WO1999048193A2

WO1999048193A2 - Uninterruptible power supply

Info

Publication number: WO1999048193A2
Application number: PCT/IL1999/000149
Authority: WO
Inventors: Ronen Meir
Original assignee: Guardian On Board Ltd.
Priority date: 1998-03-17
Filing date: 1999-03-17
Publication date: 1999-09-23
Also published as: WO1999048193A3; EP1062724A2; AU2851599A; KR20010041981A; JP2002507810A

Abstract

An uninterruptible power supply (UPS) (10) for a personal computer (31), which normally operates on AC line power, the UPS including a battery (56), which stores electrical energy and an inverter (38) which receives the energy stored in the battery and converts it to an AC output voltage which is supplied to the computer in the event of a voltage variation in the line power. A line voltage detector (40) senses the voltage variation in the line power and actuates the inverter responsive thereto. The detector includes an optocoupler, which receives the line voltage, and which outputs a signal voltage responsive thereto which is substantially lower than the line voltage; and a comparator, which receives the signal output from the optocoupler and compares the signal voltage to a predetermined reference voltage.

Description

UNINTERRUPTIBLE POWER SUPPLY

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application no. 60/078,256, filed March 17, 1998. Reference is also made to co-pending U.S. Patent Application no. 09/077,025. Both of these applications are assigned to the assignee of the present patent application and incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to uninterruptible power supplies (UPSs) and specifically to UPSs in the form of cards that are insertable into a card slot of a personal computer.

BACKGROUND OF THE INVENTION

UPSs are well known in the art, as a means of providing power to a system when power from an electricity supply line fails or varies from its specifications. The reliable operation of a computer depends on the quality of the electricity supply. A power failure during a computing operation leads at best to irritation and time wasting and at worst to expensive data loss and/or damage of equipment. To deal with problems of this type, a UPS is attached between the computer and the power source. The UPS typically contains a battery which is charged while the incoming power is within specification, and which begins to generate replacement power when the incoming power is out of specification. In general UPSs are bulky and cannot be contained inside the case of a standard personal computer.

UPSs in the form of insertable cards, that is to say sufficiently compact to fit within the casing of a computer, are known. For example, PCT application PCT/FI94/00555, to

Valkeakari, Helsinki, Finland, which is incorporated herein by reference, describes a backup power device which can be installed into an unused space of a personal computer. When the computer's power source fails, the device supplies power to the computer.

A conventional UPS card, however, while powering internal components of the computer, has the disadvantage that it is not capable of powering peripheral components, such as a display monitor. The power levels required to drive the monitor cannot be achieved by standard electronics and iron or ferrite transformers within the constraints of size and form factor associated with a standard PC plug-in card. An attempt to reduce the size of the transformers and electronics in a conventional way would cause overheating within the computer case and the card itself, whereby other subsystems (such as the voltage detector or battery charger) would fail. Overheating occurs because of the relatively low efficiency of the UPS components, for example, transformers present in the UPS. Typically the UPS card only powers internal components of the computer, so that in the event of a power failure the processor will continue to work. Such a card provides backup to the computer on the DC level, i.e., low-voltage DC (±5, ±12, 3 volts). The backup voltage is connected after the PC power supply (SMPS), on its outputs, so that the SMPS is exposed to electrical abnormalities, such as surge, spikes, and EMI/RFI. Therefore, this type of "internal" UPS provides only partial backup, without protection from high-voltage abnormalities and noise It does not power the display or other peripherals, so that there will be nothing on the display monitor to guide the operator in carrying out any operations, such as orderly save operations, that the operator may wish to perform. Thus, the conventional UPS card does not meet the performance specifications of industry-standard external UPSs.

SUMMARY OF THE INVENTION

It is an object of some aspects of the present invention to provide apparatus and methods for uninterruptible power supply in a compact form for a personal computer.

It is a further object of some aspects of the present invention to provide an improved, compact connector for a UPS.

