Abstract:
A pulse width modulation (PWM) controller is provided. The PWM controller transfers a conventional enable mechanism integrated into a versatile pin (PH) and integrates it into a feedback pin (FB) of the PWM controller, so as to promote the noise reduction capability of the PWM controller and avoid false operation. Furthermore, the parasitic capacitance of an enable transistor employed in the enable mechanism of the PWM controller does not degrade the accuracy of the over-current protection performed by the PWM controller on an electronic device. Thus, the PWM controller can effectively perform the over-current protection mechanism on the electronic device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a pulse width modulation (PWM) controller. More particularly, the present invention relates to a PWM controller with a plurality of versatile pins. 
         [0003]    2. Description of Related Art 
         [0004]    Generally speaking, a PWM controller is applied in a voltage converter so as to enable voltage converter to provide a stable output voltage to an electronic device, such as a power supply required by a CPU on a mainboard.  FIG. 1  is a circuit diagram of a conventional voltage converter  100 . With regard to the architecture of a PWM controller  101  of the voltage converter  100  in  FIG. 1 , if a user tends to activate the voltage converter  100  to provide a stable output voltage Vout to the electronic device (not shown), the PWM controller  101  will not be enabled until an enable signal Ve is provided to an enable pin EN individually defined by the PWM controller  101 . 
         [0005]      FIG. 2  is a circuit diagram of a conventional voltage converter  200  integrating the enable pin EN individually defined by the PWM controller  101  in  FIG. 1  into other pins of the PWM controller  101 . The circuit diagram of the voltage converter  200  in  FIG. 2  is a technique disclosed in the ROC Patent Application No. 93120057 and mainly directed to realizing the versatile pin PH of the PWM controller  201 . The pin PH may have an enable mechanism, a mechanism of detecting an input voltage Vin and an internal power supply voltage Vcc 1  of the voltage converter  200 , and a mechanism of over-current protection electronic device, so as to increase the applicability of the pin of the PWM controller and reduce the number of pins for package. 
         [0006]    However, in order to achieve the aforementioned object, the voltage converter  200  in  FIG. 2  causes a problem that as transistors M 2  and M 3  are power transistors and a current lout flowing through the pin PH is large, a large noises is generated and fed back to the pin PH, which possibly causes false operation of the PWM controller  201 . Besides, the parasitic capacitance of the enable transistor Ml also degrades the accuracy of the over-current protection performed by the PWM controller  201  to the electronic device, thereby possibly damaging the electronic device. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, the present invention is directed to providing a PWM controller for a voltage converter, wherein the PWM controller is used to provide a stable output voltage to an electronic device. The PWM controller comprises a first output pin, a first versatile pin, a feedback unit and an enable unit. The first output pin is used to output a first output signal. The feedback unit is coupled to the first versatile pin for receiving a feedback signal to control a pulse width of the first output signal output from the first output pin, wherein the feedback signal is generated according to the output voltage. The enable unit is coupled to the first versatile pin for detecting the voltage of the first versatile pin, so as to determine whether the PWM controller is enabled or not. 
         [0008]    The PWM controller provided by the present invention transfers an enable mechanism conventionally integrated into a versatile pin (PH) and integrates it into a feedback pin (FB) of the PWM controller, so the feedback pin (FB) of the PWM controller of the present invention does not function on the operation loop of a power transistor, such that noise reduction capability is promoted and false operation of the PWM controller is avoided. Furthermore, as the enable transistor employed by the enable mechanism of the PWM controller of the present invention is not on the loop of the over-current protection electronic device, the parasitic capacitance of the enable transistor does not degrade the accuracy of the over-current protection performed by the PWM controller on the electronic device. 
         [0009]    In order to the make aforementioned and other objects, features and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below. 
         [0010]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
           [0012]      FIG. 1  is a circuit diagram of a conventional voltage converter. 
           [0013]      FIG. 2  is a circuit diagram of a conventional voltage converter integrating the enable pin individually defined by the PWM controller in  FIG. 1  into other pins. 
