Abstract: Systems and methods for producing standby uninterruptible power for an AC load rectify an AC utility input voltage to produce a rectified voltage and activate a DC battery voltage in response to a change in the AC utility input voltage to thereby produce a standby DC voltage. The rectified voltage and the standby DC voltage are connected to an AC load that includes input rectification to thereby produce standby uninterruptible power without the need for costly, bulky, and/or unreliable inverters or converters. Seamless transfer of power may be provided to support the AC load upon failure of the AC utility input voltage and upon restoration of the AC utility input voltage. The AC utility input voltage is preferably rectified by a diode rectifier, most preferably a full-wave diode rectifier including at least four diodes, to produce the rectified voltage.

Abstract: An uninterruptible power supply (UPS) includes a transformer, a low voltage converter (02), a rectifier, and a high voltage inverter (01). The low voltage converter comprises a battery, a first switching device (Q3), a second switching device (Q4), and first drive circuits (41, 42). The high voltage inverter (01) includes first and second load terminals adapted to be coupled across a load in an emergency situation; an output capacitor (C); a third switching device (Q1) and a fourth switching device (Q2), and second drive circuitry (43, 44) for driving the third and fourth switching devices from conducting to non-conducting states and vice versa so as to produce a quasi-sinusoidal output voltage waveform across the load terminals.

Abstract: A parallel redundant power supply system which does not use any inter-unit signaling is obtained by deriving all information necessary for a robust selective trip regime from the output signals of each respective power system. Each respective power system monitors its own power output and keeps a running average of its own performance to determine whether it is operating properly, rather than comparing itself to other units. The trip function is created by sampling the AC output voltage of the power system and multiplying an instantaneous difference in voltage (compared with a previous cycle) with the instantaneous difference in current (also compared with a previous cycle) of the power system's AC output power. If the two transients are in opposite directions, then the multiplicative product will be negative and indicative of a good power system. On the other hand, if the two transients are in the same direction, then the multiplicative product will be positive and indicative of a failed unit.

Abstract: A parallel redundant power supply system which does not use any inter-unit signaling is obtained by using the AC output power level of a power system to coordinate load sharing. The necessary information for load sharing is derived solely from each power system's output power level in such a manner that the output of a power system is inherently phase locked to the output of other power systems to which it is connected in parallel. Each parallel connected power system designed in accordance with the invention includes means for generating an AC output voltage from a DC input power source, means for sampling either a DC input voltage from the DC input power source or the AC output voltage from the AC output voltage generating means to provide power level samples, and means for determining the AC output power of the AC output voltage generating means from the power level samples.

Abstract: A series/parallel resonant converter includes a resonant control circuit 1 that outputs a pair of alternately high gate drive signals G.sub.1, G.sub.2 ; switches in the form of isolated gate bipolar transistors (IGBTs) Q.sub.1, Q.sub.2 ; diodes D.sub.1, D.sub.2 ; a pair of resonant capacitors C.sub.R ; a series resonant inductor L.sub.RS ; a load 2; a zero current detector 4; a bus 6, 6'; and a parallel resonant inductor L.sub.RP in parallel with the load. The input line current and voltage are converted into an alternating current I.sub.LOAD and voltage V.sub.LOAD for driving the load 2. The load 2 may include a transformer T.sub.1, half bridge rectifier, capacitor, and PWM inverter.

Abstract: An UPS system provides a true input power walk-in. The UPS adjusts the level of power supplied from an input port to a load on an output port as a function of a level of current of a power supplied from a backup power source to the load on the output port.

Abstract: A drive circuit for use in UPS and like devices, designed to derive high-level switching signals from low-level logic signals. The drive circuit has an input circuit which drives the primary of an air-core transformer, the input drive circuit having an oscillator with a resonant circuit producing a carrier at a carrier frequency, the resonant circuit including the primary of the transformer and a coupling circuit for coupling the logic signals to the oscillator so as to modulate the carrier signal. The use of the resonant circuit enables generation of sufficient magnetization current for the low-cost transformer while reducing the current drive required of the input drive circuit, thereby enabling a reduced cost gate drive circuit.

Abstract: A UPS device adapted for parallel connection to a load along with one or more other UPS devices, having circuitry for sharing of the load, including load harmonics. A feedback network has an error signal circuit which generates an error signal representative of the difference between the actual current provided by the device and the designated share of current it should provide. The error signal is transformed by a value representative of the effective output impedance of the UPS inverter, whereby the inverter is controlled to share the fundamental of the load current as well as the harmonics.