In some preferred embodiments of the present invention, a UPS is constructed on an industry-standard PC card comprising a standard bus connection, and the card is mounted within a personal computer via the bus connection. Most preferably, the card meets substantially all industry standards, and the dimensions of components used to construct the UPS, and the layout of the components on the card, are such as to allow the UPS to fit within a standard slot of the personal computer. The UPS comprises a DC-DC converter, preferably built around a high-efficiency planar transformer, so that heat dissipation from the transformer is minimized, and so that the overall efficiency of the UPS is high.

Thus the size and the design of the UPS enable it to be mounted within the computer while causing minimal heating of other components within the computer. Furthermore, the high overall efficiency and power rating of the UPS allow it to power peripherals of the computer, such as a display monitor of the computer, in addition to the computer itself. Furthermore, the UPS preferably meets safety and other regulatory requirements, such as Underwriters' Laboratories and Federal Communications Commission requirements.

In some preferred embodiments of the present invention, the UPS comprises a switching relay, which switches between AC line power and UPS-generated power according to a state of the line power measured by a detector. The detector is preferably optocoupler-based, so that its volume is less than one cubic centimeter. Most preferably, the detector is temperature-stabilized by adding an element to the detector, which element has a temperature characteristic complementary to that of the optocoupler. The UPS power is generated by converting low- voltage power from a rechargeable battery mounted on the PC card to a line-level DC voltage via a DC - DC converter. Voltage from the DC - DC converter is switched in a DC - AC unit so as to generate the UPS power in the form of a square wave of substantially constant open duty cycle, wherein the UPS generated power has substantially the same RMS voltage as the incoming line voltage. In some preferred embodiments of the present invention, the rechargeable battery is charged when line power is present, wherein the charging is preferably performed by a variable- rate charging system comprising a pulse-width-modulated oscillator, which receives feedback of a voltage derived from the battery. Most preferably, the charging system is constructed so as to provide a high charging rate when the battery has a low charge, and a low charging rate when the battery is substantially fully charged. Preferably, the voltage output of the DC - DC converter, and thus the output of the UPS-generated power, is maintained at a substantially constant level in the face of changes in load by a feedback signal indicative of the load. Preferably, the DC - AC unit comprises a control unit, which is driven by an oscillator which runs continuously from a battery charger auxiliary voltage, so that in the event of a line power failure, the unit is able to begin delivering AC power at substantially the same instant as the power failure occurs.

There is therefore provided, in accordance with a preferred embodiment of the present invention, a power connector for a personal computer, which receives input line power and has an internal bus, preferably an industry-standard bus, and a plurality of mutually parallel slots on the bus with a predetermined spacing therebetween for insertion of extension cards thereinto, the connector having an overall width generally equal to or less than the predetermined spacing of the slots, and including: an input connection for receiving the input line power; an output connection for providing output line power; and a common ground link for the input and output power. Preferably, the connections and ground link are arranged in a single row. Alternatively, the ground link comprises a connection intermediate the input connection and the output connection. Preferably, the complies with mandated safety standards and has an internal fuse that is accessible external to the personal computer, without the necessity of opening the computer case.

There is further provided, in accordance with a preferred embodiment of the present invention, an uninterruptible power supply (UPS) for a personal computer, which normally operates on AC line power, the UPS including: a battery, which stores electrical energy; an inverter which receives the energy stored in the battery and converts it to an AC output voltage which is supplied to the computer in the event of a voltage variation in the line power; and a line voltage detector, which senses the voltage variation in the line power and actuates the inverter responsive thereto, the detector including: an optocoupler, which receives the line voltage, and which outputs a signal voltage responsive thereto which is substantially lower than the line voltage; and a comparator, which receives the signal output from the optocoupler and compares the signal voltage to a predetermined reference voltage.

Preferably, the optocoupler has a known temperature response, and the UPS includes a temperature-responsive element having a temperature response complementary to that of the optocoupler, so that a response of the line voltage detector to the variation in the line power is substantially temperature-independent.

