Over-current latch-up protection apparatus for scr inverter circuits and the like

Claim 1

Over-current protection apparatus having, in combination, switching circuit means comprising direct-current supply means connected with normally non-conductive switching means adapted to be periodically rendered conductive for predetermined conduction intervals; inductance-capacitance network means including seriesconnected inductance and shunt-connected capacitance connected between the supply means and the switching means and tuned to a resonant frequency of period substantially greater than said predetermined conduction intervals to serve during normal operations of the switching circuit means as a low-pass filter; and the network means being adjusted such that, upon the development of a fault short-circuiting the supply means, the network means discharges through the fault and the switching means and momentarily causes the voltage applied to the switching means to reverse sign, permitting the recovery of the switching means and thereby limiting the duration of the fault current, said capacitance being shunted by means for dissipating energy during the time the capacitance is of negative voltage, and said inductance being shunted by means for dissipating energy as soon as the inductance voltage becomes negative.