GB2071366A - Power supply arrangement for electronic watches and similar portable apparatus - Google Patents

Abstract

A power supply arrangement in an electronic timepiece Fig. 1, includes a thermo-electric generator TG which charges a buffer accumulator ACC via a chopper circuit comprising TR5, TR6 and a transformer formed by primary windings PW1, PW2 and the drive winding MW of the timepiece stepping motor which also functions as the transformer secondary. The AC voltage induced in the secondary MW is full-wave rectified by TR7 to TR10. A comparator COMP is activated periodically and controls a flip-flop FF to block the rectifier and chopper transistors and prevent possible discharge of the accumulator ACC via the rectifier if the thermo-electric voltage is too small. The whole of the drive energy for the watch is then provided by the accumulator. The motor drive current is fed via TR1 to TR4 which are controlled by outputs from a decoder DEC. <IMAGE>

Description

SPECIFICATION A miniature electronic device The present invention relates to a miniature electronic device.

By the expression "miniature device", there is to be understood a portable device, an instrument or an apparatus with small measurements whose power consumption is very small. The object therefore is to create a device with a compact supply unit and with as little energy loss as possible. An electronic wristwatch is a typical example of such a miniature device or instrument.

Other applications are, for example, digital-display thermometers, monitoring instruments worn on the body such as pulse frequency measuring devices or other bio-medical miniature apparatus, devices for locating persons, miniature calculators and the like, i.e. miniaturised electronic devices in general.

Miniature devices with an energy converter supplying an electric voltage are known. Thus, electronic calculators, watches and the like which have so-called solar cells for converting incident iight directly into electrical energy for activating the circuit, are known. More recently, thermoelectrical wristwatches have also been proposed, i.e. watches for which the energy for operating is produced with the aid of thermoelements, which make use of temperature differences between the warm casing base, when it is worn, and the cooler outer casing component, thermally isolated from this. Even by using a very large number of thermo-elements, connected in series, the available d.c. voltage is still very small so that there is no alternative but to increase the d.c. voltage with the aid of a chopper, a transformer and a rectifier.

In such devices, the current supply source of the miniature device can include, separate from a voltage generator, which apart from the energy converter can have means for altering the voltage produced by the converter, an accumulator able to be charged by the d.c. voltage generator. This can take over the supply of the device during a predetermined operating phase of the device and, above all, ensures that the device still functions if the d.c. voltage generator temporarily provides too little energy or too little current for the perfectly accurate working of the device.

In such a device with a buffer accumulator, a monitoring of the functioning of the current source must take place. Above all, it must be established whether the accumulator is to be charged. An essential criterion for this is the power of the energy converter. Now, it would be possible to compare the voltage of the d.c. voltage generator constantly with the voltage of the accumulator and, when the voltage of the d.c. voltage generator is insufficient, not to load this any further, until its energy level has reached a predetermined value again.

Such permanent control of the mode of operation of both main component parts of the source (d.c. voltage generator with energy transformer and accumuiator) is uneconomical and above all, with miniaturised electronic devices which are operated with weak energy sources and which may only have a very small power capacity, causes unnecessary energy losses.

According to the present invention, there is provided a miniature electronic device, including a current source for providing the device with current, which source has a d.c. voltage generator with a converter which transforms non-electrical into electrical energy and a buffer accumulator able to be charged by the d.c. voltage generator, the device further including an electronic comparator for monitoring operation of the source and, by comparing electrical magnitudes, producing electrical controlling signals determined by the mode of operation of the source, wherein there are means for establishing discrete chronologically spaced timing intervals and means for activating the comparator circuit during these timing intervals.

The invention is based amongst other things on the observation that with miniature devices of the type under consideration here, rio frequent or very sudden changes in the mode of operation of the energy converter normally occur. Particularly with the use of thermo-electric elements, the converter operates with considerable inertia. As a result, a constant control becomes unnecessary, presenting the possibility of improving the energy consumption by reducing the use of current.

Taking advantage of this knowledge, a miniature electronic device according to the present invention has, on the one hand, means for establishing discrete, chronologically spaced timing intervals, and, on the other hand, means for activating the comparison circuit during these timing intervals.

