GB2230405A - Portable radio telephone power supply - Google Patents

Abstract

An electrical power supply for a hand portable cellular radio telephone having receiver and transmitter stages (3,4) operable at different voltage levels comprises a stack of series-connected rechargeable voltaic coils 5a-5f. In call mode both the receiver 3 and transmitter 4 are powered by the full cell stack developing maximum voltage, e.g. 7.2V. In stand-by the transmitter 4 is disabled by a switch S3 and the receiver 3 is powered by half, a group of, preferably the cells 5a-5c or 5d-5f providing only a portion of, preferably half, the full voltage e.g. 3.6V. Power consumption is thus reduced, e.g. by 10 - 15 mA, in stand-by mode thus increasing battery life. Switches S1 and S2 are operated in tandem in the stand-by mode to connect alternately the first half of the cell stack 5a-5c and then the second half of the cell stack 5d-5f on a periodic basis. <IMAGE>

Description

PORTABLE RADIO TELEPHONE POWER SUPPLY This invention relates to an electrical power supply particularly, but not exclusively, for a hand held portable cellular radio telephone.

For the sake of brevity, the term hand portable telephone will be used herein to refer to a hand-held portable cellular radio telephone.

As the name suggests, a hand portable telephone is relatively lightweight and small in size and operates from an internal power supply generally in the form of a rechargeable battery pack so that it may readily be carried around by the user.

Typically, the battery pack may comprise six nickel cadmium cells each having nominal electromotive force (e.m.f.) of 1.2V. A hand portable telephone has the advantage that it can be used anywhere within range of a transmitting and receiving base station, but has the drawback of having a limited stand-by and talk time.

As is well known in the art, the term "stand-by time" means the life of the internal battery pack in "stand-by mode", i.e. when the telephone is not being used either for making or receiving a call, and "talk time" is the battery life in call mode", i.e. when the telephone is being used for making and/or receiving a call.

In call mode, both the transmitter and receiver circuits of the radio telephone are operational. Of the transmitter and receiver stages it is the transmitter stage which consumes most power. In stand-by mode the receiver circuits (and associated logic circuits) must remain on to monitor possible incoming calls. The transmitter is not required and so may be switched off to reduce overall power consumption.

The Technophone PC105 is a hand portable telephone manufactured by the present applicant. (Technophone is a registered trademark of the present applicant.) This particular model employs six rechargeable cells each having a nominal e.m.f. of 1.2V so that the complete battery pack has an e.m.f. of 7.2V. The receiver and transmitter stages are operated at the same voltage, i.e. 7.2V, both in the call and the stand-by modes. In call mode, when both the transmitter and receiver stages are operational the power consumption is approximately 400mA whereas in the stand-by mode, when the transmitter stage is switched out, the power consumption is reduced to 60mA.

In current portable radio telephones the talk time is typically in the range of 1-2 hours and the stand-by time is in the range of 6-18 hours. There is a great deal of research effort being made in the art generally to find new ways of extending the operational endurance of the battery still further than was hitherto available.

According to the present invention there is provided an electrical power supply for a hand portable radio telephone having circuitry with stages operable at different respective voltage levels, the power supply comprising a plurality of Voltaic cells, means for connecting to said circuitry a first group of said cells collectively having a first e.m.f., means for connecting to said circuitry a second group of the said cells collectively having substantially the same e.m.f. as the first group, means for connecting to the said circuitry a third group of cells collectively having a second e.m.f.

higher than the first e.m.f., and switching means which in a first mode of operation connects the first and second groups of cells alternately to the circuitry and in a second mode of operation connects the third group of cells to the circuitry.

The present invention recognises the fact that the receiver stage (and associated logic circuits) of a hand portable telephone may be operated at a significantly lower voltage than the transmitter stage. In prior art hand portable telephones this has been achieved by regulating the voltage electronically to reduce the voltage at the receiver stage.

An alternative is to use the same current twice at stages operating at different voltage levels, but this adds to circuit complexity by requiring additional decoupling/regulating devices, and furthermore may result in one of the stages using more current than is strictly necessary. In short, these prior art solutions are wasteful of energy.

