Abstract:
An automatic switching device for the power source input range of a personal computer monitor is installed within the switchmode power source circuit of the monitor and includes a comparator and a relay arranged so that, irrespective of whether the power source is at a 110V or 220V voltage level, the rectifying circuit of the switchmode power source circuit is automatically switched to a voltage doubler circuit or a bridge rectifier circuit as appropriate for reducing power losses and saving energy.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an automatic switching device for the power supply input range of a monitor connected with a personal computer, and especially to an automatic range switching device of a low loss rapidly restoring power supply commonly used in voltages of 110V and 220V. 
     According to the statistics, nowadays at least 250,000,000 monitors of personal computers are used. Assume the average power consumption of each monitor is 50V, the total power consumption will be a very great number. Thus many consumer organizations and energy management institutions have called for reducing the power consumption. 
     In order to be conveniently manufactured and sold, and to prevent the consumer from making a mistake while using, the specifications of the globally used monitors are called “Auto Range”: AC110V±20% and AC220V±20%, or Full Range: AC86V˜264V. This wide range of power supply design can&#39;t meet the purpose of using the least power of the monitors. The following table lists the power circuits of commercial monitors: 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 MAX. 
                 MAX. 
                 Input range 
               
               
                   
                   
                 horizontal 
                 Power 
                 of power 
               
               
                 Brand 
                 Size 
                 frequency 
                 consumption 
                 supply 
               
               
                   
               
             
             
               
                 OPTIQUEST 
                 17″ 
                 69 KHz 
                 80 W 
                 AUTO 
               
               
                 V775 
               
               
                 TATUNG 
                 17″ 
                 94 KHz 
                 105 W  
                 AUTO 
               
               
                 17N 
               
               
                 APPLE 
                 15″ 
                 48 KHz 
                 70 W 
                 FULL 
               
               
                 M2943 
               
               
                 TATUNG 
                 15″ 
                 64 KHz 
                 75 W 
                 FULL 
               
               
                 15VHR 
               
               
                   
               
             
          
         
       
     
     NOTE 1: The circuit control of automatic range is shown in FIG. 1 a.  If the input voltage of the power supply is 110V, the Triac I 801  turns on to make the circuit become a voltage doubler. If the power source is 220V the Triac I 180  cut off, the circuit become bridge rectifier. 
     NOTE 2: The full range circuit control is shown in FIG. 1 b.  No matter whether the input voltage of power source is 100V or 220V, the circuit functions as the bridge rectifier. 
     In the auto range controlling, when the input power source is 110V(i.e. 110V±20% ), the rectifying circuit does the function of a voltage doubler, so that the output voltage is the same as that from a 220V power source (i.e. 220V±20% ). Now referring to FIG. 1 a,  the voltage value of Vc is in the range of {square root over (2)}×220V×(1±20% )=249V˜373V. This value is different from that in the full range, in which VC=124V˜373V. When the input voltage of the power source is 100V, the current consumption in the full range is approximately twice that in the auto range. For, example, in the OPTIQUEST V775 with power consumption of 80 W, the former has a current of 1.06 A, while the latter has a current of 0.53 A. However, when the input voltage of the power source is 220V, both have a power consumption of 0.53 A. As shown in Table 2, assuming that the power consumption is 80 W for the two circuits, the specifications of the related components are listed as follows 
     
       
         
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Specification 
               
             
          
           
               
                 control 
                 Auto range 
                 Full range 
                   
               
               
                 circuits 
                 (A) 
                 (B) 
                 Description 
               
               
                   
               
               
                 Power 
                 Q805 = 
                 Q805 = 
                 When input is 110 V, the 
               
               
                 transistor 
                 4A/500 V 
                 8A/500 V 
                 current of B circuit is twice 
               
               
                   
                   
                   
                 of that of A Circuit. 
               
