GB2296581A

GB2296581A - Limited power systems

Info

Publication number: GB2296581A
Application number: GB9426478A
Authority: GB
Inventors: Thien Luong Huynh; Bernard Dugerdil; Patrick Clement; Philippe Jouen
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1994-12-22
Filing date: 1994-12-22
Publication date: 1996-07-03
Anticipated expiration: 2014-12-22
Also published as: GB9426478D0; GB2296581B

Abstract

A telephone set provided with power from a subscriber line 40, 50 includes essential circuits 2 and a main voltage regulator 3 for regulating the voltage provided to the essential circuits 2. Power to non-essential circuits 8 such as a loudspeaker and loudspeaker amplifier, are controlled by an auxiliary voltage regulator 9. A power sensing circuit 6 senses the power provided to the essential circuits 2 and main voltage regulator 3 and controls the auxiliary voltage regulator 9 according to the sensed power. <IMAGE>

Description

LIMITED POWER SYSTEMS Field Of The Invention This invention relates to systems, such as telephone line circuits, portable computers or other battery powered equipment which have a limited supply of power available. In such systems, when only a small amount of power is left available, it must be reserved for the most important tasks that the system must perform.

Background Of The Invention Such systems usually have essential circuits, which must be powered at all times for the system to function, and non-essential circuits, which, even when unpowered, still allow the system to operate, albeit, perhaps, in a limited way. In, for example, telephone line circuits, such non-essential circuits include auxiliary circuits such as loudspeaker and loudspeaker amplifier circuits.

In general, the subscriber line current IL is split into two parts of which one part IE supplies the essential circuits via a shunt regulator, and the second part 1A supplies the auxiliary circuits, where: lE =k IL (O < k < 1) IA = (1 - k). IL.

This type of power management has the following drawback : the k factor has to be high to guarantee the full supply of the essential circuits at the lowest values of IL SO at the largest values of I the auxiliary circuits do not have the maximum power they could have. To reduce this drawback, in the prior art the k factor is increased for I > IL threshold. But as both k factor and IL threshold are internal variables, the user cannot adjust them to optimise the current splitting between the essential and auxiliary circuits.

It is therefore an object of the present invention to provide a power management system which overcomes, or at least reduces, the disadvantages of the prior art.

Brief Summary Of The Invention Accordingly, the invention provides a system having a power source, essential circuits including a voltage regulator coupled to the power source for regulating the voltage provided to the remainder of the essential circuits, non-essential circuits including a voltage control means coupled to the power source for controlling the voltage provided to the remainder of the non-essential circuits, and a power sensing circuit sensing the power provided by the power source excluding the power used by the nonessential circuits and controlling the voltage control means according to the sensed power.

In a preferred embodiment, the voltage control means comprises a switch means controlled by the power sensing circuit for decoupling the non-essential circuits from the power source. Preferably, the voltage regulator includes a shunt transistor for sinking current in excess of that required by the remainder of the essential circuits and the power sensing circuit includes a current detector for detecting the flow of current through the shunt transistor and for controlling the voltage control means according to whether current is detected. The current detector preferably includes a comparator for comparing the voltage across the emitter base junction of the shunt transistor with a reference voltage and an output of the comparator is used to control the voltage control means.

Preferably, the power sensing circuit includes a sensing resistor coupled in series between the power source and the essential circuits and a voltage comparator comparing the voltage across the sensing resistor with a reference voltage and controlling the voltage control means according to the results of the comparison.

Brief Description Of The Drawings Various embodiments of the invention will now be more fully described, by way of example, with reference to the drawings, of which: FIG. 1 is a partial block and schematic diagram showing a first embodiment of the invention; FIG. 2 is a schematic diagram of the embodiment of FIG. 1, with the power management control block shown in more detail; FIG. 3 is a partial block and schematic diagram showing a second embodiment of the invention; and FIG. 4 shows a third embodiment of a power management control block.

