Abstract:
Disclosed is a Power Factor Correction Controller, which comprises a boost converter, a current sensing unit, an arithmetic unit, and a switch driving unit. The current sensing unit can sense or derive the current that pass through the energy delivery device, which is normally implemented by a diode or a switch. The current sensing unit can also sense the inductor current, or the switch current. With the current sensing unit, the arithmetic unit can calculate the optimum switch on-time or when to turn off the switch, without direct-sensing of the load. The disclosed method reduces the system cost by removing the needs to sense the load condition as in the prior arts. The disclosed method also improves the system response by sensing the delivered current at energy delivery side, rather than the receiver side as in the prior arts.

Description:
FIELD OF THE INVENTION 
     The present invention relates to switch-mode power supplies (SMPS), and more particularly, to power factor correction (PFC) circuits in switch-mode power supplies (SMPS). 
     BACKGROUND OF THE INVENTION 
     The power factor (PF) which can be achieved with an active switch-mode PFC controller is nearly 1 (i.e. 100%). The use of PFC controller, therefore, minimizes the power wasted in the harmonics and out-of-phase current. 
     A PFC converter is generally configured as a boost converter, with an inductor, a switch, and an energy delivery device. The energy delivery device is normally implemented as a diode or a MOS. The PFC controller controls on and off of the switch and diode to achieve unity power factor and to provide regulated DC output. 
     A PFC controller can be operated in continuous conduction mode (CCM), critical conduction mode (CRM), or discontinuous conduction mode (DCM). CRM and DCM modes are normally the choice for lower power consumption applications. 
     To provide load regulation for PFC output, a common method is used to sense the output voltage directly. The sensed output voltage is feedbacked to PFC controller to adjust the switch on/off timing. This conventional practice complicates the system design, and increases the board area and components. 
     Please refer to  FIG. 1 , which is a schematic diagram showing a conventional PFC switch-mode power supply having a load sense circuit to sense voltage at the converter output according to the prior art. In  FIG. 1 , the general configuration of the switch-mode power supply has a boost converter  11  and a PFC controller  12 . The boost converter  11  is configured by an inductor  114 , a resistor  117 , an output stage  118 , as well as an energy delivery device. The energy delivery device is usually implemented by a diode  115  or a transistor switch  116 . The PFC controller  12  is configured by a AC voltage sense unit  121 , an inductor current sense unit  122 , a load sense unit  123 , an arithmetic unit  124 , a comparator  125  and a switch control unit  126 . The PFC controller  12 , through the load sense unit  123 , senses the voltage from the load output stage  118  to control the on/off of the switch  116  and diode  115 , realizes the effect promotion of the power factor, and provides a regulated DC voltage output. 
     Please refer to  FIG. 2 , which is a schematic diagram showing another conventional PFC switch-mode power supply having a load sensing circuit to sense voltage at the converter output according to the prior art. In  FIG. 2 , the general configuration of the switch-mode power supply has a boost converter  21  and a PFC controller  22 . The boost converter  21  is configured by an inductor  214 , an output stage  217 , as well as an energy delivery device. The energy delivery device is usually implemented by a diode  215  or a transistor switch  216 . The PFC controller  22  is configured by a AC voltage sense unit  221 , an inductor current sense unit  222 , a load sense unit  223 , an arithmetic unit  224 , a switch on-time unit  225 , and a switch control unit  226 . The PFC controller  22 , through the load sense unit  223 , senses the voltage from the load output stage  217  to control the on/off of the switch  216  and diode  215 , realizes the effect promotion of the power factor, and provides a regulated DC voltage output. 
     Although a regulated output voltage can be provided by a conventional switch-mode power supply according to the prior art, it can only be realized by adding an additional sense unit. Therefore, the increases of the weight, components and the board area are still the inevitable defects of the prior art. 
     A solution of the above drawback in the prior art is not only to remove the voltage sense circuit from the load terminal of the switch-mode power supply but also to decrease the overall weight, components and the board area. Thus the invention of the case “switch-mode power supplies” would be the best way to solve the deficiencies of conventional means. 
     SUMMARY OF THE INVENTION 
     The present invention provides a switch-mode power supply for use in power factor correction. The switch-mode power supply includes an inductor, a switch, an energy delivery device, and an inductor current sensing circuit to produce and output at critical points of inductor current changes. The load-terminal output voltage detection circuit can be removed so as to reduce the overall weight and volume. 