By contrast, the power supply in accordance with the present invention provides a lower voltage level (e.g. 3.6V) for the receiver stage in the stand-by mode and a higher voltage level (e.g. 7.2V) to both the receiver and transmitter stages in the call mode. It is not so important that the receiver stage is operated at the higher voltage level in call mode since the overriding contribution to the power consumption in this mode is from the transmitter stage, and the power saving contribution, perhaps 10 to 15mA, which would otherwise be available, would be a negligible proportion of the total power consumption.On the other hand, in the stand-by mode, a 10 to 15mA saving represents a substantial proportion of consumed power, in the region of 508. Clearly then, a power supply in accordance with the invention dramatically reduces power consumption in the stand-by mode, greatly enhancing stand-by time and consequently the overall battery life.

Preferably, there are the same number of cells, each having substantially the same nominal e.m.f., in both the first and the second groups. The third group may comprise all of the cells of the first and second groups respectively.

In a preferred embodiment there is provided an even number of cells, the first group comprising half of the cells and the second group comprising the other half.

Preferably the cells of the first group are disposed in mutually adjacent relationship and, similarly, the cells of the second group are disposed in mutually adjacent relationship next to the first group.

Suitably, timing means are included which regulate the switching means in the first mode of operation such that the first and second groups of cells are connected respectively to the circuitry for substantially equal periods of time.

The switching frequency may, for example, be in the range of 1 to 600 times per minute, e.g. once per second, or substantially lower, e.g. once every 5 minutes.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing in which: the single figure is a schematic circuit diagram of a hand portable cellular radio telephone incorporating a power supply in accordance with the invention.

In the figure, the hand portable telephone includes a power supply 1 coupled to a radio 2 comprising a receiver stage 3 and a transmitter stage 4. The transmitter 4 is connected to the positive terminal of the power supply by a switch S3.

The receiver 3 may include associated logic circuitry (not shown) for processing incoming signal data.

The power supply includes a battery pack 5 comprising a stack of six series-connected voltaic cells 5a-5f, e.g.

rechargeable nickel cadmium cells, each having a nominal e.m.f. of 1.2V. The total e.m.f. of the battery pack 5 is thus 7.2V. The positive terminal of cell 5a is connected to the positive terminal of the radio 2 via terminals 6a and 6b of switch S1. The negative terminal of cell 5f is connected to the negative terminal of radio 2 via terminal 7a and 7b of switch S2. A further connection 8 is made to the battery pack 5 at the common point between the negative terminal of cell Sc and the positive terminal of cell 5a. Connection 8 has two terminals 6c and 7c. Terminal 6c forms part of switch S1 and terminal 7c forms part of the switch S2. Both switches S1 and S2 are regulated by an electronic clock 9, itself well known in the art.

The figure shows a state of operation at a point in time during the stand-by mode. Switch 3 in the radio 2 is open so that the transmitter 4 is disconnected from the power supply, the receiver 3 (and associated logic circuitry) remaining operational. The switch S1 is in the position bridging terminal 6b and 6a, while switch S2 is in the position bridging terminals 7b and 7c. Thus the positive terminal of cell Sa is connected to the positive input of radio 2 and the negative terminal of cell Sc is connected to the negative input of the radio. The voltage supplied to the receiver stage 3 of the radio is therefore 3.6V.

After a preselected amount of time, 1 second for example, determined by the clock 9, switches S1 and S2 are actuated simultaneously to connect terminal 6c with 6b and terminal 7a with 7b respectively. Consequently, the positive terminal of cell 5d now becomes connected to the positive input of the radio and the negative terminal of cell 5f becomes connected to the negative input of the radio. The voltage supply to the receiver stage 3 thus remains at 3.6V. After the preselected time period determined again by the clock 9, the switches S1 and 52 are thrown back to the positions shown in the Figure to reconnect cells 5a-5c to the radio and disconnect cells 5d-5f. This procedure continues periodically the whole time the telephone is in stand-by mode.The periodic switching between the two sub-stacks of cells 5a-5c and 5e-5f has the effect of drawing substantially equal power from all the individual cells so that no particular cell or group of cells becomes depleted more quickly than the others. The switching frequency may vary over a wide range, but may for example be in the range from 1 to 600 times per minute, suitably once per second.

