Abstract:
The present invention discloses a quasi-resonant valley voltage detecting method, comprising the steps of: generating a valley detection signal by detecting a valley of a first quasi-resonant signal; generating a count value by counting the valley detection signal; and determining a level transition instance of a gating signal according to the count value, wherein the level transition instance of the gating signal is pulled back by the valley detection signal to trace the valley of the first quasi-resonant signal. The present invention also provides a quasi-resonant valley voltage detecting apparatus.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to switching power conversions, and more particularly relates to switching power conversions capable of performing soft switching on a primary side power switch. 
     2. Description of the Related Art 
     To reduce the power dissipation, electromagnetic interference, etc. of the switching power converters, soft switching is widely adopted due to the advantage of low conduction loss of the primary side power switch. 
     Taking the fly-back AC-to-DC power adapter using soft switching as an example,  FIG. 1  shows the circuit diagram of a typical fly-back AC-to-DC power adapter. As shown in  FIG. 1 , the typical fly-back AC-to-DC power adapter includes an AC plug  101 , an input rectification and filtering unit  102 , a main transformer and output rectification and filtering unit  103 , a feedback network  104 , a PWM IC  105 , a V CC  regulator  106 , an NMOS transistor  107  and a resistor  108 . 
     In the architecture, the AC plug  101  is used for providing an AC input. 
     The input rectification and filtering unit  102  is used to generate a main input voltage according to the AC input. 
     The main transformer and output rectification and filtering unit  103 , having a primary side coupled to the main input voltage and a secondary side coupled to a combination of a diode and a capacitor, is used to convert power from the AC input to the output V out  of the adapter. 
     The feedback network  104  is used to generate a feedback signal V FB  according to an error signal derived from a reference voltage and the output V out . 
     The PWM IC  105  is used to generate a gating signal V G  according to a quasi-resonant (QR) signal V A , the feedback signal V FB  and a current sensing signal V CS  to drive the NMOS transistor  107 , wherein the gating signal V G  is expected to issue a high level at the instance when the quasi-resonant (QR) signal V A  is at its valley voltage to reduce the conduction loss on the NMOS transistor  107 . 
     The V CC  regulator  106  is used to generate a DC supply voltage V CC  and the quasi-resonant (Q) signal V A  for the operation of the PWM IC  105 , wherein the resonant waveform of the quasi-resonant (QR) signal V A  is proportional to the drain voltage of the NMOS transistor  107  when the NMOS transistor  107  is off, and the valley of the quasi-resonant (QR) signal V A  is corresponding to the valley of the drain voltage of the NMOS transistor  107 . 
     The NMOS transistor  107 , responsive to the gating signal V G , is used to control the power conversion via the main transformer and output rectification and filtering unit  103 . 
     The resistor  108  is used to carry the current sensing signal V CS . 
     Through a periodic soft switching of the NMOS transistor  107 , which is driven by the gating signal V G  generated from the PWM IC  105 , the input power is transformed through the main transformer and output rectification and filtering unit  103  to the output with less conduction loss on the NMOS transistor  107 . 
     However, it is not easy to turn on the primary side power switch right at the valley of the quasi-resonant voltage because the delay contributed by the power switch and the main transformer, being unknown and dependent on the application, has to be taken into account in determining the turn-on instance of the primary side power switch. 
     According to this problem, a prior art U.S. Pat. No. 7,426,120 B2 has proposed a switching control circuit. Please refer to  FIG. 2   a - 2   c , which shows the waveform for detecting the valley voltage and phase lock according to the prior art switching control circuit for a fly-back AC-to-DC power converter. As shown in  FIG. 2   a - 2   c , the V M  is an inverted version of a voltage from an auxiliary winding, and the prior circuit needs two sets of sampling circuit and related processing circuit to accomplish the soft switching. Due to the complex circuit structure, the prior art U.S. Pat. No. 7,426,120 B2 is not robust enough in implementing power converters, so there is a need of a concise and robust solution for soft switching the primary side power switch. 
     SUMMARY OF THE INVENTION 
     One objective of the present invention is to provide a novel quasi-resonant valley voltage detecting method for a switching power converter to soft switching a primary side power switch in a robust way. 
