Patent Publication Number: US-10790755-B2

Title: Controlled power circuit with adjusted voltage feedback to regulate the output power

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 16/010,071, filed on Jun. 15, 2018, now pending, which is a continuation of U.S. application Ser. No. 15/438,026, filed Feb. 21, 2017, now U.S. Pat. No. 10,027,236, which issued on Jul. 17, 2018. U.S. application Ser. No. 15/438,026 and U.S. application Ser. No. 16/010,071 are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Disclosure 
     The present invention relates generally to power converters and more specifically power converters with controlled power. 
     2. Background 
     Electronic devices use power to operate. Switched mode power converters are commonly used due to their high efficiency, small size, and low weight to power may of today&#39;s electronics. Conventional wall sockets provide a high voltage alternating current. In a switching power converter, the high voltage alternating current (ac) input is converted to provide a well-regulated direct current (dc) output through an energy transfer element. The switched mode power converter usually provides output regulation by sensing one or more inputs representative of one or more output quantities and controlling the output in a closed loop. In operation, a power switch is utilized to provide the desired output by varying the duty cycle (typically the ratio of the on time of the switch to the total switching period), varying the switching frequency, or varying the number of pulses per unit time of the switch in a switched mode power converter. 
     The power converter may provide a regulated output current, output voltage, or output power. In general, when regulating the output current to a desired value, the output current is measured and one or more parameters of the power switch is varied until the output current reaches the desired value. Similarly, output voltage is generally sensed when regulating the output voltage to a desired value. Output power is the product of the output voltage and the output current. In regulating output power, the output voltage is generally measured and one or more parameters of the power switch is varied until the output current reaches the target value which provides the desired output power. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. 
         FIG. 1  illustrates one example of a power converter which includes an output power control circuit in accordance with teachings of the present invention. 
         FIG. 2  illustrates an example graph of the relationship between output current and output voltage of the power converter of  FIG. 1  in accordance with the teachings of the present invention. 
         FIG. 3  illustrates an example output power control circuit shown in  FIG. 1  in accordance with the teachings of the present invention. 
         FIG. 4  illustrates another example power converter which includes a primary controller and a secondary controller coupled to a output power control circuit in a monolithic circuit in accordance with the teachings of the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. 
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present invention. In other instances, well-known materials or methods have not been described in detail in order to avoid obscuring the present invention. 
     Reference throughout this specification to “one embodiment”, “an embodiment”, “one example” or “an example” means that a particular feature, structure or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment”, “in an embodiment”, “one example” or “an example” in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures or characteristics may be combined in any suitable combinations and/or subcombinations in one or more embodiments or examples. Particular features, structures or characteristics may be included in an integrated circuit, an electronic circuit, a combinational logic circuit, or other suitable components that provide the described functionality. In addition, it is appreciated that the figures provided herewith are for explanation purposes to persons ordinarily skilled in the art and that the drawings are not necessarily drawn to scale. 
     Output power is the product of the output voltage and the output current. In regulating output power, the output voltage is generally measured and one or more parameters of the power switch are varied until the output current reaches the target value which provides the desired output power. However, output voltage changes quickly over time as compared to the output current and this may result in a constant adjustment of the output current and instability of the control loop. 
     In embodiments of the present invention, the output current is measured and the one or more parameters of the power switch are varied until the output voltage reaches the target value and the power converter provides the desired output power. Further, the measurement of the output current and subsequent calculation of the output voltage to provide a controlled output power is implemented digitally. 
     The controller of the power converter receives a current sense signal, representative of the output current of the power converter and converts the current sense signal to a digital current sense signal. The digital current sense signal is then filtered and stabilized. Using the filtered signal, the controller calculates the desired output voltage signal and provides an adjust signal. The adjust signal modifies either a feedback signal or a reference signal such that the sensed output voltage reaches a target value which provides the desired output power. 
     To illustrate,  FIG. 1  illustrates one example of a power converter  100  including a controller  120  with an output power control circuit  126  in accordance with the teachings of the present invention. The power converter  100  is coupled in a flyback topology with a synchronous rectifier, also referred to as a secondary switch, as the output rectifier  112 . However, it should be appreciated that other converter topologies could be used as well as non-synchronous output rectifiers, such as a diode. The power converter  100  provides output power to the load  116  from an unregulated input voltage V IN    102 . In one example, the input voltage V IN    102  is a rectified ac input voltage. The input voltage V IN    102  is received by the energy transfer element T 1   104  which is shown as including two windings, a primary winding  105  and a secondary winding  106  and is utilized to transfer energy between the input and the output of the power converter  100 . The primary winding  105  is coupled to power switch S 1   110  which is then further coupled to input return  109 . The clamp circuit  108  is shown as coupled across the primary winding  105  and limits the voltage across the power switch S 1   110 . The secondary winding  106  is shown as coupled to the output rectifier  112 , exemplified as a transistor used as a synchronous rectifier. Both the output capacitor C 1   114  and the load  116  are shown as coupled to the output rectifier  112 . An output is provided to the load as regulated output voltage V O    117 , regulated output current I O    118 , or a combination of the two (such as a regulated output power). 
     The controller  120  is shown as including the output power control circuit  126 , resistors  128 ,  130 , a comparator  132 , and a drive circuit  134 . The controller  120  is coupled to receive a voltage sense signal  124  representative of the output voltage V O    117  and a current sense signal  122  representative of the output current I O    118 . The controller  120  also outputs the secondary drive signal U SR    141 , which controls the output rectifier  112 , and the primary drive signal U PR    142 , which controls the switching of the power switch S 1   110 . The controller  120  controls the output rectifier  112  and the power switch S 1   110  to regulate the output voltage V O    117 , output current I O    118 , or output power to a desired value. In one example, the controller  120  senses the output current I O    118  to modify the output voltage V O    117  to regulate the output power to a desired value. 
