Abstract:
A parameter setting and circuit protecting method applied in a power converter are disclosed. An input voltage of the power converter is detected to generate a first detecting signal related to the input voltage. The first detecting signal will be thence compared with a threshold so as to generate a protecting signal for protecting the power converter. When a parameter setting signal is triggered, a current is provided so as to make the first detecting signal to generate a variation, thereby setting a parameter in accordance with the variation.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is related generally to an input voltage detection circuit applied in a power converter and, more particularly, to an input voltage detection circuit with a parameter setting function and a parameter setting and circuit protecting method. 
       BACKGROUND OF THE INVENTION 
       [0002]    In an AC power system, the many protection functions need the information of the input voltage, such as the brown-in/out protection function.  FIG. 1  shows an AC power converter with a brown-in/out protection function. Wherein, a control IC  10  controls a switching of a power switch  12  that is serially coupled to a primary coil Lp of a transformer T 1  so as to generate an output voltage Vo. In order to achieve the brown-in/out protection function, the control IC  10  needs a pin HV to acquire the information of an input voltage VAC. Generally, the AC power converter works normally when the input voltage VAC is over 90V. When the input voltage VAC is below 90V, the performance of the AC power converter will be unsatisfactory. In addition, when the input voltage VAC is below 90V for a long time, the employed power device may be burned down if the quality of the power device is poorer. A power device of good quality might solve aforementioned problem; however, such power device of good quality results in a higher bill of materials cost. The brown-in/out protection can not only control the performance issue caused by the low input voltage VAC, but also is conducive to employ the cheaper power device. Thus, the brown-in/out protection is necessary in the AC power converter. 
         [0003]    In some applications, the AC power converter also needs a parameter setting function, such as a burst mode level setting or a frequency reduction point setting.  FIG. 2  shows an AC power converter with the burst mode level setting function and the frequency reduction point setting function. In which, a control IC  14  controls the switching of the power switch  12  that is serially coupled to the primary coil Lp of the transformer T 1  so as to generate the output voltage Vo. In this kind of AC power converter, the level of an entry point of the burst mode is set by adjusting a resistor Rss that is coupled to a pin BURST. Moreover, the frequency reduction point is set by adjusting a resistor Rcs_rc that is coupled to a pin CS. Namely, the burst mode level setting function and the frequency reduction point setting function need a pin respectively to achieve the parameter setting. 
         [0004]    As shown by  FIGS. 1 and 2 , the protecting function and the parameter setting function of the AC power converter need a pin respectively. However, in the control IC of a low pin-count, for example the control IC with  6  pins, insufficient pins serve the protecting function and the parameter setting at the same time. Although the control IC with more pins can be utilized, the cost of such control IC is rather high. Herein, in order to reduce the using amount of the pins, some methods are proposed to achieve multiple functions with a single pin. For example, a U.S. patent publication no. 2013/0083562 discloses a method utilizing a single pin to achieve the brown-in/out protection function and the overheat protection function. 
         [0005]    Therefore, it is desired a circuit and a method utilizing a single pin to achieve the protecting function and the parameter setting function. 
       SUMMARY OF THE INVENTION 
       [0006]    An object of the present invention is to provide an input voltage detection circuit with a parameter setting function applied in a power converter and a parameter setting and circuit protecting method thereof. 
         [0007]    Another object of the present invention is to provide a circuit and a method utilizing a single pin in the power converter to protect circuits and set parameters. 
         [0008]    According to the present invention, an input voltage detection circuit with a parameter setting function applied in a power converter comprises a first detecting circuit, a protecting circuit, a current source, and a second detecting circuit. The first detecting circuit detects an input voltage of the power converter to generate a first detecting signal related to the input voltage. The protecting circuit generates a protecting signal according to the first detecting signal so as to protect the power converter. In time of setting the parameter, the current source provides a current to make the first detecting signal to generate a variation. The second detecting circuit acquires the variation in order to set the parameter. 
         [0009]    According to the present invention, a parameter setting and circuit protecting method of the power converter comprises detecting an input voltage of the power converter to generate the first detecting signal related to the input voltage. Thence, a protecting signal is generated according to the first detecting signal so as to protect the power converter. In time of setting the parameter, the method of the present invention provides a current to make the first detecting signal to generate a variation, and detects the variation to set the parameter. 
