Patent Publication Number: US-9906144-B2

Title: Systems and methods for protecting power conversion systems from thermal runaway

Description:
1. CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/151,209, filed Jan. 9, 2014, which claims priority to Chinese Patent Application No. 201310656906.4, filed Dec.6, 2013, both of the above-referenced applications being commonly assigned and incorporated by reference herein for all purposes. 
     This application is related to U.S. patent application Ser. Nos. 13/857,836, 13/071,384, 12/581,775, and 12/502,866, incorporated by reference herein for all purposes. 
    
    
     2. BACKGROUND OF THE INVENTION 
     Certain embodiments of the present invention are directed to integrated circuits. More particularly, some embodiments of the invention provide a system and method for protecting one or more circuit components. Merely by way of example, some embodiments of the invention have been applied to power conversion systems. But it would be recognized that the invention has a much broader range of applicability. 
     Schottky rectifying diodes with low forward voltages are often used in power conversion systems to improve system efficiency. Generally, a conventional power conversion system often uses a transformer to isolate the input voltage on the primary side and the output voltage on the secondary side. To regulate the output voltage, certain components, such as TL431 and an opto-coupler, can be used to transmit a feedback signal from the secondary side to a controller chip on the primary side. Alternatively, the output voltage on the secondary side can be imaged to the primary side, so the output voltage is controlled by directly adjusting some parameters on the primary side. Then, some components, such as TL431 and an opto-coupler, can be omitted to reduce the system costs. 
       FIG. 1  is a simplified diagram showing a conventional flyback power conversion system with primary-side sensing and regulation. The power conversion system  100  includes a primary winding  110 , a secondary winding  112 , an auxiliary winding  114 , a power switch  120 , a current sensing resistor  130 , an equivalent resistor  140  for an output cable, resistors  150  and  152 , and a Schottky rectifying diode  160 . For example, the power switch  120  is a bipolar junction transistor. In another example, the power switch  120  is a MOS transistor. 
     To regulate the output voltage within a predetermined range, information related to the output voltage and the output loading often needs to be extracted. For example, when the power conversion system  100  operates in a discontinuous conduction mode (DCM), such information can be extracted through the auxiliary winding  114 . When the power switch  120  is turned on, the energy is stored in the secondary winding  112 . Then, when the power switch  120  is turned off, the stored energy is released to the output terminal during a demagnetization process. The voltage of the auxiliary winding  114  maps the output voltage on the secondary side as shown below. 
                     V   FB     =           R   2         R   1     +     R   2         ×     V   aux       =     k   ×   n   ×     (       V   0     +     V   F     +       I   0     ×     R   eq         )                 (     Equation   ⁢           ⁢   1     )               
where V FB  represents a voltage at a node  154 , and V aux  represents the voltage of the auxiliary winding  114 . R 1  and R 2  represent the resistance values of the resistors  150  and  152  respectively. Additionally, n represents a turns ratio between the auxiliary winding  114  and the secondary winding  112 . Specifically, n is equal to the number of turns of the auxiliary winding  114  divided by the number of turns of the secondary winding  112 . V o  and I o  represent the output voltage and the output current respectively. Moreover, V F  represents the forward voltage of the rectifying diode  160 , and R eq  represents the resistance value of the equivalent resistor  140 . Also, k represents a feedback coefficient as shown below:
 
     
       
         
           
             
               
                 
                   k 
                   = 
                   
                     
                       R 
                       2 
                     
                     
                       
                         R 
                         1 
                       
                       + 
                       
                         R 
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
       FIG. 2  is a simplified diagram showing a conventional operation mechanism for the flyback power conversion system  100 . As shown in  FIG. 2 , the controller chip of the conversion system  100  uses a sample-and-hold mechanism. When the demagnetization process on the secondary side is almost completed and the current I sec  of the secondary winding  112  almost becomes zero, the voltage V aux  of the auxiliary winding  114  is sampled at, for example, point A of  FIG. 2 . The sampled voltage value is usually held until the next voltage sampling is performed. Through a negative feedback loop, the sampled voltage value can become equal to a reference voltage V ref . Therefore,
 
 V   FB   =V   ref   (Equation 3)
 
     Combining Equations 1 and 3, the following can be obtained: 
                     V   0     =         V   ref       k   ×   n       -     V   F     -       I   0     ×     R   eq                 (     Equation   ⁢           ⁢   4     )               
Based on Equation 4, the output voltage decreases with the increasing output current.
 
