PARTITIONED UNINTERRUPTIBLE POWER SUPPLIES

Abstract: An uninterruptible power supply has a power supply housing (11) containing an input for receiving AC utility power, and an AC to DC converter (2) and a switching means (4) for supplying a chopped DC signal to a primary winding (5) of a transformer (6). A pair of secondary windings (7, 8) supply DC power to a pair of regulated DC outputs. The housing (11) also contains a high power FET switch (12) which is connected between one of the secondary windings (6, 7) and a terminal of a connector provided in a wall of the housing (11). An external control module (10) is arranged to be coupled to the connector to complete an auxiliary power supply circuit. When the AC utility power fails, power is coupled from a rechargeable battery, through the control module (10) and the FET switch (12), to the regulated DC outputs of the supply.

Description: PARTITIONED UNINTERRUPTIBLE POWER SUPPLIES The present invention relates to uninterruptible power supplies and in particular, though not necessarily, to uninterruptible power supplies for computers. Uninterruptible power supplies are required for many applications where the loss of mains power has serious implications. For example, where computer systems are used to transfer large amounts of data over a network, it is essential that a backup power supply is available in the event that mains power is lost, in order to prevent the loss of valuable information. Document WO 91/07803 describes an uninterruptible power supply for integration into an internal electrical device power supply and which includes an AC to DC converter and an inverter circuit used to couple power through a transformer into a set of secondary windings arranged to provide regulated DC output voltages for internal use by the electrical device. A rechargeable battery is coupled directly to one of the secondary windings of the transformer and is arranged to provide electrical power to the regulated DC outputs when the input AC voltage fails or drops below a predetermined level. Whilst the uninterruptible power supply described in WO 91/07803 represents a significant advance over earlier uninterruptible power supplies there remains a reluctance on the part of some manufacturers to incorporate these power supplies into their devices as standard due to the added cost. In addition, because the uninterruptible power supply of WO 91/07803 integrates the components of the AC supply and the auxiliary supply it is extremely inconvenient to retrofit this type of supply to a device which has already been provided with a conventional mains supply. It is an object of the present invention to overcome or at least mitigate certain of the disadvantages of existing uninterruptible power supplies. It is a second object of the present invention to provide an AC mains supply, arranged to be contained within a power supply housing of an electrical device, which is provided with "hooks" to enable an auxiliary power supply to be retrofitted to the AC mains supply. According to the present invention there is provided a mains driven power supply for powering an electrical device and built into a power supply housing, the supply comprising: an input for receiving AC utility power; an AC to DC converter coupled to said input for receiving AC power therefrom; switching means selectably operable to couple DC power from the AC to DC converter to at least one regulated DC output of the supply; a plurality of high current components of an auxiliary power supply; and connection means provided in the housing for coupling the supply to a circuit arranged externally of the housing and comprising the remaining components of the auxiliary power supply including energy storage means. The present invention thus enables the electrical device to be powered in the normal way even if said external circuit is not connected. Connection of this circuit is only required when the auxiliary backup facility is required. In a preferred embodiment of the present invention, the AC to DC converter comprises a transformer to which a chopped DC signal is supplied by said switching means. The duty cycle of the chopped signal is controlled by a pulse width modulator in order to maintain the DC output level(s) of the supply at the correct level(s). One of said high current components of the auxiliary power supply which are contained within the power supply housing is a high power switch, for example a FET, controlled by the pulse width modulator when the power supply is connected to the external circuit and when an AC utility power failure is detected. According to a second aspect of the present invention there is provided an uninterruptible power supply comprising a mains driven power supply according to the above first aspect of the invention and an external control module, containing said remaining components of the auxiliary supply with the possible exception of the energy storage means, for coupling to said connection means in order to complete the auxiliary power supply. Preferably, the energy storage means of the external circuit is a rechargeable battery and the mains power supply includes means for providing power from one of said regulated DC outputs to a terminal of said connection means for supplying power to recharge the battery. Preferably, the external control module includes means for detecting failure of AC utility power to the AC input of the mains power supply. The external control module may also comprise a battery recharger and optionally a battery management system, in the case where the external storage means is a rechargeable