Abstract:
An apparatus for and a method of measuring, in real-time, and indicating power consumption of a product powered by a switching mode power supply (SMPS). Power is supplied to the product through a transformer having a predetermined primary coil inductance, wherein a current of a primary coil of the transformer is turned ON and OFF by pulse-width modulation to supply the power to the electronic device. A drive voltage across the primary coil is monitored and a pulse waveform having a first level corresponding to an ON time of the current in the primary coil and a second level corresponding to an OFF time of the current in the primary coil is developed. Power consumption is calculated based on the drive voltage, the ON time of the current in the primary coil, the predetermined primary coil inductance, and a switching frequency of a pulse width modulator of the SMPS.

Description:
BACKGROUND OF THE INVENTION 
   This application claims the priority of Korean Patent Application No. 2002-52825, filed Sep. 6, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   1. Field of the Invention 
   The present invention relates to an apparatus for measuring power and, more particularly, to an apparatus for measuring, in real-time, and indicating power consumption of a product using a switching mode power supply (SMPS). 
   2. Description of the Related Art 
   Power consumption is a quantitative indication of the ratio of how much energy is consumed or how much work is done per unit of time, and indicates the amount of energy supplied or consumed in a unit second. An energy consumption efficiency grade of a product varies in accordance with the consumption power, and a low-grade product wastes energy during the entire life of the product. Therefore, it is desirable to confirm the energy consumption efficiency grade and purchase a higher-grade product if possible. 
   As an understanding of energy savings has recently become higher, various products now have a power saving function and keep the power consumption below a certain level even during normal operation. However, it would be highly desirable to indicate actual power consumption of a product while the product is in use. Displaying the actual power consumption has not been considered due to the complexity of a circuit needed to implement such a function and cost. Accordingly, the actual power consumption of a product has been measured in the product development stage using a separate measuring device. Further, consumers have not had a way to know the actual power consumption of a currently used product other than the maximum power consumption stated in the product manual or on a label attached to the product. However, as the consumers&#39; understanding of energy saving functions and efficiencies have gradually changed, a need has arisen to provide a function for measuring, in real-time, and indicating the power consumption of a product while the product is in use. 
   SUMMARY OF THE INVENTION 
   To solve the above and/or other problems, it is an aspect of the present invention to provide an apparatus for measuring, in real-time, and indicating power consumption of a product. 
   Additional aspects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention. 
   According to an aspect of the present invention, an apparatus for measuring power consumption comprises a rectifying unit which rectifies and smoothes an AC voltage input to the rectifying unit, a transforming unit which receives the rectified voltage from the rectifying unit and produces a voltage at a secondary coil of the transforming unit in accordance with current fluctuations at a primary coil of the transforming unit, a switching unit which switches on or off the output voltage at the primary coil of the transforming unit with pulse-width modulation (PWM) control signals generated from a feedback voltage and a synchronous signal, a voltage regulating unit which regulates the output voltage at the primary coil of the transforming unit to calculate a turn-on time of the switching unit, and a control unit which calculates the turn-on time from the output of the voltage regulating unit and calculates power consumption from the calculated turn-on time, the switching frequency of the switching unit and the inductances of the transforming unit. 
   According to an aspect of the present invention, the apparatus for measuring power consumption may further comprise a display unit which indicates the power consumption calculated by the control unit. 
   According to an aspect of the present invention, the voltage regulating may comprise a voltage decreasing section which decreases the voltage at the primary coil of the transforming unit below a certain level, a first clamp which clamps the decreased voltage at a first constant voltage level, a transformer which transforms the first clamped voltage, and a second clamp which clamps the transformed voltage at a second constant voltage level. 
   According to an aspect of the present invention, an apparatus for measuring power consumption comprises a rectifying unit which rectifies and smoothes an AC voltage input to the rectifying unit, a transforming unit which receives the rectified voltage from the rectifying unit and produces a voltage at a secondary coil of the transformer in accordance with current fluctuations at a primary coil of the transformer, a switching unit which switches on or off the output voltage at the primary coil of the transforming unit with pulse-width modulation (PWM) control signals generated from a feedback voltage and a synchronous signal, a voltage regulating unit which regulate the voltage at the secondary coil of the transforming unit to calculate a turn-on time of the switching unit, and a control unit which calculates the turn-on time from the output of the voltage regulating unit and calculates power consumption from the calculated turn-on time, the switching frequency of the switching unit and the inductances of the transforming unit. 
   According to an aspect of the present invention, an the apparatus for measuring power consumption may further comprise a display unit which indicates the power consumption calculated by the control unit. 
   According to an aspect of the present invention, the voltage regulating unit may comprise a voltage decreasing section which decreases the voltage at the secondary coil of the transforming unit below a certain level, and a clamp which clamps the output of the voltage decreasing section at a constant voltage level. 
   According to an aspect of the present invention, an apparatus for measuring power consumption comprises a rectifying unit which rectifies and smoothes an AC voltage input to the rectifying unit, a transforming unit which receives the rectified voltage from the rectifying unit and produces a voltage at a secondary coil of the transforming unit in accordance with current fluctuations at a primary coil of the transforming unit, a switching unit which switches on or off the output voltage at the primary coil of the transforming unit with pulse-width modulation (PWM) control signals generated from a feedback voltage and a synchronous signal, a voltage regulating unit which regulates the voltage at one of the primary coil and the secondary coil of the transforming unit to calculate a turn-on time of the switching unit, and a control unit which calculates the turn-on time from an output of the voltage regulating unit and calculates power consumption from the calculated turn-on time, the AC input voltage at the primary coil, the switching frequency of the switching unit and the inductances of the transforming unit. 