           [0014]      FIG. 3  is a circuit diagram of a voltage converter according to a preferred embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0015]      FIG. 3  is a circuit diagram of a voltage converter  300  according to a preferred embodiment of the present invention. The voltage converter  300  in this embodiment has the function of providing a stable output voltage Vout to an electronic device (not shown), such as (but not limited to) a CPU on a mainboard. A PWM controller  301  in this embodiment is not limited to be applied in the field of controlling power supply. That is to say, the electronic devices as long as using a PWM signal all fall in the protection scope claimed in the present invention. 
         [0016]    Referring to  FIGS. 2 and 3 , the main difference between the architecture of the PWM controller  301  in this embodiment and the architecture of the PWM controller  201  as shown in  FIG. 2  of the prior art lies in that the PWM controller  201  as shown in  FIG. 2  of the prior art integrates the enable mechanism, the mechanism of detecting an input voltage Vin and an internal power supply voltage Vcc 1  of the voltage converter  200 , and the mechanism of over-current protection electronic device into a pin PH, while the PWM controller  301  in this embodiment maintains the mechanism of detecting an input voltage Vin and an internal power supply voltage Vcc 1  of the voltage converter  300  and the mechanism of over-current protection electronic device and integrates them into the pin PH, and transfers and integrates the enable mechanism into a feedback pin (FB). 
         [0017]    Firstly, the circuit operation flows of two mechanisms related to the first versatile pin FB are explained. In the PWM controller  301  in this embodiment, two units are coupled to the versatile pin FB, in which one is an enable unit, and the other is a feedback unit. The enable unit is used to detect the voltage state of the versatile pin FB, so as to enable the PWM controller. In this embodiment, the enable unit is composed of an enable switch M 1  (such as an NMOS transistor) and an enable comparator EC, wherein the enable switch M 1  is controlled by an enable signal Ve, and when the enable signal Ve is at a high potential, the enable switch M 1  is turned on and the voltage level of the versatile pin FB is raised to be the voltage level of the internal power supply voltage Vcc 1  of the PWM controller  301 . 
         [0018]    Then, as the voltage level of the versatile pin FB is equal to the voltage level of the power supply voltage Vcc 1  at this time, the voltage level of a positive input end (+) of the enable comparator EC is also equal to the voltage level of the power supply voltage Vcc 1 , and is then compared with an enable reference voltage Von predetermined at a negative input end (−), so as to determine whether the PWM controller  301  is enabled or not. That is to say, when an output end of the enable comparator EC is activated, namely, an output signal SHDN is output; it indicates that the PWM controller  301  is in an enable state. Otherwise, when the output end of the enable comparator EC is not activated, namely, the output signal SHDN is not output, it indicates that the PWM controller  301  is in a disabled state. 
         [0019]    The feedback unit receives a feedback signal, and controls the pulse widths of a first output signal Vc 1  and a second output signal Vc 2  respectively output from a first output pin UGATE and a second output pin LGATE of the PWM controller  301  according to the feedback signal. The feedback signal is generated according to the output voltage Vout provided by the voltage converter  300  to the electronic device, and the phase difference between the first output signal and the second output signal respectively output from the first output pin UGATE and the second output pin LGATE of the PWM controller  301  is  180  degrees, namely, the first output signal and the second output signal are opposite in phase. It is well known that the feedback unit is mainly used to provide a stable operation of the overall PWM controller  301 . 
         [0020]    In this embodiment, the feedback unit is composed of an error amplifier EA, a feedback comparator CMP and a logic splitter LS. A negative input end (−) of the error amplifier EA, after receiving the feedback signal, compares the feedback signal with an error reference voltage Verr predetermined at a positive input end (+), and compensates and outputs an error signal ES to a positive input end (+) of the feedback comparator CMP. 