               
                 Filtering 
                 C809 = 
                 C808 = 
                 Since Cv = it , when 110 V 
               
               
                 capacitor 
                 150μ/200 V 
                 300μ/400 V 
                 power input, the voltage of B 
               
               
                   
                 C810 = 
                   
                 circuit will be halved, while 
               
               
                   
                 150μ/200 V 
                   
                 when i is doubled, then the 
               
               
                   
                   
                   
                 voltage of C is four times of 
               
               
                   
                   
                   
                 that of A circuit. 
               
               
                 output end 
                 D811 = 
                 D811 = 
                 The number of windings in 
               
               
                 rectifier 
                 100 V 1A 
                 200 V 1A 
                 the primary terminals of A/B 
               
               
                   
                 D812 = 
                 D812 = 
                 circuits are 116 and 231, 
               
               
                   
                 200 V 1A 
                 400 V 1A 
                 respectively, while in the 
               
               
                   
                   
                   
                 secondary terminal, A/B 
               
               
                   
                   
                   
                 circuits has the same winding 
               
               
                   
                   
                   
                 numbers. That is in the 
               
               
                   
                   
                   
                 primary terminal, the ratio 
               
               
                   
                   
                   
                 of winding number A/B is 
               
               
                   
                   
                   
                 0.5. When input is 220 V, the 
               
               
                   
                   
                   
                 reverse voltage of B circuit is 
               
               
                   
                   
                   
                 twice of that of A circuit. 
               
               
                 Voltage 
                 1802 = 
                 unnecessary 
                 When input is 110 V, the A 
               
               
                 multiplier 
                 10A/500 V 
                   
                 circuit need a voltage 
               
               
                 and switch 
                 (STR81145A) 
                   
                 multiplier and switch. 
               
               
                   
               
             
          
         
       
     
     In table II, for the sizes of the parts used in the A and B circuits, the larger the size, the more expensive the cost. Thus the cost is the primary concern in selecting a circuit. After analyzing, it is known that the power consumption is smaller than 80 W, the circuit has an economic cost by using the full range control, and vice versa. 
     But from the viewpoint of energy saving, no matter whether the control circuit is operated in full range or in auto range, the prior circuit structures are not preferable. Following are the explanations: 
     For the circuit operating in auto range: referring to FIG. 2 a,  a voltage multiplying and switch device(I 801 ), such as integrated circuit STR80145A. is used. Since a triple directional silicon control rectifier (Triac) is built therein and a voltage decreasing resistor is connected, some loss will occur, as shown in FIG. 2 b.    
     For the circuit operating in full range: in the highest efficiency, the voltage is in a middle range between 88V˜264V; this range is between the range of the 132V˜176V. When the voltage of power supply is closer to an upper limit or a lower limit, the power consumption is larger and the efficiency will become worse. 
     Table 3 may prove the above description. For example, for a monitor operated in auto range (17 inches monitor), when the power supply is AC110V, the average power consumption is larger than that in of a power supply of AC220V with a value of                66.6   +   67.1   +   97.6   +   94.7     4        W     -         64.5   +   66.3   +   91.4   +   92.2     4        W       =     2.9                 W                            
     Also, for a for monitor operated in full range (15 inches monitor) with a lower limit of 88V and an upper limit of 264V, then the average power consumption is larger than that operated in the range of AC132V˜AC176V with a value of                61.5   +   63.0   +   59.2   +   59.7     4        W     -         59.8   +   60.0   +   57.6   +   57.7     4        W       =     2.1                 W                            
     
       
         
               
             
               
               
             
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Pattern cross hatch;  Timing: F H  = 31.5 KHz;  F V  = 70 Hz 
               
             
          
           
               
                   
                 Input power supply voltage 
               
             
          
           
               
                 Specification 
                 AC110 V 
                 AC220 V 
               
             
          
           
               
                   
                   
                 Max. 
                   