     According to an aspect of the present invention, there is provided a switch-mode power supply for providing an output voltage, including a boost converter enhancing a level of the output voltage according to an internal inductor current, an AC voltage and a switch current, a switch current sensing unit sensing the switch current to provide a reference potential, an arithmetic unit receiving the internal inductor current, the AC voltage and the sensed switch current to provide a test potential, and a comparator comparing the reference potential with the test potential and providing a reset signal to activate the boost converter. 
     Preferably, the output voltage is provided according to an input voltage being a utility line AC power. 
     Preferably, the boost converter has an EMI-protection circuit, a rectifier, an energy storage device and an output stage, the switch current sensing unit, the arithmetic unit and the comparator are configured in a power factor correction controller coupled to the boost converter, and the arithmetic unit operates the internal inductor current, the AC voltage and the sensed switch current to provide the test potential. 
     Preferably, the rectifier is a full-bridge rectifier. 
     Preferably, the energy storage device includes an inductor providing the internal inductor current, a switch having an input terminal, a controlling terminal and an output terminal, wherein the input terminal is coupled with the inductor and the switch is controlled by the reset signal, a resistor coupled to the output terminal of the switch to provide the switch current, and a diode coupled to the inductor and the input terminal of the switch. 
     Preferably, the switch is a transistor. 
     Preferably, the output stage includes a filter capacitor connected to the energy storage device in parallel, and an output load connected to the filter capacitor in parallel to provide the output voltage. 
     Preferably, the switch-mode power supply further includes an inductor current sensing unit coupled to the boost converter to sense the internal inductor current, provides the sensed inductor current to the arithmetic unit, an AC voltage sensing unit coupled to the boost converter to sense the AC voltage, and provides the sensed AC voltage to the arithmetic unit, and a switch control unit is coupled to the boost converter and receives the reset signal to activate the boost converter. 
     Preferably, the inductor current sensing unit provides a setting signal to the switch control unit according to the internal inductor current and controls a switching action of the boost converter. 
     According to another aspect of the present invention, there is provided a switch-mode power supply, including a boost converter, an arithmetic unit coupled to the boost converter, receiving an inductor current and an AC voltage and providing a reset signal, and a switch on-time unit receiving and transmitting the reset signal to activate the boost converter. 
     Preferably, the output voltage is provided according to an input voltage being a utility line AC power. 
     Preferably, the boost converter has an EMI-protection circuit, a rectifier, an energy storage device and an output stage and enhances a level of the output voltage according to the inductor current and the AC voltage, and the arithmetic unit and the switch on-time unit are configured in a power factor correction controller coupled to the boost converter. 
     Preferably, the rectifier is a full-bridge rectifier. 
     Preferably, the energy storage device includes: an inductor providing the inductor current, a switch having an input terminal, a controlling terminal and an output stage, wherein the input terminal is coupled with the inductor and the switch is controlled by the reset signal, and a diode coupled to the inductor and the input terminal of the switch. 
     Preferably, the switch is a transistor. 
     Preferably, the output stage includes: a filter capacitor connected to the energy storage device in parallel, and an output load connected to the filter capacitor in parallel to provide the output voltage. 
     Preferably, the switch-mode power supply further includes an inductor current sensing unit coupled to the boost converter to sense the inductor current, provides the sensed inductor current to the arithmetic unit, an AC voltage sensing unit coupled to the boost converter to sense the AC voltage, and provides the sensed AC voltage to the arithmetic unit, and a switch control unit is coupled to the boost converter and receives the reset signal to activate the boost converter. 
     Preferably, the inductor current sensing unit further provides a setting signal to the switch control unit according to the inductor current and controls a switching action of the boost converter. 
     According to an additional aspect of the present invention, there is provided a power supply including a sensing unit sensing a switch current to provide a reference potential, a calculating unit receiving an inductor current, an AC voltage and the sensed switch current to provide a test potential, and a comparator comparing the reference potential with the test potential and providing a reset signal. 
     Preferably, the power supply generates an output voltage and further including a boost converter being activated by the reset signal and enhancing a level of the output voltage according to the inductor current, the AC voltage and the switch current. 
     The foregoing and other features and advantages of the present invention will be more clearly understood through the following descriptions with reference to the drawings, wherein: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a conventional PFC switch-mode power supply having a load sense circuit to sense voltage at the converter output according to the prior art. 
