External backup power supply

Abstract: An external DC (direct current) power supply (10) is provided for supplying backup DC power to a supported device having an AC input connector. The power supply includes an AC (alternating current) voltage source. A voltage rectifier (22) is coupled to the AC voltage source for rectifying the AC voltage source. An energy storage device (32, 138) coupled in parallel to the voltage rectifier provides a predetermined DC voltage threshold level. A connector (16) of the external DC power supply (10) applies a power output of the parallel combination of the voltage rectifier (22) and the energy storage device (32, 138) to the AC input connector (18) of the supported device (20B). The external DC power supply (10) is capable of reliably, effectively and efficiently supplying backup power to the AC power input of a supported system (20B) without requiring any special wiring or modification of the supported system using only the AC input plug for connection to the supported system.

Description: The present invention relates to an uninterruptible external power supply for supplying backup power to a supported device having an AC input connector. Backup power supply systems are increasingly used for applications, such as computer, security, data processing and communications equipment, to avoid interruptions resulting from a primary AC power source. Various arrangements have been employed to provide a backup or standby power supply to prevent such interruptions. Standby power supply systems are disclosed e.g. in US-A-3,790,822, 4,401,895, 4,327,298, 4,313,060, 4,362,951, 4,366,389, 4,395,639, 4,400,626, 4,647,787, 4,468,571 and 4,885,521. Disadvantages of the known arrangements include complexity, expense and unreliability. Several of the known arrangements, require modifications and/or direct wiring interconnections within the power supply circuit of the supported device, such as disclosed by US-A-4,401,895, 4,327,298 and 4,885,521. Others, such as disclosed in US-A-4,468,571 employ DC-to-AC converting means to supply AC supporting power to an AC line input connector of the supported device. US-A-4,313,060 discloses a continuous type uninterruptible power supply including a controlled ferroresonant regulator and rectifier combination supplying independent DC outputs and driving an inverter. The inverter is arranged to provide a plurality of AC and DC outputs. US-A-4,885,521 discloses a supplemental battery backup power system for personal computers that, in the absence of AC line voltage, supplies DC voltages directly to the computer DC power bus and by-passes the internal AC computer power supply. A special harness assembly connects the supplemental battery backup power system with the computer. The harness assembly must be adapted for an output array of voltages and currents in a specific, physical arrangement of a power input connector for a specific computer processing unit to which the backup power is supplied. US-A-4,468,571 discloses an independent, modular unit including a complex system comprised of relays, trigger circuitry, a plurality of rectifier means, a DC to AC inverter, transformers and the like in addition to a battery to supply AC backup power to output connectors thereof. US-A-4,401,895 (from which, by its pre-characterizing portion, claim 1 starts) discloses a low voltage uninterruptible DC power supply for a supported device such as a micro-computer or a microprocessor. This system includes a rectifier rectifying, under normal conditions, AC power from the line. The rectified line power is then transformed by a power switch into the low voltage power delivered to the supported device. A DC energy storage assembly consisting of a DC to DC up converter powered by a rechargeable battery is connected in parallel to the output of the rectifier to supply supporting DC power automatically when the rectifier provides a voltage amplitude below the voltage level from the DC to DC up converter. Whereas this system is relatively simple, as mentioned before, it supplies low voltage DC power to a supported device that is normally integrated in a larger assembly and thus not directly accessible for power supply from outside. All this in mind, the present invention aims at providing an inexpensive, compact uninterruptible external power supply for a supported device, such as a computer, the power supply not requiring any modification of the supported device. This is achieved by the invention as claimed in that the respective power supply supplies DC power to the AC line input of the supported device, giving consideration to the fact that in any supported device of the kind here concerned its AC line input is (nowadays) directly followed by a rectifier assembly, i.e. without employing any AC dependent elements such as a transformer. Additionally, by feeding the AC line input of the supported device, a down converter, such as the aforementioned power switch of the system of US-A-4,401,895, can be avoided. Thus, the uninterruptible power supply of the present invention is very simple. Nevertheless, it does not require any special wiring or modification on the side of the supported device, it does not require any switching, and it does not effect normal operation of the supported device when back up power is not needed. The present invention, together with the above and other objects and advantages, may best be understood from the following detailed description of embodiments of the invention illustrated in the accompanying drawings, wherein: FIG. 1 is a perspective view of an external DC power supply in accordance with the principles of the present invention. FIG. 2 is an electrical schematic diagram representation of the external DC power supply