   According to an aspect of the present invention, the apparatus for measuring power consumption may further comprise a display unit which indicates the power consumption calculated by the control unit. 
   According to an aspect of the present invention, where the voltage regulating unit regulates the voltage at the primary coil of the transforming unit to calculate the turn-on time of the switching unit, the voltage regulating unit may comprise a voltage decreasing section which decreases the voltage at the primary coil of the transforming unit below a certain level, a first clamp which clamps the decreased voltage at a first constant voltage level, a transformer which transforms the first clamped voltage, and a second clamp which clamps the transformed voltage at a second constant voltage level. 
   According to an aspect of the present invention where the voltage regulating unit regulates the voltage at the secondary coil of the transforming unit to calculate the turn-on time of the switching unit, the voltage regulating unit may comprise a voltage decreasing section which decreases the voltage at the secondary coil of the transforming unit below a certain level, and a clamp which clamps the output of the voltage decreasing section at a constant voltage level. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and/or other aspects and advantages of the present invention will become more apparent by describing in detail embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is a circuit diagram of an apparatus for measuring power consumption according to an embodiment of the present invention; 
       FIGS. 2A-2G  show waveforms for explaining an operation of the apparatus shown in  FIG. 1 ; 
       FIG. 3  is a circuit diagram of an apparatus for measuring power consumption according to another embodiment of the present invention; and 
       FIGS. 4A-4I  show waveforms for explaining an operation of the apparatus shown in FIG.  3 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Typically, power consumption of a product is measured with an exclusive measuring device at AC input lines to which power is supplied. Such a measuring device requires a complex circuit, and is inapplicable to a product. The present invention provides a method of measuring power consumption using a voltage V s  at a secondary coil of a transformer T 11  as shown in  FIG. 1 and a  method of measuring power consumption using a voltage V ds  at a primary coil of a transformer T 31  as shown in FIG.  3 . 
   With reference to FIGS.  1  and  2 A- 2 G, a method of measuring power consumption using the voltage V s  at the secondary coil of the transformer T 11  will be described below.  FIG. 1  is a circuit diagram of an apparatus for measuring power consumption according to a first embodiment of the present invention. The apparatus shown in  FIG. 1  comprises a rectifying section  100 , a switching section  101 , a snubber circuit  102 , a transformer T 11 , a voltage regulating section  104 , a control section  105 , and a display section  106 . 
   The rectifying section  100  rectifies and smoothes input AC current power to produce a DC voltage. The smoothed DC voltage is applied to a first end of a primary coil of the transformer T 11 . The switching section  101  switches on or off the voltage output at a second end of the primary coil of the transformer T 11  with pulse-width modulation (PWM) control signals. The switching section  101  comprises a PWM control section  101 - 1  which generates PWM signals based on feedback voltages from a feedback block  101 - 2  and synchronous signals from a synchronous (SYNC) block  101 - 3 , and a field effect transistor (FET) Q 11  which switches the second end of the primary coil in response to the PWM signals. 
   The snubber circuit  102  prevents the destruction of the FET Q 11  by suppressing surge voltages generated when the FET Q 11  turns off. The snubber circuit  102  comprises an upper snubber circuit comprising a resistor R 11 , a capacitor C 12  and a diode D 15 , and a lower snubber circuit comprising a resistor R 12 , a capacitor C 13  and a diode D 16 . With regard to the upper snubber circuit, when the FET Q 11  turns-off, a surge voltage generated at the primary coil of the transformer T 11  rapidly increases, and if the surge voltage exceeds a predetermined voltage, then the switching section  101  is destroyed. Therefore, the upper snubber circuit prevents the destruction of the FET Q 11  by suppressing voltage surges in such a way that the voltage surge generated when the FET Q 11  turns off charges the capacitor C 12  through the diode D 15  and, then, gradually discharges through the resistor R 11 . The lower snubber circuit prevents the destruction of the FET Q 11  by suppressing a surge voltage when the FET Q 11  turns off so that the surge voltage generated at the primary coil of the transformer T 11  charges capacitor C 13  through the diode D 16  and, then, gradually discharges through the resistor R 12 . 
   The transformer  103  stores energy at its primary coil L p  when the FET Q 11  turns on and provides energy to its output when the FET Q 11  turns off. Operation of the transformer  103  in time intervals t 1 , t 2  and t 3  will be described with reference to  FIGS. 2A through 2G . Referring now to  FIG. 2A , during the time interval t 1 , when a gate voltage of about 10V is applied to the FET Q 11 , the FET Q 11  turns on and, accordingly, the voltage V ds  becomes 0V (FIG.  2 B). The smoothed DC voltage from the rectifying section is applied across the primary coil L p  of the transformer  103  and a current I p  starts to flow (FIG.  2 C). When the current I p  flows, the primary coil L p  is charged with an energy of ½L p *I p   2  joules. At this moment, since a voltage having a reverse polarity is applied across the secondary coil L s  (FIG.  2 D), a current I s  does not flow (FIG.  2 E). 
   During the time interval t 2 , the FET Q 11  turns off at the instant the gate voltage V gs  of the FET Q 11  becomes 0V ( FIGS. 2A and 2B ) and, accordingly, the current I p  does not flow ( FIG. 2C ) so that the polarity across the primary coil L p  is changed by a counter electromotive force caused by the inductor characteristic for keeping the previous magnetic flux. Therefore, the inductor energy, ½L p * I p   2  joules, stored at the primary coil L p , moves to the secondary coil (FIG.  2 D). During the time interval t 3 , after all of the energy stored at the primary coil has been transferred to the secondary coil, the current I s  becomes 0A ( FIG. 2E ) so that no more current flows through the secondary coil. 
   The diodes D 11  through D 14  of the rectifying section  100  rectify and smooth the AC voltages at the capacitor C 11  corresponding to the following equation (1):
 