battery. The battery charger may derive power from a regulated DC output of the mains supply. Preferably, the external control module includes a DC to AC converter for generating AC power from power supplied from the energy storage means when the AC input fails. Where the power supply AC to DC converter comprises a transformer, the DC to AC converter is preferably coupled to the primary winding of the transformer to receive power from the energy storage means. AC power generated in this way may be used, for example, to power a computer monitor. For a better understanding of the present invention and in order to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 shows a conventional mains driven DC power supply which does not include an auxiliary power supply; Figure 2 shows a partitioned uninterruptible power supply including an auxiliary power supply; and Figure 3 shows in detail the external control module of the uninterruptible power supply of Figure 2. There is shown in Figure 1 a conventional mains driven power supply which is arranged to provide regulated DC voltages of 5V and 3.3V at its outputs. AC utility power is received from the power mains via an ON/OFF switch 26. The supply includes an electromagnetic interference (EMI) filter 1 at its input and a full wave rectification circuit, comprising a four diode arrangement, the output of which is controlled by a power factor corrected (PFC) pre-regulator to provide at a storage capacitor 28 a constant DC voltage of 384V. The PFC pre-regulator comprises a FET 2 which is switched on and off by a pulse width modulator 3. An inverter, comprising a FET 4 provides a chopped DC signal_to a primary winding 5 of a transformer 6. The current flowing in the primary winding induces corresponding, stepped-down, voltages on a pair of secondary windings 7, 8 of the transformer. Respective diode pairs and inductor/capacitor filter arrangements smooth the outputs from the two secondary windings to provide the regulated DC output voltages. Voltage feedback from one of the DC outputs is provided via a shaping circuit 14a and an opto-isolator 14c to a pulse width modulation controller 9 which varies the duty cycle of a switching signal provided to the gate of the FET 4 of the inverter in order to maintain the output voltages at their correct levels. The PWM controller 9 also has current feedback from a current sensing resistor 4a connected in series with the FET 4 to control the rate of change of the duty cycle output. Figure 2 shows how the power supply of Figure l may be modified to include "hooks" which enable the power supply to act as an uninterruptible power supply when an external control module 10 is coupled thereto. It is envisaged that the modified power supply including these hooks will have internal electrical connections leading to an interface mounted in a sidewall of the power supply housing 11 (see below) . This interface allows the external control module 10 to be electrically coupled to the modified power supply. The additional components which act as "hooks" for the existing power supply provide the minimum number of high current circuit components at only a modest cost penalty and include an n-channel FET 12 connected between a battery +ve terminal 11B of the interface, via a battery capacitor 12a connected to the battery -ve terminal lie which acts to smooth the current drawn from the battery and to reduce voltage spikes in the circuitry, and one of the secondary windings 8 of the transformer. It is important that the FET switch 12, and also the capacitor 12a, be within the supply housing 11, physically close to the transformer 6, in order to prevent the creation of current loops which would otherwise create significant amounts of electromagnetic interference. Where the battery voltage of the external control module 10 is less than the amplitude of the chopped waveform induced on the secondary winding 8 from the primary winding 5, a commutation diode 13 is connected between the FET 12 and the secondary winding 8. However, in cases where the battery voltage is greater than the voltage induced on the secondary winding, the diode is not necessary. A current sensor 14, including an inductive coupling to the line which conducts current from the FET 12 to the secondary winding, provides a current feedback signal to the pulse width modulation controller 9 in cases where AC utility power fails and power is drawn from the auxiliary supply. An inductive coupling 15 to the filter inductors of the regulated DC outputs of the supply is arranged to supply a battery charging current through a corresponding battery charger supply terminal 11A of the interface to recharge an external battery. Figure 3 shows in more detail three sub-modules of the external control module 10. The control modules each have a set of connection pins, shown along the top of the modules in Figure 3, which mate with corresponding terminals 11A to UK of the interface of the main power supply. A control logic module 16 comprises an AC fail detector 17 which operates through a control gate 18 to selectively enable or disable the switching signals provided to the FET 12 of the auxiliary power supply via terminal 11D. The AC fail detector functions by monitoring the duty cycle of the switching signal output by the PWM controller and received by the fail detector at terminal HE. If the duty cycle exceeds a predefined limit, indicative of an AC failure, the PWM signal output by the PWM controller 9 is routed via an optical isolator 18a and a driver and level shifter 18b to the auxiliary power supply FET 12. The FET 12 is