Abstract:
In a feedback circuit of a power supply, an electrical level of an output voltage is stabilized corresponding to changes of an electrical level of a pulse width modulation signal, and effects, which are caused by spikes, on passive elements are decreased to a lowest degree. The electrical level of the output voltage is stabilized by storing a voltage corresponding to a low-to-high electrical level of the PWM signal with a capacitor, by discharging the stored voltage with a high-to-low electrical level of said PWM signal, and by regulating a discharging path of the stored voltage with a diode, which is not conducted. The abovementioned disposition may be utilized on various power-consuming devices, a duty cycle of each of which is controlled with a PWM signal, for stabilizing output voltages of said power-consuming devices, and for reducing effects, which are caused by spikes, on passive elements inside said power-consuming devices.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a power supply, and more particularly, to a power supply for relieving spikes. 
         [0003]    2. Description of the Prior Art 
         [0004]    Conventional passive elements have their respective operating voltage ranges or operating current ranges. When the conventional passive elements are not operated under their operating voltage ranges or their operating current ranges, the passive elements do not operate normally or exceed their loadings so that permanent damage is caused. For neutralizing these defects resulting from applying inappropriate operating voltages or inappropriate operating currents, certain controlling mechanisms are used on various circuits for limiting their operating voltages or operating currents within appropriate ranges. Various techniques are also utilized for protecting passive elements inside a same circuit. 
         [0005]    Please refer to  FIG. 1 , which is a diagram of a conventional power supply  100 , where a feedback controlling mechanism is utilized on the power supply  100  with the aid of constant voltages and constant currents. The power supply  100  includes a transformer  102 , a diode  104 , a first capacitor  106 , an inductor  108 , a second capacitor  110 , a first resistor  112 , a switch  114 , a plurality of light emitting diodes  116  connected in series, a second resistor  118 , a third resistor  120 , a feedback circuit  122 , and a pulse width modulation (PWM) integrated circuit  124 . An input voltage source V in  is coupled to a first input terminal of the transformer  102 . The diode  104  has a first terminal coupled to a first output terminal of the transformer  102 . The first capacitor  106  has a first terminal coupled to a second terminal of the diode  104 , and a second terminal coupled to both ground and a second output terminal of the transformer  102 . The inductor  108  has a first terminal coupled to a second terminal of the diode  104 . The second capacitor  110  has a first terminal coupled to a second terminal of the inductor  108 , and a second terminal coupled to the second terminal of the first capacitor  106 . The plurality of light emitting diodes  116  has a first terminal coupled to a second terminal of the inductor  108 . The first resistor  112  has a first terminal coupled to the second terminal of the second capacitor  110 . The switch  114  may be an N-type metal oxide semiconductor transistor or a P-type metal oxide semiconductor transistor. The switch  114  has a first terminal coupled to a second terminal of the plurality of light emitting diodes  116 , a base coupled to a pulse width modulation signal source PWM 2 , and a second terminal coupled to a second terminal of the first resistor  112 . The second resistor  118  has a first terminal coupled to the second terminal of the inductor  108 . The third resistor  120  has a first terminal coupled to a second terminal of the second resistor  118 , and a second terminal coupled to ground. The feedback circuit  122  includes a first operational amplifier  126  and a second operational amplifier  128 . The first operational amplifier  126  has a positive input terminal coupled to a reference voltage source V ref , and a negative input terminal coupled to the second terminal of the switch  114 . The first operational amplifier  126  is utilized for receiving a voltage difference across the first resistor  112 , where the voltage difference is generated from a constant current outputted from the second terminal of the switch  114  and passing through the first resistor  112 . A constant current controlling mechanism of the power supply  100  is accomplished by comparing the reference voltage source V ref  with the voltage difference across the first resistor  112  with the aid of the first operational amplifier  126 , where the constant current is