Abstract:
A power converter capable of receiving either an AC input voltage or a DC input voltage and generating a programmable DC output voltage. The converter comprises a first circuit that converts an AC input voltage to a predetermined DC first output voltage, and a second circuit that converts a DC input voltage to a predetermined second DC output voltage. The converter also comprise a third circuit which is adapted to receive the first and second DC voltages from first and second circuits to generate a selectable output DC voltage. In selected embodiments, the first and second DC output voltages provided by the first and second circuits, respectively, are generally the same value and are coupled to a common node that feeds the input terminal of the third circuit. Moreover, the third circuit is adapted to provide a selectable output DC voltage which may be set higher or lower than its DC input voltage. The third circuit may also be adapted to couple a set of removable programming keys that provide for a different associated DC output voltage. The programming key comprises a resistor, which may provide for a variety of functions, such as current-limiting, over-voltage protection, output voltage programming, and wrong-tip circuit protection.

Description:
[0001]    This invention is related to and claims priority under 35 U.S.C. §119(e)(1) from the following co-pending U.S. Provisional Patent Application: serial application ______ by Charles Lord, et al., entitled “Dual Input AC/DC to Programmable DC Output Converter” and filed on Oct. 31, 2001. The aforementioned patent application is hereby incorporated by reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention generally relates to the field of power converters, and more particularly to a power converter adapted to provide a selectively programmable DC voltage output based on either an AC or DC voltage input.  
         BACKGROUND OF THE INVENTION  
         [0003]    As the use of mobile electronic products, such as PC notebooks, PDAs, Cellular Telephones and the like, continues to increase, the need for low costs, compact power supplies to power and recharge these products, also, continues to increase. Today, in order to meet their customer&#39;s mobile power supply needs, most manufacturers included mobile power adapters along with their mobile products.  
           [0004]    Today&#39;s power adapters are typically AC-to-DC, or DC-to-DC power converters which are configured to either step-up or step-down the DC voltage input delivered to the mobile device. With AC-to-DC adapters, for example, users can power most mobile devices by simply plugging the adapter into a simple AC wall outlet found in most homes or offices. Similarly, when only DC input power is available, such as in an automobile or airplane, users can still power their mobile devices by simply using a DC-to-DC converter adapter. Often, these adapters are specifically designed and tailored to provide a regulated DC output voltage, which range from between 5VDC to 30VDC depending on the kind of mobile device being powered.  
           [0005]    Although these power adapters conveniently provide direct power and recharging capabilities, users are often required to carry separate adapters to provide power to each individual mobile device. This often means that users have to carry multiple adapters: one for an AC input power source, and another for a DC input power source. Thus, by carrying more than one device at a time, mobile device users are often forced to carry extra bulk in the form of two distinct power supplies to power two distinct mobile devices.  
           [0006]    Accordingly, there exists a need for a power conversion device that resolves the system management problems associated with carrying all of the different power supply components necessary to power a wide variety of mobile or portable devices. Moreover, such a device would advantageously encompass serving the power supply needs of all these different mobile devices, while supplying a steady, regulated DC power output in response to either a changing AC or DC input voltage.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention achieves technical advantages as a power converter capable of supplying a DC output from either an AC or DC input covering a wide range of voltage and current combinations, through external programmability, and suitable for a variety of mobile or stationary product offerings. Such a invention resolves the system management problems associated with carrying all of the different interface components necessary to power a wide variety of mobile or portable products.  
           [0008]    In one embodiment, the invention is generally a power converter capable of receiving either an AC input voltage or DC input voltage and generating a programmable DC output voltage. The converter comprises a first circuit that converts an AC input voltage to a predetermined DC first output voltage, and a second circuit that converts a DC input voltage to a predetermined second DC output voltage. The converter also comprise a third circuit which is adapted to receive the first and second DC voltages from first and second circuits so as to generate a selectable output DC voltage.  
           [0009]    In selected embodiments, the first and second DC output voltages provided by the first and second circuits, respectively, are generally the same value and are coupled to a common node that feeds the input terminal of the third circuit. Moreover, the third circuit is adapted to provide a selectable output DC voltage which may be set higher or lower than its DC input voltage. The third circuit may also be adapted to couple a set of removable programming keys that provide for a different associated DC output voltage. The programming key comprises a resistor, which may provide for a variety of functions, such as current-limiting, over-voltage protection, output voltage programming, and wrong-tip circuit protection.  
