POWER SUPPLY CIRCUIT, TELECOMMUNICATION DEVICE AND METHOD FOR MULTIPLE DC SLOPE POWER MANAGEMENT

Abstract: A power supply circuit for application in telephone devices optimises a supply voltage usable for facilities such as handsfree, listening-in and the like. When the telephone line power exceeds a predefined value this is being sensed and this information is provided to a controllable line voltage stabiliser which increases the line voltage and therewith the supply voltage to the maximum level prescribed by the national telephone authorities.

Description: Power supply circuit, telecommunication device and method for multiple DC slope power management. The present invention relates to a power supply circuit comprising a line voltage forming circuit to be coupled to a telecommunication line having a line voltage for providing a supply voltage. The present invention also relates to a telecommunication device comprising such a power supply circuit. Furthermore the present invention concerns a method for deriving a supply voltage from a telecommunication line voltage. Such a power supply circuit, telecommunication device and method are being applied in telecommunication, in particular telephone ICs' wired or wireless subscriber telephones, a facsimile, a Web-television having a telephone card, a personal computer having a telephone card etc. These are known from Philips Semi-conductors Application Note AN 94069. The power supply IC described therein provides for facilities of a telephone subscriber set, such as handsfree facilities, listening-in facilities, dialling features, loudspeaker features etc. The stabilised power for these facilities is being supplied by and derived from the telecommunication line voltage. However the behaviour of the line power extracted from the telecommunication line is prescribed by the national telecommunication authorities, such as the PTT in the Netherlands. Within the line voltage versus line current characteristic the DC load line is precisely defined to lie in between forbidden area's. The growth of the features however, poses increasing demands on the maximum supply voltage which is necessary for these features to function optimally. It is an object of the present invention to provide tools for optimum power management between, at the one hand what is allowed by the national telecommunication authorities and at the other hand what is required for the facilities to operate in their full working area. Thereto the present invention is characterised in that the power supply circuit is provided with a sensing circuit having an input to be coupled with the telecommunication line, and an output for providing an output signal which is representative for the power taken from the telecommunication line, and that the line voltage stabiliser is provided with a stabilised facility supply voltage control input coupled with the output of the sensing circuit. Thereto the method according to the invention is characterised in that a signal representing the power taken from the telecommunication line is being used to influence the line voltage and therewith the supply voltage. It is an advantage of the present invention, that it provides the possibility to use the non-forbidden area to a fuller extend by providing measures to influence the lie of the load line, and in particular to position the load line as closely and as optimally as possible in the vicinity of what is prescribed to be the maximum reachable. By doing this the thus adjustable lie of the load point on the load line can be optimally adjusted to the requirements with respect to the stabilised facility supply voltage of the facilities. According to one embodiment the power supply circuit according to the invention is characterised in that the sensing circuit is provided with a threshold means for controlling the voltage forming circuit such that its supply voltage is increased every time the power taken from the telecommunication line exceeds one or more thresholds. Its an advantage of the embodiment of the power supply circuit according to the invention that a step-wise optimal adjustment can be effected in a relatively simple way. At present the invention will be elucidated further together with the other advantages under reference to the accompanying drawing, whereby corresponding parts in the different Figures are indicated by the same reference numerals. In the drawing: Fig. 1 shows a possible graph of the line voltage (Vline) versus the line currenl (Iline), wherein allowable load lines (1) and (2) are drawn; Fig. 2 shows one possible embodiment of the power supply circuit according to the invention; Fig. 3 shows an other embodiment of the power supply circuit according to the invention; Fig. 4 shows a worked-out example of the embodiment of Fig. 2; Fig. 5 shows a worked-out example of the embodiment of Fig. 3; Fig. 6 shows a graph which is similar to the graph shown in Fig. 1; and Fig. 7 schematically shows a telecommunication device provided with a power supply circuit according to the present invention. Fig. 1 shows a graph indicating the line voltage (Vline) versus the line current (Iline) on a telecommunication line having terminals LN- and LN- indicated in the Figures 2, 5. By the national telecommunication authorities area's indicated A and B are declared to be forbidden areas. Each national telecommunication authority may proclaim specific area's to be forbidden. Figure 6 shows a graph similar to the graph of Figure 1 , which however applies to the United Kingdom. (1) is a load line known to be allowable. By means of a power supply circuit to be described, from Vline there is to be derived a stabilised facility supply voltage VDD which is always smaller than the line voltage wherefrom it is derived. The voltage VDD is used in for example a telephone subscriber set to power facilities, such as listening in, loudspeaker facilities etc. In order to optimise the operational voltage of these facilities the load line (1) is being influenced to create a tilted load line (2). An alternative multiple tilted load line (3) is shown in the graph of Figure 6, in order to optimise VDD as much as possible within the limits of the forbidden area's A and B. Figure 2 shows schematically a possible embodiment of a power supply circuit 4. In this embodiment the power supply circuit 4 comprises a current mirror means 5. The main part of the line current from terminal LN-I- is conveyed through a line voltage forming circuit 6, which can be a stabiliser, which stabilises the line voltage LN- A small part of the line current from the current mirror means 5 is conveyed through a current comparator 7 which will be described later on. The mean part N of the line current is also conveyed through a supply voltage stabilizer 8 of the power supply circuit 4. The stabilizer 8 generates the stabilized facility supply voltage VDD, which is used to provide the facilities with the necessary power. The operation of the Figure 2 embodiment is such that as long as the line current remains under a value, which is related to Ithrl, load line (1) (see Figure 1) will be followed. As soon as the line current exceeds a value whereby its mirrored current exceeds Ithrl the load line (2) will be followed. At that stage a the correction current Icon is generated in order to increase the line voltage LN+ . Because the voltage VDD follows the line voltage LN+ , VDD is increased too. Again schematically, Figure 4 details this operation. Transistor Tl in Figure 4 conveys the main part (N) of the line current through a stabiliser part 8' of the supply voltage stabiliser 8. In fact the stabiliser part 8' stabilises the differences between the line voltage LN+ and the stabilised facility supply voltage VDD under command of an external control signal, not further described. If the l/(N-f-2) part of Iline 1, which is Iline 2, after adequate filtering by C2, exceeds the current source current Ithrl the exceeding part is lead through a current mirror T4, T5 and additionally through a further current mirror T6, T7. Finally a correcting current Icorr is generated, which is added to a current Idc of its current source, which by means of a differential amplifier 9 leads to an increase of the line voltage LN + and thus to an increase of the supply voltage VDD. This gives rise to an increased positive slope of load line (2) in Figure 1. A further increase of the line current such that its mirrored part Iline 3 exceeds the current Ithr2 leads to a negative correction on the correction current Icorr as a consequence of which the load line (2) is bent back parallel to the load line (1), but above this load line (1). This gives rise in this area to an increased line voltage and thus to an increase of the voltage VDD for optimising the power to the facilities. In a similar, though complementary way the further embodiment of Figure 3 of the power supply circuit 4 shows how voltage sources can do a similar job in the voltage domain. The unknown line current Iline from terminal LN+ is lead through the line voltage stabiliser 6 and the externally controlled supply voltage stabiliser 8 via earth 10 through resistor Rs to line terminal LN-. The voltage across resistor Rs, which contains a measure for the line current is conveyed to a voltage comparator 11. The DC component of the line current is used to derive there from a correction current Icorr for points on the load line wherein Vthrl (see figs. 1 and 6) is being exceeded. Again the correction current is used to shift to load line (2) by increasing the line voltage Vline. Figure 5 is only meant to schematically show a way whereon Icorr can be generated. The voltage across Rs is lead to a difference amplifier 12. After filtering the AC component by capacitor C2 the voltage part exceeding Vthrl is converted into a current by circuit 13 and fet to a current mirror T10, Tl 1 to generate Icorr. As described earlier Icorr will lead to load points on lifted load lines (2,3). Of course the mechanisms describes above can be used to introduce to three or more tilting points as indicated in Figure 6. Figure 7 schematically shows a network 14 with several lines LN connected thereto. A telecommunication device 15 is connected to such a line LN. The device 15 comprises a telephone 16 having facilities 17 connected to the power supply circuit 4 through terminal VDD.