generated from a feedback voltage, which is generated by the voltage at the first output terminal of the transformer  102  and the plurality of light emitting diodes  116 . The second operational amplifier  128  has a positive input terminal coupled to the reference voltage source V ref , and a negative input terminal coupled to the first terminal of the third resistor  120 . The second operational amplifier  128  is utilized for receiving a divided voltage at the intersection of the second resistor  118  and the third resistor  120 , where variable resistance is inducted from the second resistor  118  and the third resistor  120 . The divided voltage is generated as part of the voltage at the first output terminal of the transistor  102 , and is outputted into the feedback circuit  122 . When the voltage at the first output terminal of the transformer  102  is constant, the divided voltage must be a constant voltage also. Therefore, the constant voltage controlling mechanism of the power supply  100  is implemented by comparing the reference voltage source V ref  with the constant divided voltage with the aid of the second operational amplifier  128 . The PWM integrated circuit  124  has an input terminal coupled to an output terminal of the feedback circuit  122  so as to generate a pulse width modulation signal PWM 1  according to a control signal, which is generated by the feedback circuit  122  according to the constant voltage controlling mechanism or the constant current controlling mechanism. The PWM integrated circuit  124  has an output terminal coupled to a second input terminal of the transformer  102  so as to control both a duty cycle and an output voltage of the transformer  102  according to the generated pulse width modulation signal PWM 1 . Primary characteristics of the power supply  100  shown in  FIG. 1  lie in the constant voltage controlling mechanism and the constant current controlling mechanism, each of which takes AC or DC input voltages and cooperates with two operational amplifiers respectively. 
         [0006]    When the pulse width modulation signal PWM 2  is high, the switch  114  is switched on so that the plurality of light emitting diodes  116  connected in series is conducted. At this time, with the aid of the constant voltage and current controlling mechanisms, the duty cycle of the pulse width modulation signal PWM 1  is lengthened so that the duty cycle of the output signal of the transformer  102  is lengthened as well, and the loading of the plurality of light emitting diodes  116  is thus increased. Therefore, when the pulse width modulation signal PWM 2  is low then, the switch  114  is switched off so that the plurality of the light emitting diodes  116  is not conducted. At this time, according to the constant voltage and current controlling mechanisms, the duty cycle of the pulse width modulation signal PWM 1  is shortened so that the duty cycle of the output signal of the transformer  102  is shortened as well, and the loading of the plurality of light emitting diodes  160  is decreased. With alternative high and low of the pulse width modulation signal PWM 2 , average loading of the plurality of light emitting diodes  116  is decreased to a certain degree. 
         [0007]    However, under such controlling mechanisms, instant and severe variations in voltage or current may still damage the plurality of light emitting diodes  116 . Please refer to  FIG. 2 , which is a schematic diagram of the operating voltage, i.e., the voltage difference, across the plurality of light emitting diodes  116  versus the voltage level of the pulse width modulation signal PWM 2  while the plurality of light-emitting diodes  116  is under external luminance-modulation. The term “external luminance-modulation” indicates the function of modulating luminance of light-emitting electronic products, such as televisions, with the aid of external devices, such as remote controllers. For example, the operating voltage of a single light emitting diode  116  is assumed to be 3.5 volts, and the number of the plurality of light emitting diodes  116  is assumed to be 10. Therefore, the operating voltage of the plurality of light emitting diodes  116 , which varies with the voltage level of the pulse width modulation signal PWM 2 , ranges between 30 and 40 volts. However, when the pulse width modulation signal PWM 2  is switched from low to high, i.e., from off to on, violent voltage variation is generated on the operating voltage of the plurality of light emitting diodes  116 , where the voltage variation is illustrated in the form of area surrounded with a dotted line in  FIG. 2 . The voltage variation inducts additional burst current into the plurality of light emitting diodes  116  so that the lifespan of the plurality of light emitting diodes  116  is shortened. 