                 Lower 
                 Upper 
                 Lower 
                 Upper 
               
               
                   
                 Size 
                 horizontal 
                   
                 limit 
                 limit 
                 limit 
                 limit 
               
               
                 Brand 
                 (inch) 
                 freq. 
                 Rectifier 
                 88 V 
                 132 V 
                 176 V 
                 264 V 
               
               
                   
               
             
          
           
               
                 OPTIQUEST 
                 17″ 
                 69 KHz 
                 Auto range 
                 1.097 
                 A 
                 0.769 
                 A 
                 0.554 
                 A 
                 0.369 
                 A 
               
               
                 V775 
                   
                   
                   
                 66.6 
                 W 
                 67.1 
                 W 
                 64.5 
                 W 
                 66.3 
                 W 
               
               
                 TATUNG 
                 17″ 
                 94 KHz 
                 Auto range 
                 1.503 
                 A 
                 1.028 
                 A 
                 0.746 
                 A 
                 0.499 
                 A 
               
               
                 17N 
                   
                   
                   
                 97.6 
                 W 
                 94.7 
                 W 
                 91.4 
                 W 
                 92.2 
                 W 
               
               
                 APPLE 
                 15″ 
                 48 KHz 
                 Full range 
                 1.025 
                 A 
                 0.699 
                 A 
                 0.517 
                 A 
                 0.353 
                 A 
               
               
                 M2943 
                   
                   
                   
                 61.5 
                 W 
                 59.8 
                 W 
                 60.0 
                 W 
                 63.0 
                 W 
               
               
                 TATUNG 
                 15″ 
                 64 KHz 
                 Full range 
                 0.956 
                 A 
                 0.657 
                 A 
                 0.488 
                 A 
                 0.335 
                 A 
               
               
                 15VHR 
                   
                   
                   
                 59.2 
                 W 
                 57.6 
                 W 
                 57.7 
                 W 
                 59.7 
                 W 
               
               
                   
               
             
          
         
       
     
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a low loss and power saving automatic switching device for the input range of the power source of a monitor. 
     For a monitor, the power consumption of 2˜3 W almost may be neglected. However, through calculating, it has been discovered that this power is 17% of the power consumption of a monitor. Then, if the power consumption all over the world are added together, it will be appreciated that the total amount is a very large number. Thus, through a long period of research, the inventor of the present invention has derived the following results: 
     1. The input of a power source is operated in auto range so that the working point of the transformer is within the range of {square root over ( 2 )}×220V(1±20%) for increasing the working efficiency. 
     2. The Triac within the voltage multiplying, rectifying and switching device are changed to be controlled by the contacts of a relay for dissipating the heat consumption V F ×I F  (V F  is the forward voltage of the Triac in the integrated circuit; I F  is the forward current of the Triac in the integrated circuit) induced from voltage multiplying and rectifying. 
     3. The working current of the voltage multiplying and rectifying device is changed so that it is supplied from the secondary terminal of the transformer for decreasing the power consumption generated from the voltage decreasing circuit. 
     The TATUNG 17N shown in Table 1 is used as an example, in which the TATUNG 17N has been improved by the above three results. The power consumption is listed in Table 4: 
     
       
         
               
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
             
             
               
                   
                   
               
               
                   
                 Power 
               
             
          
           
               
                 Input 
                 Horizontal 
                 110 V level 
                 220 V level 
               
             
          
           
               
                 Comparing 
                 frequency 
                 88 V 
                 132 V 
                 176 V 
                 264 V 
               
               
                   
               
             
          
           
               
                 Before change 
                 31 KHz 
                 97.6 W 
                 94.7 W 
                 91.4 W 
                 92.2 W 
               
               
                   
                 94 KHz 
                 105.5 W 
                 101.2 W 
                 97.7 W 
                 99.2 W 
               
               
                 After change 
                 31 KHz 
                 92.7 W 
                 91.0 W 
                 89.0 W 
                 88.9 W 
               
               
                   
                 94 KHz 
                 101.2 W 
                 98.0 W 
                 95.2 W 
                 96.1 W 
               
             
          
           
               
                 Power consumption before and after changing 
               
             
          
           
               
                 Result 
                 31 KHz 
                 4.9 W 
                 3.7 W 
                 2.4 W 
                 3.3 W 
               
               
                 (power saved) 
                 94 KHz 
                 4.3 W 
                 3.2 W 
                 2.5 W 
                 3.1 W 
               