         FIG. 2  is a schematic diagram showing another conventional PFC switch-mode power supply having a load sensing circuit to sense voltage at the converter output according to the prior art. 
         FIG. 3  is an exemplary schematic block diagram of PFC switch-mode power supply with load regulation without output voltage sensing. 
         FIG. 4  is another exemplary schematic block diagram of PFC switch-mode power supply with load regulation without output voltage sensing. 
         FIG. 5  is the current and timing waveform for inductor, switch, and diode, in a DCM mode PFC switch-mode power supply. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more specially with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for the purposes of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed. 
     Please refer to  FIG. 3 , which is an exemplary schematic block diagram showing a PFC switch-mode power supply with load regulation without output voltage sensing according to the first embodiment of the present invention. The PFC switching power supplies  3  includes a boost converter  31  and a PFC controller  32 . The boost converter  31  includes a utility line AC power input stage  311 , an EMI protection circuit  312 , a rectifier  313 , a inductor  314 , a diode  315 , a switch  316 , a resistor  317  and an output stage  318 . The PFC controller  32  includes an AC voltage sense unit  321 , an inductor current sense unit  322 , a switch current sense unit  323 , an arithmetic unit  324 , a comparator  325  and a switch control unit  326 . 
     In  FIG. 3 , AC voltage VAC is received by the utility line AC power input stage  311 , through EMI protection circuit  312  and rectifier  313 , turning into an input voltage Vin. Then the input voltage Vin is sensed by the AC voltage sense unit  321  coupled to the boost converter  31 . At the same time, the inductor current detection unit  322  coupled to the boost converter  31  also senses the inductor current IL. According to the inductor current IL, the inductor current sense unit  322  provides a set signal to switch control unit  326  to control the action of the switch  316  of the boost converter  31 . 
     The arithmetic unit  324  receives and processes three signals individually from the switch current sense unit  323 , the inductor current sense unit  322  and the AC voltage sense unit  321  to provide a test potential to the comparator  325 . The comparator  325  compares the test potential generated from the arithmetic unit  324  and the reference potential sensed from the switch current sense unit  323  to provide a reset signal to the switch control unit  326 , to control the action of the switch  316  of the boost converter  31  based on the reset signal. 
     If the reference potential is less than the test potential, the switch peak current increases and the reset signal turns off the switch  316 , allowing more energy to be sent to load output stage  318 . If the reference potential is higher than the test potential, the switch peak current decreases and the switch  316  turns on. It limits the energy sent to the load output stage  318  to control the output potential no longer increased. 
     Please refer to  FIG. 4 , which is an exemplary schematic block diagram showing a PFC switch-mode power supply with load regulation without output voltage sensing according to the second embodiment of the present invention. The PFC switching power supplies  4  includes a boost converter  41  and a PFC controller  42 . The boost converter  41  includes a utility line AC power input stage  411 , an EMI protection circuit  412 , a rectifier  413 , a inductor  414 , a diode  415 , a switch  416  and an output stage  417 . The PFC controller  42  includes an AC voltage sense unit  421 , an inductor current sense unit  422 , an arithmetic unit  423 , a switch on-time unit  424  and a switch control unit  425 . 
     In  FIG. 4 , AC voltage VAC is received by the utility line AC power input stage  411 , through EMI protection circuit  412  and rectifier  413 , turning into an input voltage Vin. Then the input voltage Vin is sensed by the AC voltage sense unit  421  coupled to the boost converter  41 . At the same time, the inductor current detection unit  422  coupled to the boost converter  41  also sense the inductor current IL. According to the inductor current IL, the inductor current sense unit  422  provides a set signal to switch control unit  425  to control the action of the switch  416  of the boost converter  41 . 
     The arithmetic unit  423  receives and processes two signals individually from the inductor current sense unit  422  and the AC voltage sense unit  421  to provide a reset signal to the switch on-time unit  424 . Thus the switch control unit  425  can control the action of the switch  416  of the boost converter  41  based on the reset signal from the switch on-time unit  424 . 
     In the boost converter  41 , the switch on-time unit  424  determines whether the energy will be stored in the inductor  414  or not. The time of the diode  415  turned on determine whether the energy will be transferred to the load terminal  415  or not. The boost converter  4  operates in discontinuous conduction mode or boundary conduction mode, the relation between the switch  416  on-time and the diode  415  (energy delivery device) on-time is given by: 
     