     Another objective of the present invention is to further provide a quasi-resonant valley voltage detecting apparatus with concise architecture, for a switching power converter to soft switching a primary side power switch in a robust way. 
     To achieve the foregoing objectives of the present invention, a quasi-resonant valley voltage detecting method is proposed, the method comprising the steps of: generating a valley detection signal by detecting a valley of a first quasi-resonant signal; generating a count value by counting the valley detection signal; and determining a level transition instance of a gating signal according to the count value, wherein the level transition instance of the gating signal is pulled back by the valley detection signal to trace the valley of the first quasi-resonant signal. 
     To achieve the foregoing objectives, the present invention further provides a quasi-resonant valley voltage detecting apparatus, comprising: a valley detector, used for generating a valley detection signal according to voltage comparison of a first quasi-resonant signal and a second quasi-resonant signal, wherein the second quasi-resonant signal is a delayed version of the first quasi-resonant signal; a counter unit, used for generating a count value according to a counting of the valley detection signal; a delay unit, used for delaying a first set signal with a delay time to generate a second set signal, wherein the delay time is determined by the count value; a comparator, used for generating the first set signal according to the first quasi-resonant signal and a reference voltage; and a latch, used for generating a gating signal according to the second set signal and a reset signal. 
     To achieve the foregoing objectives, the present invention further provides a quasi-resonant valley voltage detecting apparatus, comprising: a valley detector, used for generating a valley detection signal according to voltage comparison of a first quasi-resonant signal and a second quasi-resonant signal, wherein the second quasi-resonant signal is a delayed version of the first quasi-resonant signal; a counter unit, used for generating a count value according to a counting of the valley detection signal; a digital to analog converter, used for generating an adjustable reference voltage according to the count value; a comparator, used for generating a set signal according to the first quasi-resonant signal and the adjustable reference voltage; and a latch, used for generating a gating signal according to the set signal and a reset signal. 
     To make it easier for our examiner to understand the objective of the invention, its structure, innovative features, and performance, we use preferred embodiments together with the accompanying drawings for the detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is the circuit diagram of a typical fly-back AC-to-DC power adapter utilizing a soft switching scheme. 
         FIGS. 2   a - 2   c  shows the waveform for detecting the valley voltage and phase lock according to a prior art switching control circuit for a fly-back AC-to-DC power converter. 
         FIG. 3  is the circuit diagram of a valley voltage detecting circuit according to a preferred embodiment of the present invention. 
         FIGS. 4   a - 4   b  shows the waveform for detecting the valley voltage according to the valley voltage detecting circuit in  FIG. 3 . 
         FIG. 5  is the circuit diagram of a valley voltage detector according to a preferred embodiment of the present invention. 
         FIG. 6  shows the waveform for detecting the valley voltage according to the valley voltage detector in  FIG. 5 . 
         FIG. 7  is the block diagram of a soft switching controller according to a preferred embodiment of the present invention. 
         FIG. 8  is the block diagram of a soft switching controller according to another preferred embodiment of the present invention. 
         FIG. 9  is the flow chart of a soft switching method according to a preferred embodiment of the present invention. 
         FIG. 10  is the flow chart of a soft switching method according to another preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described in more detail hereinafter with reference to the accompanying drawings that show the preferred embodiment of the invention. 
     Please refer to  FIG. 3 , which shows the circuit diagram of a valley voltage detecting circuit according to a preferred embodiment of the present invention. As shown in  FIG. 3 , the circuit according to a preferred embodiment of the present invention includes a resistor  301 , a capacitor  302  and a comparator  303 . 
     In the architecture, the resistor  301  and the capacitor  302  are used as a delay unit for delaying a first quasi-resonant signal V A  to generate a second quasi-resonant signal V B . 
     The comparator  303  is used to generate a valley detection step signal V C  according to the first quasi-resonant signal V A  and the second quasi-resonant signal V B . 
