Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Patent
1997-05-07
1998-09-01
Nguyen, Matthew V.
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
G05F 156
Patent
active
058015205
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to an apparatus for automatically switching a load between different supply voltages in response to varying voltage demands of the load.
BACKGROUND
A subscriber line interface circuit (SLIC) which is to supply a two-wire circuit, has a feeding characteristic that makes the line voltage as well as the line current a function of the line load.
When the line is open, it is supplied with maximum voltage at the same time as the current is zero. In order for the SLIC to function, it must have access to a supply voltage which is somewhat higher than the required line voltage.
When the line is closed, i.e. when the line is loaded, the line voltage will decrease and the line current will increase in dependence on the sum of the resistances of the line and the load.
The difference between the supply voltage and the line voltage will be applied across the SLIC through which the line current flows. This causes power dissipation in the SLIC.
The power dissipation in the SLIC will be highest for short lines, i.e. for a low total resistance value of the line and the load.
In many cases, one accepts the power dissipation in the SLIC. In certain cases, a DC/DC converter can be utilized in each line in order to keep the maximum power loss low. The output voltage from the respective converter is then controlled continuously in order to be adapted to the present line load. However, the utilization of such converters causes certain disadvantages in the form of interfering radiation and an increased circuit complexity.
By having access to a plurality of different supply voltages, the power losses in the SLIC can be reduced by switching to the supply voltage which, for the moment, has the lowest adequate absolute value.
It is known to utilize a switch in order to apply a suitable supply voltage. However, such a solution requires that the decision-level for the switching between different voltages has a certain hysteresis so that one does not end up in a situation where the switches merely switch back and forth all the time. Moreover, the switching between different voltages causes a stepwise change of the supply voltage to the driving amplifiers of the SLIC, which causes disturbances.
SUMMARY
The object of the invention is to provide a supply voltage switching apparatus which does not exhibit the disdvantages stated above, and which minimizes the power loss in a load having varying voltage demands.
This is attained by the apparatus according to the invention for automatically switching a load between different supply voltages in response to varying voltage demands of the load, mainly, in that it comprises a number of analog series regulators, the supply voltage connection terminals of which to be connected to an individual one of said supply voltages, the output terminals of which to be connected to the load to individually conduct current to/from the load in one and the same direction, and the reference voltage input terminals of which to be supplied with an individual reference voltage in response to the voltage demand of the load in such a manner that a series regulator connected to a supply voltage of a larger absolute value, is adapted to be supplied with a reference voltage of a smaller absolute value than a series regulator connected to a supply voltage of a smaller absolute value and, hereby, strive to output an output voltage on its output terminal, which is of a smaller absolute value than the output voltage which a series regulator connected to a supply voltage of a smaller absolute value strives to output.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be described more in detail below with reference to the appended drawing on which the single FIGURE shows an embodiment of an apparatus according to the invention at a load in the form of a schematically indicated SLIC.
DETAILED DESCRIPTION
On the drawing, 1 generally denotes an apparatus for automatically switching a load between a predetermined number of different supply voltages in response to varying voltage d
REFERENCES:
patent: 3889173 (1975-06-01), Klusmann et al.
patent: 4617473 (1986-10-01), Bingham
patent: 4694430 (1987-09-01), Rosier
patent: 5335272 (1994-08-01), Lofmark et al.
patent: 5369472 (1994-11-01), Raj et al.
patent: 5579196 (1996-11-01), Pezzini
Eriksson Hans Oskar
Hellberg Henrik Helmer
Malmgren Carl-Henrik
Nguyen Matthew V.
Telefonaktiebolaget LM Ericsson
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