Abstract:
A power converter has simple coupled inductor circuit process the power and drive the semiconductor switch perfectly to reduce the power loss and eliminate the needs of high circuit complexity controller, improve the conversion efficiency and reduce the component counts to reach low cost and high reliability at one time.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to DC-to-DC converters, AC-to-DC converters. The major characteristic of this converter is that transfer energy from input to output with high efficiency and low cost.  
       BACKGROUND OF THE INVENTION  
       [0002]     In the field of power conversion technology, increasing the conversion efficiency and improve the reliability are the most important demands. Basically, conventional buck converter technology is desirable as it transfers the power from input to output with controlled function. However, the efficiency of conventional buck converter is limited at 90% maximum due to the power loss of fly-wheeling diode is proportioned with its junction voltage drop that dominate the total power loss. In order to overcome limitations in power loss and heat, the prior art has been devised the synchronous rectification technology.  
         [0003]      FIG. 1   a  shows the synchronous rectification buck converter named as SR-Buck converter below. The SR-Buck converter has been derived from conventional buck converter by using the semiconductor switch such as MOSFET to replace fly-wheeling diode. The forward switch S FW  is drive by a PWM signal for turned ON and turned OFF periodically to transfer the energy from input voltage source V I  through inductor L O  to smooth capacitor C O  and load R L . The fly-wheeling switch S FL  is also drive by a PWM signal that complementary with the drive signal of forward switch S FW  for turned ON and OFF periodically to discharge the stored energy of inductor L O  to the smooth capacitor C O  and load R L . A small period of dead time between the turn ON time of forward switch S FW  and fly-wheeling switch S FL  is required to prevent the damage from short through behavior between S FW  and S FL .  FIG. 1   b  shows the timing diagram of the circuit of FIG  1   a.    
         [0004]     SR-Buck converter reduces the voltage drop of diode and its power loss allows the conversion efficiency is greater then 90% that the power handling of converter is improved. However, the optimal gate drive waveform is generated from high circuit complexity controller to keep the turned ON time of forward switch S FW  and fly-wheeling switch S FL  never overleap but as small as possible to obtain highest efficiency that the component selection is difficult to meet high reliability and cost effective requirement.  
         [0005]      FIG. 2   a  shows the resonant reset forward converter with secondary passive drive synchronous rectifier circuit named as SR-Forward converter below. The secondary synchronous rectifier circuit has been derived from conventional rectifier by using semiconductor switch such as MOSFET to replace semiconductor diode each leg. The forward switch S FW  is drive by secondary winding W S  to selects connecting the output inductor to secondary winding transfer energy to smooth capacitor C O  and load RL when the primary switch S P  is turned ON to connect primary winding W P  with input voltage source V I . The fly-wheeling switch S FL  may selects connecting the output inductor to ground during the reset time of transformer when the primary switch S P  is turned OFF. The gate drive signal of primary switch S P  is supplied from a simple PWM controller and the gate driving signals of forward switch S P  and fly-wheeling switch S FL  are supplied from transformer secondary directly.  FIG. 2   b  shows the timing diagram of the circuit of  FIG. 2   a.    
         [0006]     The SR-Forward converter reduce the power loss with minimum circuit complexity of controller, it take advantage from synchronous rectifier circuit to reach high efficiency just like most topologies. However, the fly-wheeling switch S FL  will be turned OFF due to the reset voltage drop to zero before primary switch S P  turned ON, it cause extra power loss due to low speed high voltage drop body diode conduct the load current limit the input voltage range for efficient operation.  
         [0007]     What is the best power conversion technology? Higher efficiency, less circuit complexity of converter and wide range operation are the most important demands of power conversion technology.  
       SUMMARY OF THE INVENTION  
       [0008]     The invention utilizes a power converter with new circuit concept to enhance the performance and reduce the circuit complexity at once. Briefly, this circuit consists of a coupled inductor, a forward switch and a fly-wheeling switch. The coupled inductor provides two paths for carry the load current during different operation stage. The forward switch provides a path to transfer the energy from input voltage source through the first winding of the coupled inductor to the load when it is turned ON, the fly-wheeling switch provides a path to discharge the energy stored in the coupled inductor through the second inductor winding of the coupled inductor to the load when forward switch is turned OFF.  
         [0009]     The new circuit provides optimal performance for buck derived power converters: It improve the input voltage range for efficient operation, as it eliminate the body diode conduct stage; It simplifies converter construction, as it can be implemented without extra control circuits; It is worked well and do not require any additional devices, as it can be widely used with low cost. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1   a  shows the SR-Buck converter.  
