# Patent

## Title
Switching controller for power sharing of parallel power supplies

## Abstract

A switching controller for power sharing of power supplies is disclosed. The switching controller includes an input circuit coupled to an input terminal to receive an input signal for generating a phase-shift signal, a first integration circuit coupled to the input circuit to generate a first integration signal in response to a pulse width of the input signal, and a control circuit coupled to the first integration circuit to generate a switching signal for switching the power supply, wherein the switching signal is enabled in response to the phase-shift signal, and a pulse width of the switching signal is determined in accordance with the first integration signal.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to switching controllers, and more particularly to a switching controller of parallel power supplies.
2. Description of the Related Art
In order to fulfill the high-speed need for computer and communication systems, a power supply is required to deliver more current to CPU and its peripherals. However, such a high current demand increases power losses in the power supply. The power loss of the power supply is proportional to the square of its switching current.

PLOSS=I2×R  (1)

where I is the switching current of the power supply, and R is the impedance of the switching devices such as the resistance of the inductor and the transistor, or the like.
Higher output current results in lower efficiency and the efficiency is more adversely affected for the power supply with low output voltage. In recent development, parallel-output technologies have been developed to solve this problem. Examples are, for instance, “DC-to-DC controller having a multi-phase synchronous buck regulator”, U.S. Pat. No. 6,262,566 to Dinh; “Multi-phase converter with balanced currents” by Walters et al., U.S. Pat. No. 6,278,263; “Multi-phase switching converters and methods” by Ashburn et al., U.S. Pat. No. 6,362,608 and “Multi-phase and multi-module power supplies with balanced current between phases and modules” by Yang et al., U.S. Pat. No. 6,404,175. However, one problem of these prior arts is the limited parallel channels. Typically, mere two or three channels are developed in terms of the disclosures of the prior art. The limited parallel channels cause inflexibility of the application of the parallel-output technologies, especially for off-line power supplies. Another disadvantage is the balance current approach that requires the measurement of the switching current. The switching current measurement normally causes power losses.
SUMMARY OF THE INVENTION
An objective of the present invention is to provide a switching controller with power sharing capability for parallel power supplies that requires no current measurement and enhances flexibility of application of parallel channels.
In order to achieve the above and other objectives, the switching controller for parallel power supplies according to the present invention comprises an input circuit to receive an input signal for generating a phase-shift signal, a resistor determining a delay time in between the input signal and the phase-shift signal, a first integration circuit coupled to the input circuit to generate a first integration signal in response to a pulse width of the input signal, and a control circuit to generate the switching signal for switching the power supply. The switching controller for a power supply further comprises a second integration signal for generating a second integration signal in response to a pulse width of a switching signal.
The switching signal is enabled in response to an enabling of the phase-shift signal, and is disabled in response to the comparison of the first integration signal and the second integration signal. The time constant of the first integration circuit is correlated with the time constant of the second integration circuit. Therefore, the pulse width of the switching signal is determined in accordance with the level of the first integration signal. The level of the first integration signal is increased in response to the increase of pulse width of the input signal, while the pulse width of the switching signal is decreased in response to the decrease of the integration signal. The pulse width of the switching signal will be same as the pulse width of the input signal to achieve the power sharing. Furthermore, a detection circuit is provided to detect the input signal, allowing the switching signal to be enabled in response to a pulse signals if the input signal were detected by the detection circuit to be not available. An oscillator is further provided to generate the pulse signal and a ramp signal, and a feedback terminal is coupled to the output of the power supply to receive a feedback signal. It allows the switching signal is disabled in response to the comparison of the feedback signal and the ramp signal.
The switching controller with power sharing capability of the present invention can be stand-alone or parallel operation to provide high output current for power supply. The number for the parallel arrangement of the switching controller has no limit theoretically. Synchronization and phase shift can be further utilized to spread switching noise and reduce ripple. As power sharing is used instead of the balance current, no current measurement is needed, which simplifies the circuit and further improves the efficiency of power supply.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,
FIG. 1 shows a preferred embodiment of parallel power supplies according to present invention.
FIG. 2 shows a switching controller according to present invention.
FIG. 3 shows a power sharing circuit of the switching controller according to present invention.
FIG. 4 is a preferred embodiment of an input circuit according to present invention.
FIG. 5 shows a circuit schematic of a pulse generator.
FIG. 6 is a detection circuit for detecting the input of the input signal.
FIG. 7 shows an integration circuit according to present invention.
FIG. 8 shows an oscillation circuit.
FIG. 9 shows a circuit schematic of a multiplexer.
FIG. 10 shows a reset circuit according to present invention.
FIG. 11 shows key waveforms of the switching controller according to, present invention.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a preferred embodiment of parallel power supplies according to present invention. A switching controller 10, a transistor 12 and a transformer 15 develop a first power converter. The output terminal SW of the switching controller 10 is coupled to control the transistor 12. The transistor 12 is used for switching the transformer 15. A rectifier 16 and a capacitor 17 are connected to the transformer 15 to generate the output for the first power converter. A switching controller 20, a transistor 22 and a transformer 25 develop a second power converter. A rectifier 27 and a capacitor 27 are connected to the transformer 25 to generate the output of the second power converter. A switching controller 40, a transistor 42 and a transformer 45 develop a fourth power converter. A rectifier 46 and a capacitor 47 are connected to the transformer 45 to produce the output of the fourth power converter. The output of the first power converter, the output of the second power converter and the output of the fourth power converter are parallel connected to the output voltage VO of the power supply. The transformer 15 is coupled to an input voltage VIN. When the switching controller 10 is on, a switching current I10-sw is generated. It is given by,




