Power supply system for heavy traction loads

Claim 1

In a power supply circuit adapted to supply heavy direct current loads from an alternating current input source, control valve means coupled between the alternating current input source and a said load, said control valve means having gating electrode means for normally operating said control valve means to provide unilateral conduction therethrough during a time when the alternating input to the control valve means has a given polarity, sensing means for detecting current to said load, and circuit means responsive to said detected load current in a first high current range for controlling said gating electrode means of said control valve means to limit such load current in a first range thereof by operating said control valve means later during the said alternating input of said given polarity, the said circuit means having nonlinear properties for reducing the response of said circuit means to predetermined high current values in a second and higher range, said circuit means comprising a first operational amplifier responsive to the input of said sensing means and operative at least above a given input level to provide an amplifier output, said operational amplifier having nonlinear feedback means operative above a second and higher input level to provide negative feedback in said operational amplifier for reducing the gain of said operational amplifier, a second operational amplifier receiving the output of the first, said second operational amplifier having a time constant feedback circuit rendering the same responsive to the level of input provided thereto, charging means and triggerable means operated thereby for triggering said control valve means, and means operable during positive alternating current half-cycles for charging said charging means at a rate determined by the output of said operational amplifier.