It is noted that some circuits would be able to tolerate a momentary, but complete, interruption of the power supply during switch over between the two substacks of cells 5a-5c and 5d-5e. In practice, however, the inherent capacitance of the circuitry means that instead of a complete interruption the power supply will suffer merely a drop in voltage over a short period of time. It will, of course, be evident to a person in the art that a capacitive element may be included in the circuit specifically to minimize the interruptive effect during swit over. For example, if the particular circuit design permitted a voltage drop of 100mV over a period of 1 microsecond, the desired capacitance, whether inherent or included specifically for this purpose, would be 0.6 microfarads.

When the telephone enters the call mode switch 53 is closed to reconnect the transmitter 4 to the power supply. Switch S1 is thrown to the position shown in the Figure, connecting terminals 6a and 6b, while switch S2 is thrown the other way connecting terminals 7a and 7b. Hence, the complete stack of six cells 5a-5f becomes connected to the radio 2 supplying a voltage of 7.2V required for transmission.

In view of the foregoing description, it will be evident to a person skilled in the art that various modifications may be made within the scope of the present invention. For example, the stack of cells may be divided into more than two groups.

With a total of six cells in the battery pack, three groups of two cells may be used with switches for connecting each of the groups in turn on a periodic basis, assuming that the e.m.f. of the individual groups is adequate for the circuit stage they are powering. Neither is it necessary for the cells in a particular group to be physically adjacent but they may be disposed in any arrangement, e.g. the cells of the first group may be disposed alternately with the cells of the second group. Furthermore it is not necessary for the switching between groups of cells in stand-by mode to be time dependent. Thus, instead of a clock, a voltage detector may be employed and the first group of cells would be disconnected in favour of the second group when the e.m.f.

of the first group falls below a first predetermined level.

The first group would be reconnected when the e.m.f. of the second group of cells falls below the same first predetermined level. Switching between the groups may again occur at several other, gradually decreasing, predetermined values of e.m.f..

Claims (9)

1. An electrical power supply for a hand portable radio telephone having circuitry with stages operable at different respective voltage levels, the power supply comprising a plurality of voltaic cells, means for connecting to said circuitry a first group of said cells collectively having a first e.m.f., means for connecting to said circuitry a second group of said cells collectively having substantially the same e.m.f. as the first group, means for connecting to the said circuitry a third group of cells collectively having a second e.m.f. higher than the first e.m.f., and switching means which in a first mode of operation connects the first and second groups of cells alternately to the circuitry and in a second mode of operation connects the third group of cells to the circuitry.

2. An electrical power supply for a hand portable radio telephone as claimed in claim 1, wherein each of the cells has substantially the same nominal e.m.f..

3. An electrical power supply for a hand portable radio telephone as claimed in claim 2, wherein the first and second groups comprise the same number of cells.

4. An electrical power supply for a hand portable radio telephone, wherein the third'group comprises all the cells of the first and second groups respectively.

5. An electrical power supply for a hand portable radio telephone, wherein there is provided an even number of voltaic cells, the first group comprising half of the cells, and the second group comprising the other half of the cells.

6. An electrical power supply for a hand portable radio telephone, wherein the cells comprising the first group are disposed in mutually adjacent relationship and the cells comprising the second group are disposed in mutually adjacent relationship next to the first group.

7. An electrical power supply for a hand portable radio telephone, including timing means which regulate the switching means in the first mode of operation such that the first and second groups of cells are connected respectively to the circuitry for substantially equal periods of time.

8. An electrical power supply for a hand portable radio telephone, wherein the first and second groups of cells are connected respectively to the circuitry at a frequency in the range of 1 to 600 times per minute.

9. An electrical power supply for a hand portable radio telephone substantially as herein described with reference to the accompanying drawing.