     But thermal runaway may occur in the Schottky diode  160  if the temperature of the diode  160  exceeds a threshold, and a reverse leakage current increases in magnitude drastically. If the output load of the power conversion system  100  is reduced, the reverse leakage current continues to increase in magnitude and the temperature of the diode  160  does not decrease. As such, once the thermal runaway occurs in the Schottky diode  160 , the temperature of the diode  160  keeps higher than a normal operating temperature even if the output load is reduced, which may cause safety problems. For example, the outer shell of the power conversion system  100  may be melted due to the high temperature of the Schottky diode  160 . 
     Hence it is highly desirable to improve the techniques of system protection. 
     3. BRIEF SUMMARY OF THE INVENTION 
     Certain embodiments of the present invention are directed to integrated circuits. More particularly, some embodiments of the invention provide a system and method for protecting one or more circuit components. Merely by way of example, some embodiments of the invention have been applied to power conversion systems. But it would be recognized that the invention has a much broader range of applicability. 
     According to one embodiment, a system controller for protecting a power conversion system includes a protection component and a driving component. The protection component is configured to receive a feedback signal, a reference signal, and a demagnetization signal generated based on at least information associated with the feedback signal, process information associated with the feedback signal, the reference signal, and the demagnetization signal, and generate a protection signal based on at least information associated with the feedback signal, the reference signal, and the demagnetization signal. The demagnetization signal is related to multiple demagnetization periods of the power conversion system, the multiple demagnetization periods including a first demagnetization period and a second demagnetization period. The driving component is configured to receive the protection signal and output a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system. The protection component is further configured to: process information associated with the feedback signal and the reference signal during a first detection period, the first detection period including a first starting time and a first ending time, the first starting time being at or after a first demagnetization end of the first demagnetization period, determine, during the first detection period, a first number of times that the feedback signal changes from being smaller than the reference signal to being larger than the reference signal in magnitude, and determine whether the first number of times exceeds a predetermined threshold at the first ending time. The protection component and the driving component are further configured to, in response to the first number of times not exceeding the predetermined threshold at the first ending time, output the drive signal to cause the switch to open and remain open in order to protect the power conversion system. 
     According to another embodiment, a system controller for protecting a power conversion system includes a protection component and a driving component. The protection component is configured to receive a feedback signal, a reference signal, and a demagnetization signal generated based on at least information associated with the feedback signal, process information associated with the feedback signal, the reference signal, and the demagnetization signal, and generate a protection signal based on at least information associated with the feedback signal, the reference signal, and the demagnetization signal. The demagnetization signal is related to multiple demagnetization periods of the power conversion system, the multiple demagnetization periods including a first demagnetization period and a second demagnetization period. The driving component is configured to receive the protection signal and output a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system. The protection component is further configured to: process information associated with the feedback signal and the reference signal during a first detection period, the first detection period including a first starting time and a first ending time, the first starting time being at or after a first demagnetization end of the first demagnetization period, determine, during the first detection period, a first number of times that the feedback signal changes from being larger than the reference signal to being smaller than the reference signal in magnitude, and determine whether the first number of times exceeds a predetermined threshold at the first ending time. The protection component and the driving component are further configured to, in response to the first number of times not exceeding the predetermined threshold at the first ending time, output the drive signal to cause the switch to open and remain open in order to protect the power conversion system. 
     According to yet another embodiment, a method for protecting a power conversion system includes: receiving a feedback signal, a reference signal, and a demagnetization signal generated based on at least information associated with the feedback signal, processing information associated with the feedback signal, the reference signal, and the demagnetization signal, and generating a protection signal based on at least information associated with the feedback signal, the reference signal, and the demagnetization signal, the demagnetization signal being related to multiple demagnetization periods of the power conversion system, the multiple demagnetization periods including a first demagnetization period and a second demagnetization period. The method additionally includes: receiving the protection signal, processing information associated with the protection signal, and outputting a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system. The processing information associated with the feedback signal, the reference signal, and the demagnetization signal includes: processing information associated with the feedback signal and the reference signal during a first detection period, the first detection period including a first starting time and a first ending time, the first starting time being at or after a first demagnetization end of the first demagnetization period, determining, during the first detection period, a first number of times that the feedback signal changes from being smaller than the reference signal to being larger than the reference signal in magnitude, and determining whether the first number of times exceeds a predetermined threshold at the first ending time. The outputting a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system includes: in response to the first number of times not exceeding the predetermined threshold at the first ending time, outputting the drive signal to cause the switch to open and remain open in order to protect the power conversion system. 
     According to yet another embodiment, a method for protecting a power conversion system includes: receiving a feedback signal, a reference signal, and a demagnetization signal generated based on at least information associated with the feedback signal, processing information associated with the feedback signal, the reference signal, and the demagnetization signal, and generating a protection signal based on at least information associated with the feedback signal, the reference signal, and the demagnetization signal, the demagnetization signal being related to multiple demagnetization periods of the power conversion system, the multiple demagnetization periods including a first demagnetization period and a second demagnetization period. The method further includes: receiving the protection signal, processing information associated with the protection signal, and outputting a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system. The processing information associated with the feedback signal, the reference signal, and the demagnetization signal includes: processing information associated with the feedback signal and the reference signal during a first detection period, the first detection period including a first starting time and a first ending time, the first starting time being at or after a first demagnetization end of the first demagnetization period, determining, during the first detection period, a first number of times that the feedback signal changes from being larger than the reference signal to being larger than the reference signal in magnitude, and determining whether the first number of times exceeds a predetermined threshold at the first ending time. The outputting a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system includes: in response to the first number of times not exceeding the predetermined threshold at the first ending time, outputting the drive signal to cause the switch to open and remain open in order to protect the power conversion system. 
     Depending upon embodiment, one or more benefits may be achieved. These benefits and various additional objects, features and advantages of the present invention can be fully appreciated with reference to the detailed description and accompanying drawings that follow. 
    
    
     
       4. BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified diagram showing a conventional flyback power conversion system with primary-side sensing and regulation. 
         FIG. 2  is a simplified diagram showing a conventional operation mechanism for the flyback power conversion system as shown in  FIG. 1 . 
         FIG. 3  is a simplified diagram showing a power conversion system with primary-side sensing and regulation. 
         FIG. 4  is a simplified diagram showing at least certain components of a constant-current component as part of the power conversion system as shown in  FIG. 3 . 
         FIG. 5  is a simplified timing diagram for the power conversion system as shown in  FIG. 3  in a constant-current mode. 
         FIG. 6  is a simplified timing diagram for the power conversion system as shown in  FIG. 3  in a constant-voltage mode. 
         FIG. 7  is a simplified timing diagram for the power conversion system as shown in  FIG. 3  in a constant-voltage mode under thermal runaway of a rectifying diode according to one embodiment. 
         FIG. 8  is a simplified diagram showing a power conversion system with primary-side sensing and regulation according to an embodiment of the present invention. 
         FIG. 9  is a simplified diagram showing a protection component as part of the power conversion system as shown in  FIG. 8  according to an embodiment of the present invention. 
         FIG. 10  is a simplified timing diagram for the power conversion system as shown in  FIG. 8  according to an embodiment of the present invention. 
     
