Device for protection in the case of d.c. supply-voltage drop
AssigneeU.S. Philips Corporation
InventorsJean-Claude Kaire, Jean-Claude G. Six
Life of this patent
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Abstract
A device for protection against power failures, having a programmable current source with two levels, which are controlled by a threshold detector, the current from the source being large at high voltages and reduced at low voltages.
Claims5
A device for protection for a circuit in the case of a drop of the voltage of a d.c. power supply having a capacitor in parallel with its terminals, said device including first and second supply voltage inputs and two outputs between which a circuit to be powered may be included, said device comprising:
- a programmable current source with two levels to energize said outputs;
- a threshold-voltage detector in parallel with said inputs which, depending on the relative values of the input voltage and the threshold voltage detected by said detector selects a first level of the current from said programmable current source at high voltages and a second level at low voltages, said second current level being lower than said first level;
- said programmable current source comprising:
- a bridge of series resistors, a switch;
- at least one of said resistors being connected in parallel with said switch whose change-over is controlled by said threshold detector, said switch being closed at high voltages and open at low voltages;
- said detector specifically comprising:
- a first and a second complementary transistor, the base of said first transistor being connected to the collector of said second transistor, the emitter of the first transistor being connected to a first input, and the emitter of the second transistor being connected to a second input via a current source, the collector of said first transistor influencing the base of a third transistor of the same type as the first transistor, whose emitter also constitutes the first input and whose collector constitutes the output of the detector;
- a diode;
- a current source;
- said collector of said first transistor being connected to a current source and, through at least one diode in the forward direction, to the base of said second transistor, which in its turn is connected to said current source.
A device for protection of a circuit in the case of a drop of the voltage of a d.c. power supply having a capacitor in parallel with its terminals, said device including first and second supply voltage inputs and two outputs between which a circuit to be powered may be included, said device comprising:
- a programmable current source with two levels to energetic said outputs;
- a threshold-voltage detector in parallel with said inputs which, depending on the relative values of the input voltage and the threshold voltage detected by said detector selects a first level of the current from said programmable current source at high voltages and a second level at low voltages, said second current being lower than said first level;
- said programmable current source comprising:
- a bridge of series resistors;
- a switch;
- at least one of said resistors is connected in parallel with a switch whose change-over is controlled by said threshold detector, said switch being closed at high voltages and open at low voltages;
- said current source specificaly comprising:
- a switch;
- a combination of at least two parallel-connected resistors, in series with said circuit to be powered, of which one resistor is connected in series with the switch whose change-over is controlled by said threshold detector, said switch being closed at high voltages ad open at low voltages;
- said detector specifically comprising:
- a first and a second complementary transistor, the base of said first transistor being connected to the collector of said second transistor, the emitter of the first transistor being connected to a first input, and the emitter of the second transistor being connected to a second input via a current source, the collector of said first transistor influencing the base of a third transistor of the same type as the first transistor, whose emitter also constitutes the first input and whose collector constitutes the output of the detector;
- a diode;
- a current source;
- said collector of said first transistor being connected to a current source and, via at least one diode in the forward direction, to the base of said second transistor, which in its turn is connected to a current source.
Dependencies are inferred from the claim text.