, fail to provide effective solutions to the problems of possible electric shock and internal arcing and fire. 
         [0008]    In the prior art mentioned above, the double shock protection switches with mechanical actuation mechanisms protruding outwards from both ends of the LLT lamp are proposed to be used in the LLT lamp. However, a length control of the LLT lamp becomes critical to operate the LLT lamp because sometimes the double shock protection switches may not be actuated by the mechanical actuation mechanisms. Also, the conventional LLT lamp is so vulnerable because it may cause internal fire if consumers abusively tweak the mechanical actuation mechanisms at both ends of the LLT lamp operable with an electronic ballast during relamping. It is therefore the purpose of the present disclosure to disclose an electronic approach to electric shock detection and prevention, to be used in the LLT lamp to eliminate above-mentioned electric shock and internal fire hazards and to work more reliably to protect consumers. 
       SUMMARY 
       [0009]    A linear light-emitting diode (LED)-based solid-state lamp comprising two lamp bases respectively connected to two ends of a housing, each lamp base comprising at least one electrical conductor connecting to a lamp fixture socket; at least one rectifier; an LED driving circuit; LED arrays; and an electric current flow control module, is used to replace a fluorescent tube or a conventional LED tube lamp without the electric current flow control module in an existing lamp fixture. The LED driving circuit comprises a control loop compensation device that is originally used to precisely control a closed-loop electric current to flow into the LED arrays. The electric current flow control module uses the same control loop compensation device in a way that it detects an electric shock and determines if the LED-based solid-state lamp is operated in a normal mode or in an electric shock hazard mode. When an installer touches an exposed at least one electrical conductor on a lamp base in an electric shock hazard, the electric current flow control module detects such an electric shock hazard and shuts off a return current flow from the LED arrays to reach the at least one rectifier, thus eliminating an overall through-lamp electric shock current. 
         [0010]    The electric current flow control module comprises an electric shock detection module, a timer and power-up control, a logic control module, a switch control device, and at least one switch configured to connect or disconnect the electric current return from the LED arrays. The at least one switch is connected between the LED arrays and the at least one rectifier. When the control loop compensation device sends a control loop correction signal to the electric current flow control module, the electric shock detection module detects if an electric shock occurs. Because an input voltage to the LED driving circuit decreases when such an electric shock occurs whereas the LED driving circuit is designed to provide the LED arrays with a predetermined current over a wide range of the input voltages, a voltage drop due to the electric shock causes a closed-loop current control signal to vary in response to the electric shock. Therefore, the control loop correction signal from the control loop compensation device can be used to detect the electric shock that occurs at an exposed at least one electrical conductor. The electric current flow control module controls the at least one switch to connect or disconnect the electric current flow over the at least one switch, thus turning on or off the power delivering to the LED arrays. The timer and power-up control manages initial timing sequences in the electric current flow control module to enable or disable power to deliver into the electric shock detection module and the logic control module in order to reduce its power consumption and current to meet maximum leakage current requirement. The logic control module in the electric current flow control module manages several electric shock scenarios and maintains the at least one switch in its “on” or “off” state even after power is removed from the timer and power-up control. For instance, once the electric shock is detected when the first bi-pin in LLT lamp is inserted in a socket and the second bi-pin is exposed and touched by an installer, the logic control module maintains the at least one switch in “off” state until the exposed at least one electrical conductor is removed from the installer and normally installed in the lamp fixture socket receiving a normal AC voltage. When the electric shock detection module detects no electric shock, the electric current flow control module controls the at least one switch to continue “on”, thus the electric current being able to continue to flow out from the LED arrays. The scheme can effectively reduce a risk of electric shock hazard to users during relamping or maintenance. 
         [0011]    The LED driving circuit further comprises a Buck control circuit comprising a power factor correction (PFC) and control device, an electronic switch with its on and off controlled by the PFC and control device, an inductor with its current charging and discharging controlled by the electronic switch, and a diode. The control loop compensation device is always connected at a low electric potential side along an LED current path with a low electric potential terminal of the control loop compensation device directly connecting to the at least one rectifier through the at least one switch in the electric current flow control module. 