  
    
      
        
          I
          
            10
            -
            SW
          
        
        =
        
          
            
              V
              IN
            
            
              L
              15
            
          
          ×
          
            T
            
              ON
              -
              10
            
          
        
      
    
    
      
        (
        2
        )
      
    
  




where the L15 is the inductance of the primary winding of the transformer 15; TON-10 is the on time of the switching controller 10; VIN is the input voltage.
The feedback terminal FB of the switching controller 10 is coupled to the output voltage VO through the feedback circuit 50 to regulate the output voltage VO of the power supply. The feedback circuit 50 normally includes an error amplifier and an optical coupler to generate a feedback signal VFB is response to the output voltage VO of the power supply. The output terminal SW of the switching controller 10 is coupled to the input terminal SYN of the switching controller 20. Its previous switching controller controls the switching controller 40 through the input terminal SYN. A resistor 21 is connected to the switching controller 20 to determine the delay time between switching signals of the switching controller 10 and 20. A resistor 41 is connected to the switching controller 40 to determine the delay time between switching signals of the switching controller 40 and its previous controller. The switching controller 10 is operated as a master controller, while the switching controllers 20 and 40 are activated as slave controllers. The output of power converters is connected to the output voltage VO. Slave controllers can be connected as a daisy chain for the synchronization and power sharing. The on-time and the switching period of slave controllers will follow the on-time and the switching period of the master controller.
The output power PO of the power supply can be expressed as,




  
    
      
        
          P
          O
        
        =
        
          
            1
            2
          
          ×
          L
          ×
          
            I
            2
          
        
      
    
    
      
        (
        3
        )
      
    
  
  
    
      
        
          P
          10
        
        =
        
          
            
              
                (
                
                  V
                  IN
                
                )
              
              2
            
            ×
            
              
                (
                
                  T
                  
                    ON
                    -
                    10
                  
                
                )
              
              2
            
          
          
            2
            ×
            
              L
              15
            
            ×
            
              T
              10
            
          
        
      
    
    
      
        (
        4
        )
      
    
  
  
    
      
        
          P
          20
        
        =
        
          
            
              
                (
                
                  V
                  IN
                
                )
              
              2
            
            ×
            
              
                (
                
                  T
                  
                    ON
                    -
                    20
                  
                
                )
              
              2
            
          
          
            2
            ×
            
              L
              25
            
            ×
            
              T
              20
            
          
        
      
    
    
      
        (
        5
        )
      