         [0011]      FIG. 1   b  shows the timing diagram of the circuit of FIG  1   a.    
         [0012]      FIG. 2   a  shows the SR-Forward converter.  
         [0013]      FIG. 2   b  shows the timing diagram of the circuit of FIG  2   a.    
         [0014]      FIG. 3   a  shows the coupled inductor SR-Buck converter.  
         [0015]      FIG. 3   b  shows the voltage control network circuits with SR switch.  
         [0016]      FIG. 3   c  shows the topological variations of coupled inductor SR-Buck converter.  
         [0017]      FIG. 4  shows the timing diagram of circuit in  FIG. 3   a.    
         [0018]      FIG. 5   a  shows the forward transition stage of circuit in  FIG. 3   a.    
         [0019]      FIG. 5   b  shows the forward stage of circuit in  FIG. 3   a.    
         [0020]      FIG. 5   c  shows the fly-wheeling transition stage of circuit in  FIG. 3   a.    
         [0021]      FIG. 5   d  shows the fly-wheeling stage of circuit in  FIG. 3   a.    
         [0022]      FIG. 6   a  shows the coupled inductor SR-Forward converter.  
         [0023]      FIG. 6   b  shows the coupled inductor SR-Forward converter with different connection.  
         [0024]      FIG. 6   c  shows the topological variation of coupled inductor SR-Forward converter.  
         [0025]      FIG. 7  shows the timing diagram of the circuit in  FIG. 6   a.    
         [0026]      FIG. 8   a  shows the forward transition stage of circuit in  FIG. 6   a.    
         [0027]      FIG. 8   b  shows the forward stage of circuit in  FIG. 6   a.    
         [0028]      FIG. 8   c  shows the fly-wheeling transition stage of circuit in  FIG. 6   a.    
         [0029]      FIG. 8   d  shows the fly-wheeling stage of circuit in  FIG. 6   a.   
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     Referring now to the drawings, and more particular to  FIG. 3   a , a coupled inductor SR-Buck converter in accordance with the present invention is illustrated. A coupled inductor SR-Buck converter comprises input voltage source V I , fly-wheeling switch S FL , clamp diode D, gate voltage control network N FL , coupled inductor including two inductor windings L FW  and L FL  and smooth capacitor C O . The windings of coupled inductor are identical in the inductance and large enough to use as an output DC current source, and the output smooth capacitor is large enough to use as an output voltage source V O  for theoretical analysis. The forward switch SFW provides a path to transfer the energy from input voltage source V I  through inductor winding L FW  to smooth capacitor C O  when it is turn ON. The fly-wheeling switch S FL  was either drive by the voltage of inductor winding L FW  directly or through a gate voltage control network N FL , and here the voltage control network can be a voltage damper or a voltage divider or even just a wire that no active function to control the timing of gate drive signal. Three typical circuits of voltage control network with the switch were shown as  FIG. 3   b . The clamp diode D some time was required for providing a path to discharge the energy that stored in the leakage inductance of coupled inductor when the stored energy is large enough to affect the efficiency greatly or an unacceptable voltage spike is generated by the energy that possible to damage the forward switch S FW  and fly-wheeling switch S FL . The discharge path of the stored energy in the leakage inductance may be through parasitic capacitance of forward switch SFW if the clamp diode is not connected.  
         [0031]     A coupled inductor SR-Buck converter show in  FIG. 3   a  is easy to reorganize the power circuit and components by applying the duality principle simply to derive the topological variation show as  FIG. 3   c . The typical operation waveforms of coupled inductor SR-Buck converter were show in  FIG. 4  is different from the prior art of conventional SR-Buck converter. Under steady-state operation, the coupled inductor SR-Buck converter has four stages are equal to four equivalent circuits within one switching cycle shown in  FIG. 5   a  to  FIG. 5   d.    
         [0032]     Referring to  FIG. 5   a , during T 0  to T 1  interval, the forward switch S FW  is turned ON at T 0 , apply the voltage V I /2 to the leakage inductance of inductor winding L FW  cause the current of inductor winding L FW  increased rapidly from zero to I O  and decrease the current of inductor winding L FL  from I O  to zero simultaneously. Ideally, the voltage on the ideal coupled inductor is equal to V O −V I /2 during this period may ensure the absolute current change rate on both inductor windings are identical but it can adjust automatically to cover the difference of leakage inductance on each winding at practical applications. The fly-wheeling switch S FL  is turned OFF before the current of inductor winding L FL  reach to zero but still allow current flow through its body diode as a single direction switch. While the end of this interval, the current of inductor winding L FW  is reached to I O  at T 1 .  