    
    
     5. DETAILED DESCRIPTION OF THE INVENTION 
     Certain embodiments of the present invention are directed to integrated circuits. More particularly, some embodiments of the invention provide a system and method for protecting one or more circuit components. Merely by way of example, some embodiments of the invention have been applied to power conversion systems. But it would be recognized that the invention has a much broader range of applicability. 
       FIG. 3  is a simplified diagram showing a power conversion system with primary-side sensing and regulation. The power conversion system  300  includes a primary winding  310 , a secondary winding  312 , an auxiliary winding  314 , a power switch  320 , a current sensing resistor  330 , an equivalent resistor  340  for an output cable, resistors  350  and  352 , a rectifying diode  360 , and a controller  370 . The controller  370  includes a sampling component  302 , a demagnetization detector  304 , a capacitor  306 , a switch  307 , a reference-signal generator  308 , a ramp-generator-and-oscillator component  316 , an AND gate  318 , a driving component  322 , an OR gate  324 , comparators  326  and  328 , a flip-flop component  336 , a leading edge blanking (LEB) component  386 , resistors  384  and  388 , an error amplifier  390 , a modulation component  392 , and a constant-current (CC) component  394 . For example, the power switch  320  is a bipolar transistor. In another example, the power switch  320  is a MOS transistor. In yet another example, the controller  370  includes terminals  372 ,  374 ,  376 ,  378  and  380 . In yet another example, the rectifying diode  360  is a Schottky diode. For example, the ramp-generator-and-oscillator component  316  generates a clock signal  369  and a ramp signal  368 . 
     For example, the auxiliary winding  314  is magnetically coupled to the secondary winding  312 , which, with one or more other components, generates an output voltage  393 . In another example, information related to the output voltage is processed by a voltage divider of the resistors  350  and  352 , and is used to generate a feedback voltage  354 , which is received by the terminal  372  (e.g., terminal FB) of the controller  370 . In another example, the sampling component  302  samples the feedback voltage  354  and the sampled signal is held at the capacitor  306 . As an example, the error amplifier  390  compares the sampled-and-held voltage  362  with a reference signal  364  generated by the reference-signal generator  308 , and outputs a comparison signal  366  associated with the error of the sampled-and-held voltage  362  with respect to the reference signal  364 . As another example, the comparison signal  366  is received by the modulation component  392 . In some embodiments, the modulation component  392  receives the ramp signal  368  and/or the clock signal  369  from the ramp-generator-and-oscillator component  316  and outputs a signal  356  (e.g., CV_ctrl). 
     For example, the comparison signal  366  is used to control the pulse width for pulse-width modulation (PWM) and/or the switching frequency for pulse-frequency modulation (PFM) in order to regulate the output voltage in a constant-voltage mode. In another example, the demagnetization detector  304  determines the duration of a demagnetization period based on the feedback voltage  354  and outputs a detection signal  358  to the constant-current component  394  which generates a signal  346  (e.g., CC_ctrl). In yet another example, both the signal  356  and the signal  346  are received by the AND gate  318  to affect the flip-flop component  336  and in turn the driving component  322 . In yet another example, the driving component  322  outputs a drive signal  348  through the terminal  376  to affect the status of the switch  320 . In yet another example, a primary current  396  flowing through the primary winding  310  is sensed using the resistor  330 , and a current-sensing signal  342  is generated through the LEB component  386  and received by the comparators  326  and  328 . In yet another example, the comparator  326  receives a threshold voltage  332  (e.g., V thocp ), and the comparator  328  receives another threshold voltage  301  associated with the comparison signal  366  (e.g., V comp ). In yet another example, the comparator  326  and the comparator  328  output comparison signals  334  and  338  respectively, to the OR gate  324  to affect the flip-flop component  336 . As an example, when the sampled-and-held voltage  362  is smaller than the reference signal  364  in magnitude, the error amplifier  390  outputs the comparison signal  366  at a logic high level. The power conversion system  300  operates in a constant-current mode, in some embodiments. For example, when the sampled-and-held voltage  362  is equal to the reference signal  364  in magnitude, the comparison signal  366  has a fixed magnitude. The power conversion system  300  operates in the constant-voltage mode, in certain embodiments. 
       FIG. 4  is a simplified diagram showing at least certain components of the constant-current component  394  as part of the power conversion system  300 . The constant-current component  394  includes a NOT gate  402 , current sources  404  and  406 , a switch  408 , a capacitor  414 , a comparator  410  and a reference-signal generator  412 . 
     For example, when the detection signal  358  is at a logic low level, the switch  408  is open (e.g., being turned off) and the switch  416  is closed (e.g., being turned on). In another example, the current source  404  provides a current  418  (e.g., I 0 ) to charge the capacitor  414 , and in response a signal  420  increases in magnitude. As an example, when the detection signal  358  is at a logic high level, the switch  416  is open (e.g., being turned off) and the switch  408  is closed (e.g., being turned on). As another example, the capacitor  414  is discharged through the current source  406  which provides a current  424  (e.g., I 1 ), and the signal  420  decreases in magnitude. For example, the comparator  410  receives the signal  420  and a reference signal  422  generated by the reference-signal generator  412  and outputs the signal  346 . In certain embodiments, the modulation component  392  receives the clock signal  369  and/or the ramp signal  368  from the ramp-generator-and-oscillator component  316 . 
       FIG. 5  is a simplified timing diagram for the power conversion system  300  in a constant-current mode. The waveform  602  represents the feedback voltage  354  as a function of time, the waveform  604  represents the detection signal  358  as a function of time, and the waveform  606  represents the signal  420  as a function of time. The waveform  608  represents the signal  346  (e.g., CC_ctrl) as a function of time, the waveform  610  represents the signal  348  as a function of time, the waveform  612  represents the current-sensing signal  342  as a function of time, and the waveform  618  represents the signal  356  (e.g., CV_ctrl) as a function of time. 
     Four time periods are shown in  FIG. 5 . A switching period T s1  includes an on-time period T on1  and an off-time period T off1  and corresponds to a modulation frequency. The off-time period T off1  includes a demagnetization period T demag1 . The on-time period T on1  starts at time t 0  and ends at time t 1 , the demagnetization period T demag1  starts at the time t 1  and ends at time t 2 , and the off-time period T off1  starts at the time t 1  and ends at time t 3 . For example, t 0 ≦t 1 ≦t 2 ≦t 3 . 