switched on and off (in synchrony with the FET 4) to provide a chopped DC signal to the secondary windings 7,8 of the transformer. The driver and level shifter 18b is coupled to the source of FET 12, which is floating, such that the generated gate drive output signal is above or below the source level by the required amount to ensure correct switching of the FET 12. Following an AC failure, the AC fail detector 17 continuously tests the PWM signal to see if its duty cycle falls below a predetermined threshold level indicative of the return of AC power. When the AC utility power does return to the AC input, the control logic module 16 ceases routing switching signals from the PWM controller 9 to the FET 12 of the auxiliary power supply and causes the battery to commence recharging. The control logic module 16 also contains timing logic 19 which receives an AC failure signal from the AC fail detector 17 indicative of AC failure. The timing logic causes a buzzer 19a to be sounded when the power fails, giving an audible warning to a user, and at regular intervals thereafter. A further, distinctive warning may be sounded when the battery is nearly exhausted. The timing logic also sends an "inhibit charge" signal to a battery management module (see below) . The ON/OFF switch comprises a spare pole 27 which is closed when the AC power is deliberately switched off. Closing the spare pole couples a "shutdown" input of the PWM controller to earth, causing the PWM signal to be terminated. This prevents the back-up power supply being activated when the supply is deliberately turned off. The spare pole may need to be added to the main power supply as a "hook" although many conventional power supplies already have such a spare pole. The external control module 10 has a battery management module 20 which receives charging current through terminal HA of the interface as described above. When AC utility power is present at the AC input the received charging current is controlled by a battery charger 21 to charge a battery (not shown) which is coupled to appropriate input terminals ("BATTERY +VE INPUT" and "BATTERY -VE INPUT") of the battery management module 20. This module also includes a battery management unit 22 which is arranged to provide an indication of the power levels remaining in the battery. When the battery management unit 22 receives an "inhibit charging" command from the control logic module 16 charging of the battery is stopped. This prevents the battery from being recharged from its own power. An AC inverter module 23 is provided for supplying AC power, for example, to power a video display unit of a computer. Where the AC supply is functioning normally, the switch 23a is maintained in position 2 such that terminals UK and 11J are short circuited. The utility AC line input is therefore coupled directly to the AC live output of the supply. In the event that AC utility power failure is detected by the control logic module 16, an AC failure signal is transmitted from the control module to a power switch 24 of the AC inverter module and to the switch 23a. This failure signal causes the switch 23a to move to position Z, coupling terminal UK and the AC live output to an output of the power switch 24. The power switch receives 384V DC from a connection made across the energy storage capacitor 28 (terminals 11G and 11F) which, when the AC fail signal is received, is chopped in an "H" bridge inverter of the power switch 24 to provide a 50/60HZ stepped signal at the output now coupled to terminal UK. The power switch 24 is connected to both the utility and the output neutral lines via terminal 11H. In circumstances where the external control module is not present and it is required to operate the power supply as a normal unbacked power supply, a dummy connector is coupled to the supply interface. The dummy connector short-circuits terminals UK and 11J allowing AC power to be coupled to the AC out line. The control module 16 has an additional gate drive output (Gate DR2) , as shown in Figure 3, in order to allow the module to be used in cases where the AC to DC converter of the auxiliary power supply comprises two power switches (e.g. requiring in-phase and out of phase drive signals) . The PWM signal supplied to the second date drive input is received from a second PWM signal output (PWM2) . This arrangement can also be used to operate two completely independent power supplies with a single external control module and battery. As will be apparent from Figure 2 in particular, the additional components, or hooks, which must be added to the basic power supply to enable the subsequent hook-up of the external control module are relatively few and inexpensive. The majority of components are contained within the external control module which may be supplied to the user as an optional extra. The provision of an interface connector on the basic power supply also ensures that completion of the UIPS is a relatively simple procedure. It will be appreciated that the supply described above, when completed with the external control module 10 and the battery, operates in substantially the same way as the power supply described in WO 91/07803. It will also be appreciated that various modifications may be made to the above described embodiment without departing from the scope of the present invention. For example, the battery may be contained in the external control module instead of being external to it. The external control module may be arranged outside of the power supply housing but inside the electrical device housing or may be external to both these housings.