of FIG. 1 together with an AC power supply of a supported system; FIG. 3 is chart providing exemplary voltage waveforms to illustrate how operating power is supplied by the external DC power supply of FIG. 1; FIGS. 4-10 are electrical schematic diagram representations of alternative external DC power supplies arranged in accordance with the principles of the present invention. Referring now to the drawing, in FIGS. 1 and 2 there is illustrated an uninteruptible external DC power supply generally designated by the reference numeral 10. The external DC power supply 10 is a separate module including a housing 12. At its INPUT, the external DC power supply 10 includes an AC input plug 14 for connecting to a primary AC line input and at its OUTPUT, the external DC power supply 10 includes an AC output receptacle 16 for connecting to an AC input plug 18 of a supported device generally designated as 20. Additionally, a safety adapter (not shown) could be used between a nonstandard output receptacle 16 and the AC input plug 18 to prevent use of the supply 10 by a non-compatible device 20. As shown in FIG. 2, the DC power supply 10 includes a bridge rectifier 22 including four diodes 24, 26, 28 and 30, and a series connected combination of a battery 32 and a diode 34 connected across the + and - center connections of the bridge rectifier 22. At the junction V D of diode 34 and the + center connection of the bridge rectifier 22, a predetermined DC voltage threshold level or amplitude is selectively provided by the rating of the battery 32. Battery 32 supplies battery current only when the RMS value of the AC line input supply drops below the predetermined threshold amplitude at junction V D as illustrated in FIG. 3. Although various different arrangements can be used within the supported device 20, the conventional source of AC line voltage is full-wave rectified at its input to provide a DC voltage. Typically, the supported device 20 includes a bridge rectifier 36 including four diodes, as shown. The rectifier 36 is connected in parallel with a filtering capacitor 38 providing a rectified DC voltage input V C to a DC-to-DC converter 39. Many different types of DC-to-DC converters are used to provide an array of DC output voltages at various current to be distributed within a particular supported device 20. Any suitably rated diode can be used for the diodes 24, 26, 28, 30, 34, for example, such as a device type 1N4722 or 1N1204 having a reverse breakdown rating of 400 volts and a conduction current rating of 3 amperes and 12 amperes, respectively. Various commercially available batteries can be used for the battery 32 that can either be of the rechargeable type or primary cells to be thrown away when discharged. For examples, rechargeable lead-acid or gel-type cells, such as sold by Panasonic Corp. and others can be used for the battery 32. The battery 32 can include multiple 12 volt units that can be stacked to provide the selected voltage V D in conjunction with the diode 34. FIG. 3 provides exemplary voltage waveforms to illustrate the operation of the external DC power supply 10. In the top chart, voltage levels are represented in kilovolts versus time in seconds. A first line labelled AC LINE INPUT illustrates near opposite ends a normal sinusoidal AC line voltage with a central zero level power outage portion shown. Next at a line labelled V D , the corresponding voltage levels at V D in FIG. 2 across the OUTPUT of the external DC power supply 10 are illustrated. In the lower chart, voltage levels are represented in volts versus time in seconds. A line labelled V C represents the corresponding supply voltage at the DC-to-DC converter 39 of the supported device 20 as it appears at the junction V C of Fig. 2, and a line labelled IB represents the corresponding battery supply current applied to the DC-to-DC converter 39. As shown, normally no DC current is supplied by the battery 32. This is because the supported power supply 20 draws its current only at the peaks of the AC cycle. When, following a power outage, the voltage at V C drops to a selected threshold level V thr , DC current is supplied instantaneously by the battery 32 through the diode 34 without requiring any switching between the conventional source of AC line power and the DC power supply from battery 32. In FIG. 4, there is shown an alternative external DC power supply, generally designated by the reference numeral 40, together with the supported device 20. External DC power supply 40 uses an alternative rectifier than the bridge rectifier 20 in FIG. 1. The same reference numerals are used in FIG. 4 for similar components as those of FIG. 2. External DC power supply 40 includes a split phase transformer 42 in parallel with a pair of oppositely, polled diodes 44 and 46, as shown. The series connection of battery 32 and diode 34 is connected between a center tap of the split phase transformer 42 and the anode junction of the series connection of the battery 32 and diode 34 to provide similar backup power functions as the external DC power supply 10. In FIG. 5, there is shown an alternative external DC power supply generally designated by the reference numeral 56 together with the supported device 20. The same reference numerals are used in FIG. 5 for similar components as those of FIG. 2. External DC power supply 56 further includes a transformer 58 having its primary winding 60 connected across LINE and NEUTRAL of the AC line input voltage. The secondary winding 62 of the transformer 58 provides an AC voltage supply to a battery charger 64. The battery charger 64 is connected in parallel with a battery 66 for charging the battery 66. The battery 66 is connected in series with a DC converter 68 and diode 34 for providing