Thanks to the fact that the monitoring of the current source is no longer carried out permanently, but only takes place for example during the periodic timing intervals, the total current used by the device can be reduced. This can be of great significance in the case of miniature devices where the energy consumption is critical. Furthermore, this lends the possibility of controlling the release of the timing intervals, the length of which is advantageously very short and constant, so that the comparison measurements take place each time as long as the current usage of the device is not subject to any fluctuations (thus outside the time required by motor impulses or the like). In this way, clear criteria for the control of the device may be ascertained.

Observance of this condition is not guaranteed in the case of permanent control.

If the miniature device should include a rectifier circuit which rectifiers a chopped and transformed voltage, a further problem arises. The diodes suitable for rectification have a threshold voltage of about 0.5-0.6 V, even in the case of integrated diodes. Since the necessary supply voltage in the case of miniature devices is normally very small (typical value 1.5 V), one is obliged for example when two rectifying diodes are used, to produce an a.c. voltage amounting to about double the voltage which would have to be available if the diodes were to be actuated with even the smallest voltages, and pass current. As a result of this, considerable disadvantages result (power losses, less compact structure of the transformer etc.).These disadvantages can be eliminated in the sense of a further inventive concept with the aid of a rectifier circuit, which, instead of diodes, includes controllable semiconducting elements or integrated micro-switches controlled by electric fields, which are synchronously controlled by the chopper or by means controlling this. Such synchronously controlled rectifier elements require exceptionally little energy and can be integrated with little additional cost on the same chip as other circuit elements of the miniature device (at least on the same chip as the circuit components of the chopper circuit).

On the basis of this concept, one can, for example, rectify the transformed a.c. voltage which can be sinusoidal or consist of a train of pulses of opposite polarity, with integrated MOSfield effect transistors, which are directly controlled by a synchronisation circuit comprising logic elements which also controls the chopper.

One could also derive a train of pulses for the control of the rectifier circuit or the other components functioning as controllable switching elements directly from the chopper, also enabling the necessary synchronisation between the chopper and the rectifier circuit necessary for accurate and loss-free working.

In place of transistors, controllable switching elements of another type may possibly come into consideration, for example integrated microswitches which are actuated by an electric field.

Micro-switches of this type are already known, which can form part of an integrated circuit and which can be produced according to the customary technologies for integrated switches (conventional photo-lithographic and IC-process technology). Such switches have a controlling dimension of less than 1 mm and can consist essentially of a moveable silicon dioxide, metal covered blade and a mating contact.

The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a partly simplified circuit diagram of the electronics of an analogue wristwatch, with hands and a thermogenerator; and Figure 2 is a pulse diagram showing a series of pulse trains.

The watch illustrated schematically in Figure 1 includes, as a time norm, a quartz crystal Qwith a frequency of 32768 Hz for example. A frequency divider DIV reduces this frequency to 1 Hz at an output c. A voltage with a frequency of 8192 Hz is produced at an output a and the frequency at an output b amounts to 64 Hz. These three frequency divider outputs supply a decoder circuit DEC, which defines different timing intervals in a known way with the aid of logical switching means for the length of motor driving impulses, short-circuit duration of a motor-stator winding and detection by a comparator circuit.

The hands of the watch are driven by a bi-polar stepping motor, a stator winding MW of which is supplied by way of MOS-FET drive transistors TR 1 -TR4. Control of these transistors is effected by the decoder circuit DEC by way of NAND-gates NAND1 and NAND2 as well as inverters INV1 and INV2.

The stator winding MW fulfils the function of a secondary winding of a voltage transformer at the same time. This includes, furthermore, an elongate ferro-magnetic core CO as well as a two-piece primary winding PW1, PW2, or a primary winding with a centre tapping. The latter is connected to an electrically positive pole of a thermogenerator TG. Between an electrically negative pole of the generator TG and the terminals of the primary winding PW1, PW2 are the source and drain terminals of two MOS-FET chopper transistors TR5 and TR6, controlled in a push-pull arrangement by way of AND-gates AND1 and AND2.