               
                   
               
             
          
         
       
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  shows a rectifier circuit of a prior art monitor the power source of which is controlled by an auto range mode; 
     FIG. 1 b  shows a rectifier circuit of a prior art monitor the power source of which is controlled by a full range mode; 
     FIG. 2 a  shows the circuit structure of the integrated circuit of a voltage doubler; 
     FIG. 2 b  shows the P T -I T  characteristic diagram as the integrated circuit STR80145A is conducted; 
     FIG. 3 shows the block diagram of a monitor; 
     FIG. 4 a  shows the circuit structure of the integrated circuit UC3842A used in a switchmode power supply; 
     FIG. 4 b  shows a Vcc-Icc characteristic diagram of the integrated circuit UC3842A; 
     FIG. 5 a  shows a circuit diagram of the full range control of a switchmode power supply; 
     FIG. 5 b  shows a circuit diagram of the auto range control of a switchmode power supply; and 
     FIG. 6 shows the circuit diagram of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 3, the monitor of the present invention comprises a power supply  10 , a synchronous signal processor  20 , a microprocessor  25 , a deflection circuit  30 , a deflection drive circuit  35 , a high voltage circuit  40 , a video pre-amplifier  50  and a video output amplifier  55 . The primary advantage of the present invention is to control the action of a power supply  10 . In the embodiment of the present invention, the power supply  10  is a switchmode power supply  10 . The operation theory of the synchronous signal processor  20 , the microprocessor  25 , the deflection circuit  30 , the deflection drive circuit  35 , the high voltage circuit  40 , the video pre-amplifier  50  and the video output amplifier  55  are well known by those skilled in the art, and thus not be described herein. 
     The operation of the power supply  10  of the present invention will be described in the following: 
     (1) The integrated circuit I 802  is UC3842A, used by the switchmode power supply  10  of the present embodiment, and the applied embodiment thereof is shown in FIG. 5 a.  The integrated circuit I 802  is a high performance current mode controller. 
     (2) Rectifying Circuit: The alternating current (A.C.) power supply is connected to the rectifier D 801  through the resistor R 803  for rectifying, then through a capacitor C 809 , the circuit being further divided into a start-up circuit and a driving circuit. 
     (3) Start-Lip Circuit: The capacitor C 815  is charged through a resistor R 811  by a current. When the voltage of the capacitor C 815  has increased to 16V, the capacitor C 815  is connected with the seventh pin of the integrated circuit I 802  so that the integrated circuit I 802  will be activated. Then the pulsed modulated signal (PWM) will be sent out from the sixth pin. The activating current of the integrated circuit I 802  is smaller than 1 mA, and the working current is smaller than 17 mA, referring to FIG. 4 b.  It is appreciated that after the integrated circuit I 802  has been activated, when the working current is larger than the charging current of the resistor R 811 , if the current of the diode D 810  does not feedback, then when the terminal current of the capacitor C 815  has reduced to below 10V, the integrated circuit I 802  will be idle. 
     (4) Driving Circuit: When the pulse sent out from the sixth pin of integrated circuit I 802  has transferred to a transistor Q 805  through the resistor R 815 , if the pulse is in high voltage, the transistor Q 805  will conduct, and vice versa. When transistor Q 805  is conducted, the current will return to capacitor C 809  through path →T 801 →Q 805 →R 831 , and the primary inductor L of the transformer T 801  will store the energy induced from ½·Li 2  in the coils of the windings. After the transistor Q 805  has been cut off, then the magnetic energy is converted into electric energy which will be released from the secondary terminal of the transformer so that each set of the power sources can generate voltage. 