Preferably, the inverter includes an oscillator which oscillates at a line frequency substantially constantly, whereby when the line voltage detector actuates the inverter, the AC output voltage is supplied to the computer immediately, most preferably within a few milliseconds. Preferably, the UPS resides within the personal computer.

There is further provided, in accordance with a preferred embodiment of the present invention, an uninterruptible power supply (UPS) for a personal computer, which normally operates on AC line power at a predetermined line voltage and frequency, the UPS providing an AC output into a load and including: a battery, which stores electrical energy at a voltage substantially lower than the line voltage; a DC-to-DC converter, which receives the energy stored in the battery and converts it to a DC output at a voltage generally comparable to the line voltage; and an inverter which receives the output from the DC-to-DC converter and generates the AC output with a substantially constant open duty cycle, with output voltage stability irrespective of the load.

Preferably, the DC-to-DC converter comprises a planar transformer. Alternatively, the DC-to-DC converter varies the DC output voltage responsive to the load.

Preferably, the DC-to-DC converter receives a feedback signal indicative of the load.

Preferably, the DC-to-DC converter includes a high-frequency oscillator, which generates width-modulated pulses for controlling the variable DC output voltage. Preferably, the UPS resides within the personal computer.

There is further provided, in accordance with a preferred embodiment of the present invention, a method for supplying uninterruptible power to a personal computer, which normally operates on AC line power at a predetermined line voltage and frequency, including: storing electrical energy in a battery at a voltage substantially lower than the line voltage; receiving the energy stored in the battery and converting it to a DC output at a voltage generally comparable to the line voltage; and inverting the DC output to generate an AC output into a load with a substantially constant open duty cycle, irrespective of the load. The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: BRIEF DESCRD7TION OF THE DRAWINGS

Fig. 1 is a schematic block diagram of a UPS card according to a preferred embodiment of the present invention;

Figs. 2A-2P are circuit diagrams corresponding to the block diagram of Fig. 1; Fig. 3 is a perspective drawing of a connector, according to a preferred embodiment of the present invention; and

Fig. 4 is a schematic, pictorial view showing the UPS card of Fig. 1 installed in a computer, according to a preferred embodiment of the present invention.

DESCRD7TION OF THE PREFERRED EMBODIMENTS

Fig. 1 is a schematic block diagram of an uninterruptible power supply (UPS) 10, and Figs. 2A-2P are electronic diagrams corresponding to Fig. 1, according to a preferred embodiment of the present invention. Preferably, UPS 10 is constructed on an industry- standard personal computer (PC) card 11, which is mounted in a slot on an industry-standard bus within a PC 31, so that the UPS supplies power to the computer and associated peripheral components such as a display monitor 41.

An AC connector 20 (JP1 Fig. 2 A) receives input from an AC line power source, and outputs AC to computer 31 and peripherals. Connector 20 and its mounting are described in more detail below. AC connector 20 conducts the AC line power to an EMI/RFI filter 32, comprising inductors LI, L3, L5, and L6, and capacitors C17, C77, and C78 (Fig. 2A), which reduces electromagnetic and radio-frequency noise input from the AC line. Filter 32 further comprises a metal-oxide varistor V2, which protects UPS 10 and components supplied by the UPS against spikes present on the AC line power.

AC line power from filter 32 is transferred to a two-state switching relay 36 (Kl and K3, Fig. 2A). In a first guarding state shown in Fig. 1 and Fig. 2A, relay 36 transfers the AC power, via a further surge suppression varistor 34 (VI), to output supply pins on connector 20. Preferably, relay 36 remains in its guarding state while the AC line power is within acceptable limits, the detection of which is described in more detail below. When the AC line power from filter 32 is not within acceptable limits, for example, when there is a power outage or a power spike, relay 36 switches to a second active state. In this state, the AC line power is disconnected from the output supply pins, and UPS 10 generates AC power internally and supplies the generated power to the output supply pins of connector 20. Most preferably, relay 36 is a DPDT relay capable of switching between the two states in a time of the order of about 5 ms. During switching times of this order, computer 31 and its associated peripherals will continue to be powered by their respective internal capacitors. The gap between contacts of relay 36 is preferably greater than 1.4 mm, so that UPS 10 complies with IEC950/UL1950 safety standards.

