Abstract:
A surge protector for portable personal computers, or notebooks, of the shunting type, employs two differently rated metal oxide varistors in a manner enabling operation with several differently rated AC power services. The surge protector is designed to provide an optimum effective clamping voltage with a low let-through voltage.

Description:
CROSS-REFERENCE TO RELATED ACTIONS  
       [0001]    This application is a continuation of National filing of U.S. application Ser. No. 09/601,228, filed Sep. 15, 2000, entitled Universal Surge Protector for Notebook Computers. 
     
    
     
       FIELD  
         [0002]    The inventions presented herein relate to method and apparatus for diverting of harmful electrical voltage and current disturbances on alternating current (“AC”) power lines supplying power to portable personal computers, hereinafter referred to as “notebook computers,” a “notebook” or “notebooks.” 
         BACKGROUND  
         [0003]    Generally, manufacturers and/or re-sellers of notebook computers powered by a 16 volt direct current (“dc”) battery, for example, make available to their customers a power adapter to produce a 16 volt dc output from different rated alternating current (“AC”) power services available from public or private electric power utility companies. For example, a power adapter generates the 16 volt dc voltage to run a notebook from a 120 volt, 60 cycles per second (“cps”) power service commonly available throughout the United States at a wall mounted outlet in most homes and places of business. In addition, the power adapter simultaneously re-charges the notebook&#39;s battery. The power adapters also produce the required 16 volt dc voltage from AC power sources used in other countries of the world including: A 100 VAC, 50 cps, rated service used in Japan; and a 240 volt 50 cps rated service used in Europe, Asia, the Middle East, South America and Africa.  
           [0004]    It is known among manufacturers of notebooks to locate a power adapter inside the housing of a notebook. For brevity the following discussion is limited to power adapters which are external to the notebook housing. The housing for an external power adapter is generally rectangular in shape and about the size of a audio cassette tape. Characteristically power adapters include both AC and dc power cords. The dc power cord is anchored at one end to the power adapter and has a female dc plug at a free end for mating with a male dc receptacle mounted in the notebook housing. The AC power cord is a removable, specialized, electrical extension cord. The AC power cord has a two wire female AC plug at one end for mating with a male AC receptacle mounted in the housing of the power adapter and a two wire male AC plug at its other end for coupling to an AC power service at a standard female AC receptacle, wall mounted, for example.  
           [0005]    Detachable AC power cords are available from or through notebook manufacturers. These AC power cords include the required male AC plug needed to fit the unique configuration of a female AC power receptacle of the AC power utility of a given country or region of the world. Consequently, an international traveler is advised to bring as many AC power cords having country specific AC plugs as required for mating with the unique mating connector of each power utility encountered on a multi-country trip.  
           [0006]    An additional consideration for notebook computer owners is an electrical surge protector for notebooks to protect their notebooks from harmful electrical disturbances such as voltage and current transients which can damage a notebook. A damaged notebook normally means the owner looses the use of the notebook for getting productive work done. Harmful electrical disturbances occur on AC power lines for several well-known reasons including switching ON or OFF an electric motor or a circuit breaker carrying large electrical currents. Lightening strikes of AC power lines during electrical storms are another well-known cause for harmful electrical disturbances appearing on AC power lines.  
           [0007]    Protection of notebooks from the foregoing and other harmful electrical disturbances is a concern to users of notebook computers regardless of the country or utility district in which a notebook is operated. In the United States. Underwriters Laboratories (“UL”), an electrical product safety standard setting and testing organization, provides criteria for evaluating the performance of surge protectors when coupled to a 120 VAC rated AC power service. Specifically the UL 1449 standard sets forth: (1) a let-through voltage criteria and (2) an effective clamping voltage criteria. Each test criteria is useful for evaluating the performance of surge protector equipment intended to guard notebook computers from harmful electrical AC line disturbances.  