 V   i ( dc )= V   in ( ac )×√{square root over (2)}×0.9 [V   dc ]  (1)
 
   At the instant the FET Q 11  switches, the current I p  flows from the capacitor C 11  to the FET Q 11 , and the power consumption at this instant corresponds to the following equation (2): 
             P   =       1   2     ⁢     L   p     ×     I   p   2     ×     f   ⁡     [   W   ]                 (   2   )             
 
   In equation (2), f is the switching frequency of the switching section  101 , and L p  is the inductance of the primary coil of the transformer  103 , which is known to the manufacturer. Therefore, if the current I p  is known at the instant the FET Q 11  turns on, the resultant power consumption may be calculated by equation (2). However, there is a difficulty in measuring the value of the current I p , because an exclusive measuring device is normally required for that purpose. Nevertheless, the value of the current I p  may be obtained from the following equation (3): 
               I   p     =       1     L   p       ⁢       (       V   i     ×     t   on       )     ⁡     [   A   ]                 (   3   )             
 
   That is, the value of the current I p  may be obtained by the turn-on time of the FET Q 11 , and the resultant power consumption may be calculated by the following equation (4): 
             P   =       1   2     ⁢         V   i   2     ×     t   on   2         L   p       ×     f   ⁡     [   W   ]                 (   4   )             
 