     Please refer to  FIG. 4   a - 4   b , which shows the waveform for detecting the valley voltage according to the valley voltage detecting circuit in  FIG. 3 . When the primary side power switch (as the NMOS transistor  107  in  FIG. 1 ) is turned on at a time before the first quasi-resonant signal V A  reaches its valley, the resultant waveform of V A , as shown in  FIG. 4   a , will be always lower than V B , and the valley detection step signal V C  will stay at a low level. When the primary side power switch (as the NMOS transistor  107  in  FIG. 1 ) is turned on at a time after the first quasi-resonant signal V A  has reached its valley, the resultant waveform of V A , as shown in  FIG. 4   b , will be higher than V B  after the cross over of V A  and V B , and the valley detection step signal V C  will exhibit a low to high transition. 
     According to the circuit in  FIG. 3 , the present invention further proposes a valley voltage detector capable of issuing a pulse when the cross over of V A  and V B  is present. Please refer to  FIG. 5 , which shows the circuit diagram of a valley voltage detector according to a preferred embodiment of the present invention. As shown in  FIG. 5 , the valley voltage detector  500  includes a comparator  501 , a comparator  502 , an AND gate  503 , a resistor  504 , a capacitor  505 , a capacitor  506  and an AND gate  507 . 
     The comparator  501  is used for generating a first step signal according to the first quasi-resonant signal V A  and a first threshold voltage V TH1 . 
     The comparator  502  is used for generating a second step signal according to the first quasi-resonant signal V A  and a second threshold voltage V TH2 . 
     The AND gate  503  is used for generating a window signal V W  according to the first step signal and the second step signal. 
     The resistor  504  and the capacitor  505  are used as an RC delay circuit to generate a second quasi-resonant signal V B  according to the first quasi-resonant signal V A . 
     The comparator  506  is used for generating a valley detection step signal V C  according to the first quasi-resonant signal V A  and the second quasi-resonant signal V B . 
     The AND gate  507  is used for generating a valley detection signal V P  according to the window signal V W  and the valley detection step signal V C . 
     Please refer to  FIG. 6 , which shows the waveform for detecting the valley voltage according to the valley voltage detector  500  in  FIG. 5 . As shown in  FIG. 6 , the window signal V W  is defined by the first threshold voltage V TH1  and the second threshold voltage V TH2 . The valley detection step signal V C  has a rising edge corresponding to the valley of the first quasi-resonant signal V A , and the valley detection signal V P  is generated by performing logic-AND operation on the valley detection step signal V C  and the window signal V W . 
     According to the valley voltage detector  500  in  FIG. 5 , the present invention further proposes a soft switching controller. Please refer to  FIG. 7 , which shows the block diagram of a soft switching controller according to a preferred embodiment of the present invention. As shown in  FIG. 7 , the soft switching controller includes a valley detector  500 , a comparator  701 , a delay unit  702 , a counter unit  703  and a latch  704 . 
     The valley detector  500 , as specified above in  FIG. 5 , is used to generate a valley detection signal V P  according to a quasi-resonant signal V A . 
     The comparator  701  is used for generating a first set signal V SET1  according to the quasi-resonant signal V A  and a reference voltage V TH3 . 
     The delay unit  702  is used for delaying the first set signal V SET1  with a delay time to generate a second set signal V SET2 , wherein the delay time is determined by a count value B out . 
     The counter unit  703  is used for generating the count value B out  according to a counting of the valley detection signal V P . 
     The latch  704  is used for generating a gating signal V G  according to the second set signal V SET2  and a reset signal V RESET , wherein the gating signal V G  will issue a high level when the S input of the latch  704  is triggered by the second set signal V SET2 . 
     Through the implementation of the soft switching controller as shown in  FIG. 7 , the timing of the rising edge of the gating signal V G  can be adjusted in a way that if the cross over is present then the delay time will be reduced to draw back the instance of the rising edge of the gating signal V G , and the conduction loss of the primary side power switch is reduced to minimum. 
       FIG. 8  shows the block diagram of a soft switching controller according to another preferred embodiment of the present invention. As shown in  FIG. 8 , the soft switching controller includes a valley detector  500 , a comparator  801 , a latch  802 , a counter unit  803  and a digital to analog converter  804 . 