         [0008]    Please refer to  FIG. 3 , which is a schematic diagram of the operating voltage of the plurality of light emitting diodes  116  versus the operating current of the plurality of light emitting diodes  116  while the plurality of light-emitting diodes  116  is under external luminance-modulation. The curve LED indicates the characteristic curve of a single light emitting diode  116 , whereas both the other curves LED 1  and LED 2  define a supposed upper bound and a supposed lower bound of the characteristic curve of the plurality of light emitting diodes  116 . Since different light emitting diodes  116  have slightly different characteristics because of fabrication procedure, the characteristic curve of the plurality of light emitting diodes  116  has difference with the characteristic curve of a single light emitting diode  116  and lies between the characteristic curves LED 1  and LED 2 . In other words, when the plurality of light emitting diodes  116  is biased according to the characteristic curve of a single light emitting diode  116  without taking differences in fabrication procedure into consideration, unexpected burst voltages and burst currents are generated so that the plurality of light emitting diodes  116  suffer damage and shortened lifespan of different degrees. 
       SUMMARY OF THE INVENTION 
       [0009]    The claimed invention discloses a power supply for relieving spikes. The power supply comprises a power supplying circuit, a power controlling circuit, a first switch, a pulse width modulation signal source, and a feedback circuit. The power controlling circuit has an output terminal coupled to an input terminal of the power supplying circuit. The pulse width modulation signal source is coupled to a first terminal of the first switch. The feedback circuit comprises a first operational amplifier, a first resistor, a first diode, a first capacitor, a second resistor, a second diode, a third resistor, a second operational amplifier, and a fourth resistor. The first operational amplifier has a first input terminal coupled to a first reference voltage source, and a second input terminal coupled to a second terminal of the first switch. The first resistor has a first terminal coupled to an output terminal of the first operational amplifier. The first diode has a first terminal coupled to a second terminal of the first resistor. The first capacitor has a first terminal coupled to a second terminal of the first diode, and a second terminal coupled to ground. The second resistor has a first terminal coupled to the second terminal of the first diode. The second diode has a first terminal coupled to a second terminal of the second resistor. The third resistor has a first terminal coupled to a second terminal of the second diode, and a second terminal coupled to the second terminal of the first capacitor. The second operational amplifier has a first input terminal coupled to a second reference voltage source, a second input terminal coupled to the second terminal of the second diode, and an output terminal coupled to an input terminal of the power controlling circuit. The fourth resistor has a first terminal coupled to the output terminal of the second operational amplifier, and a second terminal coupled to the first terminal of the third resistor. 
         [0010]    Other objectives, features and advantages of the present invention will be further understood from the further technology features disclosed by the present invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention. 
         [0011]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a diagram of a conventional power supply, where a feedback controlling mechanism is utilized on the conventional power supply with the aid of constant voltages and constant currents. 
           [0013]      FIG. 2  is a schematic diagram of the operating voltage across the plurality of light emitting diodes versus the voltage level of the pulse width modulation signal PWM 2  shown in  FIG. 1 . 
           [0014]      FIG. 3  is a schematic diagram of the operating voltage of the plurality of light emitting diodes versus the operating current of the plurality of light emitting diodes shown in  FIG. 1  while the plurality of light-emitting diodes is under external luminance-modulation. 
           [0015]      FIG. 4  is a diagram of a power supply according to a preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” and “coupled,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. 
         [0017]    A power supply for relieving spikes is disclosed in the present invention. Other objectives and advantages are fully understood from the following disclosures. 
