Abstract:
The present invention is an apparatus for providing an uninterruptible power supply for an electronic device. The apparatus includes an AC-to-DC power supply that receives an external AC voltage supply and outputs a DC voltage to the electronic device. The power supply includes a bridge rectifier that rectifies the AC voltage from the external AC voltage supply, a boost power factor correction (PFC) converter that boosts the rectified voltage, and a line isolated DC-to-DC converter that changes the boosted voltage to the operating voltage range of the electronic device. The apparatus also includes an uninterruptible power supply (UPS) subsystem that contains, a controller that monitors the external AC voltage supply for interruptions, and a high voltage isolated DC-to-DC (HVDC) converter that supplies high voltage DC power directly to the PFC converter if the controller detects an interruption in the external AC voltage supply.

Description:
FIELD OF THE INVENTION 
   The invention relates generally to a power supply for electronic devices. More specifically, the invention relates to an uninterruptible power supply. 
   BACKGROUND ART 
   A continuous and reliable power supply is necessary for almost all electronic devices.  FIG. 1  shows a block diagram of an AC to DC power supply system in accordance with the prior art. As with most power supplies for electronic devices, it converts alternating current (AC) to direct current (DC) that is output  22  to the device. In this example, the AC input  10  will typically range from 90-264 Volts at a frequency of 50-60 Hz. Once the AC switch  12  is closed the AC power is applied to the AC to DC Power Supply  14 . The power supply  14  includes a Bridge Rectifier  16  that converts the AC into a unidirectional current. The use of a bridge rectifier circuit is well known to one of ordinary skill in the art. The rectified output is then input into a Boost PFC (Power Factor Correction) Converter  18 . The boost PFC converter maintains a constant DC bus voltage on its output while drawing input current that is in phase with the input voltage. The output of the boost PFC converter is 375 Volts DC in this example. Finally, the Line Isolated DC to DC converter  20  creates the necessary operating voltages for the electronic device. These voltages are delivered as the output of the power supply to the electronic device. 
   Prior Art solutions to provide a backup power source have involved the use of various sizes of batteries. However, these backups typically involve some type of interruption of the power supply while the backup battery is engaged. Additionally, most batteries cannot provide an adequate backup power supply for a necessary period of time without adding a great deal of weight to the system. Therefore, an efficient uninterruptible power supply is desired. 
   SUMMARY OF THE INVENTION 
   In some aspects, the invention relates to an apparatus for providing an uninterruptible power supply for an electronic device, comprising: an AC-to-DC power supply that receives and external AC voltage supply and outputs a DC voltage to the electronic device comprising, a bridge rectifier that receives AC voltage from the external AC voltage supply and rectifies the voltage, a boost power factor correction (PFC) converter that boosts the rectified voltage from the bridge rectifier, and a line isolated DC-to-DC converter that changes the boosted voltage to the operating voltage range of the electronic device; and an uninterruptible power supply (UPS) subsystem comprising, a controller that monitors the external AC voltage supply for interruptions, and a high voltage isolated DC-to-DC (HVDC) converter that supplies high voltage DC power directly to the PFC converter if the controller detects an interruption in the external AC voltage supply. 
   In other aspects, the invention relates to an apparatus that provides an isolated DC-to-DC power supply for an electronic device, comprising: a DC input source; a plurality of isolated DC-to-DC voltage converters that receive the input from the DC input source and generate an isolated DC output; and where the plurality of isolated DC-to-DC voltage converters are arranged in series to produce the isolated DC output. 
   In other aspects, the invention relates to an apparatus for providing an uninterruptible power supply for an electronic device, comprising: a DC-to-DC power supply that receives an external DC voltage supply and outputs a DC voltage to the electronic device comprising, a boost power factor correction (PFC) converter that boosts the rectified voltage from the bridge rectifier, and a line isolated DC-to-DC converter that changes the boosted voltage to the operating voltage range of the electronic device; and an uninterruptible power supply (UPS) subsystem comprising, a controller that monitors that external AC voltage supply for interruption, and a high voltage isolated DC-to-DC (HVDC) converter that supplies high voltage DC power directly to the PFC converter if the controller detects an interruption in the external AC voltage supply. 
   In other aspects, the invention relates to an apparatus for providing an uninterruptible power supply for an electronic device, comprising: an AC-to-DC power supply that receives an external AC voltage supply in combination with an external DC voltage supply as a backup voltage supply, where the power supply outputs a DC voltage to the electronic device comprising, a bridge rectifier that receives DC voltage from the external DC voltage supply and rectifies the voltage, a boost power factor correction (PFC) converter that boosts the rectified voltage from the bridge rectifier, and a line isolated DC-to-DC converter that changes the boosted voltage to the operating voltage range of the electronic device; and an uninterruptible power supply (UPS) subsystem comprising, a controller that monitors the external AC voltage supply for interruptions, and a high voltage isolated DC-to-DC (HVDC) converter that supplies high voltage DC power directly to the PFC converter if the controller detects an interruption in the external AC voltage supply. 