         [0010]    Since the present invention utilizes the first detecting signal to protect circuits and set parameters, it only needs one single pin to receive the first detecting signal so as to achieve circuit protect function and parameter setting function. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    These and other objectives, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments according to the present invention taken in conjunction with the accompanying drawings, in which: 
           [0012]      FIG. 1  is a conventional AC power converter with a brown-in/out protection function; 
           [0013]      FIG. 2  is a conventional AC power converter with a burst mode level setting function and a frequency reduction point setting function; 
           [0014]      FIG. 3  is an AC power converter employing the present invention; 
           [0015]      FIG. 4  is an embodiment of the present invention; and 
           [0016]      FIG. 5  shows a waveform drawing for illustrate the operation of the circuit in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]      FIG. 3  shows an AC power converter employing the present invention. In which, a control IC  20  controls the switching of a power switch  12  that is serially coupled to a primary coil Lp of a transformer T 1  so as to generate an output voltage Vo. This AC power converter utilizes a single pin BNO to achieve a circuit protecting function and a parameter setting function.  FIG. 4  shows an embodiment of the present invention that comprises a first detecting circuit  22 , a parameter setting circuit  25 , and a protecting circuit  38 . The parameter setting circuit  25  includes a current source  26 , a switch  28 , a second detecting circuit  30 , and a counter  36 . The first detecting circuit  22  and the protecting circuit  38  are utilized to provide a brown-in/out protection function. The first detecting circuit  22 , the current source  26 , the switch  28 , the second circuit  30  and the counter  36  are utilized to achieve the parameter setting function.  FIG. 5  shows a waveform drawing for illustrate the operation of the circuit in  FIG. 4 , in which comprises a waveform  50  of a threshold Vbn, a waveform  52  of a first detecting signal Vd 1 , a waveform  54  of an enabling signal PWM_EN, and a waveform  56  of a variation ΔV of the first detecting signal Vd 1 . 
         [0018]    Referring to  FIGS. 4 and 5 , the first detecting circuit  22  detects an input voltage VAC to generate the first detecting signal Vd 1  related to the input voltage VAC. The first detecting circuit  22  includes a rectifying circuit  24 , a first resistor R 1  and a second resistor R 2 . The rectifying circuit  24  rectifies the input voltage VAC to generate a rectified voltage HV. The first resistor R 1  and the second resistor R 2  are serially coupled between the rectifying circuit  24  and a ground for dividing the rectified voltage HV so as to generate the first detecting signal Vd 1 , as shown by the waveform  52  in  FIG. 5 , at a node N 1  between the first resistor R 1  and the second resistor R 2 . The protecting circuit  38  couples to the first detecting circuit  22  via the pin BNO and generates a protecting signal BNIO according to the first detecting signal Vd 1  for protecting the AC power converter. The protecting circuit  38  includes a comparator  40  and a counter  42 . The comparator  40  compares the first detecting signal Vd 1  with a threshold Vbn. When the first detecting signal Vd 1  is larger than the threshold Vbn, the comparator  40  ends a comparing signal Sc. Herein, the input voltage VAC is sufficient to support a normal work of the AC power converter. Accordingly, the enabling signal PWM_EN is triggered so as to start up the AC power converter as shown by the waveforms  50 ,  52 ,  54  and time t 2 . When the first detecting signal Vd 1  is lower than the threshold Vbn, the comparator  40  generates the comparing signal Sc, and the counter  42  counts a duration of the comparing signal Sc. While the duration of the comparing signal Sc reaches a preset time TB as shown by t 3  to t 4  in  FIG. 5 , it means that the input voltage VAC is too low to support the normal work of the AC power converter. Accordingly, the counter  42  generates the protecting signal BNIO so as to end the enabling signal PWM_EN, thereby turning off the AC power converter and achieving the brown-in/out protection. The present invention is not limited in the brown-in/out protection in this preferred embodiment. Other circuit protection functions with an input voltage information are also included in the inventive spirit of the present invention. 
         [0019]    In time of setting parameters, a parameter setting signal TA is triggered to turn on the switch  28 . Accordingly, the current I 1  of the current source  26  flows through the second resistor R 2  via the switch  28  and the pin BNO. At the same time, the first detecting signal Vd 1  generates a variation ΔV=I 1 ×R 2 . The second detecting circuit  30  includes a sample and hold circuit  32  and a subtractor  34 . While the parameter setting signal TA is triggered, the sample and hold circuit  32  samples and holds the first detecting signal Vd 1  so as to generate a second detecting signal Vd 2  as shown by time t 1  and the waveform  52  in  FIG. 5 . The subtractor  34  subtracts the second detecting signal Vd 2  from the first detecting signal Vd 1  so as to acquire the variation ΔV. The counter  36  counts the variation ΔV and sets the parameter in accordance with the variation ΔV, thereby achieving the parameter setting function. Take the frequency reduction point setting function as an example. When the variation ΔV is 0.1V, the frequency reduction point is set 2.35V. When the variation ΔV is 0.2V, the frequency reduction point is set 2.25V. In the present invention, a pulse width of the parameter setting signal TA is quite short (about 100 μs). Thus, the operation of the protecting circuit  38  will not be influenced. In the circuit of  FIG. 4 , the first resistor R 1  and the second resistor R 2  determine a voltage dividing ratio. Thus, a resistance of the second resistor R 2  is not easy to be varied for setting parameters. Accordingly, a third resistor R 3  is set between the node N 1  and an output terminal (the pin BNO) of the first detecting circuit  22  for determining the variation ΔV=I 1 ×(R 2 +R 3 ). Wherein, the third resistor can be a variable resistor. Hereby, a resistance of the third resistor R 3  can be adjusted from the external part of the control IC  20 , and the variation ΔV can be controlled. Therefore, the parameter for setting can be controlled. It should be noted that controlling the current I 1  of the current source  26  can also readily adjust the variation ΔV. 
         [0020]    While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.