Lockheed Martin Corporation

Loral Federal Systems Company

Scott C Willis

Mark J Jones

Richard M Brosh

Charles A Dennis

Rene D Mock

A power transistor switched power supply connecting a power source to a capacitive load, including a circuit and method for limiting the inrush surge current through the power transistor. The control gate of a junction field effect transistor (JFET) is coupled between the conductive path of the power transistor and the load to sense voltage drop across the power transistor. The conductive controlled path of the JFET is connected to control the impedance of the power transistor. The JFET shunts some of the power transistor control terminal current during the on transition allowing the power transistor to only turn partially on for a period of time, thus limiting the current through the power transistor from the power source to the load. Because the inrush surge current is limited, the accompanying transient power source voltage drop is reduced with less impact to other circuits connected to the power source.

Circuit for limiting inrush current through a transistor

A redundant power supply with a number of loads is coupled to each half of the redundant supply by a respectively different MOSFET switch, with logic gates coupling control signals to the MOSFET switches. The control signal is coupled as one input to the logic gate and the output of the logic gate is connected to the MOSFET switch. The other input of the logic gates for a particular power supply is the output of an overvoltage detection circuit whose output is coupled as an input to all the gates for that power supply. The output of the gates opens the MOSFET switches in response to detection of an overvoltage condition.

Multi-channel overvoltage protection circuit

A power distribution system in which the loads are connected in series to a current source. At each load, a current source to voltage source convertor provides alternative current paths. A serial power distribution current path includes a modulated switch (e.g. a pulse width modulated switch) to control the amount of power delivered to the load via a load current path. The load current path includes a diode which couples a capacitor across the switch, providing a semi-regulated voltage input to a d.c. to d.c. convertor connected across the capacitor. The d.c. to d.c. convertor provides a regulated output voltage, which is connected to the load. The control circuit for modulating the opening and closing of the switch is connected in parallel across the capacitor.

Fault tolerant power distribution

A MOSFET switched, redundant power supply has a back-to-back MOSFET switch connecting respectively each power supply to a single load. Each power supply has a positive and negative gate voltage source. In a specific N-channel MOSFET embodiment, the positive (i.e. on) bias is coupled to each switch via a radiation hardened, redundant analogue switch capable of being driven by, for example, a TTL or CMOS microprocessor signal. The negative (i.e. off) bias is coupled to each via a redundant diode pair. In addition, the gates of the back-to-back MOSFET switch for one power source are also connected to the negative bias of the other power source. In this way the MOSFET switch for a failed power supply will be maintained in an off state by the negative bias provided by the redundant supply.

Fault tolerant MOSFET driver

A power bus digital communication system reduces power and signal cabling in a space satellite by transformer coupling digital signal sources to power bus circuits, the transformer coupling devices in all power bus circuits being in parallel relation and electrically isolated from a power supply whereby the digital communication sources may communicate among themselves at a DC power level using a square wave modulated according to a Manchester code.

Power bus digital communication system

Two power sources are connected to a load by a pair of MOSFET control switches, each connected respectively in series between one of the sources and the load, with their integral diodes forwardly biased between the power source and load. An isolating MOSFET switch is connected in series between the pair of MOSFET control switches and the load with its integral diode back biased between the power sources and the load. Two control lines control the on-off state of all three MOSFET switches so that the isolating MOSFET switch is on when either control switch is on and is off when both control switches are off.

Efficient fault tolerant switching circuit for redundant d. c. power

In a current overload protection circuit, a full wave rectifier bridge circuit is connected between an AC or DC power source to supply AC or DC power to a load through the output circuit of a solid-state relay. A current sensing resistor is connected across the DC terminals of the bridge circuit to sense the magnitude of the current flowing through the load. When an overload fault occurs, the voltage developed across the current sensing resistor will trigger a shunt regulator to turn on an optical isolation circuit, which upon being turned on will discharge a capacitor in an RC timing circuit. The discharge of the capacitor and the RC timing circuit triggers a Schmidt trigger circuit, which cuts off current flow to the input circuit of the solid-state relay, thereby cutting off current to the load. The shunt regulator then turns off de-energizing the optical isolator which, upon being de-energized, causes the current discharge path of the capacitor to be interrupted. The capacitor then charges through the resistor of the RC timing circuit and, upon being charged up to a predetermined level, will actuate the Schmidt trigger circuit to again allow current to flow through the input circuit of the solid-state relay, thus allowing current to again flow through the load.

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Manassas, VA, United States of America

Scott C Willis