To determine if the AC line power is within acceptable limits, an optocoupler-based detector 40, comprising a diode bridge Bl (Fig. 2B) and an optocoupler UIO, is used to detect the state of the AC line power input. This is in contrast to conventional detectors which generally use a transformer or inductor. The voltage signal that is output by optocoupler UIO is proportional to, but much smaller than, the rectified line voltage that it is measuring. As detector 40 is based on optocoupler U10, its volume can be kept to less than one cubic centimeter. Most preferably, detector 40 operates in a linear fashion and is temperature- stabilized by virtue of using a special low-current temperature-stabilized Darlington-type 6N169 optocoupler U10. Signals from optocoupler U10 are fed via diode D2 and transistors Q14 and Q15 to a first comparator, comprising an amplifier U1C, and a second comparator, comprising an amplifier U1D (Fig. 2E). The first and second comparators use an output of a voltage regulator REG3 (Fig. 2E) as their voltage reference. The output of the comparators, after passing through a delay unit 42 whose function is described below, is used to decide in which of its two states relay 36 should be.

Delay unit 42, comprising transistors Q17 and Q18, an amplifier U13A, and diodes D33 (Fig. 21), utilizes the signal provided by amplifier U1C and U1D. Delay unit 42 operates following a power failure, that is to say during the time that power is being restored. Using the signal from amplifier U1C and U1D, delay unit 42 checks the quality of the line power supply. If the line voltage is found to be unstable, for example, it stays within the normal range for less than about 2 sec (as determined by comparators U1C and U1D), then the delay unit maintains relay 36 in the active state and delays switching back to the line supply. When the quality of the line supply is satisfactory, the signal output from D33 of unit 42 switches relay 36, via a transistor Q2 (Fig. 2F), to its guarding state. In order to generate AC power stably and efficiently from an internal battery 56, UPS

10 first generates a high-voltage (120 V or 220 V) stabilized DC level in a DC - DC power unit 46, controlled by a pulse- width-modulated (PWM) oscillator 44. The output from unit 46 is fed via a filter 50 to a DC - AC converter 38, and thence to relay 36. The frequency at which converter 38 operates is governed by an oscillator 52. The construction and operation of oscillator 44, unit 46, filter 50, converter 38, and oscillator 52 are described in detail hereinbelow. PWM oscillator 44 comprises an industry-standard SG3625A integrated circuit U6 (Fig.

2M). Preferably, oscillator 44 provides width-modulated pulses at a frequency of approximately 45 kHz in order to power unit 46. The width of the pulses is regulated via a feedback signal from unit 46. Most preferably, oscillator 44 also receives an alert signal from delay unit 42, via a transistor Q3 (Fig. 2F), which can be used to switch off modulation, thereby halting operation of unit 46 and the supply of power from UPS 10. The alert signal is generated, for example, when UPS 10 is running off the batteries, and a sudden drop in voltage is detected, such as may be caused by an internal short or when an abnormally high output load exists.

Power unit 46 comprises a first pair of transistors Q6 and Q7 (Fig. 2L), and a similar, second pair of transistors Q8 and Q9 (Fig. 2N), which receive pulses from oscillator 44.

Transistors Q6, Q7, Q8, and Q9 in turn switch two MOSFET power transistors Q4 and Q5 supplied by battery 56, via terminals BC2 and BC1 (Fig. 2L). The MOSFET power transistors have a very low drain source ON level (RDS ON), so that power dissipation is low. The switched power output from the power transistors is fed into a center-tapped primary of a transformer T2 (Fig. 2N). Most preferably, transformer T2 is a planar transformer constructed from layers of printed circuit board, used in place of coils, around a central planar ferrite core, enabling efficient operation at high frequencies with very small volume and height. Such transformers are produced, for example, by Payton Group International, of Rishon LeZion,

Israel. Use of such a planar transformer has two advantages. Firstly, the transformer is much more compact than conventional transformers having the same power rating, for example it can have a height of as little as 15 mm and a base of 50 x 30 mm. Secondly, the power conversion efficiency of the transformer is high, being of the order of 98%.

