Abstract:
The configurations of an isolated DC/DC converter and an isolated DC/AC converter and the controlling methods thereof are provided. The proposed isolated DC/DC converter includes a DC/AC switching device, a transformer, a rectifier, and a duty ratio and frequency modulating apparatus coupled to the rectifier and the DC/AC switching device for generating a driving signal to adjust a duty ratio and a frequency of the switching device so as to regulate an output DC voltage of the converter.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an isolated DC/DC converter and an isolated DC/AC converter. More particularly, the present invention relates to an isolated DC/DC converter having a duty ratio and frequency modulating apparatus and an isolated DC/AC converter having a duty ratio and frequency modulating apparatus. 
       BACKGROUND OF THE INVENTION 
       [0002]    Please refer to  FIG. 1 , which shows a schematic circuit diagram of an isolated DC/DC converter having a frequency modulating apparatus in the prior art. The isolated DC/DC converter having a frequency modulating apparatus  1  includes a DC/AC switching device  11 , a frequency modulating device  12 , a rectifier  13 , an input capacitor C I , a block capacitor C B , a leakage inductor Lk, a transformer TR and an output capacitor C O . In which, the DC/AC switching device receives an input DC voltage V IN  for outputting a first AC output voltage (not shown) and includes a first power switch module having a first power switch Q 1  and a first diode D 1 , a second power switch module having a second power switch Q 2  and a first diode D 2 , a third power switch module having a third power switch Q 3  and a third diode D 3  and a fourth power switch module having a fourth power switch Q 4  and a fourth diode D 4 . The frequency modulating apparatus  12  includes a voltage sensor  121 , a comparator  122  and a frequency modulator  123 . The rectifier  13  includes a first rectifying diode Dr 1  and a second rectifying diode Dr 2 . The frequency modulating apparatus  12  generates an error signal based on a sensed voltage generated by the voltage sensor  121  and a reference voltage via the comparator  122  (see  FIG. 1 , the error signal is a feedback signal), and the error signal is inputted to a feedback terminal of the frequency modulator  123 . The frequency modulator  123  generates a driving signal according to the error signal, and the driving signal is outputted from a gate drive terminal of the frequency modulator  123  and is sent to the respective control terminals of the first to the fourth power switches (Q 1 -Q 4 ) for modulating the frequency of the DC/AC switching device  11  (the waveform of the frequency is shown as a waveform diagram at the connecting node of C B  and Lk in  FIG. 1 ) so as to regulate a DC output voltage V O , which is a voltage in between the output capacitor C O  and a ground. 
         [0003]    Please refer to  FIG. 2 , which shows a schematic circuit diagram of an isolated DC/DC converter having a duty ratio modulating apparatus in the prior art. The isolated DC/DC converter having a duty ratio modulating apparatus  2  includes a DC/AC switching device  11 , a duty ratio modulating device  21 , a rectifier  13 , an input capacitor C I , a block capacitor C B , a leakage inductor Lk, a transformer TR and an output capacitor C O . In which, the duty ratio modulating apparatus  21  includes a voltage sensor  121 , a comparator  122  and a duty ratio modulator  211 . The duty ratio modulating apparatus  21  generates an error signal (see  FIG. 2 , the error signal is a feedback signal) based on a sensed voltage generated by the voltage sensor  121  and a reference voltage via the comparator  122 , and the error signal is inputted to a feedback terminal of the duty ratio modulator  211 . The duty ratio modulator  211  generates a driving signal according to the error signal, and the driving signal is outputted from a gate drive terminal of the duty ratio modulator  211 , and is sent to the respective control terminals of the first to the fourth power switches (Q 1 -Q 4 ) for modulating the duty ratio of the DC/AC switching device  11  (the waveform of the duty ratio is shown as a waveform diagram at the connecting node of C B  and Lk in  FIG. 2 ) so as to regulate a DC output voltage V O , which is the voltage in between the output capacitor C O  and the ground. 
