WO1991012644A1

WO1991012644A1 - Emergency power source

Info

Publication number: WO1991012644A1
Application number: PCT/NL1991/000017
Authority: WO
Inventors: Gerben Simon Hoeksma
Original assignee: N.V. Nederlandsche Apparatenfabriek Nedap
Priority date: 1990-02-08
Filing date: 1991-02-07
Publication date: 1991-08-22
Also published as: NL9000296A

Abstract

Emergency power source for use with a switching supply supplied from the mains, and switching supply for use with an emergency power source. The emergency power source comprises at least one battery, a converting device which can convert the battery voltage to the voltage to be provided to a DC voltage output by the emergency power source, drive means for driving the converting device, and means for charging the at least one battery, the DC voltage output being designed to be detachably connected to the switching supply and the means for charging the at least one battery being part of the converting device and in operation receiving DC supply voltage from the switching supply. The switching supply comprises an input rectifier, a capacitor connected in parallel therewith and a DC-DC-converter and further comprises a connector with at least two connecting members between which prevails the voltage prevailing across said capacitor.

Description

Title: Emergency power source

The invention relates to an emergency power source for use with a switching supply supplied from the mains, comprising at least one battery, a converting device which can convert the battery voltage to the voltage to be provided to a DC voltage output by the emergency power source, drive means for driving the converting device and means for charging the at least one battery.

Such emergency power sources are used for apparatus which desirably continues operating when the mains voltage, and hence the regular supply, fails, for instance process control computers or so-called "servers" in a computer network. Well known are central emergency power sources that generate an AC voltage as soon as the mains voltage fails . These central emergency power sources, however, are rather expensive. Another solution is to couple the emergency power source to the switching supply which supplies the apparatus that is to continue operating when the mains fails, as described, for instance, in an article by Patrick Hunter entitled "Battery Backed Switcher Provides UPS Capability" published in the journal PCIM Europe, November 1989. In this article, various possibilities are described to provide a so-called battery- back-up, which, however, all have in common that for charging the batteries a separate battery-charger is employed. From the publication "Analysis of the control behaviour of a bidirectional high-frequency DC-DC-converter", published in the Proceedings of the Fifteenth International PCI-Conference, June 6-9, 1988 - Munich, pp. 344 ff, it is further known that energy can be passed through a DC-DC-converter in two directions. Accordingly, in the circuit shown in Fig. 5 of the Hunter article, the battery charger could be omitted, if the upconverter were of bidirectional design. Further, in the known solutions for emergency power supplies, a supervision and control circuit is required, which controls the charging of the batteries and the switching on of the emergency power source, and the entire emergency power circuit is built into the supply, as shown for instance in Figs . 6 and 7 of the Hunter article. This increases the cost price of the supply considerably. Although the batteries can be connected externally to provide for the cases where an emergency power source is indeed required, this means an unnecessary increase in cost price in cases where this emergency power source is not desirable.

Further, the publication EDN Electrical Design News vol 28, no. 13, June 1983, pp. 143-148: Technology Update: "Auxiliary battery inputs transform switchers into uninterruptible power supplies" discloses an emergency power source of the type described hereinabove, in which the regular supply and the emergency power source is connected via a kind of OR gate to the apparatus to be provided with supply voltage. For charging the batteries of the emergency power source a separate charging device of the type trickle charger is required.

The object of the invention is to overcome the drawbacks outlined and more particularly to provide an emergency power source which can be coupled to a switching supply according as desired, without the cost price of this supply being appreciably increased. It is a further object of the invention to provide an emergency power source which can be manufactured at low cost by virtue of its simplicity. To that effect, according to the invention an emergency power source of the type described is characterized in that the DC voltage output is designed to be detachably connected to the switching supply and that the means for charging the at least one battery are part of the converting device and in operation receive DC supply voltage from the switching supply. A switching supply for use with an emergency power source, which switching supply comprises an input rectifier, a capacitor connected in parallel therewith and a DC-DC- converter, is characterized according to the invention by a connector with at least two connecting members, between which prevails the voltage prevailing across the capacitor. Hereinafter, the invention will be explained, by way of example, with reference to the accompanying drawings of one embodiment. In said drawings:

Fig. 1 is a block diagram of an embodiment of a switching supply with additional connection for emergency power supply according to the invention;

Fig. 2 is a block diagram of an embodiment of an emergency power source according to the invention;

Fig. 3 is a more detailed diagram of an embodiment of an emergency power source according to the invention; and

Fig. 4 is a schematic time diagram of the course of a number of voltages against time in the case of mains failure.

