Patent Publication Number: US-2022239232-A1

Title: Resonant power converter circuit

Description:
The present specification relates to systems, methods, apparatuses, devices, articles of manufacture and instructions for power supplies. 
     SUMMARY 
     According to an example embodiment, a switch mode power supply (SMPS) circuit configured to receive an input voltage and generate an output voltage, comprising: a set of switching devices configured to receive the input voltage; a first transformer, having an input winding coupled to the switching devices, and an output winding configured to generate the output voltage; a second transformer, having an input winding coupled to receive the output voltage from the first transformer, and an output winding configured to generate an output voltage monitoring signal; and a controller configured to control the switching devices based on the output voltage monitoring signal. 
     In another example embodiment, the controller is configured to control the switching devices based only on the output voltage monitoring signal. 
     In another example embodiment, the output voltage monitoring signal is also configured as a power supply for the switch mode power supply. 
     In another example embodiment, the output voltage monitoring signal is also configured as a power supply for the controller. 
     In another example embodiment, the controller is solely powered by the output voltage monitoring signal. 
     In another example embodiment, the controller is solely powered by the output voltage monitoring signal after the switch mode power supply circuit reaches a stable operating state. 
     In another example embodiment, the input voltage is a rectified supply (Vbus) voltage. 
     In another example embodiment, the switching devices form a half-bridge. 
     In another example embodiment, the input winding of the second transformer is coupled directly to the output winding of the first transformer. 
     In another example embodiment, the output winding of the second transformer is coupled directly to the controller. 
     In another example embodiment, the first transformer is a resonant transformer and the second transformer is an auxiliary transformer. 
     In another example embodiment, the switch mode power supply (SMPS) is a resonant power converter. 
     In another example embodiment, in the second transformer, a ratio of a number of wire turns in the input winding to a number of wire turns in the output winding is a non-integer number. 
     In another example embodiment, the output winding of the second transformer is center tapped to enable full wave rectification. 
     In another example embodiment, a magnetic flux of the first transformer is isolated from a magnetic flux of the second transformer. 
     In another example embodiment, the output winding of the first transformer is configured to be coupled to a load drawing a load current; and the second transformer is configured to draw a current that is independent of the load current. 
     In another example embodiment, the switching devices are switching transistors. 
     In another example embodiment, the controller is also configured to receive the input voltage as a power supply for the controller. 
     In another example embodiment, further comprising an LC circuit coupling the switching devices and the first transformer&#39;s input winding. 
     According to another example embodiment, a resonant power converter configured to receive an input voltage and generate an output voltage, comprising: a set of switching devices configured to receive the input voltage; a first transformer, having an input winding coupled to the switching devices, and an output winding configured to generate the output voltage; a second transformer, having an input winding coupled to receive the output voltage, and an output winding configured to generate an output voltage monitoring signal; and a controller configured to control switching of the switching devices based on the output voltage monitoring signal. 
     The above discussion is not intended to represent every example embodiment or every implementation within the scope of the current or future Claim sets. The Figures and Detailed Description that follow also exemplify various example embodiments. 
     Various example embodiments may be more completely understood in consideration of the following Detailed Description in connection with the accompanying Drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  represents an example switch mode power supply with a single transformer. 
         FIG. 2  represents an example of the single transformer in the switch mode power supply. 
         FIG. 3  represents a first example switch mode power supply with two transformers. 
         FIG. 4  represents a second example switch mode power supply with two transformers. 
     
    
    
     While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that other embodiments, beyond the particular embodiments described, are possible as well. All modifications, equivalents, and alternative embodiments falling within the spirit and scope of the appended claims are covered as well. 
     DETAILED DESCRIPTION 
     Switch mode power supplies are used in many power supply applications for many electronic devices. At start-up, such Switch mode power supplies may be bootstrapped by a rectified supply voltage, but then quickly switch to being powered by their own regulated output voltages sent to a set of downstream circuits to be supplied and protected. 
     Such switch mode power supplies are also configured to receive a sensing and/or monitoring signal that is intended to roughly parallel the switch mode power supplies&#39; actual output voltage and which is used for supply of the controller and/or feedback for protection and/or regulation of the output voltage. For example, some switch mode power supplies use an auxiliary winding from a same transformer to generate the sensing signal. 
       FIG. 1  represents an example  100  switch mode power supply  102  with a single transformer. The example  100  includes the switch mode power supply  102  coupled to receive an input voltage (Vbus)  104  and generate an output voltage (Vout)  106 . The switch mode power supply  102  includes a controller  108 , switching devices  110 , an LC circuit (formed by Ls, Lm, Cr as shown in  FIG. 1 ) and a transformer  114 . The transformer  114  includes input winding  116  on a primary/high-voltage/hot side, output winding  118  on a secondary/low-voltage/cold side, and an auxiliary winding  120 . In some example embodiments (e.g. half bridge designs) the controller  108  can be split up into a controller and a level shifter. 