Claims: CLAIMS: 1. Power supply circuit comprising a line voltage forming circuit to be coupled to a telecommunication line having a line voltage for deriving a supply voltage there from, characterised in that the power supply circuit is provided with a sensing circuit having an input to be coupled with the telecommunication line and an output for providing an output signal which is representative for the power delivered by the telecommunication line, and that the line voltage forming circuit is provided with a line voltage control input coupled with the output of the sensing circuit. 2. Power supply circuit according to claim 1 , characterised in that the sensing circuit is provided with a threshold means for controlling the line voltage forming circuit, such that its supply voltage is modified if the power delivered by the telecommunication line exceeds one or more thresholds. 3. Power supply circuit according to claim 2, characterised in that the threshold means comprises one or more current sources coupled to at least one current comparator. 4. Power supply circuit according to claim 2, characterised in that the threshold means comprises one or more voltage sources coupled to at least one voltage comparator. 5. Telecommunication device provided with a power supply circuit according to one of the claims 1-4. 6. Method for deriving a supply voltage from a telecommunication line voltage, characterised in that a signal representing the power delivered by the telecommunication line is being used to influence the line voltage and therewith the supply voltage. 7. Method according to claim 6, characterised in that if the power delivered by the telecommunication line exceeds one or more power thresholds, the line voltage and therewith the supply voltage is being modified.

Inventors: LABBE ERIC CHRISTOPHE, MULDER JACOB, THUS FRANSISCUS JOHANNES MARIA, LABBE, ERIC, CHRISTOPHE, MULDER, JACOB, THUS, FRANSISCUS, JOHANNES, MARIA
Applicants: LABBE ERIC CHRISTOPHE, MULDER JACOB, PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, THUS FRANSISCUS JOHANNES MARIA, LABBE, ERIC, CHRISTOPHE, MULDER, JACOB, PHILIPS ELECTRONICS N.V., THUS, FRANSISCUS, JOHANNES, MARIA
Application year: 1997
Main classification: H04M19
IPC codes: H04M1, H04M19