The output voltage from a main secondary winding of transformer T2 is rectified by diodes D17 and D18, which preferably are ultra-fast switching diodes. Preferably, a set of jumpers Jl lO and J230 enable transformer T2 to be changed from a center-tapped arrangement, which supplies 110 V, to a non-center-tapped arrangement, using extra diodes

D34 and D35, which together with diodes D17 and D18 form a bridge connection that supplies 230 V The jumpers are most preferably set according to the local voltage standard.

A filter 50, comprising a 1 mH inductor L4 and a 4.7 μF capacitor C16, is connected to the output of diodes D17 and D18 (together with diodes D34 and D35 for 230 V output), i.e., the output of power unit 46, in order to smooth the DC output. The smoothed output of power unit 46 is preferably limited to a maximum voltage (130 V for 110 V operation and 250 V for 230 V operation) by a tranzorb diode D45 (Fig 2O) This ensures that the power output is capped at a reasonable limit in the event of failure of the power level feedback loop between oscillator 44 and power unit 46

Feedback to oscillator 44 is provided by an auxiliary voltage tap on the smoothed output from the main secondary winding of transformer T2. The voltage tap is taken via a 100 kohm resistor R41 (Fig. 2N) to an optocoupler U3 (Fig. 2K). Pin 5 of optocoupler U3 provides the feedback to oscillator 44, modifying the width of the pulses produced therein, thereby stabilizing the voltage output from the main secondary

Preferably, transformer T2 has an auxiliary secondary winding whose output is rectified by a diode bridge B2 (Fig. 2N). The rectified output is then fed to a voltage regulator REG2 (Fig. 2O), which supplies regulated DC to oscillator 52 and converter 38.

The DC stabilized voltage output derived from T2 is converted in DC - AC converter 38 to a square wave AC power output having a substantially fixed duty cycle, and the square wave power output is transferred to relay 36 Converter 38 comprises two half-bridge drivers U4 (Fig 2C) and U7 (Fig. 2D), most preferably industry-standard HIP2500IB integrated circuits or other compatible devices. The drivers can also be made from discrete components. Driver U4 feeds power transistors Q10 and Q12, and driver U7 feeds power transistors Ql l and Q13 Most preferably, Q10, Ql l, Q12, and Q13 are MOSFET power transistors which switch the DC stabilized voltage, providing their switched AC output at the junction of transistors Q10 and Q12, and at the junction of transistors Ql l and Q13. The frequency at which converter 38 operates is governed by an oscillator 52, which generates pulses at the local line frequency

Oscillator 52 comprises an integrated circuit U8 (Fig. 2G), preferably an SG3525A, acting as a pulse-width-modulated (PWM) oscillator Most preferably, oscillator 52 operates continuously, receiving power from battery 56 or from a battery charger 54 Thus, in the event of a power failure, when power is supplied from DC - DC unit 46, AC power will be available with substantially negligible delay.

Battery 56 preferably comprises either a nickel-cadmium (NiCad) or nickel-metal hydride (NiMH) battery pack, having a nominal output of 16.8 V, which when fully charged has a voltage of approximately 20 V. (NiCad and NiMH batteries are smaller and lighter than lead- acid batteries of the same capacity, have better charging and recovery specifications, and, at least in the case of NiMH, are more environmentally friendly.) Preferably, the nominal voltage is higher than the 12 V used in other UPSs, since a higher voltage permits a lower discharge current, which in turn means greater efficiency of the UPS. Battery 56 preferably comprises fourteen 1.2 V cells. In a preferred embodiment, "sub C" type battery cells are used. Preferably, battery 56 is held by a bracket connector in UPS 10, approximately at the middle of card 11, in a cut that is sized to receive the battery. The printed circuit board area above and below the cut are used to deliver electric power and signals from the bracket connector to the rest of the card. In another preferred embodiment, the battery is located off the card, at any convenient location inside PC 31, and connected by two wires to a connector at the back end of the card. The card itself occupies one PC slot, as described hereinabove, but this embodiment simplifies and reduces the cost of manufacturing the UPS, since no electrical wires are required on card 11.