     For example, as shown in the waveform  618 , the signal  356  (e.g., CC_ctrl) keeps at a magnitude (e.g., 1) without changing in the constant-current mode. In another example, at the beginning of the on-time period T on1  (e.g., at t 0 ), the signal  348  changes from a logic low level to a logic high level (e.g., as shown by the waveform  610 ), and in response the switch  320  is closed (e.g., being turned on). In yet another example, the transformer including the primary winding  310  and the secondary winding  312  stores energy, and the primary current  396  increases in magnitude (e.g., linearly). In yet another example, the current-sensing signal  342  increases in magnitude (e.g., as shown by the waveform  612 ). 
     As an example, the threshold voltage  332  (e.g., V thocp ) is smaller in magnitude than the threshold  301  (e.g., V div ). In another example, when the current-sensing signal  342  reaches the threshold voltage  332  (e.g., V thocp ), the comparator  326  changes the comparison signal  334  in order to turn off the switch  320 . As another example, during the on-time period, the detection signal  358  (e.g., Demag) keeps at a logic low level (e.g., as shown by the waveform  604 ). As yet another example, the switch  408  is open (e.g., being turned off) and the switch  416  is closed (e.g., being turned on). As yet another example, the capacitor  414  is charged (e.g., at I 0 ), and the signal  420  increases in magnitude (e.g., linearly) as shown by the waveform  606 . 
     In one example, at the beginning of the demagnetization period T demag1  (e.g., at t 1 ), the signal  348  changes from the logic high level to the logic low level (e.g., as shown by the waveform  610 ), and in response the switch  320  is opened (e.g., being turned off). In another example, the energy stored in the transformer is released to the output terminal, and the demagnetization process begins. In yet another example, a secondary current  397  that flows through the secondary winding  312  decreases in magnitude (e.g., linearly). In yet another example, a voltage  395  at the auxiliary winding  314  maps the output voltage  393 , and the feedback voltage  354  is generated through the voltage divider including the resistors  350  and  352 . As an example, when the secondary current decreases to a low magnitude (e.g., 0), the demagnetization process ends. As another example, the transformer including the primary winding  310  and the secondary winding  312  enters a resonant status. As yet another example, a voltage  395  at the auxiliary winding  314  has an approximate sinusoidal waveform. In an example, during the demagnetization period, the detection signal  358  (e.g., Demag) keeps at a logic high level (e.g., as shown by the waveform  604 ). In yet another example, the switch  416  is opened (e.g., being turned off) and the switch  408  is closed (e.g., being turned on). In yet another example, the capacitor  414  is discharged (e.g., at I 1 ), and the signal  420  decreases in magnitude (e.g., linearly) as shown by the waveform  606 . In yet another example, if the feedback voltage  354  becomes larger than the reference signal  516  (e.g., 0.1 V) in magnitude, it is determined that the demagnetization process has begun. In yet another example, if the feedback voltage  354  becomes smaller than the reference signal  516  (e.g., 0.1 V) in magnitude, it is determined that the demagnetization process has ended. 
     As one example, after the demagnetization process ends (e.g., at t 2 ), the detection signal  358  changes from the logic high level to the logic low level (e.g., as shown by the waveform  604 ). As another example, the switch  408  is open (e.g., being turned off) and the switch  416  is closed (e.g., being turned on). As yet another example, the capacitor  414  is charged again, and the signal  420  increases in magnitude (e.g., linearly) again as shown by the waveform  606 . As yet another example, when the signal  420  becomes larger than a threshold voltage  614  (e.g., the reference signal  422 ) in magnitude (e.g., at t 3 ), the comparator  410  changes the signal  346  (e.g., CC_ctrl) from the logic low level to the logic high level (e.g., as shown by the waveform  608 ). As yet another example, in response to the signal  346  being at the logic high level, the driving component  322  changes the signal  348  from the logic low level to the logic high level (e.g., at t 3  as shown by the waveform  610 ). 
       FIG. 6  is a simplified timing diagram for the power conversion system  300  in a constant-voltage mode. The waveform  702  represents the feedback voltage  354  as a function of time, the waveform  704  represents the detection signal  358  as a function of time, and the waveform  706  represents the signal  420  as a function of time. The waveform  708  represents the signal  346  (e.g., CC_ctrl) as a function of time, the waveform  716  represents the signal  368  as a function of time, and the waveform  720  represents the comparison signal  366  as a function of time. In addition, the waveform  718  represents the signal  356  (e.g., CV_ctrl) as a function of time, the waveform  710  represents the signal  348  as a function of time, and the waveform  712  represents the current-sensing signal  342  as a function of time. 
     Four time periods are shown in  FIG. 6 . A switching period T s2  includes an on-time period T on2  and an off-time period T off2  and corresponds to a modulation frequency. The off-time period T off2  includes a demagnetization period T demag2 . The on-time period T on2  starts at time t 6  and ends at time t 7 , the demagnetization period T demag2  starts at the time t 7  and ends at time t 8 , and the off-time period T off2  starts at the time t 7  and ends at time t 10 . For example, t 6 ≦t 7 ≦t 8 ≦t 9 ≦t 10 . 
     For example, at the beginning of the on-time period T on2  (e.g., at t 6 ), the signal  348  changes from a logic low level to a logic high level (e.g., as shown by the waveform  710 ), and in response the switch  320  is closed (e.g., being turned on). In yet another example, the transformer including the primary winding  310  and the secondary winding  312  stores energy, and the primary current  396  increases in magnitude (e.g., linearly). In yet another example, the current-sensing signal  342  increases in magnitude (e.g., as shown by the waveform  712 ). In yet another example, at the beginning of the on-time period T on2  (e.g., at t 6 ), the signal  356  changes from the logic low level to the logic high level (e.g., as shown by the waveform  718 ) in order to close the switch  320 . 
     As an example, the threshold voltage  332  (e.g., V thocp ) is larger in magnitude than the threshold  301  (e.g., V div ). In another example, when the current-sensing signal  342  reaches the threshold voltage  301  (e.g., V div ), the comparator  328  changes the comparison signal  338  in order to turn off the switch  320 . As another example, during the on-time period, the detection signal  358  (e.g., Demag) keeps at a logic low level (e.g., as shown by the waveform  704 ). As yet another example, the switch  408  is open (e.g., being turned off) and the switch  416  is closed (e.g., being turned on). As yet another example, the capacitor  414  is charged (e.g., at I 0 ), and the signal  420  increases in magnitude (e.g., linearly) as shown by the waveform  706 . 