   In other aspects, the invention relates to an apparatus for providing an uninterruptible power supply for an electronic device, comprising: an AC-to-DC power supply that receives an external AC voltage supply in combination with an external DC voltage supply and an external battery as a backup voltage supply, where the power supply outputs a DC voltage to the electronic device comprising, a bridge rectifier that receives DC voltage from the external DC voltage supply and rectifies the voltage, a boost power factor correction (PFC) converter that boosts the rectified voltage from the bridge rectifier, and a line isolated DC-to-DC converter that changes the boosted voltage to the operating voltage range of the electronic device; and an uninterruptible power supply (UPS) subsystem comprising, a controller that monitors the external AC voltage supply for interruptions, and a high voltage isolated DC-to-DC (HVDC) converter that supplies high voltage DC power directly to the PFC converter if the controller detects an interruption in the external AC voltage supply. 
   Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     It should be noted that identical features in different drawings are shown with the same reference numeral. 
       FIG. 1  shows a block diagram of an AC to DC power supply system in accordance with the prior art. 
       FIG. 2  shows a block diagram of a power supply system with an uninterruptible power supply in accordance with one example of the present invention. 
       FIG. 3  sows a block diagram of a power supply system with an uninterruptible power supply in accordance with an alternative example of the present invention. 
       FIG. 4  shows a block diagram of DC to DC converter in accordance with one example of the present invention. 
       FIG. 5  shows a detailed schematic diagram of a DC to DC converter shown in  FIG. 4 . 
   

   DETAILED DESCRIPTION 
   The present invention provides a novel approach for implementing an uninterruptible power supply (UPS) that is compact, power efficient and low cost. In general, the UPS solution is applicable to any power supply that has a full range global input voltage capability of 90V-26V. The output voltage is intended to power electronic devices of a wide variety including supplemental and peripheral devices in addition to the primary device. Other embodiments of the invention are applicable to fixed input voltage power supplies. The present invention may not require to DC to AC voltage conversion present on most UPS systems and therefore may eliminate the power loss and circuitry associated with that conversion process. The advantages of the present invention are derived from leveraging the existing infrastructure of the power supply. 
     FIG. 2  shows a block diagram of a power supply system with an uninterruptible power supply in accordance with one example of the present invention. As shown previously in the prior art system of  FIG. 1 , a bridge rectifier  16  in the AC-to-DC power supply  14  is used to convert the AC input to rectified, but unfiltered DC voltage. In this embodiment, the AC input  32  is sampled by a controller  30  to detect any anomalies or problems in the supply. If a problem with the AC input  32  is detected, the controller  30  switches on  52  a high voltage isolated DC-to-DC (HVDC) converter  38  that supplies a rectified AC or high voltage DC (HVDC)  46  to the input of the boost PFC converter  18 . The HVDC converter  38  is supplied with a low voltage, high current DC supply  44  from a battery  40 . In this embodiment, the battery is a 28 V lithium-polymer battery. 
   During normal operations where the AC input  32  is adequate, the controller  30  switches off  52  the HVDC converter  38 . Instead, a battery charger  36  charges the battery  40  with a low voltage DC supply  42 . The battery charger is powered from the output of the boost PFC converter  48 . The battery charger is operating whenever AC power is applied to the power supply. Note: The battery charger will operate if the soft power switch turns off the computer but the power cord is plugged into the wall and the hard power switch  12  is closed. In this case the computer is off and the battery chargers input voltage will be in the range of 127V to 375 VDC (rectified AC input). The controller itself is controlled by a user interface  50  and is powered by a 12 V DC supply from the output of the power supply  22 . In alternative embodiments, the power supply for the controller  30  could be a 5 V from a Universal Serial Bus (USB). In still other embodiments, the controller could sample the rectified AC or HVDC  46  supplied to the boost PFC converter  18  to monitor battery performance and the health of the power supply. Additional functions of the controller  30  may include logging historical data of power performance. The historical data may be recalled to assist in troubleshooting the system. Also, the controller  30  may conduct an orderly shutdown of system peripherals through the USB for preserving data integrity. 
   By injecting a DC voltage after the bridge rectifier the present invention does not require a DC to AC conversion process. An added advantage is that the bridge rectifier provides an input “OR-ing” function. This enables the power system to be driven from the standard AC power source of the UPS system or both simultaneously. This makes the UPS control circuitry easy to implement and resilient during brown out conditions. 
   The boost power factor correction (PFC) converter  18  shown in  FIG. 2  is used to provide power factor correction and also to provide a wide compliance range for acceptable AC input. The UPS system of the present invention takes advantage of this wide compliance range provided by the PFC converter circuitry. The UPS system can supply any loosely regulated voltage before the PFC converter and rely on the PFC converter to boost and regulate the voltage for the rest of the power system. Since the UPS only requires loose regulation an open-loop converter can be design which is very efficient and requires few components. 
   The UPS technique of Pre-Boost converter HVDC injection uses a loosely regulated high voltage DC (HVDC) that is generated from a battery and supplied before the PFC converter circuitry. The high voltage DC (HVDC) should be less than the maximum AC line voltage to guarantee there is not an excessive voltage stress on the components in the power supply. For auto-ranging power supplies, the maximum rectified AC voltage is typically 264V RMS or 374V peak in this embodiment. The minimum voltage for the HVDC is determined by the power supply loading. For full load, the minimum voltage for the HVDC is the minimum RMS voltage specified for the power supply. For auto-ranging power supplies this minimum is 90V RMS or 127V peak. Therefore, the compliance range of the generated HVDC is between 90 VDC and 374 VDC. 