         [0012]    Although configurations of a Buck control circuit may be different for different designs, the control loop compensation device originally working with the Buck control circuit can effectively provide a control loop correction signal for the electric current flow control module to detect the electric shock and manage to shut off the electric shock current. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Non-limiting and non-exhaustive embodiments of the present disclosure are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various figures unless otherwise specified. 
           [0014]      FIG. 1  is an embodiment of an LLT lamp installed in lamp fixture sockets connected with AC power sources according to the present disclosure. 
           [0015]      FIG. 2  is an embodiment of an LED driving circuit configured to work with an electric current flow control module to detect an electric shock according to the present disclosure. 
           [0016]      FIG. 3  is another embodiment of an LED driving circuit configured to work with an electric current flow control module to detect electric shock current according to the present disclosure. 
           [0017]      FIG. 4  is an embodiment of an electric shock detection module and a logic control module configured to work with either an electronic ballast or AC mains. 
           [0018]      FIG. 5  is timing sequences provided by a timer and power-up control. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIG. 1  is an embodiment of an LLT lamp installed in lamp fixture sockets connected with alternate current (AC) sources according to the present disclosure. The LLT lamp  500  comprises a housing having two ends; two lamp bases  660  and  760  each having at least one electrical conductor  250  and  350  at each end of the housing; an electric current flow control module  700 ; a pair of electrical contacts  410  and  420  of at least one switch  400  controlled by the electric current flow control module  700 ; at least one rectifier  603  comprising diodes  611 ,  612 ,  613 , and  614  interconnected at ports  402 ,  404 ,  503 , and  504 ; an LED driving circuit  100  having a first and a second inputs  503  and  420 ; and LED arrays  214  disposed between the two ends of the housing with the LED arrays  214  connected to the LED driving circuit  100 . The LLT lamp  500  may further comprise an interface module  251  and  351  for each lamp base configured to work with an electronic ballast for maximum compatibility. The interface module may comprise a resistor, a resistor in parallel with capacitor, a jumper, or simply a passing-through connection such as a direct connection between a connection point  401  and the interconnection port  402  for the interface module  251  and a direct connection between a connection point  405  and the interconnection port  404  for the interface module  351 . In the context followed, such direct connections will be used for simplicity unless otherwise specified. Please note that neither of the interface modules  251  and  351  includes a fuse or any EMI (electro-magnetic interference) filters. 
         [0020]    The LED driving circuit  100  comprises a Buck control circuit  101  and a control loop compensation device  120  connected to the Buck control circuit  101 , which is further connected to the LED arrays  214 . When the at least one electrical conductor  250  and the at least one electrical conductor  350  in each lamp base are respectively inserted into the lamp fixture sockets  810  and  820 , the at least one rectifier  603  receives AC power through the at least one electrical conductors  250  and  350  at each end of the housing and converts into a DC (direct current) voltage to supply the LED driving circuit  100 . A normal LED current will flow into the LED arrays  214  and return to the Buck control circuit  101 . The control loop compensation device  120  receives a signal from the Buck control circuit  101  and maintains a voltage signal at a port  109  connecting to electric current flow control module  700 . Because the at least one electrical conductor  250  and the at least one electrical conductor  350  in each lamp base are inserted into the lamp fixture sockets  810  and  820 , the at least one rectifier  603  receives a normal input AC voltage and converts into a DC voltage without a compromise. The Buck control circuit  101  delivers a current equal to a preset value to the LED arrays  214 . In this case, the voltage signal appearing at the port  109  relative to ground represents a voltage value in a normal mode. The electric current flow control module  700  receives the voltage signal appearing at the port  109 , determines that no electric shock occurs, and controls the at least one switch  400  to turn on through a control link  110  such that the electrical contacts  410  and  420  of the at least one switch  400  are electrically connected. Whereas the at least one switch  400  is on, the electric current returned from the LED arrays  214  and the Buck control circuit  101  can flow back to the at least one rectifier  603  to complete a power transfer. 