The thermogenerator TG supplies an exceptionally slight voltage. Correspondingly, the voltage transformed must have a comparatively high step-up ratio.

The alternating voltage induced in the winding MW must be rectified to enable the circuit to be supplied. To this end, because of the conditions described above, four MOS-FET circuit transistors TR7-TR1 0 are present instead of diodes, which form a full wave rectifier and are directly connected to a buffer accumulator ACC. The task of the accumulator ACC consists in supplying the watch circuit if the voltage produced by the thermogenerator sinks below a certain level (if, for example, the watch is not worn for a period).

Additionally, the accumulator serves as a current supply source during certain short intervals, particularly for supplying the motor-stator winding MW with drive pulses.

The chopper transistors TR5, TR6 (via gates AND1 and AND2) and the circuit transistors TR7-TR1O (via AND3, INV3 and AND4, INV4), are synchronously controlled by AND-gates AND5 and AND6 which are themselves connected to inverters INV5 and INV6.

It is evident that the current source of the watch includes, on the one hand, a d.c. current generator, comprising the thermo-generator TG, a chopper and a rectifier, and on the other hand, the accumulator ACC.

If no special measures were taken, the accumulator ACC could be discharged by way of the transistors TR7-TR1 0 and the winding MW, if the current supplied by the rectifier fell below the level of the accumulator voltage. For this reason, a comparator circuit COMP if provided, whose input is fed by the current induced in the winding MW, and whose output determines the state of a flip-flop FF. This has three inputs, namely D (data), CK (clock), and R (reset) as well as an output Q.

The comparator circuit COMP acts, so to speak, as a detector circuit which rectifies the voltage taken from the winding MW and is compared with the voltage of the accumulator ACC. An OR-gate OR 1 activates or blocks the chopper transistors TR5 and TR6 according to the state of its inputs.

The mode of operation of the circuit is as follows.

The pulse diagram according to Figure 2 shows that the decoder circuit DEC emits a pulse MDSC every second, whose length is about 10 ms.

Additionally, a pulse MDC1 appears every second in alternation with a pulse MDC2 with a duration of about 10 ms also. The 8192 Hz pulses shown in the pulse diagram are illustrated in another time scale to aid clarity (the length in comparison to other pulses is stretched 40 times).

It should be assumed that, by means of corresponding coincidences of the pulse trains which are supplied to the inputs of the decoder circuit DEC (cf. the 8192 Hz train recognisable in the diagram according to Figure 2), pulse MDC2 is produced first of all. Thereby, the n-channel transistor TR4 passes into the conductive state. Although simultaneously a pulse also appears at the output MDSC, the p-channel transistor TR3 cannot conduct, as no signal appears at the output of the inverter INV2 and thus the signal appearing at the output of the gate NAND2 blocks this transistor. From the following (cf. Figure 2), it is evident that the p-channel transistor TR1 passes into the conductive state whereas the transistor TR2 (n-channel) remains blocked.In this way, the stator winding contains a drive pulse, the duration of which corresponds to the length of the pulse MDC2. In a similar way, the transistors TR2 and TR3 pass into the conductive state and the transistors TR 1 and TR4 remain blocked as soon as a pulse MDC1 is emitted. This means that the motor contains a drive pulse of opposite polarity at the beginning of the next second.

One can gather from the pulse diagram that a pulse MDSC beginning with the motor-controlling pulse MDC1 or MDC2, lasting however about 20 ms, is emitted from the decoder DEC every second. This pulse reaches respective inputs of the gates NAND1 and NAND2, and, in relation with each motor pulse respectively, has the result that during about 10 ms, the transistors TR3 and TR4 block (short-circuit interval). Between two pulses MDSC several drive transistors TR1-TR4 remain blocked.

The a-output of the frequency divider transfers 8192 Hz pulses to one input of each of gates ANDS and AND6 (the latter by way of inverter INV6). This means that 8192 Hz pulse trains are emitted from the outputs of these gates in phaseopposition as long as no pulse MDSC is present.

