Abstract:
A control integrated circuit for a power factor correction converter has a pin for detecting an alternating-current information and a direct-current information of an input signal. The control integrated circuit comprises a signal peak detector for detecting a peak value of the input signal to the pin to obtain the direct-current information of the input signal. Since the alternating-current information and the direct-current information of the input signal can be obtained through the same pin, the pin count of the control integrated circuit can be decreased.

Description:
FIELD OF THE INVENTION 
     The present invention is related generally to a signal peak detector and detection method and, more particularly, to a signal peak detector and detection method for a power factor correction (PFC) converter. 
     BACKGROUND OF THE INVENTION 
     A power factor correction (PFC) converter requires alternating-current (AC) information and direct-current (DC) information of the input signal to the PFC converter for various applications, such as establishing a current in proportion to the waveform of the input signal, detecting the valley of the input signal, and determining total harmonic distortion (THD) to improve trip point by using the AC information, and determining the value of the input signal, achieving brown in/brown out protection, etc. by using the DC information. Traditionally, the DC information is obtained by detecting the peak or root-mean-square (RMS) value of the input signal. 
       FIG. 1  shows a traditional control integrated circuit (IC)  2  for a PFC converter. An AC voltage Vac supplied to the PFC converter is rectified by a bridge rectifier  4  and becomes an input signal Vin, which is divided by a divider circuit  6  to generate an input signal Vd for a pin MULT of the control IC  2 . The control IC  2  may obtain the alternating-current information of the input signal Vin from the input signal Vd on the pin MULT. The PFC converter uses a signal peak detector  8  to detect the peak of the input signal Vd to obtain the DC information of the input signal Vin. In the signal peak detector  8 , an ideal diode  10  consisting of a diode and an operational amplifier provides the input signal Vd to a capacitor C 1 , to generate a peak signal Vpeak. A conversion circuit  12  obtains the DC information of the input signal Vin according to the peak signal Vpeak. A resistor Rff connected in parallel to the capacitor C 1  acts as a discharging path for allowing the capacitor C 1  to discharge slowly. However, this method for detecting the DC information requires a large capacitor C 1  to stabilize the peak signal Vpeak. Since such a large capacitor C 1  cannot be integrated into the control IC  2 , an additional pin VFF has to be used to connect the large capacitor C 1  outside the control IC  2 . Thus, the traditional PFC converter needs two pins MULT and VFF to obtain the alternating-current information and the DC information of the input signal Vin. 
     In addition, when the peak of the input signal Vin drops, the method using the capacitor C 1  to obtain the peak signal Vpeak has relatively slow transient response. Particularly, referring to  FIG. 2 , between time points t 1  and t 2 , the input signal Vin turns to a high peak from a low peak, and the peak signal Vpeak on the capacitor C 1  soon raises to a second level VL 2  from a first level VL 1 . However, when the input signal Vin turns from a high peak to a low peak, as happening between time points t 3  and t 4 , since the capacitor C 1  discharges slowly, the peak signal Vpeak will not drop to the first level VL from the second level VL 2  until several cycles TP of the input signal Vin lapse. Thus, in the signal peak detector  8  of  FIG. 1 , when the input signal Vin has its peak turning from high to low, the transient response of the peak signal Vpeak is relatively slow. 
     In some applications, a PFC converter may give up the alternating-current information and only obtain the DC information in order to reduce the number of the pins required.  FIG. 3 ,  FIG. 4  and  FIG. 5  show detectors for detecting the DC information without obtain the alternating-current information.  FIG. 3  is a conventional RMS detector  14 , which comprises a filter that consists of resistors R 3  and R 4  and a capacitor C 1  and serves to obtain an RMS value Vrms of the input signal Vin for the control IC  2 . The RMS value Vrms has the DC information of the input signal Vin, so the control IC  2  can accordingly obtain the DC information of the input signal Vin.  FIG. 4  shows another signal peak detector  8 , which comprises a capacitor C 1 , resistors R 3 , R 4 , Rff and a diode D 1 . The resistors R 3  and R 4  divide the input signal Vin to generate a input signal Vd. The input signal Vd charges the capacitor C 1  via the diode D 1  to generate a peak signal Vpeak for the control IC  2  such that the control IC  2  can accordingly obtain the DC information of the input signal Vin. The resistor Rff that is connected in parallel with the capacitor C 1  acts as a discharging path for the capacitor C 1  to discharge slowly. In the signal peak detector  8  of  FIG. 4 , the forward bias of the diode D 1  causes an error between the peak signal Vpeak and the peak of the input signal Vd. This error can be eliminated by adding a diode D 2  between an anode of the diode D 1  and the resistor R 4 , as shown in  FIG. 5 . However, the detectors of  FIG. 3 ,  FIG. 4  and  FIG. 5  also have the problem about slow transient response when the peak of the input signal Vin turns to low from high. 