         [0021]    When either one of the at least one electrical conductor  250  and the at least one electrical conductor  350  in each lamp base is inserted into the lamp fixture sockets  810  or  820  that is connected with “L” of AC mains, the LLT lamp  500  does not light up but is live and energized, meaning that there is an electric shock hazard. If an installer touches the exposed at least one electrical conductor  250  or at least one electrical conductor  350  in each lamp base without the at least one switch  400  in place to control the current returned from the LED arrays  214 , an electric shock current can flow from the LED arrays  214  through the Buck control circuit  101  and the at least one switch  400  to reach the at least one rectifier  603 , further flowing to earth ground through the installer&#39;s body, creating an electric shock hazard. However, when such a situation occurs, the at least one rectifier  603  receives a compromised AC voltage according to a divided voltage because a human body is analogous to a 500 ohm-resistor. When a DC voltage provided by the at least one rectifier  603  is not as high as a normal DC voltage, an electric current provided to drive the LED arrays  214  by the Buck control circuit  101  is lower than a preset value, the same as the electric current returned from the LED arrays  214  to the Buck control circuit  101 . The Buck control circuit  101  detects a current decrease and sends a correction signal internally to compensate the current decrease. This forms a closed control loop. The control loop compensation device  120  receives the correction signal from the Buck control circuit  101  and maintains the correction voltage signal at the port  109 . Thus, the electric current flow control module  700  can detect electric shock and control the at least one switch  400  through the control link  110  to turn off an electrical connection between the electrical contacts  410  and  420  of the at least one switch  400 . Thus, the electric shock current is blocked, no substantial leakage current possibly flowing out to the exposed at least one conductor on either lamp base. As can be seen in  FIG. 1 , two sockets in each of the external fixture lamp sockets  810  and  820  are shunted, meaning that as long as both the at least one electrical conductor  250  in the lamp base  660  and the at least one electrical conductor  350  in the lamp base  760  connect to the AC power sources, the LLT lamp  500  can get a power to operate. Furthermore, as long as an operating current that operates the electric current flow control module  700  is within a certain limit specified by UL standard  935 , the LLT lamp  500  can be deemed safe for users because a through-lamp electric current is restricted to the operating current of the electric current flow control module  700  rather than a substantial current flow returned from the LED arrays  214  once the electric shock occurs. 
         [0022]      FIG. 2  is an embodiment of an LED driving circuit configured to work with an electric current flow control module to detect an electric shock according to the present disclosure. The at least one rectifier  603  connecting to an AC power source, either the AC mains or an electronic ballast, converts an AC into a DC voltage. The LED driving circuit  100  comprises a Buck control circuit, connecting to the at least one rectifier  603 , comprising an input filter  102  used to filter the input voltage and to suppress EMI noise created in the LED driving circuit  100 , a power factor correction (PFC) and control device  103 , a Buck converter  200  in communicating with the PFC and control device  103 , a switch  201  controlled by the PFC and control device  103 , an output capacitor  105  in parallel with a resistor  106  connected to the Buck converter  200  to build up an output voltage and to power the LED arrays  214 , a current sensing device  107 , and a voltage feedback module  300  extracting partial energy from the output voltage to sustain the PFC and control device  103 . The at least one rectifier  603  has four input/output ports, among which a high electric potential appears at the input/output port  503 , and a low electric potential appears at the input/output port  504  respectively connecting to the high side and the low side of the input filter  102  with the low electric potential port  504  as a common ground. The LED driving circuit  100  further comprises a control loop compensation device  120 . The control loop compensation device  120  receives a control loop correction signal from the PFC and control device  103  and maintains the control loop correction voltage signal at a port  109  as an input to the electric current flow control module  700 . Thus, the electric current flow control module  700  can detect electric shock and control the at least one switch  400  through the control link  110  to turn off an electrical connection between the electrical contacts  410  and  420  of the at least one switch  400 . 
