Patent Publication Number: US-11381070-B1

Title: LCDI power cord circuit

Description:
BACKGROUND 
     1. Field of Use 
     This invention relates to leakage current detection and interruption (LCDI) power cord circuits for detecting a leakage current and open or faulty shields in a power cord. 
     2. Description of Prior Art (Background) 
     With the wide use of household electrical appliances, such as air conditioners, washing machines, refrigerators, etc., more attention is being paid to the safety of using such appliances. An appliance typically has a power cord of one meter or longer. 
     Power cords may age due to long-term use, or become damaged when the appliance is moved, which may cause a current leakage between the phase line and the neutral or ground lines in the cord. Such leakage current may cause sparks, which may cause fire and property damages. To quickly and accurately detect leakage current in the power cord, an additional conductor is often provided and electrically connected to a metal sheath surrounding the phase line and the neutral line. Leakage current can be detected by detecting a voltage on the metal sheath. The metal sheaths are conventionally made by weaving thin copper wires. 
     Further, the metal sheath can fail due to failure in structural integrity or corrosion. Failure of the metal sheath to provide continuity between the power cord source and the power cord load may allow leakage current to not be detected by an LCDI circuit. 
     Prior art solutions often provide a circuit for detecting an open metal, i.e., failed structural integrity and a separate circuit for detecting leakage current. Multiple circuits require more components, increased footprint, and longer production cycles. Therefore, a need exists for a single circuit for detecting leakage current, metal sheath structural integrity, and metal sheath corrosion that could interfere with leakage current detection. 
     BRIEF SUMMARY 
     Accordingly, the present invention provides a power cord circuit useful for appliances such as air conditioners, washing machines, refrigerators, etc. 
     In accordance with one embodiment of the present invention a Leakage Current Detection Interrupter (LCDI) circuit for interrupting AC power from an AC source connected to a load via an insulated neutral wire surrounded by a neutral wire shield (NWS) and an insulated line wire surrounded by a line wire shield (LWS) is provided. The LCDI circuit includes a power supply circuit for supplying a rectified voltage waveform and a floating load connected to the power supply circuit. The floating load includes a power cord fault circuit (PCFC) for monitoring the NWS and LWS integrity and leakage current. The LCDI does not include any discrete capacitors as in other prior art solutions, thereby reducing cost, footprint, and production times. 
     The invention is also directed towards an A Leakage Current Detection Interrupter (LCDI) circuit for interrupting AC power from an AC source connected to a load via an insulated neutral wire and an insulated line wire, wherein the insulated neutral wire and an insulated line wire are surrounded by a conductive shield (CS). The LCDI circuit includes a power supply circuit for supplying a rectified voltage waveform and a floating load connected to the power supply circuit. The floating load includes a power cord fault circuit (PCFC) for monitoring the CS integrity and detecting leakage current. The PCFC includes a solid-state amplifier (SSA) connectable to the CS; a bi-stable latching device having on/off states. The SSA connected to the bi-stable latching device being selectively turned on and off based upon sufficient application of a portion of the rectified signal positive pulse to a base of the SSA. The LCDI does not include any discrete capacitors as in other prior art solutions, thereby reducing cost, footprint, and production times. 
     In accordance with another embodiment of the present invention a power cord circuit comprising a floating load is presented. The floating load includes a power cord fault circuit (PCFC) for monitoring power cord integrity and detecting leakage current. The PCFC includes a solid-state amplifier (SSA) connectable to a conductive shield (CS). The bi-stable latching device having on/off states and wherein the SSA connected to the bi-stable latching device being selectively turned on or off based upon application of a portion of a rectified signal positive pulse to a base of the SSA. The PCFC does not include any discrete capacitors as in other prior art solutions, thereby reducing cost, footprint, and production times. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a circuit block diagram of the LCDI Power Cord Circuit in accordance with the present invention; 
         FIG. 1A  is a detailed schematic diagram of the block diagram shown in  FIG. 1 ; 
         FIG. 2  is an alternate circuit block diagram of the circuit block diagram shown in 
         FIG. 1 ; 
         FIG. 2A  is a detailed schematic diagram of the block diagram shown in  FIG. 5 ; 
         FIG. 3  is a waveform diagram for the normal operating condition of the Power Cord Circuit shown in  FIG. 1, 1A, 2 , or  2 A; 
         FIG. 4  is a waveform diagram for the leakage current detection condition of the Power Cord Circuit shown in  FIG. 1, 1A, 2 , or  2 A; and 
         FIG. 5  is a waveform diagram for the shield open or degraded detection condition of the Power Cord Circuit shown in  FIG. 1, 1A, 2 , or  2 A. 
     
    
    
     DETAILED DESCRIPTION 
     The following brief definition of terms shall apply throughout the application: 
     The term “comprising” means including but not limited to, and should be interpreted in the manner it is typically used in the patent context; 
     The phrases “in one embodiment,” “according to one embodiment,” and the like generally mean that the particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the present invention, and may be included in more than one embodiment of the present invention (importantly, such phrases do not necessarily refer to the same embodiment); 
     If the specification describes something as “exemplary” or an “example,” it should be understood that refers to a non-exclusive example; and 
     If the specification states a component or feature “may,” “can,” “could,” “should,” “preferably,” “possibly,” “typically,” “optionally,” “for example,” or “might” (or other such language) be included or have a characteristic, that particular component or feature is not required to be included or to have the characteristic. 
     Referring to  FIG. 1  there is shown a circuit block diagram of a LCDI POWER CORD CIRCUIT  10  (LCDI). LCDI circuit  10  includes shield  14 , switch  18 , power supply circuit  100 , power cord fault circuit (PCFC)  110 , relay  16 ; and, mechanically latched double pole switches  12 ,  12 A, hereinafter referred to as the manual reset switch or mechanically latched double pole switch. As shown herein the PCFC comprises a floating load with respect to the power supply  100 . 
     As is described in more detail herein, when manual reset switches  12 ,  12 A are set line voltage is connected to LOAD and to power supply circuit  10  via relay  16 . Power supply circuit  100  supplies bias voltages to PCFC  110 , and shield. Shield  14 , having a load end,  14 A and a line end  14 B, is connected in series between power supply  100  and PCFC  110 . As is discussed and shown in more detail herein, the PCFC  110  allows a small amount of relay current to flow through relay  16  but less than the energizing current needed to energize relay  16  to disengage manual reset switches  12 A, 12 B. It is appreciated that not starting from zero energizing current allows solenoid  519  to energize faster when a fault is detected. 
     Referring also to  FIG. 1A  there is shown a detailed circuit  10 A of the block diagram  10  shown in  FIG. 1 . LCDI circuit  10 A includes shield  14 A, switch  18 , power supply circuit  100 A, and PCFC  110 A. PCFC  110 A includes solid state amplifying transistor Q 1  and bi-stable latching device silicon-controlled rectifier SCR 1 . Transistor Q 1  may be operated in a full conduction state, e.g., as a switch, or in a partial conduction state, e.g., as an amplifier, when a fault is detected. Shield  14  may be any suitable conductive shield surrounding the line and neutral wires. As is described in more detail herein, when manual reset switches  12 ,  12 A are set line voltage is connected to LOAD and to power supply circuit  100 A via relay  16 . Power supply circuit  100 A supplies bias voltages to PCFC  110 A, and shield  14 . As is discussed and shown in more detail herein, the PCFC  110 A allows a small amount of relay current to flow through relay  16  but less than the energizing current needed to energize relay  16  to disengage manual reset switches  12 ,  12 A. It is appreciated that not starting from zero energizing current allows relay  519  to energize faster when a fault is detected. 
     Referring now to  FIG. 1A  and  FIG. 3 . When switches  12 ,  12 A are mechanically (manually) engaged AC line voltage is connect to LOAD. 60 Hz AC line voltage is also connected to power supply circuit  110 A via relay  16 . Power supply circuit  110 A, comprising bridge rectifier (diodes D 1 -D 4 ) outputs a rectified unsmoothed DC signal at BRIDGEOUT. The rectified unsmoothed DC signal at BRIDGEOUT is routed through R 1  to Q 1  base via shield  14 . The rectified unsmoothed DC signal at BRIDGEOUT is also routed through R 2  to Q 1  collector and SCR 1  gate. 
     Still referring to  FIG. 1A  and  FIG. 3 , the rectified unsmoothed DC signal at BRIDGEOUT is routed to the base of npn transistor Q 1 , R 1  and R 3  biasing Q 1  into an on condition during the positive cycle of the rectified unsmoothed DC, dropping the rectified voltage across R 2 . When Q 1 (B) voltage drops below V BE  Q 1  turns off and the voltage at Q 1 (C) is near 0 v due to the unsmoothed DC signal at BRIDGEOUT dropping to near 0 v in the cycle. When the unsmoothed DC signal at BRIDGEOUT swings positive, Q 1  is again biased on, dropping the unsmoothed DC signal at BRIDGEOUT across R 2 , keeping SCR 1  in an off condition during normal operation. It will be further appreciated that during normal operation as the transistor Q 1  is forward biased, the gate of SCR 1  is essentially tied to the SCR 1  cathode and that this action minimizes nuisance tripping. 
     Still referring to  FIG. 1A , it is understood that under normal conditions the rectified unsmoothed DC signal at BRIDGEOUT is dropped across resistor R 2  and that R 2  is sized to allow an amount of AC current less than the relay  16  energizing current to flow through R 2  through Q 1  back to neutral when Q 1  is conducting. During Q 1 &#39;s off state, or non-conducting state, relay  16  inductively opposes the change in current until Q 1  again turns on, thus maintaining, or nearly maintaining the current flow through SOL 1   519 . It is understood and appreciated that the small amount of relay current flowing through relay  16  is less than the energizing current needed to energize relay  16  to disengage manual reset switches  12 , 12 A. It is further appreciated that not starting from zero energizing current allows relay  16  to energize faster when a fault is detected. 
     Still referring to  FIG. 1A  and now  FIG. 5 , when shield  14  integrity is compromised, such as, for example, a break in shield  14 , or a voltage drop across areas of corrosion within the power cable, the bias-on voltage V BE  at the base of Q 1  is insufficient to bias Q 1  in its full conductive on-state, thus the voltage on Q 1  collector is an amplified voltage of the signal at Q 1  base. The voltage at the Q 1  collector (V(SCRGATE)) begins to rise on the first positive rectified input cycle to trigger SCR 1  into an on condition, sufficiently increasing current flow through relay  16  to energize relay  16  to disengage manual reset switches  12 , 12 A. Thus, interrupting power from the AC line source to the load. It is understood and appreciated that the full wave bridge rectifier  100 A enables the PCFC  110 A to detect and disconnect the AC line source from the load when a fault is detected during the positive or negative cycle of an input AC waveform (not shown). In other words, the PCFC  110 A detects and interrupts power between the AC line source and load within approximately 1 ms or less for a 60 Hz AC source. 
     Still referring to  FIG. 1A  and now  FIG. 4 , when shield  14  integrity is compromised, such as, for example, a leakage current, the bias-on voltage V BE  at the base of Q 1  is insufficient to keep Q 1  in its full conductive state. The voltage at the Q 1  collector (V(SCRGATE)) begins to rise on the second positive rectified input cycle to trigger SCR 1  into an on condition, sufficiently increasing current flow through relay  16  to energize relay  16  to disengage manual reset switches  12 , 12 A. Thus, interrupting power from the AC line source to the load. It is understood and appreciated that the full wave bridge rectifier  100 A enables the PCFC  110 A to detect leakage current and disconnect the AC line source from the load when a fault is detected during the negative cycle of an input AC waveform (not shown). In other words, the PCFC  110 A detects and interrupts power between the AC line source and load within approximately 17 ms. or less for a 60 Hz AC source. 
     Referring to  FIG. 2  there is shown a circuit block diagram of a LCDI POWER CORD CIRCUIT  10  (LCDI). LCDI circuit  10  includes shields  24 A,  248 , switch  18 , power supply circuit  100 , power cord fault circuit (PCFC)  110 , relay  16 ; and, manually engaged ganged switches  12 ,  12 A, hereinafter referred to as the manual reset switch. As shown herein the PCFC comprises a floating load with respect to the power supply  100 . 
     As is described herein, when manual reset switches  12 ,  12 A are set line voltage is connected to LOAD and to power supply circuit  10  via relay  16 . Power supply circuit  100  supplies bias voltages to PCFC  110 , and shields  24 A and  24 B. Shields  24 A and  24 B are connected in series at the Load end, are connected in series between power supply  100  and PCFC  110 . As is discussed and shown in more detail herein, the PCFC  110  allows a small amount of relay current to flow through relay  16  but less than the energizing current needed to energize relay  16  to disengage manual reset switches  12 A, 12 B. It is appreciated that not starting from zero energizing current allows solenoid  519  to energize faster when a fault is detected. 
     Referring also to  FIG. 2A  there is shown a detailed circuit  10 A of the block diagram  10  shown in  FIG. 2 . LCDI circuit  10 A includes shield  14 A, switch  18 , power supply circuit  100 A, and PCFC  110 A. Shield  14  may be any suitable conductive shield surrounding the line and neutral wires. As is described in more detail herein, when manual reset switches  12 ,  12 A are set line voltage is connected to LOAD and to power supply circuit  100 A via relay  16 . Power supply circuit  100 A supplies bias voltages to PCFC  110 A, and shields  24 A and  24 B. As is discussed and shown in more detail herein, the PCFC  110  allows a small amount of relay current to flow through relay  16  but less than the energizing current needed to energize relay  16  to disengage manual reset switches  12 ,  12 A. It is appreciated that not starting from zero energizing current allows relay  519  to energize faster when a fault is detected. 