     (5) Voltage Feedback: The voltage generated by the feedback secondary winding of the transformer T 801  is used to charge the capacitor C 815  through rectifying of a diode D 812 , filtering of a capacitor C 816  and a diode D 815  (the detail may refer to the description of the activating circuit), so that the voltage of the capacitor C 815  may stay with the range of 10V˜35V (set to be 12V) for operating the integrated circuit I 802 . Then it is connected to the voltage divider of the resistor R 825  and resistor R 826  for connecting to the second pin of the integrated circuit I 802 . When the dividing voltage is larger than 2.5V, the sixth pin of the integrated circuit I 802  will stop outputting voltage immediately. Thereby, the output voltages of all the power supply outputs are controlled to the predetermined value. 
     (6) Protection of Current Limitation: When the transistor Q 805  is activating, in order to avoid an over-current phenomenon, a resistor R 831  is connected in series with the source so that the voltage decrement of the I S ×R 831  is smaller than 1V. Otherwise, the overload of the third pin of the integrated circuit I 802  will force the integrated circuit I 802  to stop. The current I S  is the source current of the transistor Q 805 . 
     (7) Frequency Control: When the integrated circuit I 802  is working, the eighth pin will generate a reference voltage 5V used by the resistor R 817  and capacitor C 820  oscillating circuit. The oscillating frequency is determined by the resistor R 817  and the capacitor C 820 . If the resistor R 817 =4.3K and the capacitor C 820 =0.022 μF, from the specification of the integrated circuit I 802 , it is known that the frequency is approximately equal to 20 KHz. 
     (8) Error Compensation: There is an amplifier in the integrated circuit I 802 . The gain of the amplifier is controlled by a resistor R 823 , while the reaction is controlled by a capacitor C 818 . Since the feedback value of the voltage in the second pin of the integrated circuit I 802  is equal to 2.5V±Δυ′ Δυ=error value, the value of Δ υ is directly proportional to the voltage error of each set of power supply outputs. In other words, if the voltage value is larger, then the error of the output voltage for each set of power supplies of the transformer T 801  is large, and if the error is smaller, then the working voltage of the integrated circuit I 802  will become short so that the power loss of the transistor Q 805  is large and the temperature will increase. The error of the output voltage is negatively proportional to the value of the resistor R 823 , but is positively proportional to the value of the capacitor C 818 . 
     (9) Elimination of Inducing Voltage: Since the transformer T 801  is an inductive load, when the transistor Q 805  is cut off from conduction, the primary terminal of the transformer T 801  will generate a reverse electromotive force which is formed by L×di/dt, wherein L is the inductance of primary terminal of transformer T 801 , i is the induction current of transistor Q 805 ; and t is the fall time for cutting off the transistor Q 805 . This inducing voltage has a value of several volts and, thus it exceeds the breakdown voltage of Q 805  so that the transistor will be destroyed. Therefore, a snubber circuit is needed for absorbing the energy from the electromotive force formed by L×di/dt, so that the voltage will decrease to a value within the range which may be endured by the transistor. The capacitor C 814  resistor R 833  and diode D 807  form one eliminating circuit, and another elimination circuit is formed by the capacitor C 813  resistor R 813  and diode D 806 . 