   Therefore, if the turn-on time of the FET Q 11  is known, the resultant power consumption may be calculated by the equation (4). Now, the voltage regulating section  104  that provides the signals for calculating the turn-on time of the FET Q 11  with the voltage V s  at the secondary coil of the transformer  103  will be described. 
   At the instant the FET Q 11  turns off, the waveform of the voltage V s , which is generated at the secondary coil of the transformer  103  due to the counter electromotive force, rises as shown in FIG.  2 D. As shown in  FIG. 2D , a time interval when the secondary voltage V s  decreases below the ground level corresponds to the turn-on time of the FET Q 11 . In the voltage regulating section  104  shown in  FIG. 1 , the resistors R 13  and R 14  form an attenuator which decreases the secondary voltage V s  to provide an attenuated waveform V a  shown in  FIG. 2F. A  clamp device such as a Zener diode ZD 11  clamps voltages above 5.1V to 5.1V and voltages below −0.7V to −0.7V to provide a clamped waveform V c  shown in FIG.  2 G and outputs the clamped signal to the control section  105 . 
   The control section  105  calculates the switching frequency (1/T) of the switching section  101 , which is provided from the voltage regulating section  104 , and the turn-on time of the FET Q 11 , which corresponds to the time interval shown as the low level area in FIG.  2 G. Therefore, the resultant power consumption may be obtained by substituting the calculated turn-on time of the FET Q 11  in the equation (4). Such calculated power consumption may be indicated by a display section  106 , if consumers wish to have such a display. 
   With reference to  FIGS. 3 and 4A  through  4 I, a method of measuring power consumption using a voltage V ds  at a primary coil of a transformer  303  will be described below.  FIG. 3  is a circuit diagram of an apparatus for measuring power consumption according to a second embodiment of the present invention. The apparatus shown in  FIG. 3  comprises, a rectifying section  300 , a switching section  301 , a snubber circuit  302 , the transformer T 31 , a voltage regulating section  304 , a control section  305 , and a display section  306 . 
   The rectifying section  300  rectifies and smoothes input AC current power to produce a DC voltage. The smoothed DC voltage is applied to a first end of a primary coil L p  of the transformer T 31 . The switching section  301  switches on or off the voltage output at a second end of the primary coil of the transformer T 31  with PWM control signals. The switching section  301  comprises a PWM control section  301 - 1  which generates PWM signals based on feedback voltages from a feedback block  301 - 2  and synchronous signals from a synchronous (SYNC) block  301 - 3 , and a field effect transistor (FET) Q 31  switches the second end of the primary coil L p  in response to the PWM signals. 
   The snubber circuit  302  prevents the destruction of the FET Q 31  by suppressing surge voltages generated when the FET Q 31  turns off. The snubber circuit  302  comprises an upper snubber circuit comprising a resistor R 31 , a capacitor C 32  and a diode D 35 , and a lower snubber circuit comprising a resistor R 32 , a capacitor C 33  and a diode D 36 . With regard to the upper snubber circuit, when the FET Q 31  turns-off, a surge voltage generated at the primary coil L p  of the transformer T 31  rapidly increases, and if the surge voltage exceeds a predetermined voltage, then the switching section  301  is destroyed. Therefore, the upper snubber circuit prevents destruction of the FET Q 31  by suppressing voltage surges in such a way that the voltage surge generated when the FET Q 31  turns off charges the capacitor C 32  through the diode D 35  and, then, gradually discharges through the resistor R 31 . The lower snubber circuit prevents destruction of the FET Q 31  by suppressing surge voltages when the FET Q 31  turns off so that the surge voltage generated at the primary coil of the transformer T 31  charges the capacitor C 33  through the diode D 36  and, then, gradually discharges through the resistor R 32 . 
   The transformer T 31  stores energy in the primary coil L p  when the FET Q 31  turns on and provides energy to a secondary coil L s  when the FET Q 31  turns off. The operation of the transformer T 31  in the time intervals, t 2  and t 3  will be described with reference to  FIGS. 4A through 4I . During the time interval t 1 , when a voltage of about 10V is applied to the gate of the FET Q 31  (FIG.  4 A), the FET Q 31  turns on and, accordingly, the voltage V ds  becomes 0V (FIG.  4 B). With the DC input voltage applied across the primary coil L p  of the transformer T 31 , a current I p  starts to flow (FIG.  4 C). When the current I p  flows, the primary coil L p  is charged with energy of ½L p *I p   2  joules. At this moment, since a voltage having a reverse polarity is applied across the secondary coil L s  (FIG.  4 D), the current I s  does not flow (FIG.  4 E). During the time interval t 2 , the FET Q 31  turns off when the gate voltage V gs  of the FET Q 31  becomes 0V ( FIGS. 4A and 4B ) and, accordingly, the current I p  does not flow ( FIG. 4C ) so that the polarity across the primary coil L p  is changed by a counter electromotive force caused by the inductor characteristic for keeping the previous magnetic flux. Therefore, the inductor energy, ½L p *I p   2  joules, stored at the primary coil L p  moves to the secondary coil L s  (FIG.  4 D). During the time interval t 3 , after all of the energy stored at the primary coil has been transferred to the secondary coil, the current I s  becomes 0A ( FIG. 4E ) so that no more current flows through the secondary coil. 
   The diodes D 31  through D 34  of the rectifying section  300  rectify and smooth the AC voltages at the capacitor C 31  corresponding to the following equation (5):
 