     In this example, the controller  108  chip is placed on the primary/high-voltage/hot side and connected to the input winding  116  and to the auxiliary winding  120 . The controller  108  controls the switching devices  110  (e.g. switching transistors) that are coupled by the LC circuit to the transformer  114  to control the output voltage (Vout)  106 . An optical control circuit  122  provides output voltage (Vout)  106  feedback to the controller  108  for controlling the switching devices  110 . The controller  108  can also use the auxiliary winding  120  to indirectly sense/monitor the output voltage (Vout)  106 . 
     In some example embodiments during startup the controller  108  chip is directly supplied from the input voltage (Vbus)  104  (i.e. high-voltage rectified voltage (Vbus)). After startup the controller  108  chip may be also supplied from auxiliary winding  120  on the transformer  114  as shown in  FIG. 1 . The secondary output winding  118  and the auxiliary winding  120  are center tapped to enable full wave rectification. A secondary winding output voltage from the output winding  118  is provided to a rectification circuit, represented by diodes D 1 , D 2  but which in some applications (e.g. high power) can be any variety of synchronous rectification circuits. 
       FIG. 2  represents an example  200  of the single transformer  114  in the switch mode power supply  102 . The example  200  transformer  114  shows: the input winding  116  (e.g. primary winding) having Nprim turns and Rprim  202  total winding resistance; the output winding  118  (e.g. secondary winding) having Nsec turns and Rsec  204 / 206  total winding resistance on either side of the center-tap; and the auxiliary winding  120  having Naux turns and Raux  208  total winding resistance. A secondary winding output voltage (Vsec)  202  is shown as generated by the output winding  118 . 
     In this configuration, the auxiliary voltage (V aux ) is in the first order determined by the turns ratio Naux/Nsec and the secondary winding output voltage (Vsec)  202 . The V aux  is not only used to supply the controller  108  chip (IC), but also for output overvoltage/undervoltage detection because the V aux  ideally should reflect the value of the secondary winding output voltage (Vsec)  202 . Vout is kept constant by using either the optical control circuit  122  coupled to the controller  108  (e.g. labeled SNSFB in  FIG. 1 ) or by feeding Vaux into the controller  108  chip (e.g. labeled SNSOUT in  FIG. 1 ) which then controls the switching devices  110  so that the secondary voltage (Vsec) will also be constant and at a selected regulated voltage value. 
     This switch mode power supply  102  works well for applications with a relatively low output current where the secondary voltage Vsec is only a little bit below an induced voltage (E sec =N sec *dΦ/dt) in the transformer  114 . 
     However, in applications with high output currents (e.g. &gt;40 A), a voltage drop across the resistance Rsec becomes significant. Vsec is kept constant by the control loop, so at higher secondary currents, the value of the induced voltage (E sec ) and thus ΔΦ/Δt the must be higher in order to compensate for the loss in Rsec. The auxiliary winding is experiencing the same ΔΦ/Δt, so E aux  will also rise at higher secondary output currents, but the current in the auxiliary winding is low. 
     In some example embodiments, an end result of this circuit configuration is an auxiliary voltage (V aux ) that rises when the output current increases, and thus the auxiliary voltage would not reliably mimic the output voltage (Vout)  106  anymore and could not be used for output voltage (Vout)  106  overvoltage detection. In some example embodiments, the V aux  rise at high secondary output currents can become so large that V aux  exceeds a maximum supply voltage of the controller  108  chip and thus could damage the controller  108 . 
     In some example applications, with high output currents, the output/secondary winding  118  consists of only one winding. Because then the turns ratio Naux/N sec  is a whole number, the auxiliary voltage is a multiple of the output voltage (Vout)  106 . For example, if the output voltage (Vout)  106  is 12V, then the auxiliary voltage would be 12V, 24V, 36V, and so on depending upon the number of whole turns. Since the controller  108  chip could have a limited supply voltage (e.g. labeled SUPIC (Supply IC) in  FIG. 1 ) range, together with an auxiliary voltage rise at higher currents, the controller  108  could not use the auxiliary winding as a power supply for the controller  108  chip. 
     Such high-currents are becoming more and more prevalent in applications such as data center power supplies and fast charging personal electronic devices and when charging electric cars. 
     Now discussed is a more robust switch mode power supply circuit for both sensing/monitoring an output voltage provided to downstream circuits and for powering the switch mode power supply itself using a second transformer coupled to receive a secondary winding output voltage. 
       FIG. 3  represents a first example  300  switch mode power supply  302  with two transformers. The example  300  switch mode power supply  302  is coupled to receive an input voltage  304  and generate an output voltage  306 . The switch mode power supply  302  includes a controller  308 , switching devices  310  (e.g. transistors), an LC circuit  312 , a first transformer  314 , a second transformer  316 , and a rectification circuit  320 . 