           [0010]    Accordingly, the invention advantageously provides an inventive embodiment that allows mobile product users to supply power or recharging capabilities to a variety of mobile products with a single, low cost, compact device. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    Advantages of the invention and the specific embodiments will be understood by those of ordinary skill in the art by reference to the following detailed description of preferred embodiments taken in conjunction with the drawings, in which:  
         [0012]    [0012]FIG. 1 shows a block diagram of a dual input AC/DC power converter in accordance with the present invention;  
         [0013]    [0013]FIG. 2 is a schematic overview of the power converter circuit as depicted in FIG. 1 in accordance with the present invention; and  
         [0014]    [0014]FIG. 3 shows a schematic diagram of the power converter having an AC converter circuit, an up-converter circuit and a down-converter circuit in accordance with an exemplary embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    The numerous innovative teachings of the present applications will be described with particular reference to the presently preferred exemplary embodiments. However, it should be understood that this class of embodiments provides only a few examples of the many advantageous uses and innovative teachings herein. In general, statements made in the specification of the present application do not necessarily delimit any of the various claimed inventions. Moreover, some statements may apply to some inventive features, but not to others.  
         [0016]    [0016]FIG. 1 shows a block diagram of a dual input AC/DC power converter  10  in accordance with the present invention. The power converter  10  comprises a power converter circuit  20  having input terminals  12  and  14  which are adapted to receive an AC input voltage and a DC input voltage, respectively. The power converter circuit  20  also includes an output terminal  16  adapted to provide an programmable DC output voltage which is received at connector pin  18 . The power converter  20  is seen housed in housing  13  which has a predetermined slot for receiving a set of function key  15 , comprising a set of resistors, adapted to interface circuits  26 ,  28 ,  32 , and  34 , as will be discussed shortly in regards to FIG. 3.  
         [0017]    Referring now to FIG. 2, there is illustrated a schematic overview of the power converter  20  circuit as depicted in FIG. 1 in accordance with the present invention. The converter circuit  20  is seen having an AC input portion  36  and a DC input portion  40  providing outputs which feed into a common node  2 . The converter circuit  20  is also seen to have a programmable DC output portion  38  coupled to node  2  and adapted to provide a regulated DC voltage output.  
         [0018]    Referring now to FIG. 3, there is shown a schematic diagram of an dual input AC/DC power converter  10  having an AC input circuit  21 , an up-converter circuit  22  and a down-converter circuit  24  in accordance with an exemplary embodiment of the present invention. The AC input circuit is shown at  21  and is configured in as a fly-back converter. The AC voltage input is fused by F 1  and has EMI suppression with C 1 , L 1 , C 2 , C 8 . The AC voltage is then fill wave rectified through D 1  and C 3 -C 5 . This higher DC voltage (367 v max) is fed to the main controller chip U 1 . This chip is designed for wide mains applications and can be tied directly to the DC rail. The frequency of operation is preset by the manufacturer depending on which version is called out; for example the frequency is typically set at 100 khz. The clock on the chip together with the error amplifier, then modifies the output drive duty cycle to power field-effect transistors (FETs) Q 2  and Q 5 . These FETs then switch the main power transformer T 1  to deliver pulse width energy through output rectifier D 5  and also to the output filter capacitors C 6 , C 7  and C 10 . I 2  and C 9  provide additional filtering to reduce ripple and noise at the output.  
         [0019]    An auxiliary winding is used on the main transformer T 1  to provide for a lower VC to the chip than the mains and a reasonable voltage for Q 3  and Q 4  to operate from. These FETs provide for faster turn on and turn off times for the gates of the power FETs Q 3  and Q 4 . Q 2  is the “on component” switch for the power FETs and Q 5  is the “off component” switch that drives the FETs to a hard ground necessary for the parasitic capacitance that resides at these gates. The diodes D 3 , D 4  and C 12  completes the bootstrap auxiliary supply. This auxiliary supply also provides a method where if the power converter circuit  20  had a certain failure mode, the power converter  10  would shut down through SCR Q 1  and the ac input would have to be recycled to allow the power converter  10  to come up again. If the fault condition still existed, then the power converter  10  would not turn on. This is often used in off-line switchers.  