         [0021]    Next, the feedback comparator CMP compares the error signal ES received at the positive input end (+) with a triangular wave signal received at a negative input end (−), and then modulates it into a PWM signal to be output to the logic splitter LS. The logic splitter LS receives the PWM signal output from the feedback comparator CMP and converts it into the first output signal Vc 1  and the second output signal Vc 2  which are opposite in phase and output to corresponding gate drivers A 4  and A 3 , respectively, so as to be respectively output from the first output pin UGATE and the second output pin LGATE of the PWM controller  301  and switch the power transistors M 2  and M 3 . 
         [0022]    Additionally, the circuit operation flows of two mechanisms related to the second versatile pin PH are explained. In the PWM controller  301  in this embodiment, two units are coupled to the versatile pin PH, in which one is a power supply sensing unit, and the other is an over-current protection unit. The power supply sensing unit is used to sense the voltage of the versatile pin PH and the power supply voltage Vcc 1  inside the PWM controller  301 , so as to determine whether the input voltage Vin of the voltage converter  300  and the power supply voltage Vcc 1  inside the PWM controller  301  are activated or not. 
         [0023]    In this embodiment, the power supply sensing unit is composed of a power supply comparator A 2  and a dual-power supply sensor DPD, wherein the dual-power supply sensor DPD is used to sense the power supply voltage Vcc 1  inside the PWM controller  301  to determine whether the PWM controller  301  is activated or not and also to determine whether the input voltage Vin of the voltage converter  300  is activated or not according to a power supply comparison signal PORE output from the power supply comparator A 2 . When the dual-power supply sensor DPD in this embodiment senses the power supply voltage Vcc 1  inside the PWM controller  301 , the dual-power supply sensor DPD also outputs a confirmation signal pre_chk to the gate driver A 4 , so as to turn on the power transistor M 2 . At this time, the power supply comparator A 2  receives the voltage level of the versatile pin PH with its positive input end (+), and then compares it with a power supply reference voltage Vinpor predetermined at the negative input end (−) of the power supply comparator A 2 , so as to determine whether to generate a power supply comparison signal PORE to the dual-power supply sensor DPD or not. 
         [0024]    As described above, when the voltage level of the versatile pin PH is higher than or equal to the power supply reference voltage Vinpor, the output end of the power supply comparator A 2  is activated, namely, the power supply comparison signal PORE is output, indicating that the input voltage Vin of the voltage converter  300  is activated. Otherwise, it indicates that the input voltage Vin of the voltage converter  300  is not activated. 
         [0025]    Then, when the dual-power supply sensor DPD senses that the power supply voltage Vcc 1  inside the PWM controller  301  is also activated, the dual-power supply sensor DPD outputs a signal POR, such that the feedback unit of the PWM controller  301  generates the first output signal Vc 1  and the second output signal Vc 2 , and the power transistors M 2  and M 3  are switched through the gate drivers A 4  and A 3 , respectively. As a result, an output current lout is generated at the versatile pin PH, so as to provide an output voltage Vout (i.e., the result of multiplying the output current Iout by a load RL of the voltage converter  300 ) to the electronic device. 
         [0026]    In this embodiment, the over-current protection unit is used to detect the voltage level of the versatile pin PH, so as to prevent the output current Jout output from the versatile pin PH being too large and damaging the electronic device. In this embodiment, the over-current protection unit is composed of a current source I and an over-current comparator A 5 , wherein the current source I provides a constant current If to the versatile pin PH and a negative input end (−) of the over-current comparator A 5 , and a positive input end (+) of the over-current comparator A 5  receives an over-current reference voltage Voc. Therefore, when the voltage level (i.e., the result of multiplying the current If by the resistance Rs) of the versatile pin PH is lower than the over-current reference voltage Voc, it indicates that the output current lout output from the versatile pin PH is too large, and the output end of the over-current comparator A 5  outputs an over-current comparison signal OC to make the feedback unit of the PWM controller  301  stop switching the power transistors M 2  and M 3 , thereby stopping the operation of switching the power transistors M 2  and M 3  to protect the electronic device. 
         [0027]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.