    
  
  
    
      
        
          P
          40
        
        =
        
          
            
              
                (
                
                  V
                  IN
                
                )
              
              2
            
            ×
            
              
                (
                
                  T
                  
                    ON
                    -
                    40
                  
                
                )
              
              z
            
          
          
            2
            ×
            
              L
              45
            
            ×
            
              T
              40
            
          
        
      
    
    
      
        (
        6
        )
      
    
  
  
    
      
        
          P
          O
        
        =
        
          
            P
            10
          
          +
          
            P
            20
          
          +
          ...
          +
          
            P
            40
          
        
      
    
    
      
        (
        7
        )
      
    
  




where L25 and L45 is the inductance of the transformer 25 and 45 respectively; TON-20 and TON-40 is the on time of the switching controller 20 and 40 correspondingly; T10, T20 and T40 are switching period of the switching controller 10, 20 and 40; P10 is the output power of the first power converter; P20 is the output power of the second power converter; P40 is the output power of the fourth power converter.
Because the on-time and the switching period of the slave controllers are designed equal to the on-time TON and the switching period T of the master controller, the output current of each power converter will be same if the inductance of the transformer is similar.
FIG. 2 shows a preferred embodiment of the switching controller according to the present invention. The switching controller includes a power-sharing circuit (PSC) 100 connected to the input terminal SYN for receiving the input signal SYN, allowing the input signal SYN to be the output signal of another switching controller. The power sharing circuit (PSC) 100 is also coupled to an input terminal DLY to receive an input current IDLY. The resistor such as the resistor 21 or 41 determines the input current IDLY. The power-sharing circuit (PSC) 100 is used to generate a phase-shift signal S2, a control signal CNT and a first integration signal VT in response to the input signal SYN. The phase-shift signal S2 is generated after a delay time TDLY when the input signal SYN is enabled. The input current IDLY determines the delay time TDLY. The control signal CNT indicates the availability of the input signal SYN. The first integration signal VT is produced in accordance with the pulse width of the input signal SYN.
An oscillator (OSC) 200 is utilized to generate a pulse signal PLS and a ramp signal RAMP. The pulse signal PLS and the phase-shift signal S2 are connected to a multiplexer (MUX) 250. The control signal CNT is connected to control the multiplexer 250. The multiplexer (MUX) 250 outputs the phase-shift signal S2 when the control signal CNT is enabled. The multiplexer (MUX) 250 will output the pulse signal PLS if the control signal CNT is disabled. The output signal ON of the multiplexer (MUX) 250 is coupled to set a flip-flip 80. The flip-flop 80 and an AND gate 85 form a control circuit to generate a switching signal PWM at the output of the AND gate 85. Inputs of the AND gate 85 are connected to the output of the flip-flop 80 and the output of the multiplexer (MUX) 250. The flip-flop 80 is reset by a reset signal OFF. A reset circuit 300 is developed to generate the reset signal OFF in response to the first integration signal VT or the feedback signal VFB. When the control signal CNT is disabled, the reset signal OFF is generated in response to the feedback signal VFB. The feedback signal VFB compares with the ramp signal RAMP to generate the reset signal OFF. The control signal CNT is disabled when the switching controller is operated as the master controller. If the switching controller is operated as the slave controller, the control signal CNT will be enabled and the reset signal OFF will be generated in response to the first integration signal VT. The switching signal PWM is coupled to the output SW of the switching controller through a drive circuit 90.
FIG. 3 shows the power sharing circuit 100. It includes an input circuit 110 and a first integration circuit (INT) 160. The input circuit 110 is coupled to the input terminal SYN and the input terminal DLY to receive the input signal SYN and the input current IDLY for generating the control signal CNT, the phase-shift signal S2 and an input-shaping signal S1. The input-shaping signal S1 is connected to the first integration circuit (INT) 160. The first integration circuit (INT) 160 generates the first integration signal VT in response to the input-shaping signal S1 and the switching signal PWM.