In the switching supply 1 shown in Fig. 1 the input AC mains voltage U_ac is rectified by rectifier 2 and smoothed by capacitor 3. A DC-DC-converter 4 converts the DC voltage across capacitor 3 to one or more galvanically separated output voltages Ui, U2 indicated at 5. The DC voltage U c across capacitor 3 is also applied to the terminal pins or sockets 8 and 9 of a connector 7 arranged in the supply and to which an emergency power source can be connected. Provided further in the embodiment shown is an additional connection with an additional pin or socket 10 of the connector 7. In operation the pin or socket 10 carries an auxiliary voltage which is typically 5V to 30V DC relative to pin or socket 9. Such a DC voltage is already present in many switching supplies for the supply of the primary drive circuits in the DC-DC-converter 4 of Fig. 1. Further, via a signal switch 6, the DC-DC-converter can be switched on and off. Accordingly, the only additional provision in the supply is the connector 7 with connecting wires to the pins or sockets 8, 9 and 10. A block diagram of an embodiment of an emergency power source according to the invention is shown in Fig. 2. Via a connecting cable 18 with conductors 11, 12, and 13 and with a connector 14 at the end, which can be connected to the connector 7, the DC voltage of capacitor 3 of the supply and the auxiliary voltage are applied to a bidirectional DC-DC- converter 15, which is connected to batteries 16 and to a control circuit 17. The operation is as follows. As long as a mains voltage is present, the DC voltage is across capacitor 3, including a ripple voltage with double mains frequency between two values Umin amd Umax (see also Fig. 4) . If necessary, the batteries can now be recharged via the bidirectional converter 15 in a known per se manner. In the case of lead batteries, this can for instance be done according to any one of the methods indicated in standard DIN 57510. When the mains voltage U_ac fails, as indicated in Fig. 4 at time tl, the voltage across capacitor 3 will fall slowly until a predetermined value Ut,_u s reached at time t2. This event is detected by the control circuit 17 which subsequently causes the converter 15, from that moment onwards, to provide power to the supply from the batteries via the lines 11,13, the voltage across capacitor 3 being kept approximately constant. This continues until the mains voltage returns or until the battery voltage has fallen too far, or until the emergency power source is switched off by a control command via a connection, not shown. Such a command can for instance be given by the apparatus, for instance a computer, which is provided with supply energy by the supply 1.

During emergency supply operation the lines 11, 13 form a DC output of the emergency power source, but in normal operation serve to feed energy to the emergency power source for charging the batteries 16.

As can be seen in Fig. 3, in this embodiment the control circuit 17 and drive circuits 20,21 of the emergency power supply are supplied by the auxiliary voltage which is drawn from the supply via the connection 10,12. In this manner the batteries are prevented from running down when the emergency power source is switched off, when the supply is inoperative or when the emergency power source is uncoupled (connector 14 being disconnected, for instance during storage before delivery) . Thus it is also accomplished that when the connector 14 is pulled from the connector 7 of the supply, the emergency power source will not begin to operate. If the control and drive circuits were supplied by the batteries, upon uncoupling the connector 14 from connector 7, the control circuit 17 would detect too low a DC voltage whereby the emergency power source would be actuated and the batteries would run down very soon. When the supply is switched off via signal switch 6, there is no auxiliary voltage U_aux present either, but there is a DC voltage across capacitor 3. When in this condition, the mains voltage fails, for instance as a result of the removal of the mains plug (not shown) via which the mains AC voltage U_ac is applied, the emergency power source shown cannot be actuated either because the auxiliary voltage, which supplies the control circuit of the emergency power source, is then absent as well. This manner of switching on/off further prevents the emergency power source from being actuated each time the DC voltage across capacitor 3 fails, as would be the case if switching the supply on and off were effected by a switch that switches the mains voltage U_ac on and off directly. Heavy duty on the part of the batteries would be the result, certainly if this were to happen once or more than once every day. This would lead to a considerable reduction of the lifetime of the batteries or necessitate the use of much more costly batteries.