Battery 56 is charged by a battery charger 54, which is powered directly from the line with minimal filtering and rectification. As described in more detail below, charger 54 comprises a variable-charging-rate system utilizing pulse width modulation. The charging rate is adjusted according to the state of the battery, as is known in the art.

Charger 54 comprises a diode bridge B3 (Fig. 2K), which rectifies the incoming line voltage. The rectified voltage then feeds a TOP211PF1 integrated circuit Ul 1 (Fig. 2P), which drives a primary winding (pins 3 - 4) of a high frequency ferrite transformer Tl. Integrated circuit Ul 1 comprises a PWM controller and a MOSFET power transistor, and supplies pulses at a frequency of approximately 100 kHz to transformer Tl. (Transformer Tl does not have the same efficiency requirements as transformer T2, because the power levels are significantly lower.) Preferably, transformer Tl is small in size. Voltage generated in a main secondary winding (pins 9 -10) of transformer Tl is rectified by a Schottke diode D29 and then passes through an isolation diode D37 for charging battery 56 via a positive battery electrode +BF.

Transformer Tl comprises an additional secondary winding (pins 1 - 6), the output of which is rectified, filtered, and transferred to a 4N35 optocoupler U12 as part of a feedback loop to maintain the rectified voltage from the first secondary winding at 20V. The feedback loop comprises a 15 V Zener diode D31 used as a reference. Optocoupler U12 supplies a feedback signal to Ul 1 (pin 4) in order to adjust the current driving the primary winding of transformer Tl . Use of optocoupler U12 in a feedback loop as described hereinabove means that the charging level can be maintained to an accuracy of 1% for a range of input line voltages from 80 V to 240 V. Thus, it is not necessary to make any adjustments to charger 54 for different countries. Preferably, transformer Tl comprises a further secondary winding (pins 2 - 5), the output of which is rectified by a diode D12, so as to power oscillator 52 as long as transformer Tl receives input power, as described above.

Most preferably, charger 54 utilizes the circuits of the main and additional secondary windings to check the internal resistance of battery 56. If the battery is fully charged, charger 54 supplies a very low charging current of the order of 10 mA - 40 mA. If battery 56 is empty, a high charging current of the order of 300 mA is generated for a period of the order of about one hour in order to return the battery to a charged state relatively quickly. Using this system, after half an hour of charging a completely empty battery, it is possible to have two minutes of backup time in the event of a power failure. Preferably, after approximately one hour of high- rate charge, charger 54 returns to low-current operation as described hereinabove.

An alarm and indication unit 58 is preferably supplied within UPS 10, in order to provide:

• an alarm for a low-battery state, for example by sounding a piezoelectric buzzer BUZ 1 (Fig. 2E);

• an alarm showing that the battery is in operation, for example by sounding buzzer BUZ 1 intermittently, and flashing an LED Dl (Fig. 2C); • a line power indicator, showing that line power is being received and that the battery is charging correctly, for example by lighting an LED D6 (Fig. 2A); and

• a connection indicator, showing that the card of UPS 10 has been correctly inserted into its mating slot, for example by lighting an LED D3 (Fig. 2L).

Buzzer BUZ 1 is operated by an NEC555 integrated circuit U9 (Fig. 2K). The methods by which LEDs Dl, D6, and D3 operate will be apparent to those skilled in the art. Most preferably, the battery output voltage is monitored to provide further protection. The output voltage is fed to a comparator U1B to compare with a reference voltage provided by R3 and R8 (Fig. 2E). If a situation such as a sudden drop in voltage is detected, then the output of the comparator is fed to oscillator 44, thereby switching oscillator 44 off and halting operation of the UPS. This is helpful in the event of an internal short or when an abnormally high load is placed at the output. This circuit also protects the battery from deep discharge.