     U.S. Pat. No. 6,731,230 teaches a signal peak detection method that detects an input signal to generate an output peak signal. During the input signal rises, if the output peak signal is smaller than the input signal, the output peak signal is risen in a relatively high speed. During the input signal falls, a reference voltage is used for detecting the input signal to remain the output peak signal at the peak voltage level of the input signal. When the input signal remains lower than the reference voltage over a predetermined number of clock cycles, the output peak signal is stopped from dropping with the input signal. However, this method also has the problem about slow transient response when the peak of the input signal turns to low from high. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a control integrated circuit and method for a PFC converter using one pin to obtain the alternating-current information and DC information of an input signal. 
     Another objective of the present invention is to provide a signal peak detector and detection method for a PFC converter. 
     Further objective of the present invention is to provide a signal peak detector with quick transient response and a detection method thereof. 
     According to the present invention, a control integrated circuit for a power factor correction converter comprises: a pin for receiving an input signal for the control integrated circuit to obtain an alternating-current information of the input signal; and a signal peak detector connected to the pin, for detecting a peak of the input signal to generate an output peak signal having a DC information of the input signal. The signal peak detector comprising: a first comparator for generating a comparison signal when the input signal is greater than an internal peak signal; a first counter for increasing a count it outputs according to the comparison signal and resetting the count according to a resetting signal; a first digital-to-analog converter for converting the count into the internal peak signal; a storage unit for obtaining from the first counter and storing the count in response to a sampling signal; a second comparator for generating the sampling signal when the input signal is lower than a reference voltage, and generating the resetting signal when the sampling signal ends; and a second digital-to-analog converter for converting the count stored in the storage unit into the output peak signal. The control integrated circuit can obtain the alternating-current information and DC information of the input signal by one pin to decrease the number of the pins. The first counter of the signal peak detector will re-count in each period of the input signal such that the output peak signal can immediately adjust to a target level at next period. Thereby, the signal peak detector has a quick transient response whether the peak of the input signal turns to high from low or turns to low from high. 
     According to the present invention, a control integrated circuit for a power factor correction converter comprises: a pin for receiving an input signal for the control integrated circuit to obtain an alternating-current information of the input signal; and a signal peak detector connected to the pin, for detecting a peak of the input signal to generate an output peak signal having a DC information of the input signal. The signal peak detector comprising: a comparator for comparing the input signal with the output peak signal to generate a rising signal or a falling signal; a counter for increasing and decreasing a count it outputs according to the rising signal and the falling signal, respectively; and a digital-to-analog converter for converting the count into the output peak signal having a DC information of the input signal. Wherein the count is increased in a first frequency and is decreased in a second frequency that is lower than the first frequency. The control integrated circuit can obtain the alternating-current information and DC information of the input signal by one pin to decrease the number of the pins. 
     According to the present invention, a signal peak detector comprises: a first comparator for generating a comparison signal when an input signal is higher than an internal peak signal; a first counter for increasing a count it outputs according to the comparison signal, and resetting the count according to a resetting signal; a first digital-to-analog converter for converting the count into the internal peak signal; a storage unit for obtaining from the first counter and storing the count according to a sampling signal; a second comparator for generating the sampling signal when the input signal is lower than a reference voltage, and generating the resetting signal when the sampling signal ends; and a second digital-to-analog converter for converting the count stored in the storage unit into an output peak signal related to a peak of the input signal. The first counter of the signal peak detector will re-count in each period of the input signal such that the output peak signal can immediately adjust to a target level at next period. Thereby, the signal peak detector has a quick transient response whether the peak of the input signal turns to high from low or turns to low from high. 
     According to the present invention, a signal peak detector comprises: a comparator, for comparing an input signal of the signal peak detector with an output peak signal to generate a rising signal or a falling signal; a counter connected to the comparator, for increasing and decreasing a count it outputs according to the rising signal or the falling signal, respectively; and a digital-to-analog converter connected to the counter and the comparator, for converting the count to generate the output peak signal. Wherein the count is increased in a first frequency and is decreased in a second frequency that is lower than the first frequency. 
     According to the present invention, a control method for a power factor correction converter comprises the steps of: using a pin to receive an input signal to obtain the alternating-current information of the input signal; providing a count; converting the count to generate an internal peak signal; increasing the count when the input signal is greater than the internal peak signal; storing the count when the input signal is smaller than a reference voltage; generating an output peak signal that has the DC information of the input signal according to the stored count; and resetting the count after the count is stored. The control method can obtain the alternating-current information and DC information of the input signal by one pin to decrease the number of the pins. In addition, the count will re-count in each period of the input signal such that the output peak signal can immediately adjust to a target level at next period. Thereby, the control method has a quick transient response whether the peak of the input signal turns to high from low or turns to low from high. 
