Telephonic communications – Subscriber line or transmission line interface – Power supply
Reexamination Certificate
1998-08-26
2001-07-03
Korzuch, William R. (Department: 2641)
Telephonic communications
Subscriber line or transmission line interface
Power supply
C307S098000, C307S099000, C323S223000, C323S299000
Reexamination Certificate
active
06256385
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a power supply adapter circuit intended to be connected between a power supply terminal called line terminal and reference potential terminal, the circuit having an output terminal intended to supply an output voltage to a load connected between the output terminal and the reference potential terminal, which output voltage has a value called regulation value, the circuit comprising:
a comparator module having a first and a second input respectively intended to receive a voltage that represents the output voltage and a voltage that has a predetermined value, and an output intended to deliver a signal which represents the result of the comparison between said voltages, and
a regulation module having an input connected to the output of the comparator module, and intended to adjust the value of the output voltage to a predetermined nominal regulation value.
BACKGROUND OF THE INVENTION
A circuit of this type is often used for generating a regulated voltage for feeding other electronic components, which then form the load of the adapter circuit, inside a telephony device. The power used for generating the regulated voltage comes in this case from a telephone line to which the device is connected. The actual telephony device is often associated with an extra device called peripheral such as, for example, a telephone answering machine or a facsimile machine. Such a peripheral receives, in principle, the power it needs from a power grid and may thus form for the telephony device a better performing power supply source than the telephone line. It is thus desirable to provide the possibility of connecting the external power supply source formed by the peripheral to the load fed by the power supply adapter circuit. If the external power supply source delivers an output voltage having a higher value than the regulation value of the regulation module, the latter will attempt to lower this value without, however, managing it, since it is then the external power supply source that imposes the potential of the output terminal of the circuit. These attempts will, at best, cause a considerable waste of power, and, in the worst case, a breakdown of the external power supply source because of the very large consumption of power which the regulation module will spend on these vain correcting efforts.
It is an object of the present invention to remedy these drawbacks by proposing a power supply adapter circuit whose regulation module is inhibited when the output of the circuit is connected to an external power supply source which imposes on said output a voltage whose value is higher than the nominal regulation value.
SUMMARY OF THE INVENTION
Indeed, a power supply adapter circuit as defined in the opening paragraph is characterized, according to the invention, in that it comprises means for adjusting the regulation value to the value of a voltage delivered to the adapter circuit by an outside voltage source when said voltage source is connected to the load.
In such an adapter circuit, everything takes place as if the value of the voltage delivered by the outside voltage source became the nominal regulation value. The regulation module will thus no longer attempt to modify the value of the output voltage, but, in contrast, will tend to maintain the output voltage at this new nominal regulation value, thus giving greater stability to the association of the adapter circuit with the outside voltage source.
In one of its possible embodiments, an adapter circuit according to the invention is characterized in that the regulation module comprises a capacitor connected between the line terminal and the reference potential terminal, and a transistor having a bias terminal connected to the output of the comparator module, a reference terminal and a transfer terminal, the main current path of which transistor, defined as being the junction between the transfer terminal and the reference terminal, is connected in parallel to said capacitor.
This embodiment of the regulation module, which is advantageous in its simplicity, enables a stabilization of the output voltage thanks to the storage capability of the capacitor. When the value of the output voltage, that is to say, the voltage present on the terminals of the capacitor, exceeds the nominal regulation value, this transgression is detected by the comparator module whose output controls the turning on of the transistor of the regulation module. This causes a partial discharging of the capacitor to occur through the main current path of the transistor. When the value of the output voltage drops below the nominal regulation value, the output of the comparator module switches again and interrupts the conduction of the transistor. The capacitor may thus again charge itself, because it is connected to the line terminal, until the next transgression which will cause the cycle described above to be reproduced.
In a particular embodiment of the invention, a power supply adapter circuit is characterized in that it additionally includes a measuring module intended to deliver on an output a signal that represents the value of a current, called output current, which passes through the output terminal of the circuit, and a voltage divider bridge formed by at least a first and a second resistor connected in series between the line terminal and the reference potential terminal, and featuring between them an intermediate node connected to the first input of the comparator module, and in that the regulation module includes injection means, activated by the output of the measuring module when the output current flows from the outside to the inside of the circuit, for injecting a current in that of the divider bridge's resistors which separates the line terminal from the first input of the comparator module.
In such an adapter circuit, the measuring module detects the presence of an outside voltage source connected to the load and supplying a voltage that has a value that is higher than the nominal regulation value, when the output current flows from the outside to the inside of the circuit. The injection means are then put into action. These injection means will perform a correction of the nominal regulation value. The injection of the current into that of the divider bridge's resistors which separates the line terminal from the first input of the comparator module, the first resistor as it is, results in an increase of the value of the voltage drop on the terminals of said first resistor and thus in a drop of the value of the voltage received by the comparator module on its first input. Accordingly, a higher output voltage is necessary for making the output of the comparator module switch and activating the regulation means. The structure described above automatically ensures that the value of the total voltage drop on the terminals of the first resistor is such that the sum of this value and of the predetermined voltage is equal to the value of the voltage delivered by the outside voltage source, which would be equivalent to a configuration where the nominal regulation value becomes equal to the value of the voltage delivered by the outside voltage source. Indeed, as long as the correction made by way of the injection means is not large enough, the output current continues to flow from the outside to the inside of the adapter circuit. The injection means thus receive from the measuring module a signal that tells them to carry out a more significant current injection and thus a correction that is larger until a state of balance is reached, that is to say, until the new nominal regulation value and the value of the voltage delivered by the outside voltage source are equal, which balance is translated in theory by a reduction to zero of the value of the output current. In practice, one will rather see an overshoot, that is to say, a change of direction of the output current due to a correction of too large a magnitude, following which overshoot the value of the injected current will diminish until the output curr
Korzuch William R.
Slobod Jack D.
U.S. Philips Corporation
Wieland Susan
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