         [0033]     Referring to  FIG. 5   b , during T 1  to T 2  interval, the forward switch S FW  was turned ON carry the current I O  from input source V I  through inductor winding L FW  to the output voltage source V O . While the end of this interval, the forward switch S FW  is turned OFF at T 2  and the conducting path through inductor winding L FW  and forward switch S FW  is blocked.  
         [0034]     Referring to  FIG. 5   c , during T 2  to T 3  interval, the forward switch S FW  is turned OFF at T 2 , the node voltage of inductor winding L FW  connected with forward switch S FW  is decreased rapidly, it drive the fly-wheeling switch S FL  ON to carry current I O  through inductor winding L FL  avoid it flow through high voltage drop low speed body diode. The current of inductor winding L FW  is conducted through clamp diode D to discharge the stored energy in the leakage inductance of inductor winding L FW . While the end of this interval, the current of inductor winding L FL  is increased to I O  and the current of inductor winding L FW  is decreased to zero at T 3 .  
         [0035]     Referring to  FIG. 5   d , during T 3  to T 0  interval, the fly-wheeling switch S FL  was turned ON during full period of this interval automatically to conduct the current I O  through inductor winding L FL  to output voltage source V O . While the end of this interval, the forward switch S FW  is turn ON to carry the current I O  from input voltage source V I  again to starting the next switching cycle.  
         [0036]     The gate drive voltage of fly-wheeling switch S FL  is discharged by the forward switch S FW  before the load current I O  fully coupled from inductor winding L FL  to inductor winding L FW , it eliminate the damage of short-through behavior between forward switch S FW  and fly-wheeling switch S FL  without the needs of precise gate drive control signal that generated from a high circuit complexity controller.  
         [0037]     After the success on the coupled inductor SR-Buck converter, employing the same concept to several types of conventional SR-Forward converter would be the next step perfectly. The key concept of coupled inductor SR operation is concerning on its self-drive structure of the fly-wheeling switch only as coupled inductor SR can be cooperated perfectly with all buck-derived converters. A resonant reset coupled inductor SR-Forward converter was used as an example for better understanding and discussion shown as  FIG. 6   a.    
         [0038]     The typical coupled inductor SR-Forward converter comprises the key primary side circuit of forward converter (input source V I , primary switch S P  and a transformer has primary winding W P  and secondary winding W S  with turn ratio N:1, where the reset technology of transformer is irrelevant), a secondary side circuit that similar to coupled inductor SR-Buck converter (forward switch S FW , fly-wheeling switch S FL , clamp diode D, gate voltage control networks N FW  and N FL , coupled inductor including two inductor windings L FW  and L FL  and smooth capacitor C O . The windings of coupled inductor are identical in the inductance and large enough to used as an output DC current source, and the smooth capacitor C O  is large enough to worked as an output voltage source V O  for theoretical analysis).  
         [0039]     The forward switch S FW  is drive by a signal from a drive transformer winding or a external driver that synchronous with primary switch S P  to turned ON and turned OFF but in the most case is drive by the voltage of transformer secondary winding through a gate voltage control networks N FW , and here the voltage control network can be a voltage damper or a voltage divider was shown as  FIG. 3   b  or even just a wire that no active function to control the timing of gate drive signal. The operation is similar to coupled inductor SR-Buck converter described above as it just like the forward switch S FW  connected with a mirrored voltage source from primary side provides a path to transfer the energy through inductor winding L FW  to smooth capacitor C O  when primary switch S P  is turn ON, The clamp diode D can be an option to discharge the stored energy in the leakage inductance of coupled inductor to smooth capacitor C O  when the forward switch S FW  is turned OFF, the stored energy in the leakage inductance of coupled inductor will discharge back to input voltage source V I  through the body diode of forward switch SFW and transformer if the clamp diode D is not applied. The fly-wheeling switch S FL  is drive by inductor winding L FW  through a gate voltage control network N FL , and here the voltage control network can be a voltage damper or a voltage divider was shown as  FIG. 3   b  or even just a wire that no active function to control the timing of gate drive signal. There is an alternative signal to drive the fly-wheeling switch S FL  for low voltage application that the mirrored transformer reset voltage on the transformer secondary winding can be super-positioned on the voltage of inductor winding L FW  to have better drive performance when the forward switch S FW  was connected between transformer secondary winding W S  and inductor winding L FW  also can be seen in  FIG. 6   b.    
