Abstract: A communications adapter card includes a circuit arrangement for causing an electrical voltage to be supplied to the card from a first voltage source, even if a second voltage source is available, and from the second voltage source if the first voltage source is not available. The circuit arrangement includes a Field Effect Transistor (FET) with its gate electrode connected to a control circuit which puts the FET in an off-state to inhibit the second voltage source from supplying voltage to the card if the first voltage source is available, and puts the FET in an on-state to supply voltage to the card if the first voltage source is not available. The invention makes it possible for a single communications adapter card to be used to attache power managed and non-power managed personal computers (PCs) to a Local Area Network (LAN).

Abstract: A full reset flyback regulator includes a power transformer having a primary winding and at least one secondary winding coupled to a load. A single control winding on a primary side of the power transformer is coupled through control circuitry to a gate electrode of a switching device that is connected to the primary winding. The voltage polarity on the control winding alternates so that if the switching device is "ON" a drive voltage is provided on its gate electrode and if the switching device is "OFF" a bias voltage is provided to the error amplifier control circuit. Each cycle of the regulator is initiated via a sync pulse which is provided from the high voltage flyback transformer of a display or monitor subsystem.

Abstract: A power supply for a video display device includes a protection circuitry which shutdown the power supply to prevent damage to the power supply or the display device. The protection circuitry monitors sync pulses generated in the video display device and disables the power supply switching transistor in the absence of the sync pulses. The protection circuitry is triggered in the event a fault occurs in the power supply or the video display device.

Abstract: Described is a novel power supply for generating a constant d.c. voltage from a variable a.c. voltage supply line. The power supply includes a plurality of switch circuits which monitor voltage levels on respective secondary windings of a power transformer and as voltage levels change, one of the plurality of switch circuits is selected to charge a capacitor which provides a range of d.c. voltages which are processed to provide the constant d.c. voltage.

Abstract: A non-interfering power supply includes a free-running blocking oscillator power supply subsystem and a circuit arrangement that synchronizes the blocking oscillator power supply subsystem to operate at the horizontal operating frequency of a display subsystem. Synchronizing signals representative of the horizontal operating frequency of the display subsystem are generated and are used to activate the circuit arrangement that causes the blocking oscillator to change its mode of operation from free-running to a fully reset fixed frequency flyback converter. When activated, a switch in the circuit arrangement extends the off-time of a switching transistor in the blocking oscillator power supply control circuit. As a result, the oscillator is forced to run at an operating frequency lower than its free-running frequency.

Abstract: A protective circuit arrangement is provided for shutting down a power supply at the occurrence of a fault condition. The circuit arrangement allows current limiting in a switching transistor during a power on and/or power off cycle, but shuts down the power supply if current limiting occurs at any other time.