The emergency power source shown in Fig. 3 comprises a bidirectional DC-DC-converter 15 with a transformer 19. The coil 24 of the transformer coupled to cable 18 is connected in series with a bidirectional semiconductor switch 22 which is driven by drive circuit 20. Similarly, the coil 25 connected to the batteries is connected in series with a bidirectional semiconductor switch 23 which is driven by drive circuit 21.

The bidirectional semiconductor switches 22 and 23 may for instance be transistors of the MOSFET type and the built-in antiparallel diodes can be used as rectifiers . Because the dynamic properties of said diodes are rather poor, oftentimes a diode (not shown) is incorporated in series with the MOSFET and a separate parallel diode is used (not shown either) . It goes without saying that use can also be made of other types of semiconductors which can block the voltage in one direction, and can allow current to pass in two directions, this passage being controllable in one direction. The drive circuits for the semiconductor switching elements of the DC- DC-converter may alternatively be fed from the DC voltage prevailing across the contacts 11 and 13 or the battery voltage, but only then when a special signalling cable or a special signalling contact which can for instance be part of the connector indicates that the emergency power source is connected to the switching supply. In this manner, too, it is avoided that the emergency power source will begin to operate if the connection with the switching supply were interrupted It is observed that after the foregoing various modifications will readily occur to those skilled in the art. Thus, the emergency power source could for instance comprise two DC-DC converters, one of them serving to charge the batteries 16 and the other serving to feed supply energy from the batteries to the supply which the emergency power source is connected to.

These and similar modifications are understood to fall within the scope of the invention.

Claims

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1 . An emergency power source for use with a switching supply supplied from the mains, comprising at least one battery, a converting device which can convert the battery voltage to the voltage to be provided to a DC voltage output by the emergency power source, drive means for driving the converting device and means for charging said at least one battery, characterized in that the DC voltage output is designed to be detachably connected to the switching supply and that the means for charging said at least one battery are part of the converting device and in operation receive DC supply voltage from the switching supply.

2. An emergency power source according to claim 1, characterized in that the converting device comprises a bidirectional DC-DC-converter which can both transmit power from said at least one battery to the DC voltage output and transmit power from the DC voltage output to said at least one battery.

3. An emergency power source according to claim 1 or 2, characterized in that the emergency power source is provided with a connector with at least two connecting members, which form the DC voltage output, which connector is designed to be detachably connected to a connector of the switching supply, which likewise comprises at least two connecting members, which in turn are connected to the DC voltage end of an input rectifier of the switching supply.

4. An emergency power source according to any one of the preceding claims, characterized in that the converting device comprises a plurality of semiconductor switching elements which in operation are driven by drive circuits and that the drive circuits are provided with supply voltage from an auxiliary voltage present in the switching supply via an additional electrical connection between the switching supply and the emergency power source.

5. An emergency power source according to claim 4, characterized in that said additional electrical connection is detachable.

6. An emergency power source according to claims 3 and 5, characterized in that the detachable additional electrical connection is formed by additional connecting members of the respective connectors.

7. An emergency power source according to any one of the preceding claims, characterized by a control circuit which in operation causes power to be provided from the DC voltage output to said at least one battery, if said at least one battery is not yet fully or practically fully charged and when the DC voltage on the DC voltage output is above a predetermined first level.

8. An emergency power source according to claim 7, characterized in that the control circuit in operation causes power to be supplied from said at least one battery to the DC voltage output, as soon as the DC voltage on the DC voltage output has fallen to a second level, lower than said first level, the transmitted power then being controlled in such a way that in emergency power supply operation this second level is substantially maintained.

9. An emergency power source according to any one of the preceding claims, characterized by signalling means which indicate whether the emergency power source is connected to a switching supply.

10. A switching supply for use with an emergency power source according to any one of the preceding claims, in which the switching supply comprises an input rectifier, a capacitor connected in parallel therewith and a DC-DC-converter, characterized by a connector with at least two connecting members, between which prevails the voltage prevailing across said capacitor.

11. A switching supply according to claim 10, characterized in that the connector comprises a third connecting member, carrying an auxiliary DC voltage prevailing in the DC-DC- converter in operation.

12. A switching supply according to claim 10 or 11, characterized by an on/off switch connected to the DC-DC- converter.

13. Assembly of a switching supply according to any one of claims 10-12 and an emergency power source according to any one of claims 1-9.