           [0008]    A main component of prior art surge protectors for use with notebooks coupled to a 120 volt rated AC power service is a metal oxide varistor (“MOV”) or other voltage and current diverting and absorbing semiconductor devices, such as, transorbs and sidactors. A MOV is the diverting and absorbing semiconductor device used in the majority of prior art surge protectors to protect notebooks from harmful electrical disturbances. A typical prior art surge protector employs a single MOV in combination with a fuse to protect a notebook from harmful electrical disturbances.  
           [0009]    Therefore, a first aspect of the present surge protector is to improve the performance of surge protectors for use with notebook computers by designing them to achieve an effective clamping voltage of 330 volt, while coupled to an AC power service rated from about 100 to about 120 volts, which is the best clamping voltage rating under the UL 1449 standard.  
           [0010]    Accordingly an important aspect of the present surge protector is to improve the level of protection for notebooks from harmful electrical disturbances over that achieved by prior art surge protectors while coupled to AC power services rated from about 100 to about 120 VAC which substantially achieves the UL 1449 standard 330 volt best clamping voltage and a low let-through voltage.  
           [0011]    Another significant aspect of the present surge protector is the universal ability to protect a notebook from harmful electrical disturbances appearing on an AC power line in nearly every developed country and in many undeveloped countries, of the world.  
           [0012]    Still another novel aspect of the present surge protector is that it employs two, differently rated, MOVs for protecting a notebook wherein a first, higher rated MOV protects a notebook while the surge protector is coupled to a high rated 240 VAC power service and a second, lower rated MOV protects the notebook while the surge protector is coupled to a lower rated AC power service of from about 100 to about 120 VAC.  
           [0013]    Yet another aspect of this surge protector is that it includes a switch comprising a switching circuit which automatically connects a lower rated MOV across an AC power line when the AC power line is coupled to a lower rated AC power service and automatically disconnects the lower rated MOV from the AC power line when the AC power line is coupled to a higher voltage service leaving the higher rated MOV to protect a load, such as a notebook.  
         SUMMARY  
         [0014]    The present surge protector overcomes the limitations of existing surge protectors used with notebooks to the benefit of international travelers who carry notebooks along with them into countries having different rated AC power utilities. As pointed out above, an important aspect of the present surge protector is the ability to use a single surge protector unit to protect a notebook in multiple countries each having differently rated AC power services or within one country having two or more differently rated AC power services. Specifically the present surge protector is operable to protect notebooks when they are coupled to either a high rated AC voltage source. such as 240 VAC. 50 or 60 cps. or a low rated AC voltage source. such as a I 00 or 120 VAC. 50 or 60 cps AC power service. The surge protector offers protection for notebooks while coupled to AC power services rated from about 70 VAC to about 290 VAC.  
           [0015]    The ability to protect notebooks when coupled to variously rated AC power sources is achieved by organizing the surge protector into two parts or sections. A first section of the surge protector includes a first MOV for protecting a notebook from electrical disturbances appearing on an AC power line coupled to a 240 volt AC power service. A second section, coupled in parallel with the first section, includes a second MOV for protecting a notebook from electrical disturbances appearing on an AC power line coupled to an AC power service rated from 100 to 120 VAC. Consequently, the single surge protector described herein is useable, for example, successively in Japan, the United States and Canada which offer low AC power services rated at 100 and 120 VAC, respectively, and in various European, Asian. African and South American countries which offer high AC power services rated at 240 VAC.  
           [0016]    Both sections of the present surge protector are automatically selected to protect a power adapter and associated notebook when the AC power line is coupled to a low rated AC power source, for example, a 120 VAC rated AC power service. Only the first section of the surge protector is selected to protect the power adapter and notebook when the AC power line is coupled to a high rated AC power service. for example, a 240 VAC rated power service. A switch within the second section of the surge protector includes an electrical-mechanical relay which automatically connects the second MOV across an AC power line when the line is coupled to a low rated AC power service and automatically disconnects the MOV from the AC power line when the line is coupled to a high rated AC power service.  
           [0017]    The two MOVs relay and other electrical components of the surge protector are mounted on a printed circuit board (“PCB”) and are coupled to one another by conductive tracings on the PCB. The particulars of the surge protector circuits are given below.  