         [0023]    In  FIG. 2 , when the power is on, an input current enters the input filter  102  and then the PFC and control device  103 , turning on the switch  201 . Whereas the diode  202  is reverse-biased, the input current goes from the resistor  106  and the LED arrays  214 , a primary winding of the transformer  206 , the switch  201 , and the current sensing device  107  to the common ground  504 . The primary winding of the transformer  206  serves as an inductor. When the input current goes into the primary winding of the transformer  206 , energy is stored in it. The PFC and control device  103  detects the input voltage level and control the switch  201  on and off in a way that a desired or otherwise predetermined output voltage V o  across the LED arrays  214  is reached to light up the LED arrays  214 . When the switch  201  is off, the diode  202  is forward-biased, and the primary winding of the transformer  206  releases the energy stored, resulting in a loop current flowing from the diode  202  and the LED arrays  214 , back to the primary winding of the transformer  206 , completing the energy transfer to the LED arrays  214 . When the switch  201  is on, the input current flows into the LED arrays  214 , the primary winding of the transformer  206 , the switch  201 , and the current sensing device  107 , creating a voltage drop across the current sensing device  107 . The voltage appearing at the port  204  of the current sensing device  107  inputs to the PFC and control device  103  to control the off-time of the switch  201 . The voltage feedback module  300  has two connection ports  301  and  302 , with the first connection port  301  connecting to a high side of a secondary winding  207  in the transformer  206  and with the second connection port  302  connecting to the PFC and control device  103 . The voltage feedback module  300  continuously monitors the output voltage by using the secondary winding  207  in the transformer  206 . When the voltage at the high side of the secondary winding  207  is higher than a becoming lower operating voltage in the PFC and control device  103  due to increased internal operations, the diode (not shown) in the voltage feedback module  300  conducts to supply energy in time through the second connection port  302  to sustain the operating voltage in the PFC and control device  103 . In brief, as long as the PFC and control device  103  continues to receive power and to maintain its operation, the switch  201  is controlled to turn on and off such that the electric current continues to pump into and out of the LED arrays with a preset value. 
         [0024]    In  FIG. 2 , the LED driving circuit  100  is further connected to the electric current flow control module  700  via the port  109  with the control loop correction voltage signal directly entering the electric current flow control module  700 . The electric current flow control module  700  comprises an electric shock detection module  505 , a logic control module  506 , a timer and power-up control  507 , a switch control device  508 , and at least one switch  400  configured to connect or disconnect the electric current return from the LED arrays  214 . The electric shock detection module  505  receives the control loop correction voltage signal from the port  109  connecting to the control loop compensation device  120 . The control loop correction voltage signal from the port  109  represents a closed loop control signal to control the current flowing into and out of the LED arrays  214  to the preset value mentioned above. When an electric shock occurs, the supplied DC voltage from the at least one rectifier  603  drops, the control loop correction voltage signal from the control loop compensation device  120  tends to increase to compensate the voltage drop in order to maintain the current flowing into and out of the LED arrays  214  to the preset value. The electric shock detection module  505  compares the control loop correction voltage signal with reference voltages associated with different input voltages, determines if the electric shock occurs, and converts an analog voltage signal into a bilevel signal to send to the logic control module  506  via a data bus  511 , subsequently controlling the switch control device  508  to control the at least one switch  400  to switch on when an electric shock is not detected or to switch off when an electric shock is detected. The reference voltages are preset as an optimum threshold to minimize an error probability of the through-lamp electric shock detection. The timer and power-up control  507  dictates the switch control device  508  to turn on the at least one switch  400  only for a short power-up period after the power is on no matter whether an input voltage is normal or compromised due to the electric shock. After the short power-up period, the logic control module  506  takes over the control of the switch control device  508  to turn the at least one switch  400  on or off based on the bilevel signal received. The logic control module  506  comprises one or more one-bit memory to latch the at least one switch  400  in a way that the at least one switch  400  will remain “on” if the electric shock is not detected and remain off if the electric shock is detected in the short power-up period. This function ensures that the LLT lamp can operate more reliably without flickering when an input voltage accidentally becomes lower than a normal line voltage due to possible power grid fluctuations for a long run. In  FIG. 2 , the electric current flow control module further comprises a detection and timing signal data bus  509  between the timer and power-up control  507  and the electric shock detection module  505  and a timing signal data bus  510  between the timer and power-up control  507  and the logic control module  506 . Details of timing sequences will be discussed in  FIG. 4  and  FIG. 5 . 
