IE46201B1

IE46201B1 - Electrical supply arrangements for electric clocks

Info

Publication number: IE46201B1
Application number: IE255/78A
Authority: IE
Original assignee: Heliowatt Werke
Priority date: 1977-02-09
Filing date: 1978-02-06
Publication date: 1983-03-23
Also published as: LU78837A1; FR2380582A1; DE2705919A1; NL7714130A; IT1092390B; DK56878A; BE863498A; IE780255L; GB1582318A; IT7819962A0

Abstract

Electronic drive circuit for charging clock with stepper motor, mechanism and time disc. The accumulator for the power supply in the event of a mains failure is mounted, independently of the power supply of the drive circuit, so that in the event of a defective accumulator normal operation on the network is not possible. assigned, the charging current of the accumulator being programmable by means of a combination of resistance of which one is a thermistor, the motor drive circuit provided with a current limitation, the programmable motor current and, in case of network failure automatically switched to an auxiliary oscillator.

Description

This invention relates to electrical supply arrangements for electric clocks, and is particularly but not exclusively concerned with time switches incorporating such arrangements.

There are known electronic clock drives comprising 5 stepping motors, generally simple bipolar motors having permanent magnet rotors, which are activated by integrated switching circuits (for example, in accordance with the CMOS technique). There are used as energy sources, for example, dry batteries whose voltage is exactly known and whose voltage drop during their lifetime is only small.

Time switch clocks are usually supplied with mains energy, an accumulator often being provided to act as an energy source in the event of mains failure. The accumulator is connected in parallel with the supply voltage terminals of the drive arrangement and charged, and kept fully charged, by a small trickle current during mains operation. However, accumulators, and particularly nickel-cadmium accumulators which are often used, have a tendency to spontaneous short-circuiting, even when they are fully charged. In the event of such a short20 circuit, the clock would stop even in mains operation, in previously proposed arrangements of which we are aware.

Preferred embodiments of the invention comprise time switches which are improved in this respect.

According to the present invention, there is provided an electrical supply arrangement for an electric clock, the -24 63(11 arrangement comprising: a first set of input terminals for receiving a mains supply; a second set of input terminals for receiving a supply frcm an accumulator; < a set of output terminals for connection to a clock; charging circuitry for charging an accumulator connected to the second set of input terminals when a mains supply is present at the first set of input terminals, the charging circuitry including in a resistance ccnbinaticn a temperature-dependent resistor having a specific tenperature characteristic, for providing temperature compensation of the charging current; and control circuitry arranged to provide on the output terminals an output constituted by or derived frcm the mains supply in normal use of the arrangement and the accumulator supply upon failure of the mains supply, the arrangement being such that, when a mains supply is present, the second set of input terminals is isolated frcm the first set of input terminals and frcm the output terminals to the extent that, in the event of an accumulator being absent or defective, normal mains output terminals is substantially unaffected.

To assist understanding of the invention, there will new be described, by way of exanple, a preferred embodiment of the invention, comprising an electric time switch which is provided with an electric clock having a stepping motor, gearing, a time dial, and exchangeable slideable maribers on the time dial for operating contacts of the switch.

The electric clock is also provided with an electrical supply arrangement which comprises first and second sets of input terminals, and a set of output terminals. The first set of input terminals Is connected to receive a mains supply, and the second set of input terminals is connected to receive .3 a supply from an accumulator, such as, for example, a nickelcadmium accumulator. The supply arrangement is arranged to provide an output on the output terminals, which are connected to supply the clock.

Under normal conditions of use, control circuitry of the supply arrangement provides on the output terminals an output derived from the mains supply. However, in the event of a failure of the mains supply, the control circuitry is arranged to provide on the output terminals an output derived from the accumulator supply. Whilst the clock is being supplied, under normal conditions, from the mains, charging circuitry of the supply arrangement is operative to charge the accumulator, and to maintain the accumulator fully charged..

The accumulator has its own separate charging circuit, and is not directly connected in parallel with the first set of input terminals. Thus, when a mains supply is present, the second set of input terminals is isolated from the first set of input terminals and from the output terminals to the extent that , in the event of an accumulator being absent, or defective (for example short circuited), normal mains output from the output terminals is substantially unaffected.