         [0020]    Input and output isolation is provided by T 1  transformer and its secondary. Further isolation is given through the opto-coupler U 4 . The converter&#39;s circuit  20  feedback path to provide for a regulated output goes through this device and is referenced against a shunt regulator U 3  on the secondary side. It is the sole purpose of AC input circuit  21  is to provide isolation from the ac line and also to produce a regulated DC output voltage of approximately 28V, which is subsequently feed to a common node  2 , as will also be discussed shortly.  
         [0021]    In operation, the AC circuit  21  is by no means a programmable supply nor does it contain any “smart” circuitry other than to provide a fixed regulated DC output. Common node  2  is the node at which the AC circuit&#39;s output (TP 3 ) comes into the output of the up-converter circuit  22 , which is also the same as the input to the down-converter circuit  24 . Moreover, this is the main node that allows the down-converter to operate off of either input to the power converter circuit  20  as a whole. It should be understood that depending on which country the invention is used in, there will be different AC plugs available that will allow the supply to interface with their outlets.  
         [0022]    In one preferred embodiment, the up-converter circuit  22  is configured in a standard “boost” topology and is adapted to receive a DC input voltage ranging between 11-16 vdc, though a particular voltage range is not to be inferred. This voltage range, however, is common in most air and automobile environments. The DC voltage itself is fed into an EMI filter consisting of C 1 , I 2 , C 2 -C 4  and then into the controller U 3  and the up inductor  13 . The frequency of operation was chosen to be around 80 khz for U 3 . This is externally set by R 33  and C 23 . Output and duty cycle is determined by U 3  and drives Q 8  and Q 10  eventually into power FETs Q 6  and Q 7 . Feedback and voltage output set point is determined by R 20  and R 30  into pin  1  of U 3  and is referenced against the 5.1 v on board reference divided down by R 18  and R 25  into the non-inverting input error amplifier of U 3 . This completes most of the control loop except for some loop stability components R 39 , C 24  and C 25 . L 3  is then charged by FETs Q 6  and Q 7  in the on mode and  13  is then discharged through D 3  into filter caps C 5 - 6 . Moreover, in a standard boost operation, R 38  offers a bleeder resistance to ground in the event Q 6 - 7  are unable to receive a signal from its drivers Q 8 - 9 , so as to prevent unwanted turn on of these FETs. D 9  also prevents an over-voltage spike entering the gates of Q 6 - 7  and damaging the gate to source junction. C 11  and C 12  and R 12  and R 14  are adapted for wave shaping and function as snubbers due to leakage inductance of  13 . Q 11  forms a hard off to ground due to the parasitic capacitance of the gates on Q 6 - 7 .  
         [0023]    It should be understood that the up-converter circuit  22 , as shown, does not have any additional circuitry other than to convert from an 11-16V input to approximately 28VDC and is not programmable. U 3  has a feature that allows another controller to be frequency slaved to it as is done in this supply with the down converter side. Advantageously, this allows for easier EMI suppression when one operating frequency is filtered versus two. In addition, the output of the up-converter circuit  22  is preferably the same node  2  as the output of the AC/DC supply TP 17 .  
         [0024]    As for the down-converter circuit  24 , it is configured to receive, from any source, an input voltage of around 28VDC. More importantly, the down-converter circuit  24  need not recognize an AC input voltage or DC input voltage. As such, no voltage switch-over is required, which advantageously makes this function transparent to the down-converter  24 . Nevertheless, when an ac input voltage is provided to the AC input circuit  21 , the up-converter circuit  22  is not switching and is only running its clock for U 2  its slave.  
         [0025]    Still referring to FIG. 3, there is shown a down-converter circuit  24  configured in a standard “buck” topology. Here, the down-converter circuit  24  receives a DC input voltage at node  2 , which is the same node at which the AC input circuit  21  and the up-converter circuit  22  provide their DC voltage outputs. U 2  is the same part as the controller on the up side. The operating frequency is determined by and is slaved to U 3  of the up side. This supply does not require input EMI filtering for this is taken care of by up stream filtering done on both sides of the dual input regulators as discussed earlier. Output drive signals from U 2  develops through pre-drivers Q 4 - 5  and Q 2  to the P-channel power FETs Q 1 , 3 . The FETs on time and duty cycle charge power inductor  11  and then the catch diode D 2  supplies the rest of the cycle during Q 1 , 3  off time for normal “buck” operation. The 28V input was chosen to be slightly above the highest output required by the load application of 24V to keep the down-converter circuit  24  in operation V IN &gt;V OUT .  
         [0026]    In a selected embodiment, the power converter  10  has a small plug-in module, comprising key  15 , that contain four resistors each internally housed and are plugged into the power converter  10  so as to change the power converter&#39;s output voltage to conform to a particular load requirement. Load requirements often change depending on the application, such as in laptop computer where different laptops have different voltage operating requirements. With the present invention, these resistors, individually, will program the output voltage, the current limit, the over-voltage protection, and the tip-matching program, as will be discussed shortly.  
         [0027]    Still referring to FIG. 3, there is shown at  26  an output voltage programming circuit. Voltage programming is established by R 34  which comprises a resistor module. This resistor sets a voltage divider into the non-inverting input pin  2  of U 2  which is referenced to the output voltage being fed back through r 1  into the inverting input of U 2  at pin  1 , so as to achieve the desired duty cycle. Components C 13 , C 16  and R 17  are included to provide compensation for the error amplifier within U 2  to keep the control loop stable over all conditions of line and load values.  
         [0028]    Still referring to FIG. 3, there is shown at  28  a current limiting circuit. A current limiting function may be programmed by setting removable module R 37  to ground. Further, U 1   b  is seen to have its input referenced around a divider coming from the onboard reference of U 2  and divided down through R 29  and R 32 . Q 9  and D 7  allows for a constant current setup to operate regardless of output voltage level. R 3  and R 5  are the current sense resistors to provide the differential voltage required across the inputs of U 1   a  pins  2  and  3  required to begin the forward bias of D 6  which will begin to limit the power to the output via the inverting input of U 2 . U 1  has its VCC tied to the input side of the power converter circuit  20  such that any sensing can be done close to the output voltage and will not require a rail-to-rail costly op-amp.  
         [0029]    Still referring to FIG. 3, an overprotection circuit is seen at  32 . Over-voltage programming is set by R 55  to ground and is a module resistor. U 5   b  has a reference set up from the onboard reference of U 3  to pin  6  via R 58  and R 57  divider. Output voltage is sensed and divided down through R 59  and R 55  provides the other half. In the event of the output attempting to go beyond a prescribed point due to some internal component failure, pin  7  of U 5   b  will switch high and shutdown both U 3  and U 2  via shutdown pin  10  from D 14 . Q 13  will then trigger holding U 5   b  in a constant high state until input power is cycled.  
         [0030]    Still referring to FIG. 3, a voltage-correction circuit is seen at  34 . Module resistor R 42 , the fourth resistor, is valued at the same value and tolerance as the tip module resistor R 46 . These resistors are compared through U 4   a  and  b . If these values match, then we allow the green led D 15  to enable and the user is fairly confident he has the correct voltage programmed for the particular device he is powering with the correct tip. In the event that the tip resistor R 46  does not match the module resistor R 42 , we will enable the red led D 10  and also produce an low level audible ping from a piezo telling the user he has incorrectly installed the wrong tip or incorrectly programmed the output in which case another attempt should be made.  
         [0031]    As further shown in FIG. 3, a thermal shutdown circuit, depicted at  30 , will prevent the supply from overheating based on a preset temperature value measured on the case of the supply. U 5   a  has a fixed 2.5 v reference set on pin  2  of the comparator via R 51  and R 54  off of the reference voltage of U 3  controller. R 53  is a positive temperature coefficient thermistor that will be placed at a key location on the supply to prevent the supply from over heating (ie. Covered up in a blanket). As temperature increases, the resistance value of R 53  also increases raising pin  3  to a point above pin  2  where the comparator switches to a high state and through diode D 13  switches off U 3  and U 2  via their shutdown pin  10  which is active high. As the supply cools and U 5   a  switches low, the supply will turn on and operate until another over temperature condition occurs.  
         [0032]    Though the invention has been described with respect to specific preferred embodiments, many variations and modifications will become apparent to those skilled in the art upon reading the present application. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.