the desired voltage level at the junction V D . For example, a 12 volt battery 66 can be used with the DC converter 68 adapted for providing a 120 volt DC level at its output. In FIG. 6, there is shown an alternative external DC power supply generally designated by the reference numeral 76 together with a supported device 20A including a voltage doubler arrangement. The same reference numerals are used in FIG. 6 for similar components as those of FIGS. 2 and 5. External DC power supply 76 is similar to the supply 56 of FIG. 5 except that it is adapted for selective operation with either an AC line input supply of 120 volts nominal or 240 volts nominal. The external DC power supply 76 includes a DC converter 69 providing double the voltage amplitude of the DC converter 68 of FIG. 5. For example, the DC voltage output of converter 69 can be about 240 volts as compared to a DC voltage output of 120 volts for the DC converter 68. The external DC power supply 76 further includes a manually operable voltage selecting switch 78 for use in conjunction with a similar manually operable switch 80 provided within the supported device 20. A pair of additional capacitors 82 and 84 of the external DC power supply 76 are connected in series across the center connections of the bridge rectifier 22. Nominal voltage selecting switch 78 is connected between the junction of capacitors 82 and 84 and the NEUTRAL of the AC line input. The supported device 20A includes a pair of capacitors 86 and 88 in conjunction with the switch 80, as shown. In operation the nominal voltage selecting switch 78 is closed for an AC line input supply of 120 volts nominal with the supported device switch 80 also in the closed position. The nominal voltage selecting switch 78 is opened for an AC line input supply of 240 volts nominal with the supported device switch 80 also in the open position. In FIG. 7, there is shown an alternative external DC power supply generally designated by the reference numeral 90 together with a supported device 20B adapted for 3-phase operation. At its input, the external DC power supply 90 includes a 3-phase AC plug 92 for connection with the 3-phase AC line supply. A 3-phase AC plug 94 of the supported device 20B is connected to a corresponding receptacle 96 of the external DC power supply 90, as shown. The external DC power supply 90 includes a 3-phase bridge rectifier 98 including six diodes 100, 102, 104, 106, 108 and 110, and a series connected combination of a battery 112 and a diode 114 connected across the 3-phase bridge rectifier 98. The supported device 20B includes a 3-phase bridge 118 including six diodes 120, 122, 124, 126, 128 and 130 with a filtering capacitor 132 connected across the 3-phase bridge 118. The parallel combination of the series connected battery 112 and diode 114 and the 3-phase rectifier 98 is connected via receptacle 96 and 3-phase plug 94 to the 3-phase bridge 118, as shown. The external DC power supply 90 provides similar backup power functions for 3-phase operation as e.g. the external DC power supply 10, for 2-phase operation. In FIG. 8 there is shown an alternative external DC power supply generally designated by the reference numeral 136 together with the supported device 20. The same reference numerals are used in FIG. 8 for similar components as those of FIG. 2. External DC power supply 136 includes a capacitor 138 replacing the battery 32 and diode 34 combination of FIG. 2. The capacitor 138 provides a backup power source for a time period of a selected number of cycles proportional to its energy storage capacity. A 250 volt or 450 volt rated capacitor having a capacitance rating in a range between 250 and 10,000 microFarad advantageously is used for the capacitor 138. Various commercially available capacitors can be used for the capacitor 138, for example, such as an aluminum electrolytic type Series 36DX sold by Sprague, Inc. In FIG. 9, there is shown an alternative external DC power supply generally designated by the reference numeral 146 together with the supported device 20. The same reference numerals are used in FIG. 9 for similar components as those of FIGS. 2 and 8. External DC power supply 146 further includes a resistor 148 and a diode 150 in combination with the capacitor 138, as shown. The resistor 148 provides a path for slowly charging the capacitor 138 during normal operation of the AC line input. The capacitor 138 is discharged through the diode 150 when the AC line input power fails. In FIG. 10, there is shown an alternative external DC power supply generally designated by the reference numeral 156 together with the supported device 20. The same reference numerals are used in FIG. 10 for similar components as those of FIG. 2. External DC power supply 156 includes a second bridge rectifier 158 including four diodes 160, 162, 164 and 166. The bridge rectifier 158 is connected at its input to an alternative AC power source. The series connected combination of the battery 32 and diode 34 is connected across the + and - center connections of the bridge rectifiers 22 and 158. External DC power supply 156 provides backup battery power to the supported device 20 in the event of failure of both the normal AC line power and the alternative AC power source. The normal AC line power and the alternative AC power source are not required to be synchronous or to have the same frequency. In summary, multiple external DC power supply arrangements have been disclosed for simply and economically providing backup power for various types of supported devices. A significant advantage of all of these external DC power supplies is that the need for access to wiring within a particular supported device is eliminated and that this is achieved with simple means.