         [0040]     The typical coupled inductor SR-Forward converter is easy to reorganize the power circuit and components by applying the duality principle simply to derive the topological variation show as  FIG. 6   c . The typical operation waveforms show in  FIG. 7  is different from the prior art of conventional SR-Forward converter. Under steady-state operation, the secondary circuit of coupled inductor SR-Forward converter has four stages are equal to four equivalent circuits within one switching cycle shown in  FIG. 8   a  to  FIG. 8   d.    
         [0041]     Referring to  FIG. 8   a , during T 0  to T 1  interval, the primary switch S P  is turned ON to connect input voltage source V I  to the primary winding W P  of transformer. The forward switch S FW  is also turned ON at T 0  by the voltage V I /N of the secondary winding W S  apply the voltage V I /2N to the leakage inductance of inductor winding L FW  cause the current of inductor winding L FW  increased rapidly from zero to I O  and decrease the current of inductor winding L FL  from I O  to zero simultaneously. Ideally, the voltage on the ideal coupled inductor is equal to V O −V I /2N during this period may ensure the absolute current change rate on both inductor windings are identical but it can adjust automatically to cover the difference of leakage inductance on each winding at practical applications. The fly-wheeling switch S FL  is turned OFF before the current of inductor winding L FL  reach to zero but still allow current flow through its body diode as a single direction switch. While the end of this interval, the current of inductor winding L FW  is reached to I O  to transfer energy from mirrored input voltage source V I /N through inductor winding L FW  to the output voltage source V O , the primary switch S P  and the forward switch S FW  are turned OFF at T 1  and the conducting path through inductor winding L FW  is blocked.  
         [0042]     Referring to  FIG. 8   b , during T 1  to T 2  interval, the forward switch S FW  was turned ON carry the current I O  from mirrored input source V I /N through inductor winding L FW  to the output voltage source V O . While the end of this interval, the forward switch S FW  is turned OFF at T 2  and the conducting path through inductor winding L FW  and forward switch S FW  is blocked.  
         [0043]     Referring to  FIG. 8   c , during T 2  to T 3  interval, the primary switch S P  and forward switch S FW  are turned OFF at T 2 , the node voltage of inductor winding L FW  connected with forward switch S FW  is increased rapidly, it drive the fly-wheeling switch S FL  ON to carry current I O  through inductor winding L FL  avoid it flow through high voltage drop low speed body diode. The current of inductor winding L FW  is conducted through clamp diode D to discharge the stored energy in the leakage inductance of inductor winding L FW . While the end of this interval, the current of inductor winding L FL  is increased to I O  and the current of inductor winding L FW  is decreased to zero at T 3 .  
         [0044]     Referring to  FIG. 8   d , during T 3  to T 0  interval, the fly-wheeling switch S FL  was turned ON during full period of this interval automatically to conduct the current I O  through inductor winding L FL  to output voltage source V O . While the end of this interval, the forward switch SFW is turn ON to carry the current I O  from input voltage source V I  again to starting the next switching cycle.  
         [0045]     The gate drive voltage of fly-wheeling switch S FL  is discharged by the forward switch S FW  before the load current I O  fully coupled from inductor winding L FL  to inductor winding L FW , it eliminate the damage of short-through behavior between forward switch S FW  and fly-wheeling switch S FL  without the needs of precise gate drive control signal that generated from a high circuit complexity controller.  
         [0046]     A power converter with coupled inductor SR circuit eliminate the body diode conduction stage, as it keep fly-wheeling switch turn ON automatically during forward switch OFF period; it prevent the damages from the short through between forward switch and fly-wheeling switch inherently, as it can turn fly-wheeling switch OFF before forward switch began conduct the current inherently; It simplifies converter construction, as it can be implemented without extra control circuits; It is worked well and do not require any additional devices, as it can be used widely with low cost.  
         [0047]     Based on analysis above, the key concept of this invention is concerning on its self-drive structure of the fly-wheeling switch only as this invention can be used with all buck-derived converters, and while the invention has been described in terms of a single preferred embodiment, those skilled in the art will recognize that the invention can be practiced with modification on different transformer reset technology and different drive method of forward switch still within the spirit and scope of the appended claims.