     In one example, at the beginning of the demagnetization period T demag2  (e.g., at t 7 ), the signal  348  changes from the logic high level to the logic low level (e.g., as shown by the waveform  710 ), and in response the switch  320  is opened (e.g., being turned off). In another example, the energy stored in the transformer is released to the output terminal, and the demagnetization process begins. In yet another example, a secondary current  397  that flows through the secondary winding  312  decreases in magnitude (e.g., linearly). In yet another example, a voltage  395  at the auxiliary winding  314  maps the output voltage  393 , and the feedback voltage  354  is generated through the voltage divider including the resistors  350  and  352 . As an example, when the secondary current decreases to the low magnitude (e.g., 0), the demagnetization process ends. As another example, the transformer including the primary winding  310  and the secondary winding  312  enters the resonant status. As yet another example, the voltage  395  at the auxiliary winding  314  has an approximate sinusoidal waveform. In an example, during the demagnetization period, the detection signal  358  (e.g., Demag) keeps at the logic high level (e.g., as shown by the waveform  704 ). In yet another example, the switch  416  is opened (e.g., being turned off) and the switch  408  is closed (e.g., being turned on). In yet another example, the capacitor  414  is discharged (e.g., at I 1 ), and the signal  420  decreases in magnitude (e.g., linearly) as shown by the waveform  706 . In yet another example, if the feedback voltage  354  becomes larger than the reference signal  516  (e.g., 0.1 V) in magnitude, it is determined that the demagnetization process has begun. In yet another example, if the feedback voltage  354  becomes smaller than the reference signal  516  (e.g., 0.1 V) in magnitude, it is determined that the demagnetization process has ended. 
     As one example, after the demagnetization process ends (e.g., at t 8 ), the detection signal  358  changes from the logic high level to the logic low level (e.g., as shown by the waveform  704 ). As another example, the switch  408  is open (e.g., being turned off) and the switch  416  is closed (e.g., being turned on). As yet another example, the capacitor  414  is charged again, and the signal  420  increases in magnitude (e.g., linearly) again as shown by the waveform  706 . As yet another example, when the signal  420  reaches a threshold  714  (e.g., the reference signal  422 ) in magnitude (e.g., at t 9 ), the comparator  410  changes the signal  346  (e.g., CC_ctrl) from the logic low level to the logic high level (e.g., as shown by the waveform  708 ). In yet another example, the signal  420  keeps at the threshold  714  until the end of the off-time period T off2  (e.g., until t 10  as shown by the waveform  706 ). For example, the signal  368  increases in magnitude during the off-time period T off2 . In another example, when the signal  368  reaches the comparison signal  366  in magnitude at the end of the off-time period T off2  (e.g., at t 10  as shown by the waveforms  716  and  720 ), the signal  356  changes from the logic low level to the logic high level (e.g., as shown by the waveform  718 ) in order to close the switch  320 . As shown in  FIG. 6 , when the rectifying diode  360  operates normally, multiple rings appear in the feedback voltage  354  during a resonance time period (e.g., T r ) from the end of the demagnetization period (e.g., t 8 ) to the end of the off-time period (e.g., t 10 ), as shown by the waveform  702 . 
       FIG. 7  is a simplified timing diagram for the power conversion system  300  in a constant-voltage mode under thermal runaway of the rectifying diode  360  according to one embodiment. The waveform  802  represents the feedback voltage  354  as a function of time. As shown in  FIG. 7 , few rings or no rings appear in the feedback voltage  354  during the resonance time period (e.g., T r ), which indicates that the transformer including the primary winding  310  and the secondary winding  312  does not enter a resonant status. 
       FIG. 8  is a simplified diagram showing a power conversion system with primary-side sensing and regulation according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The power conversion system  900  includes a primary winding  910 , a secondary winding  912 , an auxiliary winding  914 , a power switch  920 , a current sensing resistor  930 , an equivalent resistor  940  for an output cable, resistors  950  and  952 , a rectifying diode  960 , and a controller  970 . The controller  970  includes a sampling component  902 , a demagnetization detector  904 , a capacitor  906 , a switch  907 , a reference-signal generator  908 , a ramp-generator-and-oscillator  916 , an AND gate  918 , a driving component  922 , an OR gate  924 , comparators  926  and  928 , a flip-flop component  936 , a leading edge blanking (LEB) component  986 , resistors  984  and  988 , an error amplifier  990 , a modulation component  992 , a protection component  903 , and a constant-current (CC) component  994 . For example, the power switch  920  is a bipolar transistor. In another example, the power switch  920  is a MOS transistor. In yet another example, the controller  970  includes terminals  972 ,  974 ,  976 ,  978  and  980 . In yet another example, the rectifying diode  960  is a Schottky diode. 
     According to one embodiment, the auxiliary winding  914  is magnetically coupled to the secondary winding  912 , which, with one or more other components, generates an output voltage  993 . For example, information related to the output voltage is processed by a voltage divider of the resistors  950  and  952 , and is used to generate a feedback voltage  954 , which is received by the terminal  972  (e.g., terminal FB) of the controller  970 . In another example, the sampling component  902  samples the feedback voltage  954  and the sampled signal is held at the capacitor  906 . As an example, the error amplifier  990  compares the sampled-and-held voltage  962  with a reference signal  964  generated by the reference-signal generator  908 , and outputs a comparison signal  966  associated with the error of the sampled-and-held voltage  962  with respect to the reference signal  964 . As another example, the comparison signal  966  is received by the modulation component  992  which receives a ramping signal  968  and/or a clock signal  969  from the ramp-generator-and-oscillator  916  and outputs a signal  956  (e.g., CV_ctrl). 
     According to another embodiment, the comparison signal  966  is used to control the pulse width for PWM and/or the switching frequency for PFM in order to regulate the output voltage in a constant-voltage mode. For example, the demagnetization detector  904  determines the duration of a demagnetization period based on the feedback voltage  954  and outputs a detection signal  958  to the constant-current component  994  which generates a signal  946  (e.g., CC_ctrl). In another example, the protection component  903  receives the feedback voltage  954  and the detection signal  958  and outputs a blanking signal  905  and a fault signal  907 . In yet another example, the AND gate  918  receives the signal  956  (e.g., CV_ctrl), the signal  946  (e.g., CC_ctrl) and the blanking signal  905  and outputs a signal  919  that is received by the flip-flop component  936  (e.g., at a set terminal “S”). In yet another example, the flip-flop component  936  outputs a signal  937  (e.g., at a terminal “Q”) to the driving component  922 . In yet another example, the driving component  922  also receives the signal  907  (e.g., fault) and outputs a drive signal  948  through the terminal  976  to affect the status of the switch  920 . In yet another example, a primary current  996  flowing through the primary winding  910  is sensed using the resistor  930 , and a current-sensing signal  942  is generated through the LEB component  986  and received by the comparators  926  and  928 . In yet another example, the comparator  926  receives a threshold voltage  932  (e.g., V thocp ), and the comparator  928  receives another threshold voltage  901  associated with the comparison signal  966  (e.g., V comp ). In yet another example, the comparator  926  and the comparator  928  output comparison signals  934  and  938  respectively, to the OR gate  924 . In yet another example, the OR gate  924  outputs a signal  925  to the flip-flop component  936  (e.g., at a reset terminal “R”). As an example, when the sampled-and-held voltage  962  is smaller than the reference signal  964  in magnitude, the error amplifier  990  outputs the comparison signal  966  at a logic high level. The power conversion system  900  operates in a constant-current mode, in some embodiments. For example, when the sampled-and-held voltage  962  is equal to the reference signal  964  in magnitude, the comparison signal  966  has a fixed magnitude. The power conversion system  900  operates in the constant-voltage mode, in certain embodiments. 