Abstract: A UPS system comprising a resonant control circuit 100, a gate drive circuit 200, a resonant converter 300, a bootstrap power supply circuit 400 for supplying an isolated DC supply voltage to the resonant control circuit, a bootstrap battery charger 500, and a variable speed fan drive circuit 600.

Abstract: A voltage source having a current feedback control loop for enhanced source impedance control of the output of the voltage source. Current feedback is used for a voltage-source amplifier wherein the source impedance is increased/decreased and/or reshaped by the voltage source amplifier's closed-loop gain and the additional current feedback. In particular, the enhanced source impedance control is accomplished through feedback of the output current of the voltage source to an analog error amplifier at an input to the voltage control loop. The output impedance Z.sub.desired is then adjusted in accordance with the equation Z.sub.desired =Z.sub.inv1 {1+G(s) H(s)}, where G(s) is the voltage source amplifier's closed-loop transfer function, H(s) is the transfer function of the output current feedback circuit and Z.sub.inv1 is the original source impedance of the voltage controlled voltage amplifier.

Abstract: An uninterruptible power supply including a transformer having a first input winding normally coupling an inverter AC source with a critical AC load, which transformer also includes a second input winding operable to supply power from a bypass source to the load in the event of malfunction of the inverter circuit. The inverter is of the four-quadrant pulse-width-modulated type, thereby to permit recharging of the battery which serves as the DC source to the inverter. An inductance is provided for varying the phase relationship between a utility voltage source and the inverter voltage to produce minimum real inverter current and the "break-even" operating conduction, and a step-up device is provided for increasing the utility voltage to further minimize the break-even inverter current required during normal operation, and to maximize the through-put efficiency.

Abstract: A high-frequency converter of the bridge circuit type includes a snubber circuit connected across the output terminals of the bridge for connecting pairs of charged switching capacitors with an inductor upon the switching of the transistors of the bridge to their OFF conditions. The snubber circuit includes parallel-connected oppositely-poled additional switching devices with reverse blocking characteristic connected in series with the inductor, whereby the energy of the discharging switching capacitors is temporarily stored in the inductor in a substantially loss-free manner, and is pumped in the same direction to assist in the charging of the other capacitors.

Abstract: An access control system for use in connection with a data communication system, particularly a data processing system having a computer apparatus, at least one user terminal and a communication link for providing communication between the computer apparatus and the user terminal is comprised of a controller switch and a first programmed computer means. The controller switch is connected to permit transmission of electrical signals between the computer apparatus and the communication link. The first programmed computer means is connected to the controller switch for actuating the controller switch to connect the computer apparatus and the communication link only upon verification by the first programmed computer that an authorized user is operating the user terminal. The access control system also includes an accessor switch and a second programmed computer means. The accessor switch is connected to permit transmission of electrical signals between the user terminal and the communication link.

Abstract: A secure communication link is provided for transmitting signals between a host computer and at least one authorized terminal. The communication link includes a host modem for modulating and demodulating the signals transmitted between the host computer and the authorized terminal and an access controller. The access controller stores enquiry and reply sequences of bits and is operable to compare incoming signals from the host modem with the stored sequences of bits. Where there is agreement between the signals from the host modem and the stored sequences of bits, the controller establishes the communication link. Where there is no agreement or no reply from the host modem, the controller disconnects the host modem from the link.

Abstract: A warning device (10), typically situated in an illuminated exit warning sign, broadcasts voice commands generated by a synthetic speech synthesizer (U3) via speaker (SP1). A programmable microcomputer (U2) senses a loss of AC power and generates a user initiated voice command. Upon the detection of a fire or smoke condition, the microcomputer (U2) generates a priority warning. The device (10) includes a self-contained, charged power supply (12) that powers the microcomputer (U2) and the synthesizer (U3) in the event that the externally supplied AC power ceases. Constant illumination is provided by lamps (32) or (40). A user operated switch aids in programming the microcomputer to provide two sets of audible phrases.

Abstract: A method and apparatus for controlling a resonant power module comprising a resonant power circuit which is coupled to a load. First and second switching elements are coupled to the resonant circuit for alternately supplying a flow of current. Trigger generator means are provided for supplying trigger signals to alternately enable the first and second switching elements. A control means is coupled to the trigger generator for operating the power module in a first mode in which the resonant circuit current is controlled by varying the repetition rate of the trigger signals. The control means operates the power module in a second mode by maintaining the trigger signal repetition rate at a fixed limit and controlling the resonant circuit current by varying the on/off duty cycle of the power module.