Detailed Description FIG. 1, shows a telephone circuit for coupling to a 2-wire subscriber telephone line via terminals 40 and 50 and includes a line driver interface 36 coupled to terminal 40 via a power transistor 35. In the telephone set there are essential circuits 2, which have to be supplied all the time that the handset is off-hook and auxiliary circuits 8, which need not be fully supplied all the time but only when enough power is available from the subscriber line. The transistor 35 absorbs current from the subscriber line and feeds it to the auxiliary circuits 8 via node 41 and to the essential circuits 2 via node 44.

In the present invention each of the above mentioned types of circuits is supplied by its own voltage regulator: the essential circuits 2 are supplied by a main voltage regulator 3 and the auxiliary circuits 8 are supplied by an auxiliary voltage regulator 9. These two regulators 3 and 9 are used in a master-slave configuration. The main regulator 3, which supplies the essential circuits 2, is active all the time that the handset is off-hook. The auxiliary regulator 9, which supplies the auxiliary circuits 8, is only enabled under two conditions: firstly, when the main regulator has settled and secondly, when the required amount of current for the essential circuits is available through the main regulator.

A sensing resistor 4 is provided in series between the nodes 41 and 44. The voltage across resistor 4 is given by the product of the resistor value Re and of the current IMAIN flowing via node 44 into the main voltage regulator 3, the essential circuits 2 and a reservoir capacitor 1 coupled in parallel to the essential circuits 2. A power management control block 6 is coupled across resistor 4 to sense the voltage across resistor 4 and to the main voltage regulator 3 via node 45.

After the telephone circuit is powered up and when the main regulator 3 has settled (signal at node 45 is high), if the voltage across resistor 4 is equal to or higher than a voltage reference VR then the power management control block 6 closes a switch 10, thus enabling the auxiliary voltage regulator 9. This gives the following relationships between the currents IMAIN, IAUX, and the line current IL: for IL < VR/Re IAUX = O, IMAIN = IL for IL > VR/Re IAUX = IL - VR/Re, IMAIN = VR/Re A diode 5 is coupled in parallel with the resistor 4 to allow the capacitor 1 to charge faster than with the time constant defined by capacitor 1 and resistor 4 at the on-hook to off-hook transition. When the line current is cut, e.g. during a flashing during pulse dialling or at off-hook to on-hook transition, the voltage across resistor 4 falls below VR and the switch 10 is turned off so that the auxiliary regulator 9 is immediately disabled.

However, during flashing, or pulse dialling, the capacitor 1 maintains an appropriate voltage on node 44. This insures that the essential circuits 2 are powered during these periods.

FIG. 2 shows one particular realisation of the system with the power management control block 6 shown in more detail. In this case, the power management control block 6 includes a current source 11 coupled to the main regulator 3 via node 45. When the main regulator 3 has settled i.e. it shunts current, the current source 11 having value I is turned on by the voltage on node 45.A voltage loop is provided by a resistor 12, having resistance Ri, a transistor 13, sensing resistor 4 and a transistor 14, which gives the following equations: VBEl3 + Re Ie - VBE14 - Ri .1 I = 0 where VBE13 is the base emitter voltage of transistor 13; VBE14 is the base emitter voltage of transistor 14; and 1e is the current flowing through resistor 4; so that 1e = (Ri .I) /Re = IMAIN ( since VBE13 is almost equal to VBE14) With 1e around this value, the collector current of transistor 14 starts rising, which turns on the switch, implemented by transistor 10, by means of the gain provided by transistor 16 and resistor 15, coupled between transistor 14 and switch transistor 10. This closes the current path for the slave voltage regulator 9 to node 50. Although Ri and I have fixed values, Re may be chosen in order to optimise (Ri. I 'Re according to the consumption of all the circuits connected to node 44.The circuits connected to the auxiliary regulator 9, between nodes 41 and 43, will be powered for line currents above the limit set by Re.

When the auxiliary circuits try to consume more current than available, it tends to make 1e decrease below (Ri .1) 'Re. The loop gain provided by transistors 14 and 16 and resistor 15 maintains this decrease at a very small value by controlling the base current of transistor 10 so that its collector current is equal to IL - (Ri .1) 'Re. The excess consumption of the auxiliary circuits 8 is taken from a tank capacitor 7 coupled in parallel therewith. This will decrease the voltage supply of the auxiliary circuits 8 and their consumption. For example, with a loudspeaker amplifier, the peak signals will be clipped.But, since voice signals are made of brief high levels and long low or medium levels, a large value of the tank capacitor 7 can smooth the auxiliary supply sufficiently so that the distortion is kept low.