To enable orderly shutdown of computer 31 to be performed in the event of a power failure, a serial output 64 (JP3 Fig. 2H) is preferably provided which may be connected to a serial port of the computer. An opto-switch 62 (U2 Fig. 2H) receives a signal derived from optocoupler-based detector 40. When the power failure occurs, the signal causes opto-switch 62 to close, so that output JP3 effectively changes from an open to a closed circuit. The change may be utilized by computer 31 to initiate the shutdown. Most preferably, the change is readable by shutdown software that is supplied with UPS 10 and installed on the computer at the time of installation of the UPS or at a later time. In an alternative embodiment, the signal derived from detector 40 is fed to the computer's industry-standard bus via the slot holding UPS 10. The shutdown software can then directly read the signal from the bus, so that serial output 64 is not provided.

Most preferably, UPS 10 comprises a safety unit 66 to ensure correct connection of the UPS card to the computer bus when the UPS is placed in its mating slot. Preferably, unit 66 comprises a relay K2 (Fig. 2L) connected across a connector PCI of the UPS card to the computer bus. When the card is correctly placed in the computer bus slot, current flows through relay K2, which closes and thereby connects the positive electrode of battery 56 to a number of locations within UPS 10. UPS 10 cannot operate unless these locations are powered, and thus the UPS will not function unless it is properly connected within the slot. This prevents accidental switching on of UPS 10 in many circumstances and makes accidental electrocution less likely. Also, because parts of UPS 10 are powered by the very machine the UPS is meant to power, a very helpful safety loop is added. Unit 66 also acts as a power switch and makes the use of a separate on-off switch (used by UPSs known in the art) unnecessary.

Unit 66 also protects against overload of UPS 10, or incorrect use by an end-user, while the UPS is supplying power. For example, if too large a current is drawn through the output pins of connector 20, then the battery voltage will drop, and computer 31 will turn off. Once the computer turns off, relay K2 opens, and UPS 10 shuts down. The UPS will remain shut down until both line power returns and an on/off switch of the computer is switched on.

Reference is now made to Fig. 3, which is a perspective drawing of connector 20, in accordance with a preferred embodiment of the present invention. Connector 20 is mounted via a supporting bracket 13 onto PC card 11. The connector has dimensions sufficiently small so that it can fit on the bracket, and keep the overall width of UPS 10 no larger than the width of a standard PC slot. Connector 20 comprises a pair of connections 15, preferably pins, used to input line power, and a connector 17 comprising a pair of connections 19, preferably sockets, used to output line power. Connector 17 further comprises a connection socket 21 used as a common ground link for input and output power. Preferably, after installation of UPS 10 in computer 31, external line power and an external ground (typically the AC line ground) are connected to connections 15 and socket 21 respectively. Power connections are made from connections 19 to computer 31 and to computer peripherals such as display monitor 41, via one or more connectors mating with connector 20. Most preferably, connections for the input line power and the output power are different physically so as to prevent inadvertent wrong connection. Preferably, as described above and shown in Fig. 3, the input connectors are male-type connections, and the output connectors are female. Alternative methods for physically differentiating the input and output connections, such as separating the pairs of connections for the input and output by different distances, will be apparent to those skilled in the art. Fig. 4 is a schematic, pictorial illustration showing UPS card 11 installed in computer

31, in accordance with a preferred embodiment of the present invention. A power cord 81 has a special connector 83 which mates with connector 20 on bracket 13 so as to couple card 11 to an AC lines power socket 82. Lines power out of connector 83 is distributed to computer 31 and to monitor 41, preferably via a junction box 84. In addition, card 11 is preferably coupled via a serial communications cable 85 to convey RS-232 messages to a COM port 86 of the computer, as described hereinabove. Optionally, a telephone connection to a modem 87 in the computer is also passed through the UPS card.

It will be appreciated that the preferred embodiments described above are cited by way of example, and the full scope of the invention is limited only by the claims.