These pulses are designated in Figure 2 by CRC1 and CRC2 (chopper and rectifier control). The pulses CRC1 (from AND-gate AND5), as well as CRC2 (from AND-gate AND6), serve, on the one hand, to control the chopper transistors TR5 and TR6 (via the AND gates AND2 and AND1) and, on the other hand, to control the transistors TR7-TR1 0 (by way of AND3 and INV3 and AND4 and INV4) which operate the rectification of the alternative voltage induced in the winding MW.

The synchronous working of the chopper and the rectifier can be seen from this. Obviously, the input of the rectifier must be connected in this case with the terminals of the secondary winding in such a way that the polarity of the d.c. voltage of the rectifying output is consistent with that of the accumulator ACC.

As a result of the phase-opposition state of the 8192 Hz pulses supplied to the AND-gates AND2 and AND1 ,the chopper transistors TR5 and TR6 work in a push-pull action, guaranteeing maximum usage of the energy generated by the thermogenerator. This also effects the full-wave rectification. In any case, rectification only takes place for reasons described below, as long as a signal is available at the output Q of the flip-flop FF. From the logical function of AND3 and INV3, a conductive state of the p-channel transistor TR7 and the n-channel transistors TR8 results if an 81 92 Hz pulse is present at the input of the gate AND3 (and the output Q of flip flop FF emits a signal at the same time).The transistors TR9 and Tor 10 controlled by the gate AND6 and the gate AND4 work in phase-opposition with the transistors TR7 and TR8. The pulse trains emitted from the outputs of gates AND3 and AND4 are illustrated in the pulse diagram and are designated CR1 and CR2 respectively.

It would, for example, be fundamentally possible by means of constant monitoring of the voltage produced from the thermogenerator TG and by establishing the relationship between this voltage and the voltage of the accumulator ACC, to undertake a continuous comparison (for the purpose of putting the rectifier out of operation if the voltage from the thermogenerator is insufficient). However, one could also use another electrical variable, indirectly or directly dependent on the thermogenerator voltage for this monitoring process, like for example the direction and/or the exceeding or falling-short of a predetermined threshold of the current flowing between the rectifier and the buffer accumulator.

Because of the reasons already outlined above, the object however is to eliminate the disadvantages associated with a permanent monitoring, so that the comparator circuit is only activated during predetermined timing intervals.

In the present exemplary embodiment, such a comparison procedure takes place periodically, in fact once a second during the timing pulse MEAP produced by the decoder circuit. This timing pulse is transferred directly after the end of each pulse MDSC to the comparator circuit COMP and has a duration of about 10 ms (see the pulse diagram).

The timing interval is therefore very short in comparison with a full cycle which lasts a second.

During the timing duration, the detection and comparison circuit COMP establishes the relationship between the voltage of the accumulator ACC, and a d.c. voltage gained by the rectification of the a.c. voltage produced in the winding MW, and activates the flip-flop FF, so that a signal appears at the output Q as long as the voltage derived from the transformer and rectified, lies within a certain limit or exceeds a certain value. This value is adjusted according to the accumulator voltage. One could also effect the comparison with a reference voltage stabilised by a zener diode. The flip-flop FF is reset at the beginning of an interval of a second by means of a pulse MMYR (memory reset) which is also derived from the decoder circuit DEC (see the pulse diagram).The result of this is that the flip-flop remains reset during the whole course of the pulse MDSC as well as the timing pulse MEAP following it (see the voltage course FF-Q in the diagram).

The OR-gate OR1 ensures by way of gates AND2 and AND 1, that the chopper operates, as long as the flip-flot FF is set. Furthermore, the chopper remains in operation during the whole timing interval, because the timing pulse output MEAP of the decoder DEC leads to an output of the gate OR1.

The flip-flop output Q is finally connected with each of the inputs of the gates AND3 and AND4.

As a result, when the flip-flop is not set, no 8192 Hz pulses can be transferred to the gates of the transistors TR7-TR1 0. These rectifier transistors functioning as switching elements then remain blocked.