One difficulty of this embodiment is the calculation of Re which should take into account the worst case consumption of the essential circuits 2. Otherwise, for too large a value of Re some kind of oscillation could occur. This is because the essential circuits 2 include an ear piece amplifier which sinks an AC current, so that the main regulator 3 may run out of current. Then, the current source 11 and the transistor 10 would turn off and current IL could flow through resistor 4 and diode 5 to the master regulator which would settle again; starting a new oscillation cycle.

Although capacitor 1 would provide some filtering to this oscillation, in a preferred embodiment of the invention, shown in FIG. 3, the control signal is provided by the shunt current in the master regulator instead of the voltage drop across a sensing resistor. This preferred embodiment is shown in FIG. 3, in which a more detailed drawing of the main regulator 3 is included, but other elements have identical reference numerals to those same elements in the previous embodiments.

In this embodiment, the main regulator 3 includes an amplifier stage 19 controlled by a self-biasing block 22, which reduces the power consumption of the voltage regulator. The amplifier stage 19 has a noninverting input coupled to a current divider network formed by resistors 17 and 18 and an inverting input coupled to a voltage source 20. The output of amplifier stage 19 is coupled to the base of a transistor 21, whose collector is coupled to self-biasing block 22 and whose emitter is coupled to the base of a shunt transistor 23, which is coupled between nodes 44 and 50.The base of shunt transistor 23 is coupled, via node 45, to the input of a comparator formed by transistors 25 and 26 having their emitters coupled together and to a current source 24, the base of transistor 25 to node 45 and the base of transistor 26 to a voltage reference source 27 and the collector of transistor 26, as the ouput of the comparator, coupled, via node 46, to the base of transistor 10 to control the current for the auxiliary circuits 8.

Thus, when current IL is larger than the consumed currents, transistor 23 is used to shunt the excess current to node 50. This is the sign that the essential circuits are fully supplied. If this shunted current is larger than a threshold IMlNflxed by the reference voltage source 27, then transistor 10 is turned on by current source 24 via transistor 26. This closes the current path for the auxiliary circuits 8. A gain stage 28 is used in a voltage feedback loop to prevent transistor 10 from entering saturation and has its non-inverting input coupled to a voltage source 29 and its inverting input coupled to node 43.The gain stage 28 provides voltage regulation for the auxiliary circuits 8 equal to Vregl - V3 for Vreg1 = (1 + R2/R1) .V1 where Vregl is the voltage regulation set by the master regulator; V1 is the voltage provided by voltage source 20; V3 is the voltage provided by voltage source 29; R1 is the resistance of resistor 17; and R2 is the resistance of resistor 18.

When the current consumption rises above ILX the current in transistor 23 drops. When it is approximately IMIN, then the gain of the comparator formed by the balanced transistor pair 25, 26 controls the base current of transistor 10 so that the shunt current is kept around IMIN- The extra consumption of the auxiliary circuits is taken from the tank capacitor 7. This decreases the supply voltage of the auxiliary circuits 8 and thus cancels the loop gain realised by the collector-emitter voltage of transistor 10 and the gain stage 28. Obviously, as in the previous embodiment, the conduction of transistor 10 can start only when the master regulator 3 has settled. This means that the settling time of the essential circuits 2 is not altered by the auxiliary circuits 8.

The advantages of this preferred embodiment over the first embodiment are that there is no sensing resistor, so that no worst case calculation of consumption is required, thereis no extra voltage drop (i.e.

VR) between the collector of transistor 35 and the master regulator 3; this allows the telephone set to work at the lowest possible voltage, the gain stage 28 is much simpler and less silicon consuming than the auxiliary regulator 9 which must be able to sink large currents, and transistor 10 is kept out of saturation by the direct means of the gain stage 28 and not by indirect means (Vregl + VR - Vreg2 where Vreg1 is the voltage regulation of the master regulator 3, Vreg2 is the voltage regulation of the auxiliary regulator 9 and VR the voltage drop in the sensing resistor 4); this avoids the inaccuracy of several mismatches.