Claims

1. A power connector for a personal computer, which receives input line power and has an internal bus and a plurality of mutually parallel slots on the bus with a predetermined spacing therebetween for insertion of extension cards thereinto, the connector having an overall width generally equal to or less than the predetermined spacing of the slots, and comprising: an input connection for receiving the input line power; an output connection for providing output line power; and a common ground link for the input and output power.

2. A connector according to claim 1, wherein the connections and ground link are arranged in a single row.

3. A connector according to claim 1 or 2, wherein the ground link comprises a connection intermediate the input connection and the output connection.

4. An uninterruptible power supply (UPS) for a personal computer, which normally operates on AC line power, the UPS comprising: a battery, which stores electrical energy; an inverter which receives the energy stored in the battery and converts it to an AC output voltage which is supplied to the computer in the event of a voltage variation in the line power; and a line voltage detector, which senses the voltage variation in the line power and actuates the inverter responsive thereto, the detector comprising: an optocoupler, which receives the line voltage, and which outputs a signal voltage responsive thereto which is substantially lower than the line voltage; and a comparator, which receives the signal output from the optocoupler and compares the signal voltage to a predetermined reference voltage.

5. A UPS according to claim 4, wherein the optocoupler has a known temperature response, and comprising a temperature-responsive element having a temperature response complementary to that of the optocoupler, so that a response of the line voltage detector to the variation in the line power is substantially temperature-independent.

6. A UPS according to claim 4 or 5, wherein the inverter comprises an oscillator which oscillates at a line frequency substantially constantly, whereby when the line voltage detector actuates the inverter, the AC output voltage is supplied to the computer substantially without delay.

7. A UPS according to any of claims 4-6, wherein the UPS resides within the personal computer.

8. An uninterruptible power supply (UPS) for a personal computer, which normally operates on AC line power at a predetermined line voltage and frequency, the UPS providing an AC output into a load and comprising: a battery, which stores electrical energy at a voltage substantially lower than the line voltage; a DC-to-DC converter, which receives the energy stored in the battery and converts it to a DC output at a voltage generally comparable to the line voltage; and an inverter which receives the output from the DC-to-DC converter and generates the AC output with a substantially constant open duty cycle, irrespective of the load.

9. A UPS according to claim 8, wherein the DC-to-DC converter comprises a planar transformer.

10. A UPS according to claim 8 or 9, wherein the DC-to-DC converter varies the DC output voltage responsive to the load.

11. A UPS according to claim 10, wherein the DC-to-DC converter receives a feedback signal indicative of the load.

12. A UPS according to claim 10 or 11, wherein the DC-to-DC converter comprises a high- frequency oscillator, which generates width-modulated pulses for controlling the variable DC output voltage.

13. A UPS according to any of claims 8-12, wherein the UPS resides within the personal computer.

14. A UPS according to claim 13, wherein the personal computer includes a plurality of mutually parallel slots on an internal bus with a predetermined spacing therebetween for insertion of extension cards thereinto, and wherein the UPS comprises a printed circuit card which occupies a single one of the slots.

15. A UPS according to claim 14, wherein the battery is housed inside the personal computer, but is not mounted on the printed circuit card.

16. An uninterruptible power supply (UPS) for supplying lines power to a personal computer having an internal bus and a plurality of mutually parallel slots on the bus, the UPS comprising: a printed circuit card having circuit components mounted thereon which is inserted into one of the slots; and a safety unit, which verifies proper insertion of the card into the slot and prevents the

UPS from supplying lines power if it is not properly inserted.

17. A UPS according to claim 16, wherein the safety unit acts as a power switch, such that no separate on-off switch is connected to the printed circuit card.

18. A method for supplying uninterruptible power to a personal computer, which normally operates on AC line power at a predetermined line voltage and frequency, comprising: storing electrical energy in a battery at a voltage substantially lower than the line voltage; receiving the energy stored in the battery and converting it to a DC output at a voltage generally comparable to the line voltage; and inverting the DC output to generate an AC output into a load with a substantially constant duty cycle, irrespective of the load.