           [0018]    The surge protector disclosed herein is contained in a small housing large enough to hold the above-described PCB and all the components carried by the PCB further including a male AC receptacle for mating with a female AC plug at one end of an AC power cord. Under normal operating conditions the housing is not noticeably warm to the touch when the surge protector is coupled to AC power services rated form 100 to 240 VAC. 
       
    
    
     THE DRAWINGS  
       [0019]    The foregoing and other aspects of the disclosed surge protector will be apparent from a reading of the specification with reference to the drawings which are:  
         [0020]    [0020]FIG. 1 is a schematic diagram of a portable personal computer, or notebook, showing the disclosed AC to dc voltage converter system, including a power adapter and a surge protector, ready to be coupled to a notebook and an AC power cord ready to be coupled to a wall mounted, female AC receptacle, representative of an AC power service.  
         [0021]    [0021]FIG. 2 is an electrical circuit of a two part, or section, universal surge protector for protecting a notebook from electrical disturbances associated with power lines coupled to differently rated AC power services.  
         [0022]    [0022]FIG. 3 is a circuit diagram of a switching circuit comprising the switch used in the second section of the two part surge protector of FIGS. 1 and 2 to connect and disconnect the second MOV to an AC power line. 
     
    
     DETAILED DESCRIPTION  
       [0023]    With reference to FIG. 1, the universal power surge protector  11 , the power adapter  12  and the AC power cord  13  comprise an AC to dc voltage converter system  14  for supplying a dc voltage to notebook computer  16  generated from an AC power source represented by the wall mounted female receptacle  17 . The notebook  16  is representative of present day notebooks available from several manufacturers for example: IBM®, Compaq®, Dells®, Hewlett-Packard® and Apples® Computer and many others. Certain currently marketed notebooks are designed for portable operation from a dc 16 volt battery, for example, stored inside (and outside) the computer housing or are designed for a tethered, stationary operation from a dc 16 volt output, for example, generated by a power adapter from an AC power service available, by means of the proper AC power cord, at the wall mounted female receptacle  17 .  
         [0024]    A power adapter, typically includes a switching power supply that produces a fixed dc voltage output, 16 volts, for example, from several differently rated AC power services including those rated at 100, 120, 208 and 240 VAC, at 50 or 60 cps. The operation and design of switching power supplies used by power adapters intended for use with notebooks are well understood in the art. Detailed information on the design and operation of switching power supplies is available in data sheets and other product information obtainable from the above-identified notebook manufacturers or their re-sellers, the disclosures of which are hereby incorporated by reference.  
         [0025]    Power adapter  12  includes a dc output cord  18  permanently connected at one end to a printed circuit board inside the power adapter housing and connected at a free end to a dc female plug  19  for mating with a recessed male dc receptacle  21  mounted within the housing of the notebook. A recessed two pin AC male receptacle  22  is mounted in the power adapter housing for coupling directly to an AC power line via an AC power cord  13  or through the surge protector  11  and its AC power cord  23 .  
         [0026]    The AC power cord  23  of the surge protector includes a female AC plug  24  at one end for mating with the male AC receptacle  22  of the power adapter. The other end of cord  23  is coupled to a printed circuit board (“PCB”) within the surge protector housing. The surge protector also includes a two pin male AC receptacle  26  mounted within its housing. AC power cord  13  includes an AC female plug  27  at one end for mating with either the male AC receptacle  26  of the surge protector or the male AC receptacle  22  of the power adapter  12 . The male AC plug  28  at the other end of cord  13  is configured to mate with a United States standard female AC power line receptacle  17 , shown mounted in a wall of a room within an office building or home for example. Of course, a power cord  13  must include an appropriately configured male plug  28  for mating with the specific standard design of an AC power line receptacle employed in each country, or AC power service region, within which the user intends to use a notebook computer.  