     As shown, the comparator  132  is coupled to receive the reference V REF    139  and the feedback signal U FB    138 . In one example, comparator  132  may be referred to as a reference feedback circuit. In the example shown, the voltage sense signal  124  is received by the resistors  128 ,  130 , which are coupled as a voltage divider. In one example, the resistors  128 ,  130  may be referred to as a sense circuit. The feedback signal U FB    138  is the output of the voltage divider of resistors  128 ,  130  and as such, the feedback U FB    138  is also representative of the output voltage V O    117 . In other words, the feedback signal U FB    138  is the voltage across resistor  130 . The output power control circuit  126  receives the current sense signal  122  and the power signal U POWER    166 . Power signal U POWER    166  is representative of the desired value of the output power of the power converter  100 . In one example, the power signal U POWER    166  may be set by a user and provided to the controller via an interface, such as an inter-integrated circuit (I2C). The output power control circuit  126  outputs the adjust signal U ADJ    136  to comparator  132 . The output of the output power control circuit  126  is coupled between resistors  128 ,  130  and adjusts the feedback signal U FB    138  in response to the output current I O    122 . 
     The output of comparator  132  is the drive signal U DR    140 , which is received by the drive circuit  134 . Drive signal U DR    140  is representative of the switching of power switch S 1   110 . In other words, the drive signal U DR    140  indicates to the drive circuit  134  whether or not the power switch S 1   110  should be turned on. For the example illustrated, the drive circuit  134  receives the drive signal U DR    140  and generates the primary drive signal U PR    142  and the secondary drive signal U SR    141  in response to the drive signal U DR    140 . As mentioned above, the primary drive signal U PR    142  controls opening and closing of the power switch S 1   110 . It is generally understood that a switch that is closed may conduct current and is considered on, while a switch that is open cannot conduct current and is considered off. In one example, the switch S 1   110  may be a transistor such as a metal-oxide-semiconductor field-effect transistor (MOSFET). In another example, controller  120  may be implemented as a monolithic integrated circuit or may be implemented with discrete electrical components or a combination of discrete and integrated components. Controller  120  and switch S 1   110  could form part of an integrated circuit that is manufactured as either a hybrid or monolithic integrated circuit. 
     In operation, the power converter  100  provides a regulated output voltage V O    117 , output current I O    118 , or output power P O  by controlling the transfer of energy between the primary winding  105  and the secondary winging  106 . The transfer of energy is controlled by controlling the operation of the power switch S 1   110  and the output rectifier  112 . For providing a controlled output power P O , the controller  120  senses the output current I O    118  to modify the output voltage V O    117  to regulate the output power P O  to the desired value. The output power control circuit  126  receives the sensed output current I O    118  and the power signal U POWER    166  and calculates the wanted output voltage V O    117  which would provide the desired output power P O . The output power control circuit  126  then outputs the adjust signal U ADJ    136 , which alters the feedback signal U FB    138 . As such, the drive signal U DR    140  is then altered and the output voltage V O    117  is modified to a value which provides the desired output power P O . 
       FIG. 2  illustrates a graph  200  of the relationship between output current I O    218  and output voltage V O    217 . The graph  200  further shows the different operating regions of the power converter  100  discussed above with respect to  FIG. 1 . As shown, the power converter has three regions of operation: a controlled voltage region  243 , a controlled current region  244 , and a controlled power region  245 . For the controlled voltage region  243 , the output voltage V O    217  is substantially constant while the output current I O    218  may vary, as illustrated by the line parallel with the horizontal axis. In general, the output voltage V O    217  is sensed to regulate the output voltage V O    217  in the controlled voltage region  243 . Similarly, for the controlled current region  244 , the output current I O    218  is substantially constant while the output voltage V O    217  may vary, as illustrated by the line parallel with the vertical axis. The output current I O    218  is generally sensed to regulate the output current I O    218  in the controlled current region  244 . 
     For the controlled power region  245 , the line is arched to indicate that the output power P O  is controlled to a desired value. In one example, the desired value is substantially constant. Examples of the present disclosure sense the output current I O    218  to control the output voltage V O    217  to a value which regulates the output power P O  to the desired value. 
       FIG. 3  illustrates an example output power control circuit  326 , which is one example of the output power control circuit  126  discussed with respect to  FIG. 1 . As shown, the output power control circuit  326  includes an analog-to-digital converter (ADC), stabilizing transfer function circuit  348 , controlled power circuit  350 , a range decoder  352 , and current sources  354 ,  356  with currents I 1  and I 2 , respectively. Further shown in  FIG. 3  are resistors  328 ,  330 , which are the same as resistors  128 ,  130  in  FIG. 1 . It should be appreciated similarly named and numbered elements couple and function as described above. 
     The output power control circuit  326  is coupled to receive the current sense signal  322  (representative of the output current I O ) at the ADC  346 . The ADC  346  converts the analog sensed output current I O  to a digital signal. The output of the ADC  346  is the current measure signal I MEASURE    362 , which is an M-bit digital signal representative of the output current I O . In one example, the current measure signal I MEASURE    362  is an eight-bit digital word. In general, the greater number of bits correspond with greater resolution of the measurement of the output current I O . 
     The stabilizing transfer function circuit  348  is coupled to receive the current measure signal I MEASURE    362  and outputs the filter signal I FILTER    364 . In one example, the filter signal I FILTER    364  is also an M-bit digital signal. The stabilizing transfer function circuit  348  applies a digital transfer function to reshape the current measure signal I MEASURE    362  to stabilize the control loop of the controller. The stabilizing transfer function circuit  348  allows the controller to gradually change the output voltage V O  to a value which regulates the output power P O . The outputted filter signal I FILTER    364  is a function of the previously outputted filter signal I FILTER    364 , the current measure signal I MEASURE    362 , and the constant K:
 