         [0018]    Please refer to  FIG. 4 , which is a diagram of a power supply  400  according to a preferred embodiment of the present invention. The power supply  400  includes a power supplying circuit  404 , a power controlling circuit  406 , a first switch  408 , a pulse width modulation (PWM) signal source  410 , and a feedback circuit  412 . The power controlling circuit  406  has an output terminal coupled to an input terminal of the power supplying circuit  404  for controlling both the voltage level of the output voltage and the duty cycle of the power supplying circuit  404 . The PWM signal source  410  is coupled to a first terminal of the first switch  408  so as to control both the state and the duty cycle of the first switch  408  with pulse width modulation signal output by the PWM signal source  410 . In a preferred embodiment of the present invention, the first switch  408  is implemented with a transistor, such as an N-type metal oxide semiconductor transistor or a P-type metal oxide semiconductor transistor. Besides, the power supplying circuit  404  has a first output terminal coupled to an input terminal of a light module  402  for supplying power for the light module  402 . Note that the power supply  400  may also be applied on various types of modules other than the light module  402  so that the light module  402  is not limitations to applications of the present invention. 
         [0019]    The feedback circuit  412  includes a first operational amplifier  414 , a first resistor  416 , a first diode  418 , a first capacitor  420 , a second resistor  422 , a second diode  424 , a third resistor  426 , a second operational amplifier  428 , and a fourth resistor  430 . In another embodiment of the present invention, the feedback circuit  412  further includes a fifth resistor  432  and a second capacitor  434 , both of which constitute a low pass filter for filtering off noises from entering the first operational amplifier  414 . The following descriptions are based on the existences of both the fifth resistor  432  and the second capacitor  434 , though both the fifth resistor  432  and the second capacitor  434  are optional in embodiments of the present invention. The fifth resistor  432  has a first terminal coupled to a second terminal or a source of the first switch  408 . The first operational amplifier  414  has a first negative input terminal coupled to a first reference voltage source V ref1 , and a second positive input terminal coupled to the second terminal or the source of the first switch  408  via the fifth resistor  432 . The first resistor  416  has a first terminal coupled to an output terminal of the first operational amplifier  414 . The first diode  418  has a first terminal coupled to a second terminal of the first resistor  416 . The first capacitor  420  has a first terminal coupled to a second terminal of the first diode  418 , and a second terminal coupled to ground. The second capacitor  434  has a first terminal coupled to a second terminal of the fifth resistor  432 , and a second terminal coupled to the second terminal of the first capacitor  420 . The second resistor  422  has a first terminal coupled to the second terminal of the first diode  418 . The second diode  424  has a first terminal coupled to a second terminal of the second resistor  422 . The third resistor  426  has a first terminal coupled to a second terminal of the second diode  424 , and a second terminal coupled to the second terminal of the first capacitor  420 . The second operational amplifier  428  has a first positive input terminal coupled to a second reference voltage source V ref2 , a second negative input terminal coupled to the second terminal of the second diode  424 , and an output terminal coupled to an input terminal of the power controlling circuit  406 . The fourth resistor  430  has a first terminal coupled to the output terminal of the second operational amplifier  428 , and a second terminal coupled to the first terminal of the third resistor  426 . 
         [0020]    The power supplying circuit  404  includes a voltage source  436 , a third capacitor  438 , a transformer  440 , a third diode  442 , a fourth capacitor  444 , a sixth resistor  446 , a fifth capacitor  448 , an inductor  450 , a sixth capacitor  452 , and a seventh resistor  454 . The voltage source  436  is a DC voltage source or an AC voltage source, especially a domestic AC voltage source. The third capacitor  438  has a first terminal coupled to the voltage source  436 , and a second terminal coupled to ground. The transformer  440  has a first input terminal coupled to the first terminal of the third capacitor  438 , a second input terminal coupled to the output terminal of the power controlling circuit  406 , and a first output terminal coupled to ground. The third diode  442  has a first terminal coupled to a second output terminal of the transformer  440 . The fourth capacitor  444  has a first terminal coupled to the first terminal of the third diode  442 . The sixth resistor  446  has a first terminal coupled to a second terminal of the fourth capacitor  444 , and a second terminal coupled to a second terminal of the third diode  442 . The fifth capacitor  448  has a first terminal coupled to the second terminal of the third diode  442 , and a second terminal coupled to the first output terminal of the transformer  440 . The inductor  450  has a first terminal coupled to the second terminal of the third diode  442 . The sixth capacitor  452  has a first terminal coupled to a second terminal of the inductor  450 , and a second terminal coupled to the first output terminal of the transformer  440 . The seventh resistor  454  has a first terminal coupled to the first output terminal of the transformer  440 , and a second terminal coupled to the second terminal or the source of the first switch  408 . 