       FIG. 9  is a simplified diagram showing the protection component  903  as part of the power conversion system  900  according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The protection component  903  includes a comparator  1002 , a timer component  1004 , an OR gate  1006 , NOT gates  1008 ,  1016  and  1024 , a counter-and-logic component  1010 , flip-flop components  1012  and  1026 , and a trigger component  1014 . The counter-and-logic component  1010  includes flip-flop components  1018 ,  1020  and  1022 . 
     According to one embodiment, the comparator  1002  receives the feedback voltage  954  and a reference signal  1028  and output a comparison signal  1030  to the OR gate  1006 . For example, the OR gate  1006  also receives a signal  1032  from the NOT gate  1024  and outputs a signal  1034  to the counter-and-logic component  1010  which outputs a signal  1036  to the NOT gate  1024 . In another example, the timer component  1004  outputs a signal  1038  to the flip-flop component  1012  (e.g., at a terminal “D”) which also receives the signal  958  (e.g., at a terminal “CLK”). In yet another example, the flip-flop component  1012  outputs a signal  1042  (e.g., at a terminal “Q”) to the timer component  1004  and the trigger component  1014  which provides a signal  1040  to the flip-flop component  1012  (e.g., at a terminal “R”) and the NOT gate  1016 . In yet another example, the flip-flop component  1026  receives the signal  1032  (e.g., at a terminal “D”) and the blanking signal  905  (e.g., at a terminal “CLK”) and outputs the fault signal  907  (e.g., at a terminal “Q”). In yet another example, a rising edge of the signal  1042  (e.g., q 1 ) corresponds to a falling edge of the signal  1038 . In yet another example, the flip-flop component  1018  receives the signal  1034  (e.g., at a “CLK” terminal). 
       FIG. 10  is a simplified timing diagram for the power conversion system  900  according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The waveform  1102  represents the signal  1038  as a function of time, the waveform  1104  represents the feedback voltage  954  as a function of time, and the waveform  1106  represents the signal  958  as a function of time. In addition, the waveform  1108  represents the signal  1042  (e.g., q 1 ) as a function of time, the waveform  1110  represents the blanking signal  905  as a function of time, and the waveform  1112  represents the signal  1030  (e.g., qr_det) as a function of time. The waveform  1114  represents the signal  1032  (e.g., Qcounter) as a function of time, the waveform  1116  represents the signal  948  (e.g., DRV) as a function of time, and the waveform  1118  represents the fault signal  907  (e.g., fault) as a function of time. For example, t 15 ≦t 16 ≦t 17 ≦t 18 ≦t 19 ≦t 20 ≦t 21 ≦t 22 ≦t 23 ≦t 24 . 
     Referring to  FIG. 8 ,  FIG. 9  and  FIG. 10 , the timer component  1004  changes the signal  1038  from a logic low level to a logic high level from time to time (e.g., with a time interval T d ) as shown by the waveform  1102 , in some embodiments. For example, at t 15 , the detection signal  958  changes from a logic high level to a logic low level (e.g., as shown by the waveform  1106 ), which indicates the end of the demagnetization period T demag3 . For example, the timer component  1004  outputs the signal  1038  at a logic low level (e.g., as shown by the waveform  1102 ), and in response, the flip-flop component  1012  (e.g., DFF1) outputs the signal  1042  (e.g., q 1 ) at the logic low level (e.g., as shown by the waveform  1108 ). The power conversion system  900  operates normally, in certain embodiments. For example, the time interval T d  is about 10 ms. 
     According to one embodiment, between t 15  and t 16 , the signal  1038  keeps at the logic low level, and the signal  1042  (e.g., q 1 ) keeps at the logic low level. For example, the fault signal  907  keeps at the logic low level, even if the signal  1032  (e.g., Qcounter) changes from the logic high level to the logic low level. In another example, at t 16 , the timer component  1004  changes the signal  1038  from the logic low level to the logic high level (e.g., as shown by the waveform  1102 ). In yet another example, between t 16  and t 21  (e.g., T d ), the timer component  1004  keeps the signal  1038  at the logic high level if no falling edge is detected in the detection signal  958 . In yet another example, at t 17 , the detection signal  958  changes from the logic low level to the logic high level (e.g., as shown by the waveform  1106 ), which indicates the beginning of the demagnetization period T demag4 . In yet another example, at t 18 , the detection signal  958  changes from the logic high level to the logic low level (e.g., as shown by the waveform  1106 ), which indicates the end of the demagnetization period T demag4 . In yet another example, upon detection of the falling edge in the detection signal  958  (e.g., at t 18 ), the timer component  1004  changes the signal  1038  from the logic high level to the logic low level (e.g., as shown by the waveform  1102 ). In response to the change of the signal  1038 , the trigger component  1014  changes the signal  1040 , and the blanking signal  905  changes from the logic high level to the logic low level, in some embodiments. For example, the flip-flop component  1012  changes the signal  1042  (e.g., q 1 ) from the logic low level to the logic high level (e.g., at t 18  as shown by the waveform  1108 ). The power conversion system  900  enters into a thermal-runaway-detection mode, in some embodiments. For example, a clock associated with the timer component  1004  is restarted toward a next time interval T d . As an example, T d  is predetermined, and is longer than multiple switching periods associated with the power conversion system  900 . 
     According to another embodiment, when the blanking signal  905  is at the logic low level, i.e., during a detection period (e.g., T blank ), the signal  919  from the AND gate  918  is at the logic low level so that the switch  920  is kept open (e.g., being turned off), regardless of the signal  956  (e.g., CV_ctrl) and the signal  946  (e.g., CC_ctrl). As an example, a starting time of the detection period (e.g., T blank ) is at t 18  and an ending time of the detection period (e.g., T blank ) is at t 20 . In another example, the blanking signal  905  changes from the logic low level to the logic high level after the detection period (e.g., at t 20 , as shown by the waveform  1110 ). As an example, the comparator compares the feedback voltage  954  and the reference signal  1028  (e.g., 0.1 V), and determines whether multiple resonance rings occur in the feedback voltage  954 . As another example, the counter-and-logic component  1010  determines the number of the resonance rings in the feedback voltage  954 . As yet another example, the detection period (e.g., T blank ) is about 20 μs. For example, a resonance ring corresponds to the feedback voltage  954  becoming smaller than the reference signal  1028  in magnitude. In yet another example, the detection period (e.g., T blank ) starts when the timer component  1004  changes the signal  1038  from the logic high level to the logic low level. In yet another example, the detection period (e.g., T blank ) ends when the flip-flop component  1012  changes the signal  1042  (e.g., q 1 ) from the logic high level to the logic low level. 