     Referring now to  FIG. 2A  and  FIG. 3 . When switches  12 ,  12 A are mechanically (manually) engaged AC line voltage is connect to LOAD. 60 Hz AC line voltage is also connected to power supply circuit  110 A via relay  16 . Power supply circuit  110 A, comprising bridge rectifier (diodes D 1 -D 4 ) outputs a rectified unsmoothed DC signal at BRIDGEOUT. The rectified unsmoothed DC signal at BRIDGEOUT is routed through R 1  to Q 1  base via shields  24 A,  24 B. The rectified unsmoothed DC signal at BRIDGEOUT is also routed through R 2  to Q 1  collector and SCR 1  gate. 
     Still referring to  FIG. 2A  and  FIG. 3 , the rectified unsmoothed DC signal at BRIDGEOUT is routed to the base of npn transistor Q 1 , R 1  and R 3  biasing Q 1  into an on condition during the positive cycle of the rectified unsmoothed DC, dropping the rectified voltage across R 2 . When Q 1 (B) voltage drops below V BE  Q 1  turns off and the voltage at Q 1 (C) is near 0 v due to the unsmoothed DC signal at BRIDGEOUT dropping to near 0 v in the cycle. When the unsmoothed DC signal at BRIDGEOUT swings positive, Q 1  is again biased on, dropping the unsmoothed DC signal at BRIDGEOUT across R 2 , keeping SCR 1  in an off condition during normal operation. 
     Still referring to  FIG. 2A , it is understood that under normal conditions the rectified unsmoothed DC signal at BRIDGEOUT is dropped across resistor R 2  and that R 2  is sized to allow an amount of AC current less than the relay  16  energizing current to flow through R 2  through Q 1  back to neutral when Q 1  is conducting. During Q 1 &#39;s off state, or non-conducting state, relay  16  inductively opposes the change in current until Q 1  again turns on, thus maintaining, or nearly maintaining the current flow through SOL 1   519 . It is understood and appreciated that the small amount of relay current flowing through relay  16  is less than the energizing current needed to energize relay  16  to disengage manual reset switches  12 , 12 A. It is further appreciated that not starting from zero energizing current allows relay  16  to energize faster when a fault is detected. 
     Still referring to  FIG. 2A  and now  FIG. 5 , when either of the shields  24 A or  24 B integrity is compromised, such as, for example, a break in either shield, or a voltage drop across areas of corrosion within the power cable, the bias-on voltage V BE  at the base of Q 1  is insufficient to keep Q 1  in its full conductive state. The voltage at the Q 1  collector (V(SCRGATE)) begins to rise on the first positive rectified input cycle to trigger SCR 1  into an on condition, sufficiently increasing current flow through relay  16  to energize relay  16  to disengage manual reset switches  12 , 12 A. Thus, interrupting power from the AC line source to the load. It is understood and appreciated that the full wave bridge rectifier  100 A enables the PCFC  110 A to detect and disconnect the AC line source from the load when a fault is detected during the positive or negative cycle of an input AC waveform (not shown). In other words, the PCFC  110 A detects and interrupts power between the AC line source and load within approximately 1 ms or less for a 60 Hz AC source. 
     Still referring to  FIG. 2A  and now  FIG. 4 , when either of the shields  24 A or  24 B integrity is compromised, such as, for example, a leakage current, the bias-on voltage V BE  at the base of Q 1  is insufficient to keep Q 1  in its full conductive state. The voltage at the Q 1  collector (V(SCRGATE)) begins to rise on the second positive rectified input cycle to trigger SCR 1  into an on condition, sufficiently increasing current flow through relay  16  to energize relay  16  to disengage manual reset switches  12 , 12 A. Thus, interrupting power from the AC line source to the load. It is understood and appreciated that the full wave bridge rectifier  100 A enables the PCFC  110 A to detect leakage current and disconnect the AC line source from the load when a fault is detected during the negative cycle of an input AC waveform (not shown). In other words, the PCFC  110 A detects and interrupts power between the AC line source and load within approximately 17 ms. or less for a 60 Hz AC source. 
     It should be understood that the foregoing descriptions are only illustrative of the invention. It will be appreciated that the PCFC accomplishes leakage current detection and open shield detection. It will also be appreciated the PCFC does not include any discrete capacitors; thus, reducing the number of components and associated product production cycles. Thus, various alternatives and modifications can be devised by those skilled in the art without departing from the invention. For example, solid state devices SCR 1  or Q 1  can be any suitable solid-state device. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances that fall within the scope of the appended claims.