         [0021]    The power controlling circuit  406  includes a PWM circuit  456 , a light coupling circuit  458 , a second switch  460 , and an eighth resistor  462 . The light coupling circuit  458  has an input terminal coupled to the output terminal of the second operational amplifier  428  for coupling to the feedback circuit  412 , and an output terminal coupled to an input terminal of the PWM circuit  456 . In a preferred embodiment of the present invention, the second switch  460  is a transistor, such as an N-type metal oxide semiconductor transistor or a P-type metal oxide semiconductor transistor. The second switch  460  has a first terminal or a gate coupled to a first output terminal of the PWM circuit  456 , a second or a source coupled to a second output terminal of the PWM circuit  456 , and a third terminal or a drain coupled to the input terminal of the power supplying circuit  404 . The eighth resistor  462  has a first terminal coupled to the second output terminal of the PWM circuit  456 , and a second terminal coupled to ground. The design purpose of the light coupling circuit  458  is to electrically isolate primary from secondary in the power supply  400 , where the primary in the power supply  400  indicates the part closer to the voltage source  436 , i.e., closer to domestic sockets, and the secondary in the power supply is the part closer to user, i.e., the part around the feedback  412 . Note that in electric safety regulations, the secondary is more strictly regulated than the primary. Implementations of the light coupling circuit  458  is known by those who skilled in the art so as not to be described further. 
         [0022]    In a preferred embodiment of the present invention, the light module  402  includes a plurality of light emitting diodes  464  connected in series, and provides power for the plurality of light emitting diodes  464  with the output voltage at the output terminal of the second operational amplifier  428 . 
         [0023]    Compared with the conventional power supply  100 , the power supply  400  of the present invention has improvements on the feedback  412  for reaching the aim of reducing the influence of burst currents and burst voltages, i.e., relieving spikes, to a smallest degree under the constant current controlling mechanism and the constant voltage controlling mechanism. Note that other implementations of the power supplying circuit  404  and the power controlling circuit  406  are not limitations to the present invention. 
         [0024]    How the feedback circuit  412  works is described as follows. Since the gate of the first switch  408  is coupled to the PWM signal source  410 , both the state and the duty cycle of the first switch  408  is determined according to the voltage level of the PWM signal source  410 . When the power supply  400  is initiated, and when the voltage level of the PWM signal source  410  is low, the first switch  408  is switched off so that the voltage level of the input voltage at the positive input terminal of the first operational amplifier  414  is 0. After comparing the input voltage with the reference voltage V ref1  at the negative input terminal of the first operational amplifier  414 , a negative output voltage is generated at the output terminal of the first operational amplifier  414 . At this time, the first diode  418  having a negative voltage difference is not conducted so that the first capacitor  420  is not charged; no current flows through both the second resistor  422  and the second diode  424 ; there is no voltage difference on the third resistor  426  for performing the constant current controlling mechanism; and thus the light module  402  is not damaged by an overly-high voltage at the output terminal of the second operational amplifier  428 . Note that a voltage V, which is at the intersection of the third resistor  426  and the fourth  430 , may be expressed in terms of an output voltage V out  as follows: 
         [0000]    
       
         
           
             
               
                 
                   V 
                   = 
                   
                     
                       V 
                       out 
                     
                     * 
                     
                       
                         R 
                         2 
                       
                       
                         
                           R 
                           1 
                         
                         + 
                         
                           R 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    , where R 1  indicates the resistance of the fourth resistor  430 , R 2  indicates the resistance of the third resistor  426 . As can be observed in the equation (1), the output voltage V out  at the output terminal of the second operational amplifier  428  is adjusted with the constant voltage controlling mechanism based upon the voltage V and both the resistances R 1  and R 2 . Therefore, the output voltage at the output terminal of the second operational amplifier  428  is stabilized so as to protect the light module  402 . 