         [0004]    Please refer to  FIG. 3 , which shows a schematic circuit diagram of an isolated DC/AC converter having a frequency modulating apparatus in the prior art. The isolated DC/AC converter having a frequency modulating apparatus  3  includes a DC/AC switching device  11 , a frequency modulating device  31 , an input capacitor C I , a block capacitor C B , a plurality of transformers (each of which is represented by TR), a leakage inductor Lk, and a plurality of fluorescent lamps (Cb 1 +Lp 1 , Cb 2 +Lp 2  . . . Cbn+Lpn), in which Cb 1 , Cb 2  . . . Cbn are a plurality of ballast capacitors, and Lp 1 , Lp 2  . . . Lpn are a plurality of fluorescent lamp tubes. The frequency modulating apparatus  31  includes a current sensor  311 , a comparator  122  and a frequency modulator  312 . The frequency modulating apparatus  31  generates an error signal based on a sensed current generated by the current sensor  311  and a reference voltage via the comparator  122  (see  FIG. 3 , the error signal is a feedback signal), and the error signal is inputted to a feedback terminal of the frequency modulator  312 . The frequency modulator  312  generates a driving signal according to the error signal, and the driving signal is outputted from a gate drive terminal of the frequency modulator  312  and is sent to the respective control terminals of the first to the fourth power switches (Q 1 -Q 4 ) for modulating the frequency of the DC/AC switching device  11  (the waveform of the frequency is shown as a waveform diagram at the connecting node of C B  and the transformer TR in  FIG. 3 ) so as to regulate an AC output voltage (not shown) across the two connecting nodes of the plurality of the fluorescent lamps electrically connected in parallel (which are equivalent to a load). 
         [0005]    Please refer to  FIG. 4 , which shows a schematic circuit diagram of an isolated DC/AC converter having a duty ratio modulating apparatus in the prior art. The isolated DC/AC converter having a duty ratio modulating apparatus  4  includes a DC/AC switching device  11 , a duty ratio modulating apparatus  41 , an input capacitor C I , a block capacitor C B , a plurality of transformers (each of which is represented by TR), a leakage inductor Lk, and a plurality of fluorescent lamps (Cb 1 +Lp 1 , Cb 2 +Lp 2  . . . Cbn+Lpn), in which Cb 1 , Cb 2  . . . Cbn are a plurality of ballast capacitors, and Lp 1 , Lp 2  . . . Lpn are a plurality of fluorescent lamp tubes. The frequency modulating apparatus  41  includes a current sensor  311 , a comparator  122  and a duty ratio modulator  411 . The duty ratio modulating apparatus  41  generates an error signal based on a sensed current generated by the current sensor  311  and a reference voltage via the comparator  122  (see  FIG. 4 , the error signal is a feedback signal), and the error signal is inputted to a feedback terminal of the duty ratio modulator  411 . The duty ratio modulator  411  generates a driving signal according to the error signal, and the driving signal is outputted from a gate drive terminal of the duty ratio modulator  411  to the respective control terminals of the first to the fourth power switches (Q 1 -Q 4 ) for modulating the duty ratio of the DC/AC switching device  11  (the waveform of the duty ratio is shown as a waveform diagram at the connecting node of C B  and the transformer TR in  FIG. 4 ) so as to regulate an AC output voltage (not shown) across two connecting nodes of the plurality of the fluorescent lamps electrically connected in parallel (which are equivalent to a load). 
         [0006]    Please refer to  FIG. 5 , which shows a waveform diagram of input voltage (from 300 V to 400 V) vs. frequency (from 55 K to 65 K) while the frequency is modulated to achieve the voltage regulation for a conventional isolated converter and the duty ratio is fixed at 90%. One with an ordinary skill in the field would know that the drawbacks of achieving the voltage regulation via modulating the frequency are that the variation range of the switching frequencies are relatively larger, and certain frequencies of which interfere with other electrical equipments. For example, certain channels of the TV sets are interfered by certain frequencies of which. In order to avoid such an interference phenomenon, the design works for the electronic elements of the aforementioned DC/DC and DC/AC isolated converters are even harder. 
         [0007]    Please refer to  FIG. 6 , which shows a waveform diagram of input voltage (from 300 V to 400 V) vs. duty ratio (from 67.5% to 90%) while the duty ratio is modulated to achieve the voltage regulation for a conventional isolated converter and the frequency is fixed at 55 K. One with an ordinary skill in the field would know that the drawbacks of achieving the voltage regulation via modulating the duty ratio are that the switching noises of the above-mentioned isolated DC/DC and DC/AC converters are relatively larger while they are operating under a relatively high voltage. 
