Abstract: A DC-to-AC power inverter includes a transformer with a secondary winding and a center-tapped primary. The center tap is connected to one pole of the DC source, and each end of the primary winding is connected to the other pole of the source by a switch. The switches are controlled in a 50% duty cycle mode, a mode in which both switches are ON simultaneously, and/or a mode in which both switches are periodically OFF simultaneously. The both-ON switch condition short-circuits the transformer, with the result that more current flows through the inductor, which has the effect of boosting transformed voltage above that of the 50% duty cycle mode. The both-OFF mode reduces the inductor current and decreases the transformed voltage. The amount of overlap of the both-ON and both-OFF conditions controls the output voltage. A rectifier arrangement may be coupled to the secondary winding to convert the AC output voltage to DC.

Abstract: A base drive circuit particularly well adapted for use with bipolar power transistors in high frequency power conversion systems. When utilized in a transformer isolated inverter system, the base drive circuits present a polarity insensitive input impedance which eliminates the effects of cross-conduction between base drive circuits connected to the secondary side of the transformer.

Abstract: A base drive circuit particularly well adapted for use with bipolar transistors in high frequency power conversion schemes. The base drive circuit allows achieving desired values for both forward and reverse base drive currents simultaneously regardless of the characteristics of the bipolar transistor driven. When utilized in a transformer isolated inverter system, the base drive circuit additionally presents a polarity insensitive input impedance which eliminates the effects of cross-conduction between base drive circuits connected to the secondary side of the isolation transformer.

Abstract: This high-speed differential protective arrangement discriminates between a fault occurring in a differentially-protected zone of a power circuit and operation of a lightning arrestor connected to the power circuit in said zone. The protective arrangement comprises a relay which operates in response to such a fault but which remains inactive despite operation of the lightning arrestor. Despite this insensitivity to lightning-arrestor operations, the relay is still able to operate relatively fast at levels of fault-produced voltage across input terminals to the protective arrangement much lower than those developed across these terminals by lightning-arrestor follow-through current.

Abstract: A signal amplitude monitor and relay driver circuit. The input signal is applied to a plurality of diodes connected in series with a set of normally closed relay contacts and a first resistor. A second resistor is connected in parallel with the series connected diodes through a set of normally open contacts of the relay. A third resistor is connected in parallel with the combination of the first resistor and normally closed contacts. A transistor circuit is connected with its emitter-base circuit responsive to the signal developed across the first resistor. The transistor output drives an amplifier which energizes the relay coil. When the normally closed contacts are closed the input signal must exceed a first predetermined level before the transistor circuit becomes conductive causing the amplifier to energize the relay coil.