Particularly in the case of nickel-cadmium accumulators, temperature compensation of the charging current is desirable both with normal cells and with sintered cells. For this purpose, the charging circuitry includes a resistance combination -446201 which consists of an ordinary resistor and a temperaturedependent resistor having a specific temperature characteristic. Preferably, the temperature-dependent resistor is readily removable such that it may be replaced by a temperature5 dependent resistor of different value, in dependence upon the type of accumulator being used with the supply arrangement.

It is conceivable that the output voltage of such a supply arrangement could fluctuate appreciably, both in mains operation and in accumulator operation. Thus, for example, depending upon the state of charge and the temperature, the voltage of two battery cells may vary between 2 volts and 3.2 volts. When the stepping motor of the clock is driven by a voltage generator, the current absorption and torque increase with the supply voltage. This is generally undesirable, because the motor may be caused to rotate jerkily, thus having a wearing effect on the gearing of the clock. In order to overcome this, therefore, the supply arrangement includes means for limiting the output current through the output terminals. This is preferably achieved by employing a current-limited voltage generator to produce the output on the output terminals. As an alternative to this, a current generator may be employed,but this is generally less advantageous, because the motor circuit would be affected by the very high internal resistance of the generator. As a result of this, dynamic braking of the motor may effectively disappear, such that the motor tends to oscillate -54 6 2 01 considerably about its positions of rest, possibly to the extent that the motor may rotate backwards under heavy loading.

Advantageously, the arrangement for limiting the current of the voltage generator is programmable, so as to permit adjustment of the limit of the output current through the output terminals.

Timing pulses for the clock are derived, in normal mains operation, from the mains frequency. However, this reference frequency is no longer available upon a mains failure. For 10 this reason, the supply arrangement includes an auxiliary reference frequency oscillator, which may be, for example, either an HC oscillator or a quartz oscillator. The auxiliary oscillator is arranged automatically to take over control of the supply arrangement in the event of mains failure.

The electrical supply arrangement is preferably an allelectronic arrangement, and is advantageously integrated on a large-scale switching circuit, for example, in accordance with

Claims

1. CLAIMS!

1. An electrical supply arrangement for an electric clock, the arrangement comprising: a first set of input terminals for receiving a mains supply: a second set of input terminals for receiving a supply from an accumulator; a set of output terminals for connection to a clock; charging circuitry for charging an accumulator connected to the second set of input terminals when a mains supply is present at the first set of input terminals, the charging circuitry including in a resistance combination a temperaturedependent resistor having a specific temperature characteristic, for providing temperature compensation of the charging current; and control circuitry arranged to provide on the output terminals an output constituted by or derived from the mains supply in normal use of the arrangement and the accumulator supply upon failure of the mains supply, the arrangement being such that, when a mains supply is present, the second set of input terminals is isolated from the first set of input terminals and from the output terminals to the extent that, in the event of an accumulator being absent or defective, normal mains output from the output terminals is substantially unaffected. i

2. An arrangement according to claim 1, wherein the temperature-dependent resistor is readily removable such that it may be replaced by a temperature -dependent resistor of different value in dependence upon the type of accumulator to be g used with the arrangement.

3. An arrangement according to claim 1 or 2, including means for limiting the output current through the output terminals.

4. An arrangement according to claim 3, wherein the currentlimiting means is programmable so as to permit adjustment of the jLo limit of the output current through the output terminals.

5. An arrangement according to any preceding claim, including a reference frequency oscillator, the control circuitry being arranged to respond to a frequency of a mains supply when present and to respond to an output of the oscillator upon failure of the 15 mains supply. -846201

6. An arrangement according to claim 3 or 4 or to claim 5 as appendant thereto, including a voltage generator for providing the output on the output terminals.

7. An arrangement according to any preceding claim, arranged 5 to provide on the output terminals an output suitable for driving a stepping motor.

8. An arrangement according to any preceding claim, being an all-electronic arrangement.

9. An arrangement according to claim 8, constructed as an 10 integrated circuit.

10. An arrangement according to any preceding claim, including the accumulator.

11. An arrangement according to claim io, wherein the accumulator is a nickel-cadmium accumulator. 15

12. An electrical supply arrangement according to claim 1 and substantially as hereinbefore described.

13. An electric clock provided with a supply arrangement according to any preceding claim. -946301

14. An electric clock having a stepping motor and provided with a supply arrangement according to claim 12, or to claim .7, or to any one of claims 8 or lias appendant to claim 7.

15. An electric time switch provided with a clock according to 5 claim 13 or 14.

16. A time switch according to claim 15, including gearing, a time dial, and exchangeable slideable members on the time dial for operating contacts of the switch.