         [0008]    Keeping the drawbacks of the prior arts in mind, and employing experiments and research full-heartily and persistently, the applicant finally conceived the isolated DC/DC and DC/AC converters and the controlling methods thereof having a relatively better effectiveness. 
       SUMMARY OF THE INVENTION 
       [0009]    It is therefore an object of the present invention to provide an isolated DC/DC converter having a relatively better effectiveness to regulate a DC output voltage via adjusting a duty ratio and a frequency of the converter so as to achieve the advantages of having a relatively broader input voltage range and decreasing variation amounts of the duty ratio and the frequency. 
         [0010]    It is therefore another object of the present invention to provide an isolated DC/AC converter having a relatively better effectiveness to regulate an AC output voltage via adjusting a duty ratio and a frequency of the converter so as to achieve the advantages of having a relatively broader input voltage range and decreasing variation amounts of the duty ratio and the frequency. 
         [0011]    According to the first aspect of the present invention, the isolated DC/DC converter includes a DC/AC switching device receiving a DC input voltage for outputting a first AC output voltage, a transformer receiving the first AC output voltage for outputting a second AC output voltage, a rectifier receiving the second AC output voltage for outputting a DC output voltage and a duty ratio and frequency modulating apparatus coupled to the rectifier and the DC/AC switching device for generating a driving signal to adjust a duty ratio and a frequency of the DC/AC switching device so as to regulate the DC output voltage accordingly. 
         [0012]    Preferably, the duty ratio and frequency modulating apparatus includes a voltage sensor coupled to the rectifier for generating a sensed voltage, a comparator receiving the sensed voltage and a reference voltage for generating a feedback signal and a duty ratio and frequency modulator receiving the feedback signal for generating the driving signal to modulate the duty ratio and the frequency accordingly. 
         [0013]    Preferably, the feedback signal is a voltage signal. 
         [0014]    Preferably, the duty ratio and frequency modulating apparatus is switched between one of a first operational mode and a second operational mode according to the feedback signal, wherein the first operational mode is used to control the frequency, the second operational mode is used to control the duty ratio, the feedback signal is used to modulate the frequency within a first phase range when the duty ratio and frequency modulating apparatus is working under the first operational mode, and the feedback signal is used to modulate the duty ratio within a second phase range when the duty ratio and frequency modulating apparatus is working under the second operational model. 
         [0015]    Preferably, the DC/AC switching device has a first input terminal, a second input terminal, a first output terminal and a second output terminal, and further includes a first power switch module including a first power switch having a first terminal coupled to the first input terminal, a second terminal coupled to the second output terminal and a control terminal, and a first diode having an anode coupled to the second terminal of the first power switch and a cathode coupled to the first terminal of the first power switch, a second power switch module including a second power switch having a first terminal coupled to the first output terminal, a second terminal coupled to the second input terminal and a control terminal, and a second diode having an anode coupled to the second terminal of the second power switch and a cathode coupled to the first terminal of the second power switch, a third power switch module including a third power switch having a first terminal coupled to the first terminal of the first power switch, a second terminal coupled to the first output terminal and a control terminal, and a third diode having an anode coupled to the second terminal of the third power switch and a cathode coupled to the first terminal of the third power switch, and a fourth power switch module including a fourth power switch having a first terminal coupled to the second terminal of the first power switch, a second terminal coupled to the second terminal of the second power switch and a control terminal, and a fourth diode having an anode coupled to the second terminal of the fourth power switch and a cathode coupled to the first terminal of the fourth power switch, in which the respective control terminals of the first to the fourth power switches are coupled to the duty ratio and frequency modulating apparatus and receive the driving signal. 
         [0016]    Preferably, the isolated DC/DC converter further includes a block capacitor having a first terminal coupled to the first output terminal of the DC/AC switching device and a second terminal, a leakage inductor having a first terminal and a second terminal coupled to the rectifier and an output capacitor having a first terminal coupled to the rectifier and a second terminal coupled to a ground, in which the transformer further includes a primary winding coupled to the second terminal of the block capacitor and the second output terminal of the DC/AC switching device, and a secondary winding having a first terminal coupled to the first terminal of the leakage inductor, a second terminal coupled to the rectifier and a central tap coupled to the second terminal of the output capacitor. 
