Method for triggering a controlled rectifier and for keeping it conductive and a generator for that purpose

Claim 1

A circuit for controlling the supply of current to an inductive load, the circuit comprising: a controlled rectifier, of the type having a control electrode and a main current path, said inductive load being connected in series with said main current path; control generator means having an output; pulse generator means and signal generator means each having an input connected to said output of said control generator means, and each having an output; said pulse generator means further comprising a capacitor, means for charging said capacitor, a pulse transformer and means controlled by said generator means for discharging said capacitor through said pulse transformer; summing means having an input connected to said outputs of said pulse generator means and said signal generator means, and an output connected to said controlled rectifier; said pulse generator means being operative to supply to said control electrode via said summing means a short duration pulse of relatively large amplitude with high transconductance per unit of time to cause said main current path to become conducting and current to start to flow in said inductive load; and said signal generator means being operative to supply to said control electrode via said summing means a train of discrete pulses of relatively small amplitude, said supply of pulses being maintained at least until a predetermined current is flowing in said main current path and in said inductive load; and said circuit further comprising delay means connected between said output of said control generator means and said input of said signal generator means to delay supply of said pulse train to said control electrode until the amplitude of said short duration pulse is falling towards the amplitude of the pulses forming said train.