Claims: CLAIMS 1. A mains driven power supply for powering an electrical device and built into a power supply housing, the supply comprising: an input for receiving AC utility power; an AC to DC converter coupled to said input for receiving AC power therefrom; switching means selectably operable to couple DC power from the AC to DC converter to at least one regulated DC output of the supply; a plurality of high current components of an auxiliary power supply; and connection means provided in the housing for coupling the supply to a circuit arranged externally of the housing and comprising the remaining components of the auxiliary power supply including energy storage means. 2. A power supply according to claim 1, wherein the AC to DC converter comprises a transformer to which a chopped DC signal is supplied by the switching means. 3. A power supply according to claim 2, wherein the auxiliary power supply comprises second switching means coupled between the energy storage means and a secondary winding of the transformer, the second switching means being arranged to couple DC power from the energy storage means to the or each DC output of the supply when the AC utility power level drops below a threshold level. 4. A power supply according to claim 3, wherein the second switching means comprises a high power switch controlled by a pulse width modulator, the switch being contained within the power supply housing. 5. A power supply according to any one of the preceding claims, wherein the energy storage means of the external circuit is a rechargeable battery and the power supply includes means for providing power from a regulated DC output to a terminal of the connection means for supplying power to recharge the battery. 6. An uninterruptible power supply comprising a mains driven power supply according to any one of the preceding claims and an external control module which contains said remaining components of the auxiliary supply with the exception of the energy storage means, the control module being arranged to connect with said connection means and an energy storage means in order to complete the auxiliary power supply. 7. An uninterruptible power supply comprising a mains power supply according to any one of claims 1 to 5 and an external control module which contains all of said remaining components of the auxiliary power supply, the control module being arranged to connect with said connection means in order to complete the auxiliary power supply. 8. A power supply according to claim 6 or 7 when appended to claim 3 wherein the external control module includes detection means for detecting failure of AC utility power to the AC input of the mains power supply and, in the event that such a failure is detected, for switching off the first switching means and for switching on the second switching means. 9. A power supply according to claim 8, wherein the failure detection means comprises a comparator for detecting a fall in the DC output of a regulated DC output of the supply. 10. A power supply according to any one of claims 6 to 9 when appended to claim 5 wherein the external control module comprises a battery recharging circuit and a battery management system. 11. A power supply according to any one of claims 6 to 10, wherein the external control module comprises an AC to DC converter coupled to, or arranged to be coupled to, the energy storage means for generating AC power when the AC input fails.

Inventors: LAVIN J VINCENT, PUCHIANU SILVIU, STANLEY ALASTAIR, LAVIN, J., VINCENT, PUCHIANU, SILVIU, STANLEY, ALASTAIR
Applicants: LAVIN J VINCENT, MAGNUM POWER SOLUTIONS LTD, PUCHIANU SILVIU, STANLEY ALASTAIR, LAVIN, J., VINCENT, MAGNUM POWER SOLUTIONS LIMITED, PUCHIANU, SILVIU, STANLEY, ALASTAIR
Application year: 1996
Main classification: H02J9
IPC codes: H02J9