         [0017]    Preferably, the isolated DC/DC converter further includes a block capacitor having a first terminal coupled to the first output terminal of the DC/AC switching device and a second terminal, a leakage inductor having a first terminal coupled to the second terminal of the block capacitor and a second terminal, and an output capacitor having a first terminal coupled to the rectifier and a second terminal coupled to a ground, in which the transformer further includes a primary winding coupled to the second terminal of the leakage inductor and the second output terminal of the DC/AC switching device and a secondary winding having a first and a second terminals coupled to the rectifier and a central tap coupled to the second terminal of the output capacitor. 
         [0018]    Preferably, the rectifier is a half-bridge rectifier. 
         [0019]    According to the second aspect of the present invention, the isolated DC/AC converter includes a DC/AC switching device receiving a DC input voltage for outputting an AC output voltage and a duty ratio and frequency modulating apparatus coupled to the DC/AC switching device for generating a driving signal to adjust a duty ratio and a frequency of the DC/AC switching device so as to regulate the AC output voltage accordingly. 
         [0020]    Preferably, the isolated DC/AC converter further includes a transformer having a secondary winding, in which the duty ratio and frequency modulating apparatus includes a current sensor coupled to the secondary winding for generating a sensed current, a comparator receiving the sensed current and a reference voltage for generating a feedback signal and a duty ratio and frequency modulator receiving the feedback signal for generating the driving signal to modulate the duty ratio and the frequency accordingly. 
         [0021]    Preferably, the feedback signal is a current signal. 
         [0022]    Preferably, the isolated DC/AC converter further includes a block capacitor having a first terminal coupled to the first output terminal of the DC/AC switching device and a second terminal, a leakage inductor having a first terminal and a second terminal, a load having a first terminal coupled to the second terminal of the leakage inductor and a second terminal coupled to the duty ratio and frequency modulating apparatus and a transformer having a primary winding coupled to the second terminal of the block capacitor and the second output terminal of the DC/AC switching device, and a secondary winding coupled to the first terminal of the leakage inductor and the duty ratio and frequency modulating apparatus. 
         [0023]    Preferably, the isolated DC/AC converter further includes a block capacitor having a first terminal coupled to the first output terminal of the DC/AC switching device and a second terminal, a leakage inductor having a first terminal coupled to the second terminal of the block capacitor and a second terminal, a load having a first terminal and a second terminal coupled to the duty ratio and frequency modulating apparatus and a transformer having a primary winding having a first terminal coupled to the second terminal of the leakage inductor and a second terminal coupled to the second output terminal of the DC/AC switching device, and a secondary winding having a first terminal coupled to the first terminal of the load and a second terminal coupled to the duty ratio and frequency modulating apparatus. 
         [0024]    According to the third aspect of the present invention, the controlling method for an isolated DC/DC converter, in which the converter includes a DC/AC switching device, a rectifier and a duty ratio and frequency modulating apparatus coupled to the rectifier and the DC/AC switching device, includes the steps of: (a) receiving a DC input voltage via the DC/AC switching device for outputting an AC output voltage; (b) receiving the AC output voltage via the rectifier for outputting a DC output voltage; and (c) generating a driving signal via the duty ratio and frequency modulating apparatus for adjusting a duty ratio and a frequency of the DC/AC switching device so as to regulate the DC output voltage accordingly. 
         [0025]    Preferably, the step (c) further comprises the steps of: (c1) generating a feedback signal via the duty ratio and frequency modulating apparatus such that the duty ratio and frequency modulating apparatus is switched between a first operational mode and a second operational mode accordingly; (c2) controlling the frequency through the first operational mode and controlling the duty ratio through the second operational mode; (c3) modulating the frequency within a first phase range based on the feedback signal so as to generate the driving signal when the duty ratio and frequency modulating apparatus is working under the first operational mode; and (c4) modulating the duty ratio within a second phase range based on the feedback signal so as to generate the driving signal when the duty ratio and frequency modulating apparatus is working under the second operational mode. 
         [0026]    Preferably, the duty ratio and frequency modulating apparatus includes a voltage sensor coupled to the rectifier for generating a sensed voltage, in order to output the feedback signal accordingly. 