         [0027]    It should be apparent that female AC receptacles  22  and  26  mounted in the housings of the power adapter and surge protector respectively, are identical and that the female AC plug  24  at the free end of cord  23  is identical to female AC plug  27  at one end of AC power cord  13 . Consequently, a power adapter can be coupled directly to an AC power source by power cord  13  when a surge protector is not available to protect a notebook from harmful electrical disturbances.  
         [0028]    As stated above the surge protector includes the two sections shown in FIG. 2. The first section of the surge protector includes a slow acting fuse  31  and a first high voltage MOV  32  coupled in series and in parallel, respectively with the line  33  and neutral  34  sides of an AC power line. Slow acting fuse  31  protects the notebook the power adapter, and the surge protector, in particular MOV  32 , from a sustained over current condition on AC power line  33  created, for example, by a short circuit occurring at any of the foregoing three devices. Fuse  31  protects the three devices by changing from an electrical conductor to an open circuit to disconnect and, thereby electrically isolate the notebook, power adapter and the surge protector from the AC power line under a short circuit condition existing in one of the three devices.  
         [0029]    MOV  32  protects the power adapter and notebook against electrical voltage disturbances by diverting disturbances from the devices and by absorbing energy associated with the disturbances that, for example, exceed the maximum allowable voltage rating of MOV  32 , which is 300 VAC. Absent large AC line disturbances, the impedance of MOV  32  is in the megohm range which effectively appears as an open circuit between the line  33  and neutral  34  sides of an AC power line coupled to a 240 VAC rated AC power service. MOV  32  switches to low impedance levels in response to large voltage disturbances appearing across the line  33  and neutral  34  sides of the AC power line. At the low impedance levels, MOV  32  diverts the electrical disturbances away from a notebook  16  and power adapter  12  and absorbs a portion of the energy associated with the disturbance.  
         [0030]    The second section of surge protector  11  includes thermal fuse  36  and a second, lower rated MOV  41 . Fuse  36  is selected for specifications which are compatible with MOV  41  in order to disconnect the surge protector, power adapter and notebook from the AC power line in the event MOV  41  goes into a thermal run-a-way condition in response to a significant sustained electrical disturbance.  
         [0031]    The second section of the surge protector also includes a switching circuit  37  for adding or connecting and removing or disconnecting MOV  41  across the line  33  and neutral  34  sides of the AC power line. The switching circuit includes an electro-mechanical relay  38  which has a coil and a moveable conductive arm. The moveable arm is in an open circuit position when the relay coil is not energized and is in a closed circuit position when the coil is energized. Consequently, MOV  41  is coupled across the line  33  and neutral  34  sides of an AC power line when the relay coil of relay  38  is energized, and is disconnected from the AC power line when the relay coil of relay  38  is not energized. The switching circuit  37  energizes the relay coil to couple MOV  41  across the AC power line while the AC power line is coupled to a 100 to 120 VAC rated power service. The switching circuit prevents, that is, inhibits, the energizing of the relay coil of relay  38  while the AC power line is coupled to a 240 VAC rated AC power service.  
         [0032]    Turning to FIG. 3, MOV  41  is coupled between the line  33  and neutral  34  sides of an AC power line when the moveable contact switch arm  39  of relay  38  is at the closed circuit arm position represented by solid line  39 . The relay arm is at the closed circuit position while the coil  40  of relay  38  is energized from a 100 to a 120 VAC rated AC power service. The moveable contact arm moves to and stays at the closed circuit position  39  while transistor  44  is turned ON, enabling current to flow through relay coil  40 . While transistor  44  is OFF, no current flows through relay coil  40  and the relay arm moves to its open circuit position represented by relay arm  39  A, shown with a dashed line. With arm  39  at the open circuit position MOV  41  is disconnected from across the AC power line.  
         [0033]    Relay coil  40  is automatically energized by transistor  44  when the surge protect is coupled to an AC power service rated from 100 to 120 VAC. Transistor  44  is prevented from being turned ON by transistor  43  when the surge protector is coupled to an AC rated power service rated at 240 VAC.  