     The valley detector  500 , as specified above in  FIG. 5 , is used to generate a valley detection signal V P  according to a quasi-resonant signal V A . 
     The comparator  801  is used for generating a set signal V SET  according to the quasi-resonant signal V A  and an adjustable reference voltage V TH4 . 
     The latch  802  is used for generating a gating signal V G  according to the set signal V SET  and a reset signal V RESET . 
     The counter unit  803  is used for generating the count value B out  according to a counting of the valley detection signal V P . 
     The digital to analog converter  804  is used for generating an adjustable reference voltage V TH4  according to the count value B out . 
     Through the implementation of the soft switching controller as shown in  FIG. 8 , the timing of the rising edge of the gating signal V G  can be adjusted in a way that if the cross over is present then the adjustable reference voltage V TH4  will be increased to draw back the instance of the rising edge of the gating signal V G , and the conduction loss of the primary side power switch is reduced to minimum. 
     According to the apparatus in  FIG. 7 , the present invention further proposes a quasi-resonant valley voltage detection method. Please refer to  FIG. 9 , which shows the flow chart of a soft switching method according to a preferred embodiment of the present invention. As shown in  FIG. 9 , the method includes the steps of: performing voltage comparison on a first quasi-resonant signal and a reference voltage to generate an initial driving signal (step a); delaying the first quasi-resonant signal to generate a second quasi-resonant signal (step b); performing voltage comparison on the first quasi-resonant signal and the second quasi-resonant signal to generate a valley detection signal (step c); determining a delay time according to the valley detection signal (step d); and delaying the initial driving signal with the delay time to generate a rising edge of a gating signal (step e). 
     In step a, the initial driving signal is for presetting a turn-on instance of the primary side power switch. 
     In step b, the first quasi-resonant signal and the second quasi-resonant signal will have a cross over if the primary side power switch is turned on after the valley of the first quasi-resonant signal has appeared. 
     In step c, the valley detection signal will issue a pulse if the cross over in step b is present. 
     In step d, the delay time is adjusted in a way that when the valley detection signal issues a pulse, the delay time is decreased by a predetermined value. 
     In step e, the instance of the rising edge of the gating signal is adjusted by the delay time to meet the valley of the first quasi-resonant signal in a negative feedback manner. If the cross over is present then the delay time will be reduced to draw back the instance of the rising edge of the gating signal V G , and the conduction loss of the primary side power switch is reduced to minimum. 
     According to the apparatus in  FIG. 8 , the present invention further proposes a quasi-resonant valley voltage detection method. Please refer to  FIG. 10 , which shows the flow chart of a soft switching method according to another preferred embodiment of the present invention. As shown in  FIG. 10 , the method includes the steps of: delaying a first quasi-resonant signal to generate a second quasi-resonant signal (step a); performing voltage comparison on the first quasi-resonant signal and the second quasi-resonant signal to generate a valley detection signal (step b); counting the valley detection signal to generate a reference signal (step c); and performing voltage comparison on the reference signal and the first quasi-resonant signal to generate a rising edge of a gating signal (step d). 
     In step a, the first quasi-resonant signal and the second quasi-resonant signal will have a cross over if the primary side power switch is turned on after the valley of the first quasi-resonant signal has appeared. 
     In step b, the valley detection signal will issue a pulse if the cross over in step b is present. 
     In step c, the reference voltage is adjusted in a way that when the valley detection signal issues a pulse, the reference voltage is increased by a predetermined value. 
     In step d, the instance of the rising edge of the gating signal is adjusted by the reference voltage to meet the valley of the first quasi-resonant signal in a negative feedback manner. 
     Through the implementation of the present invention, a more concise architecture in soft switching for power module applications is achieved. The cross over concept and the digital adjustment manner according to the present invention, having superior performance in locating the valley of a quasi-resonant voltage, have created a novel and robust way of soft switching the primary side power switch in power converter applications. 
     While the invention has been described by way of example and in terms of preferred embodiments, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures. 
     In summation of the above description, the present invention herein enhances the performance than the conventional structure and further complies with the patent application requirements and is submitted to the Patent and Trademark Office for review and granting of the commensurate patent rights.