 V   i ( dc )= V   in ( ac )×√{square root over (2)}×0.9 [V   dc ]  (5)
 
   At the instant when the FET Q 31  switches on, the current I p  flows from the capacitor C 31  through the FET Q 31 , and the power consumption at the instant of switching corresponds to the following equation (6): 
             P   =       1   2     ⁢     L   p     ×     I   p   2     ×     f   ⁡     [   W   ]                 (   6   )             
 
   In the above equation (6), f is the switching frequency of the switching section  101 , and L p  is the inductance of the primary coil of the transformer, which is known to the manufacturer. Therefore, if the current I p  is known at the instant when the FET Q 31  turns on, the resultant power consumption may be calculated by the equation (6). However, there is a difficulty in measuring the value of the current I p , because an exclusive measuring device is normally required for that purpose. Nevertheless, the value of the current I p  can be obtained from the following equation (7): 
               I   p     =       1     L   p       ⁢       (       V   i     ×     t   on       )     ⁡     [   A   ]                 (   7   )             
 
   That is, the value of the current I p  may be obtained by the turn-on time of the FET Q 31 , and the resultant power consumption may be calculated by the following equation (8): 
             P   =       1   2     ⁢         V   i   2     ×     t   on   2         L   p       ×     f   ⁡     [   W   ]                 (   8   )             
 
   Therefore, if the turn-on time of the FET Q 31  is known, the resultant power consumption can be calculated by the above equation (8). 
   The voltage regulating section  304  provides signals for calculating the turn-on time of the FET Q 31  with the voltage V ds  at the primary coil of the transformer T 31  and will be described below. 
   Resistors R 34  and R 35  form an attenuator which attenuates the level of the primary voltage V ds  shown in  FIG. 4D  to a convenient level, such as for example, a level of 1/20 V ds . A waveform of the attenuated primary voltage V ds  is illustrated in  FIG. 4F. A  first clamp device such as a Zener diode ZD 31  clamps the voltage of the attenuated primary voltage V a1  above 12V to 12V (V c1 ) as shown in  FIG. 4G. A  transformer T 32  transfers the clamped primary voltage V c1  to a secondary coil of the transformer T 32  as a voltage V t1 . The mutual inductances of the transformer T 32  transfer the signals as an AC signal to obtain the waveform as shown in FIG.  4 H. It is noted that, in the waveform of  FIG. 4H , the upper and lower portions with reference to 0V have a same amplitude. A second clamp device such as a Zener diode ZD 32  clamps a voltage above 5.1V to 5.1V and a voltage below −0.7V to −0.7V to provide waveform V c2  shown in FIG.  4 I and outputs the clamped signal to the control section  305 . 
   The control section  305  calculates the switching frequency (1/T) of the switching section  301 , which is provided from the voltage regulating section  304 , and the turn-on time of the FET Q 31 , which corresponds to the time interval shown as the low level area (−0.7V) in FIG.  4 I. Therefore, the resultant power consumption may be obtained by substituting the calculated turn-on time of the FET Q 31  in the above equation (8). Such calculated power consumption may be indicated by a display section  306 , if consumers wish to have such a display. 
   According to the above description of the present invention, a method of measuring power consumption by using the voltage V s  at the secondary coil of a transformer T 11  or a method for measuring power consumption by using the voltage V ds  at the primary coil of a transformer T 31  may be implemented. However, a circuit may be constructed in view of the above disclosure which implements both methods in the same circuit. 
   According to the present invention, by measuring, in real-time, and indicating the power consumption of a product using a SMPS as described above, normal operation of the product may be confirmed by consumers and reliability of the product is improved. 
   While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.