     According to yet another embodiment, if the counter-and-logic component  1010  determines the number of the resonance rings appearing in the feedback voltage  954  (e.g., the feedback voltage  954  becoming smaller than the reference signal  1028 ) during the detection period (e.g., T blank ) reaches a threshold (e.g., 4), the signal  1032  (e.g., Qcounter) changes to the logic low level (e.g., at t 19 , as shown by the waveforms  1104  and  1114 ), and the counter-and-logic component  1010  stops counting. For example, upon the rising edge of the blanking signal  905  (e.g., at t 20  as shown by the waveform  1110 ), the flip-flop component  1026  (e.g., DFF2) detects the signal  1032  (e.g., Qcounter), and outputs the fault signal  907  at the logic low level in response to the signal  1032  being at the logic low level (e.g., as shown by the waveforms  1114  and  1118 ). The power conversion system  900  is not in a thermal-runaway status, and continues to operate normally, in certain embodiments. For example, the driving component  922  outputs the drive signal  948  to close or open the switch  920  according to one or more modulation frequencies. In certain embodiments, the time period between t 20  and t 21  includes one or more switching periods. For example, the power conversion system  900  enters into the thermal-runaway-detection mode during each switching period. That is, during a detection period (e.g., T blank ) within each switching period, whether the number of the resonance rings appearing in the feedback voltage  954  reaches the threshold is determined for detecting thermal runaway. 
     In one embodiment, at t 21 , another time interval T d  begins, and the clock associated with the timer component  1004  is restarted to count the time. For example, the timer component  1004  changes the signal  1038  from the logic low level to the logic high level (e.g., at t 21  as shown by the waveform  1102 ). In another example, at t 22 , the detection signal  958  changes from the logic low level to the logic high level (e.g., as shown by the waveform  1106 ), which indicates the beginning of the demagnetization period T demag5 . In yet another example, at t 23 , the detection signal  958  changes from the logic high level to the logic low level (e.g., as shown by the waveform  1106 ), which indicates the end of the demagnetization period T demag5 . In yet another example, the timer component  1004  changes the signal  1038  from the logic high level to the logic low level (e.g., as shown by the waveform  1102 ), and in response, the flip-flop component  1012  changes the signal  1042  (e.g., 1) from the logic low level to the logic high level (e.g., as shown by the waveform  1108 ). The power conversion system  900  enters into the thermal-runaway-detection mode again, in some embodiments. 
     In another embodiment, at t 23 , the trigger component  1014  changes the signal  1040 , and as a result the blanking signal  905  changes from the logic high level to the logic low level. For example, the blanking signal  905  changes from the logic low level to the logic high level after another detection period (e.g., T blank ), as shown by the waveform  1110 . In another example, during the detection period (e.g., T blank ), the switch  920  is kept open (e.g., being turned off), regardless of the signal  956  (e.g., CV_ctrl) and the signal  946  (e.g., CC_ctrl). As an example, the comparator compares the feedback voltage  954  and the reference signal  1028  (e.g., 0.1 V), and determines whether multiple resonance rings occur in the feedback voltage  954 . As another example, the counter-and-logic component  1010  determines the number of the resonance rings in the feedback voltage  954 . 
     In yet another embodiment, if the counter-and-logic component  1010  determines the number of the resonance rings in the feedback voltage  954  during the detection period (e.g., T blank ) is smaller than the threshold (e.g., 4), the signal  1032  (e.g., Qcounter) keeps at the logic high level (e.g., as shown by the waveforms  1104  and  1114 ). For example, upon the rising edge of the blanking signal  905  (e.g., at t 24  as shown by the waveform  1110 ), the flip-flop component  1026  (e.g., DFF2) detects the signal  1032  (e.g., Qcounter), and changes the fault signal  907  from the logic low level to the logic high level in response to the signal  1032  being at the logic high level (e.g., as shown by the waveforms  1114  and  1118 ). The power conversion system  900  is determined to be in the thermal-runaway status, and enters into an auto-recovery mode or an analog latch mode, in certain embodiments. For example, the power conversion system  900  stops operation and there is no output signal from the power conversion system  900  unless the power conversion system  900  is powered down (e.g., a power cord is unplugged) and restarted (e.g., the power cord is plugged in), so that the temperature of the diode  960  can decrease for the system  900  to operate safely. In another example, the demagnetization period T demag5  is separated from the demagnetization period T demag4  by one or more switching periods associated with the drive signal  948 . 
     As discussed above and further emphasized here,  FIG. 10  is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, a resonance ring corresponds to the feedback voltage  954  exceeding the reference signal  1028  in magnitude. 
     According to one embodiment, a system controller for protecting a power conversion system includes a protection component and a driving component. The protection component is configured to receive a feedback signal, a reference signal, and a demagnetization signal generated based on at least information associated with the feedback signal, process information associated with the feedback signal, the reference signal, and the demagnetization signal, and generate a protection signal based on at least information associated with the feedback signal, the reference signal, and the demagnetization signal. The demagnetization signal is related to multiple demagnetization periods of the power conversion system, the multiple demagnetization periods including a first demagnetization period and a second demagnetization period. The driving component is configured to receive the protection signal and output a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system. The protection component is further configured to: process information associated with the feedback signal and the reference signal during a first detection period, the first detection period including a first starting time and a first ending time, the first starting time being at or after a first demagnetization end of the first demagnetization period, determine, during the first detection period, a first number of times that the feedback signal changes from being smaller than the reference signal to being larger than the reference signal in magnitude, and determine whether the first number of times exceeds a predetermined threshold at the first ending time. The protection component and the driving component are further configured to, in response to the first number of times not exceeding the predetermined threshold at the first ending time, output the drive signal to cause the switch to open and remain open in order to protect the power conversion system. For example, the system controller is implemented according to  FIG. 8 , and/or  FIG. 9 . 