 I   FILTER ( n )= I   FILTER ( n− 1)+ K ( I   MEASURE ( n )− I   FILTER ( n− 1))  K&lt; 1  (1)
 
In one example, the constant K allows adjustment of how quickly the controller responds to changes in the output current I O . Or in other words, the constant K may be used to control the dynamic response of the system. The constant K is the proportional gain factor in proportional-integral-derivative (PID) controllers. For example K substantially equal to one corresponds to a very fast response while K substantially equal to zero corresponds to no response. In one example, K is substantially equal to 0.5.
 
     Controlled power circuit  350  is coupled to receive the filter signal I FILTER    364  and outputs the update signal U UPDATE    370 . The controlled power circuit  350  also receives the power signal U POWER    366 , which is representative of the desired value of the output power P O  of the power converter. Power signal U POWER    366  may be provided by to the controller  326  by a user through a digital interface such as an inter-integrated circuit (I2C). The controlled power circuit  350  calculates the output voltage V O  to provide the desired output power P O  and determines how to update the output voltage V O . 
     As shown, the controlled power circuit  350  includes the calculator circuit  358  and the update circuit  360 . The calculator circuit  358  is coupled to receive the filter signal I FILTER    364  and the power signal U POWER    366  and calculates the value of the output voltage V O  which provides the desired output power P O . The calculated value is outputted by the calculator circuit  358  as the calculated output voltage signal U VOC    368  and can be described by the function: 
                     U   VOC     =       U   POWER       I   FILTER               (   2   )               
In one example, the calculated output voltage signal U VOC    368  is an N-bit digital signal. In one example, N is substantially twelve. The number of bits selected for the calculated output voltage signal U VOC    368  determines the resolution for how quickly the output voltage V O  may be changed.
 