     (10) Voltage Doubler: Referring to FIG. 5 a , (circuit diagram of the switchmode power supply in a full range mode) and FIG. 5 b  (circuit diagram of the switchmode power supply in an auto range mode), a voltage doubler circuit  13  is further added, which is formed by a voltage multiplying, rectifying and switching device (integrated circuit ) I 801  and a voltage biasing circuit. If the voltage of the power supply is between 88V˜132V, then the detecting circuit within the voltage multiplying, rectifying and switching device I 801  will activate and cause the Triac to conduct so that the second pin and third pin of the voltage multiplying, rectifying and switching device I 801  is shorted to become a connecting line for voltage multiplying and rectifying. If the voltage of the power supply is between 176V˜264V, then the detecting circuit within the voltage multiplying, rectifying and switching device I 801  will cut off and cause the Triac to stop so that the second pin and third pin of the voltage multiplying, rectifying and switching device I 801  are opened and only have the function of full wave rectifying. 
     The characteristic of the present invention is that the voltages of power sources are compared, then the results are outputted to drive a relay SR 803 . By the opening or closing of the contacts of the relay SR 803 , the rectifying circuit  13  may be controlled to output a voltage of one time or two times. Referring now to FIG. 6, the following will describe the voltage multiplying and rectifying circuit  13 . 
     In this embodiment, the type of integrated circuit used is LM339 in which four comparators A, B, C, and D are built. The comparators B, C, and D are connected in parallel with connecting lines for increasing the number of output ports and sink current so as to drive the relay SR 803  to activate. Thus, the comparators B, C, and D are considered as one unit (in the following call as “comparator BCD”). Also, the voltage of the first pin of the integrated circuit I 801  is defined as V 1 , and the voltage of the second pin of the integrated circuit I 801  is defined as V 2 , and so on. 
     (a) The initial condition of the input voltage of power source: 
     The power is input from P805A. When the power source switch S 801  is closed, then the current will flow through a rectifier D 801  to resistor R 811  and resistor R 812  to charge the capacitor C 815 . When the terminal voltage of the capacitor C 815  is 16V, the integrated circuit I 802  will be activated. Then, the feedback voltage of the secondary terminal of the transformer T 801  will charge the capacitor C 816  through a diode D 812 . Assuming the terminal voltage of the capacitor C 816  is 2.5V. In fact, during initially charging the capacitor C 815 , there is voltage existed on the sixth pin of the integrated circuit I 801  but the third pin (Vcc) still has no voltage. In order to avoid the voltage in the input port larger than that in the power source port to destroy the component, therefore, a diode D 804  is further added to Vcc for clamping in order to protect the component. Therefore, in the initial condition of the comparator A, since V 6 &gt;V 7 , thus V 1 =0V. When the capacitor C 816  is charged to a full voltage—12.5V ′ since V 4 =V 1 =0V, V 5 =V 7  and V 7 &gt;0V ′ the output voltage of the comparator BCD is 12.5V. Thereby the relay SR 803  will not operate. 
     (b) The input of the voltage of power source has remained in a steady condition: 
     The resistor R 808  is the forward feedback resistor of comparator A for forming a hysteresis comparing effect. Since in the initial condition, V 1 =0V, the resistor R 808  and resistor R 838  will be forced to connect in parallel (represent by R 808 //R 838 ). That is:          V   7     =     12.5                 V   ×         R   808     //     R   838           R   808     //       R   838     +     R   839                                    
     It is know from FIG.  6 : 
     