     According to another embodiment, a system controller for protecting a power conversion system includes a protection component and a driving component. The protection component is configured to receive a feedback signal, a reference signal, and a demagnetization signal generated based on at least information associated with the feedback signal, process information associated with the feedback signal, the reference signal, and the demagnetization signal, and generate a protection signal based on at least information associated with the feedback signal, the reference signal, and the demagnetization signal. The demagnetization signal is related to multiple demagnetization periods of the power conversion system, the multiple demagnetization periods including a first demagnetization period and a second demagnetization period. The driving component is configured to receive the protection signal and output a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system. The protection component is further configured to: process information associated with the feedback signal and the reference signal during a first detection period, the first detection period including a first starting time and a first ending time, the first starting time being at or after a first demagnetization end of the first demagnetization period, determine, during the first detection period, a first number of times that the feedback signal changes from being larger than the reference signal to being smaller than the reference signal in magnitude, and determine whether the first number of times exceeds a predetermined threshold at the first ending time. The protection component and the driving component are further configured to, in response to the first number of times not exceeding the predetermined threshold at the first ending time, output the drive signal to cause the switch to open and remain open in order to protect the power conversion system. For example, the system controller is implemented according to  FIG. 8 , and/or  FIG. 9 . 
     According to yet another embodiment, a method for protecting a power conversion system includes: receiving a feedback signal, a reference signal, and a demagnetization signal generated based on at least information associated with the feedback signal, processing information associated with the feedback signal, the reference signal, and the demagnetization signal, and generating a protection signal based on at least information associated with the feedback signal, the reference signal, and the demagnetization signal, the demagnetization signal being related to multiple demagnetization periods of the power conversion system, the multiple demagnetization periods including a first demagnetization period and a second demagnetization period. The method additionally includes: receiving the protection signal, processing information associated with the protection signal, and outputting a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system. The processing information associated with the feedback signal, the reference signal, and the demagnetization signal includes: processing information associated with the feedback signal and the reference signal during a first detection period, the first detection period including a first starting time and a first ending time, the first starting time being at or after a first demagnetization end of the first demagnetization period, determining, during the first detection period, a first number of times that the feedback signal changes from being smaller than the reference signal to being larger than the reference signal in magnitude, and determining whether the first number of times exceeds a predetermined threshold at the first ending time. The outputting a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system includes: in response to the first number of times not exceeding the predetermined threshold at the first ending time, outputting the drive signal to cause the switch to open and remain open in order to protect the power conversion system. For example, the method is implemented according to  FIG. 8 ,  FIG. 9 , and/or  FIG. 10 . 
     According to yet another embodiment, a method for protecting a power conversion system includes: receiving a feedback signal, a reference signal, and a demagnetization signal generated based on at least information associated with the feedback signal, processing information associated with the feedback signal, the reference signal, and the demagnetization signal, and generating a protection signal based on at least information associated with the feedback signal, the reference signal, and the demagnetization signal, the demagnetization signal being related to multiple demagnetization periods of the power conversion system, the multiple demagnetization periods including a first demagnetization period and a second demagnetization period. The method further includes: receiving the protection signal, processing information associated with the protection signal, and outputting a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system. The processing information associated with the feedback signal, the reference signal, and the demagnetization signal includes: processing information associated with the feedback signal and the reference signal during a first detection period, the first detection period including a first starting time and a first ending time, the first starting time being at or after a first demagnetization end of the first demagnetization period, determining, during the first detection period, a first number of times that the feedback signal changes from being larger than the reference signal to being larger than the reference signal in magnitude, and determining whether the first number of times exceeds a predetermined threshold at the first ending time. The outputting a drive signal to a switch configured to affect a current flowing through a primary winding of the power conversion system includes: in response to the first number of times not exceeding the predetermined threshold at the first ending time, outputting the drive signal to cause the switch to open and remain open in order to protect the power conversion system. For example, the method is implemented according to  FIG. 8 ,  FIG. 9 , and/or  FIG. 10 . 
     For example, some or all components of various embodiments of the present invention each are, individually and/or in combination with at least another component, implemented using one or more software components, one or more hardware components, and/or one or more combinations of software and hardware components. In another example, some or all components of various embodiments of the present invention each are, individually and/or in combination with at least another component, implemented in one or more circuits, such as one or more analog circuits and/or one or more digital circuits. In yet another example, various embodiments and/or examples of the present invention can be combined. 
     Although specific embodiments of the present invention have been described, it will be understood by those of skill in the art that there are other embodiments that are equivalent to the described embodiments. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims.