Abstract:
A dual input AC/DC power converter ( 10 ) having dual inputs ( 12,14 ) adapted to receive both an AC and DC input and provide a selectable DC voltage output ( 16 ) and a second DC output ( 18 ). The dual input AC/DC power converter ( 10 ) comprises a power converter circuit ( 20 ) having an AC-to-DC converter ( 22 ), a DC-to-DC booster converter ( 24 ), a feedback circuit ( 26 ), a filter circuit ( 25 ) and a DC-to-DC buck converter ( 28 ). Advantageously, the power converter ( 10 ) resolves many of the system management problems associated with carrying all of the different interface components necessary to power a wide variety of mobile products from either an AC or DC power supply. In addition, the feedback circuit ( 26 ) comprises single feedback loop having stacked photocouplers, one (PH 1 ) controlling the AC-to-DC converter ( 22 ) and the other (PH 3 ) controlling the DC-to-DC booster converter ( 24 ), to select the overall DC output voltage.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is CIP assigned U.S. patent application Ser. No. 10/005,961 filed Dec. 3, 2001, and U.S. patent application Ser. No. 10/072,074 filed Feb. 8, 2002, the teachings of which are incorporated herein by reference, which is a CIP of U.S. patent application Ser. No. 10/159,910 filed May 31, 2002. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to the field of power converters, and more particularly to a dual input AC and DC to programmable DC output power converter. 
     BACKGROUND OF THE INVENTION 
     As the use of mobile electronic products, such as PC notebooks, PDAs, cellular telephones and the like, continues to increase, the need for low cost, compact power supplies to power and recharge these products also continues to increase. Most manufacturers of mobile products typically include plug-in power adapters along with these mobile products to help facilitate the power supply needs of their customers. 
     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 commonly 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 standard, off-the-shelf DC-to-DC adapter. Normally, both adapters are designed and tailored to provide a regulated DC output voltage, which typically range from between 5 VDC to 30 VDC depending on the kind of mobile device being powered. 
     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. This often means that users are typically required to carry multiple adapters to power multiple devices. Thus, by carrying multiple mobile devices, users are often forced to carry more than one power supply adapter, thereby increasing the amount of bulk a user is required to carry. 
     Accordingly, there exists a need for a power converter 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 power converter would advantageously encompass serving the power supply needs of several different mobile devices, as it would supply a filtered and regulated DC output voltage in response to either an AC and DC input voltage. Moreover, by having a power converter that has multiple output terminals, users have the ability of providing power to several mobile devices of varying power requirements, simultaneously, regardless of whether the input voltage is AC or DC. 
     SUMMARY OF THE INVENTION 
     The present invention achieves technical advantages as a power converter capable of supplying dual DC output voltages derived from either an AC input voltage or a DC input voltage, and having a single loop feedback comprised of stacked photocouplers, one coupled to a respective converter. The single feedback loop includes a separate photocoupler, one controlling an AC/DC converter, and the other controlling the DC/DC boost converter, which provides a cost efficient and technically preferable solution. The power converter can be externally programmable to cover a wide range of voltage and current combinations, suitable for a wide variety of mobile product offerings. Moreover, the power converter also resolves the management problems associated with having several different interface components necessary to power a wide variety of mobile products. 
     In one preferred embodiment, the invention is a power converter having a first circuit adapted to receive an AC input voltage and provide a first programmable DC output voltage. The power converter includes a second circuit adapted to provide a second programmable DC output voltage in response to a DC input voltage. The power converter also includes a third circuit that, in response to receiving the first and second DC output voltages, generates a selectable DC output voltage at a first output. Moreover, the third circuit generally comprises a feedback circuit and is adapted to interface with a removable program module. This programming module feature allows users of the power converter to selectively establish the voltage level of the DC output voltage. Advantageously, the feedback circuit also comprises the single feedback loop which includes a first and a second optical device comprising a pair of photocouplers connected in series (stacked). The feedback circuit is adapted to regulate the selectable DC output voltage generated at the first output in response to the on and/or off status of either series photo-coupler. The power converter also includes a fourth circuit that is coupled to first output. The fourth circuit provides a second DC output voltage as a second output which is independent of, and substantially lower than the selectable DC output voltage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1A shows a block diagram of a dual input AC and DC power converter having dual DC voltage outputs in accordance with the present invention; 
     FIG. 1B shows an exploded view of the converter with the detachable buck circuit; 
     FIG. 2 shows a schematic diagram of the power converter circuit as illustrated in FIG. 1 in accordance with the present invention; and 
     FIG. 3 shows a detailed schematic diagram of a DC-to-DC buck converter circuit in accordance with the present invention; and 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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. 
     There is shown in FIG. 1A a block diagram of a dual input AC/DC power converter  10  having dual programmable DC voltage outputs in accordance with the present invention. Preferably, the dual input AC/DC power converter  10  comprises a power converter circuit  20  having an AC-to-DC converter  22 , a DC-to-DC booster converter  24 , a feedback circuit  26 , a filter circuit  25  and a DC-to-DC buck converter  28 . The power converter circuit  20  is seen housed in housing  13  and advantageously provides a first programmable DC output voltage at DC output terminal  16  and a second programmable DC output voltage at terminal  18 . Both of these DC output voltages may be generated as a function of both AC and DC input voltages. 
     In operation, the AC-to-DC converter  22  receives an AC signal via input terminal  12  and provides a regulated DC output voltage at node N 1 . Similarly, the DC-to-DC booster converter  24  may receive a DC input voltage at its input via input terminal  14  and may also provide a regulated DC output voltage at node N 1 . 
     Input terminals  12  and  14  are integrated into a single common connector  17  such that different power cords adapted to receive input power from different sources are received by the common connector  17 . For instance, DC power from an airplane or car power source are wired to couple to input  12  and AC source is wired to couple to input  14 . In a selected embodiment, the AC-to-DC converter  22  is adapted to generate a DC output voltage of between 15 VDC and 24 VDC in response to an AC input voltage at terminal  12  ranging between 90 VAC and 265 VAC. Likewise, the DC-to-DC booster converter  24  is adapted to provide a DC output voltage which is substantially similar to that of converter  22 , but which is generated in response to a DC input voltage supplied at input terminal  14 . Preferably, DC-to-DC booster converter  24  is adapted to receive a voltage in the range of between 11 VDC and 16 VDC. Advantageously, AC-to-DC conversion, via AC-to-DC converter  22 , allows users of the power converter  10  to power high-power mobile devices, such as a laptop computer wherever AC input power is available, such as in the home or office, for example. Conversely, the DC-to-DC booster converter  24  of the power converter  10  is capable of powering similar high-power devices by stepping up most low amplitude DC input signals, such as those found in automobile and/or airplane environments. 
     As shown, filter circuit  25  has its input tied to the respective outputs of the converter  22  and  24 . In a preferred embodiment, the filter circuit is adapted to provide a filtered DC output voltage at second node N 2 , which, thereafter, feeds output terminal  16 , at an output power of 75 watts, for example. 
     The single feedback circuit  26  is shown coupled to the output of filter circuit  25  at node N 2 . In a preferred embodiment, the feedback  26  circuit, through a single feedback loop, regulates the voltage level of the filtered DC output voltages generated by both converters  22  and  24 . Additionally, the feedback circuit  26  is adapted to receive a removable programming module that allows mobile device users to provide a selectable DC output voltage at output  16  via node N 2 . The programming module comprises a key  15  comprising a resistor, wherein different associated values of the resistor establish different associated DC output voltages at output  16 . By allowing users to selectively change the voltage level of the filtered DC output voltage, the power converter  10  may be adapted to power a variety of different mobile electronic devices, having different associated power requirements. Moreover, the power converter&#39;s  10  programming module may also be adapted to provide the additional function of output current limiting. 
     The DC-to-DC buck converter  28  has its input coupled at node N 2 , providing a second DC output voltage that is then fed to output terminal  18 , having an output power of 10 watts, for example. Preferably, buck converter  28  discreetly steps down the filtered DC voltage and produces a second DC output voltage at a separate output terminal  18 . In a selected embodiment, the buck converter  28  steps down the filtered DC output voltage to a range of about 3 VDC and 15 VDC. Advantageously, this second DC output voltage generated by converter  28  is independent of, and substantially lower than the DC output voltage at terminal  16 . This allows users of the present invention to power not only a high-power peripheral, such as a laptop computer, but also, a second, low-power peripheral, such as a cell phone, PDA, and the like. Moreover, the present invention allows for these peripherals to be powered simultaneously by a single converter, regardless if the input voltage is AC or DC. The buck converter  28  is physically detachable from the main housing  13  as shown in FIG. 1B, allowing different buck circuits providing different output voltages to be selectively attached to housing  13  and tap the DC output voltage from output terminal  18 . 
     Referring now to FIG. 2 there is shown a schematic diagram of the power converter circuit  20  of the dual input AC/DC power converter  10  as depicted in FIG. 1 in accordance with an exemplary embodiment of the present invention. As described herein in greater detail, the power converter circuit  20 , in a preferred embodiment, comprises three separate converters: AC-to-DC power converter  22 , DC/DC boost converter  24 , and DC-to-DC buck converter  28 . 
     AC-to-DC Converter 
     The AC-to-DC power converter  22  includes a true off line switcher which is configured in a fly-back topology. Full-wave rectification of an AC input signal, received at input terminal  12 , occurs using a full-wave bridge rectifier BD 1  and a filter capacitor C 1 , which creates a DC voltage bus from which the switcher operates. Inductor L 1  offers additional EMI filtering of the AC signal after the signal has been rectified through the full-wave bridge. The AC-to-DC converter  22  also includes a main controller IC 1  configured as a current mode pulse-width modulator (PWM). Main controller IC 1  is also configured to have a single-ended output with totem pole driver transistors coupled thereto. The AC-to-DC power converter  22  has a main power switch Q 1  which drives the main transformer T 1 . In a preferred embodiment, the transformer T 1 , Schottky diode D 11 , and filter capacitors C 24  and C 25  combine to provide the DC output voltage at node N 1 . 
     As noted earlier, filter circuit  25  allows for additional filtering of the DC output voltage derived from node N 1 . The filter circuit  25  itself comprises inductor L 3 , capacitor C 26  and transformer NF 1 . Advantageously, the filter circuit  25  produces a filtered DC output voltage at output  16  having less than 100 mv peak-to-peak noise and ripple. 
     The feedback circuit  26 , through a single feedback loop, is capable of regulating the filtered DC output voltages provided by the converters  22  and  24 . The feedback circuit  26  is also adapted to be coupled to a removable programming module having a key  15 , comprising resistor R 53 . As such, the present invention allows users to selectively program the DC output voltage later received at output terminal  16 . The feedback circuit  26  includes a photocoupler circuit comprising a pair of photocouplers PH 1  and PH 3  connected in series (i.e., stacked), each being coupled to the outputs of operational amplifiers IC 4 -A and IC 4 -B. Advantageously, these photocouplers are arranged along the feedback loop of the feedback circuit  26  with photocoupler PH 1  and PH 3  coupled respectively to converters  22  and  24 . Through a single feedback loop, the feedback circuit  26  efficiently regulates the filtered DC output voltage provided at node N 2 . Moreover, by stacking the photo-couplers, the present invention also allows the power converter  10  to maintain proper input/output isolation between respective terminals  12  and  14  and output terminal  16 . 
     Preferably, the output current limiting function of converter  22  is accomplished via integrated circuit IC 4 A, resistors R 33 , R 37 , R 38 , and R 39  and programming resistor R 54 . 
     Over voltage protection of AC-to-DC converter  22  is achieved using photocoupler PH 2  and zener diode ZD 2 . In a preferred embodiment, zener diode ZD 2  is set at 25V such that when in avalanche mode it causes the transistor side of photocoupler PH 2  to bias transistor Q 1  into the on state. When it is the on state, transistor Q 3  pulls low pin  1  of integrated controller IC 1  and pulls the operating duty cycle of the integrated controller towards 0%. This takes the DC output voltage to 0 volts. Also, when transistor Q 1  is on, transistor Q 2  is also forced on which then forces these two transistors become latched. If transistors Q 1  and Q 2  are latched, input power must be recycled in order for the power converter  10  to be turned on again. 
     DC-to-DC Converter 
     The DC-to-DC converter  24  is configured in a boost topology and utilizes the same kind of integrated controller, IC 2 , as used in converter  22 . In the DC-to-DC converter  24 , transistor Q 8  acts as the main power switch and diode D 6  as the main rectifier. Preferably, inductor L 2  is adapted to function as a power boost inductor, which is comprised of a toroid core-type inductor. It should be understood that the cathode leads of diodes D 11  and D 8  are connected, forming an ORed configuration, requiring only one output filter. Advantageously, this eliminates the board space needed for a second set of filter capacitors. 
     Like the AC-to-DC converter  22 , the DC-to-DC converter  24  is also designed to operate at a frequency of around 80 KHZ. For the AC-to-DC converter  22 , the operating frequency is set by resistor R 13  and capacitor C 7 . Likewise, the operating frequency of the DC-to-DC converter  24  are set by resistor R 28  and capacitor C 28 . 
     The DC-to-DC converter  24  includes an over-voltage protection circuit comprising zener diode ZD 2 , resistor R 23 , R 24 , R 48 , transistor Q 415 , and silicon-controlled rectifier SC 1 . Zener diode ZD 2  sets the over-voltage protection point (OVP) which is preferably set at 25 VDC. Generally, there is no current flowing through resistor R 48 . If, however, when zener diode ZD 2  begins to conduct current, the drop across R 48  is significant enough to bias transistor Q 6  on, pulling its collector terminal high, and thereby turning silicon controlled rectifier SC 1  on. When silicon control rectifier SC 1  is on, it pulls pin  1  of the integrated controller IC 2  low. Thus, if pin  1  of integrated controller IC 2  is low, the output drivers thereof are forced to operate at a duty cycle of 0%, thereby producing a DC output voltage of 0 volts at pin  6 . Advantageously, the silicon controlled rectifier SC 1  functions as a power latch circuit that requires that input power be recycled in order to turn on the power converter  10  if a voltage above 25 VDC is detected at node N 1 . 
     The temperature of the housing  13  of the power converter  10  is monitored using a thermistor NTC 3 . If, for example, there is a corresponding increase in the temperature of the housing  13 , it will result in a decrease in the resistive value of thermistor NTC 3 , thereby causing transistor Q 9  to turn on and pull low pin  1  of integrated circuit IC 2  of converter  24 . Moreover, this causes the photo-coupler PH 2  to be biased enough to activate a latch circuit comprising transistors Q 1  and Q 2  that will shutdown the power converter  22 . In addition, the power converter&#39;s  10  thermal protection feature is adapted to operate regardless of whether an AC or DC input voltage is being received at their respective input terminals. 
     FIG. 3 shows a detailed schematic diagram of the DC-to-DC buck converter  28  in accordance with the present invention. The buck converter  28  has an integrated circuit controller IC 1 , similar to converters  22  and  24 , which is adapted to generate an on-time duty cycle to power transistor switch Q 1 . The operating frequency of controller IC 1  is set by capacitor C 6 , which is coupled between pin  4  of IC 1  and ground, and resistor R 1 , which is coupled between pins  4  and  8 . In a selected embodiment, the diode D 1  functions comprises a Schottky diode and functions as “catch” diode. Inductor L 1  is a output power inductor and couples the gate of power transistor Q 1  to V out . Fuse F 1  is shown coupled between V in  and the drain terminal of power transistor Q 1 , and advantageously provides current protection to buck-converter  28 . 
     Furthermore, the input V in  of the buck converter  28  is coupled to the output of filter circuit  25  at node N 2 , wherein V in  receives the filtered DC output voltage therefrom. In a preferred embodiment, the buck converter  28  provides a second DC output voltage at V out , coupled to output terminal  18 . Advantageously, the buck convert  28  discreetly steps down the filtered DC output voltage and provides a second DC output voltage at output terminal  18  which is independent of, and substantially lower than the DC output voltage at output terminal  16 . Likewise, the DC output voltage of the buck converter  28  enables users of the present invention to power low-power peripherals, such as, cell phones, PDAs, and/or similar mobile devices. In a selected embodiment, the buck convert  28  may also be adapted to provide a DC output voltage at output terminal  18  ranging between 3 VDC and 15 VDC, selectively determined as a function of the chosen value of resistor R 1  used in the particular buck converter  28 , with a total power delivery of 10 watts, for example. As previously mentioned, the buck converter  28  may be housed in a separate, detachable program module that enables users to selectively program the DC output voltage at terminal  18  as a function of different associated buck converter modules. 
     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.