         [0027]    According to the fourth aspect of the present invention, the controlling method for an isolated DC/AC converter, in which the converter includes a DC/AC switching device and a duty ratio and frequency modulating apparatus coupled to the DC/AC switching device, includes the steps of: (a) receiving a DC input voltage via the DC/AC switching device for outputting an AC output voltage; and (b) generating a driving signal via the duty ratio and frequency modulating apparatus for adjusting a duty ratio and a frequency of the switching device so as to regulate the AC output voltage accordingly. 
         [0028]    Preferably, the step (b) further comprises the steps of: (b1) generating a feedback signal via the duty ratio and frequency modulating apparatus such that the duty ratio and frequency modulating apparatus is switched between a first operational mode and a second operational mode accordingly; (b2) controlling the frequency through the first operational mode and controlling the duty ratio through the second operational mode; (b3) modulating the frequency within a first phase range based on the feedback signal so as to generate the driving signal when the duty ratio and frequency modulating apparatus is working under the first operational mode; and (b4) modulating the duty ratio within a second phase range based on the feedback signal so as to generate the driving signal when the duty ratio and frequency modulating apparatus is working under the second operational mode. 
         [0029]    Preferably, the isolated DC/AC converter further includes a transformer having a secondary winding, and the duty ratio and frequency modulating apparatus includes a current sensor coupled to the second winding for generating a sensed current, in order to output the feedback signal accordingly. 
         [0030]    The present invention may best be understood through the following descriptions with reference to the accompanying drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  shows a schematic circuit diagram of an isolated DC/DC converter having a frequency modulating apparatus in the prior art; 
           [0032]      FIG. 2  shows a schematic circuit diagram of an isolated DC/DC converter having a duty ratio modulating apparatus in the prior art; 
           [0033]      FIG. 3  shows a schematic circuit diagram of an isolated DC/AC converter having a frequency modulating apparatus in the prior art; 
           [0034]      FIG. 4  shows a schematic circuit diagram of an isolated DC/AC converter having a duty ratio modulating apparatus in the prior art; 
           [0035]      FIG. 5  shows a waveform diagram of input voltage vs. frequency while the frequency is modulated to achieve the voltage regulation for a conventional isolated converter and the duty ratio is 90%; 
           [0036]      FIG. 6  shows a waveform diagram of input voltage vs. frequency while the duty ratio is modulated to achieve the voltage regulation for a conventional isolated converter and the frequency is 55 K; 
           [0037]      FIG. 7  shows a schematic circuit diagram of an isolated DC/DC converter having a duty ratio and frequency modulating apparatus according to the first preferred embodiment of the present invention; 
           [0038]      FIG. 8  shows a schematic circuit diagram of an isolated DC/AC converter having a duty ratio and frequency modulating apparatus according to the second preferred embodiment of the present invention; 
           [0039]      FIG. 9  shows a waveform diagram of input voltage vs. frequency and duty ratio while the duty ratio and the frequency of the provided converter according to the first/the second preferred embodiments of the present invention are modulated to achieve a relatively broader input voltage range; 
           [0040]      FIG. 10  shows a waveform diagram of input voltage vs. frequency and duty ratio while the duty ratio and the frequency of the provided converter according to the first/the second preferred embodiments of the present invention are modulated to achieve relatively lower changing amounts of duty ratio and frequency; 
           [0041]      FIG. 11(   a ) shows a waveform diagram of feedback voltage vs. frequency/duty ratio, which indicates a decrease of the feedback voltage while changing the frequency within a first phase range when the duty ratio and frequency modulating apparatus of the first/the second preferred embodiments of the present invention is working under a first operational mode, and changing the duty ratio within a second phase range when the duty ratio and frequency modulating apparatus is working under a second operational mode respectively; and 