         [0025]      FIG. 3  is another embodiment of an LED driving circuit configured to work with an electric current flow control module to detect electric shock according to the present disclosure.  FIG. 3  has all the components as in  FIG. 2 , except that interconnections are different, that the control loop compensation device  120  is connected with the at least one switch  400  at the electrical contact  410  in the at least one switch  400 , and that a center-tapped inductor  203  in  FIG. 3  replaces the transformer  206  in  FIG. 2 . In  FIG. 3 , the same numerals are used for the same components as in  FIG. 2 . In  FIG. 3 , the Buck converter  200  comprises a switch  201  controlled by the PFC and control device  103 , a diode  202 , and an inductor  203  with its current charging and discharging controlled by the switch  201 . The PFC and control device  103  detects zero current in the inductor  203  within an AC cycle of an input voltage generating a zero-current detection signal and controls the switch  201  on and off with a constant on-time and a varied off-time controlled by the zero-current detection signal. By adapting switching frequencies for a high frequency associated with a ballast and a low frequency associated with the AC mains, the PFC and control device  103  controls the switch  201  on and off in a way that the inductor  203  is charged during on-time and discharged during off-time, and that a desired or otherwise predetermined output voltage V o  across the LED arrays  214  is reached to light up the LED arrays  214 . The average inductor current is thus equal to the output current that flows into the LED array  214 . When the switch  201  is on, the diode  202  is reverse-biased, and an input current flows from an output port  108  in the input filter  102 , the switch  201 , the first port  204  of the current sensing device  107 , the current sensing device  107  itself, and the second port  205  of the current sensing device  107 , into the inductor  203 . When the current flowing into the inductor  203  increases, the voltage across the current sensing device  107  increases. The first port  204  of the current sensing device  107  also connects with the PFC and control device  103 , which continuously receives signals and adjusts the off-time such that the output voltage and current to the LED arrays  214  are regulated to meet the output requirements. The output capacitor  105  in parallel with the resistor  106  connects to the inductor  203 , receiving energy to build up an output voltage and to power the LED arrays  214 . 
         [0026]    The inductor  203  configured as an autotransformer has a center-tapped port connecting to the voltage feedback module  300  comprising a diode. The voltage feedback module  300  has two connection ports  301  and  302 , with the first connection port  301  connecting to the center-tapped port of center-tapped inductor  203  and with the second connection port  302  connecting to the PFC and control device  103 . The PFC and control device  103  has an input capacitor (not shown) with a voltage built up to supply an internal logic control circuit (not shown) in the PFC and control device  103 . When the voltage decreases due to its increased internal operations and controls, and when the voltage at the center-tapped port of the inductor  203  is higher than the supplying voltage, the diode in the voltage feedback module  300  conducts to supply a current to the PFC and control device  103  and sustain its operations. The function of the voltage feedback module  300  is essential because the LED driving circuit  100  has a wide range of operating voltages not only 110 and 277 VAC for AC mains but also 350˜600 VAC for an electronic ballast. In the PFC and control device  103 , a start-up resistor (not shown) is so designed to operate a LLT lamp at the lowest input voltage 110 VAC. When the highest voltage 600 VAC from the electronic ballast comes in, a higher proportional voltage appears at an input of the internal logic control circuit. Therefore, an operating voltage for the internal logic control circuit must be in a wide range such as 11˜35 VDC rather than 5˜15 VDC as in a conventional logic control device. To meet requirements of start-up time and current without turn-on failure or flickering occurred at the lamp start-up, the input capacitor in the PFC and control device  103  with a minimum capacitance is designed and used at the input of the internal logic control circuit. The voltage feedback module  300  is thus needed to pump in energy in time and to sustain the operating voltage and ensure no flickering occurred when operating the LLT lamp. 