Claims: An uninterruptible DC power supply (10; 40; 56; 76; 98; 136; 146; 156) comprising: an AC power source (14; 92) under normal conditions supplying power to an output (16; 96) of said DC power supply, rectifier means (22; 98) coupled between said AC power source (14; 92) and said output (16; 96), and DC energy storage means (32; 66, 68; 66, 69; 112; 138) coupled in parallel to an output of said rectifier means (22; 98) for supplying supporting DC energy to said output (16; 96) of said DC power supply when said rectifier means (22; 98) provide a voltage amplitude below the voltage level of said DC energy storage means (36; 66, 68; 112; 138), said DC power supply being characterized in that, to form an independent modular unit for supplying power to an AC line input connector (18; 94) of a supported device (20; 20A; 20B), such as a computer, said DC power supply (10; 40, 56; 76; 98; 136; 146; 156) includes a housing (12) of its own and said output (16; 96) of said DC power supply is in the form of an output connector (16) suitable for connection to said AC line input connector (18; 94) of said supported device (20; 20A; 20B) and, further, that said output connector (16) is directly connected to said rectifier means (22; 98). An uninterruptible DC power supply (10; 40; 56; 76; 98; 136; 146; 156) as recited in claim 1 wherein said rectifier means (22; 98) consist of a full-wave rectifier. An uninterruptible DC power supply (40) as recited in claim 1 or 2 wherein said rectifier means (22) include a split phase transformer (42) connected in parallel with a pair of oppositely poled diodes. An uninterruptible DC power supply (90) as recited in claim 2 wherein said AC power source is a 3-phase AC line supply and said rectifier means comprise a six diode bridge rectifier (98). An uninterruptible DC power supply (76) as recited in any one of the preceding claims wherein, in the case of a supported device (20A) including a voltage doubler arrangement, said DC power supply (76) also comprises a voltage doubler arrangement. An uninterruptible DC power supply (76) as recited in claim 5 wherein said rectifier means (22) consist of a bridge rectifier, wherein said voltage doubler arrangement includes a switch (78) movable between an opened position and a closed position, and wherein series connected capacitance means (80, 82) are connected in parallel with said energy storage means (66) and connected between + and - center connections of said bridge rectifier, said switch (78) being connected between a junction of said capacitance means (80, 82) and said + center connection. An uninterruptible DC power supply (10; 56; 76; 90; 156) as recited in any one of the preceding claims wherein a diode (34; 114) is connected in series with said DC energy storage means (32; 66, 68; 66, 69; 112), said DC energy storage means comprising a battery (32; 66; 112), wherein said rectifier means (22) consist of a diode bridge rectifier, and wherein said series connection of said DC energy storage means and said diode is connected across an output of said diode bridge rectifier. An uninterruptible DC power supply (136; 146) as recited in any one of the claims 1 to 6 wherein said DC energy storage means comprise a capacitor (138). An uninterruptible DC power supply (146) as recited in claim 8 further comprising a parallel combination of a resistor (148) and a diode (150) connected in series with said capacitor (138). An uninterruptible DC power supply (146) as recited in claim 9 wherein said rectifier means (22) consist of a diode bridge rectifier and wherein said combination of said resistor (148), said diode (150) and said capacitor (138) is connected across an output of said diode bridge rectifier. An uninterruptible DC power supply (10; 40; 56; 76; 98; 136; 146; 156) as recited in any one of the preceding claims wherein said output connector (16; 96) is an AC voltage receptacle providing GROUND, LINE and NEUTRAL connections.

Inventors: MCCARTNEY THOMAS, MCCARTNEY, THOMAS
Applicants: ONEAC CORP, ONEAC CORPORATION
Application year: 1991
Main classification: H02J9
IPC codes: H02J9