     The update circuit  360  is coupled to receive the calculated output voltage signal U VOC    368  and output the update signal U UPDATE    370 . As shown, the update signal U UPDATE    370  is received by the range decoder  352  and as an input to the update circuit  360 . The update signal U UPDATE    370  is representative of how quickly and/or the amount which the output voltage V O  of the power converter is modified and is also an N-bit digital signal. In one example, if the previous value of the update signal U UPDATE    370  is less than to the calculated output voltage signal U VOC    368  currently received, this may indicate that the output power P O  is too low and the output voltage V O  should be increased. As such, the update signal U UPDATE    370  is set to substantially the calculated output voltage signal U VOC    368  such that the controller may vary the output voltage V O  to reach the desired output power P O . If the previous value of the update signal U UPDATE    370  is substantially equal to the calculated output voltage signal U VOC    368  currently received, the update signal U UPDATE    370  is set to the calculated output voltage signal U VOC    368 . 
     If the previous value of the update signal U UPDATE    370  is greater than the calculated output voltage signal U VOC    368  currently received, this may indicate that the output power P O  is too high and the output voltage V O  should be decreased. However, the update signal U UPDATE    370  is not immediately set to the calculated output voltage signal U VOC    368 . This may be done for increased stability. As such, the update signal U UPDATE    370  is set to substantially the previous value of the update signal U UPDATE    370  minus a constant P. Mathematically this may be represented:
 
if  U   UPDATE ( n− 1)≤ U   VOC ( n ) then  U   UPDATE ( n )= U   VOC ( n )
 
if  U   UPDATE ( n− 1)&gt; U   VOC ( n ) then  U   UPDATE ( n )= U   UPDATE ( n− 1)− P   (3)
 
Where the constant P may be a trim option set by a user to determine how quickly the update signal U UPDATE    370  is decreased to substantially the calculated output voltage signal U VOC    368 . For example, the constant P could be set to one or two.
 
     The range decoder  352  receives the update signal U UPDATE    370  and outputs first signal  372  and second signal  374  to the controlled current sources  354  and  356 , respectively. The controlled current sources  354  and  356  are coupled together such that the terminal between the current sources  354 ,  356  is the output of the output power control circuit  326  and provides the adjust signal U ADJ    336 . The range decoder  352  interprets update signal U UPDATE    370  and determines how much current (via adjust signal U ADJ    336 ) is sourced or sinked from the resistor divider of resistors  328 ,  330  via the adjust signal U ADJ    336 . Once interpreted, the range decoder  352  converts the digital update signal U UPDATE    370  to an analog signal (first signal  372  and/or second signal  374 ) which controls either the current source  354  or current source  356 . The amount of current I 1  and current I 2  provided by current sources  354 ,  356 , respectively is controlled by the first and second signal  372 ,  374 , respectively. As such, the output power control circuit  326  provides the adjust signal U ADJ    336  to adjust the feedback signal U FB    338  to control the output voltage V O  to the calculated output voltage U VOC    368  determined by the calculator circuit  358 . 
       FIG. 4  illustrates another power converter  400  which includes a controller  420  which utilizes the output power control circuit  426 . It should be understood that similarly named and numbered elements couple and function as discussed above. The power converter  400  is similar to the power converter  100  illustrated in  FIG. 1 , however the controller  420  includes a secondary controller  476  and a primary controller  478 . Primary controller  478  controls the switching of the power switch S 1   410  via the primary drive signal U PR    442 , while the secondary controller  480  controls the switching of the secondary switch  412  via the secondary drive signal U SR    441 . As mentioned above, the secondary switch  412  may be exemplified as a synchronous rectifier. The primary controller  478  and secondary controller  476  may communicate via communication link  480 . In the example shown, the secondary controller  476  includes the output power control circuit  426 . In addition, elements of the drive circuit  134  discussed with respect to  FIG. 1  would be included in both the secondary controller  476  and the primary controller  478 . For example, the drive signal  140  (of  FIG. 1 ) could be generated by the secondary controller  476  and communicated to the primary controller  478  via the communication link  480 . 
     In one example, primary controller  478  and secondary controller  476  may be formed as part of an integrated circuit that is manufactured as either a hybrid or monolithic integrated circuit, which is shown as controller  420 . In one example the power switch S 1   410  may also be integrated in a single integrated circuit package with controller  420 . In another example the secondary switch  412  may be integrated in a single integrated circuit package with controller  420 . However, in another example, it should be appreciated that both the primary controller and the secondary controller need not be included in a single controller package, and for example may be implemented in separate controller packages. In addition, in one example, primary controller  478  and secondary controller  476  may be formed as separate integrated circuits. 
     The above description of illustrated examples of the present invention, including what is described in the Abstract, are not intended to be exhaustive or to be limitation to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible without departing from the broader spirit and scope of the present invention. Indeed, it is appreciated that the specific example voltages, currents, frequencies, power range values, times, etc., are provided for explanation purposes and that other values may also be employed in other embodiments and examples in accordance with the teachings of the present invention.