FIG. 4 is a preferred embodiment of the input circuit 110. A buffer gate 130 is connected to the input terminal SYN to receive the input signal SYN. The buffer gate 130 generates the input-shaping signal S1 in response to the input signal SYN. The input-shaping signal S1 will be enabled (logic-high) when the input signal SYN is higher than the threshold voltage of the buffer gate 130. An operational amplifier 115 having a positive input connected a reference voltage VREF. The negative input of the operational amplifier 115 is coupled to the input terminal DLY. The operational amplifier 115 associates with a transistor 120 generate a current 1120 in accordance with the resistance of the resistor such as the resistor 21 or 41. Transistors 121 and 122 form a current mirror to generate a current 1122 in accordance with the current I120. The current I122 is connected to charge the capacitor 125. The input of a buffer gate 131 is connected to the capacitor 125. The output of the buffer gate 131 is connected to an input of an NAND gate 132. Another input of the NAND gate 132 is connected to the input-shaping signal S1. The output of the NAND gate 132 is coupled to generate the phase-shift signal S2 through a pulse generator 135. The delay time TDLY is thus existed in between the enabling of the input signal SYN and the enabling of the phase-shift signal S2. The resistor such as resistor 21 or 41 determines the current I120 and the current I122. The current I122 and the capacitance of the capacitor 125 determine the delay time TDLY.
A transistor 117 is connected to the capacitor 125 to discharge the capacitor 125. An NAND gate 133 is applied to control the on/off of the transistor 117. The first input of the NAND gate 133 is the input-shaping signal S1. The second input of the NAND gate 133 is connected to the switching signal PWM via an inverter 134. Therefore, the capacitor 125 is discharged once the input-shaping signal S1 is disabled or the switching signal PWM is enabled. Furthermore, a detection circuit 140 is utilized to detect the input of the input signal SYN. The detection circuit 140 will generate the control signal CNT in response to the phase-shift signal S2.
FIG. 5 shows the circuit schematic of the pulse generator 135. An inverter 151 is connected to the input of the pulse generator 135 to receive an input signal. The output of the inverter 151 is coupled to control a transistor 153 through an inverter 152. A capacitor 155 is parallel connected with the transistor 153. A current source 150 is coupled to charge the capacitor 155. An inverter 157 is connected to the capacitor 155. The output of the inverter 157 is connected to an input of an AND gate 159. Another input of the AND gate 159 is connected to the output of the inverter 151. The output of the AND gate 159 is connected to the output of the pulse generator 135. Therefore, the pulse generator 135 generates a pulse voltage in response to the falling edge of the input signal of the pulse generator 135. The current of the current source 150 and the capacitance of the capacitor 155 determine the pulse width of the pulse voltage.
FIG. 6 is the detection circuit 140. The phase-shift signal S2 is coupled to control a transistor 142. The transistor 142 is used to discharge a capacitor 145. A current source 143 is connected to charge the capacitor 145. The input of an inverter 147 is connected to the capacitor 145. The output of the inverter 147 is connected to reset a flip-flop 149. The flip-flop 149 is enabled by the phase-shift signal S2. The flip-flop 149 is used to generate the control signal CNT in response to the phase-shift signal S2. If the phase-shift signal S2 is not inputted within a time-out period, the control signal CNT will be disabled. The current of the current source 143 and the capacitance of the capacitor 145 determine the time-out period.
FIG. 7 shows a preferred embodiment of the first integration circuit 160. A current source 180 is connected to charge a capacitor 185 through a switch 190. The switch 190 is controlled by the input-shaping signal S1. A capacitor 186 is coupled to the capacitor 185 via a switch 191. The switch 191 is controller by a first-sample signal SP1. A capacitor 187 is coupled to the capacitor 186 through a switch 192 to generate the first Integration signal VT. The switch 192 is controller by a second-sample signal SP2. The second-sample signal SP2 is generated by the switching signal PWM through a pulse generator 165. A pulse generator 170 is used to generate the first-sample signal SP1 in response to the input-shaping signal S1. A transistor 181 is connected to discharge the capacitor 185 in response to the end of the first-sample signal SP1. The first-sample signal SP1 is coupled to control the transistor 181 through a pulse generator 175. Therefore, the pulse width TON1 of the input signal SYN, the current I180 of the current source 180 and the capacitance C185 of the capacitor 185 determine the level of the first integration signal VT.