     According to the present invention, a control method for a power factor correction converter comprises the steps of: using one pin to receive an input signal to obtain the alternating-current information of the input signal; providing a count; converting the count to generate an output peak signal that has the DC information of the input signal; increasing the count in a first frequency when the input signal is greater than the output peak signal; and decreasing the count in a second frequency that is smaller than the first frequency when the input signal is smaller than the output peak signal. The control method can obtain the alternating-current information and DC information of the input signal by one pin to decrease the number of the pins. 
     According to the present invention, a signal peak detection method, for detecting a peak of an input signal to generate an output peak signal, comprises the steps of: providing a count; converting the count to generate an internal peak signal; increasing the count when the input signal is greater than the internal peak signal; storing the count when the input signal is smaller than a reference voltage; generating the output peak signal according to the stored count; and resetting the count after the count is stored. The control method will re-count the count in each period of the input signal such that the output peak signal can immediately adjust to a target level at next period. Thereby, the control method has a quick transient response whether the peak of the input signal turns to high from low or turns to low from high. 
     According to the present invention, a signal peak detection method, for detecting a peak of an input signal to generate an output peak signal, comprises the steps of: providing a count; converting the count to generate the output peak signal; increasing the count in a first frequency when the input signal is greater than the output peak signal; and decreasing the count in a second frequency that is smaller than the first frequency when the input signal is smaller than the output peak signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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 of the present invention taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a traditional control IC for a PFC converter; 
         FIG. 2  shows the transient response of the peak signal Vpeak of  FIG. 1 ; 
         FIG. 3  shows a conventional RMS detector applicable to a PFC converter; 
         FIG. 4  shows a conventional signal peak detector applicable to a PFC converter; 
         FIG. 5  shows another conventional signal peak detector applicable to a PFC converter; 
         FIG. 6  shows a control IC according to the present invention; 
         FIG. 7  shows a waveform diagram of the signals of  FIG. 6 ; 
         FIG. 8  shows the transient response of the output peak signal in  FIG. 6  when the input signal has its peak changes; 
         FIG. 9  shows another embodiment of the signal peak detector of  FIG. 6 ; and 
         FIG. 10  shows a waveform diagram of the input signal Vd and the peak signal in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 6  shows an embodiment of a control IC  2  according to the present invention. Referring to  FIG. 1 , the alternating voltage Vac is rectified by the bridge rectifier  4  so that the input signal Vin is obtained. The divider circuit  6  divides the input signal Vin to generate the input signal Vd to the pin MULT of the control IC  2 , for the internal circuit of the control IC  2  to obtain the alternating-current information of the input signal Vin. In  FIG. 6 , the control IC  2  comprises a peak detector  20  using the pin MULT to detect the peak of the input signal Vd to generate the output peak signal Vpeak for obtaining the DC information of the input signal Vin. Since the same pin MULT is used to obtain the alternating-current and DC information of the input signal Vin, the control IC  2  of the present invention can reduce the number of the pins required. In the peak detector  20  of  FIG. 6 , a first comparator  22  is connected to the pin MULT for comparing the input signal Vd with an internal peak signal Vpeako. When the input signal Vd is higher than the internal peak signal Vpeako, the first comparator  22  generates a comparison signal Sc. A first counter  26  increases a count COT according to the comparison signal Sc. A first digital-to-analog converter  28  converts the count COT into the internal peak signal Vpeako. A second comparator  24  is connected to the pin MULT for comparing a reference voltage Vref with the input signal Vd, and when the input signal Vd is lower than the reference voltage Vref, generating a sampling signal S/H and a resetting signal Reset successively for a storage unit  29  and the first counter  26 , respectively. The storage unit  29  comprises a switch SWA and a second counter  30 . The second counter  30  is connected to the first counter  26  through the switch SWA. When the sampling signal S/H turns on the switch SWA, the second counter  30  obtains the count COT from the first counter  26  and stores the count COT. The second digital-to-analog converter  32  generates an output peak signal Vpeak according to the count COT stored in the second counter  30 . Therein, the working frequency of the first comparator  22  and the second comparator  24  is determined by a working clock CLK. 