       
           R   808   =R   838   =R   839 =100 K , so that  V   7 =4.17 V . 
       
     
     
       
         
           
             
               V 
               6 
             
             = 
             
               
                 2 
               
               × 
               
                 V 
                 AC 
               
               × 
               
                 
                   R 
                   810 
                 
                 
                   
                     R 
                     810 
                   
                   + 
                   
                     R 
                     812 
                   
                   + 
                   
                     R 
                     813 
                   
                 
               
             
           
         
                 
         
             
         
      
     
     As shown in FIG. 6; it is known that R 810 =100K ′ R 812 =2.7M ′ R 813 =2M ′ if 
     (I). V AC =100V level ′ then V 6 =3.24±0.65V=3.89V˜2.49V so that V 6 &lt;V 7 , and V 1 =12.5V. Thereby, resistor R 808  is serially connected with resistor R 807  to Vcc, and similarly connected with R 839  in parallel. The voltage V 7  is increased to 8.34V so to form a delaying function (referring to the description in (c)). Meanwhile, in comparator BCD, V 4 =V 1 =12.5V ′ while V 5 =V 7 =8.34V, V 4 &gt;V 5 , causing that V 2 =0V, i.e., the relay SR 803  is conducted. Before the contacts of the relay SR 803  have been closed, since when V 2 =0V, the resistor R 809  will be enforce to short, so that the resistor R 809  and the resistor R 810  are virtually in parallel for reducing one half of the voltage V 6  in order to avoid that after the contacts of the relay SR 803  are closed, the voltage multiplying and rectifying are formed so that the voltage of V 6  is increased to two times, and thus the contacts will open and close alternatively. Thus in design, it is needed that after the relay has been conducted, the voltage V 6  is still unchanged, that is:          V   6     =       2     ×     V   AC     ×         R   809     //     R   810           R   809     //       R   810     +     R   812     +     R   813                                    
      since V AC =110V level, resistor R 809 =100K, and thus V 6 =3.89V˜2.49V ′ to still remain V 6 &lt;V, so that the relay SR 803  will conduct continuously. 
     (II). V AC =220V level, then V 6 =6.48±1.30V=7.78V˜5.18V, so that V 6 &gt;V 7  and V 1  remain unchanged, i.e. V 1 =0V. Since V 4 =V 1 =0V, while V 5  V 7 =4.17V, thus V 4 &lt;V 5 . The output of comparator BCD is 12.5V, and thus the relay SR 803  will not operate. 
     (C) The input of the voltage of power source is unstable: 
     When the voltage of power source is divided as 110V and 220V, then if the power source is abnormal due to power system fault, the voltage of power source is probably between 132V˜176V, and therefore: 
     (I). When the voltage of power source increases to 132V from 88V (but not attain 176V), two times voltage rectifying and control are used. 
     (II). When the voltage of power source decreases to 176V from 264V (but not return to 132V), one time voltage rectifying and control are used. 
     The overlapping region between 132V and 176V could be controlled by the delay characteristic of this comparator. That is, if the resistance of the resistor R 808  is large, then the voltage range of the overlapping region is also large, and vice versa. In addition, since the resistor R 809  is affected by diode D 803 , only one side of delay characteristic is affected, i. e., it is affected only to the extent that the voltage is increased from 132V. According to the measuring results shown in FIG. 6, when the voltage is increased from 88V to 194V, the system is in the state of two times rectifying control, while when the voltage is decreased from 264V to 148V, the system is in the state of one time rectifying control. 
     The contact resistance of the contacts of the relay SR 803  is very small, generally smaller than 0.1 Ω. For, example, for the TATUNG in the Table 3, in AC110V, the current consumption is between 1.503A˜1.028A, and thus power consumption I 2 R is equal to 0.226 W˜0.106 W. For the same current, the power consumption in the prior art circuit driving portion (Triac) is larger than 1.5 W˜1.0 W (referring to FIG. 2 b ). Moreover, when the input is AC110 level, the relay SR 803  will operate (specification of coil: DC12V, 400 Ω). The power consumption of the voltage biasing portion thereof is 12 2 /400=0.36V, while the power consumption of the voltage biasing portion in the prior-art circuit is 0.84 W˜2.73 W (testing values). The following table (Table 5) lists the power consumption in the two conditions: 
     
       
         
               
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 5 
               
             
             
               
                   
                   
               
               
                   
                 Input of power source 
               
             
          
           
               
                   
                 AC110 V level 
                 AC220 V level 
               
             
          
           
               
                 control circuit 
                 88 V 
                 132 V 
                 176 V 
                 264 V 
               
               
                   
               
             
          
           
               
                 Prior art 
                 Biasing 
                 0.84 W 
                 1.62 W 
                 1.13 W 
                 2.73 W 
               
               
                 (STR80145A) 
                 portion 
               
               
                   
                 Driving 
                 &gt;1.5 W 
                 &gt;1.0 W 
                 0 W 
                 0 W 
               
               
                   
                 portion 
               
               
                 Present 
                 Biasing 
                 0.36 W 
                 0.36 W 
                 0 W 
                 0 W 
               
               
                 embodiment 
                 portion 
               
               
                 (LM339 + 
                 Driving 
                 &lt;0.226 W 
                 &lt;0.106 W 
                 0 W 
                 0 W 
               
               
                 Relay) 
                 portion 
               
               
                 Power saved 
                   
                 &gt;1.754 W 
                 &gt;2.154 W 
                 1.13 W 
                 2.73 W 
               
               
                 (results) 
               
               
                   
               
             
          
         
       
     
     In summary, it is to be appreciated that from the measuring value of Table 4 or from the analyzing value of Table 5, that the automatic switching device for the power source input range of the present invention saves more power than that in the prior art circuit.