Therefore, the flip-flop FF, apart from the 30 ms section (see diagram FF-Q) always remains set, as long as the indirectly detected thermogenerator voltage lies below a specific minimum value. As long as this flip-flop is set, the chopper and rectifier remain in operation. If it is established within a 10 ms long timing interval that the thermogenerator voltage or the output voltage which is dependent on this is too small (which entails the danger of a discharging of the accumulator by way of the rectifier), then the flipflop output Q remains without a signal, the chopper and rectifier then remaining passive until at least the next timing interval, and the whole energy for the operation of the watch is taken from the accumulator ACC. The detection or comparison process (timing interval) is repeated each second.The chopper is loaded - as previously mentioned -- during the timing interval in each case with 8192 Hz pulses.

In the pulse diagram according to Figure 2, it is assumed that a setting of the flip-flop FF takes place after each timing pulse MEAP, i.e. after each timing interval. Not graphically shown are the pulse ratios which occur in case the MW voltage detected by the comparator circuit does not reach the minimum value and the flip-flop FF remains reset after the end of the timing interval. In such a case, no 8192 Hz controlling pulses CR1 and CR2 are transmitted to the rectifier until the comparator circuit reactivates the flip-flop FF.

Furthermore CRC1 and CRC2 pulses are only transmitted to the chopper during the short timing intervals. The switching-off of the rectifying transistors and the chopper during an insufficient current supply has a favourable effect on the energy consumption of the circuit.

Claims (12)

1. A miniature electronic device, including a current source for providing the device with current, which source has a d.c. voltage generator with a converter which transforms non-electrical into electrical energy and a buffer accumulator able to be charged by the d.c. voltage generator, the device further including an electronic comparator for monitoring operation of the source and, by comparing electrical magnitudes, producing electrical controlling signals determined by the mode of operation of the source, wherein there are means for establishing discrete chronologically spaced timing intervals and means for activating the comparator circuit during these timing intervals.

2. A device according to claim 1, including a decoder which is connected to several outputs of a frequency divider, which divider is connected to the comparator circuit and is such that it determines timing intervals of predetermined length by means of the coincidence of pulses of different frequencies.

3. A device according to claim 2, wherein the decoder is such that it periodically produces timing impulses, the length of which determines the duration of the timing intervals.

4. A device according to any of claims 1 to 3, wherein the d.c. voltage generator has a voltage chopper coupled to the output side of the energy transformer, a transformer and a rectifier circuit for rectifying the transformed voltage, wherein the rectifier circuit includes controllable semiconductive elements or integrated micro-switches controlled by electric fields, and the control of the rectifying elements is controlled by means for controlling the chopper or synchronously by the chopper.

5. A device according to claim 4, wherein the means for controlling the rectifying elements and the chopper is such that in the course of the timing interval the chopper operates and the rectifier circuit is out of operation.

6. A device according to claim 4, wherein the comparator circuit puts the d.c. voltage generator out of operation until the next timing interval, if it is established in the course of a rectifier operation, that the criterion for supplying the device is not fulfilled by the d.c. voltage generator.

7. A device according to claim 4, wherein the comparator circuit is supplied on the one hand by a voltage collected from a secondary winding of the transformer and on the other hand by a voltage from the accumulator, and the comparator circuit has rectifying means for the purpose of a comparison of the accumulator voltage with a d.c.

voltage provided by these rectifying means.

8. A device according to claim 4, wherein the comparator circuit is provided with voltage stabilising means for the production of a reference voltage which is compared with the voltage of the accumulator.

9. A device according to any of claims 4 to 8, wherein the energy converter comprises a thermogenerator.

1 0. A device according to claim 9, designed as a thermo-electric wristwatch, such as a quartz wristwatch, with a frequency divider and a stepping motor to move the hands, the hot pole of the thermogenerator being formed by the base of the watch casing and the cold pole by a casing component thermally isolated from this, wherein the timing interval is directly related to a motor winding short-circuit pulse following each motor drive pulse.

11. A device according to any of claims 4 to 10, wherein the motor drive winding and at least one winding of the transformer are coiled round a common ferro-magnetic core.

12. A device according to claim 10 or 11, wherein the chopper and the rectifier circuit which rectifies the chopped and transformed voltage, are out of operation during the motor-drive pulse and motor winding short circuit pulse, and that the said rectifier circuit is also out of operation during each timing interval.

1 3. A miniature electronic device, substantially as herein described with reference to the accompanying drawings.