Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific voltage responsive fault sensor
Reexamination Certificate
2000-12-15
2003-05-20
Huynh, Kim (Department: 2182)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific voltage responsive fault sensor
C361S018000, C361S090000, C361S092000, C307S043000, C363S074000
Reexamination Certificate
active
06567252
ABSTRACT:
BACKGROUND
The invention is based on a protection circuit with a switching stage for a power supply unit which, in the event of a fault, for example a short-circuit, supplies a fault signal for the power supply unit.
Protection circuits of this type are often used in switched-mode power supply units in order to switch them off reliably in the event of a short-circuit in particular, so that no components, such as the switching transistor or components of the output side for example, are destroyed by overloading. DE-A-197 35 208, for example, discloses a switched-mode power supply unit which has on the primary side switching means which effect reliable switching off of the switching transistor in the event of a short-circuit on the secondary side. The arrangement of the switching means on the primary side has the effect here that, if there is a short-circuit, the voltage is reduced to a low value directly at the gate terminal of the switching transistor, so that the said transistor cannot turn on again. The occurrence of a short-circuit is detected here at an auxiliary winding of the isolation transformer on the primary side.
The object of the present invention is to specify a protection circuit for a power supply unit with a plurality of output voltages which effects reliable switching off of the power supply unit in the event of a short-circuit of one of the output voltages, and a power supply unit with a relevant protection circuit.
SUMMARY OF THE INVENTION
The protection circuit of the present invention includes a switching stage, at which at least two output voltages to be monitored are connected, these voltages being isolated from one another by means of resistors and diodes. Arranged here in the connection path of the output voltages is a diode, which turns on and thereby triggers the switching stage in the event of a fault, when there is a drop in one of the output voltages. No diode is necessary for the last output voltage. In this way, the switching stage provides a control signal which acts on a control loop of the power supply unit, so that the power supply unit switches off.
The protection circuit also includes a passive network with a resistor and a capacitor, which prescribes a time constant, after which the protection circuit permits renewed starting of the power supply unit. The switching stage of the protection circuit may be realized, for example, by a transistor stage or an operational amplifier, which provides the information signal for the event of a fault for the power supply unit when turning on occurs. This protection circuit allows a plurality of output voltages of the power supply unit concerned to be monitored in a simple way with respect to a short-circuit or an undervoltage.
Applications of the protection circuit arise in particular for television sets and video recorders, the power supply units of these devices are predominantly switched mode power supply units, in particular flyback converters. Use of the protection circuit for non-switching, linear power supply units is likewise possible, however.
REFERENCES:
patent: 4591779 (1986-05-01), Carpenter et al.
patent: 4876636 (1989-10-01), Rilly et al.
patent: 4916569 (1990-04-01), Konopka
patent: 5872704 (1999-02-01), Kim
patent: 28642 (1964-05-01), None
patent: 244447 (1987-04-01), None
Search Report for German Patent Appln. No. 19964049.1.
Das interessante IC: Spannungsuberwachung SG 1548. In: ELO, Ausg. 2, 1988, S. 81, 82.
Kizmann Eugen
Kögel Reinhard
Louvel Jean-Paul
Fried Harvey D.
Huynh Kim
Kolodka Joseph J.
Thomson Licensing S.A.
Tripoli Joseph J.
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