  
    
      
        
          V
          T
        
        =
        
          
            
              I
              180
            
            
              C
              185
            
          
          ×
          
            T
            
              ON
              ⁢
              
                
              
              ⁢
              1
            
          
        
      
    
    
      
        (
        8
        )
      
    
  




FIG. 8 shows the circuit schematic of the oscillator 200. A current source 210 is coupled to charge a capacitor 220 via a switch 211. A current source 215 is coupled to discharge the capacitor 220 via a switch 216. A comparator 230 includes a trip-point voltage VH. A comparator 231 includes a trip-point voltage VL. Comparators 230 and 231 are coupled to detect the voltage of the capacitor 220. NAND gates 235 and 236 form a latch circuit. The output of the comparator 230 and the output of the comparator 231 are connected to the latch circuit. The output of the latch circuit is connected to the input of an NAND gate 237. The output of the NAND gate 237 is connected to an inverter 240, which generates the pulse signal PLS. The pulse signal PLS is further coupled to control the on/off of the switch 216. The output of the NAND gate 237 is used to control the switch 211. The control signal CNT is utilized to discharge the capacitor 220 through a transistor 225 once the control signal CNT is enabled. The control signal CNT is further connected to disable the pulse signal PLS through an inverter 241 and the NAND gate 237. FIG. 9 shows the circuit schematic of the multiplexer 250. An AND gate 252 is connected to receive the pulse signal PLS. An AND gate 253 is connected to receive the phase-shift signal S2. The control signal CNT is connected to AND gate 253. The control signal CNT is further connected to the AND gate 252 via an inverter 251. An NOR gate 256 is used to generate the output signal ON of the multiplexer 250 in response to the output of AND gates 252 and 253.
FIG. 10 shows a preferred embodiment of the reset circuit 300. The reset circuit 300 includes a second integration circuit 310, comparators 330, 345, an NOR gate 370, AND gates 351, 352 and inverters 360, 361. The second integration circuit 330 contains a current source 320, a capacitor 325, a transistor 316 and an NAND gate 315. The switching signal PWM and the control signal CNT are connected to NAND gate 315. The output of NAND gate 315 is coupled to discharge the capacitor 325 through the transistor 316. The current source 320 is coupled to charge the capacitor 325 once the switching signal PWM and the control signal CNT are enabled. A second integration signal SAW is generated in response to the enabling of the switching signal PWM. The second integration signal SAW is connected to the comparator 330 to compare with the first integration signal VT. The output of the comparator 330 is coupled to generate the reset signal OFF through the AND gate 351 and the NOR gate 370. Therefore, the switching signal PWM will be disabled once the second integration signal SAW is higher than the first integration signal VT. The pulse width TON2 of the switching signal PWM can be expressed as,




  
    
      
        
          T
          
            ON
            ⁢
            
              
            
            ⁢
            2
          
        
        =
        
          
            
              C
              325
            
            
              I
              320
            
          
          ×
          
            V
            T
          
        
      
    
    
      
        (
        9
        )
      
    
  




where the C325 is the capacitance of the capacitor 325; I320 is the current of the current source 320. Refer to equation 8, the equation 9 can be written as,





  
    
      
        
          T
          
            ON
            ⁢
            
              
            
            ⁢
            2
          
        
        =
        
          
            
              C
              325
            
            
              I
              320
            
          
          ×
          
            
              I
              180
            
            
              C
              185
            
          
          ×
          
            T
            
              ON
              ⁢
              
                
              
              ⁢
              1
            
          
        
      
    
    
      
        (
        10
        )
      
    
  




Select the capacitance C325 correlated to the capacitance C185. Set the current I320 correlated to the current I180. The pulse width TON2 of the switching signal PWM will be same as the pulse width TON1 of the input signal SYN. Therefore, the first integration signal VT is increased in response to the increase of pulse width TON1 of the input signal SYN. The pulse width TON2 of the switching signal PWM is decreased in response to the decrease of the first integration signal VT.

