A rapid response current limiter is used in combination with first and second switching transistors and an output transformer winding connected to provide a power converter. The transistors are alternately switched by first and second square waves supplied to their base terminals, an input d.c. source being connected between a common junction of the switching transistors and a center tap of the transformer winding. Rapid response current limiting is accomplished by limiting the width of the driving square waves applied to the transistors to thereby limit the peak current that they conduct. This limiting of square wave width is accomplished by gating circuits which abruptly truncate the square wave causing the switching transistors to turn off whenever a sensed current in the circuit exceeds a given reference value. The current limiting acts virtually instantaneously so that the risk of burning out the switching transistors in the event of a sudden high current surge is substantially eliminated.