         [0025]    When the voltage level at the PWM signal source  410  is switched from low to high, the first switch  408  is switched on, and a voltage difference is generated on the fifth resistor  432  after a current passes therethrough. The voltage difference is then inputted at the positive input terminal of the first operational amplifier  414  so as to be compared with the reference voltage V ref1 . Since the voltage difference is higher than the reference voltage V ref1  at this time, a high output voltage is generated at the output terminal of the first operational amplifier  414 . The first capacitor  420  is charged with the high output voltage through both the first resistor  416  and the first diode  418 , and a discharging current is also generated so as to flow through the second resistor  422  and the second diode  424  and to reach the third resistor  426 . At this time, a voltage difference is also generated on the third resistor  426  and is inputted at the negative input terminal of the second operational amplifier  428 . Then a corresponding output voltage is generated at the output terminal of the second operational amplifier  428  and inputted at the input terminal of the light module  402  as a feedback so as to modulate a receiving voltage of the light module  402  to a predetermined voltage. 
         [0026]    When the voltage level of the PWM signal source  410  is switched from high to low again, the first switch  408  is switched off again, and the voltage difference on the fifth resistor  432  dissipates. As described above, a negative output voltage is outputted by the first operational amplifier  414  again according to a comparison between the positive and the negative input terminals of the first operational amplifier  414 , and is blocked by the first diode  418  having a negative voltage difference so that the first capacitor  420  ceases charging. At this time, since the voltage level at the second terminal of the first diode  418  is higher than the voltage level at the first terminal of the first diode  418 , the first diode  418  is not conducted. Note that the negative output voltage outputted from the first operational amplifier  418  is located at the first terminal of the first diode  418 . Under such a condition, the first capacitor  420  begins discharging to the third resistor  426  along a path through both the second resistor  422  and the second diode  424 . When the voltage level at the PWM signal source  410  is switched from high to low again, the voltage level of the output voltage V out  is maintained instead of being decreased as in  FIG. 2 , because the voltage V at the intersection of the third resistor  426  and the fourth  430 , is also maintained as a result of the first capacitor  420  applied a current to the third resistor  426 . Therefore, the voltage level of the output voltage V out  is kept the same no matter whether the PWM signal source  410  is high or low. According to the above descriptions, there are no burst voltages or burst currents, i.e., spikes, in the power supply of the present invention, and the defects in the conventional power supply are also neutralized. 
         [0027]    A power supply for relieving spikes is disclosed in the present invention for relieving and preventing burst voltages and burst currents in the conventional power supply from damaging passive elements. In the power supply of the present invention, when the pulse width modulation signal is high, sufficient electricity is stored with a capacitor so as to maintain the voltage level of an output voltage by regulating the discharging path of the capacitor when the pulse width modulation signal is switched from high to low. When the power supply for relieving spikes of the present invention is applied on a light supply, burst currents and burst voltages of a corresponding light module are neutralized. The power supply disclosed in the present invention is not merely applied on light modules but also on other power supplying systems requiring feedback circuits for relieving spikes. 
         [0028]    The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Accordingly, the foregoing description should be regarded as illustrative rather than restrictive. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. The embodiments are chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable persons skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Therefore, the term “the invention”, “the present invention” or the like is not necessary limited the claim scope to a specific embodiment, and the reference to particularly preferred exemplary embodiments of the invention does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is limited only by the spirit and scope of the appended claims. The abstract of the disclosure is provided to comply with the rules requiring an abstract, which will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Any advantages and benefits described may not apply to all embodiments of the invention. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention as defined by the following claims. Moreover, no element and component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims. 
         [0029]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.