         [0027]    When the switch  201  is off, the diode  202  is forward-biased, and the inductor  203  discharges with a loop current flowing from the LED arrays  214 , the diode  202 , the current sensing resistor  107 , back to the inductor  203 . The current sensing resistor  107  keeps track of the output current and feedbacks to the PFC and control device  103  to further control the switch  201  on and off. The closed loop operation in both on-time and off-time of the switch  201  ensures the output current to be accurately controlled within 4%. 
         [0028]    In  FIG. 3 , the LED driving circuit  100  is also connected to the electric current flow control module  700  for electric shock detection as in  FIG. 2 . Same as in  FIG. 2 , the electric shock detection module  505  in the electric current flow control module  700  receives the control loop correction voltage signal from the control loop compensation device  120  and detects for a short period after the power is on to see if the electric shock occurs. No matter whether the electric shock is detected or not, a bilevel voltage signal is generated by the electric shock detection module  505  and sent to the logic control module  508  to process. The logic control module  508  manages several scenarios, integrates results from the several scenarios, and sends a signal to the switch control, subsequently controlling the at least one switch  400  to turn “on” or “off”. If the electric shock is detected, the at least one switch  400  is turned “off”, thus blocking the electric shock current to flow to the earth ground through the installer&#39;s body. On the other hand, if the electric shock is not detected for a short power-up period after the power is on, the electric current flow control module  700  controls the at least one switch  400  to turn on and continue on, thus allowing the current return from the LED arrays  214  to reach the earth ground and completing an energy transfer to the LED arrays  214  for lighting. 
         [0029]      FIG. 4  is an embodiment of an electric current flow control module configured to work with either an electronic ballast or AC mains. Same as in  FIGS. 2-3 , the electric current flow control module  700  comprises an electric shock detection module  505 , a logic control module  506 , a timer and power-up control  507 , and a switch control device  508 . The electric shock detection module  505  comprises a high frequency detection module  803  configured to detect if the high frequency voltage from the electronic ballast is present and a comparator module  804  configured to determine if the electric shock occurs when a line voltage from AC mains is present. In  FIG. 1 , when the at least one electrical conductor  250  and the at least one electrical conductor  350  in each lamp base of the LLT lamp  500  are inserted into the lamp fixture sockets  810  and  820 , the LLT lamp  500  must first determine if the power is from an electronic ballast or AC mains because there is no concern of electric shock when the LLT lamp  500  operates with the electronic ballast. The AC voltages from the electronic ballast and the AC mains differ significantly in frequency, for instance, 25 kHz and above for the electronic ballast versus 60 Hz for the AC mains. After the AC voltages are rectified by the rectifier  603  (in  FIGS. 1-3 ), the ripples in the DC voltages show a frequency doubled. The frequency difference between the DC voltages rectified from the AC voltages provided by the electronic ballast and the AC mains can be used to detect if the high frequency voltage from the electronic ballast is present. In  FIG. 4 , if high frequency ripples are detected from the DC voltage rectified, the logic control module  506  dictates a high-level voltage to appear at the switch control device  508 , subsequently controlling the at least one switch  400  to turn “on” and to remain “on”. On the other hand, if the high frequency ripples are not detected from the DC voltage rectified, the comparator module  804  compares the control loop correction voltage signal appeared at the port  109  from the control loop compensation device  120  and converts the control loop correction voltage signal into a bilevel voltage signal and sent to the logic control module  508  to process. Four scenarios for line voltage operation from the AC mains include 120 VAC-normal, 120 VAC-electric shock, 277 VAC-normal, and 277 VAC-electric shock. Therefore, the comparator module  804  may comprise one or more comparators to precisely detect electric shock over a wide range of input AC voltages. The logic control module  506  manages to integrate these four scenarios and the high frequency scenario into one result, a high-level or a low-level voltage to the switch control device  508  to turn “on” or “off” the at least one switch  400 . In this case, the logic control module  506  may further comprise one or more logic gates such as Not gates (inverters), AND gates, and OR gates coupled between the one or more comparators and the one or more one-bit memory devices and between the one or more one-bit memory devices and the switch control device  508 . 