         [0034]    The switching of transistor  44  ON and OFF occurs as follows. The collector electrodes of transistors  43  and  44  are coupled to the dc voltage on the first dc bus or rail  42 . The rail voltage is, substantially a steady state voltage to which capacitor C 1  is charged by diode  54 , a half wave voltage rectifier coupled between the line  33  and neutral  34  sides of the AC power line by resistors R 1  and R 2  and capacitor C 1 . The voltage on rail  42  is coupled to the collector of transistor  44  through relay coil  40  and is coupled to the collector of transistor  43  through resistor R 6 . The emitter electrodes of transistors  43  and  44  are at a voltage potential slightly above that of the neutral side  34  of the AC power line to which the emitter of both transistors are coupled through resistor R 7 .  
         [0035]    The base electrodes of transistors  43  and  44  are coupled to a second dc rail  46 . The voltage of rail  46  is substantially, the steady state voltage to which capacitor C 2  is charged by half wave voltage rectifier diode  53  coupled between the line  33  and neutral  34  sides of the AC power line, by resistor R 3  and capacitor C 2  and by resistors R 3 , R 4 , R 5 , R 8  and R 9 . Resistors R 4  and R 5  establish a fixed bias to the cathode of zener diode  49  and resistors R 7  and R 8  establish a fixed bias to the cathode of zener diode  51 .  
         [0036]    The automatic switch or switching circuit  37  operates as follows when coupled to a 100 to 120 VAC rated power service: at 100 or 120 VAC, the dc potential on rail  46  is not adequate to bias the base of transistor  43  through zener diode  49  to turn ON transistor  43 . However, the dc potential on rail  46  is adequate to bias the base of transistor  44  through zener diode  51  to turn transistor  44  ON. With transistor  44  ON, current flows through the relay coil  40  causing the relay arm  39  to move from its normally open circuit position represented by arm  39 A to the closed circuit position represented by arm  39 . Upon arm  39  moving to its closed circuit position. MOV  41  is connected across the line  33  and neutral  34  sides of the AC power line to protect the load  35  from harmful electrical disturbances as long as the AC power line is coupled to a 100 to 120 VAC rated AC power service. Typically, load  35  comprises a power adapter  12  coupled to a notebook  16  or another load type.  
         [0037]    Energizing relay coil  40  to connect MOV  41  across the load  35  when the surge protector is coupled to a 100 to 120 VAC rated AC power service is preferred to energizing coil  40  when the surge protector is coupled to a 240 VAC rated power service. The reason is that the 240 VAC approach results in an inefficient use of energy and makes it more difficult to dissipate heat generated in the electrical components of the surge protector.  
         [0038]    The automatic switching circuit or switch  37  operates as follows when coupled to a 240 VAC rated AC power service: the dc potential on rail  46  is adequate to bias the base electrodes of both transistors  43  and  44  through the above noted resistors and zener diodes to turn ON both of the transistors. However, transistor  43  is turned ON first in time and, once ON, prevents or disables transistor  44  from turning ON. Transistor  43  is turned ON before transistor  44  because the time required to charge capacitor C 3  to the voltage level at which zener diode  51  conducts, turning ON transistor  44 , is longer than the time required for zener diode  49  to conduct and bias ON transistor  43 . With transistor  43  turned ON and transistor  44  OFF, the potential at the collector of transistor  43  is only slightly above that of neutral  34 . This low voltage is coupled from the collector of transistor  43  through diode  52  and resistor R 10  to the cathode of zener diode  51  preventing the zener diode from conducting and turning transistor  44  ON. With transistor  43  ON transistor  44  stays OFF and no current flows through relax coil  40  causing the relay arm to remain at the open circuit position represented by relay arm  39  A. Consequently MOV  41  is not connected across the line  33  and neutral sides  34  of the AC power line. At this time MOV  32  in the first section of the surge protector protects the notebook by diverting harmful electrical disturbances from a notebook and absorbing portions of the energy of the disturbance.  