   An alternative embodiment would eliminate the use and need for a HVDC converter and have only an acceptably high voltage battery or energy storage component. This embodiment would directly connect the battery before the PFC converter circuit and eliminate any other voltage or power conversions processes in the UPS system. Available battery sources typically limit this between 12 VDC and 56 VDC so a DC-to-DC converter is typically required. 
   It should be understood that the HVDC converter and UPS may be used with other types of power input supplies and combinations of power input supplies in addition to an AC input  10 . For example, the AC input  32  shown in  FIGS. 2 and 3  could instead by a low voltage DC lower source such as 28V from a vehicle power supply. In other embodiments, the input  32  could be a combination of AC and DC input. In this example, the external AC source would be the primary supply while the DC source would be backup. In particular, this would be used for vehicular mounted electronic devices so that the DC source would be the 28 V vehicular power supply. In the embodiments using a DC source, the PFC converter  18  should be qualified to handle DC input. Other alternatives include the use of an external battery as a supplemental backup supply to either and AC or DC input. Also, the three types of sources could conceivably be used in combination as an AC/DC/Battery source. In each of these combinations, the controller  30  may include data logic to analyze the input and determine when to switch on and off the HVDC. 
   Another alternative embodiment of the present invention is shown in  FIG. 3 . This embodiment does not require any modifications to the standard power system. Instead, the UPS subsystem  60  is a self contained unit that is located in series between the AC power input and the AC-to-DC power supply  14 . In this embodiment, the UPS subsystem may be retrofitted to existing power supply systems. 
   This alternative approach applies a high voltage DC  68  to the normally AC input of a standard power supply  14 . Again, the high voltage DC  68  can be loosely regulated due to the boost power factor correction converter circuit  18  in the standard power supply. This approach requires the additional circuitry for “OR-ing”  70  or multiplexing between the AC and UPS power feeding the external power. This approach may be less efficient due to the inherent losses in the power supply bridge rectifier. 
   An additional embodiment of the present invention is a high power and high voltage DC-to-DC (HVDC) converter using a novel approach of combining several lower power DC-to-DC converters in series.  FIG. 4  shows a block diagram of a DC-to-DC converter in accordance with one example of the present invention. In this embodiment, the individual low power converters  76   a - 76   d  are cascaded in a series arrangement to produce a common high voltage, high current and high power output  74 . In the embodiment shown, the input  72  is a DC input of 28V/30 A and the output  74  is an isolated DC output of 200V/4 A. This series DC-to-DC converter is most advantageous when the desired output voltage is greater than the input voltage. 
   The advantages of the series DC-to-DC converter topology are derived from using relative low voltage power components instead of the high voltage components required for the parallel topology. Electrical components that are created for high voltage and high current area necessarily high power components and expensive. By using low voltage and lower power devices each converter can be optimized for cost and size and efficiency. Each individual DC-to-DC converter can achieve a high efficiency which enables an overall high efficiency for the complete high power converter. 
   It is important to note that the high voltage output is divided evenly across each individual low voltage converter  76   a - 76   d . This is an important point and each low voltage converted should be capable of regulating its isolated output. The series arrangement also forces the same load current through each individual converter. With equivalent output voltage and current for each individual low voltage converter, lower sharing between each converter is accomplished. This power sharing capability is ideal when multiple converter outputs need to be combined. Also, it is important to realize what will occur when an individual converter fails. If the individual to realize what will occur when an individual converter fails. If the individual converter fails in a “short” condition the overall converter continues to operate, but at a reduced output voltage condition. If an individual converter fails in an “open” condition, power is no longer delivered to the output. By knowing this failure behavior, a redundant fail safe system can be designed. 
   Each individual low voltage converter  76   a - 76   d  uses a transformer within each low voltage converter. The circuit is divided into a “primary” section that operates at the input voltage (28V) and input current (7.5 A) and an isolated “secondary” section that operates at the output voltage (50V) and output current (4 A). A half-bridge power conversion topology was utilized but other topologies are possible. Also, the present invention may operate each converter open-loop which enables a common control circuit to drive all converters. The schematic for the individual low voltage converter  80  is shown in  FIG. 5 . The converter is shown with the input voltage  82  (Vin), the transformer  84  (T 1 ), and the output voltage  86  (Vout). Another possible embodiment uses a single transformer with multiple output windings and a single input winding. With this embodiment, the advantages of the series topology are retained for the secondary windings but the primary current requirements increase to the full input specification. 
   A HVDC converter designed in accordance with the present invention was able to utilized inexpensive 48V components that were specifically developed for the telecom industry to generate a 200V, 4A output. By utilizing high efficiency components an overall power conversions efficiently greater than 90% as achieved at an optional price and form factor. 
   While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed here. Accordingly, the scope of the invention should be limited only by the attached claims.