         [0030]      FIG. 5  is timing sequences provided by a timer and power-up control to control the high frequency detection module  803 , the comparator module  804 , and the logic control module  506 . Referring to  FIG. 4  and  FIG. 5 , the electric shock detection module  505  comprises two detection ports—“a” and “b” and two timing ports—“c” and “d”, whereas the logic control module  506  comprises one data bus  511  and one timing bus comprising two timing ports—“e” and “f”. The ports “b”, “c”, and “d” receive data from a bus  509  in  FIGS. 2-3 . The detection port “a” is connected between the control loop compensation device  120  and the comparator module  804  for the comparator module  804  to detect an electric shock. Whereas the detection port “b” receives a DC voltage with ripples to be detected, the timing signal on the port “c” is sent to and enables the high frequency detection module  803  to detect a ripple frequency and determine if the electronic ballast is present. In  FIG. 5 , the timing signal on the port “c” starts at t=0 and stops at t=T 1 . 
         [0031]    The timing signal on the port “d” is sent to the comparator module  804  to detect if the electric shock occurs. Outcomes of the high frequency detection and the through-lamp electric shock detection are sent to the logic control module  506  via the data bus  511  in  FIGS. 2-4 . The timing signal on the port “d” starts at t=T 2  and stops at t=T 3 . The two timing ports—“e” and “f” receive timing information from the timer and power-up control module  507  via the timing bus  510 . In  FIG. 5 , timing sequence on the port “f” is sent to the one or more one-bit memory used to store a status of the outcomes from the high frequency detection and the through-lamp electric shock detection. The one or more one-bit memory receives a high-level voltage at all time starting as soon as the LLT lamp  500  receives the power (t=0). The port “e” receives a high-level voltage to enable the switch control device  508  for a short power-up period from t=0 to t=T 3  so that an LED driving current can flow into and out of the LED arrays  214 , and the control loop correction voltage signal from the control loop compensation device  120  can be sent to the electric shock detection module  505  to determine if the electric shock occurs. After the detection (t&gt;T 3 ), the port “e” receives a low-level voltage, and the status (a high- or a low-level voltage) on the one or more one-bit memory determines if the switch control device  508  receives the high- or the low-level voltage. That is to say, the timer and power-up control  507  is configured to respectively turn on and off power supplied to the at least one switch  400 , the high frequency detection module  803 , and one or more comparators  804  in a predetermined timing manner such as T 3 &gt;T 2 &gt;T 1 &gt;0 whereas T 3  is less than several milliseconds. 
         [0032]    In  FIGS. 1-3 , the electrical contacts  410  and  420  of the at least one switch  400  may be an electrical, an electronic, an electro-mechanical, or a mechanical switch such as one in a solid-state relay, an electronic relay, an electro-mechanical relay, a pair of mechanical contacts, or other bidirectional and unidirectional current control devices such as a triac, a back-to-back thyristor, a silicon-controlled rectifier (SCR), a transistor, a metal-oxide-semiconductor field-effect transistor (MOSFET), a field-effect transistor (FET), a transistor, or various combinations thereof. Also, such devices may be connected with some snubber circuits to maintain their functionality under voltage spikes. Please note that although the LED arrays  214  are used throughout the context, the LED arrays may mean one or more LED arrays. The control loop compensation device  120  in  FIGS. 1-3  may comprise a capacitor or a capacitor in series with a resistor. 
         [0033]    Whereas preferred embodiments of the present disclosure have been shown and described, it will be realized that alterations, modifications, and improvements may be made thereto without departing from the scope of the following claims. Another kind of the through-lamp electric shock prevention schemes in an LED-based lamp using various kinds of combinations to accomplish the same or different objectives could be easily adapted for use from the present disclosure. Accordingly, the foregoing descriptions and attached drawings are by way of example only, and are not intended to be limiting.