           [0042]      FIG. 11(   b ) shows a waveform diagram of feedback voltage vs. frequency/duty ratio, which indicates an increase of the feedback voltage while changing the frequency within a first phase range when the duty ratio and frequency modulating apparatus of the first/the second preferred embodiments of the present invention is working under a first operational mode, and changing the duty ratio within a second phase range when the duty ratio and frequency modulating apparatus is working under a second operational mode respectively. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0043]    Please refer to  FIG. 7 , which shows a schematic circuit diagram of an isolated DC/DC converter having a duty ratio and frequency modulating apparatus according to the first preferred embodiment of the present invention. The isolated DC/DC converter having a duty ratio and frequency modulating apparatus  5  includes a DC/AC switching device  11 , a duty ratio and frequency modulating apparatus  51 , a leakage inductor Lk, a transformer TR, a rectifier  13 , an input capacitor C I , a block capacitor C B  and an output capacitor C O . In which, the DC/AC switching device  11  receives an input DC voltage V IN  for outputting a first AC output voltage (not shown) and includes a first power switch module having a first power switch Q 1  and a first diode D 1 , a second power switch module having a second power switch Q 2  and a first diode D 2 , a third power switch module having a third power switch Q 3  and a third diode D 3  and a fourth power switch module having a fourth power switch Q 4  and a fourth diode D 4 . The duty ratio and frequency modulating apparatus  51  includes a voltage sensor  121 , a comparator  122  and a duty ratio and frequency modulator  511 . The rectifier  13  includes a first rectifying diode Dr 1  and a second rectifying diode Dr 2 . The duty ratio and frequency modulating apparatus  51  generates an error signal (see  FIG. 7 , the error signal is a feedback signal) based on a sensed voltage generated by the voltage sensor  121  and a reference voltage via the comparator  122 , and the error signal is inputted to a feedback terminal of the duty ratio and frequency modulator  511 . The duty ratio and frequency modulator  511  generates a driving signal according to the error signal, and the driving signal is outputted from a gate drive terminal of the duty ratio and frequency modulator  511  and is sent to the respective control terminals of the first to the fourth power switches (Q 1 -Q 4 ) for modulating the frequency of the DC/AC switching device  11  (respectively the waveforms of duty ratio and frequency are shown as two waveform diagrams at the connecting node of C B  and Lk in  FIG. 7 ) so as to regulate a DC output voltage V 0 , which is the voltage in between the output capacitor C O  and a ground. 
         [0044]    Please refer to  FIG. 8 , which shows a schematic circuit diagram of an isolated DC/AC converter having a duty ratio and frequency modulating apparatus according to the second preferred embodiment of the present invention. The isolated DC/AC converter having a duty ratio and frequency modulating apparatus  6  includes a DC/AC switching device  11 , a duty ratio and frequency modulating apparatus  61 , an input capacitor C I , a block capacitor C B , a plurality of transformers (each of which is represented by TR), a leakage inductor Lk, and a plurality of fluorescent lamps (Cb 1 +Lp 1 , Cb 2 +Lp 2  . . . Cbn+Lpn), in which Cb 1 , Cb 2  . . . Cbn are a plurality of ballast capacitors, and Lp 1 , Lp 2  . . . Lpn are a plurality of fluorescent lamp tubes. The duty ratio and frequency modulating apparatus  61  includes a current sensor  311 , a comparator  122  and a duty ratio and frequency modulator  611 . The duty ratio and frequency modulating apparatus  61  generates an error signal based on a sensed current generated by the current sensor  311  and a reference voltage via the comparator  122  (see  FIG. 8 , the error signal is a feedback signal), and the error signal is inputted to the feedback terminal of the duty ratio and frequency modulator  611 . The duty ratio and frequency modulator  611  generates a driving signal according to the error signal, and the driving signal is outputted from a gate drive terminal of the duty ratio and frequency modulator  611  and is sent to the respective control terminals of the first to the fourth power switches (Q 1 -Q 4 ) for modulating a duty ratio and a frequency of the DC/AC switching device  11  (respectively the waveforms of duty ratio and frequency are shown as two waveform diagrams at the connecting node of C B  and the transformer TR in  FIG. 8 ) so as to regulate the AC output voltage (not shown) across the two connecting nodes of the plurality of fluorescent lamps electrically connected in parallel (which are equivalent to a load). 
         [0045]    Please refer to  FIG. 9 , which shows a waveform diagram of input voltage (a DC input voltage V IN ) vs. frequency and duty ratio while the duty ratio and the frequency of the provided converter according to the first/the second preferred embodiments of the present invention are modulated to achieve a relatively broader input voltage range. Firstly, if the frequency is modulated and the duty ratio is 90%, the DC input voltage V IN  is modulated within the range of 300 V to 400 V while the corresponding frequency is modulated within the range of 55 K to 65 K. Secondly, when the DC input voltage V IN  reaches 400 V and the corresponding frequency reaches 65 K, the frequency is fixed at 65 K, and the modulation of duty ratio begins. When the duty ratio is modulated within a range, which decreases from 90% to 67.5%, the corresponding DC input voltage V IN  is modulated within the range of 400 V to 533 V. That is to say, the DC input voltage V IN  has a relatively broader input range. 