       FIG. 7  is a waveform diagram of the signals of  FIG. 6 . Referring to  FIG. 6  and  FIG. 7 , when the input signal Vd rises, as shown between time points t 1  and t 2  in  FIG. 7 , the input signal Vd is greater than the internal peak signal Vpeako, so the comparison signal Sc is outputted under the control of the working clock CLK of the first comparator  22  for the first counter  26  to increase the count COT, thereby rising the internal peak signal Vpeako. Thus, the internal peak signal Vpeako rises with the input signal Vin. When the input signal Vd reaches the peak, it starts to fall, as shown at the time point t 2 . During the input signal Vd is falling, the input signal Vd is smaller than the internal peak signal Vpeako, so the first comparator  22  stops outputting the comparison signal Sc, so the count COT stops increasing. Since the count COT remains unchanged, the internal peak signal Vpeako remains unchanged. When the input signal Vd is smaller than the reference voltage Vref, as shown at the time point t 3 , the second comparator  24  first generates the sampling signal S/H to turn on the switch SWA, to make the second counter  30  obtain and store the count COT. The second digital-to-analog converter  32  then generates the output peak signal Vpeak according to the count COT stored in the second counter  30 . After the sampling signal S/H ends, the second comparator  24  sends out the resetting signal Reset to the first counter  26  for resetting the count COT, which in turn makes the internal peak signal Vpeako rest. The signal peak detector  20  at the beginning of each cycle recount the count COT to detect the peak of the input signal, and determines the output peak signal Vpeak for the next cycle according to the obtained count COT. Therefore, no matter the peak of the input signal Vin is turning to high from low or turning to low from high, the peak detector  20  can have a quick transient response. 
     More particularly, referring to  FIG. 6  and  FIG. 8 , during the period TP 1  of the input signal Vin, the peak of the input signal Vin is higher than that of the previous period. At the beginning of the period TP 1 , recounting is performed to obtain the count COT related to the peak of the input signal Vin. At the beginning of the period TP 2  following the period TP 1 , the second counter  30  stores the count COT obtained in the cycle TP 1  to generate the output peak signal Vpeak corresponding to the peak of the input signal Vin in the period TP 1 . During the period TP 3 , the peak of the input signal Vin is lower than that in the previous period TP 2 . At the beginning of the period TP 3 , the count COT recounts. At the beginning of the period TP 4  that follows the period TP 3 , the second counter  30  stores the count COT obtained in the period TP 3  to generate the output peak signal Vpeak corresponding to the peak of the input signal Vin in the period TP 3 . As can be seen from  FIG. 8 , no matter the peak of the input signal Vin is turning to high from low or turning to low from high, the signal peak detector  20  needs only one cycle to adjust the output peak signal Vpeak to the target level, so it can provide fast transient response. 
       FIG. 9  shows another embodiment of the signal peak detector  20 , which also uses the pin MULT detecting the alternating-current information to detect the peak of the input signal Vd, to generate the output peak signal Vpeak for obtaining the DC information of the input signal Vin. Since the same pin MULT is used to obtain the alternating-current information and the DC information of the input signal Vin, the number of pins required is reduced. The signal peak detector  20  of  FIG. 9  comprises a clock generator  40 , a comparator  42 , a counter  44  and a digital-to-analog converter  46 . The comparator  42  is connected to the pin MULT of the control IC  2  and serves to compare the output peak signal Vpeak with the input signal Vd to generate a rising signal UP or a falling signal DN. When the input signal Vd is greater than the output peak signal Vpeak, the comparator  42  sends out the rising signal UP. When the input signal Vd is smaller than the output peak signal Vpeak, the comparator  42  sends out the falling signal DN. The counter  44  increases the count COT according to the rising signal UP or decreases the count COT according to the falling signal DN. The digital-to-analog converter  46  generates the output peak signal Vpeak according to the count COT. The clock generator  40  provides a working clock CLK 1  or CLK 2  for the comparator  42 , to determine the working frequency for the comparator  42 . Therein, the frequency of the working clock CLK 1  is higher than the frequency of the working clock CLK 2 . When the input signal Vd is greater than the output peak signal Vpeak, as shown between time points t 1  and t 2  and between time points t 3  and t 4  in  FIG. 10 , the comparator  42  sends out the rising signal UP. When the clock generator  40  receives the rising signal UP, it provides the working clock CLK 1  to the comparator  42 , so that comparator  42  has a higher working frequency, and thereby the count COT is increased in a higher frequency, making the output signal peakVpeak rises with the input signal Vin quickly. When the input signal Vd is smaller than the output peak signal Vpeak, as shown between the time points t 2  and t 3  in  FIG. 10 , the comparator  42  sends out the falling signal DN. When the clock generator  40  receives the falling signal DN, it provides the working clock CLK 2  to the comparator  42 , so the working frequency of the comparator  42  is lowered, and the count COT will decrease in a low frequency, thereby stabilizing the output peak signal Vpeak at the peak. 
     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.