The output of the comparator 345 is connected to the AND gate 352. Anther input of the AND gate 352 is coupled to the control signal CNT through the inverter 360. The second input of the NOR gate is connected to the output of the AND gate 352. The feedback signal VFB and the ramp signal RAMP are coupled to the comparator 345 to generate the reset signal OFF signal when the control signal CNT is disabled. The third input of the NOR gate is coupled to a power-on reset signal PWRST through the inverter 361.
FIG, 11 shows waveforms of the input signal SYN and the switching signal PWM, The input signal SYN is coupled to generate the switching signal PWM after the delay time TDLY. The first integration signal VT is generated in accordance with the pulse width TON1 of the input signal SYN. Once the switching signal PWM is generated, the second integration signal SAW will be generated accordantly. The switching signal PWM will be disabled once the second integration signal SAW is higher than the first integration signal VT. The pulse width TON2 of the switching signal PWM is thus same as the pulse width TON1 of the input signal SYN. The power sharing is therefore achieved for parallel power converters.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims or their equivalents.

## Claims

1. A switching controller for power sharing of parallel power supplies, the switching controller comprising:
an input circuit coupled to an input terminal to receive an input signal for generating a phase-shift signal;
a first integration circuit coupled to the input circuit to generate a first integration signal in response to a pulse width of the input signal;
a control circuit coupled to the first integration circuit to generate a switching signal for switching the power supply;
an oscillator generating a pulse signal and a ramp signal; and
a feedback terminal coupled to an output of the power supply to receive a feedback signal;
wherein if the input signal is not available, the switching signal is enabled in response to the pulse signal, and is disabled in response to a comparison of the feedback signal and the ramp signal, and
wherein the switching signal is enabled in response to the phase-shift signal, and a pulse width of the switching signal is determined in accordance with the first integration signal.

2. The switching controller as claimed in claim 1, further comprising a resistor for determining a delay time between an enabling of the input signal and an enabling of the phase-shift signal.

3. The switching controller as claimed in claim 1, wherein the first integration signal is increased in response to an increase of the pulse width of the input signal, and the pulse width of the switching signal is decreased in response to a decrease of the first integration signal.

4. The switching controller as claimed in claim 1, wherein the input circuit comprises a detection circuit to detect an input of the input signal.

5. The switching controller as claimed in claim 1 further comprising a second integration circuit coupled to generate a second integration signal in response to the pulse width of the switching signal, wherein the input circuit further generates another phase-shift signal, and the switching signal is disabled in response to a comparison of the first integration signal and the second integration signal.

6. The switching controller as claimed in claim 1, wherein the phase-shift signal is generated after a delay time when the input signal is enabled.

7. A power sharing circuit for parallel power supplies, the switching controller comprising:
an input circuit for receiving an input signal and generating a phase-shift signal;
a first integration circuit coupled to the input circuit for integrating the input signal and generating a first integration signal;
a control circuit coupled to the input circuit and enabled in response to the input signal to generate a switching signal;
a second integration circuit coupled to the control circuit for integrating the switching signal and generating a second integration signal;
an oscillator generating a pulse signal and a ramp signal; and
a feedback terminal coupled to an output of the power supply to receive a feedback signal;
wherein if the input signal is not available, the switching signal is enabled in response to the pulse signal, and is disabled in response to a comparison of the feedback signal and the ramp signal, and
wherein the switching signal is disabled once the second integration signal is higher than the first integration signal.

8. The switching controller as claimed in claim 7 further comprising a resistor coupled to the input circuit for determining a delay time in between the input signal and the phase-shift signal.

9. The switching controller as claimed in claim 7, wherein the time constant of the second integration circuit is correlated with the time constant of the first integration circuit.

10. The power sharing circuit as claimed in claim 7, wherein the first integration signal is increased in response to an increase of the pulse width of the input signal, and the pulse width of the switching signal is decreased in response to a decrease of the first integration signal.