         [0046]    Please refer to  FIG. 10 , which shows a waveform diagram of input voltage (DC input voltage V IN ) vs. frequency and duty ratio while the duty ratio and the frequency of the provided converter according to the first/the second preferred embodiments of the present invention are modulated to achieve relatively lower changing amounts of duty ratio and frequency. Firstly, if the duty ratio is modulated and the frequency is fixed at 65 K, the DC input voltage V IN  is modulated within the range of 400 V to 360 V while the corresponding duty ratio is modulated within the range of 81% to 90%. Secondly, when the DC input voltage V IN  reaches 360 V and the duty ratio is fixed at 90%, the modulation of frequency begins. When the frequency is modulated within a range, which decreases from 65 K to 60 K, the corresponding DC input voltage V IN  is modulated within the range of 360 V to 300 V. Through the two stages of frequency modulation and duty ratio modulation, the DC input voltage V IN  of the converter is modulated within the range of 400 V to 300 V, the duty ratio is modulated within the range of 81% to 90%, and the frequency is modulated within the range of 65 K to 60 K. As compared with  FIGS. 5 and 6  of the prior art, when the DC input voltage V IN  of the converter is modulated within the range of 400 V to 300 V, the frequency is modulated within the range of 55 K to 65 K according to  FIG. 5 , and the duty ratio is modulated within the range of 67.5% to 90% according to  FIG. 6 . Thus, the relative results generating via modulating the duty ratio and the frequency of the first/second preferred embodiments of the present invention do achieve relatively lower changing amounts of duty ratio and frequency. 
         [0047]    Please refer to  FIG. 11(   a ), it shows a waveform diagram of feedback voltage vs. frequency/duty ratio, which indicates a decrease of the feedback voltage while changing the frequency within a first phase range when the duty ratio and frequency modulating apparatus  51 / 61  of the converter of the first/the second preferred embodiments of the present invention is working under a first operational mode, and a decrease of the feedback voltage while changing the duty ratio within a second phase range when the modulating apparatus is working under a second operational mode respectively. In which, the feedback voltage is a voltage value of the error signal (the feedback signal) receiving by the feedback terminal of the duty ratio and frequency modulating apparatus  51 / 61 , and the feedback voltage is decreased gradually via changing the frequency during the first phase range and via changing the duty ratio during the second phase range. 
         [0048]    Please refer to  FIG. 11(   b ), it shows a waveform diagram of feedback voltage vs. frequency/duty ratio, which indicates an increase of the feedback voltage while changing the frequency within a first phase range when the duty ratio and frequency modulating apparatus  51 / 61  of the converter of the first/the second preferred embodiments of the present invention is working under a first operational mode, and an increase of the feedback voltage while changing the duty ratio within a second phase range when the modulating apparatus is working under a second operational mode respectively. In which, the feedback voltage is a voltage value of the error signal (the feedback signal) receiving by the feedback terminal of the duty ratio and frequency modulating apparatus  51 / 61 , and the feedback voltage is increased gradually via changing the frequency during the first phase range and via changing the duty ratio during the second phase range. One with an ordinary skill in the field would know that the first phase range and the second phase range could be either overlapped or not overlapped. 
         [0049]    According to the aforementioned descriptions, an isolated DC/DC converter having a relatively better effectiveness is provided to regulate a DC output voltage via adjusting a duty ratio and a frequency of the converter so as to achieve the advantages of having a relatively broader input voltage range and decreasing variation amounts of the duty ratio and the frequency. Besides, an isolated DC/AC converter having a relatively better effectiveness is also provided to regulate an AC output voltage via adjusting a duty ratio and a frequency of the converter so as to achieve the advantages of having a relatively broader input voltage range and decreasing variation amounts of the duty ratio and the frequency. 
         [0050]    While the invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention need not be limited to the disclosed embodiment. 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. Therefore, the above description and illustration should not be taken as limiting the scope of the present invention which is defined by the appended claims.