         [0039]    In one embodiment resistor R 2  and capacitor C 1  are implemented in a three level ladder network with the capacitance of capacitor C 1  comprising the combined capacitance of three series connected capacitors. The resistance of resistor R 2  is the combined resistance of three series connected resistors. Each end of the three resistors and three capacitors are electrically coupled together to form the ladder network. The ladder network enables the voltage drop across each of the capacitors to be evenly distributed making the voltage on rail  42  more stable.  
         [0040]    Also, in the foregoing embodiment, resistors R 1 , R 3  and R 6  are each implemented as three separate series connected resistors. The use of multiple series resistors in place of one enables I 2 R producing heat created in the resistors while coupled to an AC power service to be dissipated over a larger resistor surface area and over a wider area on the PCB carrying the resistor and other circuit components of surge protector  12 .  
         [0041]    The division of the specific identified resistors of FIG. 3 into separate resistors increases the total resistance surface area for dissipating heat. Locating the multiple resistors at spaced locations over the surface of the PCB avoids hot spots and helps lower the temperature on the outside of the surge protector housing. The outside surface temperature of the surge protector housing is near that of the ambient temperature when the surge protector is coupled form a AC power service rated from about 100 to about 240 VAC.  
         [0042]    The surge protector, while coupled to a 120 VAC rated power service achieved an effective clamping voltage of 330 volts which is the UL 1449 standard best rating when tested with a 6000 V. 500 amp, 100 kHz. Catagory A combined surge, defined by American National Standards Institute (“ANSI”) procedure C62.41. In addition the present surge protector achieved a let-through voltage of 161 VAC when subjected to a 6000 V. 200 amp 100 kHz. Category A ringwave test. The let-through voltage is the difference between the clamping voltage and the standard peak voltage of 169 for a 120 VAC rated power service.  
         [0043]    The values of the resistors and capacitors and the identity of the transistors and the MOVs employed in surge protector  12  are listed in TABLE 1 below. Light emitting diode (“LED”)  60  shown in FIG. 3 emits a green light whenever the surge protector is coupled to an AC power service to indicate that it is available for protecting against harmful disturbances on the AC power line.  
                           TABLE A                                   Component   Type/Rating                           FUSE 31   MINI, UL. CA               4 A/250 V           FUSE 36   Thermal               4 A/100° C.               520-0005           MOV 32   ERZV14D471               125 J, 300 Vrms           MOV 41   ERZV20D201               100 J, 130 Vrms           Diodes           52, 53 and 54   IA, 1000 V, SMA           Zener   6.8 V, 225 MW           Diode 49   SMD           Zener           Diode 51   9.1 V, 225 W               SMD           Capacitor C1   AL, ELECT, 85 c           (a)   10 uf, 100 V           (b)   10 uf, 100 V           (c)   10 uf, 100 V           Capacitor C2   10 uf, 100 V               AL, ELECT, 85 c           Capacitor C3   22 uf, 25 V               C 6 − 3 × 4 − 5           Relay 38   48 Vdc Coil               120 V/10 A           Transistor 43   MMBTA42LTI               Motorola           Transistor 44   FMMT458               Zetex           LED 60   Green               R/A PCMNT           R1   Resistor           a   1.2 kΩ 1 W, 5% RC2512           b   ″           c   ″               Σ = 3.6 kΩ           R2           a   470 kΩ, {fraction (1/8 )}W, 5%, RC1206           b   ″           c   ″               Σ = 1.41 MΩ           R3           a   10 kΩ, 5%, 1W, RAD, RES, MOF           b   ″           c   ″               Σ = 30 kΩ           R4   30 kΩ, {fraction (1/4 )}W, 5%               RC2010           R5   7.5 kΩ, {fraction (1/8 )}W, 5%           R6           a   56 kΩ, 1 W, 5%, RC2512           b   ″           c   ″           R7   56 Ω, {fraction (1/8 )}W, 5%               RC 1206           R8   110 kΩ, {fraction (1/8 )}W, 5%               RC 1206           R9   68 kΩ, {fraction (1/8 )}W, 5%               RC1206           R10   2.7 kΩ, {fraction (1/8 )}W, 5%               RC1206