A difficulty with this embodiment is the stability of the master regulator 3 when the current consumption is higher than 1L because in this state the master regulation loop includes the transistors 25, 26 and 10.

When IL is large, these elements do not influence the regulation loop because transistor 25 is almost off. This difficulty can be overcome by realising the gain stage 19 with a PNP transistor pair supplied by an image of the base current of transistor 23. As in this state, transistor 23 is working at a low collector current IMIN, this gives a low DC gain and a low frequency pole and zero couple to the gain stage 19 with respect to the characteristics of the transistor pair 25, 26 which then mainly determine the stability of the regulation loop.

Finally, FIG. 4 shows a further embodiment, which is a modification of the system of FIG. 3. In FIG. 4, the only changes are in the comparator, which is replaced by a current detector detecting the current flowing through the shunt transistor 23 and the remaining elements, being identical to those in FIG. 3, are not shown. The current detector includes a mirror transistor 30 mirroring the current flow through the shunt transistor 23 and a comparator for comparing the collector current of the mirror transistor 30 with a reference current from a current source 31. The comparator includes a current mirror formed by transistors 32, 33, and 39, whose output is coupled via a transistor 34 and resistor 38 to node 46 to control the switch transistor 10.

It will be appreciated that although only particular embodiments of the invention have been described in detail, various modifications and improvements can be made by a person skilled in the art without departing from the scope of the present invention For example, although the switch transistor 10 has been described as a bipolar transistor, it could alternatively be a MOS transistor.

Claims

1. A system having a power source, essential circuits including a voltage regulator coupled to the power source for regulating the voltage provided to the remainder of the essential circuits, non-essential circuits including a voltage control means coupled to the power source for controlling the voltage provided to the remainder of the non-essential circuits, and a power sensing circuit sensing the power provided by the power source excluding the power used by the non-essential circuits and controlling the voltage control means according to the sensed power.

2. A system according to claim 1, wherein the voltage control means comprises a switch means controlled by the power sensing circuit for decoupling the non-essential circuits from the power source.

3. A system according to either claim 1 or claim 2, wherein the voltage regulator includes a shunt transistor for sinking current in excess of that required by the remainder of the essential circuits and the power sensing circuit includes a current detector for detecting the flow of current through the shunt transistor and for controlling the voltage control means according to whether current is detected.

4. A system according to claim 3, wherein the current detector includes a comparator for comparing the voltage across the emitter base junction of the shunt transistor with a reference voltage and an output of the comparator is used to control the voltage control means.

5. A system according to claim 3, wherein the current detector includes a mirror transistor mirroring the current flow through the shunt transistor and a comparator for comparing the collector current of the mirror transistor with a reference current and an output of the comparator is used to control the voltage control means.

6. A system according to any one of claims 2 to 5, wherein said switch means is a switch transistor.

7. A system according to claim 6, wherein the switch transistor is a bipolar transistor and has its collector coupled to the non-essential circuits and its emitter coupled to the power source.

8. A system according to claim 6, wherein the switch transistor is a MOS transistor and has its drain coupled to the non-essential circuits and its source coupled to the power source.

9. A system according to any preceding claim, wherein said voltage control means further comprises an auxiliary voltage regulator.

10. A system according to claim 8, wherein the voltage control means further comprises a voltage feedback loop coupled between the drain and the gate of the switch transistor to prevent saturation of the switch transistor

11. A system according to claim 7, wherein the voltage control means further comprises a voltage feedback loop coupled between the collector and the base of the switch transistor to prevent saturation of the switch transistor

12. A system according to either claim 1 or claim 2, wherein the power sensing circuit comprises a sensing resistor coupled in series between the power source and the essential circuits and a voltage comparator comparing the voltage across the sensing resistor with a reference voltage and controlling the voltage control means according to the results of the comparison.

13. A system substantially as hereinbefore described with reference to the drawings.