     The controller  308  in some example embodiments is coupled to receive the input voltage  304 . The set of switching devices  310  (e.g. switching transistors) are also coupled to receive the input voltage  304 . The first transformer  314  includes an input/primary winding coupled to the switching devices  310  via the LC circuit  312 . The first transformer  314  also includes an output/secondary winding configured to generate a secondary winding output voltage  322 . The rectification circuit  320  receives the secondary winding output voltage  322  and generates the output voltage  306 . 
     The second transformer  316  is not flux coupled to the first transformer  314 , but instead has its own input/primary winding coupled to directly receive the secondary winding output voltage  322 . The second transformer  316  also includes an output/secondary winding configured to generate an output voltage monitoring signal  318  from the secondary winding output voltage  322 . 
     In some example embodiments, the controller  308  is configured to control the switching devices  310  and thus the output voltage  306 , based on the output voltage monitoring signal  318 . In various example embodiments, the output voltage monitoring signal  318  is also used as a power supply for the switch mode power supply  302  and/or the controller  308 . 
     The example  300  switch mode power supply  302  thus provides an option of providing an output voltage  306  without a need for an additional controller or switches, either on the primary or secondary side of the first transformer  314 . Note in some example embodiments the switch mode power supply  302  is a resonant power converter. 
       FIG. 4  represents a second example  400  switch mode power supply  402  with two transformers. The example  400  switch mode power supply  402  is configured to receive an input voltage (Vbus)  404  and generate an output voltage (Vout)  406 . The switch mode power supply  402  includes a controller  408 , switching devices  410 , an LC circuit (formed by Ls, Lm, Cr as shown in  FIG. 4 ), a first transformer  414 , a second transformer  420 , and an optical control circuit  428 . 
     The first transformer  414  includes input winding  416  and output winding  418 . The second transformer  420  includes an input winding  422 , an output winding  424  and is configured to generate an output voltage monitoring/sensing signal  426  from a secondary winding output voltage (Vsec)  430 . The optical control circuit  428  provides output voltage (Vout)  406  feedback to the controller  408  for controlling the switching devices  410 . The controller  408  can also use the second transformer  420  to directly sense/monitor the secondary winding output voltage  430  for better regulation of the output voltage (Vout)  406 . 
     The switch mode power supply  402  operates in a manner similar to that discussed for the switch mode power supply  302  in  FIG. 3 . As can be seen, the first transformer  414  and the second transformer  420  are not flux coupled. By keeping the flux of the first transformer  414  and the second transformer  420  separate, the concern that high output currents from the first transformer  414  would affect the output voltage monitoring/sensing signal  426  based on the output voltage (Vout)  406  is no longer a concern. 
     Using the separate second transformer  420  to generate the output voltage monitoring/sensing signal  426 , instead of using a voltage from an auxiliary winding coupled to the first transformer  414  (as discussed in  FIGS. 1 and 2 ) has the advantage that the output voltage monitoring/sensing signal  426  is not distorted by the secondary current from the first transformer  414  since the output voltage monitoring/sensing signal  426  is now based on the secondary voltage (Vsec) rather than the shared flux from the primary winding  416  in the transformer  414 . In this way the output voltage monitoring/sensing signal  426  voltage is a reliable reflection of the output voltage (Vout)  406 . 
     Also, because there is a separate second transformer  420 , there is a larger design freedom for choosing a turns ratio (N prim /N sec ) so as to get the desired output voltage monitoring/sensing signal  426  voltage range. 
     For example, assume the output voltage (Vout)  406  is to be regulated to 12V and the controller&#39;s  408  supply voltage (SUPIC) is to be 18V. Assuming a diode (i.e. the diode between the second transformer  420  and the controller  408 ) forward voltage is 0.6V. This leads to a voltage Vsec=12.6V and the input voltage of second transformer  420  will be 2×12.6V=25.2V. The output voltage monitoring/sensing signal  426  will be 18V+0.6V=18.6V. So for the second transformer  420 , a turns ratio of 25.2/18.6 must be realized which can be done by making N prim =42 and N sec =31. 
     Various instructions and/or operational steps discussed in the above Figures can be executed in any order, unless a specific order is explicitly stated. Also, those skilled in the art will recognize that while some example sets of instructions/steps have been discussed, the material in this specification can be combined in a variety of ways to yield other examples as well, and are to be understood within a context provided by this detailed description. 
     In some example embodiments these instructions/steps are implemented as functional and software instructions. In other embodiments, the instructions can be implemented either using logic gates, application specific chips, firmware, as well as other hardware forms. 
     It will be readily understood that the components of the embodiments as generally described herein and illustrated in the appended figures could be arranged and designed in a wide variety of different configurations. Thus, the detailed description of various embodiments, as represented in the figures, is not intended to limit the scope of the present disclosure, but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by this detailed description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. 
     Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussions of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment. 
     Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention. 
     Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present invention. Thus, the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.