       
         
           
             
               
                 td 
                 ton 
               
               = 
               
                 Vin 
                 
                   Vout 
                   - 
                   Vin 
                 
               
             
             , 
           
         
       
     
     Here, “td” is the on-time of the diode  415  (energy delivery device). “ton” is the on-time of the switch  416 . “Vin” is the boost converter  41  input voltage. “Vout” is the converter  41  output voltage. With “td”, “ton”, and “Vin” known, the “Vout” can be derived without direct sensing. 
     In particular, “ton” have a fixed relationship with “Vout” for a power factor correction converter, as depicted by: 
     
       
         
           
             
               ∑ 
               
                   
               
               ⁢ 
               
                 
                   ( 
                   
                     ton 
                     T 
                   
                   ) 
                 
                 2 
               
             
             = 
             
               
                 K 
                 · 
                 
                   Vout 
                   
                     V 
                     rms 
                     2 
                   
                 
               
               ⁢ 
               
                 ( 
                 
                   Vout 
                   - 
                   Vin 
                 
                 ) 
               
             
           
         
       
     
     Here, “T” is cycle time of the switch, K is a constant depends on loading and converter configuration, and Vrms is the input root-mean-square average. The “Vout” derived from “td” can be used in this equation to calculate an optimized on-time. Therefore, both the inductor  414  peak and zero currents are sensed by inductor current sensing unit  422 . Peak and zero current events are sent to arithmetic unit  423  to calculate for the “td” and then derived for the “Vout”. The calculated “Vout” is then sent from arithmetic unit  423  to the switch on-time unit  424 . On-time of the switch  416  will be longer if the Vout is less than desired voltage “Vref”. On-time of the switch  416  will be shorter if the Vout is larger than desired voltage “Vref”. 
     Please refer to  FIG. 5 , which is the current and timing waveform for inductor, switch, and diode, in a DCM mode PFC switch-mode power supply.  FIG. 5(   a ) shows the changing relationship between the inductor current IL and the time t, wherein the vertical-axis represents the sensed inductor current IL, the horizontal-axis represents the time t. On the horizontal-axis, “ton” is the duration when the switch is turned on, and “td” is the duration when the diode is turned on. The inductor current in periods of the “td” and “ton” can always be sensed (such as the solid line showed), and at the same time the inductor zero and peak current can be measured.  FIG. 5(   b ) shows the changing relationship between the switch current Is and the time t, wherein the vertical-axis represents the sensed switch current Is, the horizontal-axis represents the time t. On the horizontal-axis, “ton” is the duration when the switch is turned on. The switch current in periods of the “td” and “ton” can always be sensed (such as the dotted line showed).  FIG. 5(   c ) shows the changing relationship between the diode current ID and the time t, wherein the vertical-axis represents the sensed diode current ID, the horizontal-axis represents the time t. On the horizontal-axis, “td” is the duration when the diode is turned on. The diode current in periods of the “td” can be sensed (such as the dotted line showed). 
     According to the above graph of  FIGS. 5(   a ), ( b ) and ( c ), we can find “ton” is the time sensed from the inductor zero current to peak current, which is the time sensed from the switch zero current to peak current. “td” is the time sensed from the inductor peak current to zero current, which is the time from the switch peak current to the inductor zero current. Therefore, the sensing of “td” requires no extra devices, and both the zero current of the inductor and the peak current of the switch can be sensed. In either cases, the “ton” and “td” will be known, and therefore “Vout” can be derived. 
     To sum up, both the inductor zero current and the peak current can be sensed in the first embodiment of the present invention and both the inductor zero current and the switch peak current can be sensed in the second embodiment of the present invention. Therefore, under either case, “td” and “ton” are always known, the “Vout” can be derived without any load sense unit. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.